CNC Machining Process Flow

        Process planning refers to the entire manufacturing process, which cannot be judged based on the nature of a certain process or the processing of a certain surface. For example, some positioning reference surfaces need to be processed very accurately in the semi precision machining stage or even in the rough machining stage. Sometimes, in order to avoid size chain conversion, semi finishing of certain secondary surfaces can also be arranged during the finishing stage.

Method for dividing processing procedures：

The parts processed on CNC machine tools are generally divided into processes according to the principle of process concentration, and the methods of division include the following:

1) Divided by the tools used

The division method of using the same tool to complete the process as one process is suitable for situations where there are many surfaces to be machined on the workpiece. This method is often used to complete machining centers.

2) Divided by the number of workpiece installations

The process that can be completed by clamping the parts in one go is considered as a process. This method is suitable for processing parts with limited content, and can complete all processing content in one clamping while ensuring the quality of the part processing.

3) Divided by rough and fine processing

Take the part of the process completed in rough machining as one process, and the part of the process completed in precision machining as another process. This division method is suitable for parts with strength and hardness requirements, requiring heat treatment or high precision requirements, effectively removing internal stress, and parts with large deformation after processing, which need to be divided into rough and fine machining stages.

4) Divide the part of the manufacturing process that completes the same profile according to the processing location as one process.

For parts with multiple and complex machining surfaces, the sequence of CNC machining, heat treatment, and auxiliary processes should be arranged reasonably, and the connection problem between processes should be solved well. The principle of dividing processing steps is that parts are composed of multiple surfaces, which have their own precision requirements, and there are corresponding precision requirements between each surface. In order to meet the design accuracy requirements of the parts, the processing sequence arrangement should follow certain principles.

5）The principle of rough first and then refined

The processing sequence of each surface is carried out in the order of rough machining, semi precision machining, precision machining, and finishing machining, with the aim of gradually improving the accuracy and surface quality of the machined parts. If all surfaces of the parts are machined by CNC machines, the process arrangement is generally carried out in the order of rough machining, semi precision machining, and precision machining, that is, after all rough machining is completed, semi precision machining and precision machining are carried out. During rough machining, most of the machining allowance can be quickly removed, and then each surface can be precision machined in sequence, which can improve production efficiency and ensure the machining accuracy and surface roughness of the parts. This method is suitable for machining surfaces that require high positional accuracy. This is not absolute. For some machining surfaces that require high dimensional accuracy, considering the requirements of part stiffness, deformation, and dimensional accuracy, these machining surfaces can also be completed in the order of rough machining, semi precision machining, and precision machining. For machining surfaces with high precision requirements, it is best to let the parts rest for a period of time between rough and fine machining processes, so that the surface stress of the rough machined parts can be completely released and the degree of stress deformation on the part surface can be reduced. This is beneficial for improving the machining accuracy of the parts.

6) Principle of first processing the reference surface

At the beginning of processing, the surface used as the precision machining reference is always machined out, because the surface of the positioning reference is precise and the clamping error is small. Therefore, in the machining process of any part, rough machining and semi precision machining are always carried out on the positioning reference surface first, and if necessary, precision machining is also carried out. For example, for shaft parts, rough machining and semi precision machining are always carried out on the positioning reference surface before precision machining. For example, for shaft parts, the center hole is always machined first, and then the hole system and other surfaces are machined based on the center hole surface and positioning hole as precision benchmarks. If there is more than one precision datum plane, the machining of the datum plane should be arranged according to the order of datum conversion and the principle of gradually improving machining accuracy.

7) Principle of Face First, Hole Later

For parts such as boxes, brackets, and bodies, the planar contour dimensions are relatively large, and using planar positioning is more stable and reliable. Therefore, the planar surface should be machined first, and then the holes should be machined. In this way, not only does it provide a stable and reliable plane as a positioning reference for subsequent processing, but it also makes it easier to process holes on a flat surface, which is beneficial for improving the machining accuracy of holes. Usually, the machining process can be divided according to the machining location of the parts. Simple geometric shapes are usually machined first, followed by complex geometric shapes; Process the parts with lower precision first, and then process the parts with higher precision; First process the plane, then process the hole.

8) The principle of internal first and external second

For precision sleeves, the coaxiality between the outer circle and the hole is required to be high. Generally, the principle of "hole first, outer circle later" is adopted, that is, the outer circle is used as the positioning reference to process the hole first, and then the high-precision hole is used as the positioning reference to process the outer circle. This can ensure a high coaxiality requirement between the outer circle and the hole, and the fixture structure used is also very simple.

9) The principle of reducing the number of tool changes

In CNC machining, the machining sequence should be arranged as much as possible according to the order in which the tool enters the machining position.