(2) Benchmark processing principle

At the beginning of the processing, 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, the shaft parts always machine the center hole first, and then the hole system and other surfaces are processed with the center hole surface and the positioning hole as the fine reference. If there is more than one fine datum, the machining of the datum should be arranged in accordance with the order of the reference conversion and the principle of gradually improving the machining accuracy.

(3) Principle of first face and back hole

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 the precision sleeve, 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. Round, this ensures a high degree of concentricity between the outer circle and the hole, and the fixture structure used is also very 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. This requires reducing the number of tool changes, reducing the idle stroke and saving the auxiliary time without affecting the machining accuracy. After the parts are clamped, use the same tool to complete more machining surfaces. When a tool completes all the parts that may be processed, try to do some pre-processing for the next process, and then change the knife to finish the finishing or processing other parts. For some unimportant parts, use the same tool to complete the multi-process of the same station.

(6) Principle of continuous processing

When machining semi-closed or closed inner and outer contours, the pause in CNC machining should be avoided as much as possible. Since the process system of parts, tools and machine tools is temporarily in a dynamic equilibrium state during the machining process, if the equipment suddenly stops feeding due to the NC program arrangement, the cutting force will be significantly reduced, and the original process system will be lost. Stable state, leaving the tool with scratches or dents at the standstill. Therefore, the phenomenon of feed stop should be avoided in the contour machining to ensure the machining quality of the parts.

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