12 CNC machining experience summary

CNC machining, also known as numerical control machining, refers to machining performed with numerical control machining tools. Because numerical control machining is programmed and then controlled by a computer, CNC machining has the advantages of stable machining quality, high machining accuracy, high repetition accuracy, ability to process complex surfaces, and high machining efficiency. In the actual machining process, human factors and operating experience will largely affect the final machining quality. Next, let's take a look at the twelve valuable experiences summarized by an old driver with ten years of CNC machining experience...

1. How to divide the CNC machining process?

The division of CNC machining processes can generally be carried out in the following ways:

1. The tool concentration sequencing method is to divide the process according to the tools used, and use the same tool to CNC all the parts that can be completed on the parts. Then use the second and third tools to complete the other parts that they can complete. This can reduce the number of tool changes, compress idle time, and reduce unnecessary positioning errors.

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

3. For parts that are prone to CNC processing deformation, they need to be corrected due to the deformation that may occur after rough processing. Therefore, generally speaking, all rough and fine processing must be separated. In summary, when dividing the process, it is necessary to flexibly grasp it according to the structure and processability of the parts, the function of the machine tool, the amount of CNC processing content of the parts, 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. It should be determined according to the actual situation, but it must be reasonable. If you want to learn UG processing programming knowledge, group 565120797 can help you.

2. What principles should be followed in the arrangement of CNC processing sequence?

The arrangement of the processing sequence should be based on the structure and blank condition of the parts, as well as the need for positioning and clamping. The key point is that the rigidity of the workpiece is not destroyed. The sequence should generally be carried out according to the following principles:

1. The CNC processing of the previous process cannot affect the positioning and clamping of the next process, and the general machine tool processing process in the middle should also be considered comprehensively.

2. First carry out the inner shape and inner cavity processing process, and then the outer shape processing process.

3. The processes of CNC processing with the same positioning, clamping method or the same tool are best connected to reduce the number of repeated positioning, tool changes and plate movement.

4. For multiple processes carried out in the same installation, the process that causes less damage to the rigidity of the workpiece should be arranged first.

3. What aspects should be paid attention to in determining the workpiece clamping method?

When determining the positioning reference and clamping scheme, the following three points should be paid attention to:

1. Strive to unify the reference of design, process, and programming calculation.

2. Minimize the number of clamping times, and try to CNC process all the surfaces to be processed after one positioning.

3. Avoid using manual adjustment schemes that occupy the machine.

4. The fixture should be open, and its positioning and clamping mechanism should not affect the tool movement during CNC processing (such as collision). When encountering such a situation, it can be clamped by using a vise or adding a bottom plate to extract screws.

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

1. The tool point can be set on the part to be processed, but note that the tool point must be the reference position or the part that has been finely processed. Sometimes the tool point is destroyed by CNC processing after the first process, which will make it impossible to find the tool point in the second process and later. Therefore, when setting the tool in the first process, pay attention to setting a relative tool position in a place with a relatively fixed size relationship with the positioning reference, so that the original tool point can be found according to the relative position relationship between them. This relative tool position is usually set on the machine tool workbench or fixture. The selection principles are as follows:

1) Easy to align.

2) Convenient programming.

3) Small tool error.

4) Convenient and traceable inspection during processing.

2. The origin 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 and 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, during processing, the workpiece coordinate system and the programming coordinate system are consistent.

5. How to choose the tool path?

The tool path refers to the movement trajectory and direction of the tool relative to the workpiece during CNC machining. The reasonable selection of the machining route is very important because it is closely related to the CNC machining accuracy and surface quality of the part. When determining the tool path, the following points are mainly considered:

1. Ensure the machining accuracy requirements of the part.

2. Facilitate numerical calculation and reduce programming workload.

3. Seek the shortest CNC machining route and reduce the idle tool time to improve CNC machining efficiency.

4. Minimize the number of program segments.

5. Ensure the roughness requirements of the workpiece contour surface after CNC machining. The final contour should be arranged for the last tool to be processed continuously.

6. The tool's entry and exit (cutting in and out) route should also be carefully considered to minimize the tool marks left by stopping at the contour (elastic deformation caused by sudden changes in cutting force), and to avoid scratching the workpiece by cutting vertically on the contour surface.

6. How to monitor and adjust during CNC processing?

After the workpiece is aligned and the program is debugged, it can enter the automatic processing stage. During the automatic processing, the operator must 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. Process monitoring Rough processing mainly considers the rapid removal of excess excess on the surface of the workpiece. During the automatic processing of the machine tool, according to the set cutting amount, the tool automatically cuts according to the predetermined cutting trajectory. At this time, the operator should pay attention to observing the changes in cutting load during automatic processing through the cutting load table, and adjust the cutting amount according to the tool's bearing capacity to maximize the efficiency of the machine tool.

2. Monitoring of cutting sound during cutting process During the automatic cutting process, when cutting begins, the sound of the tool cutting the workpiece is stable, continuous and brisk, and the movement of the machine tool is stable. As the cutting process proceeds, when there are hard spots on the workpiece or the tool is worn or the tool is clamped, the cutting process becomes unstable. The instability is manifested by changes in the cutting sound, mutual collision between the tool and the workpiece, and vibration of the machine tool. 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 stopped to check the condition of the tool and the workpiece.

3. Monitoring of finishing process Finishing is mainly to ensure the processing size and surface quality of the workpiece, with high cutting speed and large feed rate. At this time, attention should be paid to the influence of built-up edge on the processing surface. For cavity processing, attention should also be paid to overcutting and cutting at the corners. To solve the above problems, first, pay attention to adjusting the spray position of the cutting fluid to keep the processing surface in cooling conditions at all times; second, pay attention to observing the quality of the processed surface of the workpiece, and avoid quality changes as much as possible by adjusting the cutting amount. If the adjustment still has no obvious effect, the machine should be stopped to check whether the original program is reasonable. It is particularly important to pay attention to the position of the tool during the pause inspection or shutdown inspection. If the tool stops during the cutting process and the spindle stops suddenly, tool marks will be produced on the surface of the workpiece. Generally, the shutdown should be considered when the tool leaves the cutting state.

4. Tool monitoring The quality of the tool determines the processing quality of the workpiece to a large extent. In the process of automatic machining and cutting, the normal wear and abnormal damage of the tool should be judged by sound monitoring, cutting time control, pause inspection during cutting, workpiece surface analysis and other methods. According to the processing requirements, the tool should be handled in time to prevent the occurrence of processing quality problems caused by the failure to handle the tool in time.

VII. How to reasonably choose the processing tool? What are the major factors of cutting consumption? How many materials are there for tools? How to determine the tool speed, cutting speed, and cutting width?

1. When plane milling, you should use a carbide end mill or end mill that does not need to be reground. In general milling, try to use secondary tooling. The first tooling is best to use an end mill for rough milling, and continuous tooling along the surface of the workpiece. The width of each tooling is recommended to be 60%-75% of the tool diameter.

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

3. Ball cutters and round cutters (also known as round nose cutters) are often used to process curved surfaces and variable angle contours. Ball cutters are mostly used for semi-finishing and finishing. Round cutters with carbide inserts are mostly used for roughing.

8. What is the role of the machining program sheet? What should be included in the machining program sheet?

1. The machining program sheet is one of the contents of CNC machining process design. It is also a procedure that operators need to follow and implement. It is a specific description of the machining program. The purpose is to let the operator know the contents of the program, the clamping and positioning methods, and the problems that should be paid attention to when using the tools selected for each machining program.

2. The machining program sheet should include: drawing and programming file names, workpiece names, clamping sketches, program names, tools used for each program, maximum cutting depth, machining properties (such as roughing or finishing), theoretical machining time, etc.

9. What preparations should be made before CNC programming?

After determining the processing technology, before programming, you need to understand:

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 select the tool used for processing;

4. What tools are in stock-to avoid modifying the program due to the lack of this tool during processing. If this tool must be used, it can be prepared in advance.

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

The principle of setting the safety height: generally higher than the highest surface of the island. Or set the programming zero point at the highest surface, which can also minimize the risk of collision.

11. Why do we need to post-process after the tool path is compiled?

Because different machine tools can recognize different address codes and NC program formats, it is necessary to select the correct post-processing format for the machine tool used to ensure that the compiled program can run.

12. What is DNC communication?

The program transmission method can be divided into two types: CNC and DNC. CNC means that the program is transmitted to the memory of the machine tool through media (such as floppy disks, tape readers, communication lines, etc.) and stored. During processing, the program is called out from the memory for processing. Since the capacity of the memory is limited by size, DNC can be used for processing when the program is large. Since the machine tool reads the program directly from the control computer during DNC processing (that is, it is sent while doing), it is not limited by the size of the memory capacity.

1. There are three major factors in cutting amount: cutting depth, spindle speed and feed speed. The overall principle of cutting amount selection is: less cutting, fast feed (that is, small cutting depth and fast feed speed)

2. According to material classification, tools are generally divided into ordinary hard white steel knives (material is high-speed steel), coated tools (such as titanium plating, etc.), and alloy tools (such as tungsten steel, boron nitride tools, etc.).