The process planning refers to the whole process, and cannot be judged by the nature of a certain process and the processing of a certain surface. For example, some positioning datums need to be processed accurately in the semi-finishing stage and even in the roughing stage. Sometimes in order to avoid dimensional chain conversion, semi-finishing of certain secondary surfaces can also be arranged during the finishing stage.
After the processing method and processing stage of the surface of the part are determined, the processing of each surface in the same processing stage can be combined into several steps.
1. Method of dividing processing steps
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) According to the tool used
The process of completing the same tool as a process, this division method is suitable for the case where the workpiece has a large number of surfaces to be processed. Processing centers are often done this way.
(2) Divided by the number of workpiece installations
The process that can be completed in one part of the part is used as a process. This method is suitable for processing parts with few contents, and all the processing contents are completed in one setup under the premise of ensuring the processing quality of the parts.
(3) divided by rough finishing
The part of the process completed in the roughing process is taken as one process, and the part of the process completed in the finishing process is taken as another process. This method of division is applicable to parts with strength and hardness requirements, heat treatment or high precision of parts, effective removal of internal stress, and large deformation after machining. It is necessary to process parts according to the rough and finishing stages.
(4) According to the processing part
The part of the process that completes the same profile is used as a process. For parts with many complicated surfaces and complicated parts, the order of NC machining, heat treatment and auxiliary processes should be arranged reasonably, and the connection problem between the processes should be solved.
2. Principles of division of processing operations
The parts are made up of multiple surfaces that have their own accuracy requirements and the corresponding accuracy requirements 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 is 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 with high positional accuracy requirements.
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 machining surfaces in the order of roughing, semi-finishing, and finishing. carry out.
For the machining surface with high precision requirements, between the roughing 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.
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