Common Problems in CNC Machining
August 21, 2021
SCZY is one of the leading suppliers who is professional in various CNC Machining Parts customization. Today we would like to tell something about the common problems in CNC machnining.Due to the complexity of CNC Machining (such as different machine tools, different materials, different tools, different cutting methods, different parameter settings, etc.), it is decided to engage in CNC machining (whether machining or programming) to reach certain The level must pass a relatively long period of time. This manual is summarized by the engineers of the laboratory in the long-term actual production process. Some aspects related to the numerical control machining process, the process, the selection of common tool parameters, and the monitoring during the processing. A summary of the experience, for everyone to participate.
I. Q: How to divide the processing process? A: The division of CNC machining operations can generally be carried out as follows: (1) Tool concentration sorting method: It is to divide all the parts that can be completed on the part with the same tool according to the dividing process of the tool used. Then use the second knife and the third to complete other parts that they can complete. This reduces the number of tool changes, compresses the dead time, and reduces unnecessary positioning errors. (2) Sorting method of processing parts: For parts with a lot of processing contents, the processing part can be divided into several parts according to its structural characteristics, such as inner shape, shape, curved surface or plane. Generally, the plane, the positioning surface, and the rear processing hole are first processed; the simple geometric shape is processed first, and the complicated geometric shape is processed; the lower precision part is processed first, and the processing precision requirement is higher. (3) The method of coarse and fine processing: For parts that are prone to processing deformation, it is necessary to perform the shape correction due to the deformation that may occur after roughing. Therefore, in general, the process must be performed for roughing and finishing. separate. In summary, when dividing the process, it must be based on the structure and process of the part, the function of the machine tool, the amount of CNC machining content of the part, the number of installations and the production organization status of the unit. It is also recommended to adopt the principle of process concentration or the principle of process dispersion, which should be determined according to the actual situation, but it must be reasonable. two. Q: What should be noted in the determination of the workpiece clamping method? A: The following three points should be noted when determining the positioning reference and clamping scheme: (1) Strive to unify the benchmarks of design, process, and programming calculations. (2) Minimize the number of clamping operations and, as far as possible, machine all the surfaces to be machined after one positioning. (3) Avoid using the manual adjustment scheme. (4) The fixture should be opened smoothly, and its positioning and clamping mechanism can not affect the cutting in the machining (such as collision). When such a situation is encountered, it can be clamped by means of a vise or a bottom plate. three. Q: What principles should be followed in the arrangement of processing orders? A: 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 for positioning and clamping. The key point is that the rigidity of the workpiece is not destroyed. The order should generally be based on the following principles: (1) The processing of the previous process cannot affect the positioning and clamping of the next process, and the intermediate machining process must be considered in the middle. (2) First, the inner cavity is added, and then the outer shape processing step is performed. (3) It is best to connect the same positioning, clamping method or the same tool to reduce the number of repeated positioning, the number of tool changes and the number of moving plates. (4) In the multiple processes carried out in the same installation, the process of reducing the rigidity of the workpiece should be arranged first. four. Q: How to determine the correct point of the knife? What is the relationship between the workpiece coordinate system and the programmed coordinate system? 1. The tool point can be set on the part to be machined, but note that the tool point must be the reference position or the finished part. Sometimes the tool point is destroyed after the first process, which will lead to the second process and After the tool setting point is not searchable, it is necessary to set a relative tool setting position in the relative fixed size relationship with the positioning reference in the first process, so that the original position can be retrieved according to the relative positional relationship between them. The point of the knife. This relative pair of tool positions is usually located on the machine table or fixture. The selection principle is as follows: 1) It is easy to find. 2) Easy to program. 3) The tooling error is small. 4) Easy inspection during processing. 2. The origin position of the workpiece coordinate system is set by the operator. After the workpiece is clamped, it is determined by the tool setting. It reflects the positional relationship between the workpiece and the machine zero. Once the workpiece coordinate system is fixed, it is generally not changed. Both the workpiece coordinate system and the programmed coordinate system must be uniform, that is, the workpiece coordinate system and the programmed coordinate system are identical during machining. Fives. Q: How to monitor and adjust during the machining process? After the workpiece is aligned and the program is commissioned, it can enter the automatic machining stage. During the automatic machining process, the operator monitors the cutting process to prevent workpiece quality problems and other accidents caused by abnormal cutting. The following aspects are mainly considered for monitoring the cutting process: 1. Process monitoring: Roughing is primarily concerned with the rapid removal of excess allowance on the surface of the workpiece. During the automatic machining of the machine tool, the tool automatically cuts according to the predetermined cutting path according to the set cutting amount. At this time, the operator should pay attention to observe the change of the cutting load during the automatic machining process through the cutting load table, adjust the cutting amount according to the bearing capacity of the tool, and maximize the efficiency of the machine tool. 2. Monitoring of cutting sound during cutting: In the automatic cutting process, when the cutting is started, the sound of the cutting workpiece is stable, continuous and brisk, and the movement of the machine is stable. As the cutting process progresses, the cutting process becomes unstable when there are hard spots on the workpiece or tool wear or tool feeding. The unstable performance is that the cutting sound changes, and the tool and the workpiece will collide with each other. Sound, the machine will vibrate. At this time, the cutting amount and cutting conditions should be adjusted in time. When the adjustment effect is not obvious, the machine should be suspended and the condition of the tool and workpiece should be checked. 3. Finishing process monitoring: Finishing, mainly to ensure the processing size and surface quality of the workpiece, high cutting speed, large feed. At this time, attention should be paid to the influence of the built-up edge on the machined surface. For the cavity machining, it should also pay attention to the machining of the cut and the knife at the corner. For the solution of the above problems, one should pay attention to adjust the spray position of the cutting fluid, so that the machining surface is always in the optimal cooling condition; the second is to observe the quality of the machined surface of the workpiece, by adjusting the amount of cutting, avoid as much as possible Changes in quality. If the adjustment still has no obvious effect, it should be reasonable to stop the inspection of the original program. It is important to note that when you pause or stop the inspection, pay attention to the position of the tool. If the tool stops during the cutting process, a sudden spindle stop will cause a tool mark on the surface of the workpiece. Generally, stop the machine when the tool leaves the cutting state. 4. Tool monitoring: The quality of the tool determines the quality of the workpiece. In the automatic machining and cutting process, it is necessary to judge the normal wear condition and abnormal damage of the tool through sound monitoring, cutting time control, pause check during cutting, and surface analysis of the workpiece. According to the processing requirements, the tools should be processed in time to prevent the processing quality problems caused by the tools not being processed in time. six. Q: How do I choose the route? The path of the tool is the trajectory and direction of the tool relative to the workpiece during the index control process. A reasonable choice of the machining route is very important because it is related to the machining accuracy and surface quality of the part. The following points are mainly considered in determining the route: 1) Guarantee the machining accuracy requirements of the parts. 2) Convenient numerical calculation and reduce programming workload. 3) Seek the shortest machining route and reduce the emptying time to improve the processing efficiency. 4) Minimize the number of blocks. 5) To ensure the roughness of the contour surface of the workpiece after processing, the final contour should be arranged for the last pass to be continuously processed. 6) The path of the tool's advance and retraction (cut-in and cut-out) should also be carefully considered to minimize the stopping of the knife at the contour (the elastic change of the cutting force caused by the sudden change of the cutting force) and leave the tool marks, and also avoid the vertical deviation on the contour surface. Scratch the workpiece with a knife.
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