A Comprehensive Guide to Sheet Metal Fabrication Design Solutions
What is sheet metal?
Sheet metal is sometimes also known as metal sheet, which comes from the English term “plate metal”. It generally refers to the plastic deformation of some metal sheets through manual or mold stamping, forming the desired shape and size, and further forming more complex parts through welding or a small amount of mechanical processing. Sheet metal is commonly made of steel, aluminum, copper, zinc, nickel, and lead. Cold rolling, hot rolling, or forging are usually produced into plates. The thickness of sheet metal can range from very thin foil to a few millimeters or thicker. Still, in industrial applications, sheet metal usually refers to metal plates with a 0.6mm to 6mm thickness.
What is sheet metal fabrication?
Sheet metal fabrication is a key technology that sheet metal technicians need to master, and it is also an important process for forming sheet metal products. Sheet metal fabrication includes traditional methods and process parameters such as cutting and blanking, punching and bending forming, various cold stamping mold structures and process parameters, working principles and operation methods of various equipment, and new stamping technologies and processes.
Advantages and Disadvantages of Sheet Metal Fabrication
Sheet metal fabrication is a cornerstone technique in modern manufacturing and construction. It’s a process that has evolved over the centuries, reflecting the demands and innovations of each era. This technique involves molding, shaping, and assembling metal sheets, often into components used for various applications ranging from aerospace to household items. While this manufacturing method presents many benefits, it’s only fair that we also shed light on its disadvantages.
Advantages of Sheet Metal Fabrication
a. Versatility and Flexibility
Sheet metal can be shaped into various designs catering to bespoke needs and specifications. Industries with specialized requirements can greatly benefit from sheet metal’s adaptability.
Once the initial setup costs are covered, sheet metal fabrication can be a highly economical solution for mass production. Computer Numerical Control (CNC) machines can further reduce labor costs and streamline production.
c. High Strength-to-Weight Ratio
Despite its malleability, sheet metal components are robust and durable, making them ideal for sectors that require strength without the burden of added weight, such as the automotive or aerospace industries.
d. Efficient Production
With advanced machinery and tools, sheet metal fabrication can achieve faster production cycles, thereby promptly meeting market demands.
e. Environmentally Friendly
Sheet metal, especially aluminum and steel, is recyclable. This reduces waste and is a step towards sustainable manufacturing practices, aligning with global green initiatives.
Disadvantages of Sheet Metal Fabrication
a. Initial Setup Costs
The machinery required for sheet metal fabrication, especially for automated processes, can be costly. For businesses just starting, this initial investment can be a significant barrier.
b. Technical Expertise Required
Handling and operating machinery, understanding design principles, and ensuring product quality require skilled professionals. The demand for such talent can sometimes outstrip supply, increasing labor costs.
c. Limitations in Thickness
While sheet metal fabrication boasts versatility, there’s a limitation to how thin these sheets can be before they lose structural integrity or become too challenging.
d. Risk of Corrosion
Certain metals, when exposed to environmental elements, can corrode over time. Protective measures like coatings or choosing corrosion-resistant metals can mitigate this but can add to the overall cost.
e. Precision Challenges
While advanced machinery has reduced errors, there’s always a margin of error in fabrication. Achieving absolute precision, especially for intricate designs, can be challenging.
Key points of sheet metal processing
In sheet metal processing, various methods are used to apply force to sheet metal to form the target shape, and the principle is related to the characteristics of the metal material. When a load is applied to a metal material, the material changes the distance between its constituent atoms and deforms while generating strain. At this point, the force (internal force) that the metal attempts to restore to its original state takes effect from the beginning, so when the load is small, if the load is removed, the metal will return to its original state (elastic deformation). When a continuous load is applied to a metal beyond a certain point (yield point), the metal cannot recover (plastic deformation). If the load continues to be applied, it will be overwhelmed and break. In sheet metal processing, it is important to have edge adjustment and edge processing techniques to obtain the target shape through plastic deformation.
The main equipment of sheet metal
Sheet metal fabrication uses various equipment in various processes. This will introduce the main processing equipment used in sheet metal fabrication.
• Laser cutting machine
A laser cutting machine is a processing equipment that uses a high-power laser to irradiate metal materials, causing them to partially melt, blow off the melted metal with gas, and then perform the cutting. It is skilled at high-speed machining of long peripheral and waist-shaped holes. On the other hand, if the number of holes in the board is large, the number of openings (perforations) will increase, which requires time for processing. However, in recent years, the high power of laser equipment has made high-speed processing, including opening processing, possible. However, forming processes such as threaded holes and deburring cannot be carried out.
• Turret punch
Turret punch is a processing equipment that installs many small molds on a molded bracket called a turret to press and cut metal at high speed. Due to punching one hole at a time, it is suitable for high-speed machining of porous parts and can be used for forming processes such as tapping, deburring, sinking, and louver processing. On the other hand, punching the outer and waist-shaped holes requires many punching times, and processing requires much time.
• Laser punch compound machine
This is a composite machine equipped with both processing equipment mentioned above. Blanking and forming processing are carried out in one process, such as using a laser to process time-consuming peripheral and large holes and a punch to carry out opening and forming processing. As there is no need to replace equipment for each process, there is less chance of workpiece misalignment due to replacement.
• Deburring machine
In the past, sheet metal factories usually used manual angle grinders or files to remove burrs manually, but in recent years, more and more factories have introduced deburring machines. The deburring machine adsorbs the workpiece onto the conveyor belt and rotates a brush with sandpaper installed to remove burrs evenly.
• Bending machine
In a bending machine, the upper mold (convex mold) is installed on the upper part of the equipment, and the lower mold (concave mold) is installed on the lower part. The upper part of the equipment is moved, and pressure is applied downwards to bend the metal plate. According to the method of applying pressure, there are mechanical, hydraulic, servo motor + ball screw, etc., but now the common models are those that can adjust the pressure size through NC. In recent years, models with automatic movement of rear stop gauges (bumpers), according to the program, have been popularized, playing a role in factories that require bending accuracy. The material, plate thickness, length, machinable materials, are determined by the maximum pressure (ton) and machinable length.
• Laser welding machine
Laser welding is a method that is less prone to thermal strain due to its fine and deep fusion depth and smaller heat-affected layer. The first popular method in laser welding is the “YAG laser”, widely known as a welding method to suppress deformation and maintain aesthetics. The “fiber laser welding machine” that emerged around 2015 quickly became popular due to solving the problem of insufficient strength in YAG laser and achieving low strain and high strength welding. The biggest advantage of laser welding is that even thin plates are not easily deformed, and even unskilled people can achieve the processing methods of TIG welding that only skilled artisans can perform and ultra-thin plate processing. As future equipment becomes lighter, it is estimated that laser welding will become more common as a general processing method if the use of thin plates increases.
• TIG welding machine
TIG welding is a type of arc welding that utilizes electricity and is currently the most commonly used welding method in mechanical sheet metal. Inactive gases often use argon gas, sometimes called “argon arc welding”. TIG welding applies high voltage to the electrodes to melt and bond the metal, producing excellent airtightness, water tightness, and high welding strength. On the other hand, due to the large amount of heat input into the metal, the range of heat affected zone for heat transfer around the molten pool is large, resulting in a large strain of the product. The welding technique of suppressing this strain as much as possible and eliminating the resulting strain is extremely difficult, and TIG welding is known as “craftsmanship”.
Industrial Application of Sheet Metal Parts
Sheet metal parts are widely used in industry, and their production involves converting metal sheets into various products and components through different processing processes such as punching, bending, forming, welding, etc. The following are some applications of sheet metal parts in industry:
- Electronics and communication industry: Sheet metal parts are used for manufacturing computer cases, communication equipment casings, radio equipment, mobile phones, and accessories.
- The automotive industry: Body, doors, fuel tanks, exhaust systems, etc. all require sheet metal processing technology.
- Mechanical manufacturing: Many mechanical components, such as chassis, casing, metal structure frame, baffle, heat sink, etc., are made through sheet metal processing.
- Aerospace: Many parts of airplanes, satellites, and other spacecraft require sheet metal technology for manufacturing.
- Construction industry: Sheet metal is also used in roof systems, air conditioning systems, exhaust ducts, and exterior wall decoration.
- Home appliance industry: Many household appliances, such as refrigerators, washing machines, microwaves, etc., require sheet metal processing for their shells and structural parts.
- Medical equipment: Many medical equipment and tools, such as operating beds, instrument boxes, and mechanical casings, are sheet metal.
- Energy industry: There are also a large number of sheet metal applications in solar panel installation frames, wind turbine components, and other energy-related equipment.
- Railway and transportation: Trains, subway vehicles, and other means of transportation also use many sheet metal components.
The above are just some examples of the application of sheet metal parts. Sheet metal processing technology is widely used in modern industry. It provides an economical, fast, and effective way to manufacture customized metal components and products.
Custom sheet metal manufacturing usually involves multiple steps, from design to full production. You’ve listed some key steps, which I’ll describe in detail below, and additional considerations may be added.
At this stage, you need to determine the product’s basic requirements and expected functionality. This may involve discussions with potential customers, engineers, or other team members.
Create engineering drawings:
Use CAD (Computer Aided Design) software to create detailed 2D or 3D design drawings.
These designs usually describe the part’s size, shape, material, and other necessary details in detail.
Analysis of manufacturability:
This step aims to ensure that the designed parts can be manufactured and cost-effective.
Factors that need to be considered include material selection, production process, tool availability, cost, and production time.
If the analysis results show that some design elements could be more practical or the cost is too high, the design may need to be modified.
You will manufacture one or more actual part prototypes based on the drawings in this step.
This allows you to see what the actual part will look like and how it is assembled or interacts with other parts.
The prototype is tested to meet all functional, strength, and quality requirements.
This may include mechanical testing, durability testing, temperature/environmental testing, etc.
Based on the test results, the design may need further modification.
Once the prototype is considered to meet all requirements, full production can begin.
This will involve selecting appropriate production methods, tools, equipment, and materials, as well as optimizing production processes to improve efficiency and reduce costs.
Throughout the process, continuous communication and cooperation with other team members (such as production, quality control, supply chain, etc.) is crucial to ensure the successful implementation of the project.
Sheet Metal Design Solutions
Design requirements for sheet metal parts
The design of sheet metal parts should consider functional requirements, process requirements, assembly requirements, and cost requirements. Compared with castings and forgings, products made of sheet metal parts have higher strength and lighter structural weight; Simple processing and simple equipment are used. The appearance is flat, with minimal machining allowance, which can reduce weight, shorten the production cycle, and reduce costs.
1. Functional requirements
The functional requirements mainly include meeting the structural requirements, strength requirements, shielding requirements, and grounding conductivity of the system.
The structure of a system is the location, form, connection, and assembly method of the hardware, PCB board, wire, power supply, and other spatial placement of the system. Due to their good strength, rigidity, processability, and conductivity, sheet metal parts are usually used to support most of the system’s hardware, PCB boards, wires, power supplies, etc. There are various forms of hardware placement, and their requirements may also vary.
Mechanical strength is the most important aspect of sheet metal design. Because most of the weight in the system is supported by sheet metal parts, the mechanical strength of the sheet metal parts will be affected, and the system’s overall strength will be affected. Medical instruments generally require vibration testing, drop testing, collision testing, impact testing, etc. Some machines even require strength to withstand 100g of impact, which requires sufficient mechanical strength and rigidity. Especially for sheet metal parts that need to support suspended hardware and brackets that play a major supporting role, they must have better strength.
Usually, when designing large-scale systems such as B-ultrasound, CT machines, inspection equipment, communication cabinets, etc., support brackets and frames are designed first. This type of support frame can be made of profiles (such as aluminum profiles), or thicker sheet metal parts can be bent into a “π” or “□” shape. In general, adding a bend will increase the stiffness several times.
2. Process requirements
The processing equipment for sheet metal parts mainly includes CNC punches, bending machines, punches, cutting machines, milling machines, drilling machines, welding equipment, etc. Sheet metal forming can be classified into three basic types: compression forming, elongation forming, and bending forming.
Straightening, bending, rolling, punching, and drawing in sheet metal processing all utilize the plastic deformation of metal at room temperature to form the desired shape. Therefore, the plastic deformation of metals is the foundation of metal forming.
When a metal is subjected to external forces in a cold state, its shape and size will change, which can be elastic or plastic. When the external force is released, what can restore its original shape and size is elastic deformation and vice versa is plastic deformation. The most basic form of metal plastic deformation is slip.
3. Assembly requirements
Assembly should be considered when designing sheet metal parts.
When assembling in large quantities, it is advisable to minimize the use of time-consuming and expensive structures and try to use installation methods such as stamping molds into buckles and protrusions.
When producing in small quantities, consider less. The products produced by our company belong to small batches, and we only need to consider the order and method of assembly.
4. Cost requirements
When producing in large quantities, it is necessary to shorten the assembly cycle and minimize the assembly cost, especially for overseas OEM projects (where assembly workers are more expensive). Mold stamping can be used for production.
When producing in small quantities, as much as possible, try to use simple assembly methods, such as screw connections.
The cost of using SPCC (cold gadolinium steel plate) for electroplating will increase by about 35% compared to directly using SECC.
The production cycle of SPCC (cold gadolinium steel plate) for electroplating is 2-3 days longer than that of directly using SECC.
5. Material selection
Generally, the sheet metal parts we use are thin steel plates, which are rolled by cold or hot rolling methods. According to the different uses, the materials of thin steel plates include low-carbon steel and stainless steel; some are coated with a non-ferrous metal film on the steel plate, called coated thin steel plate (such as galvanized steel plate, lead-plated steel plate, tinned steel plate), and others use aluminum plate.
Standardize the drawing of sheet metal engineering drawings, standardize professional terminology, and better adapt to production needs, thus enabling engineering drawings to guide production more effectively.
2. Applicable scope
The design, technology, and production departments of the company.
3. Responsibility, Rights
The sheet metal engineering drawings are drawn by the design department, proofread and reviewed by the technical department, and confirmed and issued by the technical supervisor.
Sheet metal engineering drawings, abbreviated as “drawings”, are production drawings that accurately reflect the cutting dimensions of parts and all related standard parts and their specifications.
5. Drawing basis
Customer specific requirements or customer’s 2D and 3D drawings (including electronic files).
6. Specific content
1) The drawings are the basic basis for the process arrangement and production of parts, and the design and production of the drawings must be signed.
2) The drawings should reflect all relevant dimensions of the part.
3) The important information about the parts must be reflected on the drawings (including name, material, relevant hole positions, cutting corners, etc.).
4) Detailed instructions must be marked if the parts have special structures (such as flipping, flipping, breakage, etc.).
5) The technical requirements should be detailed (such as burrs, welding, drilling, tapping, quantity, etc.), and the processing technology and steps of the parts and the coating requirements should be clearly defined.
6) Other information annotations (such as number of drawings, designer, design date, drawing code, etc.).
7) The perspective of drawing production must be unified (usually, the first perspective can be used for placement).
- a. The view must be able to fully reflect the structure of the parts and strive for clarity and simplicity.
- b. If necessary, use enlarged and cross-sectional views to achieve the product’s structural integrity and the drawings’ clarity.
- c. For parts with special structures, a cross-sectional view must be made to display the special structure of the part.
- d. The drawings must provide clear cross-sectional and enlarged views for hardware components.
- e. The drawing must provide a folding diagram or enlarged view for complex parts folding.
- f. All sections must strive for clarity and conciseness, and enlarged views can be made if necessary.
8) Layout of drawings
- a. The placement of each perspective on the drawing must be uniformly fixed.
- b. Each view on the drawing must strive for compactness clarity, and avoid excessive white space.
- c. Each view on the drawing should be labeled without overlap.
9) The tolerance markings must be clearly and clearly marked, and the tolerance markings for important dimensions must be listed and marked separately.
10) If there are size omissions or errors in the drawings, corresponding corrections or explanations must be made.
11) The unfolded drawing must reflect all the hole positions and dimensions of the part. Without special instructions, the unfolding diagram follows the principle of placing burrs downwards.
12) The bending line on the drawing should indicate its bending direction (the thin solid line represents the upward bending direction, and the thin dashed line represents the downward bending direction). Symmetrically made parts must be marked with “Symmetrically made.”
13) Uncertain words such as “confirmation required” are not allowed on the drawings.
Common sheet metal design errors to avoid
Some engineers need help to correctly design sheet metal parts for manufacturing. Of course, not you (blinking). Nevertheless, we have noticed that certain issues often arise in the models we must reference. Considering these issues, we have provided this list. It’s not exhaustive, but please bring yourself and see what many of your colleagues did wrong when designing and submitting RFQs for sheet metal.
Sheet metal fabrication is an intricate procedure that entails design, cutting, bending, and forming the metal into the desired product. Even adept designers can fall into pitfalls, leading to expensive alterations or discarded components. Here’s a compilation of prevalent design errors and how to sidestep them.
- 1. Overlooking Bends in CAD Files: Neglecting to incorporate bends in a CAD file is a common oversight. Crafting a single metal piece without bends becomes arduous, often necessitating extra components and labor. Ensure you specify bend angles and radii in your designs.
- 2. Cramming Features Near Bends: Positioning elements like holes or tabs adjacent to bends can lead to warped metal parts. Adhere to the 4T rule in your designs, ensuring all features remain at least 4 times the material’s thickness from any bend.
- 3. Chasing Sharp Corners: While having sharp angles in your designs is tempting, metal bending often yields a rounded corner. Avoid designing for sharp angles, which can cause material stress and cracks. Instead, determine a suitable bend radius based on material and thickness.
- 4. Glossing Over Hardware Specs in CAD: Always provide thorough hardware details in your CAD file to streamline the fabrication process. Provide specifics to avoid delays, driving up both time and cost.
- 5. Misjudging the Finish: Many overlook the dual role of finishing—it enhances appearance and offers protection against degradation. Choosing the right finishing based on aesthetic and functional requirements is pivotal.
- 6. Mismatching Metal Selection: Choosing the correct sheet metal is vital, considering its end-use. Factors like daily wear, susceptibility to corrosion, ease of manufacturing, aesthetic appeal, conductivity, and required mechanical properties should guide your choice.
- 7. Underestimating U Channel Material Strength: U channels, integral to many designs, derive their strength from the material used. Ignoring material strength can lead to fragile U channels. Select the right material and thickness based on the load and possible stresses.
- 8. Setting Overambitious Welding Standards: Occasionally, designers set unrealistic welding expectations, inflating complexity and costs. Embrace robust design for manufacturing (DFM) strategies to align your designs with existing standards.
Correct Selection of Sheet Metal Materials
Sheet metal materials are the most commonly used materials in product structure design. They understand that the comprehensive performance of the materials and the correct selection of materials impact product cost, product performance, product quality, and processing manufacturability.
Principles of Sheet Metal Material Selection
- Select common metal materials, reduce the variety of material specifications, and control them as much as possible within the scope of the company’s material manual;
- In the same product, reduce the varieties of materials and sheet thickness specifications as much as possible;
- Under the premise of ensuring the function of the parts, try to choose cheap material varieties and reduce the consumption of materials to reduce material costs;
- For cabinets and some large plug-in boxes, full consideration needs to be given to reducing the weight of the whole machine;
- In addition to the premise of ensuring the function of the parts, it is also necessary to consider that the stamping properties of the material should meet the requirements of the plus process to ensure the rationality and quality of the processing of products.
Common Sheet Metal Material Characteristics
Sheet metal processing materials generally used in cold rolled sheet (SPCC), hot rolled sheet (SHCC), galvanized sheet (SECC, SGCC), copper (CU) brass, copper, beryllium copper, aluminum (6061, 5052, 1010, 1060, 6063, duralumin, etc.), stainless steel (mirror, brushed surface, matte surface), according to the role of the product is different, the choice of different materials, generally need to be considered from the product its use and cost. Product, its use, and cost to consider.
- 1. Cold rolled sheet SPCC, mainly with electroplating and baking paint parts, low cost, easy to mold, material thickness ≤ 3.2mm.
- 2. Hot rolled sheet SHCC, material T ≥ 3.0mm, also with electroplating, baking paint parts, low cost, but difficult to mold, mainly with flat parts.
- 3. Galvanized sheet SECC, SGCC. SECC electrolytic sheet is divided into N material, P material, N material is not the main surface treatment, high cost, P material for spraying parts.
- 4. Copper is mainly used for the conductive role of the material; its surface treatment is nickel-plated, chromium-plated, or no treatment, high cost.
- 5. Aluminum plate; generally, with the surface chromate (J11-A), oxidation (conductive oxidation, chemical oxidation), high cost, silver-plated, nickel-plated.
- 6. Aluminum profiles: complex cross-section structure of the material, many boxes used in various inserts. Surface treatment with aluminum.
- 7. Stainless steel; mainly used without any surface treatment, high cost.
Table.1 Complete Guide to Metal Materials
Sheet Metal Fabrication
|Sheet Metal Fabrication|
|Aluminum 7075-T651/T6||CNC Machining||CNC Milling|
|Aluminum 7075-T7351||CNC Machining||CNC Milling|
|Aluminum AlSi10Mg||3D Printing||Direct Metal Laser Sintering|
|Aluminum 5052-H32||Sheet Metal Fabrication||Sheet Metal Fabrication|
|Aluminum 2024-T351||CNC Machining||CNC Milling|
|Brass||Brass C260||Sheet Metal Fabrication||Sheet Metal Fabrication|
|CNC Machining||CNC Milling|
|Brass C360||CNC Machining||CNC Turning|
|Cobalt Chrome||Cobalt Chrome||3D Printing||Direct Metal Laser Sintering|
|Copper||Copper C101||Sheet Metal Fabrication||Sheet Metal Fabrication|
|CNC Machining||CNC Milling|
|Copper C110||Sheet Metal Fabrication||Sheet Metal Fabrication|
|Inconel||Inconel 718||3D Printing||Direct Metal Laser Sintering|
|Low Carbon Steel||Mild Steel 1018||CNC Machining||CNC Milling|
|Low Carbon Steel CR 1008||Sheet Metal Fabrication||Sheet Metal Fabrication|
|CR Galvanized||Sheet Metal Fabrication||Sheet Metal Fabrication|
|CR Galvannealed||Sheet Metal Fabrication||Sheet Metal Fabrication|
|Stainless Steel||Stainless Steel 17-4 PH||
|Direct Metal Laser Sintering|
|Stainless Steel 304/304L||
Sheet Metal Fabrication
|Sheet Metal Fabrication|
|Stainless Steel 316||CNC Machining||CNC Milling|
|Stainless Steel 316L||Sheet Metal Fabrication||Sheet Metal Fabrication|
|3D Printing||Direct Metal Laser Sintering|
|Stainless Steel 303||CNC Machining||CNC Milling|
|Steel Alloy||Alloy Steel 4140||CNC Machining||CNC Milling|
|Titanium||Titanium Ti 6Al-4V||3D Printing||Direct Metal Laser Sintering|
|Titanium Grade 5 6Al-4V||CNC Machining||CNC Milling|
Introduction to several commonly used plates
(1) Cold rolled thin steel plate
Cold rolled thin steel plate is the carbon structural steel cold rolled plate it is from the carbon structural steel hot rolled steel strip, after further cold rolling, made of steel plate with a thickness of less than 4mm. As rolled at room temperature, it does not produce iron oxide; therefore, the cold plate surface quality, high dimensional accuracy, annealing, mechanical properties, and process properties are better than hot rolled thin steel plate. They commonly used grades for low carbon steel 08F and 10# steel, with good drop bending performance.
(2) Continuous electro-galvanized cold rolled thin steel plate
Continuous electro-galvanized cold rolled thin steel plate, that is, “electrolytic plate”, refers to the electro-galvanizing line of operation in the electric field, zinc from the zinc salt in an aqueous solution of continuous deposition to the pre-prepared steel strip performance to get the surface of the galvanized layer of the process, because of the limitations of the process, the coating is thin.
(3) Continuous hot-dip galvanized steel sheet
Continuous hot-dip galvanized steel sheet, referred to as galvanized sheet or white iron, is the thickness of 0.25-2.5mm cold rolled continuous hot-dip galvanized steel sheet and steel strip, steel strip first through the flame-heated preheating furnace, burned off the surface residual oil, at the same time in the surface of the iron oxide film generated, and then into the H2, N2 gas mixture of reduction annealing furnace heated to 710-920 ° C so that the iron oxide film is reduced to sponge iron, the surface of activated and purified! After the strip is cooled to a temperature slightly higher than the molten zinc, it enters a zinc pot at 450-460°C, and an air knife controls the surface thickness of the zinc layer. Finally, it is passivated with chromate solution to improve the resistance to white rust. Compared with the surface of an electro-galvanized sheet, its coating is thicker and is mainly used for sheet metal parts that require strong corrosion resistance.
(4) Aluminum-zinc-coated sheet
The aluminum-zinc alloy coating of the aluminum-zinc clad plate is composed of 55% aluminum, 43.4% zinc, and 1.6% silicon cured at a high temperature of 600 ℃, forming a dense quaternary crystalline protective layer with excellent corrosion resistance, normal service life of up to 25 years than galvanized plate 3-6 times longer, and stainless steel is comparable. The corrosion resistance of zinc-clad aluminum sheets comes from aluminum’s barrier layer protection function and the sacrificial protection function of zinc. When zinc is in the cut edge, scratches and plating abrasion part of the sacrificial protection, aluminum will form a cannot dissolve the oxide layer, playing the barrier protection function.
The above 2), 3), 4) steel plate collectively referred to as coated steel, widely used in domestic communications equipment, coated steel can no longer be plated after processing, painting, and cutting without special treatment, can be used directly, but also can be a special phosphating treatment to improve the ability of the incision to resist rust and corrosion. From the cost analysis, the use of continuous electro-galvanized thin steel plate, the processing plant does not have to send the parts to plating, saving plating time and transportation out of the cost, in addition to the parts before spraying also does not have to pickle, improve the processing efficiency.
(5) Stainless steel plate
Because of strong corrosion resistance, good electrical conductivity, strength, and other advantages, the use a very wide range of advantages, but also to fully consider its shortcomings: the material price is very expensive, is an ordinary galvanized sheet of 4 times; the material strength is higher on the CNC punching tool wear and tear of the CNC punching machine is generally not suitable for CNC punching machine; stainless steel plate rivet nut to be used to adopt high-strength special stainless steel materials
Pressure riveting nut of stainless steel plate to use high-strength special stainless steel material, the price is very expensive; pressure riveting nut riveting is not strong often needs to spot weld again; surface spraying adhesion is not high, the quality is not suitable for control; material rebound is large.
Not suitable for control; material rebound larger bending and stamping is not easy to ensure the shape and dimensional accuracy.
Aluminum and aluminum alloy plate
Usually used aluminum and aluminum alloy plates mainly have the following three materials: anti-rust aluminum 3A21, anti-rust aluminum 5A02, and duralumin 2A06.
Rustproof aluminum 3A21 is the old LF21, an AL-Mn alloy, the most widely used type of rustproof aluminum. The strength of this alloy is low (only higher than industrial pure aluminum) and cannot be heat-treated to strengthen. Therefore, it is often used to improve its mechanical properties by cold working methods. It has high plasticity in the annealed state and good plasticity in semi-cold hardening: cold hardening, low plasticity, good corrosion resistance, and good weldability.
Antirust aluminum 5A02, that is, for the old LF2 series AL-Mg antirust aluminum, compared with 3A21, 5A02 strength is higher, especially with high fatigue strength, plasticity, and corrosion resistance is high. Heat treatment cannot be strengthened with contact welding, and hydrogen atom welding weldability is good; argon arc welding tends to form crystalline cracks, and the alloy tends to form crystalline cracks in cold work hardening. Alloy in the cold hardening and semi-cold hardening state of machinability is good; the annealed machinability is bad and can be polished.
Duraluminum 2A06, for the old grade LY6, is a commonly used duralumin grade. Duraluminum and super duraluminum the general aluminum alloy, have higher strength and hardness and can be used as some of the panel types of material, but the plasticity is poor and cannot be bent; bending will cause the outer corner of the outer part of the rounded part of the crack or cracking.
Copper and copper alloy plate
Commonly used copper and copper alloy plates are mainly two kinds of copper, copper T2 and brass H62; copper T2 is the most commonly used pure copper; the appearance of purple, also known as purple copper, has a high degree of electrical conductivity, thermal conductivity, good corrosion resistance and formability, but the strength and hardness of brass than the much lower price is very expensive, mainly used as a conductive, thermally conductive and durable consumer products corrosion components, generally used in power supplies need to carry high current parts.
Brass H62 is a high zinc brass with high strength and excellent cold-hot workability, easy to use for various forms of pressure processing and cutting. Mainly used for a variety of deep drawing and bending of the stressed parts, its conductivity is not as good as copper but has good strength and hardness; the price is more moderate, in the case of meeting the conductive requirements, as far as possible, the use of brass H62 instead of copper, you can greatly reduce the cost of materials, such as the busbar, the vast majority of the busbar conductive piece is used in the conductive piece of brass H62, the fact that proved to meet the requirements fully.
Influence of Materials on Sheet Metal Processing
There are three main types of sheet metal processing: punching, bending, and stretching. Different processing techniques have different requirements for sheet materials, and the selection of materials for sheet metal should also be based on the general shape of the product and the processing techniques to consider the selection of sheet materials.
Influence of material on the blanking process
Punching requires that the sheet should have sufficient plasticity to ensure that the sheet does not crack during punching. Soft materials (e.g., pure aluminum, anti-corrosion aluminum, brass, copper, mild steel, etc.) have good blanking performance and after blanking, can obtain smooth sections and small inclination of the parts;
Hard materials (such as high-carbon steel, stainless steel, duralumin, super-hard aluminum, etc.) after blanking quality could be better; the unevenness of the section is large, especially for thick plate material is serious. For brittle materials, it is easy to produce a tearing phenomenon after punching, especially if the width is very small.
The influence of the material on the bending process
Plate material that needs to be bent to shape should have sufficient plasticity and a low yield limit. Plate with high plasticity, bending is not easy to crack, lower yield limit and lower modulus of elasticity of the plate, bending spring back deformation is small, easy to get the size of the accurate shape of the bend. Carbon content <0.2% of mild steel, brass aluminum, and other plastic materials are easy to bend the shape; brittle materials, such as phosphor bronze (QSn6.5 – 2.5), spring steel (65Mn), duralumin, super-hard aluminum, etc., bending must have a large relative bending radius (r/t), otherwise cracking is prone to occur in the bending process. Special attention should be paid to the choice of hard and soft state of the material; the bending performance has a great impact; For a lot of brittle materials, bending will cause the outer corner of the round corner to crack or even fracture; there are also some high carbon content of steel plate, if you choose the hard state of the bending will also result in the outer corner of the round corner of the bending cracking or even bending fracture, all of which should be avoided as far as possible.
The influence of the material on the tensile processing
Plate stretching, especially deep stretching, is one of the more difficult sheet metal processing technologies; it not only requires the depth of the stretch to be as small as possible, the shape as simple as possible, smooth transition, but the material must have good plasticity. Otherwise, it is very easy to cause the overall distortion of the parts deformation, local wrinkles, and even stretching parts of the tensile crack. The low yield limit and plate thickness directionality coefficient are large; the smaller the yield strength ratio σs/σb of the plate material, the better the stamping performance, and the greater the degree of the limit of deformation when the plate thickness directionality coefficient > 1, the deformation in the width direction is easier than that in the thickness direction. The larger the value of tensile fillet R, the less likely to produce thinning and fracture in the tensile process, and the better the tensile properties. Pure aluminum sheet metal, 08Al, ST16, and SPCD are common materials with better tensile properties.
Influence of Material on Stiffness
In sheet metal structural design, often sheet metal structural components of the stiffness cannot meet the requirements; structural designers tend to use high-carbon steel or stainless steel instead of mild steel or with higher strength and hardness of hard aluminum alloy instead of ordinary aluminum alloy, looking forward to improving the stiffness of the parts there is no obvious effect. For the same substrate materials, through heat treatment, alloying can significantly improve the material’s strength and hardness, but the change’s stiffness is very small. To improve the stiffness of the parts, only through the transformation of the material, change the shape of the parts to achieve a certain effect, the elastic modulus and shear modulus of the different materials see Table.2.
Table.2 Elastic modulus and shear modulus of common materials
|Name||Elastic modulus E GPa||Shear modulus G GPa||Name||Elastic modulus E GPa||Shear modulus G GPa|
|Grey cast iron||118-126||44.3||Rolled zinc||82||31.4|
|Carbon steel, nickel chromium steel||206||79.4||Glass||55||1.96|
|Cast steel||202||Organic glass||2.35-29.4|
|Rolled pure copper||108||39.2||Rubber||0.0078|
|Cold drawn pure copper||127||48||Bakelite||1.96-2.94||0.69-2.06|
|Rolled phosphor tin bronze||113||41.2||Sandwich phenolic plastic||3.95-8.83|
|Cold drawn brass||89-97||34.3-36.3||Celluloid||1.71-1.89||0.69-0.98|
|Rolled manganese bronze||108||39.2||Nylon 1010||1.07|
|Rolled aluminum||68||25.5-26.5||Hard tetrachloroethylene||3.14-3.92|
|Drawn aluminum wire||69||Polytetrachloroethylene||1.14-1.42|
|Cast aluminum bronze||103||11.1||Low pressure polyethylene||0.54-0.75|
|Cast tin bronze||103||High pressure polyethylene||0.147-0.24|
|Hard aluminum alloy||70||26.5||Concrete||13.73-39.2||4.9-15.69|
Table.3 Performance Comparison of Several Commonly Used Plates
|Material||Price coefficient||Lapping resistance (mΩ)||CNC Punching Machine Processing Performance||Laser Processing Performance||Bending Performance||Workmanship of Rivet Nuts||Surface Spraying||Cutting Protection Performance|
|Cold rolled steel plate coated with blue zinc||1||27||Good||Good||Good||Good||Commonly||Preferably|
|Cold-rolled steel plate coated with colored zinc||1.2||26||Good||Good||Good||Good||Commonly||Good|
|Continuous galvanized steel plate||1.7||26||Good||Good||Good||Good||Commonly||Worst|
|Hot dip galvanized||1.3||23||Good||Good||Good||Good||Commonly||Poor|
|Aluminum zinc coated plate||1.4||60||Good||Good||Good||Good||Commonly||Difference|
|Rust resistant aluminum plate||2.9||46||Commonly||Range||Good||Good||Commonly||Good|
|Hard aluminum, superhard aluminum plate||3||Commonly||Range||Range||Good||Commonly||Good|
|T2 copper plate||5.6||Good||Range||Good||Good||Commonly||Good|
- 1. The data in the table is related to the specific grade and manufacturer of the material and is only used for qualitative reference.
- 2. Aluminum alloy and copper alloy plates have poor processability in laser cutting, and laser processing is generally not acceptable.
Sheet metal fabrication is a multifaceted process that involves creating parts and structures from various metal sheets. These sheets can vary in thickness from thin foil to plates. This fabrication process can include cutting, bending, and assembling processes. Here are some solutions and methods commonly used in sheet metal fabrication:
Sheet metal processing method
- Non mold processing: The process of using equipment such as digital punching, laser cutting, shearing machines, bending machines, and riveting machines to process sheet metal. It is generally used for sample production or small batch production, with high costs. Short processing cycle and rapid response.
- Mold processing: Using fixed molds to process sheet metal, there are generally cutting molds and forming molds, mainly used for mass production with lower costs. The initial mold cost is high, and the quality of the parts is guaranteed. Long initial processing cycle and high mold cost.
Sheet Metal Fabrication Process
For any sheet metal component, it has a certain processing process, which is called the process flow. With the differences in the structure of the sheet metal component, the process flow may vary.
Design and draw part drawings of sheet metal parts → Drawing review → Punching and cutting → Forming → Riveting and tapping → Welding → Surface treatment → Testing → Assembly → Warehousing
Sheet metal processing technology: design and drawings
To design and draw the parts of a sheet metal part, also known as a three-view drawing. Its function is to express the structure of the sheet metal part in a drawing.
PROE drawing requirements
Usually, we provide sheet metal unfolding drawings to suppliers: firstly, the processability of the designed sheet metal parts can be determined from the unfolding drawings; The second is to avoid errors in supplier deployment, resulting in poor sample accuracy; The third is to shorten the time for suppliers to provide samples. There are no special requirements for sheet metal parts. In order to distinguish the compensation coefficient between general bending and Z-type bending during Pro/E unfolding, it is specified that the general bending R can only be 0.2 when drawing, while the Z-type bending R is 0.
Explanation of Pro/E bending and unfolding principle:
Pro/E definite expansion calculation formula
L = (A – T – R) + (B – T – R) + DEV.L (1)
= A + B – 2 * (T + R) + DEV.L
Among them, T = plate thickness; R = Bend the fillet.
The above DEV. L is the expansion compensation coefficient customized by Pro/E software.
The usual empirical bending and unfolding formula for suppliers Mingwei and Chaoda is:
L = A + B – δ (2)
δ= Bending material reduction coefficient (supplier’s production experience value)
Comparing equations (1) and (2), it can be obtained that:
DEV.L = 2 * (T + R) – δ (3)
By substituting (3) into the material reduction coefficient provided by the supplier, the relevant DEV. L value can be obtained.
For example, for a 90-degree T = 1.5mm bent sheet metal part, since R has been specified as 0.2mm, the supplier provides a material reduction coefficient of 2.3mm, which can be substituted into formula (3) to obtain:
DEV.L = 2 * (1.5 + 0.2) – 2.3 = 1.1mm
Due to the fact that the actual replenishment coefficient of Z-bending sheet metal parts is obtained through supplier experiments, we can only determine the final DEV. L value by substituting the DEV. L value to obtain the PROE expansion value and the value provided by the supplier.
For example, when T = 1.5mm, the unfolding value is obtained from the supplier’s experience value, while in PROE, when DEV.L = 1.0, its unfolding value is 40.6. Therefore, it can be inferred that DEV. L should be taken as 1.0 when T=1.5 is used for unfolding bent sheet metal parts.
Sheet metal processing technology: drawing review
To write the parts of the process, the first thing is to know the technical requirements of the parts of the various drawings; the drawing review is the most important part of the process to write the most important links.
- 1. Check whether the drawing is complete.
- 2. Figure view relationships, clear and complete, labeling size units.
- 3. Assembly relations assembly requirements focus on size.
- 4. The difference between the old and new versions of the drawing.
- 5. Translation of foreign language drawings.
- 6. Table at the code conversion.
- 7. The drawing of the problem of feedback and buried in the Department.
- 8. Materials
- 9. Quality requirements and process requirements.
- 10. Official release of drawings must be stamped with quality control.
Sheet metal processing technology: Punching and Blanking
Blanking and punching are two common operations in processing metal products, both of which involve using specific tools and equipment to change the shape of metal materials or remove certain areas. The following is a brief description of both:
- Definition: Blanking removes a certain part from a metal plate, strip, or other metal workpiece through stamping or cutting operations to obtain the desired shape.
- Tools/Equipment: Blanking machines, punches, etc.
- Application: In the manufacturing industry, blanking produces components of various shapes and sizes, such as vehicles, aircraft, electronic equipment, and household appliances.
- Definition: Punching is making one or more holes in metal or other materials.
- Tools/Equipment: Punches, drilling machines, or other specialized equipment.
- Application: For example, when manufacturing sheet metal components, punching can provide installation holes for screws, bolts, or other fixing devices; In electronic devices, punching can create ventilation holes or provide fixed points for components.
Both are indispensable in many manufacturing applications, providing a fast, accurate, and efficient way to process large amounts of metal materials. When choosing whether to use blanking or punching, it is necessary to consider the required shape, size, accuracy, and production volume.
What are the similarities and differences between blanking and punching?
The deformation and separation processes of the blank and the mold structure are the same for the two processes of punching and blanking.
Different purposes: The purpose of punching is to obtain perforated parts. Blanking is to obtain a material with a certain shape and size.
Different application fields:
Blanking refers to cutting workpieces that require further processing or the direct punching of workpieces. In punching, as the pipe material is a hollow cylindrical blank, the pipe wall in contact with the convex and concave molds during punching is an isolated surface rather than a flat surface like the plate, so special process measures and mold structure forms need to be taken.
Different benchmarks: punching is based on the punch. Blanking is based on punching.
Common methods of punching and blanking
CNC punching and blanking:
CNC punching and blanking refers to the use of a microcontroller on a CNC punch to pre-input processing programs (dimensions, processing paths, processing tools, and other information) for sheet metal parts, enabling the CNC punch to use various cutting tools. Various forms of punching, trimming, forming, and other processing can be achieved through rich NC instructions. CNC punching generally cannot achieve punching and blanking with complex shapes.
Features: Fast speed, saving mold. Flexible and convenient processing. It can meet the needs of sample-cutting production.
Attention and requirements:
Thin materials (t<0.6) are difficult to process and are prone to deformation; Tools, grippers, etc., limit the processing range. Moderate hardness and toughness have good punching processing performance. If the hardness is too high, it will increase the punching force and hurt the punch and accuracy. The low hardness results in severe deformation during punching, which greatly limits the accuracy. High plasticity is beneficial for forming and processing, but it is unsuitable for nibbling, continuous punching, punching, and edge cutting. Appropriate toughness is beneficial for cutting, as it can suppress the degree of deformation during punching. If the toughness is too high, it will cause severe rebound after punching, which will actually affect the accuracy.
CNC punching is generally suitable for cutting low-carbon steel, electrolytic plates, aluminum zinc-coated plates, aluminum plates, copper plates, and stainless steel plates with a T = 3.5-4mm or less thickness. The recommended thickness for CNC punching is: aluminum alloy plates and copper plates are 0.8-4.0, low-carbon steel plates are 0.8-3.5mm, and stainless steel plates are 0.8-2.5mm. For copper plate processing, there is significant deformation, and for CNC punching of PC and PVC plates, there are large burrs on the processing edges and low accuracy.
The diameter and width of the tool used for stamping must be greater than the material thickness, such as Φ 1.5 cutting tools cannot punch 1.6mm materials, and materials below 0.6mm generally do not require NCT processing.
Stainless steel materials generally do not require NCT processing. (Materials ranging from 0.6 to 1.5mm can be processed using NCT, but there is significant tool wear, and the probability of scrap occurring during on-site processing is much higher than other materials, such as GI.)
Punching and blanking of other shapes can be as simple and uniform as possible.
The dimensions of CNC punching should be standardized, such as circular holes, hexagonal holes, and process slots with a minimum width of 1.2mm.
Punching and Blanking of Cold Stamping Dies:
A sheet metal stamping mold specifically designed for punching and blanking parts with large production capacity and small dimensions to improve production efficiency. It generally consists of a convex mold and a concave mold. Concave molds generally include press-in type, inlay type, etc. The convex mold generally has a circular shape, which can be replaced or combined, Quick loading and unloading type, etc. The most common stamping dies are punching dies (mainly including open blanking dies, closed blanking dies, punching and blanking composite dies, open punching and blanking continuous dies, closed punching and blanking continuous dies), bending dies, and rolling dies.
Features: Because punching and blanking with cold stamping dies can be completed in one go, it has high efficiency, good consistency, and low cost. Therefore, the processing plant generally opens cold stamping dies for processing structural components with an annual processing capacity of over 5,000 pieces and a relatively small part size. When designing the structure, it is necessary to consider designing according to the process characteristics of opening cold stamping dies for processing. For example, parts should not have sharp corners (unless necessary for use) and should be designed as rounded corners, which can improve the quality and lifespan of the mold and also make the workpiece beautiful, safe, and durable. To meet functional requirements, the structural shape of the parts can be designed to be more complex, etc.
Dense hole punching:
Dense hole punching can be regarded as a type of CNC punching. For parts with a large number of dense holes, to improve punching efficiency, accuracy, etc., a punching die that can punch a large number of dense holes at once is specially designed to process the workpiece—for example, ventilation screens, inlet and outlet windshields, etc.
Attention and requirements for dense hole design:
The design of dense holes on the product should consider the processing characteristics of the dense hole punching mold, which is repeated punching multiple times. Therefore, when designing the layout of dense holes, the following principles should be adopted:
- 1) When designing a dense hole layout, the first consideration is to consider a dense hole mold to reduce mold costs;
- 2) When arranging dense holes of the same type, they should be unified, with a constant value specified for the row spacing and a constant value specified for the column spacing. This way, dense hole molds of the same type can be universal, reducing the number of mold openings and the cost of the mold;
- 3) The size of holes of the same type should be consistent, such as hexagonal holes that can be uniformly cut into inner circles Φ 5 hexagonal holes, which are commonly used sizes for hexagonal holes in the company, accounting for over 90% of the hexagonal dense holes;
- 4) When two rows of holes are arranged in a staggered manner with unequal numbers, two requirements must be met: (1) The distance between the holes is relatively large, and the edge distance between the two holes is greater than 2t (t is the material thickness); (2) The total number of rows should be even;
- 5) If the spacing between dense holes is very small, the number of holes in each row must be even.
When designing the layout of dense holes, try to follow the above requirements as much as possible and ensure continuity and regularity to facilitate the opening of dense hole molds and reduce stamping costs. Otherwise, only a few punches or multiple sets of molds can be used to complete the processing.
After the workpiece is cut off, necessary trimming (polishing treatment) should be carried out on the edges, burrs, and joints. At the tool joint, a flat file should be used for trimming. For workpieces with larger burrs, a polishing machine should be used for trimming. At the small inner hole joint, a corresponding small file should be used for trimming to ensure the appearance is beautiful. At the same time, the trimming of the appearance also ensures the positioning during bending so that the position of the workpiece against the bending machine is consistent. Ensure consistency in product size for the same batch.
Laser cutting is a non-contact technology that uses electronic discharge as an energy source and a laser beam generated by a reflector group as the heat source. This high-density light energy is used to achieve punching and cutting of sheet metal parts.
- Features: Diversified cutting shapes, faster cutting speed than wire cutting, small heat affected zone, no deformation of materials, fine cuts, high accuracy and quality, low noise, no tool wear, no need to consider the hardness of cutting materials, can process large, complex shapes, and other difficult to process parts. But its cost is high, and it will also damage the support platform of the workpiece, and the cutting surface is prone to depositing oxide film, making it difficult to handle. Generally, only suitable for single piece and small batch processing.
- Attention and requirements: Generally, only used for steel plates. Aluminum and copper plates are generally unsuitable because the material transfers heat too quickly, causing melting around the incision, which cannot guarantee processing accuracy and quality. There is a layer of oxide skin on the laser-cutting end face, which acid washing cannot remove. The cutting end face with special requirements needs to be polished; Laser cutting of dense holes causes significant deformation and generally does not require laser cutting of dense holes.
Wire cutting is a machining method that uses the workpiece and electrode wires (molybdenum wire, copper wire) as one pole each and maintains a certain distance to form a spark gap when there is a sufficiently high voltage. The working fluid takes away the cut material.
Characteristics: High processing accuracy but low processing speed, high cost, and can change the material’s surface properties. Generally used for mold processing and not used as production parts. Some veneer profile panels have square holes without rounded corners that cannot be milled, and because aluminum alloys cannot be cut by laser, if there is no stamping space, they can only be processed by wire cutting. The speed is slow, the efficiency could be higher, and it cannot adapt to mass production. Design should avoid this situation.
Table.4 Comparison of Three Common Punching and Blanking Processing Characteristics
|Laser cutting||CNC punching (including dense hole punching)||Cold stamping die|
|Machinable material||Steel plate||Steel plate, copper plate, aluminum plate||Steel plate, copper plate, aluminum plate|
|Machinable material thickness||1mm -8mm||0.6mm -3mm||Generally less than 4mm|
|Minimum processing size (ordinary cold rolled steel plate)||Minimum fine seam 0.2mm, minimum circle 0.7mm||Punching a circular hole 0 ≥ t; Square hole small edge W ≥ t; Long slot width W ≥ t||Punching round hole Ø≧t, small side of square hole W ≥ t, long slot width W ≥ 2t|
|Minimum distance between holes and edges of holes and edges||≥ t||≥ t||≥ 1t|
|Preferred distance between holes and edges of holes and edges||≥ 1.5t||≥ 1.5t||≥ 1.5t|
|General machining accuracy||+0.1mm||+0.1 mm||+0.1mm|
|Appearance effect||Smooth outer edge, with a layer of oxide skin on the cutting end face||Large burrs with material burrs||A small amount of burrs|
|Curve effect||Smooth and versatile in shape||Large burrs and standardized shapes||Smooth and versatile in shape|
|Processing speed||Cutting outer circle fast||Quick punching of dense holes||Fastest|
|Processing text||Etching, shallow, unrestricted in size||Stamped concave characters with deep symbols; Size limited by mold||Stamping, concave text, symbols, deeper; Size limited by mold|
|Forming||Cannot||Can be used for concave points, sinking (sinking) holes, small stretching, etc||Can achieve more complex shapes|
Note: The following data are for cold-rolled steel plates.
Common problems and solutions in sheet metal cutting
Sheet metal cutting refers to the application of significant force on sheet metal, ultimately dividing the sheet metal into several parts. The most common cutting method is shear, which applies a shear force greater than the material’s ultimate shear strength, causing the material to fail and separate at that location. Like any other manufacturing process, several defects in the final product may affect its productivity, quality, and characteristics.
Burrs and deformed edges
Burr edges are sharp, uneven metal pieces that adhere to the sheared metal workpiece. Blunt blades or their incorrect position usually cause them. Excessive gaps between blades will cause them to tear rather than shear, while smaller gaps prevent the blades from cutting the material and generating burrs. Similarly, deformed edges are caused by incorrect fixture pressure and incorrect positioning of the blades. To prevent this situation, you can refer to the shearing machine manual and obtain the correct clearance and fixture pressure based on the material type and thickness.
After completing the shearing process, the metal may have undergone some twisting along its axis. This is caused by the cutting strip needing to be narrower or using an incorrect rake angle. This can be avoided by adjusting the rake angle based on the sheet’s characteristics, geometry, and cutting parameters.
When the thickness of the sheet metal changes along its width, an arc can be observed. This situation occurs when it moves horizontally but does not twist or lift along its edges. The result is a metal that is concave, convex, and triangular. Changing the direction of metal particles and the rake angle can also minimize this problem in the early stages.
When the edge rises slightly from the plane due to improper shearing, bending occurs. It is usually observed on long and narrow, thin slices. To overcome this, the front tilt angle should be minimized as much as possible, and the sheet must be clamped with a rear support.
Sheet metal processing technology: forming
The forming of sheet metal mainly involves bending, stretching, curling, ironing, and stamping.
1. Sheet metal bending
The bending of sheet metal refers to changing the angle of the sheet metal or its components and, for example, bending the sheet into V-shaped, U-shaped, etc. In general, there are two methods for sheet metal bending: one is mold bending, which is used for sheet metal structures with complex structures, small volumes, and large-scale processing; Another type is bending machine bending, which is used to process sheet metal structures with relatively large structural dimensions or low production capacity. At present, the bending of the company’s products is mainly processed using bending machines.
These two bending methods have their principles, characteristics, and applicability.
For structural components with an annual processing capacity of over 5,000 pieces and a relatively small part size (usually 300X300), the processing manufacturer generally considers opening stamping molds for processing.
Bending machine bending:
There are two types of bending machines: ordinary bending machines and CNC bending machines. Due to high precision requirements and irregular bending shapes, the sheet metal bending of communication equipment is generally performed using a CNC bending machine. Its basic principle is to use the bending knife (upper mold) and V-shaped groove (lower mold) of the bending machine to bend and form the sheet metal parts.
- Advantages: Easy clamping, accurate positioning, and fast processing speed;
- Disadvantages: Low pressure, can only process simple forming, and has low efficiency.
A bending radius is required at the bending point when bending sheet metal. The bending radius should be a manageable size and should be appropriately selected. A too small bending radius can easily cause cracking at the bending point, while a too large bending radius can easily cause bending to rebound.
The basic principle of the bending processing sequence is to bend from the inside out, from small to large, and first bend special shapes. After the previous process is formed, it does not affect or interfere with the subsequent processes.
A bent part has a minimum bending radius. When the material is bent, the outer layer is stretched in the rounded area, and the inner layer is compressed. When the material thickness is constant, the smaller the internal bending radius, the more severe the stretching and compression of the material. When the outer layer’s tensile force exceeds the material’s limit, fracture and fracture occur.
Common problems and solutions for sheet metal bending
Sheet metal bending is an important sheet metal process because it can draw various geometric shapes of parts without needing tools and has fast delivery time, high repeatability, and automation. It also allows products to be made from a single piece of metal, utilizing plastic deformation instead of connecting multiple components through welding or riveting, thereby reducing costs, improving strength, and simplifying assembly.
(1) Cracks appear at the bending angle
The main reasons for cracks in stretched parts are poor metal flexibility and small bending radius. To avoid these defects, please use softer metal or increase its ductility by heating and cooling slowly.
(2) Unstable bending angle
The main reasons for these defects are insufficient material pressure and irregular bending pressure leading to irregular compression buckling. Asymmetric convex and concave die fillets may also cause this issue. To solve this problem, increasing the jacking force and balancing the gap in the rounded corners of the convex and concave molds is necessary.
(3) Hole deformation
The position of the hole will deform during the bending process due to friction between the concave mold surface and the outer surface.
This defect can be increased by increasing the pressure on the ejecting plate or adding a hard point to increase the friction between the surfaces above so they will not slide.
(4) Uneven bottom of the concave plate
This defect is usually caused by using an ejection device, insufficient force, or uneven material. Therefore, ensure that the ejection device is set to the correct force unit or removed completely, and ensure that the material is evenly leveled before starting the bending process.
(5) Non parallel bending to the middle of the hole
This defect is due to the bending height being less than the minimum bending height limit, resulting in curve expansion and deformation. These defects can be solved by simply increasing the height of the bent part or material.
2. Sheet metal stretching
The stretching of sheet metal is mainly completed by CNC or conventional punching, requiring various stretching punches or molds.
The shape of the stretched part should be as simple and symmetrical as possible and formed in one stretch as much as possible.
The rounded corner radius between the bottom of the stretched part and the straight wall should be greater than the thickness of the plate. The thickness of the material after stretching will vary to a certain extent. The center of the bottom generally maintains the original thickness, the material at the bottom rounded corner becomes thinner, the material near the flange at the top becomes thicker, and the material around the rounded corner of the rectangular stretched part becomes thicker.
3. Sheet metal curling
Curling is a sheet metal forming process. After the initial production of sheet metal, there are usually sharp edges with “burrs”, and the purpose of curling is to make the sharp and rough sheet metal edges smooth to meet the project’s usage requirements.
4. Sheet metal ironing
Sheet metal can also be ironed to obtain a uniform thickness. For example, many beverage cans are made of aluminum, and the aluminum metal plate is too thick for the beverage can in its original state. Hence, it must be ironed to make it thinner and more uniform.
5. Sheet metal stamping
Stamping is a common sheet metal forming process that uses stamping machines and mold sets to punch holes in the sheet metal. During processing, the sheet metal is placed between the punch and the mold, and then the punch is pressed down and passed through the metal plate, completing the punching process.
Other forming methods of sheet metal:
- Reinforcing ribs: Pressing ribs on plate-shaped metal parts helps increase structural rigidity.
- Louvers: Louvers are usually used on various covers or casings to provide ventilation and heat dissipation. The forming method of louvers is to use one edge of the convex mold to cut the material, while the rest of the convex mold simultaneously stretches and deforms the material, forming a undulating shape with one side opening.
- Hole flanging (stretching hole): Used to machine threads or increase the rigidity of the hole opening. There are many forms of hole flanging, and the common one is to process the inner hole flanging of threads.
Table.5 Tolerances and Processing Accuracy
|NCT||Tolerance items||Position tolerance||Aperture tolerance||Minimum hole spacing|
|Single hole tolerance||±0.05||±0.03||1 times the material thickness|
|Tolerance between multiple holes||±0.05||±0.06||1 times the material thickness|
|Machine tool itself tolerance||±0.05|
|Bending||Length (m)||Bend type (per bend)|
|General bending||Fold back and flatten||Circular arc||Segment difference||Angle|
|Below 1.0||±0.2mm .||±0.2mm||Large arc ± 0.5mm (above 10R)||±0.2mm||±0.5°|
|Small arc ± 0.2mm (below 10R)|
|1.0-2.0||±0.3mm||1.5-2.0mm material thickness, with a folding length of less than 5mm, ± 0.5mm||Large arc ± 0.8mm (above 10R)||±0.3mm||±1°|
|Material thickness below 1.5mm, folding length below 5mm, ± 0.3mm||Small arc ± 0.3mm (below 10R)|
|2.0-3.0||±0.5mm .||To be discussed||To be discussed||To be discussed||±1°|
Solutions to prevent errors in various processes of sheet metal fabrication
During production, various errors often occur, leading to product defects and customer complaints. If you master some error prevention guidelines, you will greatly reduce the probability of making mistakes.
Sheet metal error prevention guide
(1) Review drawings
- Check if there are missing or missing dimensions in the drawings;
- Review whether the external dimensions and quantities are consistent between the drawings and the parts list (detailed list of cutting and unfolding dimensions), whether the unfolding dimensions on the parts list are correct, whether the cutting quantity is correct, whether the materials of the used plates are consistent with the requirements of the drawings, and whether there are any missing unfolding dimensions of the parts on the parts list;
- Mutual review of drawings, with one person designing and one person reviewing and signing for confirmation after the review is completed;
- Distribute to the shearing machine operators.
(2) Shearing machine
- To reduce consumption and improve material utilization, it is necessary to adopt a reasonable calculation and cutting method.
- Whether there is a review signature for the proofreading of the parts list, and if there is no review, cutting, and blanking are not allowed;
- Carefully check which plate material is required on the parts list, whether it is stainless steel, galvanized plate, or cold plate. Stainless steel plates are divided into 201 and 304 types;
- Before cutting, determine whether the remaining plates from the previous project can be used in this project. If there are any, cut the materials first. If there are no plates, open the entire large plate. The specifications of the large plate are: galvanized plate 1250 * 2500, stainless steel 1220 * 2440, and cold rolled plate has three specifications: 1000 * 2000, 1250 * 2500, and 2216 * 1000. When cutting the entire large plate, calculate how many plates need to be used and issue a material requisition to the production department for signature and material requisition;
- When cutting the entire large plate, the operating steps correspond to cutting the size of the parts list from large to small. When cutting cold rolled plates, it is also important to pay attention to which specification of the plate is used to cut the remaining material with the least amount of material and which specification of the plate is given priority for cutting and blanking;
- When blanking, it is also necessary to consider how to arrange the nesting, shear size, and plate size, whether to save material horizontally or vertically, and whether the remaining material can be cut into plates with slightly smaller sizes;
- Self-inspection should be done when cutting the first piece of each specification and size. The size should be positive or negative 0.5 mm, and the diagonal error should be positive or negative 1 mm. If the quantity exceeds 5 pieces, each specification and size should be inspected by the quality inspection department and signed after passing the inspection before production.
- After cutting, check whether the quantity is consistent with the quantity marked at the start of the component;
- After completing the entire project, the boards are cut and transported to the area for corner cutting and punching. The remaining materials are classified according to the thickness of the boards and placed on a dedicated shelf for easy use in the next project;
- Fill out the sheet consumption record form.
(3) Cutting and punching
Check if the cut board’s material, quantity, and size are correct.
- Expand the dimensions on the corresponding parts list, check if the cutting dimensions are correct, the quantity is consistent, and the material of the plate is consistent with the requirements of the drawing;
- According to the requirements of the drawings, adjust the corner cutting, punching, and punching of the support. The first piece should be self-inspected first. If the quantity exceeds 5 pieces, the first piece of each specification and size needs to be inspected by the quality inspector and signed after passing the inspection before punching can be carried out;
- After the punching is completed and sorted, the ones that need to be bent directly are transported to the vicinity of the bending machine. In contrast, those that need CNC punching are transported to the vicinity of the CNC punching machine.
(4) CNC punching machine
Firstly, inspect the board’s material, quantity, size, cutting angle, and punching accuracy.
- According to the drawings and parts list, proofread the unfolded dimensions with the drawings to avoid errors;
- Edit the program and transfer it to the CNC punching machine through the dedicated software of the CNC punching machine;
- There are several types of punching, some of which have different punching sizes and require the use of two or more programs;
- Which program needs to punch a few boards? Please check the quantity in advance. For example, if there are 10 boards of the same size, 3 of them will use the 1 # program, 7 of them will use the 2 # program, 3 of them will be clicked by the 1 # program, and the remaining 7 boards will be opened after clicking, to avoid the situation where one program punches one more board and the other program punches one less board;
- After the first sheet is punched, it is necessary to use a tape measure to measure whether it is consistent with the drawing to avoid the following boards being punched incorrectly. If the quantity exceeds 5, the first sheet of each specification needs to be inspected by the quality inspector and signed after passing the inspection before production.
(5) Bending machine
Firstly, check whether the board’s quantity, material, and size are consistent with the drawings.
- Before bending, carefully check the engineering drawing parts list to determine the required bending plate size, thickness, and material, and edit the program;
- Pay attention to the bending direction and whether symmetrical bending is necessary when bending according to the component diagram;
- After editing the program, do not place the board for trial folding. Observe that there must be gaps between the upper and lower molds. The names and codes of the upper and lower molds in the program should be consistent with the actual assembly of the upper and lower molds, and it is not allowed to be installed incorrectly;
- Carefully check whether the quantity is consistent with the quantity written on the parts list;
- After folding the first plate of each program, measure whether the bending size, angle, and forming size are consistent with the drawing requirements. If the quantity exceeds 5 pieces, the first plate of each specification needs to be inspected by the quality inspector and signed after passing the inspection before production;
- After bending, transport to the welding workshop;
- When shutting down, lower the upper mold to the lowest point, turn off the motor power, and finally, turn off the main power supply.
Sheet metal processing technology: connection method
(1) Connection type:
Welding, screw riveting, hole riveting, etc.
(2) Comparison of connection methods
1) Spot welding
Definition: After welding components are assembled, pressure is applied through electrodes to generate resistance heat from the contact surface and nearby areas of the current joint for welding.
Aluminum and iron, aluminum and copper, stainless steel and tinplate can all be mixed welded, but spot welding between aluminum and aluminum is relatively difficult.
Process requirements for spot welding:
- a. The total thickness of spot welding shall not exceed 8mm, and the size of the welding point is generally 2T + 3 (2T represents the material thickness of the two welding parts), as the upper electrode is hollow and cooled by cooling water. Therefore, the electrode cannot be infinitely reduced, and the minimum diameter is generally 3-4mm.
- b. The workpiece for spot welding must be punched with welding points on one side that contact each other to increase welding strength. The length of spot welding is about 30mm (metal thickness 2mm-5mm).
- c. The distance between two welding points: The thicker the weldment, the greater the center distance between the two welding points. If it is too small, the workpiece is prone to deformation due to overheating, and if it is too large, the strength is not enough to cause cracks between the two workpieces. Usually, the distance between two welding points is at most 35mm (for materials below 2mm).
- e. Gap of the weldment : The gap between the two workpieces is generally not more than 0.8mm before spot welding. When the workpiece is bent and then spot welded, the position and height of the solder joints are very important at this time. If it is improper, the spot welding is easy to misplace or deform, resulting in large errors.
Defects in spot welding:
- a. The surface of the damaged workpiece and the welding points are prone to forming burrs, which require polishing and rust-prevention treatment.
- b. The positioning of spot welding must rely on positioning fixtures to complete; if positioning points are used for positioning, their stability could be better.
2) Argon welding
Definition: For arc welding using argon gas as a shielding gas, it is necessary to use a fixture for positioning, and the heat generated by argon welding is particularly high.
Large size significantly impacts the workpiece, making it prone to deformation, while thin materials are more likely to burn out.
Welding of aluminum materials:
Aluminum and its alloys have a low melting point, low strength, and plasticity at high temperatures and may burn through due to improper welding, resulting in weld beading on the weld surface. If two aluminum materials are welded on a flat surface, a salad hole is usually punched on one side to enhance the welding strength. If it is a long seam welding, segmented spot welding is generally carried out, with a length of about 30mm (metal thickness of 2mm to 5mm).
Welding of iron materials:
When two workpieces are vertically welded, it can be considered to separately open process positioning holes and positioning ports on these two workpieces so that they can be positioned themselves. The port cannot exceed the material thickness of another workpiece, and the positioning point can also be punched to position the workpiece. Using a fixture to clamp the welded area is necessary to prevent the workpiece from being affected by heat and resulting in inaccurate dimensions.
Defect: Argon arc welding can easily burn out the workpiece, resulting in notches. The welded workpiece needs to be polished and polished at the welding site.
When there is interference in the unfolding of the workpiece or the workpiece is too large, it can be considered to divide the workpiece into several parts and overcome them through argon arc welding so that it can be welded together.
3) Drawing hole riveting
Definition: One part is a drawing hole, and the other is a salad hole, made into an inseparable connecting body through riveting molds.
Advantages: The Sara hole, matched with the extraction hole, has a positioning function.
The riveting strength is high, and the riveting efficiency through the mold is also relatively high.
Defect: one-time connection, nondetachable.
4) Riveting with rivets
Pull nails are divided into flat head and round head (umbrella-shaped). The riveting of flat head pull nails must have a sand hole on the side that contacts the pull nail head. The riveting of round head rivets has a flat contact surface.
Definition: Two parts with through holes are pulled by pulling nails, and the pull rod is pulled by a pulling nail gun until it breaks, causing the external expansion of the outer sleeve of the pulling nail to become an inseparable connecting body.
Common problems and solutions in sheet metal welding
Welding is usually used to connect two or more metal sheets. Whether it is MIG welding (gas shielded welding), TIG welding (tungsten gas shielded welding), shielded metal arc welding (SMAW), or flux-cored welding (FCAW), if appropriate techniques are not used, some problems may be faced.
When droplets form near the welding arc, splashing occurs. High currents, incorrect polarity, or insufficient gas shielding usually cause it. To avoid this situation, please reduce the current and arc length and increase the angle from the welding gun to the electrode plate. Cleaning the gas nozzle can also help.
These defects are caused by hydrogen, nitrogen, and oxygen absorption in the molten pool. After solidification, they are trapped in the weld seam. Oil, moisture, paint, and rust can also cause pores. Please ensure the board’s edges are clean and dry, use new welding materials, and check the welding gun for leaks to prevent this issue.
- Reverse buckle
When using high voltage or long arc length, tripping will occur. The use of incorrect electrodes or electrodes that are too thick relative to the thickness, as well as the rapid movement speed of the welding gun, may also cause this problem. This problem can be avoided by using electrodes of the right size to ensure slow movement of the welding gun, and if horizontal fillet welding is being carried out, avoid approaching the vertical plate.
When the internal stress exceeds the strength of the weld or base metal (or both), cracks may form on the weld. They may spread over time and, therefore must be addressed immediately. These defects can be avoided by carefully cleaning, polishing, and removing burrs from the edges of the metal plate so that they can bond well together. It is also helpful to ensure the appropriate temperature while reheating both sides of the joint.
Sheet metal processing technology: surface treatment
Definition: The process of treating iron parts in a solution containing caustic sodium nitrate to produce a thin black oxide film on the surface of the parts, abbreviated as blueing or blackening.
Function: Generally used to improve the corrosion resistance of the surface of parts and achieve a beautiful appearance, such as oxidation blackening of hardware parts, springs, aluminum, etc. (No significant impact on part size and accuracy)
Oxidation of aluminum: After chemical oxidation treatment, aluminum and its alloys have good corrosion resistance in corrosive media such as seawater, sulfate solution, and ethanol. Generally, there are sandblasting or wire drawing pre-treatments.
Anodizing: Anodizing is mainly used in the surface treatment of aluminum and its alloys, which can significantly improve the corrosion and wear resistance of aluminum and its alloy products. At the same time, it has a strong ability to adsorb coatings and pigments. When the anodizing film is used for metal protection, it is often combined with other protective layers (such as paint coatings) to form multiple protective layers. At this time, the anodizing film is often used as the bottom layer, on the one hand, to ensure good bonding between the surface protective layer and the substrate; on the other hand, it can also prevent the expansion of metal corrosion under surface protection when the surface protection layer is locally damaged or penetrated by corrosive media.
Anodizing of magnesium alloys:
After oxidation, the film is brittle and porous, usually only used for decoration and intermediate process protection, rarely used alone. Generally, organic coatings such as spray paint, resin, or plastic are required.
Anodizing of copper and copper alloys:
After oxidation, a semi-glossy blue-black oxide film (mainly composed of black copper oxide) is obtained, with a thin film layer that is not highly protective, brittle, and not wear-resistant. It cannot withstand bending and impact and is only suitable for working under good conditions or for the protection and decoration of instrument parts. After immersion in oil or paint, the protective performance is improved.
(2) Wire drawing treatment
Definition: Using sandpaper to form uniform patterns on the surface of the workpiece under a certain pressure.
Process treatment of wire drawing:
- a. The patterns formed by different types of sandpaper are also different. The larger the sandpaper model, the shallower the patterns formed by the finer sand particles. Conversely, the smaller the sandpaper model, the deeper the patterns formed by the coarser sand particles. Therefore, the sandpaper model must be indicated on the engineering drawing.
- b. Drawing has directionality: it must be indicated on the engineering drawing whether straight or horizontal pattern drawing (indicated by a double arrow).
The wire drawing surface of the workpiece must not have any protrusions. Otherwise, the protrusions will be flattened.
(3) The processing circumference of the sample center wire drawing machine: the maximum width is 850mm
Note: Generally, after wire drawing, electroplating, oxidation, and other treatments must be carried out, such as iron electroplating and aluminum oxidation.
A metal film is coated on the surface of the workpiece to provide corrosion resistance, wear resistance, lubrication, conductivity, and other functions, such as white zinc plating, color zinc plating, copper plating, etc.
(4) Baking paint
Definition: Spray a layer of paint on the surface of the workpiece, commonly known as oil spray or powder spray.
Surface treatment before painting: rust removal, oil removal, phosphating treatment. General requirements for workpieces during painting:
- a. If there are through holes on the required paint surface, a 0.1mm unilateral treatment must be applied to the hole during process arrangement to avoid reducing the hole size due to paint baking.
- b. If there are through-hole studs, nuts, and direct tapping threads on the painted surface, they must be noted, and special attention should be paid to avoid the paint adhering to the threads and causing defects.
- c. The workpiece after baking paint generally cannot be subjected to external impact forces, such as bending, stamping, etc., to avoid the peeling of the baking paint layer.
- e. Inspection method for baking paint: Use a single-sided blade to cut and prick the paint film, with four lines in both vertical and horizontal directions and a line distance of 1mm to form nine small squares with a side length of 1mm. Then, use adhesive tape to tightly compact and pull upwards with force to observe the paint film.
(5) Silk screen printing
Definition: Use screen printing oil to print the required text or pattern on the workpiece.
Definition: Using a polishing machine to treat the surface of a workpiece to obtain a bright surface polishing machine. Similar to a grinding wheel, it uses materials such as cloth, which are similar in shape to grinding wheels rather than grinding wheels.
Advantage: After polishing with ordinary stainless steel, it can obtain a surface as bright as a mirror.
After spot welding, the workpiece with molten slag can be removed using a polishing machine, and it is easy to grind into uneven surfaces using a grinder.
How to inspect whether precision sheet metal parts are qualified?
Inspecting precision sheet metal parts to determine their qualifications requires a combination of visual inspection, measurement techniques, and sometimes special testing. Here is a general guideline on how to inspect precision sheet metal parts:
- Surface Quality: Check for scratches, dents, burrs, discolorations, or other surface defects.
- Edges: Ensure edges are smooth and free of burrs.
- Holes and Cutouts: Ensure they are free of burrs and are properly deburred.
Measurement and Dimensional Inspection:
- Calipers: Useful for quick checks on thicknesses, hole diameters, and other basic dimensions.
- Micrometers: Used for higher precision measurements than calipers.
- Height Gauges: Can measure distances from a reference plane.
- Coordinate Measuring Machines (CMM): Can provide precise measurements in three dimensions.
- Go/No-Go Gauges: Custom-made tools for specific dimensions that quickly determine if a part is within tolerance.
- Radius Gauges: Used to measure the radius of a curved surface.
- Protractors and Angle Gauges: Ensure the angles on bent or folded parts are correct.
- Fitment Testing: If the metal part is meant to interface with another component, a fitment test is crucial to ensure it fits correctly and functions as intended.
- Assembly Testing: If the part is one component of a larger assembly, test it in that assembly to ensure it works well with other components.
- Material Certification: Check if the sheet metal material has a certificate indicating its composition and properties.
- Hardness Testing: This can be used to check if the metal has been properly heat-treated or meets the specifications for its intended use.
- Spectroscopy: Some facilities might use spectral analysis to verify the composition of the metal.
Specialized Testing (if applicable):
- Non-destructive Testing (NDT): Techniques such as ultrasonic testing, dye penetrant inspection, magnetic particle inspection, etc., to check for internal or hidden defects without damaging the part.
- Stress Testing: Testing the part under various stresses or forces to see if it deforms or breaks.
Documentation and Traceability:
- Part Numbering: Ensure each part is correctly labeled and can be traced back to its manufacturing batch.
- Quality Records: Maintain records of all inspections and tests for each batch or part number. This provides traceability and can be used for future reference or in case of issues.
Review of Tolerances and Specifications:
- Ensure you have a copy of the blueprint or the design specification for the sheet metal part.
- Verify that all dimensions, tolerances, and other criteria specified in the blueprint or spec are met.
Environmental Testing (if applicable):
- If the parts are used in specific environmental conditions (extreme temperatures, moisture, etc.), they may need to undergo testing to ensure they’ll hold up under those conditions.
- If any defects or issues are identified, a system should be in place to provide feedback to the manufacturing or design team so continuous improvements can be made.
Remember, the exact inspection methods and tools you’ll use will depend on the specific requirements of the parts you inspect. Understanding these requirements thoroughly and having a well-trained quality inspection team is crucial.
Solutions for reducing sheet metal fabrication costs
The cost of sheet metal fabrication is usually the focus of debate among product developers. Every aspect of sheet metal fabrication projects comes with related costs – design, possible prototypes, precision machining processes, etc. In addition to the process itself, materials also require money. Therefore, developing a cost-saving plan to utilize your sheet metal project is crucial.
We summarize the various factors that affect the cost of sheet metal fabrication and various techniques for reducing costs. Before that, let’s discuss estimating sheet metal fabrication costs.
(1) Cost estimation of sheet metal products
In today’s fiercely competitive market, it is necessary to understand the cost structure to develop appropriate pricing strategies fully. There are several stages in the production cycle of sheet metal parts, including cutting, bending, rolling, forming, stamping, welding, etc.
(2) Cost estimation for sheet metal fabrication
We will discuss the sheet metal fabrication cost calculator using simple ideas and concepts.
Step 1: Decompose the production cycle
Product development involves various cycles, and the production cycle typically varies between one application and another and may have different stages. Therefore, we need to decompose the loop into simpler processes. This way, we can focus on one cycle at a time.
Step 2: Calculate the cost of raw materials
Manufacturing products involves one or more raw materials. For example, drywall columns require metal coils, wooden bricks, and straps. At this point, we need to estimate the materials required to make a product.
The sheet metal fabrication cost calculator estimates the raw material cost of each product by:
Volume x Material Density x Material Cost (kg)=Raw Material Cost
Assuming $0.9 per kilogram is the material cost for steel with a density of 7.4 kg/dm3, a plate size of 900 x 500mm, and a thickness of 2mm. We have:
Raw material cost = (9 x 5 x 0.02) x 7.4 x 0.9=5.994 US dollars
You must repeat this process for each raw material used in the process.
Step 3: Add processing costs
At this stage, you need to understand the hourly cost of the system or machine, the system’s efficiency, and the system’s productivity (cycle time).
The calculation formula for machining cost is:
(Cost per hour x cycle time for one piece)/Efficiency = Processing cost
For example, assuming a cycle time of 15 seconds, an efficiency of 90.5%, and an hourly cost of $89.4. We obtained:
Processing cost = (89.4 x 15)/(0.905 x 3600) ≈ 0.41 US dollars
Therefore, the total direct production cost of a piece is:
- Raw material cost + processing cost = total product cost
- Total product cost (1 piece) = 5.994 USD + 0.41 USD = 6.404 USD
Therefore, you will notice that saving on raw material costs can benefit production costs, as it accounts for a large proportion.
Step 4: Repeat calculations for different production stages
We now have the production cost of machine 1 from raw materials to output. Then, we can use a sheet metal fabrication cost calculator to repeat the process for other stages or machines. This will help complete the production cycle until the product delivery point.
(3) Factors affecting sheet metal fabrication costs
The cost estimation of sheet metal fabrication is crucial for project planning. Technological progress has made cost-effective projects easier to complete. Although costs are expected to decrease, estimating sheet metal fabrication costs is crucial. Here, we will briefly outline the factors affecting the cost of metal manufacturing projects.
a. Raw material cost
One of the primary tasks of metal manufacturing is material selection. It is worth mentioning that the metal market affects the overall price of parts at a specific time. The prices of raw materials often fluctuate, affecting how manufacturers comprehensively estimate their prices. In addition, considering transportation costs, the distance between the manufacturer and the raw materials is another factor that affects the overall cost.
The thickness of the metal used for manufacturing plays a crucial role in material and labor costs. If your project requires multiple materials, this may increase costs. In some cases, the supply chain may be disrupted, leading to fluctuations in raw material costs.
b. Plating and welding costs in sheet metal fabrication
Let’s look at this premise – welding pre-plated metal plates could be safer. The overheated metal can cause the release of highly toxic zinc oxide from the coating. This situation is harmful to both workers and the environment. Welding risks and labor are other aspects that affect the cost of sheet metal fabrication, especially when using pre-plated sheet metal.
c. Welding sheet metal parts
Suppose you decide to use uncoated cold rolled steel for your project. Then, a coating process is carried out after manufacturing to improve corrosion resistance. The overall effect is an increase in your costs and delivery time. Therefore, you must return to your design and carefully examine the methods to avoid welding.
d. Require physical labor
Manufacturers with high skills, including professional assembly technicians, certified welders, inspectors, etc. The amount of physical labor required to complete the metal manufacturing process will affect the labor demand for the job, i.e., the number of workers required. This will also affect the estimation of sheet metal fabrication costs.
The best manufacturing companies use computer-aided design to ensure customer satisfaction. Using CAD/CAM software in manufacturing also requires professional skills, which can also affect costs. Mechanical labor is another factor to consider. Using specialized tools and equipment incurs significant capital expenditures, and manufacturers typically include these costs in each project. Obtaining precise metal cutting and bending involves using force, heat, and pressure to improve speed and production quality.
e. Metal structure
The metal structure and the resulting design complexity will affect the cost of manufacturing sheet metal. For example, compared to parts that require multiple complex bends, sheet metal parts that can be easily manufactured with one press have lower related costs. Therefore, the lower the cost, the less bending, cutting, and welding required for the project.
Similarly, stricter tolerances and complex designs often require longer manufacturing times, ultimately affecting cost estimates. Moreover, the complexity of metal structures and designs is closely related to labor costs. Therefore, it may be necessary to use Manufacturing Design (DFM) for cost-effectiveness and quality.
(4) Tips for reducing sheet metal fabrication costs
Now that you have understood the various factors that affect the cost of sheet metal fabrication projects, let’s look at how to achieve low-cost sheet metal fabrication. The following tips will help reduce the overall cost of the project:
a. Choose suitable raw materials
Due to the impact of raw material costs on sheet metal fabrication costs, choosing the appropriate raw materials for your project will help you save money. In this case, the inventory size of the material is usually the best choice. In addition, you should choose the cheapest material for the prototype.
For example, you would like to choose aluminum instead of stainless steel. For the final production components, choose the most cost-effective material that can fully utilize the functionality of the components.
Directly purchasing manufacturers from factories can also help you negotiate material costs. Their partnership and experience with these factories ensure lower bulk pricing, which you can benefit from. Directly purchasing factory materials also means that they can transport and store these materials cost-effectively.
b. Use universal sheet metal specifications
Please ensure your design uses standard plate gauges and sizes if possible. These standard sheet sizes typically have lower costs than special-length sheets. Thicker materials may make it difficult for you to bend and cut parts. Therefore, it is best to have your design adopt universal specifications and choose material grades based on current market conditions. This will help you reduce the cost involved in variable instruments.
In addition, metal plates with variable specifications are usually ordered specifically. This specially ordered material increases the overall manufacturing cost. Therefore, it is necessary to collaborate with your manufacturer to use standard gauges to achieve your manufacturing objectives while keeping your costs to a minimum.
c. Avoid complex design elements
As mentioned earlier, the more complex your design is, the more expensive it often becomes. Parts that require multiple cutting, bending, and welding will incur higher costs. Although specialized design elements may look great, they can significantly increase costs. Most of the time, it is wise to aim for simplicity. Therefore, you hope to design simpler angle bending to reduce manufacturing costs. The internal radius of such bending should be equal to one time the thickness of the selected material.
Using small bends on large and thick components often needs to be more accurate. Therefore, you should try to avoid using them as much as possible. Keeping the bending radius consistent is another way to make manufacturing more cost-effective. If not required, you also do not want to add features such as blind holes, machined pockets, or chamfered edges. These functions typically increase delivery time and manufacturing costs. The correct sheet metal design guidelines will help you make the best decisions for your product.
d. Consider organizing options to minimize costs
Your choice of a one-stop solution for sheet metal processing in Georgia’s real estate typically depends on various factors, including the application of parts and aesthetic requirements. For example, if your part is applied in harsh environments, using pre-plated metal is sufficient.
However, there are better choices if you need pre-coated metals such as welds, galvanized metal, etc. It would be best if you also considered delaying finishes such as engraving and screen printing until the final stage of product development.
Some materials are inherently resistant to corrosion. Therefore, they only require somewhat professional finishes. Specialized finishes may also require cost estimators to obtain external quotes, increasing prices and delivery times. Some common finishes are cheaper and faster. For example, finishes such as chrome plating, passivation, anodizing, and powder coating are easily obtained with minimal cost impact.
e. Contact professional manufacturers
Manufacturers who provide comprehensive services will be the best choice if you want to carry out low-cost sheet metal processing. You should choose a manufacturing company that can complete most processes independently. For example, quickly and directly helping you complete projects from design to assembly. Therefore, there is no need for additional cost expenditures or outsourced processes.
f. Other techniques
In addition to the techniques discussed above, some design considerations for sheet metal fabrication can also help you reduce costs. They include the following content:
Adhering to appropriate strict tolerances – Parts with multiple features with tolerance effects typically incur additional costs. Some of the tolerance annotations include radius, distance, and aperture. Since only a few surfaces of a part are crucial to its functionality, it is best to assign key tolerances to these surfaces. Limiting the use of strict tolerances will make the design more cost-effective.
Utilizing the optimal bending radius – Another simple way to save sheet metal fabrication costs is to use the optimal geometric shape in part design. The internal bending radius should usually be between 0.030 inches and 1 time the material thickness. In this way, manufacturers can easily form radii using tools specifically designed for these geometric shapes.
Consider fast and frugal fasteners – using fancy fasteners in your sheet metal project can also increase costs while slowing manufacturing speed. Therefore, you should use fast, economical, and ready-made fasteners.
Multiple factors need to be considered when designing sheet metal parts, including manufacturing costs. The techniques discussed above will help you effectively reduce sheet metal fabrication costs.
Where to find a suitable sheet metal manufacturer?
Finding a suitable sheet metal manufacturer involves a series of steps to ensure that the chosen company can meet your requirements in terms of quality, price, and delivery time. Here’s a guide on how to find one:
Define Your Requirements: Before you start looking for a manufacturer, you should have a clear idea of:
- The type of metal you require.
- Dimensions and tolerances.
- Volume and frequency of your orders.
- Required certifications (e.g., ISO 9001, AS9100 for aerospace, etc.)
- Desired delivery timeframes.
- Special finishes or treatments.
- Google: There are numerous sheet metal manufacturers on Google, allowing you to filter searches based on specific requirements.
- Industry-specific directories: Some industries have specific directories that list suppliers and manufacturers. For instance, the metalworking industry might have a specialized directory.
Local vs. Overseas Manufacturers:
- Local manufacturers: Easier communication, shorter shipping times, potentially higher costs, and a clearer understanding of quality standards.
- Overseas manufacturers: Typically in countries like China, India, and others where labor costs might be lower, potentially leading to cost savings. However, there might be challenges like longer shipping times, language barriers, and sometimes variations in quality.
Trade Shows: Attending industry-specific trade shows or expos can be a great way to meet manufacturers in person, assess their capabilities, and build relationships.
Recommendations: Ask peers in your industry, friends, or colleagues if they can recommend any manufacturers they’ve worked with.
Request Quotations: Once you have shortlisted a few manufacturers, request quotes from them. This will not only give you an idea about the pricing but also about their responsiveness and customer service.
Visit the Manufacturing Facility: If possible, visit the manufacturing facility. This can give you an insight into their operations, quality control processes, and overall capabilities.
Ask for Samples: Before placing a large order, ask for samples or consider placing a small pilot order. This will give you an idea of the quality of their work and their reliability in terms of delivery.
Check Reviews and References: Look for online reviews, testimonials, or case studies. You can also directly ask the manufacturer for references.
Negotiate Terms: Once you’re satisfied with a manufacturer, negotiate terms that are favorable for both parties in terms of payment, delivery, and quality checks.
Continuous Evaluation: Even after choosing a manufacturer, it’s essential to periodically evaluate the quality of their work, their adherence to delivery timelines, and overall service.
Remember that the key is not just to find a manufacturer, but to build a long-term, reliable partnership that benefits both parties.