| The objective of this research work in this thesis is to investigate the relative effects of important process parameters by using a computer simulation method and to develop a systematic approach for design of the process specifications for the sheet metal hydroforming process. Such an approach is through a development of a three dimensional finite element based process simulation model supported by experiments.; A finite element model based on an explicit nonlinear finite element code is developed including the three dimensional solid modeling of punch, blank and die in a hydroforming process and modeling of process parameters. The process parameters which are to be modeled are: part and punch geometry and its features, material behavior in terms of anisotropic hardening and strain hardening, friction between tool and workpiece, blank holding force path as function of punch displacement, hydroforming fluid pressure path as function of punch displacements, draw bead locations and shapes, and instability of the forming process defined in terms of wrinkling and tearing.; The parametric study for the identification of importance of process variables is conducted using the developed simulation tool. The effects of the process parameters include the different fluid pressure paths on the strain distribution the stress distribution, the punch load, the wall thickness distribution and other dimensional accuracy index in a drawn sheet metal. Also the critical fluid pressure path affected by the different drawing ratios, different material and material properties, different friction conditions, different punch profile radii, and different thickness of blank is investigated to serve the need in the design of those process specifications.; The Taguchi method is used to arrive at the optimal design specifications. The trial-and-error approach regulated by the Taguchi's orthogonal arrays provides the efficient way to find out the optimal working conditions avoiding the intensive finite element calculations. A case study is conducted in which a hydroforming process of an oil pan used in an automobile vehicle is analyzed and the design specification for hydroforming such a part is developed by using the simulation model. |
