Division of processing stages
1. Nature of processing stage
(1) Rough machining stage: the task of rough machining is to cut off most of the excess metal on the blank, so that the blank is close to the finished part in shape and size, reduce the internal stress of the workpiece, and prepare for finish machining. Therefore, the main purpose of rough machining is to improve productivity.
(2) Semi finishing stage: the task of semi finishing is to make the main surface reach a certain accuracy and leave a certain finishing allowance, so as to prepare for the finishing of the main surface and complete the processing of a secondary surface. The heat treatment process is generally placed before and after semi finishing.
(3) Precision machining stage: precision machining is mainly used to process parts with high requirements for precision and surface roughness. Its main goal is to further improve dimensional accuracy and reduce surface roughness. Precision machining has little impact on position accuracy.
2. Purpose of dividing processing stages
(1) Ensure the processing quality: the workpiece is in the finishing stage, and the cutting allowance is large. Therefore, the cutting force and clamping force are large, the cutting temperature is also high, and the internal stress of the part will be redistributed, resulting in deformation. If the processing stages are not divided, the errors caused by the above reasons cannot be avoided.
(2) Reasonable use of equipment: rough machining can be processed by machine tools with high power, good rigidity and low precision, and the turning amount can also be taken as a larger value, so as to give full play to the potential of the equipment. Fine machining has less cutting force and less damage to the machine tools, thus maintaining the accuracy of the equipment. Therefore, dividing the processing stages can improve productivity and prolong the service life of precision equipment.
3. Arrangement of processing sequence
(1) The principle of processing sequence arrangement: the surface used as the precision datum should be processed first, because the more accurate the surface of the positioning datum is, the smaller the clamping error is.
(2) The principle of finishing first and then rough: the processing sequence of each surface is carried out according to the sequence of rough processing, semi finish processing, finish processing and precision processing, so as to gradually improve the processing accuracy of the surface and reduce the surface roughness.
(3) The principle of first priority and second priority: the main working surface and assembly base surface of parts should be processed first, so as to find the possible defects on the main surface of the blank as soon as possible. The secondary surface can be interspersed, which can be carried out after the main processing surface is processed to a certain extent and before the final finishing.
(4) The principle of "close first and then far": generally, after the workpiece is clamped, the part close to the tool rest is processed first, and the part far from the tool rest is processed again to shorten the tool moving distance and reduce the empty travel time.
