The Numerical Simulation And Technology Optimization Of The Stamping Forming Of Automotive Lightweight Steel And Springback Characteristics

The worldwide automotive industry had been faced with three key problems in recent ten years: energy, social effects of pollution and safety. The energy problem is very critical and has become the power of development and innovation for automotive industry. The auto lightweight technology is an important instrumentality for the economization of gas-consuming. Therefore, producing this kind of economical vehicle becomes the main method to compete during different countries'automotive industries.The application of automotive lightweight material is an important aspect of auto motive lightweight technology. Along with the application of lightweight material, some technical problems such as"new technology, new material, and new characteristic"have increasingly caused more and more attention. The new technology means the Tailor-Welded Blanks (TWBs) technology, the new material means the High-strength steel blank(Hss), and the new characteristic means spring-back characteristics of different materials. Research on the material characteristic and process optimization of automotive lightweight steel does have really practical effects and is very useful to the stamping forming and die design of auto-body panel.Supported by the Key Project of the National Natural Science Foundation of China (No.19832020), the National Outstanding Youth Foundation (No. 10125208) and the Project 985-Automotive Engineering of Jilin University,"The Numerical Simulation and Technology optimization of the Stamping Forming of Automotive Lightweight Steel and Spring-back characteristics"is its core content. By using FEM sheet forming analysis system KMAS to make the numerical simulation of TWBs, Hss and springback prediction and compensation, we did a thorough research on the numerical simulation of the forming process in this paper.During the process of TWB forming, there are many factors having effect on the formability of TWBs. The thickness ratio, the different mechanical property combination and the weld line position which play important roles in this process have been studied in this paper. In order to fulfill the study efficiently, the square box model is applied in this study and the criterions to evaluate the formability of TWB is also presented. The automotive front inner door is a typical tailor-welded part, in this paper; we simulated the forming process of this part. Besides, in order to controll welded movement we also adjusted the blank flowing resistance of the drawbeads. After our technical optimization, the formability of the part has been greatly improved. Through the contrast of the simulation result between KMAS and DYNAFORM, we can verify the validity of our technology optimization.The forming difficulty of high-strength steel blank is its low n-value (Strain hardening index) and poor forming capability. We took phosphorated high-strength steel plate B250P1 as our research object. By using the method of stain grid analysis we drew up the FLD (forming limit diagram) of this material and contrasted it with mild steel St14 on formability influence of material yield strength, strain hardening index and r-value(the coefficient of normal anisotropy). The author proposed multi-stages forming and pad equipment in stamp forming,and suggested applying these optimization schemes to the forming simulation of a vehicle pipe bracket. According to contrast between the simulation result and experiment result, we can verify the accuracy of numerical simulation and the validity of technology optimization.One of NUMISHEET 2005 BENCHMARK test is spring-back prediction of decklid inner panel. The decklid inner panel's spring-back test required participator complete a series of tests: Total upper die force (kN) vs. binder travel for full model during forming; Blank draw-in (mm) after forming at 7 Sections; True major strain on top surface, true minor strain on top surface, and thickness (not strain) at elements closest to the specified points on 4 Sections; Springback measurement at 20 points. The author compared result between experiment and FEM software simulation: KMAS, Autoform and DYNAFORM. The author analyzed the veracity of FEM simulation techniques and the reason that causes such errors. In addition, the author pointed out the insufficiency of simulation technology and provided the development goal for the improvement of the numerical simulation technology.In this paper, a tool surface compensation algorithm based on numerical simulation technique of springback process is proposed in which the independently developed dynamic explicit springback algorithm (DESA) is used to simulate springback amount. When doing the tool surface compensation, the springback amount of the projected point can be obtained by interpolation of the springback amount of the projected element nodes. So the modified values of tool surface can be calculated reversely. After repeating the springback and compensation calculations for 1~3 times, the reasonable tool surface mesh is gained. Finally, the FEM data on the compensated tool surface is fitted into the surface by CAD modeling software. The examination of a real industrial part shows the validity of present method.