Mats Sigvant

Material Characterization and Modeling for Industrial Sheet Forming Simulations

In the present paper a project carried out at Volvo Cars Corp. and Chalmers University of Technology, with the purpose of improving material characterization and modeling for sheet forming simulation, is described. One of the primary targets has been to identify a material testing procedure, which is capable of providing effective stress‐strain data at considerably larger strains than what can be achieved in a standard uniaxial tensile test. Another objective has been to advance from the common Hill ’48 material model to a more flexible one, and, furthermore, to identify suitable test procedures for determining the parameters of such a model. A third objective has been to find practical examples, in which the importance of a careful material modeling can be clearly demonstrated.

On The Influence Of The Yield Locus Shape In The Simulation Of Sheet Stretch Forming

In the present paper results from an ongoing project at Volvo Cars and Chalmers University will be presented. The object of this project is to reduce the gap between the research frontier and the industrial practice concerning material modeling. One of the targets of the project is to identify a yield function, which can fulfill the special industrial demands concerning accuracy, easy parameter identification, and computational efficiency. Lately, some new yield functions have been presented, which seem to satisfy these demands. These yield functions belong to a group of non‐quadratic yield criteria, sometimes referred to as “the Hosford family”. These criteria are characterized by a stress exponent, which has been shown to have a strong coupling to the crystallographic structure of the material. The present paper addresses the issue of how the main parameters controlling the shape of the yield locus are influencing the material flow in sheet forming simulations. Since it is a well established fact that t...

On The Prediction Of Plastic Instability In Metal Sheets

The current report presents some results from a study on the prediction of necking failure in ductile metal sheets. In particular methods for creating Forming Limit Curves (FLCs) are discussed in the present report. Three groups of methods are treated: Experimental methods, Theoretical/analytical methods, and the Finite Element Method (FEM). The various methods are applied to two different materials: An aluminum alloy and a high strength steel. These materials do both exhibit a distinct necking behavior before fracture, and they do both exhibit only a small strain rate dependence. As can be expected, the resulting FLCs from the various experimental, theoretical, and numerical methods show a substantial scatter. The reasons for these deviating results are analyzed, and some conclusions are drawn regarding the applicability of the different methods.

Including die and press deformations in sheet metal forming simulations

Structural analysis, in Abaqus, of a stamping die and subsequent morphing of the tool surfaces in AutoForm were performed to improve a sheet metal forming simulation. First, the tool surfaces of the XC90 rear door inner were scanned. They were not matching when the die was unloaded and could therefore not give any satisfying results in sheet metal forming simulations. Scanned surface geometries were then added to a structural FE-model of the complete stamping die and some influential parts of the production press. The structural FE- model was analysed with Abaqus to obtain the structural deformations of the die. The calculated surface shapes were then transferred to AutoForm where a forming simulation was performed. Results from the different sheet metal forming simulations were compared to measured draw in curves and showed a substantial increase in accuracy and ability to analyse dies in running production when the morphed surfaces were used.

Friction and lubrication modeling in sheet metal forming simulations of a Volvo XC90 inner door

The quality of sheet metal formed parts is strongly dependent on the tribology, friction and lubrication conditions that are acting in the actual production process. Although friction is of key importance, it is currently not considered in detail in stamping simulations. This paper presents a selection of results considering friction and lubrication modeling in sheet metal forming simulations of the Volvo XC90 right rear door inner. For this purpose, the TriboForm software is used in combination with the AutoForm software. Validation of the simulation results is performed using door inner parts taken from the press line in a full-scale production run. The results demonstrate the improved prediction accuracy of stamping simulations by accounting for accurate friction and lubrication conditions, and the strong influence of friction conditions on both the part quality and the overall production stability.

Characterizing the Elastic Behaviour of a Press Table through Topology Optimization

Sheet metal forming in the car industry is a highly competitive area. The use of digital techniques and numerical methods are therefore of high interest for reduced costs and lead times. One method for reducing the try-out phase is virtual rework of die surfaces. The virtual rework is based on Finite Element (FE) simulations and can reduce and support manual rework. The elastic behaviour of dies and presses must be represented in a reliable way in FE-models to be able to perform virtual rework. CAD-models exists for nearly all dies today, but not for press lines. A full geometrical representation of presses will also yield very large FE- models. This paper will discuss and demonstrate a strategy for measuring and characterizing a press table for inclusion in FE-models. The measurements of the elastic press deformations is carried out with force transducers and an ARAMIS 3D optical measurement system. The press table is then inverse modelled by topology optimization using the recorded results as boundary conditions. Finally, the press table is coupled with a FE-model of a die to demonstrate its influence on the deformations. This indicates the importance of having a reliable representation of the press deformations during virtual rework.

FE‐Simulation Of Hemming In The Automotive Industry

This paper summarizes and presents the most important results from a research project on FE simulation of hemming carried out at Volvo Cars Body Components and Chalmers University of Technology. In the automotive industry, hemming is used to join two sheet metal panels by bending the flange of the outer panel over the inner one. The final goal of the project was to simulate all of the hemming steps of production parts. In order to make three‐dimensional simulations of hemming possible within reasonable simulation times, it is necessary to use shell elements and not solid elements. On the other hand, the radius of curvature of the outer part in the folded area is very small, normally of the same order of magnitude as the sheet thickness. This fact raises the question if shell elements are applicable in FE simulation of hemming. One part of the project was therefore a thorough investigation of the order of magnitude of the errors resulting from the use of shell elements in FE simulation of hemming. Another part of the project was devoted to three‐dimensional simulations of the hemming of an automotive hood. The influence on the roll‐in from several parameters, such as shell element formulation, adhesives, and anisotropy was studied. Finally, results from a forming simulation were also mapped to the flanging and hemming models in order to study the influence from the stamping of the outer panel on the roll‐in.