Am Ad Goijaerts

Evaluation of ductile fracture models for different metals in blanking

This study is focussed on the evaluation of ductile fracture methodologies, which are needed to predict product shapes in the blanking process. In an earlier publication [Goijaerts et al., J. Manuf. Sci. Eng., Trans. ASME 122 (2000) 476], two approaches were elaborated using local ductile fracture models. The first strategy incorporates the characterisation of a ductile fracture model in a blanking experiment. The second methodology is more favourable for industry. In this approach, instead of a complex and elaborate blanking experiment, a tensile test is used to characterise a newly proposed criterion, which was shown to predict accurately the ductile fracture for different loading conditions. In this paper, finite element simulations and experiments are performed on both tensile testing and blanking to evaluate the validity of both approaches with corresponding criteria for five different metals. In the blanking process, different clearances as well as different cutting radii of the tools are considered. In conclusion, it can be stated that the first approach gives very good results close to, or within the experimental error for all five materials. The second approach, the more favourable one for industry, yields good results that deviate slightly more over the range of metals. # 2001 Published by Elsevier Science B.V.

Prediction of Ductile Fracture in Metal Blanking

This study is focused on the description of ductile fracture initiation, which is needed to predict product shapes in the blanking process. Two approaches are elaborated using a local ductile fracture model. According to literature, characterization of such a model should take place under loading conditions, comparable to the application. Therefore, the first approach incorporates the characterization of a ductile fracture model in a blanking experiment. The second approach is more favorable for industry. In this approach a tensile test is used to characterize the fracture model, instead of a complex and elaborate blanking experiment. Finite element simulations and blanking experiments are performed for five different clearances to validate both approaches. In conclusion it can be stated that for the investigated material, the first approach gives very good results within the experimental error. The second approach, the more favorable one for industry, yields results within 6 percent of the experiments over a wide, industrial range of clearances, when a newly proposed criterion is used.

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.

Experimental and Numerical Investigation on the Influence of Process Speed on the Blanking Process

In a previous work a numerical tool was presented which accurately predicted both process force and fracture initiation for blanking of a ferritic stainless steel in various blanking geometries. This approach was based on the finite element method, employing a rate-independent elasto-plastic constitutive model combined with a fracture criterion which accounts for the complete loading history. In the present investigation this work is extended with respect to rate-dependence by employing an elasto-viscoplastic constitutive model in combination with the previously postulated fracture criterion for ferritic stainless steel. Numerical predictions are compared to experimental data over a large range of process speeds. The rate-dependence of the process force is significant and accurately captured by the numerical simulations at speeds ranging from 0.001 to 10 mm/s. Both experiments and numerical simulations show no influence of punch velocity on fracture initiation.