Selection of processing method and determination of processing plan

1. Selection of processing method

The selection principle of the machining method is to ensure the machining accuracy and surface roughness of the machined surface. Since there are generally many processing methods to obtain the same level of precision and surface roughness, in the actual selection, the shape, size and heat treatment requirements of the parts should be considered comprehensively. For example, boring, reaming, grinding and other processing methods can meet the accuracy requirements for holes with IT7 precision, but the holes on the box are generally boring or reaming, not grinding.

Generally, reaming is selected for small-sized box holes, and boring should be selected when the hole diameter is large. In addition, the requirements of productivity and economy, as well as the actual situation of the production equipment of the factory, should also be considered. The economic machining accuracy and surface roughness of common machining methods can be found in the relevant process manuals robot prototype factory.

2. The principle of determining the processing plan

The machining of a relatively perfect surface on a part is often achieved gradually through roughing, semi-finishing and finishing. For these surfaces, it is not enough to select the corresponding final processing method only according to the quality requirements, but also to correctly determine the processing plan from the blank to the final shape. When determining the processing plan, the processing method required to meet these requirements should be preliminarily determined according to the requirements of the accuracy and surface roughness of the main surface. For example, for a hole with a small diameter of IT7 precision, when the processing method is fine reaming, drilling, reaming and rough reaming are usually processed before fine reaming.

The division of processes and steps

1. Division of processes

When machining parts on CNC machine tools, the process can be relatively concentrated, and most or all of the processes can be completed in one clamping as much as possible. First of all, according to the part drawing, consider whether the part to be processed can complete the processing of the entire part on one CNC machine tool. If not, it should decide which part of the part is processed on the CNC machine tool and which part is processed on other machine tools, that is, the part is processed on the part. The processing steps are divided.

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2. Division of work steps

The division of work steps is mainly considered from two aspects of machining accuracy and efficiency. In a process, different tools and cutting amounts are often used to process different surfaces. In order to facilitate the analysis and description of the more complex process, it is subdivided into work steps within the process. The following takes the machining center as an example to illustrate the principle of step division:

1)The same surface is completed in sequence by roughing, semi-finishing, and finishing, or all the machined surfaces are separately processed according to roughing and finishing.

2) For parts with both milling surfaces and boring holes, the surfaces can be milled first and then the holes can be boring. Dividing the steps according to this method can improve the accuracy of the hole. Because of the large cutting force during milling, the workpiece is prone to deformation. The surface is milled first and then the hole is boring, so that it can recover for a period of time to reduce the impact on the accuracy of the hole caused by deformation.

3) Divide the steps according to the tool. The rotation time of some machine tool worktables is shorter than the tool change time, and the work steps can be divided according to the tool to reduce the number of tool changes and improve the processing efficiency.
In short, the division of processes and steps should be comprehensively considered according to the structural characteristics and technical requirements of specific parts.

Parts installation and fixture selection

1. Basic principles of positioning and installation

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1) Strive to unify the benchmark of design, process and programming calculation.

2) Minimize the number of clampings, and try to process all the surfaces to be machined after one positioning and clamping.

3) Avoid the use of machine-intensive manual adjustment processing solutions to give full play to the effectiveness of CNC machine tools.
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2. Basic principles for selecting fixtures

The characteristics of CNC machining put forward two basic requirements for the fixture: one is to ensure that the coordinate direction of the fixture and the coordinate direction of the machine tool are relatively fixed; the other is to coordinate the dimensional relationship between the parts and the machine tool coordinate system. In addition, consider the following four points:

1) When the batch processing of parts is not large, combined fixtures, adjustable fixtures and other general fixtures should be used as much as possible to shorten the production preparation time and save production costs.

2) Only consider the use of fixtures in mass production, and strive to have a simple structure.

3) The loading and unloading of parts should be fast, convenient and reliable, so as to shorten the downtime of the machine tool.

4) The parts on the fixture should not interfere with the machining of the surfaces of the parts by the machine tool, that is, the fixture should be opened for its positioning, and the clamping mechanism components should not affect the cutting tool during processing (such as collision, etc.).

Selection of processing method and determination of processing plan

1. Selection of processing method

The selection principle of the machining method is to ensure the machining accuracy and surface roughness of the machined surface. Since there are generally many processing methods to obtain the same level of precision and surface roughness, in the actual selection, the shape, size and heat treatment requirements of the parts should be considered comprehensively. For example, boring, reaming, grinding and other processing methods can meet the accuracy requirements for holes with IT7 precision, but the holes on the box are generally boring or reaming, not grinding.

Generally, reaming is selected for small-sized box holes, and boring should be selected when the hole diameter is large. In addition, the requirements of productivity and economy, as well as the actual situation of the production equipment of the factory, should also be considered. The economic machining accuracy and surface roughness of common machining methods can be found in the relevant process manuals.

2. The principle of determining the processing plan

The machining of a relatively perfect surface on a part is often achieved gradually through roughing, semi-finishing and finishing. For these surfaces, it is not enough to select the corresponding final processing method only according to the quality requirements, but also to correctly determine the processing plan from the blank to the final shape. When determining the processing plan, the processing method required to meet these requirements should be preliminarily determined according to the requirements of the accuracy and surface roughness of the main surface. For example, for a hole with a small diameter of IT7 precision, when the processing method is fine reaming, drilling, reaming and rough reaming are usually processed before fine reaming.