| With the issue of energy and environment becoming increasingly acute, theautomobile manufacturers are focusing on developing lightweight vehicles to improvetheir market shares. One of the major tasks in the development of lightweight vehicle is todevelop lightweight auto body panels. Aluminum alloy sheet has been applied to produceauto body panel because of its high strength and low specific gravity. However, aluminumalloy sheet is more difficult to form than steel sheet due to its lower plasticity. It isnecessary to adopt warm forming process together with suitable lubricants to formaluminum alloy sheet. The warm forming process of aluminum alloy sheet is influencedby many factors, such as formability, process parameters, die structure, lubrication andfriction status, etc. So far, the warm forming process of aluminum alloy sheet is still a newtechnology, which needs further investigation. Supported by Technology Consortium ofGM and Chinese Institutes for Materials and Tribology, the author has studied keytechnologies in aluminum alloy sheet warm forming in both theoretical and experimentalapproach, and developed a program for aluminum sheet forming simulation, which lay thefoundation for optimizing the stamping process and die design. The mechanical behavior is a crucial factor that influences the aluminum alloy sheetwarm forming process. In the dissertation, Hill's yield function and the correspondinganisotropy constitutive equation are discussed. And a new three-dimensional anisotropyelasto-plastic constitutive equation, which is applicable for aluminum alloy sheet, isderived based on the Karafillis yield condition. The correlation between temperature andflow stress of aluminum alloy sheet, and hardening as well, is identified. Based on the developed three-dimensional anisotropy elasto-plastic constitutiverelationship, a finite element model for analysis of aluminum sheet forming process is setup by the author. Four-node degenerated shell elements are adopted to discretizealuminum sheet. The central difference method is used to discretize the time domain incomputation. An explicit computing algorithm is developed to avoid the convergenceproblem caused by strong nonlinear phenomena of geometry, material and contact. Thelumped mass matrix and lumped dumping matrix are used to uncouple the group ofsimultaneous equations. According to the characteristics of aluminum sheet forming, asearching algorithm and a force model are established to deal with the contact problem. The friction and lubrication status is a very important factor that influences the warmforming process of aluminum alloy sheet. Studying friction behaviors in aluminum alloysheet warm forming process, the author established the friction models of full filmlubrication and mixed lubrication according to the ratio between the film thickness and the IIIsurface roughness of die and sheet blank. The equations of friction coefficient that areused in the finite element analysis of aluminum alloy sheet forming are derived. In order to test and investigate the dynamic variation of friction in experimentalapproach, a direct tribotest method based on a new probe sensor is proposed, and an onlinetribotest system has been developed for aluminum alloy sheet warm forming process. Theexperimental results prove that the developed probe sensor and tribotest device, which laya good foundation for further study on tribological behavior and resolving the problems oftesting the friction variation during aluminum sheet warm forming process, have themerits of high sensitivity, good stability and convenient operation. Based on the developed experimental system, the formability of aluminum alloysheet 5182 in warm forming process is investigated, and online tribotests for forming oftypical aluminum alloy parts are conducted. The laws of friction coefficient variation withthe forming parameters are determined. The ex...
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