figure 1
figure 2
1 Introduction In the process of using CNC lathes, in order to reduce the surface roughness of the workpiece being machined, reduce tool wear and increase tool life, the tip of the turning tool is usually sharpened into a circular arc shape, and the arc radius is generally 0.4 to 1.6 mm. between. The use of a CNC lathe with tool nose radius compensation (G41, G42), as long as the workpiece size is programmed directly in the machining program, will not cause machining errors due to the tool nose arc; but the CNC lathe without this function will be processed. It will be affected by the arc of the tool tip. If it is serious, it will cause the workpiece to be scrapped. This issue will now be discussed with respect to the processing of the SR10-0.04 sphere in the workpiece shown in FIG. 2 Processing Error Analysis In the use of economical CNC lathes, we usually use the trial cutting method to set the knife. In this way, the tool location described by the machining program is P point (Fig. 2), and the actual cutting is the tip arc. (here the tip radius of the arc is 0.4 mm) and not the P point because this P point does not actually exist. Therefore, there are different degrees of error between the trajectory of the P point described by the machining program and the actual machining contour. However, when turning the outer circle, inner hole and end face, this error is zero. This error is significant when machining arcs and cones. The error analysis of the SR10-0.04 spherical surface is shown in Figure 2. In the figure, the M line is the trajectory of the P point described by the machining program, that is, the ideal size of the workpiece, and the actual processed contour is the N line, and the shadow is the less cutting solid part, ie, the machining error. We use the “Element Property Query†function in the CAXA electronic chart to check that the N-line is a circular arc with a radius of 9.6mm. The maximum error is about 0.17mm. If this error is within the tolerance, we can ignore it, otherwise we It is necessary to take measures to eliminate it. 3 Error elimination method Method 1: Changing the programming size When programming, adjust the trajectory of the tool tip so that the actual machining contour of the arc-shaped tool tip matches the ideal contour. Take SR10-0.04 spherical machining as an example. When programming, we only need to make the following changes to the finishing block:
N100 G00 X0 Z50
N105 G03 X10 Z42 R10 FO.1
...
N100 G00 X0 Z50
N105 G03 X10 Z42 R10.4 FO.1
Method 2: The following steps are used to program the center of the arc of the tool nose as follows: Draw a sketch of the workpiece → Draw the arc of the tool nose based on the arc radius r of the tool tip and the size of the workpiece → Calculate the circular arc trajectory feature → Programming. In this process, the drawing of the center curve of the tool tip arc and the calculation of its feature point are a little troublesome. If the drawing function of the CAD distance line and the coordinate query function of the CAD software are used to complete this work, it is very convenient. In addition, when using this method, the operator should pay attention to the following two points: 1) Check whether the r value of the tool tip arc radius used by the tool is consistent with the r value in the program; 2) When the tool is set, r The value is taken into account, ie if the cutter compensation value obtained by the tool setting is x (X-axis) and y (Z-axis), the tool offset values ​​that should actually be entered are x-2r and yr. 4 Conclusion In this paper, we mainly discuss the processing of convex outer arcs. Other types of arcs and cones also have similar problems. We will not go into details here.
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