Machining: Beginner’s Guide to Machining
Mastering machining technology: introduction to machining
Even if you know little or nothing about manufacturing, you’ve probably heard the term “machining” before. It is widely used by manufacturing companies to transform raw materials into finished products. Based on the name alone, you might think that machining simply refers to the use of any machine. While machining certainly requires the use of machines, that is not the actual definition.
What is machining?
Machining is the process of changing the form factor or performance of a workpiece by means of a mechanical device. In machining, a manufacturing company uses a machine to remove material from a workpiece until the desired size and shape is achieved. Machining is a prototyping and manufacturing process that creates the desired final shape by removing unwanted material from a larger piece of material.
Manufacturing workers who specialize in machining are called machinists and have the skills and knowledge needed to perform the process on a workpiece.
What types of materials does machining support?
Machining supports many different materials. It is most commonly used on metal workpieces, including iron, steel, aluminum, bronze and copper. That said, workpieces made of non-metallic materials can also be machined, including wood, ceramics, plastics, and composites. In general, workpieces made from harder materials require a greater amount of machining effort. For example, steel workpieces may require sharper tools and greater forces than wooden workpieces.
What are the different processes of machining?
Machining processes can be divided into three main categories: turning, milling and drilling. Turning is a process that uses a fixed tool to remove material from a rotating workpiece. Milling, on the other hand, is a machining process that uses a rotating tool to remove material from a stationary workpiece. Drilling is a mechanical process that uses a rotating tool called a drill to cut threaded holes in a workpiece.
There are other machining processes that do not fall into one of these three categories. Polishing, for example, is a process that relies on sliding contact to deform the surface of a workpiece. Polishing is often used on plastic workpieces to produce a smoother surface. Other machining processes such as polishing are unique in that they do not usually produce chips. Turning, milling and drilling are all by-products. However, other machining processes do not produce any chips or swarf.
So what are the forms of machining?
Turning is mainly due to the rotation of the workpiece, which is cut into the required shape by the turning tool. Internal and external cylindrical surfaces are obtained when the tool moves along the parallel axis of rotation. Tapered surfaces are formed when the tool moves along an oblique line intersecting with the axis. Rotary surfaces are formed on a profiling lathe or CNC lathe with controlled tool feed along a curve. Another type of rotary surface is produced by using a shaped turning tool with transverse feed. In addition to this machining threaded surfaces, end planes and eccentric shafts can also be machined by turning.
Milling machining mainly relies on the rotation of the tool. Milling is divided into horizontal milling and vertical milling. The plane of horizontal milling is formed by the edge on the outer surface of the milling cutter. Vertical milling is formed by the end face of the milling cutter. To obtain higher cutting speed and increase productivity, the speed of the milling cutter can be increased. However, due to the cutting in and out of the milling cutter teeth, the impact is formed and the cutting process is prone to vibration, thus limiting the improvement of surface quality.
Planing is mainly a reciprocating linear motion of the tool to cut the workpiece. Therefore, the speed of planing is relatively low, and thus the productivity is low. However, the accuracy and surface roughness of planing are smoother than the results of milling.
Grinding relies mainly on the rotation of the grinding wheel and abrasive to process the workpiece. When a grinding wheel is grinding, the abrasive grains on the wheel mainly perform three effects of cutting, scoring and sliding on the surface of the workpiece. The abrasive grains themselves are gradually dulled from sharp, making the cutting action worse and the cutting force greater. Therefore, after grinding for a certain period of time, it is necessary to dress the grinding wheel with diamond turning tools, etc.
5. Tooth surface processing
Tooth surface processing is a new processing method, this processing method is divided into two categories: one is the forming method, the other is the spreading method. The forming method mainly uses the ordinary milling machine for processing, and the tool is the forming milling cutter, which requires two simple forming motions, namely the rotary motion and linear movement of the tool. The common machine tools used for machining tooth surfaces by the spreading method are hobbing machines, gear shaping machines, etc.
6. Complex surface processing
For the processing of complex surfaces, CNC machine tools come in handy. Cutting of three-dimensional surfaces, mainly using profiling and CNC milling methods or special processing methods. Imitation milling must have the prototype as a model. Machining ball head profiling head, has been a certain pressure to contact the prototype surface. The motion of the profiling head is transformed into an inductive quantity, and the machining amplification controls the motion of the three axes of the milling machine to form the trajectory of the cutter head along the surface. The milling cutter is mostly a ball-ended cutter with the same radius as the profiling head. The advent of CNC technology has provided a more efficient method for surface machining.
7. Special machining
Special machining is a different type of machining from traditional cutting. Special machining can use physical (electrical, acoustic, optical, thermal, magnetic), chemical or electrochemical methods to process the workpiece material and make it into the shape we need.Special machining methods are a general term for a series of machining methods that use chemical, physical (electrical, acoustic, optical, thermal, magnetic) or electrochemical methods to process workpiece materials, as opposed to traditional cutting methods. These machining methods include: chemical machining (CHM), electrochemical machining (ECM), electrochemical mechanical machining (ECMM), electric discharge machining (EDM), electrical contact machining (RHM), ultrasonic machining (USM), laser beam machining (LBM), ion beam machining (IBM), electron beam machining (EBM), plasma machining (PAM), electrohydraulic machining (EHM ), Abrasive Flow Machining (AFM), Abrasive Jet Machining (AJM), Liquid Jet Machining (HDM), and various types of composite machining, etc.
Electric discharge machining
EDM is the use of the tool electrode and the workpiece electrode between the high temperature generated by the instantaneous spark discharge to melt the surface material of the workpiece to achieve the processing. EDM machine tools are generally composed of pulse power supply, automatic feed mechanism, machine tool body and working fluid circulation and filtration system. The workpiece is fixed on the machine table. The pulse power supply provides the energy required for processing, and its two poles are connected to the tool electrode and the workpiece respectively. When the tool electrode and the workpiece approach each other in the working fluid driven by the feed mechanism, the voltage between the poles penetrates the gap and generates a spark discharge, releasing a large amount of heat. The surface layer of the workpiece absorbs the heat and reaches a very high temperature (over 10,000°C), and its local material is etched down due to melting or even vaporization, forming a tiny crater. The working fluid circulation and filtration system forces the clean working fluid to pass through the gap between the tool electrode and the workpiece with inevitable pressure to exclude the electro-etching products in time and filter them out from the working fluid. As a result of multiple discharges, a large number of craters are produced on the surface of the workpiece. The tool electrode is driven down by the feed mechanism and its contour shape is “copied” onto the workpiece (the tool electrode material is also etched out, but at a much lower rate than the workpiece material).
- ① Processing hard, brittle, tough, soft and high melting point conductive materials.
- ② Processing of semiconductor materials and non-conductive materials.
- ③ Processing of various types of holes, curved holes and micro holes.
- ④ Processing of various types of three-dimensional curved cavities, such as mold chambers of forging dies, die-casting dies and plastic dies.
- ⑤ Used for cutting, cutting and surface strengthening, engraving, printing nameplates and marks, etc.
Wire EDM machine tools for processing two-dimensional contour-shaped workpieces with wire electrodes
Electrolytic machining is a method of forming workpieces using the electrochemical principle of anodic dissolution of metal in an electrolytic solution. The workpiece is connected to the positive terminal of the DC power supply and the tool is connected to the negative terminal, with a narrow gap (0.1mm – 0.8mm) between the two terminals. The electrolyte with the necessary pressure flows through the gap between the two poles at a high speed of 15m/s – 60m/s). When the tool cathode is continuously fed to the workpiece, the metal material is dissolved on the surface of the workpiece facing the cathode according to the shape of the cathode surface, and the electrolysis products are carried away by the high-speed electrolyte, so the shape of the tool surface is “copied” on the workpiece accordingly.
- ① Low working voltage and high working current.
- ② Processing complex shaped surfaces or cavities in one pass with simple feed motion.
- ③ It is possible to machine difficult to machine materials.
- ④ Higher productivity, about 5 – 10 times that of EDM.
- ⑤ Machining without mechanical cutting force or cutting heat, suitable for the processing of easily deformed or thin-walled parts.
- ⑥ The average machining tolerance can reach about ±0.1mm.
- ⑦ More ancillary equipment, a large footprint, high cost.
- ⑧ Electrolytic fluid both erosion of machine tools, and easy to pollute the environment. Electrolytic processing is tightly used for processing type holes, cavities, complex surface, small diameter deep holes, rifling and deburring, engraving, etc.
The laser processing of the workpiece is done by the laser processing machine. Laser processing machines usually consist of lasers, power supplies, optical systems and mechanical systems. The laser (commonly used are solid-state lasers and gas lasers) converts electrical energy into light energy to produce the required laser beam, which is focused by the optical system and then irradiated on the workpiece for processing. The workpiece is fixed on a three-coordinate precision table, which is controlled and driven by the CNC system to complete the required feed motion for machining.
- ① No machining tools are required.
- ② The laser beam has a high power density and is capable of processing almost any hard-to-process metal and non-metal material.
- ③ Laser processing is non-contact processing, and there is no force deformation on the workpiece.
- ④ The speed of laser punching and cutting is very high, and the material around the processing part is almost not hindered by the cutting heat, and the thermal deformation of the workpiece is very small.
- ⑤ Laser cutting has a narrow slit and good cutting edge quality. Laser processing has been commonly used for diamond wire drawing die, watch and jewel bearings, porous skin of dispersion air-cooled punching sheet, small hole processing of engine injection nozzle, aero-engine blade, etc. and cutting processing of many kinds of metal materials and non-metal materials.
Ultrasonic machining is a method of machining the workpiece by using ultrasonic frequency (16KHz – 25KHz) vibration of the tool end to impact the suspended abrasive in the working fluid, and the abrasive grains to impact and polish the workpiece surface. The ultrasonic generator transforms the AC power into ultrasonic frequency oscillation with a certain power output, and transforms this ultrasonic frequency oscillation into ultrasonic mechanical vibration by means of a transducer, which amplifies the displacement amplitude of the vibration from 0.005mm – 0.01mm to 0.15mm with the help of an amplification bar, driving the tool vibration. The tool end impacts the suspended abrasive particles in the working fluid during the vibration, which continuously impacts and polishes the processed surface at a special speed, crushing the material in the processed area into very fine particles and then impacting them down. Although very little material is impacted each time, the high frequency of the impact still results in an inevitable processing speed. Due to the circulating flow of working fluid, the impacted material particles are carried away in time. As the tool slowly penetrates, its shape is “copied” on the workpiece.
In the processing of difficult-to-cut materials, often ultrasonic vibration and other processing methods with composite processing, such as ultrasonic turning, ultrasonic grinding, ultrasonic electrolytic processing, ultrasonic wire cutting, etc.. These composite processing methods combine two or even more processing methods together, which can play a complementary role to make the processing efficiency, processing accuracy and surface quality of the workpiece significantly improved.
How to carry out mechanical processing?
The main content of the parts machining process in modern society, mechanical processing of parts are generally used in the form of CNC processing, so in the processing of parts, to first understand the relevant processing technology, develop a suitable processing program, in-depth study and analysis of the parts CNC machining process. First of all, in the CNC mechanical processing of parts, to choose the appropriate CNC machine tools, in the CNC machine operations, and determine what the process of processing is. Then develop a suitable machining plan for the CNC machining of parts, to be processed by the analysis of the drawings of the parts, the parts of the parts processing content and the use of suitable processing technology. The most important thing in the parts machining is to design the process of parts machining, which is related to the quality of the parts, we need to be clear about the steps of the parts machining process, the selection of the benchmark, the selection of processing tools, the selection and installation of fixtures and processing strategies and process parameters to determine, so as to develop the most appropriate processing technology. In addition, we have to prepare and check the program of CNC programming of parts machining, control the programming error and improve the programming quality and efficiency.
About the process of parts machining
The characteristics of the parts machining process parts mechanical processing is generally carried out in the form of CNC, so inevitably with the characteristics of CNC machining, but also has its own characteristics.
- (1) Parts of CNC machining requires the content of the processing process to be detailed and specific. CNC mechanical processing of parts, will be pre-developed CNC machining program, and then in the CNC machine tool operation, including the processing program, the choice of tools, processing methods and corresponding processing parameters, etc., these requirements for the mechanical processing of parts must have a specific and detailed program, the analysis of the program, and finally the formation of parts of the processing program.
- (2) Parts of mechanical CNC machining process requirements more rigorous and accurate. Parts mechanical machining process using CNC machining mode, which makes parts processing higher precision, better quality, processing does not require too many people, saving manpower, but on the other hand, the reduction of human intervention, so that parts in the process of processing if a problem can not be adjusted artificially, so parts mechanical CNC machining process in the degree of setting to be more rigorous and precise The part can not appear a small error, because the existence of error is likely to lead to processing technology can not reach the standard and make parts abandoned, or even cause mechanical accidents.
- (3) In the mechanical CNC machining of parts, to the parts of the graphics for mathematical calculations, mathematical calculations of the set value of the programming dimensions. Because the mechanical processing of parts is used in the mode of CNC, so in the processing before the programming design, the size of the parts for geometric mode, the size of the parts processing mathematical calculations, so in the programming to consider from all aspects to carry out a more optimal design of the parts.
The design principles of parts machining process analysis
The principle of positioning datum selection positioning datum refers to the surface of the relative position of the part to the machine tool and the tool when the part is machined, and the part is used in the initial processing is the most primitive surface without processing, which is the coarse datum, if the original processing is used after the positioning datum has been processed, which is the fine datum. Then, in the machining of parts, what surface should be selected as the positioning reference, which must be carefully considered in the process of machining parts. The choice of the positioning reference will affect the quality of the part processing and the complexity of the machine tool fixture structure. So what are the principles for selecting the coarse and fine datums?
Rough datum for the selection of the principles followed by the choice of coarse datum for the processing of parts, to ensure that the material to be sufficient, processing surface has sufficient margin, and the part is not processed on the surface of the size and location of the machined surface to meet the requirements of the processing drawings. If you choose a coarse reference, then ensure that the surface of the part to facilitate positioning, easy clamping and processing, and the selected fixture to be as simple as possible. When choosing a rough datum, be sure to determine the machined surface and unmachined surface, to have a precise location selection, generally unmachined surface as a rough datum. When choosing the rough datum is generally to meet the important surface for rough machining after the margin is small and uniform, the unmachined surface should be selected so that the position error of the rough datum can be evenly distributed in the unmachined surface, and the rough datum surface should be as flat and complete as possible, do not have a gap, which is conducive to the location of the setting.
The principles followed when selecting the fine reference choose the fine reference, first of all, we should observe whether the fine reference surface is convenient for positioning and clamping processing, and if a certain side is selected as the fine reference, the other side can be selected to use the selected surface positioning method to improve processing efficiency, so in the positioning of the precise surface should be carefully considered. Precision datum using the principle of precise overlap, that is, using a unified positioning principle to position other faces for finishing.
The principle of part surface processing method selection for different parts surface and different parts processing requirements and parts structure characteristics, material properties, etc., to choose the appropriate processing method to carry out the processing of the parts surface. Parts processing method to determine, generally is to determine the last processing method of the parts, and then from back to front, deduced to determine the processing method of the relevant processes in front.
(1) The principle of economic applicability
In the processing of parts, the first processing method of processing economy analysis, that is, the equipment, technology, skilled workers, processing time for the choice of analysis, that is, to determine the applicability of processing, to determine the accuracy range of processing, accuracy range to adapt to the accuracy requirements of the surface processing of parts and surface roughness requirements, in order to ensure that the processed parts meet the requirements.
(2) Production type adaptation principle
Different types of production to choose different processing methods, for mass production, often using high-efficiency machine tools and advanced processing methods, and for small batch production of parts, the general use of ordinary machine tools and conventional processing methods of production.
(3) Processing method matching principle
The machining method selected for mechanical processing of parts should match the accuracy of the shape and surface position of the machined surface, and the material of the parts, and the existing equipment conditions and workers’ skill level. Should be specific analysis of specific problems, according to the processing requirements and available resources for processing, do not blindly match, resulting in processing failure.
The principle of parts machining process sequence selection
Types of machining order parts machining process according to the nature and role of processing, divided into different processing stages. There are generally roughing stage, semi-finishing stage and finishing stage. In the roughing stage, the main is to cut the residual material on the surface of the machined parts to complete in the basic parts processing. In the semi-finishing stage, it is mainly to finish the rough machining of the part surface for secondary surface processing. In the finishing stage is the precise machining of the part to achieve the requirements of the part processing. For some demanding parts processing, but also through a more detailed processing stage.
The principle of combination of parts processing process in the initial analysis of the parts, select the appropriate processing sequence, in accordance with the structural characteristics of the parts, production type, technical requirements, equipment selection and other specific production conditions for further processing sequence determination, the development of a reasonable processing technology. Work order dispersion principle. Mechanical processing of parts to follow the principle of process dispersion, the parts to be processed often need to go through multiple processes, the process of processing technology is longer, each process requires processing content is relatively simple. On the basis of the principle of process decentralization, the selection of reasonable process equipment can reduce processing time, but also facilitate the replacement of products. The principle of process concentration. The processing of each surface of the part is concentrated in a few processes, and each process has more steps, which is the process concentration principle. In this way, the parts are processed in such a way that it is easy to use funny special equipment and improve the efficiency and productivity of processing. The process concentration principle greatly simplifies production planning and production organization, reduces the number of workers needed to process parts, and increases processing efficiency. But it increases the difficulty of adjusting and maintaining the equipment, increases the workload of production preparation, and increases the difficulty of replacing new products.
In actual production, the principle of process concentration is often used in the processing of small-lot parts, and the principle of process decentralization can be used in the processing of large-lot parts for both the assembly-line production mode and the principle of process concentration for the mechanical processing of parts.
Technical requirements for machining
1. Tolerance requirements
- (1) Unannotated shape tolerance should be consistent with the requirements of GB1184-80.
- (2) uninjected length size tolerance ± 0.5 mm.
- (3) casting tolerance zone symmetry in the basic size configuration of the blank casting.
2. Cutting processing parts requirements
- (1) Parts should be checked and accepted according to the process, and only after passing the inspection in the previous process, can be transferred to the next process.
- (2) The machined parts are not allowed to have burrs.
- (3) After finishing parts shall not be placed directly on the ground, should take the necessary support, protection measures. Processing surface is not allowed to have rust and affect the performance, life or appearance of the bump, scratch and other defects.
- (4) Rolling finishing surface, after rolling shall not have the phenomenon of peeling.
- (5) The final process after heat treatment of the parts, the surface should not have oxide skin. After finishing with the surface, the tooth surface should not be annealed
- (6) The machined thread surface should not be allowed to have defects such as black skin, bumping, messy buckle and burr.
The total thickness of the metal layer removed from a machined surface in the process of turning from a blank to a finished product is called the total machining allowance for that surface. The thickness of the metal layer removed in each process is called the inter-process machining allowance. For rotating surfaces such as external circles and holes, the machining allowance is considered from the diameter, so it is called symmetrical allowance (i.e. bilateral allowance), i.e. the actual thickness of the metal layer removed is half of the machining allowance on the diameter. The machining allowance for a flat surface is a unilateral allowance, which is equal to the actual thickness of the removed metal layer. The purpose of leaving machining allowance on the workpiece is to remove the machining errors and surface defects left by the previous process, such as cold hard layer, porosity, sand trap layer on the surface of the casting, oxide skin, decarburization layer, surface cracks on the surface of the forging, internal stress layer and surface roughness after the cutting process. So as to improve the accuracy and surface roughness of the workpiece. The size of the machining allowance has a large impact on the machining quality and productivity. Machining allowance is too large, not only increases the amount of machining labor, reducing productivity, but also increases the consumption of materials, tools and electricity, increasing the cost of processing. If the machining allowance is too small, it can not eliminate the various defects and errors in the previous process, but also can not compensate for the clamping errors in the process, resulting in scrap. The selection principle is to ensure the quality of the premise, so that the margin as small as possible. Generally speaking, the more finish machining, the smaller the process margin.
YAANG is specialized in large frame welding processing, large CNC gantry milling processing, large mechanical plate processing, large precision CNC lathe processing, horizontal CNC processing, precision mechanical parts processing, chassis sheet metal parts processing, hardware stamping parts Processing of various large high precision hardware parts and components of large mechanical processing plant.
What are the machining tools?
The machines needed for processing include digital display milling machine, digital display molding grinder, digital display lathe, EDM machine, universal grinder, machining center, laser welding, medium wire walking, fast wire walking, slow wire walking, external grinder, internal grinder, precision lathe, etc., which can be used for turning, milling, planing, grinding and other processing of precision parts. Such machines are good at turning, milling, planing, grinding and other processing of precision parts, and can process various irregular shaped parts, The machining accuracy can reach 2 μ m。
Different types of processing tools and technologies
Type of machining tool
- Boring tool. These tools are usually used as finishing equipment to expand holes previously cut in the material.
- Cutting tools. Equipment such as saws and scissors are typical examples of cutting tools. They are usually used to cut materials with predetermined dimensions, such as metal plates, into the desired shape.
- Drilling tools. This kind of tool consists of a double-edged rotating device, which can produce a circular hole parallel to the rotating axis.
- Grinding tools. These tools use a rotating wheel to achieve fine machining or light cutting on the workpiece.
- Milling tools. Milling tools use rotating cutting surfaces with several blades to create non-circular holes or cut unique designs from materials.
- Turning tools. These tools rotate the workpiece on its axis and the cutting tools shape it. Lathe is the most common type of turning equipment.
What are the benefits of machining?
Machining is the process of changing the size or performance of the workpiece through mechanical equipment. Machining plays a very important role in modern industrial production, and with the development of science and technology, there are more and more methods of machining, and the common types of machining are turning, milling, drilling, planing, grinding, etc. For the majority of users, we should not only know the classification of common tools used in machining equipment and how to improve the quality of machined workpieces, but also understand the advantages of machining, which will enable us to better choose the right processing method when designing products.
Advantages of machining
1. Effective increase in production efficiency.
High-speed machining allows the use of larger feed rates, 5-10 times higher than conventional cutting, and the rate of material removal per unit of time can be increased by 3-6 times. When machining parts that require large amounts of metal removal, this can result in a significant reduction in machining time.
2. At least 30% reduction in cutting forces.
Due to the high-speed use of very shallow depth of cut and narrow cutting width, so the cutting force is smaller, compared with conventional cutting, cutting force can be reduced by at least 30%, which can reduce the processing of rigid parts to reduce the processing machining deformation, so that some thin-walled class of fine workpiece cutting and processing is possible.
3. Machining quality is improved.
Because the excitation frequency of cutting tool is far away from the inherent frequency of the process system when rotating at high speed, it will not cause forced vibration of the process system and ensure a better machining condition. Because the depth of cut, cutting width and cutting force are small, making the tool, workpiece deformation is small, maintaining the size of the sex, also makes the cutting damage layer thinner, residual stress is small, to achieve high precision, low roughness machining.
Analysis of the formation of frequency from the kinetic point of view can be seen, the reduction of cutting forces will reduce the vibration generated by cutting forces (i.e., forced vibration) amplitude; speed increases so that the working frequency of the cutting system is far from the inherent frequency of the machine tool, to avoid the occurrence of resonance; therefore, high speed can greatly reduce the processing surface roughness, improve machining quality.
4. Reduce the processing energy consumption, saving manufacturing resources.
Due to the high metal removal rate per unit of power, low energy consumption and the short in-process time of the workpiece, thus improving the utilization of energy and equipment, reducing the proportion of cutting processing in the total resources of the manufacturing system, in line with the requirements of sustainable development.
5. Simplify the processing process.
Conventional cutting can not process the quenched material, quenching deformation must be manually trimmed or solved by electrical discharge machining. High-speed can directly process the quenched material, in many cases can completely eliminate the electrical discharge process, eliminating the problem of surface hardening caused by electrical discharge processing, reducing or eliminating the need for manual finishing process.
Disadvantages of machining
1. Very high technical requirements for machining personnel;
2. High price of machining equipment and large one-time investment.
Understanding the advantages of machining and the disadvantages of machining, you can better choose the processing method when processing the product, the current machining has been commonly used in many fields, has become a common processing method.
How to improve the quality of machined workpieces
About machining, we should not only know the machining process that affects the machining error, the main factors that easily cause the deformation of the workpiece in machining and the five principles to improve the accuracy of machining these knowledge, but also should know how to improve the quality of machined workpieces and improve the quality of machining.
Six easy to affect the machining process of machining errors
In the machine tool processing process a little inattention, will cause errors, easy to cause machining errors in the processing process which are several, you are clear understanding?
1. The production of the machine itself manufacturing errors
The manufacturing error of the production machine itself mainly includes spindle rotation error, guide error and drive chain error.
Spindle rotation error refers to the actual axis of rotation of the spindle at each instant relative to its average axis of rotation of the amount of change, it will directly affect the accuracy of the workpiece being processed. The main reasons for the spindle rotation error are the coaxiality error of the spindle, the error of the bearing itself, the coaxiality error between the bearings, spindle winding, etc. Guide rail is a machine tool to determine the relative position of the machine components of the benchmark, but also the benchmark of the machine tool movement. The manufacturing error of the guide itself, the uneven wear of the guide and installation quality is an important factor causing the guide error. Drive chain error refers to the beginning and end of the drive chain between the two ends of the relative movement of the transmission components error. It is caused by the manufacturing and assembly errors of each component link in the transmission chain, as well as the wear and tear during use.
2. Positioning error
Positioning error mainly includes the inaccuracy of the datum and the inaccuracy of the positioning sub manufacturing error. When processing the workpiece on the machine tool, a number of geometric elements on the workpiece must be selected as the positioning datum for processing, if the positioning datum selected and the design datum (used to determine the size of a surface on the part diagram, the position based on the datum) does not overlap, it will produce the datum non-coincidence error
The positioning surface of the workpiece and the positioning element of the fixture together constitute the positioning vice, and the maximum position change of the workpiece caused by the inaccurate manufacturing of the positioning vice and the clearance between the positioning vice is called the manufacturing inaccuracy error of the positioning vice. The inaccuracy of positioning sub manufacturing error will be generated only when the adjustment method is used, and will not be generated in the trial cutting method.
3. Adjustment error
In each process of machining, it is always necessary to adjust the process system in one way or another. Since the adjustment cannot be absolutely accurate, thus generating adjustment errors. In the process system, the workpiece, tool in the machine tool mutual position accuracy, is through the adjustment of the machine tool, tool, fixture or workpiece to ensure. When the machine tool, tool, fixture and workpiece blanks, such as the original accuracy of the process requirements and do not take into account the dynamic factors, the adjustment error plays a decisive role in machining errors.
4. Geometric error of the tool
Any tool in the cutting process is inevitable to produce wear, and thus cause the size and shape of the workpiece to change. Tool geometric error on the impact of machining errors vary with the type of tool: when using fixed-size tool processing, the manufacturing error of the tool will directly affect the machining accuracy of the workpiece; and the general tool (such as turning tools, etc.), the manufacturing error on the machining error has no direct impact.
5. The geometric error of the fixture
The role of the fixture is to make the workpiece equivalent to the tool and machine tool has the correct position, so the geometric error of the fixture on the machining error (especially the position error) has a great impact.
6. Measurement error
Parts in the processing or measurement after processing, due to the measurement method, gauge accuracy, as well as the workpiece and subjective and objective factors have a direct impact on the measurement accuracy.
The above six machining errors can be avoided to a certain extent, so the need for machining operators in the processing of these six easy to cause machining errors in the processing process can be more carefully and carefully tested and verified in all directions before mechanical machining operations, so that you can better reduce the impact of machining errors.
What are the main factors that can easily cause deformation of the workpiece in machining?
In the process of machining, the workpiece is easily deformed due to various machining errors or other processing errors. This problem is difficult to solve. First we must determine the specific cause of deformation, and then take measures to deal with it. Therefore, what are the main factors that tend to cause deformation of the workpiece during machining?
1. Workpiece deformation caused by workpiece clamping
What are the main factors that can easily cause workpiece deformation in machining?
Workpiece clamping can easily cause workpiece deformation. In order to avoid such deformation, it is necessary to choose a suitable clamping point, and then choose a suitable clamping force according to the position of the clamping point. Therefore, the clamping point and support point of the workpiece should be maintained as much as possible, so that the clamping force acts on the support piece, so that the clamping point is closer to the machining surface, which is less likely to cause deformation.
When the clamping force is applied to the workpiece, the sequence of clamping force should be considered and the clamping force should not be too large, in order to balance the cutting force, the clamping force should be applied at the end. It is also necessary to increase the contact area between the workpiece and the fixture or use axial clamping force. The most effective way to solve the clamping deformation is to increase the stiffness of the part. The increase in the contact area between the workpiece and the fixture helps to reduce the deformation of the workpiece during the clamping process.
2. Deformation of the workpiece caused by the material and structure of the workpiece
The size of the deformation is proportional to the complexity of the shape, aspect ratio and wall thickness, and proportional to the stiffness and stability of the material. Therefore, when designing the part, the influence of these factors on the deformation of the workpiece should be reduced as much as possible. Especially the structure of large parts should be more reasonable. Before processing, hardness, looseness and other defects should be strictly controlled to ensure the quality of the blank and reduce the deformation of the workpiece.
3. Deformation of the workpiece caused in the machining process
In the cutting process, the workpiece is subjected to cutting force to produce the tool letting phenomenon. This is the elastic deformation of the direction of the force. In order to solve this deformation problem, the tool can be improved, which can reduce the friction between the tool and the workpiece, improve the cooling capacity of the workpiece during the cutting process, and reduce the internal stress of the workpiece.
4. Deformation of the workpiece caused by stress after machining
The part itself has a relatively balanced state of internal stress after machining, although the shape of the part is relatively stable at this time, but when some materials are removed and heat treatment is carried out, the internal stress will change, so the balance of forces needs to be restored. In this case should be improved, can be solved by heat treatment, the need to straighten the workpiece folded to a certain height, the workpiece pressure purple into a flat state, and then the workpiece and workpiece together into the heating furnace, according to different parts materials, choose different heating temperature and time. After thermal straightening, the internal structure of the workpiece can be kept stable. At this time, the workpiece not only has a high degree of straightness, but also eliminates the machining hardening, which facilitates further finishing of the parts.
For the workpiece easily deformed in machining, in the blank and machining process should be improved accordingly. The above points are the main factors that easily cause the deformation of the workpiece in machining, and the large machining plants should pay attention to the training of machining operators to let them understand the main factors that cause the deformation of the workpiece.
Improve the quality of machining.
1. Improve the level of cutting processing
In machining, when the workpiece is cutting, the surface of the workpiece will form almost the same shape of the tool marks and leave a large number of scales, which tends to increase the roughness of the workpiece surface and reduce the quality of the workpiece surface. Generally speaking, in this case, the radius of the cutting tool tip should be appropriately increased and the tool feed should be appropriately reduced, so that the height of the residual area of the tool on the workpiece can be reduced as much as possible to ensure that the roughness of the workpiece surface is controlled within an appropriate range. This can effectively reduce the chip tumor and scale spur on the workpiece surface, improve the quality of the workpiece surface and prolong the service life of the workpiece.
2. Improve the cutting speed
When the workpiece is cutting, if the cutting speed is high, the plastic deformation of the workpiece surface during the cutting process can be greatly reduced, the higher the cutting speed the smaller the degree of plastic deformation, which can effectively reduce the roughness of the workpiece surface. If the cutting speed is not enough, the workpiece will produce chip tumor in the cutting process, affecting the surface quality of the workpiece.
3. Improve the precision of machining equipment
The processing of the workpiece is mainly through the machine tool to complete, the machine tool itself error will directly affect the accuracy of the workpiece. This will need to ensure the accuracy of the machine tool itself, which can effectively reduce the errors generated during processing. The error of the tool and fixture will also affect the accuracy of the machined workpiece, and corresponding measures can be taken to reduce the wear and tear of the tool, which can improve the accuracy of the machined workpiece and improve the quality of the machined workpiece.
Product quality is the key to the success or failure of enterprises, so improve the quality of machining workpieces, improve the quality of workpieces for every large machining plant is a matter of urgency.
Quality control (QC) and quality assurance (QA) in the suitable machining solution manufacturer
So far, we’ve made clear the fact that inspection and verification are critical to getting quality results in the machine workshop. That’s what quality control and quality assurance are all about. Now, how does a machine workshop perform QC and QA? You may be wondering.
The most common steps taken by machine workshops for QC and QA are as follows.
Raw Material Inspection
When materials are received that will be used for prototyping and production, the machine workshop will have their QC inspectors visually verify that the materials are ready for use.
Machine operator’s inspection
The machine operator is the first person who can determine if the part meets expectations or if there are any quality issues. They can verify the quality of the part during operation or immediately after removing the part from the CNC machine.
Machine workshops often have highly advanced machines, which allow them to use automated in-process probing to verify tolerances as part of the CNC program.
QC Department Inspection
This is the third step in quality inspection and assurance and is performed after process probing and operator verification. The QC department performs a third inspection based on a statistical process control system.
Communication with the customer
Obviously, the best way to verify the quality of the delivery is to confirm the customer’s satisfaction. And this is only possible by maintaining clear and effective communication.
Training of engineers’ skills
While the current digital world has changed the look of the machine workshop by introducing cloud computing and interconnectivity between CAD/CAM software and the machines themselves, what has not changed is the need for trained and experienced engineers, technicians and operators.
For many, the machines and their technology seem to do all the work. But that is not the case. At the end of the day, without the right inputs, machines cannot get quality results.
It is true that machines and their technological developments have made the job easier, more efficient and more accurate, but some skills are still required to make them work as expected.
The most important skills required for machining workshops include:
- Problem-solving skills to correct errors, find areas of improvement and use the machine to its full potential
- Technical knowledge of content such as CAD/CAM software programs.
- Attention to detail and awareness to identify potential problems and avoid accidents that could result in serious injury.
- Mathematical skills to understand complex instructions and ensure correct dimensioning and tolerancing of the most complex geometries
- Endurance to work under pressure and demanding conditions.
Safety in the machine workshop
Having different types of machines and tools working at the same time can become dangerous if the right measures and actions are not taken to ensure safety. At a minimum, the following should be considered in any machine workshop to ensure safety.
Provide employees with proper clothing, including protective equipment such as goggles and safety shoes.
Ensure that operators are in the correct physical and mental condition to operate the machine. A sick or tired operator can put the entire store at risk, not to mention the effects of alcohol or drugs.
Avoid distractions and prevent machines from being left unattended.
Keep machines in proper condition through regular maintenance and updates.
Have clear hazard control guidelines and emergency plans.
Have a proper waste management plan in place.
How to choose the best CNC machine workshop for you?
You do not need to have your own CNC machine workshop. If you are a product developer or own a business that needs some manufacturing services, you just need to find the best service provider. That means the best machine workshop for your specific needs. Here are some aspects you must consider when making your choice.
Value and Price
If you intend to be in the manufacturing business, you need to make sure that you have a long-term relationship with your provider. In addition, it must be valuable and competitively priced so that you can actually see a profit.
Make sure your ideas and designs are secure. They are yours and they represent your values. A confidentiality agreement is always recommended.
Quality and Reliability
Of course, you want to make sure that you can rely on your provider to provide you with high quality results. This can be supported by certifications such as ISO.
Communication and understanding
Last but not least, good and effective communication is always essential so that your provider really understands your needs and what you expect from them. If you find it difficult to get to where you are offered, then you may be better off elsewhere.
How to find a suitable machining solution manufacturer?
With the state of domestic industry nowadays, it is easy to find a few machine workshops. I think the easiest and most effective means is to attend the relevant trade shows and skate around to collect a stack of business cards and flyers.
Mechanical processing plants are mixed, in the procurement of non-standard parts such as higher-priced parts, how to identify reliable mechanical processing suppliers, I stand in the technical point of view a little, may be more one-sided.
First look at the size of the supplier
Here are two extremes to avoid, first do not greedy scale, large scale machining suppliers, although equipment, management more standardized, but often have a relatively fixed customer market, and the production of products tend to be more specialized. If the first cooperation, just to open a relatively simple mold, there is no large orders to attract suppliers, it is easy to lead to suppliers do not cooperate or simply refuse to cooperate, even if the cooperation, it is also difficult to control such suppliers, such as he promised you a month to ship you, but during his main customers suddenly asked him to produce a large single, he will in all probability give you delayed.
The other extreme is to choose a particularly small scale, or even simply their own almost no actual production, only to solicit work and then subcontracted out of the subcontracting company, but also to consider carefully. Quality, delivery, etc. are very difficult to guarantee, and even the risk of being cheated out of money. But I did make a part through a subcontractor in June, but only if I had worked with them before and had visited with him the subcontractor for each process he planned to subcontract.
The ideal size machining supplier is one that is comparable in size to your company, your current target price is attractive to him, or your company can establish a long-term relationship with him, or your company is in an industry that they want to get involved in (for example, if your company is in the automotive industry, a supplier that has never produced automotive parts before might be interested in you, because if he supplies you with the product, he can say that he has entered the industry. (For example, your company is in the automotive industry, a supplier who has never produced auto parts may be interested in you, because if he gives you a product, you can say that the door into the industry, and then give other companies to do more convenient.)
And then look at the supplier’s production capacity and quality control capabilities this principle is also enough on the line.
You need to process how much precision parts, match how much capacity of the supplier, for example, if the precision of your parts required within 0.01mm, then the mold supplier may have to be slow-walking wire cutting or EDM, or even constant temperature workshop to meet the requirements, and have enough precision of the three coordinates and other inspection tools and equipment to ensure the quality of delivery of parts. Before signing the contract must be personally inspected to confirm this matter. The inspection may encounter a problem that the supplier may say that he does not have certain equipment and needs to do it elsewhere, so it is important to examine such secondary suppliers as well for insurance purposes.
If there are conditions, you can ask the supplier which customers have done products before, how effective, what accuracy can be achieved, whether they have done similar products, etc.. But be sure to pay attention to the implementation, not what the supplier said to believe what.
Then look at the supplier’s scheduling plan and offer
Before determining the partnership, you should ask the supplier to list in detail the project cycle and time nodes of product processing, such as how long the technical exchange, what are the things to do. How long does it take for each of the processes such as material placement, rough machining, finishing, heat treatment, and fine grinding. Whether each process can be carried out immediately after the pre-processing, or need to queue (such as heat treatment, if the arrangement is not good, machining is completed but no furnace, we have to wait for a white delay), there is no risk of delivery time. After the supplier is listed, they should also be based on experience to determine whether he listed reliable, another relatively simple way is to find a few more suppliers asked separately, and then corroborate each other.
About the offer is also the same, the offer on the one hand is to examine the supplier’s attitude to cooperation (is a sincere desire to establish a cooperative relationship, or want to cheat a vote on the run) and cost control capabilities, on the other hand is also to examine the supplier’s proficiency in the industry, is not the cost of the report are reported, the price is objective. I more commonly used method is to let the supplier detailed list of product cost components, such as a set of molds, how much raw materials, how much machining, how much heat treatment, how much design and development debugging, how much sales costs, how much management costs, how much profit the supplier to stay, etc., are clearly reported (so the choice of suppliers must cooperate, see the first paragraph).
This has two benefits:
- 1. Who will not lose.
- 2. Can also be side by side to prove that the supplier’s project cycle plan is reliable.
On the offer, there is one more thing to say is never to be greedy to excessively low supplier profits, or even let the supplier to do business at a loss. Because the wool is on the sheep, he is now losing money, or later find a way to earn back (no business is really losing money), or really can not earn back to you do not. Cooperation must be a win-win situation.
Finally look at the supplier’s project control capabilities
That is, in the process of product production, never sheep, especially when the mold is very important, must be in accordance with the supplier’s previously reported project cycle and time nodes, to examine the implementation of their situation, once there are abnormalities immediately analyze the causes and discuss the treatment, remedial measures. In the contract, it is stipulated that the penalty for failure to meet the deadline is not necessarily effective, good project control should be timely detection of problems and risks and solve them, rather than have caused losses before trying to retroactive compensation.
Solutions to improve machining accuracy
Combined with the actual production process, by analyzing the factors affecting the machining accuracy, a solution to improve the machining accuracy is proposed, which ultimately promotes the processing of the workpiece to meet the quality requirements and improves the quality of the entire machining.
Machining is an important part of mechanical industrial production. The accuracy of mechanical processing largely determines the quality of mechanical parts and affects the overall quality of mechanical processing. However, due to China’s relatively late start in the field of mechanical processing, there are significant differences in the quality of professional technicians’ operations, as well as in the level of mechanical equipment operation and international standards, resulting in a large number of shortcomings and loopholes in the actual operation of mechanical processing equipment, seriously affecting the quality of the entire mechanical processing operation. Therefore, analyze the factors that affect the accuracy of mechanical processing, and propose corresponding machining solutions based on this to ensure the accuracy of mechanical processing, control the errors during the processing, and ensure the high quality of the entire machining process.
1. Analysis of factors affecting machining accuracy
1.1 The influence of cutting force
Under the action of cutting force, the cutting process system will produce the corresponding deformation in each direction of the force. Deformation of the process system force, mainly on the machining accuracy of the most sensitive direction, that is, through the normal direction of the machining surface of the tool displacement. Since the machining cutting force has been a great concern, the cutting force of the error is mainly affected by the cutting amount of the cutting knife, the collection of tool parameters on the impact of cutting, cutting fluid, props wear, and other factors, any one of the problems will affect the cutting force, thus triggering the problem of machining accuracy. For example, the amount of backdraft and feed increase, under the influence of the increase in cutting force, the front angle increases, the cutting force decreases, the negative rib of the lathe is through its width and feed ratio to affect the cutting force, the larger the ratio of the cutting force increases, the main deflection angle on the cutting force impact. In addition, under the action of cutting force, the cutting process system may be subject to the corresponding deformation from each direction of force once the process system deformation of force directly affects the machining accuracy.
1.2 Influence of temperature
The machine tool is subject to changes in the ambient temperature of the workshop, motor heat, mechanical movement friction heat, cutting heat, and cooling medium, resulting in uneven temperature rise in all parts of the machine tool, resulting in changes in the shape of the machine tool precision and machining accuracy. The temperature rises so that the temperature of each part of the parts over time, so the machine tool loses the existing adjustment accuracy, thus affecting the size of the machined workpiece.
1.3 Influence of spindle rotation
In the mechanical equipment, spindle workpiece operation problems, and the cause of unqualified workpiece processing is the spindle rotary error. Spindle rotary error is the spindle in the machining of abnormal action or inaction phenomenon, resulting in the actual rotary axis relative to the average rotary axis of the amount of change exceeding or not meeting the national standard data value, thus affecting the quality of the subsequent machining workpiece. Here, the spindle abnormal action should be analyzed: abnormal action including radial runout, axial runout, and angular swing three, and the main reason for these three kinds of abnormal action is the machining data about the spindle rotary line perpendicularity of the data information error, resulting in machining equipment cannot be normal to meet the final result of the spindle rotary problem.
1.4 The influence of the guideway error
CNC machine tool guideway has a direct impact on the machining accuracy, the processing of the movement of the benchmark, and guideway deviation from the running track; these errors will play a direct role in the processing of mechanical parts, thus affecting the precision of machining, affecting the quality of machining.
1.5 The impact of tool manufacturing
In machining tool fixtures, manufacturing errors on the entire processing will also have an impact.
The impact of tools: reamers, broach drills, and other fixed-size tools produce dimensional errors, will seriously affect the size of the processed parts, which in turn affects the interplay of parts, resulting in a significant impact on the accuracy of machining and the molding tool, it is mainly affected by the shape of the machined surface accuracy.
The impact of fixtures: for the relevant personnel in the implementation of the operator in the process, often because of some clamping errors, fixture installation errors, and positioning errors, resulting in fixture wear, resulting in machining precision parts positioning errors, serious impact on machining.
The impact of tool wear: the wear and destruction of individual tools will directly affect the surface of the parts, resulting in the location of the machines suffering damage and difficulty fitting each other; there are dimensional errors.
1.6 The influence of positioning error
Positioning error is also the biggest factor affecting the accuracy of machining. At the present machining stage, there is mainly datum not overlap error, positioning sub-manufacturing inaccuracy error, etc., which largely affects machining accuracy.
2. Solutions to improve machining accuracy
2.1 Reduce the force error
The error caused by force deformation in machining is a relatively common problem, and the change of the position of the cutting point in the machining process will cause machining errors. Therefore, the machining process should accurately calculate the location of the point of force and ensure the accuracy of the location of the point of force to avoid the reduction of machining errors.
Machining depth of cut will cause machining errors; therefore, it should be calculated before machining parts need to cut the size or use light cutting and high-traveling way of machining. In addition, the machining process should be appropriate to increase the number of times the knife, effectively reducing the processing of workpiece compound reflection error. The degree of reduction is proportional to the rigidity of the processing system. It can be realized from the known machining conditions pre-estimated mechanical workpiece machining error, and according to these error data on the cutting system, to make reasonable adjustments to reduce the error and improve machining accuracy effectively.
2.2 Reduce temperature error
Mechanical processing in the presence of temperature deformation error, in the face of such problems should implement effective temperature control measures, the need to optimize the machining environment, do a good job in the processing environment of the ventilation process, to strengthen the temperature monitoring of machining once the temperature is found to be higher than the normative range, should be taken promptly to take effective measures to avoid the temperature rises again and produces deformation error, affecting the accuracy of machining. Such as slender shaft turning due to force and heat factors making the parts bend, such as slender shaft turning, you can directly use the cutting method to reduce the error to the maximum extent possible.
2.3 Reduce the original error
Improvement of jigs, gauges, tools precision, control process system force, heat deformation, tool wear, deformation caused by internal stress, and measurement errors directly reduces the original error. To improve machining accuracy, according to the different accuracies, can is appropriate to use the compensation method. Compensation method from the name, the response to the original error, the relevant technical personnel need to establish a new error to compensate for the original error. After the original error is canceled out, the new error starts to play a role in further reducing the processing error. Human error is often the opposite of the original error, almost equal in size and almost the same effect, but in the opposite direction. Effective and reasonable use can be appropriate to reduce the processing error and strengthen the accuracy of the entire machining.
2.4 Reduce guideway error
Guideway error is the main factor affecting machining accuracy. To ensure machining accuracy should pay attention to the detection of the guideway. First of all, should be regularly on the guide rail running parameters for a comprehensive analysis; once found that the guide rail running abnormality or parameter abnormality should be taken promptly with targeted inspection, analysis of its influencing factors, and timely solution to the problem of the guide rail error, to ensure that the smooth progress of the machining, but also for the assurance of machining accuracy to provide a reliable basis. Before each machining, check whether the guide rail is normal; if there is a deviation should be adjusted in time to ensure the reliability of machining. The machining process should pay close attention to the operation of the guide rail and strengthen the detection of the guide rail to avoid processing by other factors that lead to the guide rail deviation; once found should be adjusted in time to avoid machining errors.
2.5 Homogenization error
In the machining process, the surface machining accuracy requirements of the parts can be effective through the continuous trial cutting process, gradually equalizing the error method. In production, many precision reference parts use the error equalization processing method to reduce the machining process. The practical significance of this method is to improve the machining accuracy by finding the mutual differences between the workpieces and inspections in close contact. This method reduces or even averages the original error of the machined surface through machining.
To cope with today’s society’s industrial development, China has greatly improved machining. The level of machining directly affects the development and quality of all walks of life in society and has a huge role in industrial development. In machining, the relevant staff units must seriously study the relevant knowledge, firmly grasp the factors affecting machining accuracy and the corresponding machining solutions, and seriously implement them into the work. Efforts to do a good job in every aspect of the work, clear the importance of machining accuracy, vigorously develop good machining accuracy, promote the development of the entire machinery industry, and promote the construction of China’s socialist industry.
Source: China Machining Solution Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]