To process parts on a CNC lathe, the processes should be divided according to the principle of process concentration, and most or all of the surface processing should be completed as much as possible under one clamping.

According to different structural shapes, usually choose the outer circle, end face or inner 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 processes.

1. Divide the process according to the surface of the part

That is to say, the part of the process that completes the same profile is regarded as one process. For parts with many and complex processed surfaces, it can be divided into multiple processes according to its structural characteristics (such as internal shape, shape, curved surface and plane, etc.).

The surface with high position accuracy requirements is completed in one clamping, so as to avoid errors caused by multiple positioning and clamping to affect the position accuracy. As shown in Figure 1, according to the process characteristics of the part, the rough and finish machining of the outer contour and the inner contour are each completed in one process, which reduces the number of clamping and helps to ensure the coaxiality.

2. Divide processes according to roughing and finishing

That is, the part of the process completed in rough machining is a process, and the part of process completed in finishing is a process. For parts with large blank margins and high machining accuracy requirements, rough turning and finishing turning should be separated and divided into two or more processes. The rough turning is arranged on a numerically controlled machine with lower precision and higher power, and the fine turning is arranged on a numerically controlled machine with higher precision.

This division method is suitable for parts that have large deformation after processing and need to be rough and finely processed separately, such as parts whose blanks are castings, welded parts or forgings.

Divide the process according to the type of tool used

3. Divide the process according to the type of tool used

The part of the process completed by the same tool is a process. This method is suitable for situations where there are many workpiece surfaces to be processed, the machine tool has a long continuous working time, and the preparation and inspection of the processing program are more difficult.

4. Divide the process according to the number of installations

Take that part of the process completed in one installation as a process. This method is suitable for workpieces with little processing content, and can reach the state to be inspected after processing is completed.

After a careful and careful analysis of the part drawing, the following basic principles should be followed when formulating the processing plan-first coarse and then fine, first near and far, cross between inside and outside, the least program segment, and the shortest tool path.

(1) First rough and then refined

It means to gradually improve the machining accuracy in the order of half of the rough turning and the final turning. In order to improve the production efficiency and ensure the quality of the finishing of the parts, during the cutting process, the roughing process should be arranged first. In a relatively short time, most of the machining allowance before the finishing is removed, and at the same time, try to ensure the remaining amount of the finishing. The amount is uniform.

(2) Near first and then far away

The far and near mentioned here are based on the distance between the processing part and the tool setting point. Under normal circumstances, especially during rough machining, it is usually arranged to process the parts close to the tool setting point first, and the parts far away from the tool setting point to process later, in order to shorten the tool movement distance and reduce the idle travel time.

(3) Crossing inside and outside

For parts that have both an inner surface (inner cavity) and an outer surface to be processed, when arranging the processing sequence, the inner and outer surfaces should be roughed first, and then the inner and outer surfaces should be finished.