Interferometric problems of turning tools in turning

1 Proposed issue

Figure 1 Shaped turning tool for turning a circular arc on a normal lathe

In the turning of ordinary lathes, turning of circular arcs is usually done by hand using the method of turning by experience, or turning with stereotyped turning tools (as shown in Figure 1). The former is difficult to ensure the accuracy of the mouth; the latter has a relatively high demand for tools, mainly because the shape of the tool needs to exactly match the shape of the workpiece. For low-volume, multi-standard production, tooling costs are high.

Figure 2 The appearance of a common round turning tool

With the rapid development of numerical control technology, for the arc-shaped contour of the shaft parts, people use CNC lathes to process them, and the tool used is a common external turning tool (as shown in Figure 2), and achieved a certain effect. . The profile of the arc-shaped profile machined by this machining method is accurate, but the position of its processed profile is limited, and the processed profile can only be the profile of the second quadrant (the lathe can only process the first The two-quadrant arc profile), if it is a cross-quadrant profile, may be rejected in the first quadrant due to the interference of the tool relief angle (as shown in Figure 3).

Fig. 3 Interference of common external turning tool

Therefore, through analysis, we used circular arc lathes (as shown in Figure 1) on CNC lathes to machine circular arc profiles.

Although the workpieces machined by arc turning tools are beautiful, they still have many problems. This article attempts to use programmatic methods to solve the problem of the interference of arc turning tools.

2 Turning trajectory analysis of the turning tool The following takes the part shown in Fig. 4 as an example to analyze the turning trajectory of the turning arc. Normally, the machining programs programmed by manual programming are similar to the following programs (only arc machining programs are programmed): N100 M06 TO101; Tool No. 01 is an arc tool N110 G00 X22 Z-16; Start point N120 GO1 X20 Z-16 F200 S500; Feed to the starting point of the arc N130 G02 X20 Z-34 I12 K-9: Clockwise machining arc N140 G01 X22 Z-34; Radial retraction

Figure 4 Circular contour of shaft parts

Figure 5 sharp knife arc machining surface

The processed parts are seen by the naked eye, and the outline of the arc is similar to the required circular arc and has a good appearance. However, it is not difficult to find with a caliper that the arc produced does not meet the requirements of the drawings. The distance between the start point and the end point of the arc is always larger along the Z axis. Analysis of the reasons for the increase in size, found that the circular arc cutter and the actual workpiece circular surface occurred a thousand interference, thus affecting the accuracy and quality of the parts. For this purpose, we will replace the arc turning tool with a sharp knife (as shown in Figure 5) to process the arc, which basically meets the design requirements. In the case of accuracy, tool strength and other conditions permitting, it is true that some arc surfaces can be completed with a sharp knife tool. However, this situation is limited. In addition to the limitations of surface roughness and other aspects, there are restrictions on the angle of the sharp knife. As shown in Figure 6, assume that the starting point is point A, the ending point is point B, and the highest point is point C. The knife point of the sharp knife tool follows the arc ACB. Take any point D in the arc ACB for analysis. When the tool point of the sharp knife touches the arc at the D point, it connects the OD, passes through the D point as the tangent line L2 of the arc ACB, and then makes the vertical line L3 of the Z axis, L2 and L3 form an included angle a, the arc points The slopes are not the same. From A to C, the slope of the tangent L2 gradually decreases, and the angle between these tangents and L3 gradually increases, that is, a gradually increases.

Figure 6 Knife interference analysis diagram

Figure 7 arc knife processing principle

The sharp knife has a certain angle. We define the angle between the back of the sharp knife and the vertical line of the Z axis as b. After the cutter is clamped, the value of P is fixed, and a and b determine the cutter and circle. Does the arc surface interfere? It is easy to draw from Figure 6: When a>b, the tool does not interfere with the arc surface; when a

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