D Dirk Brokken

Numerical modelling of the metal blanking process

Abstract Prediction of the properties of products of the blanking process is nowadays still mainly an empirical effort. The lack of fundamental knowledge of the process may cause lengthy process development, and obstructs process innovation. Consequently, a validated numerical model of the process would be of great value. In this paper, an elasto–plastic finite-element model will be introduced, in which the extremely large deformations occurring, are handled by an operator split arbitrary Langrange Euler (ALE) method combined with remeshing. Special attention is given to the convective part of the ALE formulation. Ductile fracture is incorporated by a discrete crack approach. To demonstrate the possibilities of the procedure, some simulation results are presented.

Predicting the shape of blanked products: a finite element approach

Abstract Prediction of the properties of products of the blanking process is nowadays still mainly an empirical effort. The lack of fundamental knowledge of the process may cause lengthy process development, and obstructs process innovation. Consequently, a validated numerical model of the process would be of great value. In this paper, an elasto-plastic finite element model will be introduced, in which the extremely large deformations which occur are handled by an operator split arbitrary Lagrange–Euler method combined with remeshing. Ductile fracture is incorporated by a discrete crack approach. To demonstrate the possibilities of the procedure, some simulation results are presented.

An experimental and numerical study of a planar blanking process

Abstract Aiming at a validated model of the blanking process, an in situ study of the displacement and strain fields is carried out in a blanking experiment using a digital image correlation technique. Specimens of 13% Cr steel, 1 mm thick, are blanked at low speed, using a planar configuration with two different clearances (2 and 10% of the specimen thickness). In addition to the displacement and strain fields, load–penetration curves are also determined for both clearances. The experimental results are in good agreement with numerical simulations, the latter of which are carried out using a plane-strain finite-element model based on an operator split arbitrary Lagrange Euler (OS-ALE) method.

Can a new experimental and numerical study improve metal blanking

Abstract Blanking is still commonly used in high volume production. Yet, since high-tech products are becoming smaller and smaller, product specifications are becoming more severe. This usually leads to lengthy trial and error in developing industrial blanking applications. The fact that the blanking process is not yet fully understood and that the process is based on empirical knowledge, leads to this trial and error. Therefore, industry needs a suitable model to help overcome the long cycle time in developing a particular blanking process. We developed a finite element model and validated it using a planar experimental set-up. We not only measured the punch load, but also the logarithmic strain-fields. Using digital image correlation, we measured the displacement fields, coupled with a second order method to calculate strain-fields. For both small and large clearances, we concluded that the numerical model describes the blanking process well, up to ductile fracture initiation. This validated model will be a good starting point from which we tackle the issue of ductile fracture in future research.

A two-dimensional paving mesh generator for triangles with controllable aspect ratio and quadrilaterals with high quality

Certain classes of problems result in solution fields of which the characteristic length scales vary with the orientation. Often the orientation of these length scales is related to the orientation of the boundaries. Such solution fields can be captured by the finite element method, using a mesh that is refined in the direction of the short length scales and coarse in the other directions. These meshes contain elements with high aspect ratios in a predefined pattern.The mesh generator presented here can render triangles with high aspect ratios through a paving algorithm. The paving algorithm that is employed applies both triangles and quadrilaterals, combining the advantages of both to render a qualitatively good, oriented triangular mesh, with a concentration of elements in the direction where the internal length scales of the solution field are the shortest.The mesh generator produces triangles with one (almost) orthogonal corner. When low aspect ratio triangles are generated, these are well suited for conversion to quadrilateral elements. Test results indicate that quadrilateral meshes converted from the mesh generator introduced here have a considerably better quality than those converted from several other triangular mesh generators.