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The principle of CNC machining technology

Machining process planning refers to the whole process, can not be judged by the nature of a process and a surface processing. For example, some positioning datum, in the semi-finishing stage or even in the rough processing stage need to be processed very accurately. Sometimes, in order to avoid size chain conversion, semi-finishing of some secondary surfaces can be arranged during the finishing stage.

When the processing method and processing stage of the surface of the parts are determined, the processing of each surface in the same processing stage can be combined into a number of work steps.

  1. The method of dividing the process

The parts processed on CNC machine tools are generally divided into processes according to the principle of process concentration. The methods of division are as follows:

1) Divide according to the tool used

With the same tool to complete the process as a process, this division method is suitable for the workpiece to be machined more surface situation. Machining centers are often completed in this way.

2) According to the number of workpiece installation

To a part clamping can complete the process as a process. This method is suitable for the processing content of the parts, under the premise of ensuring the quality of parts processing, a clip to complete all the processing content.

3) Divided by rough finishing

The part of the process completed in rough machining is regarded as one process, and the part of the process completed in fine machining is regarded as another process. This division method is suitable for parts that have strength and hardness requirements, need heat treatment or parts with high precision requirements, need to effectively remove internal stress, and parts with large deformation after processing, need to be divided according to rough and finish machining stage.

4) The part of the process that completes the same shape surface is divided as a process according to the processing parts.

For the parts with more and more complex surfaces, the order of CNC machining, heat treatment and auxiliary procedures should be arranged reasonably, and the connection between the procedures should be solved well.

  1. The principle of processing division

A part is composed of multiple surfaces, which have their own precision requirements, and there are corresponding precision requirements between the surfaces. In order to achieve the design accuracy requirements of parts, the processing sequence arrangement should follow certain principles.

1) The principle of rough before fine

The machining sequence of each surface is carried out in the order of rough machining, semi-finishing machining, finishing machining and light finishing machining. The purpose is to gradually improve the precision and surface quality of the machined surface of parts. If all the surfaces of the parts are processed by CNC machine tools, the process arrangement is generally carried out in the order of rough machining, semi-finish machining and finish machining, that is, semi-finish machining and finish machining will be carried out after all the rough machining is completed. Rough machining can quickly remove most of the machining allowance, and then finish each surface in turn, which can improve the production efficiency, but also to ensure the machining accuracy and surface roughness of parts. This method is suitable for machining surface with high position accuracy requirement. This is not absolute, such as for some machining surfaces with higher dimensional accuracy requirements, taking into account the stiffness, deformation and dimensional accuracy of the parts and other requirements, can also consider these machining surfaces according to rough machining, semi-finish machining, finish machining order. For the machining surface with higher precision requirements, between the rough and finish machining procedures, the parts had better be used for a period of time, so that the surface stress of the parts after rough machining is completely released, reduce the degree of stress and deformation of the surface of the parts, which is conducive to improving the machining accuracy of the parts.

2) The principle of processing datum first

At the beginning of processing, it is always used as the surface of the finishing datum. Because the surface of the positioning datum is accurate, the clamping error is small, so the processing process of any parts is always the first rough machining and semi-finish machining of the positioning datum, and when necessary, finish machining. For example, shaft parts are always rough machining and semi-finish machining of the positioning datum, and then finish machining. For example, shaft parts are always the first to process the center hole, and then to the center hole surface and positioning hole as the fine reference processing hole system and other surfaces. If there is more than one precision datum surface, the processing of datum surface should be arranged according to the sequence of datum conversion and the principle of gradually improving the machining accuracy.

3) The principle of face first and hole second

For the box class, bracket class, body class and other parts, the plane contour size is larger, the plane positioning is more stable and reliable, so it should be the first processing plane, after processing holes. In this way, not only the subsequent processing has a stable and reliable plane as the positioning datum, but also on the flat surface of the hole processing, processing easier, but also conducive to improve the hole processing accuracy. Usually, the process can be divided according to the processing parts of the parts, generally the first processing of simple geometric shapes, after processing complex geometric shapes; The parts with lower precision are processed first, and the parts with higher precision are processed later. The plane is processed first, and then the hole is processed.

4) The inside out principle

For precision sleeve, the coaxiality of the outer circle and the hole is relatively high. Generally, the principle of first hole and then outer circle is adopted, that is, the outer circle is used as the positioning datum to process the hole, and then the hole with higher precision is used as the positioning datum to process the outer circle, which can ensure that the outer circle and the hole have a higher coaxiality requirement, and the structure of the fixture is also very simple.

5) The principle of reducing the number of knife changes

In CNC machining, the machining sequence should be arranged as far as possible according to the order of the tool entering the machining position.

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