Introduction to the programming function of the CNC system

1 Introduction

The CNC machine tool processes the workpiece according to the part machining program. A good machining program not only guarantees the machining of the workpieces that meet the requirements, but also makes full use of the functions of the CNC machine tools to operate safely, reliably and efficiently. The part processing program is an important part of the numerical control system. According to foreign statistics, 20% to 30% of the reasons for the shutdown of the CNC machine tool are due to the inability to process the machining program. In order to improve the utilization of CNC machine tools, programmers should strive to improve programming capabilities and quickly develop excellent parts processing procedures.

2 Evaluation of part processing procedures

The machining program of a part is by no means unique. In many programs (programs), it is definitely optimal. Can you evaluate from the following aspects:

(1) The guarantee procedure is correct and the processing quality of the parts is stable.

(2) The program is easy to debug and modify, and the program is readable. For example, to change the approach step size of a non-circular curve or the path distance of a curved surface, you only need to modify one parameter without modifying the entire program.

(3) The stability of the program is good. There is no need to change the program when the tool radius changes or the part mounting position changes.

(4) Give full play to system functions and make the program the shortest. For example, the system has a cavity macro, and a command can program a milling cavity. If you don't use it, change it to a one-size-fits-all description, which will make the program lengthy.

(5) The versatility of the program is good. If you have a series of parts, you only need to edit one. If you change the key size, the program can be used.

(6) The programming cost is low. In order to compile a program, the labor and machine costs are lower. Of course, the labor cost is related to the proficiency of the programmer, and it is inconvenient to quantify. But with a calculator and a computer-aided programming (CAM) system, the cost is comparable.

(7) The operating cost should be low. Can use three-axis machine tools, try not to use four-axis machine tools; can use four-axis machine tools plus one indexing turntable, try not to use five-axis machine tools. For example, if you are milling a curved groove in a cone, you can consider the turning center. You can also consider a three-axis machine with a rotating shaft. The tapered surface is angled with a fixture, so that only a four-axis machine is sufficient, instead of a five-axis machine.

(8) Subsequent processing costs are low. For example, a mold cavity is processed by a universal ball head tool with a full surface, the tool cost is low, and the programming is easy, but the polishing process in the next process is costly and the accuracy is not easy to ensure. Specialized tool parting surface processing, although the cost of programming and cutting tools is high, but the polishing cost is low, and it is easy to ensure accuracy. Weigh the pros and cons and choose the best.

For specific parts, what kind of processing procedures are determined depends on the actual situation. In the actual programming, there must be optimization consciousness, especially the part processing program compiled by CAM. Since the post processing function of CAM is weak, it should be optimized.

3 CAM programming part processing program optimization

Because CAM has a strong graphical mathematical processing function, eliminating the cumbersome mathematical calculations in manual programming, the CAM source program is relatively popular compared to the part processing program. Due to the different CNC systems and machine tools, the post processing of CAM, despite the dedicated rear or universal rear, is still quite different from the CNC system function. In actual use, if you can fully utilize the advantages of CAM and avoid its shortcomings, and fully utilize the functions of the CNC system and the practical experience of the operators, you need to optimize the parts processing program compiled by CAM. A high-level part processing program. Optimized processing procedures are recommended from the following aspects.

3.1 Play the system tool radius compensation function

The CNC system generally has a tool radius compensation function, that is, the part contour is programmed, the tool automatically offsets a radius vector, and the tool core trajectory is automatically calculated by the system. Take the parts in Figure 1 as an example.

The part processing program in Figure 1 is derived from a CAM system. From the part program of CAM (see NC code processing program), the tool path of the outer corner is an arc around the sharp corner (equivalent to B-knife), and the numerical control system is generally a straight line away from the sharp point (C-knife) Complementary) is beneficial for keeping the cusp. The part program of CAM includes the outer corner of the transfer block, and the CNC system automatically generates the transfer block with the tool radius compensation function, which does not appear in the part program. In this way, the number of blocks is reduced and it is easy to read.

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