CNC machining process principle
Principles of CNC machining process division:
Parts are composed of multiple surfaces, which have their own accuracy requirements, and there are corresponding accuracy requirements between the surfaces. In order to meet the design accuracy requirements of parts, the processing sequence should follow certain principles.
1. The principle of rough before refined
The machining sequence of each surface shall be in accordance with the sequence of rough machining, semi finish machining, finish machining and finishing, so as to gradually improve the precision and quality of the machined surface of the part. If all surfaces of parts are processed by numerical control machine tools, the working procedure is generally arranged in the order of rough machining, semi finish machining and finish machining, that is, semi finish machining and finish machining can be carried out after all rough machining is completed.
During rough machining, most of the machining allowance can be quickly removed, and then each surface can be finished in turn, which can improve the production efficiency and ensure the machining accuracy and surface roughness of the parts. This method is suitable for machining surfaces with high position accuracy requirements.
This is not absolute. For example, for some machined surfaces with high dimensional accuracy requirements, considering the requirements of rigidity, deformation and dimensional accuracy of parts, it can also be considered that these machined surfaces are completed in the order of rough machining, semi finish machining and finish machining. For the machined surface with high accuracy requirements, it is better to leave the part for a period of time between rough and finish machining procedures to fully release the surface stress of the part after rough machining and reduce the stress deformation degree of the part surface, which is conducive to improving the machining accuracy of the part.
2. Principle of datum plane processing first
At the beginning of processing, the surface used as the precision machining reference is always processed. Because the surface of the positioning reference is accurate, the clamping error is small, so in the processing process of any part, the positioning reference plane is always rough machined and semi precision machined, and when necessary, the precision machining is also required. For example, the positioning reference plane is always rough machined and semi precision machined for shaft parts, and then finish machined. For example, shaft parts are always machined with the center hole first, and then the hole series and other surfaces are machined with the center hole surface and the positioning hole as the precision datum. If there is more than one precision datum plane, the machining of the datum plane shall be arranged according to the sequence of datum conversion and the principle of gradually improving the machining accuracy.
3. Principle of face before hole
For box type, bracket type, body type and other parts, the plane profile size is relatively large, and the plane positioning is relatively stable and reliable, so the plane should be processed first, and then the hole. In this way, not only does the subsequent processing have a stable and reliable plane as the positioning datum plane, but also it is easier to process holes on a flat surface, which is also conducive to improving the processing accuracy of holes. Generally, the process can be divided according to the processing part of the part. Generally, simple geometric shapes are processed first, and then complex geometric shapes are processed; The parts with lower accuracy shall be processed first, and then the parts with higher accuracy shall be processed; First machine the plane, then the hole.
4. The principle of "inside before outside"
For precision sleeves, the coaxiality between the outer circle and the hole is required to be high. Generally, the principle of "hole first and outer circle second" is adopted, that is, the outer circle is used as the positioning reference to process the hole, and then the hole with high accuracy is used as the positioning reference to process the outer circle. This can ensure that there is a high coaxiality requirement between the outer circle and the hole, and the used fixture structure is also very simple.
5. Principle of reducing tool change times
In numerical control processing, the processing sequence should be arranged as far as possible according to the order in which the tool enters the processing position.