PhD Thesis Presentation
Multi-axis systems such as machine tools and robots have been widely used in both subtractive and additive manufacturing industries owing to their flexibility and accuracy. Process planning is of great significance to manufacturing efficiency and accuracy. In this thesis, we propose three process planning methods for both multi-axis machining and printing of complicated parts.
First, a new process-planning method for five-axis machining is presented, which is particularly suitable for parts with complex features or weak structures. In our method, we represent the in-process workpiece as a voxel model. Facilitated by the voxel representation, a scalar field called subtraction field is then established between the blank surface and the part surface, whose value at any voxel identifies its removal sequence. This subtraction field helps identify a sequence of intermediate machining layers, which are always accessible to the tool and are free of self-intersection and the layer redundancy problem as suffered respectively by the traditional offset layering method and the morphing method. Iso-planar collision-free five-axis tool paths are then determined on the interface surfaces of these machining layers. In addition, to mitigate the deformation of the in-process workpiece and avoid potential dynamic problems such as chattering, we also propose a new machining strategy of alternating between the roughing and finishing operations, which is able to achieve a much higher stiffness of the in-process workpiece.
Next, we present a new curved layer volume decomposition method for multi-axis support-free printing of freeform solid parts. Given a solid model to be printed that is represented as a tetrahedral mesh, we first establish a geodesic distance field embedded on the mesh, whose value at any vertex is the geodesic distance to the base of the model. Then the model is naturally decomposed into curved layers by interpolating a number of iso-geodesic distance surfaces (IGDSs). These IGDSs morph from bottom-up in an intrinsic and smooth way owing to the nature of geodesics, which will be used as the curved printing layers that are friendly to multi-axis printing. In addition, to cater to the collision-free requirement and to improve the printing efficiency, we also propose a printing sequence optimization algorithm for determining the printing order of the IGDSs, which helps reduce the air-move path length.
Finally, we present a new lattice infill structure generation algorithm for multi-axis support-free printing of freeform parts, which is able to achieve both the self-supporting condition for the infills and the support-free requirement at the boundary surface of the part. The algorithm critically relies on the use of three mutually orthogonal geodesic distance fields that are embedded on the tetrahedral mesh of the solid model to print. The intersection between the iso-geodesic distance surfaces of these three geodesic distance fields naturally forms the desired lattice of infill structure. The lattice infill pattern in each curved slicing layer is trimmed to conform to a Eulerian graph so as to generate a continuous printing path, which can effectively reduce the retractions during the printing process. To the best of our knowledge, there has no published work in solving the same problem.
(Supervisor: Prof. Kai Tang )