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CNC machining process division method
Feb 12, 2019

Parts are made up of multiple surfaces that have their own accuracy requirements and that there is a corresponding accuracy requirement between the surfaces. In order to meet the design accuracy requirements of the parts, the processing sequence should follow certain principles.

(1) The principle of coarse and fine

The processing order of each surface is performed in the order of roughing, semi-finishing, finishing and finishing, in order to gradually improve the precision and surface quality of the machined surface.

If the entire surface of the part is machined by a CNC machine, the process arrangement is generally performed in the order of roughing, semi-finishing, and finishing, that is, semi-finishing and finishing are performed after the roughing is completed. During roughing, most of the machining allowance can be quickly removed, and each surface can be finished in turn, which can improve production efficiency and ensure the machining accuracy and surface roughness of the parts. This method is suitable for machining surfaces where position accuracy is required.

This is not absolute. For some machining surfaces that require high dimensional accuracy, considering the rigidity, deformation and dimensional accuracy of the parts, it is also possible to consider the order of roughing, semi-finishing and finishing. carry out.

For the machining surface with high precision requirements, between the rough and finishing processes, the parts should be kept for a period of time, so that the surface stress of the roughed parts is completely released, and the stress deformation degree of the surface of the parts is reduced, which is beneficial to improve The machining accuracy of the parts.

(2) Benchmark processing principle

At the beginning of the machining, the surface used as the finishing reference is always processed. Because the surface of the positioning reference is accurate and the clamping error is small, the machining of any part is always roughing and semi-finishing the positioning reference surface. Machining, if necessary, finishing, for example, the shaft parts always rough and semi-finish the positioning datum and then finish. For example, shaft parts always machine the center hole first, and then the hole hole and the positioning hole are used as the fine reference for machining the hole system and other surfaces. If there is more than one precision datum, the machining of the datum should be arranged in accordance with the order of the reference conversion and the principle of gradually increasing the machining accuracy.

(3) First face and back hole principle

For the box type, bracket type, body type and other parts, the plane contour size is large, and the plane positioning is relatively stable and reliable, so the plane should be processed first, and the hole should be machined later. In this way, not only the subsequent processing has a stable and reliable plane as the positioning reference plane, but also the processing of the hole on the flat surface becomes easier, and the processing precision of the hole is also improved. Generally, the process can be divided according to the processing part of the part. Generally, the simple geometric shape is processed first, and the complex geometric shape is processed later; the part with lower precision is processed first, and the part with higher precision is processed first; the plane is processed first, and the hole is processed later.

(4) Principle of internal and external

For precision sleeves, the coaxiality of the outer circle and the hole is relatively high. Generally, the principle of the outer hole after the first hole is adopted, that is, the outer circle is used as the positioning reference processing hole, and the hole with higher precision is used as the positioning reference. The circle ensures a high degree of concentricity between the outer circle and the hole, and the fixture structure used is also simple.

(5) Principle of reducing the number of tool changes

In CNC machining, the machining sequence should be arranged in the order of the tool entering the machining position.

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