Analysis of shape error in machining conical workp

2022-08-19
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Analysis of shape error when machining conical workpiece with prism shaped turning tool

when machining conical workpiece with prism shaped turning tool, whether hyperbolic error will inevitably occur because the turning tool has a rake angle, there are two different views at present. The first view is that because the turning tool has a rake angle and the cutting edge is linear, the machining result will inevitably produce shape errors; The second view is that as long as the corresponding technological measures are taken, the above shape errors will not occur. This paper makes an analysis and comparison of these two views

1. The shape error produced by the prism forming turning tool when machining conical workpiece

the first view is that the profile of the workpiece formed by the rotating body (including the width and depth of the profile) should be measured in the plane passing through its axis according to the regulations, while the section of the forming turning tool should be measured in the NN section (normal plane) perpendicular to the rear cutting surface according to the regulations. Therefore, only when the rake angle F and the rake angle F of the tool are equal to 0, the sectional shape of the forming turning tool can be completely consistent with the profile of the workpiece, but the tool with the rake angle f = 0 cannot work. When the front angle F of the prism forming turning tool is> 0 and the rear angle f is> 0, it can be seen from figure 1A that the sectional depth P on the tool will be less than the corresponding contour depth AP on the workpiece. Therefore, when designing prismatic forming turning tools, it is necessary to modify and calculate the cutting tool profile

Figure 1 Analysis of the shape error caused by the forming turning tool when machining the cone

as shown in Figure 1b, the rake face mm of the prism forming turning tool does not pass through the axis of the workpiece due to the rake angle F, that is, the cutting edge of the conical part is not in the axial section of the workpiece. The intersection of the plane mm and the conical surface of the workpiece is in the shape of a convex hyperbola. Therefore, in order to cut out the correct shape of the workpiece (i.e. circular conical surface), the shape of the cutting edge in the MM plane must be completely consistent with the corresponding convex hyperbola shape, that is, an "concave" hyperbola. But in fact, in order to simplify the design and manufacture of cutting tools, the shape of the cutting edge in the profile is often made into a straight line, which inevitably cuts off part of the material on the workpiece, resulting in shape error, that is, hyperbolic error

2. Shape error can be avoided when machining conical workpiece with prism forming lathe tool

the second view is that when machining conical workpiece with prism forming lathe tool, shape error can be avoided if the following methods are selected

(1) cone generatrix kissing method

because when designing and manufacturing prismatic forming turning tools, The cutting tool section width is equal to the profile width of the workpiece called "VOC" (in some special cases, the cutting tool section width is allowed to be greater than the workpiece profile width) Therefore, as long as the cutting edge of the tool is in the same horizontal plane with the rotation axis of the workpiece when installing the tool, and the cutting edge is consistent with the conical bus of the workpiece, the workpiece processed will not produce hyperbolic error, but a standard conical surface. In Figure 1b, as long as the turning tool is slightly twisted with the base point 1 as the axis, the cutting edge can coincide with the workpiece cone bus 12 and maintain the corresponding front and rear angles. The results are shown in Figure 2A (at this time, the cutting edge of the tool is). Under this condition, the workpiece will not produce surface shape error

(2) radial positive fitting equal rake angle and equal rake angle machining method

when grinding prism shaped turning tool with grinding wheel, make the grinding cutting edge parallel to the normal surface NN of the tool body, and make the angle between the back surface and the perpendicular line of the grinding wheel surface (F + F) (see Figure 2b). Processing workpiece 2 When the product equipment is in place, as shown in Figure 2c, make the cutting edge of the tool and the rotation axis of the workpiece in the same horizontal plane, and coincide with the cone bus of the workpiece, and make the back angle of the tool F. It is not difficult to see that the front and back corners of each point on the cutting edge of the tool are equal. Since the cutting edge is consistent with the cone bus of the workpiece, there will be no surface shape error

Figure 2 Analysis of avoiding shape error when machining cone with forming turning tool

3. Analysis and conclusion

(1) according to the second view, the process technology of machining conical workpiece with prism forming turning tool is relatively simple, and there are no complex theoretical problems. As long as the tool is grinded and installed according to the method shown in Figure 2, the shape error can also be avoided when the turning tool has a rake angle. Therefore, it is not necessary to carry out complex correction calculation on the cutter profile

(2) although the first view is correct in theoretical derivation, its understanding of the front angle f is questionable. First of all, this view holds that only when the rake angle F and the rake angle F of the tool are equal to 0, the profile of the forming turning tool can be completely consistent with the workpiece profile, which is lack of practical significance. First, when machining a workpiece with one-way conical surface (or a workpiece with double combined surfaces composed of conical surface and cylindrical surface), the cutting edge width of the turning tool is allowed to be equal to or greater than the contour width of the workpiece, so as long as the cutting edge of the turning tool is consistent with the conical generatrix of the workpiece, it is not necessary to require the two to be completely consistent; Second, figures 2a and 2C have proved that whether the cross-section of the turning tool (in fact, the cutting edge) is consistent with the workpiece profile has nothing to do with the front and rear corners of the tool. In addition, this view holds that the rake face mm of the prismatic forming turning tool does not pass through the workpiece axis due to the rake angle F, resulting in machining errors, that is, the rake angle is the premise of machining errors. The second point of view draws a completely opposite conclusion, because according to the first point of view, the orientation of the tool rake angle f is determined according to the method of determining the rake angle when machining cylindrical rotating workpiece, that is, the size of the selected rake angle f is specified in the plane perpendicular to the rotation axis of the workpiece, which can be divided into static load testing machine and dynamic load testing machine, while it is inappropriate to use this method to determine the orientation of the rake angle when machining conical workpiece, This will lead to the complexity of turning tool design theory, so that the manufacturing process of turning tool is unreasonable, and finally lead to machining shape error

when machining workpiece with conical surface, the reasonable rake angle orientation of prism forming turning tool should be specified in the plane perpendicular to the cone bus in the same horizontal plane with the rotation axis of the workpiece and close to the side of the turning tool (see Figure 2D). The second view conforms to this principle. V

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