Parametric error modeling and software error compensation for rapid prototyping.

摘要

Rapid prototyping (RP) machines can build parts of complex geometry with very little process planning and human interaction. However, inferior dimensional accuracy of these processes is a major obstacle preventing this technology from greater penetration of manufacturing activities. This research presents a generic method for improving the accuracy of RP machines by error compensation using "virtual" parametric errors.; Under this approach, the confounded effects of all errors in a RP machine were mapped into 18 "virtual" parametric errors which were used to build the machine error model. A specially designed 3D artifact was then built on the RP machine and measured by a master CMM. Measurement results were used to estimate the coefficients of the parametric error functions. Error compensation based on the derived error model was finally applied via software to the files which drive the RP machine. Two compensation methods were developed and tested. The first one applied compensation to StereoLithography (STL) files while the second applied compensation to slice files.; Experimental studies were conducted on a SLA 250 machine and a FDM 3000 system to validate and demonstrate the approach. Results showed that the volumetric error was reduced on average to around 33% of its original value for the SLA machine. In the study of a part with common features and dimensional constraints, it was found that (a) overall size of the part and feature positions on the part were considerably improved, (b) cylindrical feature sizes were improved by a small amount, and (c) dimensions along the z direction did not show obvious improvement due to " z quantization". "z quantization" was addressed in particular to eliminate multiple layers phenomenon in compensated parts. Compensation results of the FDM 3000 machine were compared with those of the SLA machine. Differences in error reduction ratios between these two machines were analyzed.; Finally, the design optimization problem of 3D artifact was studied. D-optimality criterion was employed to verify and improve the design of the 3D artifact. Mathematical programming and simulated annealing algorithm were used for optimization of the design.