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Programming skills for turning large arcs

CNC lathes are widely used in the processing of rotating surfaces, arc surfaces, multi-step shafts and other workpieces. Figure 1 shows the schematic diagram of a belt pulley produced by our factory, which adopts jwk-5gp numerical control system to finish turning r680 excircle. The processing procedure is as follows:

n0010 G00 w － 120

n0020 G00 u － 36

n0030 G01 u － 4 f60

n0040 G01 w － 2 f60

n0050 G03 U0 w － 80

i － 1357.64 K － 40 f80

n0060 g26

n0070 g29 m02

Figure 1 pulley diagram

through process sequence operation, the CNC system displays e15-0050 error message, which indicates that the end-point data deviation is too large. After careful inspection of the N0050 arc program: G03 represents clockwise interpolation, which greatly saves the manufacturing cost. W is the coordinate of the end point relative to the starting point, and I and K are the coordinates of the center of the circle relative to the starting point. The value is confirmed to be correct after repeated calculation

what's the problem? In the past, the machining of R50, R150 and other arcs can have positive fatigue resistance) and operate normally. Aiming at the error message prompt of excessive deviation of end-point data, the values of u and W were changed in the experiment. For this workpiece, the width must be turned to 80mm, so w-80 is fixed, and the value of 0 in U0 is changed. After many tests, U0 becomes u0.01, u0.02, u-0.01 and other numbers. When it becomes u-0.01, the program can run normally, so the problem is solved. The correct N0050 procedure is:

N0050 G0 the industry prospect in the field of new materials is good 3 u-0.01 w-80 i-1357.64 K-40 F80

therefore, questions are raised and the reasons for this phenomenon are analyzed

1. Can this phenomenon occur when the end point and start point of the arc are asymmetric

assuming that the center of the arc in the workpiece is unchanged, but the thickness from the left to the center is 30mm, the N0050 program in the machining program becomes:

n0050 G03 u1.03 w － 70 I － 1357.64 K － 40 f80

by calculating all programs, E15 － 0050 error message also appears. Based on the same principle, change the above procedure into:

N0050 G03 u1.02 w － 70 I － 1357.64 K － 40 F80

the procedure can operate normally. It can be seen that this phenomenon also occurs when the end point and start point of the arc are asymmetric

2. How large an arc is processed to produce this phenomenon

I and K in the program determine the size of the arc. Change the I value in N0050 program. After four or fifty times of repeated tests, the following two programs are obtained:

n0050 G03 U0 w-80 i-1119.01 K-40 f80

n0050 G03 u-0.01 w-80 i-1119.02 K-40 f80

the above two programs can operate normally. After calculation, the critical arc radius is r560.93. That is, machining arcs above r560.93 will produce this phenomenon

3. The reasons for this phenomenon

the reasons for analysis are: 1) error accumulation in data operation of CNC system. The principle of NC lathe machining arc is to adopt approximation method, and then carry out arc interpolation after point-by-point comparison. Because the radius of the processed arc is too large, the cumulative deviation from the point by point comparison to the end of the arc is too large, so it needs to be compensated in the end coordinate. The above phenomenon is to increase compensation - 0.01 in the U direction. 2) The writing format of arc interpolation program of jwk-5gp CNC system interferes with itself. The starting point coordinate of the arc is the end point of the previous procedure, which has been determined; I and K determine the coordinates of the center of the circle; The direction of the arc is determined by G02 or G03; The length of the arc only needs to be determined by the ordinate w or abscissa U of the end point, and only one of them needs to be selected. The jwk-5gp CNC system and jwk-6 CNC system are written in U, W, I and K, and u and W interfere with each other. Now more advanced CNC systems such as gwk-4t have adopted experimental machine fixtures, how to choose? W. I, K writing input mode. (end)

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