Abstract ▼ AI-Helper

Tube hydroforming is recently drawing attention of automotive industries due to its several advantages over conventional methods. It can produce wide range of products such as sub-frames, engine cradles, and exhaust manifolds with cheaper production cost by reducing overall number of process. The tu...

Tube hydroforming is recently drawing attention of automotive industries due to its several advantages over conventional methods. It can produce wide range of products such as sub-frames, engine cradles, and exhaust manifolds with cheaper production cost by reducing overall number of process. The tube hydroforming process is based on the use of an internal pressure combined with axial load. Thus the material can be fed into the deformation zone during the hydroforming process allowing more expansion and less thinning so that parts with desired specifications can be formed without any defects. Depending on the defect type, forming limits of tube hydroforming can be categorized as wrinkling, buckling, and bursting. By contrast with buckling and wrinkling, bursting is an irrecoverable failure in hydroforming process. In order to evaluate the forming limit of hydroforming process in view of bursting failures, Oyane’ ductile fracture criterion is introduced in this study. By means of this criterion, the ductile fracture integral I is evaluated from analysis. Also it is shown that the material constants used in ductile fracture criterion can be determined by using forming limit diagram obtained from a series of bulge tests. The comparison with the experimental results has shown that the busting failure is successfully predicted by the combination of the finite element simulation with the ductile fracture criterion. Also, explicit and implicit FE simulation for bursting test are used to simulate hydroforming in many cases. Explicit FE simulation program does not include flow rule. And then it needs simulation for implicit method. It was simulated to compare the result of both hydrofoming FEA. A huge amount of computation time is necessary in explicit FEM because of the small time step to solve quasi-static forming problem in real time. Therefore when we use an explicit FEM form metal forming analysis, it is conventional to convert the real problem to virtual problem with a different time scale. Time scaling and mass scaling techniques have been widely used in order to save computation time. It is expected that this numerical approach developed here can be used as an effective method of the computer aided formability evaluation system for tube hydroforming.

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