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Currently, more and more tailor-welded blanks (TWBs) are used in the automobile industry. It is very important to locate the weld line and predict its movement during the forming process. The initial weld line can be predicted by one-step finite-element analysis according to the desired weld line in the final workpiece. Meanwhile, weld line movement during the deformation process can be evaluated in advance. In this paper, the procedures of finite-element analysis of one-step FEM with TWBs are established. The contact between tool and blank and the effect of restraining forces under the blankholder due to drawbead and blankholder pressure are considered as well. Forming limit diagram (FLD) is used to show not only the tendency of reduction in thickness and fracture but also of increase in thickness and wrinkle. Hydraulic controlled pads used to clamp the weld line during the deep drawing process are simplified as static external force to eliminate the movement of the weld line. In order to speed up and ensure the convergence of Newton-Raphson iterations, energy-based 3D mesh mapping algorithm is introduced to obtain the initial solution. The above-mentioned methods have been implemented in the authors’ in-house one-step FEM code InverStamp. A rectangular cup drawing case demonstrates that this approach can be easily implemented to evaluate weld line movement and develop initial blank in sheet metal stamping with tailor-welded blanks. [ABSTRACT FROM AUTHOR]

Drucker's sixth-order yield function for isotropic materials (J Appl Mech 16:349–357, 1949) was extended by Cazacu and Barlat (Math Mech Solids 6:613–630, 2001) for modeling orthotropic sheet metals via a generalization of the two stress invariants according to the theory of representation. The constant c in the original Drucker's isotropic yield function was found by Dodd and Naruse (Int J Mech Sci 31:511–519, 1989) to be bound between –27/8 and 9/4 per the convexity requirement. In many subsequent modeling applications of orthotropic sheets, the same bound is also tacitly assumed for the constant c used in this class of the generalized Drucker's yield function CB2001. No actual proof has, however, been presented in the literature that such a bound is indeed absolutely necessary if not sufficient to guarantee the convexity of the orthotropic CB2001 yield function. In this study, the validity of assuming such a convexity bound on the adjustable constant c is examined using a recently proposed numerical convexity certification algorithm. Representative orthotropic CB2001 yield functions whose material parameters have been calibrated and reported in the literature for some 12 FCC, BCC, and HCP sheet metals are evaluated. It is found that a single convexity bound between - 27 / 8 and 9/4 on the constant c does not hold at all for any of those yield functions. This is in contrast to another class of generalized Drucker's yield function based on linearly transformed stresses where the original convexity bound on the constant c does still hold. [ABSTRACT FROM AUTHOR]

There are some problems in the CNC incremental forming with the sheet metal part containing vertical wall, such as excessive thinning and easy fracture. A new CNC incremental forming method was proposed based on the feature recognition for the multidirectional adjustment of the sheet metal posture. According to the feature recognition, the multi-feature of the sheet metal part was decomposed into a number of the forming feature units according to the size and distribution of the forming angles, so that the forming angles of the surface are less than the forming limit angle. The feature recognition and forming feature unit generation algorithm, sheet posture control method, and sheet posture surface generation algorithm were studied, and the finite element analysis and the forming experiments based on the proposed algorithms were also presented. The research results show that the proposed method can change the sheet metal posture in real time during the CNC incremental forming process and realize the non-rupture forming with the large forming angle parts such as vertical wall parts. [ABSTRACT FROM AUTHOR]