Research On Curve Smoothing Algorithm And Development Of Automated Design System For Trim Steel

In the design of automobile panel dies, manual design of trim steel always comes with large labor intensity and high error rate. The subject on the CAD system for the trim die has been researched. However the trim curves are curves in 3-dimensioal space, which will arouse many problems in the processes of offset and smoothing: Manual handling is inefficient, and relies heavily on the experience of technical personnel; Curve deformity or crossing locally will occur in automated processing and unevenness of wall thickness in curve smoothing, which will not meet the strength requirements. Therefore handling trim curve has become the bottleneck in the realization of automated design system for trim dies.Combined with the project on automated design system for trim steel of Shanghai Volkswagen Automobile Company, the problem of curve processing in the design of trimming steel is analyzed in detail. According to the problem that fairing criteria of the current smoothing algorithm cannot meet the trimming process requirements and may led to the decrease of wall thickness in the follow-up design, a fairing criteria for trim curve is proposed.In order to solve the problem of low efficiency of manual processing and unevenness of wall thickness caused by automated method in the process of handling trim curve, one curve smoothing algorithm based on rolling-circle is proposed, which uses the fairing criteria for trim curve as constraint condition. The algorithm simulates the circle rolling on one side of the curve, and generates smooth curve by fitting the contact trajectory of circle and curve, which not only realize automated process of curves to solve the problem of time consuming and high error rate, but also ensure the wall thickness to meet the design requirements.Aiming at the problem of slow speed and high complexity of the method in rolling contact detection based on the step distance, the concept of the R-curve is defined, which is a good way to transform problem of dynamic kinematics into a static contact problem. Its application in circle-rolling algorithm not only reduce the computation greatly, but also improve the stability of the algorithm.Finally the circle-rolling algorithm is integrated into the automated design system of trim steel. The effectiveness and stability of circle-rolling algorithm for trim steel are verified through many experiments. The circle-rolling algorithm not only plays an important role in the trim steel design, but also can be used as preprocessing tool of general curve to eliminate the defects of the self-intersection of curve and deformity at local area.