In nc automatic programming system, the interference problem of tool Angle exists in the automatic generation of tool path. This paper presents an algorithm for cutting tool Angle interference in numerical control turning, which is proved to be effective by practical application.

Preprocessing of part drawing before tool interference treatment

According to the characteristics of CNC turning parts, the parts can be divided into: outer (inner) surface, chamfer, back groove and thread. As a result of the characteristics of turning, in the tool interference treatment of the back groove and thread will be replaced by the external surface, so as to the parts of the tool interference treatment, only consider the surface of the tool interference.

2 tool interference processing algorithm

By preprocessing the part diagram before interference, the part contour to be processed is composed of straight line and arc, so the tool interference processing in CNC turning processing is only the interference processing in the straight line and arc processing.

In order to reduce the installation error caused by multiple installations, the CNC machining generally adopts a single clamping. For those parts that need to be turned around, the right-side tool is used for reverse cutting, and the tool interference processing algorithm for reverse cutting is similar to that for forward cutting. In addition, the tool interference processing algorithm for inner surface machining is similar to that for outer surface machining. Therefore, this paper discusses the algorithm of tool interference treatment for forward cutting of outer surface.

As shown in Figure 1, if the contour of the part is a straight line, it is represented by directed line segment; if it is an over-quadrant arc, it is decomposed. The tool is a left offset tool. The Angle between the cutting edge of the tool pair and the Z-axis is, is the Angle between the contour line of the part and the Z-axis, as shown in Figure 2.

Tool interference processing algorithm for cutting straight lines

As shown in FIG. 2, when ≤, there is no interference in the cutting process of the tool.

When >, line segment C in figure 2, where the tool is machined will leave a shadow residue in the figure. To remove the residue, either by changing the tool Angle or by reversing the cutting tool. In order to reduce the frequency of tool replacement and unify the algorithm of tool interference treatment, this algorithm adopts the method of reverse knife cutting to remove the residual parts. As shown in FIG. 2, its line segment C is converted into a straight line C 'with an Angle of, and the residual part is cut with a right offset knife at the next working step. The cutting starting point is located at point Q in the figure, and the trajectory of the tool is QDC and C is the end point. The outline shape of the part drawing can be machined by the forward and backward cutting.

Tool interference processing algorithm for cutting arcs

When the contour is the first Ⅰ quadrant circular arc, cutting tool when cutting the arc without interference.

First Ⅱ quadrant circular arc, a contour with the circular arc starting point and end point of a contour position is different, cutting tool interference may be produced. As shown in FIG. 3(a), the line L with an Angle of is tangent to the arc C with a tangent point of T, and interference exists when the starting point of the cutting arc is to the left of the tangent point T. Divide arc C into arc C 'and C ". No interference will be generated when cutting C ', but interference will be generated when cutting C ". For this reason, arc C "is replaced by its tangent TP, and the auxiliary line PD(PD is the perpendicular line that crosses the end point of this section of arc and intersects with the tangent) is added. The purpose of adding this auxiliary line is to facilitate the implementation of the algorithm. In the subsequent treatment, the arc is replaced by a tangent, just as the line is treated above. The processing of the auxiliary line is also converted into the above processing of the line.

When the contour is the first Ⅲ quadrant, cutting tool without interference.

First Ⅳ quadrant, a contour machining different visual tool Angle may produce serious interference. As shown in FIG. 3(b), the starting point of the arc is a line L with an Angle of, and the intersection point between the line and the arc is calculated. If the intersection point exists, there is no interference in the left cutting at the intersection point, while there is interference in the right cutting. Truncate the arc at the intersection and convert the arc on the right to the line L of Angle. If the intersection point is not on the arc, the arc is converted to a straight line L with an Angle of, and the end point is used as a vertical auxiliary line, as shown in FIG. 3(c). The treatment of its residue is as described above when it is removed by reverse cutting.

3 Algorithm Implementation

According to the above algorithm principle, through the analysis of the feature of the part diagram, the processing of tool interference in the program design realized by the algorithm can be divided into the following three cases:

The line is connected with the line;

The straight line is connected with the arc;

Circular arc.

The treatment of connecting lines to lines. If there is tool interference when cutting a straight line, as shown in FIG. 4(a), the straight line is replaced by a straight line L with an Angle of, and the intersection point of the straight line and subsequent straight lines is calculated. If there is an intersection point, the line is cut off at the intersection point and the right part of the intersection point is converted into a line with an Angle of alpha. If there is no intersection or the intersection is not on the line, the next line is also converted to an Angle alpha line. The z-coordinate of the end point is the Z-coordinate of the line segment, and the vertical auxiliary line is added, as shown in FIG. 4(b).

When the line after the first Ⅰ quadrant arc cutter cutting arc without interference, but cutting line interference exists, such as Angle of straight line can be converted to alpha line as shown in figure 5 (a) L. Then the starting point of the arc is modified to be the intersection point of line L and the arc. If there is no intersection point, it indicates that the arc is located under the line. At this time, the arc is also converted into a line with an Angle of, and its end point Z coordinate is the z coordinate of the end point of the arc. As shown in Figure 5(b) (considering the manufacturability of the structure, such structure should be avoided in the design).

When line after the first Ⅱ quadrant arc, the cutting tool cutting line and arc may interfere. If there is interference in the cutting line of the tool, the processing algorithm is the same as described in section 1 of this section. If a subsequent arc connected to a straight line also has tool interference, the arc is converted to a straight line at an Angle of, using the same algorithm described in section 2 of this paragraph.

When the line after the first Ⅲ quadrant arc cutter cutting arc without interference, but such as cutting line interference exists, its processing algorithm with mentioned in section 2 of this paragraph.

When the line after the first Ⅳ quadrant arc cutter cutting line at this time is likely to interfere. Cutting arcs may also interfere. If there is interference in the machining of the straight line, the processing algorithm is the same as that used for cutting the straight line. The algorithm for interference treatment of circular arc cutting is the same as that for circular arc cutting.

Algorithm block diagram

4 conclusion

The algorithm is stable and reliable. It can be applied to the automatic programming system of nc turning.

According to the algorithm described in this article, the processing parts with certain shape, after repeated many times to cutting as needed to complete, but due to machining usually have rough machining and finish machining, so for owe cutting residues produced by tool Angle smaller margin, can temporarily don't consider, when finishing or half finishing processing. Due to the improvement of cutting conditions, the probability of tool interference is much less.