Simulation Study On Galling And Spring-back Defects Of Automobiles Parts With Advanced High Strength Steel Sheets

Advanced High Strength Steels sheet(AHSSs) are widely used due to the rapid development of automobile industry. However, to produce automotive parts with advanced high strength steel by sheet metal forming technology, because of its unique properties (high strength, low ductility)many defects are observed, such as galling and spring-back, which resulted in a large number of discarded products, and reduced the life of the die.In the process of stamping of advanced high strength steel parts, sheet metal and die (geometric structure, materials, mechanical properties and surface morphology, etc.), and the forming process (stamping press, punch speed and lubrication, etc.) and other factors, the influence on galling of parts surface and spring-back is very complicated. To analyze the mechanism and control measures of galling and spring-back, theoretical analysis are used, and the establishment of appropriate evaluation criteria, using the method of finite element analysis, the factors and the location of the galling and spring-back phenomenon are analyzed and forecasted.(1) The mechanism and influence factors of the galling and spring-back are analyzed and researched, the evaluation criteria were also established according to the main factors, the final simulation results of the study shows that the evaluation criteria are reasonable.(2) The typical forming process of automobile panels and structural members are analyzed, the model of benchmark4in international conference and workshop on numerical simulation of3D sheet metal forming process (NUMISHEET2011)was set as a reference, a U-shaped channel forming model was built at last, to study the galling and spring-back of dual-phase steel DP780after stamping.(3) During investigating the galling on the surface of forming parts, the dynamic explicit elastic plastic program-Abaqus/Explicit in commercial finite element code Abaqus6.10had been used, and MATLAB numerical calculation method was used to analyze the history and field outputs of numerical simulation, got the key in stamping factors--contact pressure and sliding distance on the effects of galling,the results shows that galling always developed in the starting position of the die fillet, with the increase of the punching stroke, the contact pressure tend towards stability; towards circular fillet, with the radius increasing, limit contact pressure gradually decreases. U-shaped channel forming die and forming process had been optimized according to the results of the analysis, the process scheme which can reduce the galling on forming surface are got.(4) On the spring-back of U-shaped channel forming,DYNAFORM5.6was used to analyze spring-back quality, comparative analysis was made to check the spring-back with and without pre-strain applied to the blank. The law of blank holder force and sheet thickness on the spring-back were also researched; due to the pre-strain on the blank material, the spring-back on U-shaped channel increases. When the blank holder force increases,which can significantly reduce the spring-back amounts. The impacts of blank thickness on the spring-back are smaller than blank holder force.