Research On Constant-Scallop Height Tool Path Planning Method On Compound Surfaces

For requirements such as shape or mechanical capability, most products use compound surfaces to make the model. Among the numerous ways of machining compound surfaces,5axis CNC method is the major one. The tool path needs to be planned before machining, and the constant-scallop height method is claimed to have the highest efficiency and shortest length in the5axis tool path planning. However, this method is confined in single surface for the reasons such as the lack of topological relationship, the connection problem between adjacent surfaces. This paper tried to extend the constant-scallop height method to compound surfaces. The topological problem is solved by referring to the Euclidean space boundaries and the connection problem is solved by modifying the tool path at the connection area.Firstly, the common methods of tool path planning are introduced, and the constant-scallop height method is thoroughly explained. And then the constant-scallop height method is compared with current compound surfaces tool path planning method. This paper proposes to apply the constant-scallop height method to compound surfaces. The difficulty is the lack of topological relationship among surfaces. To build this relationship, the surface modelling approach is studied. Based on the analysis of math property of Euclidean space and parametric space, the relationship among parametric boundaries are found by referring to the Euclidean space boundaries, and the relationship among the surfaces is built based on these parametric boundaries.After the topological relationship problem is solved, the common boundaries of compound surfaces are extracted as the initial tool path. The inner tool path are got by offsets the initial ones. Because the tool path is obtained individually at each surface and then combined together, it may not meet the scallop requirement at the connection point of both paths. This problem is solved by modifying two adjacent paths. For the discontinuity problem of CL tool path, Hermite curve is used to transit.The experiment is also conducted to verify the algorithm. Because the different types of5axis machine have different post processor, this paper deduces the post process of table rotate\tilt5axis machine based on machine spatial kinematics. Finally, a model which consists of three surfaces is taken as an example to introduce the process of tool path generation and simulation in Vericut, and then the experiment is conducted. For the promotion of the precision and efficiency, this method has great significance in engineering.