1. Milling process

1. Roughing process

The comprehensive improvement of production efficiency is the key to choosing the roughing process. The so-called roughing process refers specifically to the maximum material removal rate that can be achieved within a unit of time, and specifically to the machining allowance of the rough surface, which ensures that the shape and dimensions of the rough material are as close as possible to those of the finished product. Generally speaking, after the material has been roughened, the outline of a semi-precision workpiece can be formed. Speed plays an important role in the entire process. Using a larger diameter tool can not only improve 

2. Semi-finishing process

Unlike rough machining, semi-finishing pays more attention to the organic coordination of efficiency and quality. After semi-finishing, the surface of the workpiece should be relatively smooth and the allowance should be even. Moreover, the purpose of this process is to lay a solid foundation for finishing, with a view to achieving the goal of secondary surface machining. It should be noted that in the actual machining process, as much of the excess material on the surface of the part as possible should be effectively removed to ensure that the surface of the machined part is in a flat state, and ultimately meet the standard requirements for accuracy.

3. Corner clearance machining process

The machining process for clearing the corners of workpieces does not require high machining speeds, but rather focuses on the uniformity and consistency of the mould surface. It should be noted that the purpose of machining the corners of workpieces is to completely remove excess material, which lays a solid foundation for subsequent finishing operations and further promotes the overall progress of finishing work. If a smaller diameter tool is used in this process, it is difficult to complete the cutting operation in one pass, so it is necessary to perform no less than two cutting operations, and the cutting can only be stopped when the specific requirements are met. However, the tool diameter should not exceed the diameter of the finishing tool.

4. Finishing process

The finishing process is the final process, which requires that the dimensional accuracy, surface roughness and shape accuracy of each part meet the requirements of the drawing. Generally speaking, a specific allowance is reserved on the finished surface, the main purpose of which is to ensure that the cutting edge is in a stable state during cutting, minimise the machining error of the workpiece as much as possible, and ensure that the performance meets the required standards. During the finishing process, a processing tool with a smaller diameter should be selected. The best finishing process is as follows: machining the external contour → machining raised parts → machining stepped and free-form surfaces → machining recesses → machining other low-support surfaces.

In mould manufacturing, for high-speed finishing of curved core and cavity surfaces, attention should be paid to the following: when cutting, the contact point between the tool and the workpiece must be able to follow the surface curvature of the workpiece and change accordingly with the selection of the tool radius.

If the surface of the mould to be machined is highly complex, it must be ensured that it can be completed in one process, effectively reducing the number of cuts and preserving the surface of the mould. In addition, during the cutting process, it is necessary to ensure that the direction of the tool feed is in the form of an arc, so that the cutting surface is continuous and smooth, with a certain degree of stability. Finally, in the actual machining process, the occurrence of processing stoppages should be avoided as much as possible. Once the tool stops suddenly, it is very likely to cause a slight deformation of the mold surface, which will ultimately have a negative impact on the machining accuracy. It may even cause dents at the position where the tool stops, which will in turn affect the surface quality.

2. Effective improvement of the cutting process of CNC milling machines

1.Ways to improve the roughing process

First, the area of the cutting surface can be accurately calculated with the help of machining simulation software, and the cutting rate of the material to be cut should also be calculated accordingly. Only in this way can the tool load and wear rate be kept in balance during cutting, further improving the machining quality while minimising tool wear.

Secondly, in actual cutting on a CNC milling machine, the tool should be inserted or removed diagonally as much as possible. At the same time, the problem of vertical insertion and removal should also be effectively avoided when machining mold cavities. If conditions permit, spiral cutting should be used as much as possible, as shown in Figure 1, to effectively reduce the tool load.

Figure 1 Single-edged thread milling cutter

Third, if machining of large-margin parts is required, the climbing method should be used. The most prominent advantage of this method is that it can effectively reduce the cutting force, ensure proper improvement of the degree of cutting hardening, reduce the heat generated by cutting, and comprehensively enhance the actual quality of part cutting.

Finally, when cutting on a CNC milling machine, do not suddenly change the direction of the tool feed, as this will directly affect the cutting speed, ultimately significantly reducing the cutting quality and causing residual or overcutting, and in serious cases, even causing immeasurable safety accidents.

2. Ways to improve semi-finishing processes

To improve semi-finishing processes, the cutting spacing and tolerance values are very important. To ensure stable cutting, the above sequence must be strictly followed to avoid damage to the tool as much as possible. In addition, to ensure the continuity of cutting, the processing steps should be arranged reasonably to avoid frequent retraction or tool changes.

Figure 2 General CNC milling machine cutting program design

3. Ways to improve the corner clearance machining process

The surface of the workpiece is relatively even on the basis of semi-finishing, however, the machining allowance at the position of the concave surface is still relatively large. Once the machining allowance is not even, it will inevitably affect the stability of cutting, and even directly affect the final accuracy of machining. Therefore, a reasonable corner clearance process must be arranged to remove excess material.

4. Ways to improve the finishing process

The finishing process has high requirements for quality and precision, so the cutting process must be optimally designed (as shown in Figure 2) to avoid problems such as vertical cutting and a large number of lifting cuts, and to avoid damaging the surface of the part as much as possible. In addition, during the finishing process, a smooth milling method should be used to avoid skidding. The choice of tool path should also pay close attention to machining deformation problems, and if necessary, the number of tool passes should be increased as much as possible. The most important thing is to ensure that the tool path is optimized.

Summarize

This comprehensive guide outlines the critical stages of the milling process and provides valuable strategies for improving CNC milling efficiency and precision.

The roughing process aims for maximum material removal to form the general shape of the workpiece. Using large-diameter tools at higher speeds is essential for efficiency. Semi-finishing, in contrast, balances speed and quality, ensuring smooth surfaces and uniform allowances while preparing the part for final machining. Corner clearance machining focuses on precision, especially in areas that are difficult to reach, ensuring that excess material is fully removed. Finishing, the final stage, demands high accuracy and optimal surface quality, requiring small-diameter tools and meticulous machining paths to achieve desired tolerances.

For improving CNC milling operations, several recommendations are made, including the use of machining simulation software to calculate cutting areas and balance tool load. Spiral or diagonal tool insertions can reduce stress on tools during roughing, while strategic corner clearance methods ensure even cutting stability. In finishing, optimizing tool paths and avoiding abrupt cutting motions are key to preventing part damage and enhancing overall quality.

These techniques collectively contribute to enhancing the performance of CNC milling machines, boosting both productivity and accuracy in modern manufacturing operations.