Dies in sheet metal forming simulation are commonly modeled as rigid, although they are elastic. The influence of elastic response in the dies can be split into two types, global and local deformation. Local deformation occurs where large pressure in the tool prevails typically in the die radii. A numerical study on local elastic tool deformation was performed. Three different blank materials and three tool materials were used. The geometry was from the FTF 2015 conference, triangle die. The blank was modeled with the same material model, and a simple failure criterion as a reference marker was introduced. An important result from the study was: The draw depth difference for the chosen evaluating condition between rigid tools and elastic tools was in the region 5–12.5% deeper using elastic tools.  

Friction is an important parameter in sheet metal forming since it influences the flow of material in the process. Consequently, it is also an important parameter in the design process of new stamping dies when numerical simulations are utilized. Today, the most commonly used friction model in forming simulations is Coulomb’s friction which is a strong simplification of the tribological system conditions and a contributory cause of discrepancy between simulation and physical experiments. There are micromechanical models available but with an inherent complexity that results in limited transparency for users. The objective in this study was to design a phenomenological friction model with a natural level of complexity when Coulomb’s friction is inadequate. The local friction model considers implicit properties of tool and sheet surface topography, lubricant viscosity, sheet metal hardness and strain, and process parameters such as sliding speed and contact pressure. The model was calibrated in a Bending-Under-Tension test (BUT) and the performance was evaluated in a cross shaped geometry (X-die). The results show a significant improvement of the simulation precision and provide the user a transparent tribological system. © Published under licence by IOP Publishing Ltd.

Manufacturing of components in aero engines requires attention to residual stress and final shape of the product in order to meet high quality product standards. This sets very high demands on involved manufacturing steps. The manufacturing of a V-shaped leading edge of a vane is simulated. It is made of Alloy718, which is a nickel based heat resistant material commonly used in aerospace components. The manufacturing process chain consists of forming, welding and heat treatment. The results show that the remaining residual stresses after a manufacturing process chain are affected when the residual history from the formingprocess is considered. The residual stress decrease after heat treatment is about 55-65%. Moreover, the von Mises stress profile through thickness at the centre of the radius at the weld joint is about 25% higher when full forming history is considered.

Friction is an important parameter to control in sheet metal forming since it influences the flow of material in the process. Consequently, it is also an important parameter in the design process of new stamping dies when numerical simulations are utilized. Today, the most commonly used friction model in forming simulations is Coulomb´s friction which is a strong simplification of the tribological system. In this work an advanced friction model is developed, which considers properties of tool and sheet surface topography (spatial and height), lubricant, sheet material, and process parameters such as sliding speed and contact pressure. The results show that the model can predict the frictional behavior over a wide range of influencing parameters. A regression analysis of model and experimental results, Bending-Under-Tension friction test, shows acorrelation of R2=0.89.

In order to be able to form high strength steels with low ductility, multi-step forming processes are becoming more common. Benchmark 4 of the NUMISHEET 2011 conference is an attempt to imitate such a process. A DP780 steel sheet with 1.4 mm thickness is considered. In order to understand the pre-strain effect on subsequent forming and springback, a 2D draw-bending is considered. Two cases are studied: one without prestrain and one with 8% pre-stretching. The draw-bending model is identical to the "U-bend" problem of the NUMISHEET'93 conference. The purpose of the benchmark problem is to evaluate the capability of modern FE-methods to simulate the forming and springback of these kinds of problems. The authors of this article have previously made exhaustive studies on material modeling in applications to sheet metal forming and springback problems, [1],[2],[3]. Models for kinematic hardening, anisotropic yield conditions, and elastic stiffness reduction have been investigated. Also procedures for material characterization have been studied. The material model that mainly has been used in the current study is based on the Banabic BBC2005 yield criterion, and a modified version of the Yoshida-Uemori model for cyclic hardening. This model, like a number of other models, has been implemented as User Subroutines in LS-DYNA. The effects of various aspects of material modeling will be demonstrated in connection to the current benchmark problems. The provided material data for the current benchmark problem are not complete in all respects. In order to be able to perform the current simulations, the authors have been forced to introduce a few additional assumptions. The effects of these assumptions will also be discussed. © 2011 American Institute of Physics.