Machining parts on CNC lathe should be divided into processes according to the principle of process concentration, and most or even all surfaces should be finished under one clamping as far as possible. According to different structure shapes, usually choose external circle, end face or internal hole, end face clamping, and strive to unify the design reference, process reference and programming origin. In mass production, the following methods are commonly used to divide the process.
1, according to the part processing surface division process
That is, the completion of the same part of the surface process for a process, for the processing of multiple and complex surface parts, according to its structural characteristics (such as internal shape, shape, surface and plane, etc.) into multiple processes.
The surface requiring high positional accuracy will be completed in one clamping, so as not to affect the positional accuracy of the error generated by multiple positioning clamping. As shown in Figure 1, in accordance with the process characteristics of the part, the outer and inner contours of the rough and finish machining in a process to reduce the number of clamping, which is conducive to ensuring coaxiality.
2、Dividing the process by roughing and finishing
That is, the part of the process completed in rough machining is a process, and the part of the process completed in finishing machining is a process. For the parts with large margin and high processing accuracy requirements, roughing and finishing should be separated and divided into two or more processes. Rough turning will be arranged in the lower precision, higher power CNC machine tools to carry out, the finish turning will be arranged in the higher precision CNC machine tools to complete.
This division method is suitable for parts with large deformation after machining, which require separate rough and finish machining, such as parts with blanks of castings, welded parts or forgings.
Dividing the process according to the type of tool used
3、Dividing the process according to the type of tool used
The same tool to complete the part of the process for a process, this method is suitable for the workpiece surface to be machined more, machine tools work continuously for a long time, the preparation of processing procedures and check the difficulty of the situation.
4, according to the number of times the installation process
A part of the process to complete the installation for a process. This method is suitable for workpieces with little processing content, the processing is completed to reach the state of pending inspection.
After serious and careful analysis of the part diagram, the following basic principles should be followed to develop the machining plan - coarse first, then fine, near then far, inside and outside cross, the least number of program segments, and the shortest tool route.
(1) Coarse first and then fine
It means that the machining accuracy is gradually improved according to the sequence of rough turning and half finishing turning. In order to improve production efficiency and ensure the quality of finishing parts, in the cutting process, the roughing process should be arranged first, in a shorter period of time, most of the machining allowance before finishing is removed, while trying to ensure that the finishing allowance is uniform.
(2) Near first and then far
The far and near mentioned here are according to the distance of the machining part relative to the tooling point. In general, especially in rough machining, it is usually arranged that the part near to the tool point will be machined first, and the part far from the tool point will be machined later, in order to shorten the tool movement distance and reduce the empty travel time.
(3) Internal and external crossover
For both the inner surface (inner cavity) and the outer surface of the parts to be machined, the processing sequence should be arranged so that rough machining of the inner and outer surfaces is carried out first, followed by finishing machining of the inner and outer surfaces.
