Research On Geometry Quality Evaluation And Uncertainty For S-shaped Test Part

Parts with freeform surface have been widely used in many fields such as automobile manufacturing,aerospace,mold processing and many other industrial fields.The machining precision of this kind of parts becomes increasingly strict.The precision of the surface has an important effect on the quality and performance of these parts.How to inspect the quality of these parts efficiently and accurately has played an important role in surface quality inspection of products.The complete measurement results must contain measured values and the quantitative description of the measurement quality.Evaluating the measurement uncertainty accurately is very important for the product acceptance.The evaluation algorithm of geometry quality and its uncertainty estimation of “S” shape surface were studied in this paper.A new method to evaluate the free-form surface error is proposed in this paper.Testing whether the error is within the required tolerance zone is implemented by comparing the reconstructed machined surface with the design surface.The inspection process is as follow: acquisition of measurement points on the actual surface;optimal matching between measurement points and design surface was implemented with sequential quadratic programming algorithm combine with linear differential movement model of distance function.Reconstructing the machined surface by the located points based on B-spline interpolation;subdivision approximate and iterative algorithm was used to compute the point-to-surface distance.The influencing factors of free-form surface profile measurement uncertainty were analyzed.First,the uncertainty of location points was calculated considering uncertainty of the measurement points and transformation matrix parameters.Secondly,obtaining the uncertainty of points on the reconstruction surface based on the uncertainty of location points and reconstruction process.Finally,the uncertainty of profile error uncertainty was calculated.The proposed method was verified by simulation and measuring results.For the filtration operation in evaluation of waviness and roughness,the calculation algorithm for uncertainty propagation of linear profile filter was studied.According to the filter equation of linear filter,the uncertainty propagation process from input profile to output profile was deduced.