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A Novel Two-stage Method of Selection of Sample Points for Surface Quality Estimation of Multi-hole Workpiece

The analysis of surface quality has gained more and more attentions in quality control, since the functional behavior of a machined part is significantly influenced by its surface quality. Conventional sampling methods using Coordinate Measuring Machine (CMM) for surface flatness estimation mainly focus on the continuous-surface workpieces without holes. However, multi-hole workpiece appears frequently in practical production, such as engine block and valve body. Therefore, a novel two-stage method is proposed to select sample points and improve sampling accuracy for flatness estimation of multi-hole workpiece surfaces. In first stage, a new procedure for selection of initial points using Particle Swarm optimization (PSO) algorithm is explored to search a set of initial points. In second stage, a non-uniform step-length pattern search (NUSPS) algorithm is developed to search the optimal points. The created transfer matrix is also applied in NUSPS algorithm to avoid the search into the holes and deal with points with irregular coordinate values. The results of case study show that the proposed two-stage method can be well applied in multi-hole workpiece surfaces and achieve a relatively high sampling accuracy.