On the coordinate system of CNC lathe

2022-09-22
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Introduction there are two kinds of CNC lathes in our unit. One is cjk1630 produced by Baoji Machine Tool Plant, which adopts FANUC system, and the other is cyncp320 produced by Yunnan Machine Tool Plant, which adopts Aerospace CNC system. In use, we found that the two systems were different, which made us pay special attention to the coordinate system of CNC lathe, and then analyzed it

1 introduction to CNC coordinate system

the processing of CNC machine tools is completed by program control, and then the processor stops processing this signal, so the determination and use of coordinate system is very important. According to iso841 standard, the coordinate system of CNC machine tool is determined by the right-hand Cartesian coordinate system. The CNC lathe is parallel to the spindle direction, that is, the longitudinal direction is the Z axis, perpendicular to the spindle direction, that is, the transverse direction is the X axis, and the direction of the tool away from the workpiece is the positive direction

CNC lathe has three coordinate systems, namely, mechanical coordinate system, programming coordinate system and workpiece coordinate system. The origin of the mechanical coordinate system is the origin of the fixed coordinate system when the manufacturer manufactures the machine tool, also known as the mechanical zero point. It has been determined when the machine tool is assembled and debugged, and it is the benchmark of machine tool processing. In use, the mechanical coordinate system is determined by the reference point. After the machine tool system is started, the mechanical coordinate system is established by returning to the reference point. Once the coordinate system is established, as long as the power is not cut off, the coordinate system will not change. The programming coordinate system is the coordinate system used in programming. Generally, we put the Z axis coincide with the workpiece axis, and the X axis on the end face of the workpiece. The workpiece coordinate system is the coordinate system used by the machine tool for machining, which should be consistent with the programmed coordinate system. Whether the programming coordinate system can be consistent with the industrial coordinate system is the key to the operation

in use, we found that when submitting manuc system and aerospace CNC system, please note that the mechanical coordinate system of the submitted magazine is basically the same, which is determined by returning to the reference point after the system is started

2 discussion on the determination of the coordinate system of two systems

fanuc system has three methods to determine the workpiece coordinate system

the first is to write the tool offset value into the parameters through tool setting to obtain the workpiece coordinate system. This method is simple to operate and reliable. It is closely linked with the mechanical coordinate system through the tool deviation. As long as the power is not cut off and the tool deviation value is not changed, the workpiece coordinate system will exist and will not change. Even if the power is cut off and the reference point is returned after restart, the workpiece coordinate system will still be in its original position

the second is the configuration of the fatigue testing machine for bridge concrete components: set the coordinate system with G50, and move the knife to the position set by G50 after setting the knife. In addition to having high damping characteristics and reducing vibration and noise, it can be processed outside the comfort of riding. When it comes to the benchmark knife, the knife deviation of other knives is relative to the benchmark knife

the third method is MDI parameters. Six coordinate systems can be set by using g54~g59. This coordinate system is unchanged relative to the reference point and has nothing to do with the tool. This method is suitable for batch production and the workpiece has a fixed clamping position on the chuck

the workpiece coordinate system of aerospace CNC system is established by setting the coordinate value of the current position of the tool through G92 XA ZB (similar to FANUC G50) statement. Before machining, it is necessary to set the tool first, and the reference tool is used to realize the alignment. After the tool alignment, the displayed coordinates are cleared. For other tools, the displayed coordinate values are written into the corresponding tool compensation parameters. Then measure the tool setting diameter Ф d. Move the knife to the position where the coordinate display x=a-d z=b, and then the program can be run (the origin of the programming coordinate system of this method is in the center of the right end face of the workpiece). Press the reset or emergency stop key during processing to return to the set G92 starting point to continue processing. However, if something unexpected happens, such as no servo in X or Z axis, tracking error, power failure, etc., the system can only be restarted, and the workpiece coordinate system set after resetting will disappear, so it is necessary to reset the tool. In case of batch production, return to G92 starting point to continue processing the next piece after processing one piece. If there is a slight error in the operation process, the workpiece coordinate system may be modified and the tool setting needs to be repeated. In view of this situation, we try to fix the workpiece coordinate system on the machine tool. We found that there are 16 cutter compensation values of the machine tool, which can be used, so we tried several methods

the first method: when aligning the reference tool, write the displayed reference point deviation value into the No. 9 tool compensation, and write the inverse of the tool alignment diameter into the x value of the No. 8 tool compensation. After the system restarts, move the tool to the reference point and run a program to return the tool to the starting point of workpiece G92. The program is as follows:

n001 G92 x0 Z0

N002 G00 T19;

N003 G92 X0 Z0;

N004 G00 X100 Z100;

N005 G00 T18;

N006 G92 X100 Z100;

N007 M30;

the program runs normally until the fourth sentence. When running the fifth sentence, the tool should move to the negative direction of X, but it moves abnormally to the positive direction of X and Z, and the result fails. It is suspected that the reason is caused by two tool compensations of one tool position adjusted by the same program

the second method: when aligning the reference tool, write the displayed Z value of deviation from the reference point into the Z value of No. 9 tool compensation, and write the sum of the displayed x value and the inverse of the tool alignment diameter into the x value of No. 9 tool compensation. After the system restarts, move the tool to the reference point and run the following procedure:

n001 G92 x0 Z0

N002 G00 T19;

N003 G00 X100 Z100;

N004 M30;

after the program runs, the tool is successfully moved to the starting point of workpiece G92. However, when running the workpiece program, the tool should first move to the negative direction of X and Z, but it abnormally moves to the positive direction of X and Z, and the result is failure. It is suspected that after the system runs a program, the running cutter compensation is still in the memory and is not empty. When running the next program, it must first move to eliminate the cutter compensation

the third method: use the program of the second method to move the tool to the starting point of workpiece G92, restart the system, do not directly process the reference point, and it can be processed after the test. However, this is not in line with the operating procedures of the machine tool. The conclusion is that it is feasible but not feasible

the fourth method: during tool setting, add 100 to the displayed deviation value from the reference point and write it into its corresponding tool compensation. This is the case for each tool, so that the tool compensation of each tool is relative to the reference point. The starting point of G92 of the processing program is set to X100 Z100, which is feasible after the test. The disadvantage of this method is that the starting point of each machining is the reference point, and the tool movement distance is long, but because this is G00 fast movement, it is acceptable

the fifth method: record the displayed deviation from the reference point and the tool setting diameter when aligning the reference tool. Once the system is restarted, the tool can be manually moved to the starting position of G92. This method is more troublesome, but it is also feasible

3 conclusion

the determination of workpiece coordinate system of CNC machine tool is a major factor affecting machining accuracy. There are different requirements for different types of machine tools. Only by accurately mastering and flexibly using these knowledge can we operate CNC machine tools well

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