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Research on Die Compensation Method Based on Spring-back Prediction of Sheet Metal Forming

Author: LiXiaoDa
Tutor: HeZhongBao
School: Jilin University
Course: Materials Processing Engineering
Keywords: numerical simulation spring-back die compensation KMAS surface reversing surface mapping surface fitting
CLC: TG386
Type: Master's thesis
Year: 2005
Downloads: 212
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Abstract

The energy, environmental protection, security have already become the three severe problems faced in the development of auto industry of our times. The design of lightweight vehicle has become the focus that people pay close attention to. Motor corporations in Europe & America are adopting high-strength Al-alloy, and high-strength steel to make some auto parts at present. During production, most of structure parts and auto body panels are made by blank stamp forming. The sheet metal may present the defects, such as Wrinkling and Buckling, spring-back, Flange Earring, Bottom tearing, Thickness thinning immoderate, Bulging, etc. Among them, spring-back is the most troublesome question in automobile body forming. Then it is very necessary to do some research about spring-back. Traditional method to eliminate the geometric error resulted from spring-back usually is a time-consuming and costly trial-and-error process in workshop. The numerical simulation as a modern technology is more and more employed at present. Since forming process is prior to spring-back, the accurateness of spring-back simulation is subject to that of forming process simulation. The main research content is as follows: First of all, the introduction of this paper summarized the important position of the numerical simulation in sheet metal forming. Among the troubles of the sheet metal forming, the spring-back is an important one .With the development of the lightweight vehicle, how to improve its computational accurateness and to seek a better die compensation strategy based on spring-back numerical simulation are becoming more and more a hot issue. And then, the finite element software related to the sheet metal forming are introduced. KMAS(King-mesh analysis system) is a domestic commercialized software, its computational accurateness of spring-back simulation is superior to that of other similar software. The current research about spring-back was also introduced briefly. In the chapter 2, taking example for Unconstrained Cylindrical Bending benchmark B at the Numisheet’2002 Conference, the paper studied the accurateness of spring-back simulation of KMAS. And the result indicated that KMAS has practicability in Industry. A kind of die compensation strategy based on spring-back was presented in this chapter. And the program of flow chart of this method was given. Finally, the method applied to antenna of the second planet was implemented. The result showed that the die compensation method was effective and efficient. The chapter 3 is the key content that the paper studied .After reading a paper about contact judging written by Wang Yu, ‘R-coordinate & S-coordinate mapping method’and the ‘triangle coordinate mapping method’applied to the question about the die compensation. A new method about surface mapping was presented here. For compensating the surface of the die, every tool’s node normal is computed firstly. Along the direction of the normal, we find the correct mapping mesh element on the sheet mental after stamping, and then get the coordinate of the mapping point. According to the relation of the mapping and coordinates of the nodes in the mapping mesh element, the spring-back value of the mapping point can be computed. Thus, we can modify every node on the tool .The program flow chart of this method was also given. At the end of this chapter, three examples was presented to prove this method. In the chapter 4, Reverse Engineering was introduced. Because the die compensation based on the numerical simulation is described by some discrete digital model. The discrete CAE model of the die geometry should be transferred into its CAD model. The discrete CAE model was written as point cloud format. The transformation from CAE to CAD was finished by employing CATIA. The last chapter of the paper just discussed parts of knowledge about surface fitting. Although the transformation from CAE to CAD can be finished by surface reversing, we are excepting a more effective method to

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