The Research On Some Problems About Springback Surface Mapping Method And Surface Reverse Engineering

Unloading after sheet metal forming is destined to caused to generate spring back, and it may bring on difference between the actual part shape and the part what we need if the value is larger. Maybe it can lead to failure on manufacture in the high automatization process industry. It is a significant problem that how to modify and compensate the spring back value. The spring back die compensation method is that to modiy the die's shape according to the value and distribution of its spring back, and then make its shape after spring back match the requirement of geometric precision. It is difficult to measure magnitude and distribution of spring back value in engineering practice, and it is difficult to ensure part's geometric precision by using traditional die compensation method. Consequently, it is one of the hotpoints in sheet metal forming field that how to use numerical simulation to predict spring back value and then reduce part's geometric error. It is very important that how we can transform the ultimate die's CAE digifax after die compensation into CAD digifax to be convenient for CAM processing then build CAD/CAE/CAM integrative system which is based on spring back compensation. The mainly topics this paper touched is that: the algorithm of generating CAD digifax from CAE digifax. The spring back die compensation method based on VC++6.0 explorer platform show as follows: (1) read in tool surface and mesh information, blank mesh information before spring back; (2) divide tool surface mesh into surface patches and find out boundary and inner points on each surface patch; (3) project above points on tool surface onto blank mesh; (4) according to foregoing projective relationship and spring back value of blank nodes, interpolating spring back value of projective nodes on tool surface, then reverse modifying their coordinates; (5) establish u ( v ) direction of each tool surface patch and use Accumulated Chord Length Parameterization to generate its knot vector; (6) reconstruct each surface patch through B-Spline method; (7) if the generated surface can be accepted, generate IGES file; if not, modify until it can be accepted; (8) finish. Surface reconstruction is the vital problem in the progress of CAE to CAD digifax, however, the quality of surface after reconstruction directly determines the precision of subsequent CAM processing, so it should be able to ensure the precision. Reconstructing a spatial surface needs corresponding inside and outside data points to reflect its spatial shape, however, it is very complicated to directly search for inside data points except boundary points in tool mesh information, and it is difficult to establish u ( v ) parametric information what we need. So this paper interpolates to generate surface inside data points through R ,S natural coordinates mapping method of quadrilateral element and triangle coordinates mapping method of triangular elment to resolve the shortage of information in reconstrucing. It generates interpolation surface by ACIS develop tools. This paper does deeply analysis and research on fundamental principle of surface reconstruction, and it takes B-Spline method to reconstruct spatial surface. Considerating asymmetry of data points generated by mapping method in the progress of interpolation, it takes Accumulated Chord Length Parameterization to construct asymmetrical knot vector, so it can ensure surface interpolated precision. Surface after reconstruction should be joined and faired then it can be transformed into IGES file which can be read by CAD software. This paper studies basic principle of curve and surface intersection, join and fairing, and it gives the fairing rule of curve and surface to be ready for next works. About data transportation, it takes IGES standard as the neutral file format of input and output, because it can ensure file's transplantability. It introduces surface reverse engineering about CATIA software at last.