Abstract
To manufacture metal products of accurate size and shape by deep drawing requires the precise control of a number of variables. The problem of spring-back after the load has to be avoided, and the prevention of cracks in the product requires careful control of the punch load. In this study, where drawing experiments and simulations were carried out on thin sheets of SUS304 stainless steel, the influence of the scale effect on the thin sheets also needed consideration. This was accomplished by the use of an updated Lagrangian formulation and finite element analysis. Material behavior was simulated using a micro-elastoplastic material model, the performance of which was compared with that of models involving conventional materials. The Dynaform LS-DYNA solver was used for simulation analysis, and pre and postprocessing were carried out to obtain material deformation history as well as to determine thickness change, distribution and material stress, and prepare strain distribution maps. Scaling was necessary to account for the effect of the thickness of the sheet and the relationship between punch load and stroke, the distribution of thickness, stress and strain, and the maximum size (d) of the flanged hole and the maximum height of the flange. The simulation results were compared with experimental results to confirm the accuracy of the three-dimensional finite element analysis of the elastoplastic deformation. The results showed that the size of the fillet radius of the hole (Br) had an effect on the punch load, which increased with an increase in Br. However, the minimum thickness of the formed flange decreased with an increase in Br. The maximum principal stress/strain and height of the flange also increased with an increase in Br. The punch fillet radius (Rp) also had an impact on the process. The punch load decreased with the increase in Rp, while the minimum thickness increased slightly. The average values of the minimum thickness for three models were 0.148, 0.0775, and 0.0374 mm. The forming ratio also had an influence on the process. When the forming limit of the square hole flange was FLR = 0.84, cracking occurred in the corners of the flange, and wrinkles formed over the undrawn area of the sheet. These findings can serve as a valuable reference for the design of deep drawing processes.
Highlights
The miniaturization of metal forming processes is influenced by the scale effect, and the parameter control differs from that used in general metal forming
The results showed the higher drawability of the zircon sheet and fracture location could be predicted using a combination of finite element analysis and ductile fracture criteria
The 3D finite element analysis program used in this study draws from finite deformation theory for an updated Lagrangian formulation of incremental elastoplastic deformation
Summary
During the forming process, defects, such as fractures and excessive local thinning or wrinkling, may arise as a result of insufficient formability or incorrect parameter settings. Such defects may affect the precision and life of the workpiece as well as product yield. Surface roughness of the metal and friction during the forming process, as well as plastic flow stress and spring-back, are very important This makes accurate prediction and control of the parameters in micro forming processes very important [1,2,3,4]
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