Using AHP and fuzzy sets to determine the build orientation in layer-based machining

Layer-based machining (LBM) is a hybrid CNC machining and layered manufacturing (LM) process. In the LBM process, a physical model is built layer by layer. On each layer, an object profile is shaped by machining. In principle, there is no restriction on the thickness of a layer. One critical issue in LBM is the build orientation. Determination of the build orientation is a multi-criteria and multi-level optimization problem. The preferred build orientation should have the tendency to maximize surface quality, minimize build time and build cost simultaneously. For a given part model, a different build orientation will result in variant surface quality, support design, number of stock layer, removed material volume and part stability. In this paper, the problem of determining the build orientation is modelled as a four-level hierarchy structure. Fuzzy sets are employed to rate the contribution made by alternatives, while an Analytic Hierarchy Process (AHP) is used to assign weights to the factors in different levels. The preferred orientation is then chosen according to its rank in the result of fuzzy synthesis evaluation.