Simulation Studies On The Formability Of AA7075in Hot Stamping And Cold Die Quenching Process

With the improvement of people’s living standards, the production and sales of vehicleshas increased quickly, making it very convenient for people to travel. But what follows theheavy traffic is the global shortage of oil resources, serious environment pollution, thegreenhouse effect, frequent traffic accidents and so on. Energy consumption andenvironment pollution can be decreased much by reducing the weight of the car, of whichabout30%~40%is the body. So the reduction of the autobody weight plays an important rolein the lightweight of automobile. Currently, there are three ways to lighten the car body: Thefirst way is to use lightweight materials; The second way is to develop new methods tochange the traditional forming technology; The last one is to use the finite elementsimulation technology to optimize the design of the body structure. However, each of thesethree methods is difficult to get an optimal lightweight design in the premise of ensuring thevehicle performance. The best way to optimal lightweight design is to combine these threemethods and to design according to needs.7075aluminum alloy has low density, highspecific strength and specific stiffness, and high energy absorption characteristics in theprocess of collision. If the material of AA7075is used to the car, lighter car body as well asthe same mechanical property can be obtained. However, aluminum alloy used in the carnow is mostly castings, such as the engine while it is rare for the use of aluminum alloy tothe car body. This is because the aluminum alloy sheet has a very bad forming faculty at theroom temperature and it is too difficult to form the complex body structure under thetraditional way.In this paper, a new forming process was applied to form the aluminum alloy sheetwhich is the hot forming and cold die quenching process. Aluminum alloy sheet can beformed successfully by this forming process. And the main contents of this paper are as follows:1. the damage mechanics and ways of heat transfer were introduced simply, and avery important conception (damage variable) was brought forward.2. the macro and micromechanical in the hot process was analyzed, and a group of viscoplastic continuum damageconstitutive equations which is related to the7075aluminum alloy was presented.Twenty-one material parameters were obtained which are in the constitutive equations byusing multi-objective genetic optimization algorithm and to optimize the parameters in thedamage equations by using the Matlab and Isight through the analysis of the trend ofstress-strain curve.3. the constitutive equation was programmed into the subroutine, and theuniaxial tensile model to validate these constitutive equation was established. B-pillar waschosen as the model and it was geometrically processed and meshed by Hypermesh. Thenthe boundary conditions and load were set up and the case was imported into the Ls-Dynafor finite element simulation analysis.4. the effects of different forming process parameters(the sheet temperature, the punching speed, the die temperature, the holder force, the frictioncoefficient) on the damage parameter were analyzed. In order to save the cost of computing,the orthogonal experiment method was used to analyze the size of the poor formingparameters and the influence of the five forming parameters on the biggest damage of theformed sheets are: A (sheet temperature)> E (punching speed)> C (friction coefficient)> D(holder force)> B (die temperature). And a set of optimal forming process parameters wereobtained which can provide direction for practical production.