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Processability analysis and blank selection of parts

Process analysis of the machined parts is to analyze and study the product assembly drawings and parts diagrams, become familiar with the use, performance and working conditions of the product, clarify the position and role of the machined parts in the product, and on this basis check the completeness and correctness of the drawings, review the appropriateness of the choice of materials for the parts, analyze the technical requirements of the parts, and review the processability of the structure of the parts.

Analysis and review of product assembly drawings and parts drawings

Check the completeness and correctness of the drawings

Check the completeness and correctness of the drawings is mainly to see whether the drawings have sufficient views, dimensions, tolerances and technical requirements are marked complete, complete and reasonable. If there are errors and omissions, amendments should be proposed.

Analysis of the technical requirements of the parts

The technical requirements of the part include the following aspects.

  • (1) The dimensional accuracy of the machined surface.
  • (2) The geometric shape accuracy of the machined surface.
  • (3) The mutual position accuracy between the machined surfaces.
  • (4) The roughness of the machined surface and other requirements of surface quality.
  • (5) Heat treatment requirements and other requirements.

In the analysis of the technical requirements of the part, to understand the role of these technical requirements, and to identify the main technical requirements, as well as technical requirements difficult to achieve in the process, especially for the development of the technical program to play a decisive role in the technical requirements.

Analyze the structural processability of the part

1. Overview
The structure of the part, the processing quality, production efficiency and economic efficiency have an important impact, in order to obtain better technical and economic results, in the design of the part structure, not only to consider how to meet the requirements of use, should also consider whether to meet the processing and assembly process requirements, that is, to consider the structural process of the part.
The so-called parts structure technology, refers to the parts in the premise of meeting the use of the requirements, its structure in specific production conditions to facilitate the economic manufacturing and maintenance. In other words, if the design of the product structure of the process is good, it is convenient to apply advanced, productive process, process methods, so that the manufacture of products is also the most economical.
The structural processability of the part is a relative concept. In space, different production scale or with different production conditions of the factory, the requirements of the product structure processability is different. For example, certain single-piece production of products, the structure of the single production is also reasonable, but to mass production of the product, the structure of its parts is not reasonable, must be improved. Such as the internal tooth structure shown in Figure.1, Figure.1 (a) is suitable for processing on the gear inserting machine, but to mass mass production, it should be changed to the structure of Figure.1 (b) in order to use broaching method of production. In time, with the development of science and technology, new technologies and techniques have emerged, and some structures that were considered difficult or even impossible to machine in the past have now become feasible or even easy. For example, Figure.2 (a) Shows the electro-hydraulic servo valve sleeve on the processing of precision square hole, in order to ensure that the size tolerance requirements between the square hole, the valve sleeve in the past will be divided into five rings were processed. Then connected together, this structure is considered to be a good process. However, with the improvement of EDM precision, the original assembly of five rings was changed to the overall structure (see Figure.2 (b)), and four electrodes were used to machine four square holes at the same time, which can also ensure the dimensional accuracy between the square holes. This reduces both labor and cost, so the processability of this integral structure is also good.
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Figure.1 Internal gear clutch
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Figure.2 Electro-hydraulic servo valve sleeve structure
2. General principles of part structure processability design
In the design of the part structure, in addition to considering to meet the requirements of use, in order to improve the processability of the part structure, the following principles should be noted.
(1) The structure of the part processing parts should be convenient for the tool to correctly cut into and cut out
For example, when the box flange needs to be machined holes, the location of the hole can not be too close to the box wall for processing (see Figure.3).
Figure.3 Machining of hole on box flange
Figure.4 (a) When threads cannot be machined to the root of the shoulder, a rewind slot (see Figure.4 (b)) Should be designed to facilitate rewind.
Figure.5 shows a section of keyway inserted in the hole of the part, and there is no rewind space at the bottom to easily hit the tool. A hole or an annular overrun slot should be designed at the top of the keyway (see Figure.5 (b)).
2) Standardized tools should be used for machining
When designing the thread shown in Figure.6, standard parameters should be used so that standard taps and slabs can be used for processing and standard thread gauges can be used for inspection.
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Figure.4 Machining of threads
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Figure.5 Keyway in inserted hole
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Figure.6 Design of diameter and pitch of thread
3) The part should be easy to install
If necessary, some process structures should be added to meet this requirement. For example, add process tabs, add auxiliary mounting surfaces, etc.
The part shown in Figure.7 (a) is not easy to install because of the uneven bottom surface when machining the upper surface, so it is easy to install by adding a process tab.
The large flat plate shown in Figure.8 (a) is not easily clamped when the upper surface is machined, but can be reliably clamped if a flange is added (see Figure.8 (b)).
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Figure.7 Process cams
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Figure.8 Clamping flange
Figure.9 (a) Shows the bearing cover, the outer circle and end face to be processed, if clamped at A, the general jaws are not long enough, and the B side is not easy to clamp. If the structure shown in Fig. 9(b) is changed, it can be easily clamped on the C side, or the structure shown in Fig. 9(c) can be changed to add a process cylindrical surface D for clamping.
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Figure.9 Improvement of bearing cover structure
(4) Avoid machining in the box or in the hole
The machining surface in Figure.10 (a) is inside the box, which is not convenient for machining; if the machining surface is designed outside the box (shown in Figure.10 (b)), the machining performance is improved.
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Figure.10 Avoid machining inside the box
Figure.11 (a) Shows the inlet and exhaust channels are designed inside the hole, making machining difficult. Change to the structure shown in 
Figure.11 (b), and design the intake and exhaust passages on the outer circle of the shaft, which is easier to machine.
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Figure.11 Avoid machining in the hole
5) The part structure should be rigid enough
The part structure should be rigid enough to reduce its deformation under clamping or cutting forces and to ensure machining accuracy. Sufficient rigidity also allows the use of a larger cutting amount, which is conducive to improving production efficiency.
Figure.12 (a) Shows the thin wall thickness of the pipe, easy to deformation due to clamping and cutting forces, the additional flange (see Figure.12 (b)) Improve the stiffness of the parts.
The box structure shown in Figure.13 (a) Has poor stiffness and is easy to deform the workpiece due to cutting force when planing the upper plane. After adding the rib plate (Figure.13 (b)), the stiffness is improved and a larger depth of cut and feed can be used for machining, which is easy to ensure the quality of the machined workpiece and improve productivity.
6) Minimize machining area
Figure.14 (a) Shows the support parts of the bottom surface machining area is large, changed to the structure of Figure.14 (b), reducing the machining area, thereby reducing the amount of mechanical processing, reducing material and tool consumption.
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Figure.12 Increasing the stiffness of thin-walled fittings
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Figure.13 Increased stiffness of thin-walled box pieces
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Fig.14 Structure of the base of the support
(7) Reduce the machining area to facilitate the machining of multiple workpieces together
The bottom of the groove of the fork shown in Fig.15(a) is rounded and can only be machined individually. After changing to the structure shown in Figure.15 (b), multiple workpieces can be machined together, which is conducive to increasing productivity.
8) Reduce the number of clamping on the machine
The machining of the two keyways designed on the shaft shown in Figure.16 (a) needs to be completed in two clamping sessions, but after changing the two keyways to the same direction as shown in Figure.16 (b), the machining of the two keyways only needs to be clamped once.
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Figure.15 Facilitates machining of multiple workpieces together
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Figure.16 Reducing the number of clamping on the machine
9) Reduce the number of adjustments on the machine tool
Figure.17 (a) Shows the processing of A, B surface need to adjust the machine tool separately, if the height of A, B surface as shown in Figure.17 (b) Will be changed to the same, you can complete the processing of A, B surface in one adjustment of the machine tool.
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Figure.17 Reduce the number of machine adjustments
(10) The same kind of parameters as much as possible consistent
Figure.18 (a) Shown in the shaft on the grinding wheel overrun groove width, keyway width designed to different sizes, it is necessary to use different sizes of tool processing. If the widths of these slots are changed to the same size as shown in Figure.18 (b), one tool can be used to complete the machining of all slots.
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Figure.18 Reduction of tool types
11)It helps to ensure positional accuracy
The surfaces with mutual position accuracy requirements are best machined in one setup, which not only helps to ensure the position accuracy between the machined surfaces, but also reduces the number of setups and the auxiliary time used to improve productivity.
The outer surface and the inner hole of the part shown in Fig. 19 (a) Have coaxiality requirements, but the structure shown in Fig. 19 (a) requires two clamping to machine the outer surface and the inner hole separately, which is difficult to meet the coaxiality accuracy requirements. If the structure shown in Fig.19(b) is changed, the inner and outer surface can be machined in one clamping, and the coaxiality requirement can be easily satisfied.
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Fig.19 Workpiece with coaxiality requirement
12)Easy to measure
Figure.20 (a) Shows that the dimension measurement reference is marked as A surface, which is inconvenient to measure, but after changing to Figure.20 (b), the dimension measurement reference is B surface, which is easy to measure.
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Figure.20 Measurement of inner surface
(13) Should be conducive to assembly and disassembly
The simultaneous contact of two planes in the same direction should be avoided. As shown in Figure.21 (a), the two axial surfaces A and B of the end cap are in contact at the same time, which is not conducive to processing and assembly. Change to the structure form of Figure.21 (b) or Figure.21 (c) Which is conducive to assembly, and can reduce the dimensional accuracy and form accuracy requirements of the relevant surface processing on the part, and reduce the workload of processing and assembly.
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Figure.21 Assembly of end caps
The assembly structure of bearing outer ring and bearing housing hole shown in Figure.22 (a) is not conducive to the disassembly of bearing outer ring, but after changing to the structure of Figure.22 (b), the bearing can be easily disassembled by using the disassembly tool with thread.
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Figure.22 Bearing assembly

Selection of blanks

Types of blanks

Commonly used blanks are mainly in the following forms.

  • (1) Casting. For complex shape blanks, castings are suitable, such as boxes, seats, etc.
  • (2) Profiles. There are many varieties of profiles. Commonly used sections of profiles are round, square, rectangular, hexagonal, as well as pipe, plate, strip, etc.. Profiles are hot-rolled and cold-drawn two.
  • (3) Forgings. Forgings can obtain the continuity and uniform distribution of fiber tissue, thus improving the strength of the part, so it is suitable for manufacturing strength requirements are high, the shape is relatively simple parts blank.
  • (4) Welded parts. Steel or steel plate welded into the required structural parts, the advantages of the structure is light weight, short manufacturing cycle, but the poor vibration resistance of the welded structure, the thermal deformation of the parts.
  • (5) Stamped parts. Stamped parts are more accurate, stamping production efficiency is also relatively high, suitable for processing complex shapes, larger batch of small and medium-sized plate parts.

Factors to be considered in the selection of blanks

The improvement of the quality of the blank is very beneficial to reduce the amount of machining, reduce processing costs and improve the utilization rate of processed materials. However, under the conditions of certain production technology, the improvement of blank quality will also be accompanied by an increase in the difficulty of manufacturing blanks, which means an increase in the cost of manufacturing blanks. Therefore, in the selection of blank materials and manufacturing methods, the following issues should be considered.
(1) The size of the part production program. When the parts production is large, should choose the accuracy and productivity of the relatively high blank manufacturing methods; in a single piece of small batch production, should choose lower accuracy and productivity of the blank production methods.
(2) Blank material and process characteristics. The choice of blank material is generally based on the role of the part in the machine. The main consideration is the machine work on the strength, stiffness, toughness, wear resistance, corrosion resistance and other aspects of the requirements of the parts. In the premise of meeting the requirements of use, and then consider the processing process on the blank material and processability requirements.
Forged blanks should be selected for steel parts with high mechanical performance requirements. For some materials, such as cast iron, cast aluminum, etc., can only use casting molding.
(3) The shape and size of the parts. The complexity of the shape of the part, the size of the size of the blank manufacturing method to determine has a great impact. The shape of complex parts, generally should not use metal mold casting; size of the larger blanks, often can not use die forging, die-casting, precision casting, but should choose sand casting, free forging and welding and other methods to manufacture blanks.
In addition, the manufacture of blanks must also consider the existing production conditions, fully tapping the potential to improve the quality of the blank.

Source: China Pipe Sleeve 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 sales@epowermetals.com

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