CNC machining, also known as CNC machining, refers to the machining with CNC machining tools. Because NC machining is controlled by computer after programming, CNC machining has the advantages of stable machining quality, high machining accuracy, high repetition accuracy, complex profile machining and high machining efficiency. In the actual processing process, human factors and operating experience, to a large extent, will affect the processing quality. Next, let’s take a look at 12 valuable experiences summed up by an old driver with ten years of CNC processing experience
1. How to divide CNC process
The division of CNC machining process can be generally carried out according to the following methods:
The method of tool centralized sequence is to divide the working procedure according to the tool used, and use the same tool CNC to finish all the parts that can be finished. Use the second knife and the third to finish other parts they can finish. In this way, the number of tool changes can be reduced, the empty travel time can be compressed, and the unnecessary positioning error can be reduced. For parts with a lot of CNC machining content, the machining part can be divided into several parts according to its structural characteristics, such as internal shape, shape, curved surface or plane, etc. Generally, plane and positioning surface are processed first, then hole; simple geometry is processed first, then complex geometry is processed; parts with lower precision are processed first, then parts with higher precision requirements are processed. For the parts that are easy to deform in CNC machining, the method of sorting by rough and fine CNC machining needs to calibrate the shape due to the possible deformation after rough machining, so generally speaking, the process should be separated for the parts that need rough and fine machining. To sum up, in the process division, it is necessary to flexibly grasp the structure and process of the parts, the function of the machine tool, the number of CNC machining contents of the parts, the installation times and the production organization of the unit. In addition, it is suggested that the principle of process concentration or process dispersion should be adopted, which should be determined according to the actual situation, but must be reasonable.
2. What principles should be followed in the arrangement of CNC processing sequence
The arrangement of the processing sequence should be considered according to the structure of the part and the condition of the blank, as well as the need of positioning and clamping. The key point is that the rigidity of the workpiece will not be damaged. Generally, the sequence shall be in accordance with the following principles:
The CNC machining of the previous process can not affect the positioning and clamping of the next process, and the machining process of universal machine tool inserted in the middle should also be considered comprehensively. First, process the internal cavity, then process the shape. It is connected by the same positioning and clamping method or the same tool CNC processing process to reduce the number of repeated positioning, tool change and moving of pressing plate. For multiple processes in the same installation, the process with small damage to workpiece rigidity shall be arranged first.
3. What should be paid attention to in the determination of workpiece clamping mode
The following three points should be paid attention to when determining the positioning datum and clamping scheme:
Strive to unify the design, process and programming calculation standards. Reduce the number of clamping as much as possible. After one positioning, all surfaces to be machined can be processed by CNC. Avoid manual adjustment of occupation plan. The fixture shall be smooth, and its positioning and clamping mechanism shall not affect the cutter (such as collision) in CNC machining. In such cases, it can be clamped by means of vise or screw extraction with base plate. 4. How to determine the tool setting point is reasonable? What is the relationship between workpiece coordinate system and programming coordinate system?
1. The tool setting point can be set on the part to be machined, but it must be the reference position or the part that has been finished. Sometimes the tool setting point is damaged by CNC machining after the first process, which will cause the second process and the subsequent tool setting point cannot be found. Therefore, when the first process is used for tool setting, it is necessary to set a relative pair at the place that has a relatively fixed dimension relationship with the positioning benchmark Knife position, so that the original tool setting point can be retrieved according to the relative position relationship between them. This relative tool setting position is usually set on the working table or fixture of the machine tool. The selection principles are as follows:
Alignment is easy. Easy to program. The tool setting error is small. It is easy to check during processing.
2. The origin position of the workpiece coordinate system is set by the operator himself. After the workpiece is clamped, it is determined by tool setting, which reflects the distance position relationship between the workpiece and the zero point of the machine tool. Once the workpiece coordinate system is fixed, it is generally not changed. The workpiece coordinate system and the programming coordinate system must be unified, that is, when machining, the workpiece coordinate system and the programming coordinate system are the same.
4. How to choose the cutting route
Tool path refers to the path and direction of the tool relative to the workpiece in the process of NC machining. The reasonable choice of machining route is very important, because it is closely related to the CNC machining accuracy and surface quality of parts. The following points are mainly considered in determining the tool path:
Ensure the machining accuracy of parts. It is convenient for numerical calculation and reduces programming workload. In order to improve the efficiency of CNC machining, it is necessary to find a short CNC machining route and reduce the time of blank cutting. Minimize the number of program segments. To meet the requirements of the surface roughness after CNC machining, the contour should be processed by a continuous cutter. The advance and retreat (cut in and cut out) routes of the tool should also be carefully considered to minimize the tool marks caused by tool stop (elastic deformation caused by sudden change of cutting force) at the contour, and avoid cutting vertically on the contour surface and scratching the workpiece.
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