Processability analysis of parts and selection of blanks

Parts of the process analysis

1. Check the integrity of the parts diagram: review the size of the parts diagram is complete. The structure is expressed clearly.
2. Analysis of technical requirements are reasonable.

  • (1) The dimensional accuracy of the machined surface.
  • (2) The main processing surface shape accuracy.
  • (3) The mutual position accuracy of the main processing surface.
  • (4) Surface quality requirements.
  • (5) Heat treatment requirements.

The dimensional tolerances. form tolerances and surface roughness of the parts marked. should be based on the function of the parts economically and reasonably decided. Too high requirements will increase the difficulty of processing. Too low requirements will affect the work performance. both are not allowed.

According to the processed workpiece material. contour shape. machining accuracy. etc. Select the appropriate machine tool. develop a processing program. determine the processing order of the parts. each process used tools. fixtures and cutting dosage. etc.

The reasonable choice of machine tools

In CNC machine tools for machining parts. There are generally two situations.
The first case: there are parts drawings and blanks. To choose the CNC machine tool suitable for processing the part.
The second case: there has been a CNC machine tool. To choose the machine suitable for processing parts in the machine. No matter which case. The main factors to consider are. The material and class of the blank. The complexity of the part contour shape. size. machining accuracy. The number of parts. heat treatment requirements.
To summarize. There are two points.
① To ensure that the technical requirements of the processed parts. processing a qualified product.
② Conducive to improving productivity.

CNC machining parts process analysis

CNC machining process analysis involves a wide range. here only from the possibility of CNC machining and convenience of two aspects to analyze.
(A) The size of the part drawing data should be given in line with the principle of programming convenience

  • 1. The size of the parts on the chart labeling method should be adapted to the characteristics of CNC machining in CNC machining parts chart. should be the same benchmark cited size or directly given the coordinate size. This labeling method is not only convenient for programming. but also convenient for mutual coordination between the dimensions. in maintaining the design benchmark. process benchmark. Testing benchmark and programming consistency of the origin settings bring great convenience. As the part designer generally in the size of the label more consideration in the assembly and other aspects of the use of characteristics. and had to use the local dispersion of the labeling method. which will bring a lot of inconvenience to the process arrangement and CNC machining.
  • 2. The conditions of the geometric elements that constitute the part outline should be sufficient
  • In manual programming to calculate the base point or node coordinates. In automatic programming. To define all the geometric elements that constitute the part contour. Therefore. when analyzing the part diagram. analyze whether the given conditions of the geometric elements are sufficient. For example. arcs and lines. arcs and arcs are tangent on the drawing. but according to the dimensions given on the drawing. They become intersecting or detached states when calculating the tangent conditions.

(B) The structural processability of each processing part of the part should be consistent with the characteristics of CNC machining.

  • 1) The internal cavity and shape of the part is best to use a uniform geometric type and size. This can reduce the tool specifications and the number of tool changes. so that programming is convenient and production efficiency is improved.
  • 2) The size of the inner groove rounding determines the size of the tool diameter. Thus the inner groove rounding radius should not be too small. The processability of the part is related to the height of the profile being machined. The size of the radius of the turning circle. etc.
  • 3) When milling the bottom plane of the part. The radius r of the bottom corner of the groove should not be too large.
  • 4) Uniform datum positioning should be used. In CNC machining. if there is no unified datum positioning. it will lead to the uncoordinated phenomenon of contour position and size on the two surfaces after processing due to the re-installation of the workpiece.

It is best to have a suitable hole on the part as a positioning reference hole. if not. To set the process hole as a positioning reference hole (such as adding process lugs on the blank or set the process hole on the margin to be milled in the subsequent process).

The choice of processing methods and processing program to determine

(A) The choice of processing methods
The principle of selecting the machining method is to ensure the machining accuracy and surface roughness requirements of the machined surface. As the same level of accuracy and surface roughness of the processing methods generally have many. and therefore in the actual selection. combined with the shape of the part. size and heat treatment requirements and other comprehensive consideration.
(B) The principle of processing program to determine
Parts on the more precise surface processing. often through roughing. semi-finishing and finishing gradually to achieve. For these surfaces only according to the quality requirements of the corresponding final processing method is not enough. should also correctly determine the processing program from the blank to the final shape.
When determining the machining scheme. first of all. according to the main surface accuracy and surface roughness requirements. The preliminary determination of the required machining methods to achieve these requirements. For example. for the hole diameter of the IT7 level of accuracy of the hole. The final processing method to take the fine reaming. The fine reaming hole before the usual drilling. reaming and rough reaming and other processing.

The division of the process and work steps

(A) The division of the work process
In the CNC machine tool processing parts. The process can be more focused. in a clamping as far as possible to complete most or all of the process. First of all. according to the parts drawing. consider whether the parts to be processed in a CNC machine tool to complete the entire part of the processing work. if not. you should decide which part of the CNC machine tool in the processing. which part of the other machine tool processing. That is. The parts of the processing process is divided.
(B) The division of work steps
The division of the work step is mainly from the processing accuracy and efficiency of the two aspects to consider. In a process often requires the use of different tools and cutting dosage. on different surfaces for processing. In order to facilitate the analysis and description of more complex processes. The process is subdivided into work steps. The following is an example of a machining center to illustrate the principles of work step division.

  • 1) The same surface is finished in order of roughing. semi-finishing and finishing. or all surfaces are processed separately by roughing first and then finishing.
  • 2) For parts with both milling and boring. milling can be done first and then boring. This method of dividing the work steps. you can improve the accuracy of the hole. Because of the large cutting force during milling. The workpiece is prone to deformation. Milling first and then boring. so that it has a period of time to recover and reduce the impact on the accuracy of the hole caused by the deformation.
  • 3) Division of work steps by tool. Some machine table rotation time is shorter than the tool change time. can be used to divide the work step by tool. in order to reduce the number of tool changes. improve processing efficiency.

In short. The process and the division of the work step according to the specific structural characteristics of the parts. Technical requirements and other comprehensive consideration.

The installation of parts and fixture selection

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(a) The basic principles of positioning and installation

  • 1) Strive to design. process and programming calculation of the benchmark unity.
  • 2) Minimize the number of clamping. as far as possible after a positioning clamping. processing all the surfaces to be machined.
  • 3) Avoid the use of machine manual adjustment type processing program. in order to give full play to the effectiveness of CNC machine tools.

(b) The basic principle of choosing fixture
CNC machining characteristics of the fixture put forward two basic requirements: one is to ensure that the fixture coordinate direction and the machine’s coordinate direction relative fixed; second is to coordinate the size of the relationship between the part and the machine coordinate system. In addition. The following four points should be considered.

  • 1) When the parts are not processed in large quantities. should try to use the combination of fixtures. adjustable fixtures and other general fixtures to shorten the production preparation time. save production costs.
  • 2) In batch production only consider the use of special fixtures. and strive to simple structure.
  • 3) The loading and unloading of parts should be fast. convenient. reliable. To shorten the machine downtime.
  • 4) Fixtures on the parts should not prevent the machine tool to the parts of the surface processing. That is. The fixture to open its positioning. clamping mechanism components can not affect the processing of the tool (such as collision. etc.).

The choice of tools and cutting amount of determination

(a) The choice of tools
Tool selection is one of the important elements of CNC machining process. which not only affects the machine tool processing efficiency. but also directly affects the quality of processing. Programming. The selection of tools usually take into account the processing capacity of the machine tool. process content. workpiece materials and other factors. Compared with traditional machining methods. CNC machining requires higher requirements for tools. Not only requires high precision. good rigidity and durability. but also requires dimensional stability and easy installation and adjustment. This requires the use of new high-quality materials to manufacture CNC machining tools. and the optimal selection of tool parameters.
When selecting the tool. The size of the tool should be adapted to the surface size and shape of the workpiece to be machined. In production. The processing of the peripheral contour of flat parts. often using end mills. When milling plane. carbide insert milling cutter should be selected; when processing tabs and grooves. choose high-speed steel end mills; when processing the rough surface or roughing holes. optional carbide-encrusted corn milling cutter. When choosing the end mill for processing. The relevant parameters of the tool are recommended to be selected according to the empirical data. Curved surface processing often uses ball end mills. but when processing flatter parts of the surface. The tool cuts with the top edge of the ball. and the cutting conditions are poor. so the ring-shaped tool should be used. In single or small batch production. in order to replace the multi-coordinate linkage machine tools. often use drum-shaped knife or tapered knife to process some variable bevel angle parts on the aircraft plus inserted tooth disc milling cutter. suitable for processing some spherical surface on the five-coordinate linkage CNC machine tools. its efficiency is nearly ten times higher than the use of ball milling cutter. and can obtain good machining accuracy.
In the machining center. a variety of tools are mounted on the tool magazine. according to the provisions of the program at any time for tool selection and tool change work. Therefore. There must be a set of common tool connection bar. in order to make drilling. boring. reaming. reaming. milling and other processes with the standard tool. quickly and accurately loaded to the machine tool spindle or tool magazine to go. As a programmer should understand the structure of the tool bar used on the machine tool size and adjustment methods. adjustment range. in order to determine the radial and axial dimensions of the tool when programming. At present. our machining center uses TSG tool system. whose shank has a straight shank (three specifications) And tapered shank (four specifications) of two kinds. including a total of 16 different purposes of the knife.
(b) Determination of cutting dosage
Cutting dosage includes spindle speed (cutting speed). back draft and feed. For different processing methods. you need to choose a different cutting amount. and should be programmed into the program sheet. The principle of reasonable selection of cutting amount is. rough machining. generally to improve productivity. but should also consider the economy and processing costs; semi-finishing and finishing machining. should be to ensure the quality of machining. Taking into account cutting efficiency. economy and processing costs. Specific values should be based on the machine tool manual. cutting dosage manual. and combined with experience.

The tool point and tool change point to determine

In programming. you should correctly select the “tool point” and “tool change point” location. The “tool point” is in the CNC machine tool processing parts. The tool relative to the starting point of the workpiece movement. As the program segment from the point of execution. so the tool point is also known as the “program starting point” or “starting point”.
The selection of the tool setting point is based on the following principles.

  • 1. Facilitate the use of digital processing and simplify programming.
  • 2. In the machine to find the right easy. easy to check the processing.
  • 3. Caused by the processing error is small.

Tooling point can be selected on the workpiece. also can be selected outside the workpiece (such as selected on the fixture or machine tool) but must have a certain dimensional relationship with the positioning reference of the part. In order to improve machining accuracy. The tooling point should be selected as far as possible in the design reference or process reference of the part. such as the workpiece positioned in the hole. The center of the optional hole as the tooling point. The position of the tool is corrected by the hole. so that the “tool position point” and “tool point” coincide. The common factory method is to install the micrometer on the machine tool spindle. and then rotate the machine tool spindle to make the “tool position point” and the tool point consistent. The better the consistency. The higher the accuracy of the tooling. The so-called “tool position point” refers to the turning tool. boring tool tip; drill bit tip; end mill. end mill tool tip bottom center. ball milling tool ball center.

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Parts installed after the workpiece coordinate system and the machine coordinate system has a definite dimensional relationship. After the workpiece coordinate system is set. The coordinate value of the first program segment starting from the point of the tool; for the point of the tool in the machine tool coordinate system is (X0. Y0). When programming by absolute value. regardless of whether the tooling point and the workpiece origin coincide. it is X2. Y2; when programming by incremental value. when the tooling point and the workpiece origin coincide. The coordinate value of the first program segment is X2. Y2. and when it does not coincide. it is (X1 ten X2). Y1 + Y2). The tool alignment point is both the starting point and the end point of the program. Therefore in batch production to consider the repetition accuracy of the tooling point. The accuracy of the tooling point can be used to check the coordinate value of the distance from the machine origin (X0. Y0).
The so-called “machine tool origin” refers to a fixed limit point on the machine tool. For example. for lathes. it is the intersection of the center of rotation of the lathe spindle and the end face of the turning head chuck. When tool change is required in the machining process. The tool change point should be specified. The so-called “tool change point” is the position when the tool holder is rotated to change the tool. The point can be a fixed point (such as machining center machine tools. The position of the tool changer robot is fixed). can also be any point (such as lathe). The tool change point should be located on the outside of the workpiece or fixture. in order not to touch the workpiece and other parts when the tool holder is rotated. Its setting value can be determined by actual measurement method or calculation.

The processing route to determine

In the CNC machining. The tool position point relative to the workpiece movement of the trajectory is called the machining route. Programming. processing route to determine the principle of the following points.

  • 1) Machining route should ensure the accuracy and surface roughness of the machined parts. and high efficiency.
  • 2) To make the numerical calculation simple in order to reduce the programming workload.
  • 3) The machining route should be made the shortest possible so that both program segments and empty tool time can be reduced. Degree and so on. To determine whether it is a tool walk. or multiple tool walks to complete the processing and in the milling process is the use of down milling or reverse milling and so on.
  • Point control of CNC machine tools. only require high positioning accuracy. positioning process as fast as possible. and the tool relative to the workpiece movement route is irrelevant. so this type of machine tool should be arranged according to the shortest empty range to go tool route. In addition to determine the axial movement of the tool size. its size is mainly determined by the hole depth of the parts to be machined. but should also consider some auxiliary dimensions. such as the introduction of the tool distance and beyond the amount.

Review the selection of parts materials are appropriate.

The choice of materials should meet the requirements of the use of the product. but also to consider the cost of the product. as far as possible using commonly used materials. such as 45 # steel. less use of precious metals.

The structure of the parts processability analysis.

(1) Parts structure technology: refers to the feasibility and economy of manufacturing the designed parts under the premise of meeting the use requirements.
It includes parts of the various manufacturing processes in the process of technology. There are parts of the structure of casting, forging, stamping, welding, heat treatment, cutting and other processes. It can be seen that the structure of the part process involves a wide range of comprehensive. comprehensive analysis must be comprehensive.
In the development of machining process procedures. The main parts cutting process analysis.
(2) Machining requirements for the local structure of the part processability.
Thinking problem: analyze the problems of the local structure of the parts in the following figure. and propose improvements.
(3) Machining requirements for the overall structure of the part processability
Parts are elements. dimensions of the composition of a whole. so should consider the overall structure of the part of the process. specifically the following requirements.

  • (1) Try to use standard parts. common parts.
  • (2) In order to meet the conditions of product performance. The dimensional accuracy level and surface roughness requirements marked on the parts should take the most economic value.
  • (3) As far as possible to use the material with good machinability.
  • (4) Have easy to clamp the positioning reference and clamping surface.
  • (5) Save material. reduce the quality.

The choice of blanks

1. The type of blank.

  • (1) Casting blanks: suitable for making complex-shaped parts of the blank.
  • (2) Forging blanks: suitable for making the shape of simple parts of the blank.
  • (3) Profile: suitable for shaft. flat parts of the blank.
  • (4) Welding blanks: suitable for plate. frame type parts of the blank.

2. The principle of selecting blanks.
(1) The selection principle: the shape and size of the blank should be as close as possible to the shape and size of the part to reduce mechanical processing.
(2) The blank selection should be considered factors.

  • (1) The size of the production program: for a large number of mass production. should choose a high-precision blank manufacturing methods to reduce mechanical processing. saving materials.
  • (2) Existing production conditions: the existing level of blank manufacturing and equipment capacity should be considered.


  • (1) Shaft parts: lathe spindle: 45# steel die forgings; step shaft (diameter difference is not large): bar stock.
  • (2) Box: casting or welding parts.
  • (3) Gears: small gears: bar; most medium-sized gears: die forgings; large gears: cast steel parts.

Source: China Pipe Sleeve Manufacturer – Yaang Pipe Industry Co., Limited (

(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.)

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