The automatic optimization of metal forming processes: Inverse identification of constitutive parameters for tubular materials based on hydraulic bulge test

Abstract

Tube hydroforming process is an advanced manufacturing technology for complex thin-walled tubular components applied in the aerospace, aviation and automotive industries. The fluid medium is used as a pressure source to deform tubular materials into the desired shape in this process. Finite element model is a popular method to describe and analyze this innovative process. A successful tube hydroforming operation and reliable finite element simulation depend heavily on the accurate characterization of mechanical properties of the incoming tubular materials. As a result, it is critical to determine these material parameters utilizing suitable experimental tests and evaluation procedures.This thesis presents the development of an automatic inverse parameter identification framework combining finite element models with gradientbased algorithms and its utilization in determining material parameters for thin-walled metallic tubes. The main principle of the inverse framework is the minimization of the objective function defined as the least square error between simulated results and experimental observations. Finite element methods are used to describe and analyze the experimental testing process and gradient-based optimization techniques adjust the input material parameters in the model until the calculated results have a good agreement with the experimental measurements.The feasibility and performance of this proposed inverse framework are demonstrated through applying it to different tube hydraulic bulge tests with fixed and forced end-conditions to identify the flow stress data of thin-walled aluminium tubes. The bulge height, axial compressive force and pole thickness are measured during the experiment and input into the inverse strategy. Based on the obtained material values, finite element simulated models of hydroforming processes are established and used to predict the shape properties of final products. The comparison between simulated predictions and experimental data shows that the developed inverse strategy provide a robust and effective method to determine material properties for thin-walled metallic tubes.Furthermore, a theoretical analysis is integrated into the inverse frameiii work, and the two are recombined into a hybrid strategy to avoid local minimums in the parameter identification process. The new strategy is tested by the experimental data from fixed and forced tube hydraulic bulge tests. As a result of this research, it is possible to conclude that the novel hybrid strategy does not depend heavily on the initial points and can improve the computation robustness and identify more accurate constitutive parameters for tubular materials.