CNC Knowledge: 10 valuable experiences in CNC machining, come and collect them

CNC machining, also called CNC machining, refers to processing using CNC machining tools. Since CNC machining is controlled by a computer after programming, CNC machining has the advantages of stable processing quality, high processing precision, high repeatability, ability to process complex shapes and high processing efficiency. In the processing process itself, human factors and operating experience will largely affect the final processing quality. Next, let’s take a look at the ten valuable experiences summarized by a veteran driver with ten years of CNC machining experience…

1. How to divide CNC machining processes?

The division of CNC machining processes can generally be achieved by the following methods:

1. The centralized tool sorting method is to divide the process according to the tools used, and use the same tool to CNC machine all the parts that can be completed. Use the second and third knives to finish the other pieces they can finish. This can reduce the number of tool changes, compress downtime and reduce unnecessary positioning errors.

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

3. Use coarse and fine CNC machining sequencing method. For parts prone to deformation by CNC machining, they must be calibrated due to the deformation that can occur after rough machining. Therefore, generally speaking, all rough and fine machining should be carried out. done in separate process. In summary, when dividing the process, we need to consider the structure and craftsmanship of the part, the function of the machine tool, the quantity of CNC machining of the part, the number of installations and the status organization of the unit’s production. It is also recommended to adopt the principle of process concentration or decentralization, which should be determined according to the actual situation, but should be reasonable.

2. What principles should be followed when organizing the CNC machining sequence?

The arrangement of the processing sequence should be considered based on 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 part is not destroyed. The sequence should generally be carried out according to the following principles:

1. The CNC machining of the previous process cannot affect the positioning and clamping of the next process. Careful consideration should also be given to the general processing processes of middle-interspersed machine tools.

2. Carry out the inner shape and cavity processing first, and then the outer shape processing.

3. It is best to carry out CNC machining processes with the same positioning, clamping method or tool successively to reduce the number of repeated positioning, tool changes and table movements.

4. For multiple processes carried out in the same facility, the process which will cause less rigid damage to the part should be arranged first.

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

The following three points should be considered when determining the positioning reference and tightening plane:

1. Strive to unify references in design calculations, technology and programming.

2. Minimize the number of clamping operations and try to CNC machine all surfaces to be processed in a single positioning.

3. Avoid using machine-occupied manual adjustment solutions.

4. The collet should be smooth, and its positioning and clamping mechanism should not affect the movement of the tool during CNC machining (such as collision). When you encounter such a situation, tightening can be done with a vice or by adding screws to the bottom plate. .

4. How to determine the reasonable setting point of the tool? What is the relationship between the part coordinate system and the programming coordinate system?

1. The tool set point can be set on the workpiece, but note that the tool set point must be a reference position or a completed workpiece. Sometimes the tool set point is damaged by CNC machining after the first process. , which will cause the second process and subsequent tool set points not to be found. Therefore, when setting the tool in the first process, pay attention to setting a relative setting position of the tool at a place that has a relatively fixed size relationship with. the positioning data, so that the relative position relationship between them can be determined. Recover the original setting point of the knife. This relative tool setting position is generally located on the table or machine tool fixture. The selection principles are as follows:

1) Easy to find.

2) Programming is convenient.

3) The tool setting error is small.

4) Inspection during processing is convenient and traceable.

2. The original position of the workpiece coordinate system is set by the operator himself. It is determined by the adjustment of the tool once the part is tightened. It reflects the distance and position relationship between the workpiece and the zero point of the machine tool. Once the part coordinate system is fixed, it generally does not change. 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 route of the knife?

Tool path refers to the path and direction of movement of the tool relative to the workpiece during controlled machining. The reasonable selection of processing routes is very important because it is closely related to the precision of CNC machining and the surface quality of parts. When determining the cutting path, the following points are mainly taken into account:

1. Ensure the precision requirements of parts processing.

2. Facilitate numerical calculation and reduce programming workload.

3. Find the shortest CNC machining route and reduce empty tool time to improve CNC machining efficiency.

4. Reduce the number of program segments as much as possible.

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

6. The feed and retraction (cutting and exit) routes of the tool must also be carefully considered in order to minimize the possibility of stopping the tool at the contour (elastic deformation caused by sudden changes in force cutting) and leave knife marks, and also to avoid any vertical downward movement on the contour surface. The knife could scratch the part.

6. How to monitor and adjust during CNC machining?

After the workpiece alignment and program debugging are completed, it can enter the automatic processing stage. During the automatic machining process, the operator should monitor the cutting process to avoid workpiece quality problems and other accidents caused by abnormal cutting.

Monitoring the cutting process mainly takes into account the following aspects:

1. Process monitoring The main consideration during rough machining is the rapid elimination of excess margin on the surface of the workpiece. During automatic machine tool processing, 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 observing the cutting load changes during automatic processing through the cutting load table, and adjust the cutting amount according to the bearing capacity of the tool to maximize the cutting capacity. efficiency of the machine tool.

2. Monitoring cutting sounds during the cutting process. In the automatic cutting process, usually when cutting starts, the sound of the tool cutting the workpiece is stable, continuous and rapid. At this time, the movement of the machine tool is smooth. . As the cutting process progresses, when there are hard spots on the workpiece or the tool is worn or the tool is tight, the cutting process becomes unstable. Instability manifests itself as changes in cutting noise and collisions between tool and workpiece. If the sound is heard, the machine tool is vibrating. At this time, the cutting quantity and cutting conditions should be adjusted in time. When the adjustment effect is not obvious, the machine tool should be stopped and the condition of the tool and workpiece should be checked.

3. Monitor the finishing process. Finishing mainly aims to ensure the processing size and surface quality of the workpiece. The cutting speed is high and the feed amount is large. At this stage, attention should be paid to the impact of the built-up edges on the machined surface. For cavity processing, attention should also be paid to overcutting and tool deformation when processing corners. To solve the above problems, firstly, attention should be paid to adjusting the spray position of the cutting fluid to keep the processed surface in cooling conditions at all times; , and adjust the cutting quantity to avoid quality changes as much as possible. If the adjustment still has no obvious effect, the machine should be stopped to check whether the original program is compiled reasonably. Particular attention should be paid to the tool position during paused inspection or stationary inspection. If the tool stops during the cutting process, the sudden stop of the spindle will cause tool marks on the workpiece surface. Generally, stopping should be considered when the tool leaves the cutting state.

4. Tool monitoring The quality of the tool largely determines the quality of the workpiece processing. During the automatic machining and cutting process, normal wear and abnormal damage of the tool should be determined by sound monitoring, cutting time control, pause inspection during the cutting process and analysis of the surface of the room. Tools should be processed timely according to processing requirements to avoid processing quality problems caused by tools not processed in time.

7. How to reasonably choose processing tools? What are the main factors for quantity reduction? How many materials are there for knives? How to determine the rotation speed, cutting speed and cutting width of the tool?

1. End mills or carbide end mills without sharpening should be used for surface milling. In general milling, try to use two passes for processing. It is best to use an end mill for rough milling on the first pass and continue to pass along the surface of the workpiece. It is recommended that the width of each pass be between 60% and 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 end mills and round cutters (also called round nose cutters) are often used to process curved surfaces and variable bevel contours. Ball cutters are mainly used for semi-finishing and finishing. Round knives inlaid with carbide tools are mainly used for roughing.

8. What is the function of the treatment program sheet? What content should be included in the treatment program sheet?

1. Processing program sheet is one of the contents of CNC machining process design. It is also a procedure that must be followed and implemented by the operator. This is a specific description of the treatment program. to clarify the program content, tightening and positioning methods, and each treatment. It is worth paying attention to the tools selected for the program, etc.

2. The list of processing programs must include: drawing and programming file names, part names, clamping sketches, program names, tools used in each program, maximum depth of cut and processing properties (such as roughing or finishing), theoretical processing time. , etc.

9. What preparations should be made before CNC programming?

After determining the processing technology, you must understand the following points before programming:

1. Workpiece clamping method;

2. The size of the workpiece blank – to determine the extent of processing or whether multiple clamping is required;

3. The material of the workpiece – in order to choose the type of tool to use for processing;

4. What tools are in stock? Avoid modifying the program due to the absence of this tool during processing. If you must use this tool, you can prepare it in advance.

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

The principle of adjusting the safety height: generally above the highest surface of the island. Or set the programming zero point to the highest surface to minimize the risk of tool collision.