CNC Machining: CNC Machining Programming Tips

 

 

 

First of all, there may be many people who don’t know "What is CNC machining programming?" I will give a brief science here. CNC machining programming refers to the automatic generation of CNC machining with the support of the computer and the corresponding computer software system. The process of the program. It is not automatically generated. It requires our CNC machining programmers to analyze the geometry, processing technology, cutting parameters and auxiliary information of the machining target based on experience, and then use the programming software to automatically perform the numerical value Accounting, tool center motion trajectory accounting, post-processing, generate a part processing program sheet, and imitate the processing process. This process is called numerical control programming. The process of inputting the written numerical control program into the CNC numerical control machine tool for processing , Called CNC machining.

 

 

So how can we learn CNC machining programming well? Based on my many years of experience, I would like to share with us some tips on CNC machining programming.

 

 

 

 

1. How to divide the CNC machining process?

 

 

 

The division of numerical control processing procedures can generally be carried out according to the following methods:

 

Machining Center

 

1. The tool centralized ordering method is to divide the processes according to the tools used, and use the same tool to machine all the parts that can be completed on the part. Use the second knife and the third knife to complete other parts. This can reduce the number of tool changes, reduce idle time, and reduce unnecessary positioning errors.

 

2. Using CNC machining parts ordering method For parts with a lot of machining content, the machining part can be divided into several parts according to its structural characteristics, such as inner shape, shape, curved surface or plane, etc. Generally, planes and positioning surfaces are processed first, and then holes are processed; simple geometric shapes are processed first, and then complex geometric shapes; the parts with lower precision are processed first, and then the parts with higher CNC machining accuracy requirements.

 

3. Sequential method for roughing and finishing. For parts that are prone to processing deformation, due to the deformation that may occur after roughing, they need to be corrected. Therefore, in general, all the roughing and finishing processes must be separated. In summary, when dividing processes, we must flexibly grasp the structure and manufacturability of the parts, the function of the machine tool, the number of parts CNC machining content, the number of installations and the production organization 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 must strive to be reasonable.

 

 

 

2. What principles should the CNC machining sequence follow?

 

 

The division of numerical control processing procedures can generally be carried out according to the following methods:

 

1. The tool centralized ordering method is to divide the processes according to the tools used, and use the same tool to process all the parts that can be completed on the part. Use the second knife and the third knife to complete other parts they can complete. This can reduce the number of tool changes, reduce idle time, and reduce unnecessary positioning errors.

 

2. Ordering method by CNC machining parts For CNC machining complex parts, the machining part can be divided into several parts according to its structural characteristics, such as inner shape, shape, curved surface or plane. Generally, the plane and positioning surface are processed first, and then the hole is processed; the simple geometric shape is processed first, and then the complex geometric shape is processed; the parts with lower precision are processed first, and then the parts with higher precision requirements are processed.

 

3. Sequential method for roughing and finishing. For parts that are prone to processing deformation, due to the deformation that may occur after roughing, they need to be corrected. Therefore, in general, all the roughing and finishing processes must be separated. To sum up, when dividing processes, we must flexibly grasp the structure and manufacturability of the parts, the function of the machine tool, the number of parts to be processed by CNC, the number of installations and the production organization 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 must strive to be reasonable.

 

 

 

3. Which aspects should be paid attention to in the clamping method of CNC machining workpiece? 

 

The following four points should be paid attention to when determining the positioning reference and clamping plan:

 

1. Strive to unify the design, craftsmanship, and programming calculation benchmarks.

 

2. Minimize the number of clamping times, as far as possible to be able to CNC process all the surfaces to be processed after one positioning.

 

3. Avoid using manual adjustment schemes.

 

4. The fixture should be opened smoothly, and its positioning and clamping mechanism should not affect the cutting during processing (such as collision). In such a situation, use a vise or add a base plate to draw a screw.

 

 

 

 

4. How to determine the tool setting point is more reasonable?

 

 

1. The tool setting point can be set on the part to be processed, but note that the tool setting point must be a reference position or a part that has been finished. Sometimes the tool setting point is destroyed after the first process, which will cause the it is impossible to find the tool setting points for the second process and the subsequent process. Therefore, when setting the tool in the first process, pay attention to setting up a relative tool setting position where there is a relatively fixed dimensional relationship with the positioning datum. This can be based on the relative position between them. The relationship is restored to the original point of the knife. This relative tool setting position is usually set on the machine tool table or fixture.

 

The selection principles are as follows:

 

 

1) It is easy to align. 2) Convenient programming. 3) The tool setting error is small. 4) It is convenient to check during processing.

 

2. The origin position of the CNC machining workpiece coordinate system is set by the operator. It is determined by tool setting after the workpiece is clamped. It reflects the distance position relationship between the workpiece and the CNC machining machine zero point. 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, the workpiece coordinate system and the programming coordinate system are consistent during processing.

 

 

 

 

 

 

 

5. How to choose CNC machining path?

 

 

The path of the tool is the path and direction of the tool relative to the workpiece in the index control process. The reasonable choice of the processing route is very important, because it is closely related to the processing accuracy and surface quality of the parts. When determining the path of the knife, the following points are mainly considered:

1. Ensure the CNC machining accuracy requirements of the parts.

2. Convenient for numerical calculation and reduce programming workload.

3. Seek the shortest CNC machining route, reduce the time of empty tool to improve machining efficiency.

4. Minimize the number of program segments.

5. To ensure the roughness requirements of the workpiece contour surface after processing, the final contour should be processed continuously in the last pass.

6. The advance and retreat (cut-in and cut-out) route of the tool should also be carefully considered to minimize the tool stop at the contour (a sudden change in cutting force causes elastic deformation) and leave tool marks, and avoid vertical downward on the contour surface. Knife and scratch the workpiece.

 

 

 

 

6. How to monitor and adjust during CNC machining?

 

 

 

After the workpiece is aligned and the program is debugged, it can enter the automatic processing stage. During the automatic machining process, the operator should monitor the cutting process to prevent abnormal cutting from causing workpiece quality problems and other accidents. The following aspects are mainly considered for monitoring the cutting process:

 

 

1. CNC machining process monitoring The main consideration for rough machining is the rapid removal of excess margin on the surface of the workpiece. In the automatic machining process of the machine tool, according to the set cutting amount, the tool automatically cuts according to the predetermined cutting path. At this time, the operator should pay attention to observe the cutting load changes in the automatic machining process through the cutting load table, and adjust the cutting amount according to the bearing capacity of the tool to maximize the efficiency of the machine tool.

 

2. Monitoring of cutting sound during cutting In the automatic cutting process, generally when starting cutting, the sound of the tool cutting the workpiece is stable, continuous, and brisk. At this time, the movement of the machine tool is stable. As the cutting process progresses, when there are hard spots on the workpiece, tool wear, or tool clamping, the cutting process becomes unstable. The unstable performance is that the cutting sound changes and the tool and the workpiece collide with each other. Sound, the machine tool 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 suspended to check the condition of the tool and workpiece.

 

3. Finishing process monitoring and finishing, mainly to ensure the CNC machining size and surface quality of the workpiece, the cutting speed is high, and the feed rate is large. At this time, attention should be paid to the impact of built-up edge on the machined surface. For cavity machining, attention should also be paid to over-cutting and cutting at corners. To solve the above problems, one is to pay attention to adjusting the spray position of the cutting fluid so that the machined surface is always in the best cooling condition; the second is to pay attention to the quality of the machined surface of the workpiece, and adjust the cutting amount to avoid as much as possible. Changes in quality. If the adjustment still has no obvious effect, the machine should be shut down to check whether the original program is reasonable. Special attention should be paid to the position of the tool when the inspection is suspended or stopped. If the tool stops during the cutting process, a sudden stop of the spindle will cause tool marks on the surface of the workpiece. Generally, consider stopping the tool when it leaves the cutting state.

 

4. Tool monitoring The quality of the tool largely determines the CNC machining quality of the workpiece. In the automatic machining and cutting process, it is necessary to judge the normal wear condition and abnormal damage condition of the tool through methods such as sound monitoring, cutting time control, pause inspection during cutting, and workpiece surface analysis. 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.

 

 

 

 

7. How to choose CNC machining tools reasonably?

 

 

1. When plane milling, you should choose non-reground hard alloy end mills or end mills. In general milling, it is best to use the second pass to process. The first pass is best to use the end mill for rough milling, and continue to pass along the surface of the workpiece. The width of each pass is recommended to be 60%-75% of the tool diameter.

2. End mills and end mills with carbide inserts are mainly used for processing bosses, grooves and box mouth surfaces.

3. Ball knives and round knives (also known as round nose knives) are often used to process curved surfaces and variable bevel contours. The ball knife is mostly used for semi-finishing and finishing. Round knives inlaid with cemented carbide tools are mostly used for roughing.

 

 

 

8. What is the function of the processing procedure sheet?

 

1. The processing procedure sheet is one of the contents of the numerical control processing technology design, and it is also a procedure that needs to be followed and executed by the operator. It is a specific description of the processing procedure. The purpose is to let the operator clarify the content of the procedure, the clamping and positioning method, and each processing The tool selected by the program should be paid attention to.

2. In the processing program list, it should include: drawing and programming file name, workpiece name, clamping sketch, program name, tool used in each program, maximum cutting depth, processing nature (such as roughing or finishing) , Theoretical processing time, etc.

 

 

 

9.What preparations should be made before CNC machining programming. After determining the CNC machining process, you must understand before programming:

 

1. Workpiece clamping method;

2. The size of the workpiece blank ---- in order to determine the scope of processing or whether multiple clamping is required;
3. The material of the workpiece-in order to choose which tool to use for processing;

4. What are the stocked tools? Avoid modifying the program during CNC machining because there is no such tool. If you must use this tool, you can prepare it in advance.

 

 

 

 

10. What are the principles of programming safety height setting?

 

 

The principle of setting the safety height: generally higher than the highest surface of the island. Or set the programmed zero point on the highest surface, so as to avoid the danger of hitting the knife to the greatest extent.

 

 

 

 

11. Why does the tool path need post-processing?

 

 

Because the address code and CNC machining program format recognized by different machine tools are different, the correct post-processing format must be selected for the machine tool used to ensure that the compiled program can run.

 

 

 

 

12. What is the transmission method of DNC communication program can be divided into CNC and DNC.

 

 

CNC means that the program is transmitted to the memory of the machine tool through media media (such as floppy disks, tape readers, communication lines, etc.) for storage. Call up the program in the memory for processing. Because the memory capacity is limited by the size, when the program is large, the DNC method can be used for processing. Because the machine tool directly reads the program from the control computer during DNC processing (that is, it is done while sending), it is not affected by the memory capacity Limited by size.