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In the CAD/CAM integrated system, the process design of CNC machining determines the quality and efficiency of actual production and processing. The planning of the tool path during machining has an important influence on the preparation of the process specification and the generation of the NC code, which in turn affects the machining accuracy, surface roughness and machining speed of the part. When designing, designers often only consider the choice of routing, but do not consider or neglect the optimization of the tool path, which is unfavorable for the quality control and efficiency improvement of CNC machining. Taking hole machining as an example, when machining a large number of holes on the same plane, the path of the tool is arranged to follow different principles, and the different way of cutting is selected. The effect of CNC machining is very different, if in the process of generating NC code, Optimize the position of the hole machining, shorten the path of the path as much as possible, and reduce the time of the idle stroke to improve the machining efficiency. Therefore, how to design a numerical control process, select a reasonable processing path, reduce the bad influence on the processing quality and improve the production efficiency is worth studying. This paper analyzes the optimization method of machining path in hole machining from different angles.
Hole machining path optimization is divided into path optimization of similar hole machining and path optimization of different hole mixing processes. For the same kind of hole processing, the size and processing method of each hole processed in one process are the same. At this time, the path optimization becomes a simple point optimization; for different hole machining, the hole size and processing method of one process are different. At this time, path optimization is not only point optimization, but also the process optimization of the hole. The purpose is to process more holes with one tool change.
Shortest path optimization
Since there is no need to change the tool during machining, the hole can be seen as the point at which the tool is required to stay once. In this way, the processing path is abstracted into a complete graph. The tool starts from the "starting point", processes each hole once, and finally returns to the "starting point", which is actually a Hamilton circuit. From the perspective of processing speed, the shortest processing path is required, that is, the shortest Hamilton circuit of the complete graph is obtained. To accurately solve the shortest Hamilton loop, the algorithm is very complex. For example, branching and bounding, in the worst case, the computational complexity is O(n!).
X-direction priority path optimization
Due to the CNC machine itself, the geometric error of the machine structure causes a three-dimensional position error at the machining point, which has a great influence on the accuracy of the machined workpiece. The use of the pitch and backlash compensation functions of the CNC machine tool alone cannot fully compensate for the three-dimensional position error in the machining area. The backlash of the axis of the CNC machine tool will affect the positioning accuracy of the coordinate axis. The positioning accuracy will not only affect the center distance between the holes, but also the unevenness of the machining allowance due to the low positioning accuracy. Geometric error. If the tool continuously changes the approaching direction during the machining process, the backlash of the coordinate axis will be brought into the machining, resulting in an increase in positioning error. Therefore, due to the empty back error of the CNC machine tool transmission system, in order to improve the machining accuracy (position accuracy and geometric accuracy), the movement of the workpiece or the tool is required to be unidirectional, and the tool should be approached as close as possible to the target point in one direction to avoid The introduction of null back error. The X and Y directions are both unidirectional and only a special hole arrangement can be realized. More generally, the X direction or the Y direction is required to be unidirectional.
Dynamic planning from the back to the front, first calculate the distance d1, d2, d3, d4 to the starting point, and then use the enumeration method to find the shortest path from C1, C2 through d1, d2, d3, d4 to the starting point, and then The former search b1, b2 passes C1 and C2 to the start point... until a point, thereby obtaining a shortest loop from the starting point through a, b, c, d and back to the starting point.
The above tool path is generated based on the principle that the tool approaches the target in one direction as much as possible, and the machining accuracy is improved. Although it is not the fastest machining path, the tool is fed fast during the idle stroke, so the machining time actually increases. not much.
Foreword