Process planning of multi-axis additive sub-process in hybrid manufacturing

Abstract

Hybrid manufacturing incorporating additive manufacturing and subtractive machining can produce parts of complex geometries with high surface finishing quality which are impossible to be done by either additive manufacturing or subtractive machining alone. Additive manufacturing can fabricate complex parts which is difficult or even impossible to be made by subtractive processes; while machining operation after additive manufacturing can remove the staircase effect which inevitably appeared in additive processes. However, machining after one-off fabrication of entire part may not always applicable because machining tool may be blocked by the already-printed parts, especially for parts with slender features in close proximity. To solve the problem, alternating sequence between additive manufacturing and machining is introduced to the process planning of hybrid manufacturing. The remaining question is how many times of alternating sequence will be suitable for fabrication of the parts. There exists previous literature do optimization for minimizing the number of alternations by considering the accessibility of machining tool, however, the accessibility of nozzle has never been concerned. In practice, the workpiece in hybrid manufacturing grow in a non-uniform rate which the collision between nozzle and in-process workpiece is possible especially with a large metal additive nozzle. Therefore, the main objective is to fill up the gap in previous literature by introducing an inspection to ensure all the region can be accessed in the time of printing. To achieve this goal, the manufacturability metrics for additive manufacturing, which named printability, is first formulated for determining the accessibility of printing nozzle. Then, a rectification process is presented to rectify the alternating sequence generated by the algorithm from previous literature for satisfying the newly defined metrics. The optimality of this rectification process is proven for parts with slender features. Targeting on fully utilizing the capacity of hybrid platform, the planning of multi-axis additive sub-process had been studied. In slicing procedure, sets of support-free curved layer are generated by the establishment of minimum Euclidean distance field. Later, sets of boundary-parallel contours for each layer are generated to cover the whole layers. Computer simulations and physical experiments have been done for validating the feasibility and effectiveness of the proposed methodologies.

Date of Award	2019
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology