At present, many domestic CNC machine tool operators are classified as follows: some operators are very familiar with mechanical processing, but are relatively unfamiliar with CNC machine tool programming, and some are newly graduated students who have no knowledge of mechanical processing and CNC. They are familiar with the theory of machining and programming, but lack actual machining experience; there are also many operators who have never been exposed to machining and programming, so it is very difficult for them to learn how to operate CNC machine tools.
For those who are new to CNC machine tools, it is very important to master certain CNC machine tool operating skills. On the one hand, they can avoid machine tool collision accidents, resulting in machine tool damage; on the other hand, they can quickly improve the operator’s CNC machine tool operating skills in a short period of time and become competent at their jobs. This article is especially aimed at those operators who are new to CNC machine tools. It introduces some theoretical knowledge of CNC machine tool operating skills. It is hoped that it will have some reference significance for operators of CNC machine tools who have just started working.
Machining accuracy reflects the degree of deviation between the actual geometric parameters and the ideal geometric parameters after processing of the part, that is, the size of the machining error. The size of machining errors is closely related to the level of machining accuracy. Therefore, understanding the main causes of machining errors is of great significance for improving machining accuracy.
Due to the complexity of CNC machining (such as different machine tools, different materials, different tools, different cutting methods, different parameter settings, etc.), it determines the process from engaging in CNC machining (whether processing or programming) to reaching a certain level. Level must go through a relatively long period of time. This manual is a summary of some experiences of engineers in the long-term actual production process regarding CNC machining technology, procedures, selection of commonly used tool parameters, and monitoring during the machining process. It can be For reference.
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- How to divide the processing procedures?
The division of CNC machining processes can generally be carried out according to the following methods:
(1) The tool centralized sorting method is to divide the process 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 finish other parts they can finish. This can reduce the number of tool changes, compress idle time, and reduce unnecessary positioning errors.
(2) Using the processing part sorting method, for parts with a lot of processing content, the processing part can be divided into several parts according to their structural characteristics, such as inner shape, outer 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 are processed; parts with lower precision are processed first, and then parts with higher precision requirements are processed.
(4) For parts prone to machining deformation using the roughing and finishing sequential method, deformation correction may occur due to possible deformation after roughing. Therefore, generally speaking, the processes must be separated for roughing and finishing. .
To sum up, when dividing the process, we must consider the structure and craftsmanship 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 decentralization, which should be determined according to the actual situation, but it must be reasonable.
- What principles should be followed in arranging the processing sequence?
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 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 processing of the previous process cannot affect the positioning and clamping of the next process. Comprehensive consideration must also be given to general machine tool processing processes interspersed in the middle.
(2) Carry out the inner shape and cavity processing first, and then the outer shape processing.
(3) Processes processed with the same positioning, clamping method or the same tool are best carried out in succession to reduce the number of repeated positioning, tool changes and platen movements.
(4) For multiple processes carried out in the same installation, the process that will cause less rigid damage to the workpiece should be arranged first.
- What aspects should be paid attention to when determining the workpiece clamping method?
The following three points should be noted when determining the positioning reference and clamping plan:
(1) Strive to unify the benchmarks of design, technology, and programming calculations.
(2) Minimize the number of clampings and try to process all the surfaces to be processed in one positioning.
12 little experiences in CNC machining, popular! Easy to remember! it works!
(3) Avoid using machine-occupied manual adjustment solutions.
(4) The clamp should be smooth, and its positioning and clamping mechanism should not affect the tool movement during processing (such as collision). When encountering such a situation, clamping can be done with a vise or by adding screws to the bottom plate.
- How to determine the reasonable tool setting point? What is the relationship between the workpiece coordinate system and the programming coordinate system?
- 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 damaged after the first process, which will cause the second process and There is no way to find the subsequent tool setting points. Therefore, when setting the tool in the first process, pay attention to setting up a relative tool setting position at a place that has a relatively fixed size relationship with the positioning datum. In this way, the original tool setting position can be retrieved based on the relative position relationship between them. Tool setting point. This relative tool setting position is usually located on the machine tool table or fixture. The selection principles are as follows:
1) Easy to find.
2) Programming is convenient.
3) The tool setting error is small.
4) Easy to inspect during processing.
- The origin position of the workpiece coordinate system is set by the operator himself. 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 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. picture
- How to choose the knife route?
The tool path refers to the movement trajectory and direction 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 processing accuracy and surface quality of the parts. When determining the cutting path, the following points are mainly considered:
1) Ensure the processing accuracy requirements of parts.
2) Facilitate numerical calculation and reduce programming workload.
3) Seek the shortest processing route and reduce the empty tool time to improve processing efficiency.
4) Reduce the number of program segments as much as possible.
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 tool’s advance and retreat (cut-in and cut-out) routes must also be carefully considered to minimize the possibility of stopping the tool at the contour (elastic deformation caused by sudden changes in cutting force) and leaving knife marks, and also to avoid vertical downward movement on the contour surface. The knife may scratch the workpiece.
- How to monitor and adjust during the processing?
After the workpiece alignment and program debugging are completed, it can enter the automatic processing stage. During the automatic machining process, the operator must monitor the cutting process to prevent workpiece quality problems and other accidents caused by abnormal cutting.
Monitoring the cutting process mainly considers the following aspects:
- Process monitoring The main consideration for rough machining is the rapid removal of excess margin on the workpiece surface. During the automatic processing of the machine tool, 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 efficiency of the machine tool.
- Monitoring of cutting sounds during the cutting process. In the automatic cutting process, generally when cutting starts, the sound of the tool cutting the workpiece is stable, continuous, and brisk. 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 clamped, the cutting process becomes unstable. The instability is manifested by changes in the cutting sound and collisions between the tool and the workpiece. If the sound is heard, 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 stopped and the condition of the tool and workpiece should be checked.
- Monitor the finishing process. Finishing is mainly to ensure the processing size and surface quality of the workpiece. The cutting speed is high and the feed amount is large. At this time, attention should be paid to the impact of built-up edge on the machined surface. For cavity processing, attention should also be paid to overcutting and tool yielding in corner processing. To solve the above problems, first, we must pay attention to adjusting the spray position of the cutting fluid so that the processed surface is always in the best cooling condition; second, we must pay attention to observe 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 stopped to check whether the original program is compiled reasonably.
Special attention should be paid to the position of the tool during pause inspection or shutdown inspection. If the tool stops during the cutting process, the sudden spindle stop will cause tool marks on the surface of the workpiece. Generally, shutdown should be considered when the tool leaves the cutting state.
- Tool monitoring The quality of the tool largely determines the processing quality of the workpiece. During the automatic machining and cutting process, the normal wear and abnormal damage of the tool must be determined through sound monitoring, cutting time control, pause inspection during the cutting process, and workpiece surface analysis. Tools must be processed in a timely manner according to processing requirements to prevent processing quality problems caused by tools not being processed in time.
seven. How to choose machining tools reasonably? What are the major factors of cutting quantity? How many materials are there for knives? How to determine the tool’s rotational speed, cutting speed, and cutting width?
- Non-regrinding carbide end mills or end mills 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 in the first pass 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.
- End mills and end mills with carbide inserts are mainly used to process bosses, grooves and box surfaces.
- Ball cutters and round cutters (also known as round nose cutters) are often used to process curved surfaces and variable bevel contours. Ball cutters are mostly used for semi-finishing and finishing. Round knives inlaid with carbide tools are mostly used for roughening.
- There are three major factors in cutting amount: cutting depth, spindle speed and feed speed. The general principle for selecting cutting amount is: less cutting and fast feed (that is, small cutting depth and fast feed speed).
- According to material classification, knives are generally divided into ordinary hard white steel knives (the material is high-speed steel), coated knives (such as titanium plating, etc.), and alloy knives (such as tungsten steel, boron nitride knives, etc.).
- What is the function of the processing program sheet? What content should be included in the processing program sheet?
(1) The processing program sheet is one of the contents of the China CNC machining process design. It is also a procedure that the operator needs to comply with and implement. It is a specific description of the processing program. The purpose is to allow the operator to clarify the content of the program, the clamping and positioning methods, and each There are issues that should be paid attention to when selecting tools for machining programs.
(2) The processing program list should include: drawing and programming file names, workpiece names, clamping sketches, program names, tools used in each program, the maximum depth of cutting, and processing properties (such as roughing or finishing) ), theoretical processing time, etc.
- What preparations should be made before CNC programming?
After determining the processing technology, you need 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 multiple clampings are needed; 3. The material of the workpiece— -In order to choose which tool to use for processing; 4. What tools are in stock? Avoid modifying the program due to the lack of this tool during processing. If this tool must be used, you can prepare it in advance.
- What are the principles for setting the safety height in programming?
The setting principle of safe height: generally higher than the highest surface of the island. Or set the programming zero point on the highest surface to avoid the risk of tool collision to the greatest extent.
- After the tool path is compiled, why does it need to be post-processed?
Because the address codes and NC program formats 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 programmed program can run.
- What is DNC communication?
Program transmission methods can be divided into CNC and DNC. CNC means that the program is transported to the memory of the machine tool through media media (such as floppy disks, tape readers, communication lines, etc.) and stored. The program is called out from the memory during processing. processing. Since the memory capacity is limited by the size, DNC processing can be used when the program is large. Since the machine tool directly reads the program from the control computer during DNC processing (that is, it is sent and processed at the same time), it is not affected by the memory capacity. Limited by size,