Research on the optimization method of machining p

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Research on the optimization method of hole machining path in cam

I. preface

in cad/cam, we share the characteristics of relaxation experimental machine and the installation common sense of the equipment. In the integrated system, the process design of NC machining determines the quality and efficiency of actual production and processing. The planning of tool path during machining has an important impact on the preparation of process regulations and the generation of NC code, which actually affects the machining accuracy, surface roughness and machining speed of parts. When designing, designers often only consider the selection of process route, without considering or neglecting the optimization of tool path, which is very unfavorable to the quality control and efficiency improvement of NC machining. Taking hole machining as an example, when machining a large number of holes on the same plane, arranging the cutting path follows different principles and choosing different cutting methods, the effect of NC machining is very different. If in the process of generating NC code, optimizing the point position of hole machining, shortening the cutting path as far as possible and reducing the time of empty travel, the machining efficiency can be improved. Therefore, it is worth studying how to reduce the bad influence on the processing quality and improve the production efficiency by designing the NC process and selecting the reasonable processing path. 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 mixed machining of different kinds of holes. For similar hole processing, the size and processing method of each hole processed in a process are the same. At this time, the path optimization becomes a simple point optimization; For different kinds of hole processing, the size and processing method of each hole processed in one process are different. At this time, path optimization is not only point optimization, but also hole process optimization, so that more holes can be processed with one tool change

II. Path optimization of similar hole machining (point optimization)

1 Shortest path optimization

because there is no need to change the tool during machining, the hole can be regarded as a point requiring the tool to stay once. In this way, the machining path is abstracted into a complete graph, as shown in Figure 1. In Figure 1, the tool starts from the "starting point", processes each hole once, and finally returns to the "starting point", which is actually a Hamilton circuit. Considering the processing speed, the shortest processing path is required, that is, to find the shortest Hamilton loop of a complete graph. To accurately solve the shortest Hamilton circuit, the algorithm is very complex. For example, the branch and bound method has a computational complexity of O (n!) in the worst case. Since Figure 1 (b) obviously meets the following two conditions:

A) holes to be machined b) machining path is abstracted into a complete figure

Figure 1 hole machining path

(1) is an undirected graph

(2) side length, so the fatigue test of composites can only be driven by electromechanical, which conforms to the triangular inequality

it can be approximated by the "cheap" algorithm with a computational complexity of O (N2). The algorithm is efficient and the calculation result is close to the exact value, so it is widely used

2. X-direction priority path optimization

due to the reason of the NC machine tool itself, the geometric error of the machine tool structure leads to three-dimensional position error at the machining point, which has a great impact on the accuracy of the workpiece. However, the three-dimensional position error in the machining area can not be fully compensated only by using the pitch and reverse clearance compensation functions of the NC machine tool. The reverse clearance of the axis of the NC machine tool will affect the positioning accuracy of the coordinate axis. When machining holes, the positioning accuracy will not only affect the center distance between holes, but also cause uneven machining allowance and geometric error due to low positioning accuracy. If the tool constantly changes the approach direction in the machining process, the reverse clearance of the coordinate axis will be brought into the machining, resulting in the increase of positioning error. Therefore, due to the backlash error in the transmission system of CNC machine tools, in order to improve the machining accuracy (position accuracy and geometric accuracy), the movement of the workpiece or tool is required to be one-way, and the tool should approach the target point in one direction as far as possible to avoid the introduction of backlash error. 10. Y direction is unidirectional, which can only be realized by special hole location arrangement. More generally, X direction or Y direction is required to be unidirectional. For the hole group as shown in Figure 2 (a), the processing sequence is required to be unidirectional in the X direction, and its mathematical model is shown in Figure 2 (b). In the figure, there are multiple holes with the same X coordinate, so the processing path is not 5) the physical meaning of the wear coefficient is that the ratio of the mass wear of the experimental material to that of the control material after the wear experiment is no more than one, so it is necessary to calculate a shortest path. Dynamic programming algorithm can be effectively solved

dynamic programming from back to front, first calculate the distance from D1, D2, D3, D4 to the starting point, then use the enumeration method to find the shortest path from C1 and C2 through D1, D2, D3, D4 to the starting point, and then look forward to B1 and B2 through C1 and C2 to the starting point... Until the friction force (f); Point a, so as to get a shortest circuit starting from the starting point, passing through a, B, C, D and then returning to the starting point

the tool path above is based on the principle that the tool approaches the target in one direction as far as possible, and the purpose is to improve the machining accuracy. Although it is not the fastest machining path, the tool is fast fed when the travel is empty, so the actual increase in machining time is not much

a) empty group of unidirectional machining in X direction B) mathematical model

Figure 2 unidirectional machining hole group in X direction and its mathematical model

III. optimization of mixed machining process of different types of holes

1 Process optimization

in NC machining, the time of tool change is much longer than that of fast tool walking, so to improve the processing speed, it is necessary to reduce the number of tool changes. In general, each hole has to go through several processes and be processed with several different cutters. For example, machining Φ 12.8、 Φ 14.0 and Φ For the three holes of 10.0, the tools used in each process are shown in Table 1

hole drill center hole drilling chamfer

Φ twelve point eight Φ 3.0 center hole drill Φ 12.8 drill bit Φ 19.0 straight chamfer drill

Φ fourteen Φ 3.0 center hole drill Φ 7.4 drill bit

Φ 14.0 drill bit Φ 19.0 straight chamfer drill

Φ ten Φ 19.0 straight line chamfer drill (drilling center hole and chamfer) Φ 10.0 drill bit

it can be seen from table 1 that the tools used in the process of three holes are the same. If the same process of three hole tools can be put into one process, the number of tool changes will be reduced and the processing time will be shortened. To this end, we take the process as the vertex and connect the same process of the tool with edges to form a layered network, as shown in Figure 3

after optimization, the following process arrangement is obtained: drilling center hole( Φ 12.8, Φ 14.0) → drilling( Φ 12.8) → drilling( Φ 7.4) → drilling( Φ 14.0) → chamfer( Φ 12.8, Φ 14.0, Φ 10.0) → drilling( Φ 10.0)。

Figure 3 hole processing process network

2 Processing path optimization

after process optimization, the hole set to be processed in each process is obtained, and the processing path optimization can be carried out in the hole set. The algorithm of machining path optimization is the same as that of similar hole machining

IV. application and conclusion

the tool path optimization method for hole machining discussed in this paper has been successfully applied to the newly developed cad/cam integrated system. The runtime system interface is shown in Figure 4

Figure 4 system interface

this is the mixed processing of several different types of holes. The processing procedure and processing path are optimized using the method described in section III

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