Robotic polishing of precision molds with uniform material removal control

In this paper, a uniform material removal (UMR) model is proposed for an automatic mold polishing system (AMPS). Free-form surfaces of mold geometry in IGES format are read and regenerated by the AMPS using the NURBS model. The normal vector, the principal curvatures, and the effective contact area are calculated at any point on the surface. The sensitivity of each factor that influences the material removal is determined by Taguchi experiments. The UMR model is based on maintaining constant velocity and contact pressure by controlling the polishing force according to the effective contact area. Three optical molds were polished using two path patterns with and without UMR control for comparison. The experimental results showed that even the conventional constant-force polishing scheme can achieve nearly the same surface roughness; the surface profile error of the mold with UMR control is less than 1/3 of the mold without UMR control. In addition, the actual material removal depth is less than 5.4% of error compared to the predicted value by the UMR model.