What is CNC Machining Process
CNC machining process planning refers to the whole process, and can not be judged by the nature of a process and the processing of a surface. For example, some positioning data, in the semi-finishing stage or even in the rough processing stage will need to be processed very accurately. Sometimes in order to avoid dimensional chain conversion, in the finishing stage, also can arrange some secondary surface semi-finishing.
After determining the processing method and processing stage of the part surface, the processing of each surface in the same processing stage can be combined into several steps.
The Method of Processing Procedures Division
The parts processed on CNC machine tools are generally divided into the following methods according to the principle of process concentration
1) Divided by the Tool Used
Taking the process completed by the same tool as a processing procedure, this division method is suitable for situations where there are many workpiece surfaces to be machined. Machining centers often use this method to complete.
2) Divided by the Number of Workpiece Installations
The technological process that can be completed by the parts in one clamping is regarded as a process. This method is suitable for parts with few processing contents. Under the premise of ensuring the processing quality of the parts, all processing contents can be completed in one clamping.
3) Divided by Roughing and Finishing
The part of the process completed in rough machining is regarded as one process, and the part of the process completed in finishing is regarded as another process. This division method is suitable for parts that have strength and hardness requirements, require heat treatment or require high accuracy of parts, need to effectively remove internal stress, and have large deformation after machining, which needs to be divided into rough and finish machining stages.
4) Divided by Processing Part
The part of the process that completes the same profile as a process.
For the parts with a more complicated processing surface, the sequence of CNC processing, heat treatment, and auxiliary working procedure should be reasonably arranged, and the connection problem between working procedures should be solved.
2. Principle Of Process Division
Parts are made up of multiple surfaces that have their own precision requirements and also have corresponding precision requirements between the surfaces.
In order to achieve the design precision of parts, the arrangement of the machining sequence should follow certain principles.
1) Roughing First, Finishing Later
The processing sequence of each surface is carried out in the order of roughing, semi-finishing, finishing and finishing, with the purpose of gradually improving the accuracy and surface quality of the processed surface of the part. If all surfaces of the part are processed by CNC machine tools, the process arrangement is generally carried out in the order of roughing, semi-finishing, and finishing, that is, semi-finishing and finishing are performed after all roughing are completed. During rough machining, most of the machining allowance can be quickly removed, and then each surface can be finished in sequence, which can improve production efficiency and ensure the machining accuracy and surface roughness of the parts. This method is suitable for machined surfaces that require high position accuracy. This is not absolute, such as for some higher dimensional accuracy requirements of the machining surface, taking into account the stiffness of parts, deformation and dimensional accuracy requirements can also consider these machining surface respectively according to rough machining, semi-finishing, finishing process order to complete. For machining surfaces with high precision requirements, it is best to leave the parts for a period of time between roughing and finishing processes, so that the surface stress of the parts after roughing can be completely released, and the degree of stress and deformation on the surface of the parts can be reduced, which is beneficial to improve the machining accuracy of the parts.
2) Datum Surface First Processing Principle
At the beginning of processing, the surface used as the finishing reference is always processed. Because the surface of the positioning reference is accurate, the clamping error is small. Therefore, in the processing of any part, the positioning reference surface is always roughed and semi-finished. Machining, and finishing if necessary, for example, shaft parts always rough and semi-finish the positioning reference surface before finishing.
For example, for shaft parts, the center hole is always processed first, and then the whole system and other surfaces are processed on the center hole surface and the positioning hole as a precision reference. If there is more than one precision reference surface, the processing of the reference surface should be arranged in accordance with the sequence of reference conversion and the principle of gradually improving the processing accuracy.
3) Surface Process First, Hole Process Later
For the box, bracket, machine body, and other parts, the plane outline size is larger, and the plane positioning is more stable and reliable, so the plane surface should be processed first, and then the hole should be processed. In this way, not only the subsequent processing has a stable and reliable plane as the positioning reference surface, but also the processing of holes on a flat surface makes the processing easier, and it is also conducive to improving the processing accuracy of the holes. Generally, the processes can be divided according to the processing positions of the parts, the simple geometric shapes are processed first, and then the complex geometric shapes are processed; the lower precision parts are processed first, and the higher precision parts are processed first; the plane is processed first, and the hole is processed later.
4) Inner Hole First, Outer Circle Later
For precision sleeves, the coaxial between the outer circle and the hole is required. Generally, the principle of the first hole and the outer circle is adopted, that is, the outer circle is used as the positioning reference to machine the hole, and then the hole with higher precision is used as the positioning reference to process the outer circle. Round, which can ensure a high coaxiality requirement between the outer circle and the hole, and the fixture structure used is also very simple.
5) Reduce the Number of Tool Changes Principle
In CNC machining, the machining sequence should be arranged as far as possible according to the order in which the tool enters the machining position.
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