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2．外文资料原文（与课题相关，至少1万印刷符号以上）：
Abstract: A VBHF (Variable Blank Holder Force) optimization strategy was employed to determine the optimal time-variable and spatial-variable BHF trajectories, aiming at improving the formability of automobile panels with aluminum alloy sheet. The strategy was implemented based on adaptive simulation to calculate the critical wrinkling BHF for each segmented binder of the Numisheet’05 deck lid in a single round of simulation. The thickness comparison of the stamped part under optimal VBHF and constant BHF shows that the variance of the four sections is decreased by 70%, 44%, 64% and 61%, respectively, which indicates significant improvement in thickness distribution and variation control. The investigation through strain path comparison reveals the fundamental reason of formability improvement. The study proves the applicability of the new VBHF optimization strategy to complex parts with aluminum alloy sheet.
Key words: deep drawing; variable blank holder force; aluminum alloy sheet; formability
1    Introduction
Wrinkling and cracking are two key surface issues for deep drawing parts, besides which there are other product quality requirements including uniform thickness, strain distortion, springback, etc. Engineers and researchers would normally try to regulate one or several of the process parameters such as initial blank contour, friction condition, drawbead resistance and blank holder force (BHF, FBH)[1 4] to achieve successful  drawing parts free of above defects.
In terms of BHF regulation, time-variable and spatial-variable BHFs occur in industrial deep drawing process, but typically not in an optimal manner[5]. Researchers started to build system for improving the application of variable blank holder force (VBHF) to reduce the work load associating with die surface grinding and cushion shimming. The first system established by HARDT and LEE[6] was designed to maintain a constant amount of buckling in unsupported region of the part. This work was continued by HARDT
and FENN[7], who employed closed-loop control of sheet forming operation to determine optimal BHF trajectories. SIEGERT[8] designed a blank holder made up of rigid segmented sections, providing independent control over the material. 深变压边力的优化英文文献和中文翻译(4):http://www.youerw.com/fanyi/lunwen_48238.html