Software Control System For CNC Turning Non-Circular Parts

Piston is an important part of internal combustion engine and is a typical non-circular part. The degree of cooperation between the piston and the cylinder is an important criterion to measure the quality of the engine. Nowadays, the common convex variable ellipse piston is processed by many manufacturers using the profiling method. However, since the hard profiling system needs to use mechanical or hydraulic pressure to achieve follow-up profiling, it is difficult to further improve the precision and efficiency of the profiling, and the profiling The machining is difficult and the manufacturing cost is expensive. Therefore, it is required to design a new type of CNC lathe to meet the special machining of the convex and variable circular piston.

The development of linear motor technology with frequency response characteristics makes this demand possible. During processing, the processed parts are installed on the spindle of the machine tool and rotate with the spindle, and the tool is installed on the linear motor, and the linear motor is relatively The machined parts reciprocate radially. Due to the extremely complicated shape of the center-convex variable-circular piston, the amount of data that needs to be processed during interpolation is large, and the response speed is also very demanding.

In addition, when processing the piston, two different types of motors need to be controlled at the same time, one is a position servo, and the other is a special servo linear motor for processing non-circular cross-sections. General-purpose CNC software cannot meet this special requirement for machining pistons. The software system introduced in this article adopts C language and assembly language mixed programming, and adopts independent modular design, which better solves the relationship between spindle rotation and tool linear feed.

1 The overall design of the system

The host of this system adopts industrial control 586, and the system software is stored in the hard disk of the microcomputer. After the system is started, the user can perform various operations through the menu. The system has CNC functions such as reading processing program, compiling, simulation, generating piston processing data, controlling linear motor, interpolation, M, S, T in-position detection, etc.

The system software adopts hierarchical and modular design. The system software can be divided into several modules according to functions, and each module can be edited and compiled separately. Information is passed between them through parameters or data files, and the addition, modification, and deletion of a module does not affect other modules. The system software is divided into interface layer, compilation layer, control layer and auxiliary layer, and the operations of each part are relatively independent.

2 System composition and characteristics

It can be seen that the system consists of six modules, which are widely used in mechanical manufacturing. However, the price is generally 5 to 10 times that of ordinary lathes. If a collision occurs during processing, the lighter will damage the accuracy of the product and cause waste. In the severe case, the machine tool will be damaged, causing major economic losses and personal injuries.

After observation and analysis, the author summarized several possibilities for collisions on CNC lathes, and proposed methods to avoid collisions when programming the CNC lathes.

1 When using the G00 command, collision is very likely. As shown, the workpiece needs to be grooved, the origin of the workpiece is on the right end, and the tool change point is when the groove processing is completed, in order to save time, I want the tool tip to move from the starting point fl. When reaching the tool change point>1, use N150G00X80Z50 program segment to complete the tool retraction. If the path is considered to be a straight line, it seems to be no problem, but the actual tool tip path is B and line (such as the time help function. In this system, the user can First, according to the specific requirements of the part drawing, the input of various data and the operation of each function are carried out in the interface layer in the way of man-machine dialogue. In the compilation layer, the information input by the user is compiled to generate the target code, which includes NC source program format conversion, coordinate conversion, error detection, control data calculation and list curve interpolation, rough interpolation, etc.; in the control layer, the control system is issued instructions to coordinate the functions of each part of the system; in the auxiliary layer, Provides various auxiliary functions that are convenient for system work and user operation. The entire system is controlled by keyboard and mouse. To select a menu, users only need to press the cursor, hotkey or mouse. In addition, the system also has The more powerful graphics function provides the graphic display of piston input data, the dynamic simulation function of the tool movement path, and the intuitive form shows the input data and the tool diagram la). Obviously, the tool needs to be If the step surface of the workpiece collides, the workpiece and the tool will be damaged, and the accuracy of the machine tool will be damaged.

The difference between the point positioning command G00 and the linear interpolation command G01 is not only the speed, but the more important thing is that the trajectory of the former is generally not a straight line, and the latter must reach the end point in a straight line. If it is mistaken that G00 must reach the end point in a straight line, it is very dangerous. The trajectory of the tool tip moving from the original position to the point position commanded in the G00 block is generally two straight line segments with different angles, that is, it needs to turn once in the process of traveling, and the X and Z directions of the tool post are both set according to their respective settings. Travel at a speed, each until Zengtong in that direction is finished.

To execute the retract, the tool's motion path is shown in Figure lb, so that collisions can be avoided.

The running track enables users to find operation errors in time.

3 Summary

The system adopts a top-down design method, a friendly interface, real-time help function, graphic simulation function, alarm function, etc., which can save a lot of time spent on running inspection and trial cutting processing inspection on the machine tool. The use efficiency of the machine tool reduces the production cost. The system has been successfully tested in several machine tool factories.

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