Offset Load Analysis And Topology Optimization For High-strength Steel Stamping Die

Lightweight is the inevitable trend of automobile industry development. Research resultsof automobile lightweight from main international projects, such as ULSAB-AVC, ABC andNBC, indicate that extensive use of high-strength steel (HSS) is an effective way for vehiclesto achieve mass reduction and improve safety performance. However, working conditions ofstamping die become even worse at the same time because of the much higher yield strengthand tensile strength of HSS. According to this situation, engineers usually tend to enlarge thesafety factor to guarantee the normal operation of stamping die, however, which increases theoverall weight of die directly and rises up the manufacturing costs and operation costsindirectly. In order to overcome the new challenge mentioned above, the main task of thisthesis, supported by the Advanced Technology Research&Development Program of theMinistry of Science and Technology, China (Grant#2007AA04Z130), is to develop a methodof die structure optimization, which is based on numerical simulation of sheet metal forming,die structure analysis and topology optimization of die structure, for the purpose of reducingthe weight of the tool. The binder is the only part of the step-like bottomed box drawing dieconsidered in the methodology generation. The proposed method can be applied to theanalysis and optimization of any other part of the drawing die analogously. The main contentand conclusion of this thesis show as following：The step-like bottomed box drawing die is selected as the research object to consider theoffset load for structure analysis and optimization of stamping die. A sensitivity analysis can not only clarify the use of wear plates, but also reveal the fundamental source of offset load.First of all, this research encounters a difficulty of obtaining the lateral contact forcebetween wear plates which respectively belong to punch and binder from traditional rigidtooling-plastic sheet metal FE model of sheet metal forming simulation. A partial elastictooling-plastic sheet metal FE model of sheet metal forming simulation is established byLS-DYNA to solve the problem and its effectiveness is checked by practice.The node loads, extracted from forming simulation, are applied to the structural analysisFE model of binder by load mapping method. A creative approach is to deal with the complexcontact problem by boundary conditions of force, which avoids a long process of iterativecalculation. On the basis of the structural analysis results, a depth analysis of the forcecharacteristics for binder during drawing process and the impact of lateral contact force onbinder is done. Up to now, the preliminary work for topology optimization of binder isaccomplished.Based on above research, a FE model, which considers multiple key steps of loads toobtain a more global optimization result, is founded for topology optimization of binder. Thestructural optimization solver—OptiStruct is used to solve the problem. After iterativecalculation, the initial result of topology optimization for binder will be re-designed by NX.Final optimized binder shows a weight reduction of about28%with little performancedegradation. In addition, a comparison of the topology optimization result for binder betweenconsidering and not considering lateral contact force shows the importance of lateral contactforce to binder optimization.Finally, the equivalent stress curves of the key points on original and optimized binderare obtained through the experiment of strain-stress measurement. Although the simulationresults show a certain degree of fluctuation in the comparison with experimental results, theirtrends are consistent to the experimental results. And this firmly proves the reliability of theproposed simulation method. Additionally, the result of topology optimization reaches the initial design target, which is confirmed when comparing the experimental results of originaland optimized binder.In this thesis, innovative points are：（1）obtaining the lateral contact force betweendifferent parts of die through the partial elastic tooling-plastic sheet metal FE model of sheetmetal forming simulation；（2）dealing with the complex contact problem by boundaryconditions of force, which depends on the load mapping method in structural analysis ofstamping die；（3）considering the multiple key steps of loads, in structural topologyoptimization of stamping die, to obtain a more global optimization result.