Multi-Objective Optimization of Part Orientation to Improve Process Planning in RM
In layered manufacturing, part orientation is a significant factor of influence on part and process quality. As a result of rapid advancements in the field of Rapid Prototyping and the associated attainable part complexity, determination of optimal build direction is getting more and more difficult. For reliable process planning a lot of know-how is needed to optimize part orientation with respect to all interdependencies. For instance, optimized part-building orientation can minimize the staircase effect as well as the curling effect and therefore increase sur-face quality and part accuracy respectively. Another advantage of optimized build direction is the possible consideration of form tolerances (e.g. circularity). Furthermore, different part orientations can lead to varying implementations of supports and influence part stability. These and related feedback effects have to be considered when selecting an appropriate part orientation for Rapid Prototyping applications. In the majority of cases, the required substantial experience and profound as well as extensive knowledge of the Rapid Technology is subject to Rapid Prototyping system manufacturers and machine operators. In doing so, having notice of the optimized part-building orientation in an early stage of the product development – phase of design – would be advantageous. Especially for design purposes and with respect to maintain a given surface quality the pre-optimization of build direction is suitable for the minimization of possibly necessary feedbacks in the product development process. This paper presents a multi-objective optimization to determine optimal part orientation in consideration of the mentioned factors of influence as well as related effects. In addition to further necessary experiences of the machine operators and service providers to finally set the case dependent part orientation, the introduced concept offers suggestions on the basis of an intensive geometry analysis. This can support data preparation within process planning. The presented concept uses the topological elements of the tessellated representation of the part. Appropriate algorithms from the domain of computational geometry permit a mathematical exact computation. To avoid time consuming calculations because of a wide variety of combinations, the implementation has been realized with the help of a genetic algorithm. Contrary to previous work this approach is not subject to limitations. Therefore it is possible to analyze convex as well as non-convex parts and to determine the optimized build direction with respect to minimization of part height, support volume, support contact area, build time, build costs and the optimization of part quality. Similarly, the approach is not tailored to a specific application of the Rapid Technology. In fact it enables access to process data which is stored in data bases and therefore an application dependent evaluation of the geometry analysis. The proprietary development of the implementation of the presented approach is based on the paradigm of object-oriented and generic programming and therefore versatile.
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