To share 12 experience of CNC machining

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 determined that CNC machining (whether processing or programming) reaches a certain level, It must take a long time. 

Q: How to divide the processing operations? 
A: The division of CNC machining processes can generally be performed according to the following methods: 
(1) The method of tool centralizing and dividing is to divide the process according to the used tool and use the same tool to finish all the parts that can be completed on the part. Use the second knife and the third to complete other parts that they can complete. This reduces the number of tool changes, compresses the idle time, and reduces unnecessary positioning errors.

(2) Partially-sequential processing method for parts with many processing contents, the processing part can be divided into several parts according to its structural characteristics, such as internal shape, shape, curved surface, or plane. The general processing plane, positioning surface, after processing hole; first processing a simple geometry, and then processing a complex geometry; the first processing of the lower accuracy of the site, and then processing the higher precision of the site. 

(3) The coarse and fine processing division method is required for the deformation of parts that are prone to be deformed because of the deformation that may occur after rough machining. Therefore, in general, all rough and fine machining operations must be separated from each other. . 
To sum up, in the process of division, it must be based on the structure and craftsmanship of the part, the function of the machine tool, the number of components in the numerical control process, the number of installations, and the organizational structure of the unit. It is also recommended that the principle of concentration of processes or the principle of dispersion of processes be adopted. It should be determined according to actual conditions, but it must be reasonable.

Q: What principles should be followed in the arrangement of processing sequences? 
Answer: The arrangement of the processing sequence should be based on the structure of the part and the condition of the blank, as well as the need for positioning and clamping. The 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 can not affect the positioning and clamping of the next process, and the general machining process in the middle should be considered comprehensively. 
(2) First, the internal cavity adding step is performed, and then the outline processing step is performed. 
(3) The same process of positioning, clamping, or machining the same tool is best performed to reduce the number of repeated positioning, the number of tool changes, and the number of moving platens. 
(4) In the multiple processes performed in the same installation, the process of rigidly destroying the workpiece should be arranged first. 

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 datum and clamping scheme: 
(1) Strive to unify design, process, and programming calculations. 
(2) Minimize the number of fixtures, and make it possible to machine all surfaces to be machined after one positioning. 
(3) Avoid employing manual adjustment programs. 
(4) The fixture should be open, and its positioning and clamping mechanism can not affect the cutting tool (such as collision) during machining. When encountering such a situation, it can be clamped with a vise or a bottom-mounted extraction screw.

Q: How to determine the reasonable tool point? What is the relationship between the workpiece coordinate system and the programming coordinate system? 
1. The tool-cutting point can be set on the part to be machined, but note that the tool-cutting point must be the reference position or the part that has been machined, and sometimes the tool-point is destroyed after the first operation, which will lead to the second process and There is no way to find the following tool point, so when the tool is set in the first process, it is necessary to set up a relative tool position in a place with a relatively fixed dimensional relationship with the positioning reference, so that the original position can be retrieved based on the relative position relationship between them. Tool point. This relative counter knife position is usually set on the machine table or fixture. The selection principle is as follows: 
1) Easy to find. 
2) Easy programming. 
3) The tool setting error is small. 
4) Easy inspection 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 the tool, which reflects the distance and position relationship between the workpiece and the machine zero point. Once the workpiece coordinate system is fixed, it is generally not changed. Both the workpiece coordinate system and the programming coordinate system must be unified. That is, the workpiece coordinate system and the programming coordinate system are the same when machining.

Q: How to choose a route? 
The cutting path is the trajectory and direction of the tool relative to the workpiece during the index control process. The rational choice of processing route is very important because it is closely related to the precision and surface quality of the parts. The following points are mainly considered in determining the route of the knife: 
1) Guaranteed the precision of the part's machining. 
2) Convenient numerical calculations reduce programming workload. 
3) Seek the shortest processing route and reduce the empty knife time to improve processing efficiency. 
4) Minimize the number of blocks. 
5) To ensure the roughness of the workpiece contour surface after processing, the final contour should be arranged for the last pass to be processed continuously. 
6) The tool's advance/retract knife (cut-in and cut-out) routes should also be carefully considered to minimize the need to stop the knife at the contour (abrupt changes in cutting force cause elastic deformation) to leave a tool mark, but also to avoid vertical down the contour surface Knife and scratch the workpiece.

Q: How to monitor and adjust during processing? 
After the workpiece is corrected and the program is debugged, it can enter the automatic processing stage. In the automatic processing, the operator must monitor the cutting process to prevent the occurrence of abnormal cutting quality problems and other accidents. 
The monitoring of the cutting process mainly considers the following aspects: 
1. Process monitoring The primary concern for rough machining is the rapid removal of excess headroom on the workpiece surface. In the automatic machining process of the machine tool, according to the set cutting amount, the tool is automatically cut according to a predetermined cutting trajectory. At this time, the operator should pay attention to the change of the cutting load in the automatic machining process through the cutting load table, adjust the cutting amount according to the condition of the bearing capacity of the tool, and exert the maximum efficiency of the machine tool. 
2. Cutting sound monitoring during cutting In the automatic cutting process, when the cutting process starts, the sound of the cutting tool is stable, continuous and light, and the movement of the machine tool is stable. With the progress of the cutting process, when the workpiece has a hard point or tool wear or tool clips and other reasons, the cutting process is unstable, unstable performance is the change of the cutting sound, there will be mutual impact between the tool and the workpiece 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 tool should be paused to check the status of the cutting tools and workpieces. 
3. Finishing process monitoring and finishing, mainly to ensure the workpiece size and machining surface quality, high cutting speed, a large amount of feed. At this time, attention should be paid to the influence of the built-up edge on the machining surface. For the cavity processing, attention should also be paid to the cutting and turning of the corners. To solve the above problems, one should pay attention to adjusting the spray position of the cutting fluid so that the machining surface is always at the best cooling condition; the second is to observe the quality of the processed surface of the workpiece, and to avoid as much as possible by adjusting the cutting amount. Changes in quality. If the adjustment still has no significant effect, the original procedures for the shutdown inspection should be compiled to make it reasonable. 
Special attention should be paid to the position of the tool when pausing or stopping the inspection. If the tool stops during the cutting process, a sudden spindle stop will cause a tool mark on the workpiece surface. Should generally consider stopping when the tool leaves the cutting state. 

4. Tool monitoring The quality of the tool largely determines the quality of the workpiece. In the automatic machining and cutting process, the normal wear condition and abnormal damage condition of the tool are judged through sound monitoring, cutting time control, pause inspection during cutting process, and workpiece surface analysis. According to the processing requirements, the tool should be processed in time to prevent the processing quality problem caused by the tool not being processed in time.

Q: How to choose a reasonable tool? There are several major factors in the amount of cutting? There are several materials for the tool? How to determine the tool speed, cutting speed, cutting width? 
1. Non-reground carbide end mills or end mills should be used for face milling. In general milling, try to use the second pass tooling. The first pass is preferably performed by rough milling with an end mill, and the tool is continuously moved along the surface of the workpiece. The width of each pass is recommended to 60% - 75% of the tool diameter. 
2. End mills and end mills with carbide inserts are mainly used for machining bosses, grooves and box faces. 
3. Ball knives and round knives (also known as round nose knives) are commonly used to machine curved surfaces and change the shape of the bevel outline. The ball knife is mostly used for semi-finishing and finishing. Circular knifes with carbide inserts are used for roughing. 

Q: What is the role of the processing program and what should be included in the processing program? 
A: (1) The processing program is one of the contents of the NC machining process design. It is also the procedure that the operator needs to observe and execute. It is a specific description of the machining program. The purpose is to allow the operator to specify the content, installation and positioning of the program. , The tool selected for each machining program should pay attention to the problem. 
(2) In the processing program sheet, it shall include: drawing and programming file name, workpiece name, clamping sketch, program name, the tool used for each program, the maximum depth of cutting, and processing properties (such as roughing or finishing) ), theoretical processing time, etc.

Q: What are the preparations for NC programming? 
Answer: After confirming the processing technology, it is necessary to understand before programming: 1. The workpiece clamping method; 2. The size of the workpiece blank - in order to determine the scope of processing or whether it needs multiple clamping; 3. The material of the workpiece - --- In order to select which tool to use for machining; 4, Which stock of the knife - to avoid the need to modify the program when there is no such tool, if you must use this tool, you can prepare in advance. 

Q: What are the principles for setting the safe altitude in programming? 
A: The principle of safe altitude setting is generally higher than the highest surface of the island. Or set the programmed zero point to the highest surface, which also minimizes the risk of a collision.

Question: After the tool path is compiled, why do we need to post-process it? 
A: Because different machine tools can recognize the address code and the NC program format, it is necessary to select the correct post-processing format for the machine tool used to ensure that the compiled program can run.


Q: What is DNC communication?
A: The program delivery method can be divided into two types: CNC and DNC. CNC means that the program is stored in the memory of the machine tool through the media (such as floppy disk, tape reader, communication cable, etc.), and the program is retrieved from the memory during processing. To process. Since the capacity of the memory is limited by the size, when the program is large, the DNC method can be used for processing. Since the machine tool reads the program directly from the control computer during DNC processing (that is, it is sent side by side), it is not subject to the capacity of the memory. Limited by size.

There are three major factors in the amount of cutting: depth of cut, spindle speed, and feed rate.

The general principle of the choice of cutting amount is: Less cutting, faster feeding (ie, smaller depth of cut, faster feed rate) 
According to the material classification, the tool is generally divided into ordinary hard white steel knife (high-speed steel material), coating tools (such as titanium, etc.), alloy tools (such as tungsten steel, boron nitride tools, etc.).