Investigation On The Feasibility And Autobody Application Of Hot-Stamping Structures With Partial Pressing Hardening

In recent years, with the improvement of national living standards, the domesticautomobile productions, sales and ownership increased dramatically. At the same time,the problems of the frequent traffic accidents, exhaust pollution, energy shortageshave become increasingly serious. Energy conservation and emissions reduction onthe promise of ensure driving safety are the major issues to be solved. In passivesafety structure design, the arrangement that different position with different strengthcan guide the collision force transfer and reduce the occupant injury. Base on thearrangement, the parts that were manufactured by laser tailor-welded had been widelyused in autobody. Partial pressing hardening (PPH) process is one of the latestresearch directions in hot-stamping field. PPH process can product the part thatdifferent position with different mechanical properties (like the laser tailor-weldedstructures) in one process. The study on the feasibility of PPH process and applicationeffect for autobody lightweight design that promises passive safety requirement issignificant.First of all, the material subroutines for predicting damage and austenitedecomposition phase transition were built in finite element (FE) analysis programsbased on Jingqi Cai’s thermodynamics visco-plastic damage constitutive equationsand Akerstrom’s austenite decomposition numerical model respectively. Thereliability of the subroutines had been validated by comparing the experimental data.Then the damage and phase transition status of the hot-stamping blank were analysisby FE simulation. Summarizes the analysis result, reasonable temperature fieldarrangement could decompose austenite of the blank to required phase and makedifferent area of the part with different mechanical properties. Through the work mentioned above, the feasibility of PPH process was validated. And more work couldbe done base on the damage and austenite decomposition phase transition predictingsubroutine for FE analysis.Secondly, the characters of the structures with PPH process under three pointbending test and stretch bending test had been researched. In order to ensure theeffectiveness of the research, the reliability of the material properties for FEsimulation had been validated by comparing the experimental data primarily (The FEsimulation results on U-beam three point bending test were consistent with theexperimental results). Then the deformation pattern and energy absorption capacity ofthe PPH pipe with different hardened length were test under different load conditionsin three point bending test and stretch bending test with FE method. According to theresults, the deformation pattern may change when the PPH pipe with a reasonablehardened arrangement. Subsequently, the causes of deformation pattern changingwere analyzed. The structures with PPH process could absorb more energy understretch bending load (the structure with better toughness and much harder to break).The stability of energy absorption capacity of PPH structures (under stretch bendingload) change with hardened length. Only the reasonable hardened length can ensurethe stability of energy absorption capacity under different load conditions.Finally, on the basis of the above-mentioned research, a side impact FE analysishad been done for a complete vehicle with PPH B-pillar. The result shows that thereasonable hardening distribution and structure improvement will change thedeformation shape and reduce the intrusion of occupant reserve. Base on the methoddiscussed above, autobody lightweight design was realized (four parts were simplifiedto one part) under the premise of vehicle passive safety requirement.