Research On Constitutive Relationship And Heat Transfer Coefficient Of 6063 Aluminum Alloy In Thermoforming Process

With the continuous increase of car number,the problems of excessive energy consumption and serious environmental pollution is becoming more and more prominent.Automotive lightweight technology is an important way to solve these problems effectively.Aluminum alloy has the characteristics of high specific strength,good impact resistance and good corrosion resistance,it is an ideal material to achieve automotive lightweight.However,at room temperature,its plasticity is poor,and is difficult to form without cracking,poor surface quality and large rebound.These problems restricts the wide application of aluminum alloys in the automotive industry.The new Solution Heat treatment-Forming-cold die Quenching can solve the difficult problem of aluminum alloy forming at room temperature.In this paper,the high temperature constitutive equation,interfacial heat transfer coefficient between the hot plate and mold surface and the hot forming process of 6063 aluminum alloy were studied by the combination of experiment and simulation.It is of great significance to master the high temperature forming law,formulate scientific and reasonable stamping technology,promote the development of aluminum alloy hot stamping technology and automobile lightweight technology.The main research contents of the thesis are as follows:(1)The research status of constitutive relation and interfacial heat transfer coefficient in warm forming of aluminium alloy at home and abroad is analyzed and summarized.The basic theories of material constitutive relation and heat transfer involved in the research are summarized.(2)The fixture for high temperature uniaxial tensile test was designed and fabricated.The stress-strain curves of 6063-T5 aluminum alloy at different temperatures and strain rates were obtained by thermal uniaxial tensile test.The effects of temperature and strain rate on the mechanical properties of aluminum alloys were investigated.The viscoplastic constitutive equation of 6063 aluminum alloy was established by curve fitting method,and the constitutive equation was verified.(3)The experimental die for measuring the heat transfer coefficient between the hot stamping sheet and the die was designed and manufactured.The curves of the sheet and mold temperature vs time under the pressure load of 0.5Mpa,5MPa,10 MPa and 15 MPa were measured by experiments.The heat transfer coefficient of the sheet during the transfer process and the interface heat transfer coefficient between the sheet and the mold during the hot stamping process were calculated.The influence of pressure on the interface heat transfer coefficient of warm stamping process was studied.(4)The high temperature constitutive equation and interface heat transfer coefficient of 6063 aluminum alloy obtained in the experiment were applied to the finite element simulation of a B-column.The finite element simulation model was established,the finite element simulation and process parameter optimization of the automobile B-column hot stamping forming process were carried out by using ABAQUS software.The effects of sheet forming temperature,stamping speed and friction coefficient on the stamping process of the automobile B-pillar was studied,and the optimal forming process parameters were obtained.