An Actual Summary of 12 Pieces of Experience in CNC Machining

Keywords: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 from engaging in CNC machining (whether machining or programming) to reaching a certain level A relatively long period of time must be passed. This manual is a summary of some experience about CNC machining technology, procedures, selection of commonly used tool parameters, monitoring during processing, etc., summarized by engineers in the long-term actual production process. For reference.

 

1. Question: How to divide the CNC machining process?

Answer: The division of CNC machining processes 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 machine 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) With CNC machining parts ordering method, for parts with a lot of processing content, the processing part can be divided into several parts according to its structural characteristics, such as internal 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) For parts that are prone to processing deformation by the rough and CNC machining sorting method, due to the deformation that may occur after rough machining, the shape needs to be corrected. Therefore, in general, all the processes that need to be rough and CNC machining must be separated. .

 

In summary, when dividing the process, 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. Question: What principles should be followed in the arrangement of the processing sequence?

Answer: 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 needs of positioning and clamping. The important point is that the rigidity of the workpiece is not destroyed. The order should generally be carried out according to the following principles:

 

(1) The processing of the previous process cannot affect the positioning and clamping of the next process, and the general machine tool processing processes should also be considered comprehensively.

 

(2) Carry out the inner cavity adding process first, and then the outer shape processing process.

 

(3) It is best to connect the processes of machining with the same positioning, clamping method or the same tool to reduce the number of repeated positioning, tool changes and the number of times of moving the platen.

 

(4) For the multiple procedures carried out in the same installation, the procedure should first be arranged with less rigid damage to the workpiece.

3. Question: Which aspects should be paid attention to when determining the clamping method of the workpiece?

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

 

(1) Strive to unify the design, process, and programming calculation benchmarks.

 

(2) Minimize the number of clamping times, as far as possible to be able to 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 knife during processing (such as collision). In such a situation, use a vise or add a bottom plate to draw a screw.

 

4. Question: How to determine the tool setting point is more reasonable? What is the relationship between the workpiece coordinate system and the programming coordinate system?

1. The tool setting point can be set on the part to be processed, but note that the tool setting point must be the reference position or the position that has been CNC Machined. Sometimes the tool setting point is destroyed after the first process, which will cause the second process and There is no way to find the subsequent tool setting points. Therefore, in the first process of tool setting, pay attention to setting up a relative tool setting position where there is a relatively fixed size relationship with the positioning datum, so that the original position can be retrieved according to the relative position relationship between them. Knife point. This relative tool setting position is usually set on the machine tool table or fixture. The selection principles are as follows:

 

1) Easy to align.

 

2) Easy to program.

 

3) The tool setting error is small.

 

4) It is convenient to check during processing.

 

2. The origin position of the 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 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. Question: How to choose the knife route?

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 machining accuracy requirements of the parts.

 

2) Convenient numerical calculation and reduce programming workload.

 

3) Seek the shortest processing route, reduce the empty tool time to improve processing efficiency.

 

4) Try to reduce the number of blocks.

 

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. Question: How to monitor and adjust during processing?

After the workpiece is aligned and the program is debugged, it can enter the automatic processing stage. In 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. The main consideration of the machining process monitoring rough machining is the rapid removal of the 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 cutting is started, 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 will 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 is mainly to ensure the processing 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 processing 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.

 

Seven. Question: How to choose processing tools reasonably? What are the major factors of cutting amount? How many kinds of materials are available? How to determine the speed, cutting speed, and cutting width of the tool?

 

1. When plane milling, you should choose non-reground carbide 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. Question: What is the function of the processing procedure sheet? What should be included in the processing procedure sheet?

Answer: (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, clamping and positioning methods , The cutting tools selected by each processing 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. Q: What preparations should be made before CNC programming?

Answer: After determining the processing technology, before programming, you must understand: 1. The workpiece clamping method; 2. The size of the workpiece blank-in order to determine the processing range 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 tools in stock-avoid modifying the program during processing because there is no such tool. If you must use this tool, you can prepare in advance.

 

10. Q: What are the principles for setting the safety height in programming?

Answer: 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. Question: After the tool path is compiled, why is it necessary to post-process?

Answer: Because the address code and NC program format that can be recognized by different machine tools are different, it is necessary to select the correct post-processing format for the machine tool used to ensure that the compiled program can run.

 

12. Q: What is DNC communication?

Answer: The method of program delivery can be divided into CNC and DNC. CNC means that the program is delivered to the memory of the machine tool through media media (such as floppy disk, tape reader, communication line, etc.) for storage, and the program is called from the memory during processing. For processing. Because the memory capacity is limited by the size, when the program is large, the DNC method can be used for processing. Since 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.

 

(2) There are three main elements of cutting parameters: depth of cut, spindle speed and feed speed. The overall principle of the selection of cutting parameters is: less cutting, fast feed (that is, the cutting depth is small, and the feed speed is fast).

 

(3) According to the classification of materials, tools are generally divided into ordinary hard white steel tools (materials are high-speed steel), coated tools (such as titanium-plated, etc.), alloy tools (such as tungsten steel, boron nitride tools, etc.).

 

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