J. Huetink

Thermal mechanically coupled finite element analysis in metalforming processes

A combined Eulerian-Lagrangian finite element formulation is presented for the analysis of metal-forming, coupled with thermal effects. The procedure developed involves incrementally solving a coupled set of equations for both the displacement and the temperature. The material properties may be temperature-dependent. The procedure has been applied to the upsetting and the wire-drawing process.

A Metamodel Based Optimisation Algorithm for Metal Forming Processes

Cost saving and product improvement have always been important goals in the metal forming industry. To achieve these goals, metal forming processes need to be optimised. During the last decades, simulation software based on the Finite Element Method (FEM) has significantly contributed to designing feasible processes more easily. More recently, the possibility of coupling FEM to mathematical optimisation algorithms is offering a very promising opportunity to design optimal metal forming processes instead of only feasible ones. However, which optimisation algorithm to use is still not clear. In this paper, an optimisation algorithm based on metamodelling techniques is proposed for optimising metal forming processes. The algorithm incorporates nonlinear FEM simulations which can be very time consuming to execute. As an illustration of its capabilities, the proposed algorithm is applied to optimise the internal pressure and axial feeding load paths of a hydroforming process. The product formed by the optimised process outperforms products produced by other, arbitrarily selected load paths. These results indicate the high potential of the proposed algorithm for optimising metal forming processes using time consuming FEM simulations.

The ALE-method with triangular elements: direct convection of integration point values

The arbitrary Lagrangian-Eulerian (ALE) finite element method is applied to the simulation of forming processes where material is highly deformed. Here, the split formulation is used: a Lagrangian step is done with an implicit finite element formulation, followed by an explicit (purely convective) Eulerian step. The purpose of this study is to investigate the Eulerian step for quadratic triangular elements. To solve the convection equation for integration point values, a new method inspired by Van Leer is constructed. The new method is based on direct convection of integration point values without intervention of nodal point values. The Molenkamp test and a so-called block test were executed to check the performance and stability of the convection scheme. From these tests it is concluded that the new convection scheme shows accurate results. The scheme is extended to an ALE-algorithm. An extrusion process was simulated to test the applicability of the scheme to engineering problems. It is concluded that direct convection of integration point values with the presented algorithm leads to accurate results and that it can be applied to ALE-simulations

A Mixed Eulerian-Lagrangian Finite Element Method For Simulation Of Thermo-Mechanical Forming Processes

A mixed Eulerian-Lagrangian finite element method has been developed to adapt nodal point locations independently from the actual material displacements.

Modelling of aluminium sheet forming at elevated temperatures

The formability of Al‐Mg sheet can be improved considerably, by increasing the temperature. By heating the sheet in areas with large shear strains, but cooling it on places where the risk of necking is high, the limiting drawing ratio can be increased to values above 2.5. At elevated temperatures, the mechanical response of the material becomes strain rate dependent. To accurately simulate warm forming of aluminium sheet, a material model is required that incorporates the temperature and strain‐rate dependency. In this paper simulations are presented of the deep drawing of a cylindrical cup, using shell elements. It is demonstrated that the familiar quadratic Hill yield function is not capable of describing the plastic deformation of aluminium. Hardening can be described successfully with a physically based material model for temperatures up to 200 °C. At higher temperatures and very low strain rates, the flow curve deviates significantly from the model.

Comparison of Artificial Dissipation and Limited Flux Schemes in Arbitrary Lagrangian Eulerian Finite Element Formulations

A comparison is made between Arbitrary Lagrangian-Eulerian (ALE) finite element formulations for simulation of forming processes based on an artificial dissipation scheme and a limited flux scheme. The first ALE algorithm is based on an averaging procedure used in post-processing of finite element calculations. The second ALE algorithm stems from a finite difference method for compressible fluid dynamics. Both approaches have complementary characteristics with respect to accuracy and implementation.

Flow front tracking in ALE/Eulerian formulation FEM simulations of aluminium extrusion

Even though Extrusion is often regarded as a semi stationary process, the defor- mations of the die at the beginning of the process can have great influence on the process later on. During filling of the die, the deformation of the die depends on the location of the flow front up to a point where parts of the profile will be opened or closed, especially in porthole dies. In this paper we present an accurate 2D method to simulate the filling of extrusion dies. The method is based on the pseudo concentration technique. We compare different options to model the pseudo material and choose the best.

Iterative springback compensation of NUMISHEET benchmark #1

Upon unloading after the forming stage, a sheet metal product will spring back due to internal stresses. Springback is a major problem for process-planning engineers. In industrial practise, deformations due to springback are compensated manually, by doing extensive measurements on prototype parts, and altering the tool geometry by hand. This is a time consuming and costly operation. In this paper the application of two compensation algorithms, based on the finite element simulation of the forming process are discussed. The smooth displacement adjustment (SDA) method and the springforward (SF) method have been applied to several industrial products, such as the NUMISHEET 2005 benchmark#1. With the SDA method successful compensations have been carried out. For the SF method some principal problems remain.

A mixed elastoplastic / rigid plastic material model

A new integration algorithm is described for large strain plastic deformations. The algorithm degenerates to the Euler forward elastoplastic{plastic model for small strain increments and to the rigid{plastic model for large strain increments. The model benets from the advantages of both models: accuracy and fast convergence over a large range of strain increments.

Stable incremental deformation of a strip to high strain

This paper presents the effect of combined stretching and bending on the achieved strain in incremental sheet forming ISF. A simple two dimensional model of strip undergoing stretching and travelling three point bending in cyclic form is used. The numerical model presents the effect of the ratio of stretching velocity to roll-set speed on the achieved strain and its distribution.