Authors: Hyoung Wook Lee, Geun An Lee, Duk Jae Yoon, Seo Gou Choi, Nak Kyu Lee, Hye Jin Lee, Sung Min Bae

Abstract: A micro-alloyed non-heat-treated material does not need post heat treatment processes such as quenching and tempering after the forming process in production stages. This material can be called a green material since it can reduce industrial costs and harmful pollutants generated from post heat treatments. In this paper, near-net-shape forming processes were studied in order to make an
automotive part using a micro-alloyed material. The cold forging technique using a former was utilized for the main shaping, and the cold incremental forming technique using a cross wedge rolling machine was adopted for the enhancement of strength and the final shaping of the part. In order to get more adequate process, the cross wedge rolling process is compared to the swaging process for the
micro-alloyed steel and general carbon steels through experiments.

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Authors: Teresa Primo, Gabriele Papadia, Antonio del Prete

Abstract: The authors have investigated, in other paper, the problem related to the definition of a “set of shape factors” in order to declare the feasibility of a product through sheet hydroforming. In particular the defined shape factors are three different a-dimensional coefficients by which it is possible to declare the feasibility of a product through the calculation, in different sections, of the three previous shape factors. The robustness of this methodology is related to the correct calculation of the “limit value” of each shape factor. In fact the feasibility is reached if, in any section, the calculated shape factors are higher than their respective limit values. In this paper the authors have performed an extensive numerical and experimental campaign, taking into account a different geometry respect to that of the first paper, in order to: re-calculate the limit value for each shape factor and, then, verify the correctness of the limit values exposed in the previous first paper. The numerical campaign has been used, after the evaluation of the accuracy of the numerical model, in order to study the feasibility of the product without engaging the hydroforming machine. Finite Element Analysis (FEA) has been extensively used in order to investigate and define each shape factor with a proper comparison to the macro feasibility of the chosen component geometry. The limit values that have been calculated by the authors in this paper are slightly different from those calculated in the first paper. From this point of view it is possible that, although the shape factors are a-dimensional coefficients, they are affected by different choices of the users as, for example, the dimensions of the initial blank. Anyway, the small differences in the shape factors limit values do not adversely affect the use of the shape factors in order to predict the feasibility of the product.

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Authors: Abdelkhalak El Hami, Bouchaib Radi

Abstract: In this paper, an original method is presented for evaluating the probability of failure in a precise manner in the tube hydroforming process (THP). This process consists to apply an inner pressure combined to an axial displacement to manufacture the part. During the manufacturing phase, inappropriate choice of the load paths can lead to failure. Our approach is to determine the space failure probability for each item in the area is critical. It is defined by identifying the critical element, and then a patch is defined on this item that represents the area of the most probable failure. The identification of the critical element for each failure mode is done by reference the state of strain on the forming limit curve (FLC) of the material. Access to the probability of space failure allows to give an idea on the stability of the process and also to predict the most likely area where plastic instability can appear. The failure probability estimation based on a characterization probabilistic principal strains (major and minor) for each failure mode and for each element. Access to this probability of failure in a direct manner is impossible given the complexity of the treated problem and the huge number of calculations by finite elements necessary. To compensate for this problem, approximation techniques have been used to replace the real model by metamodel that enables to evaluate the response quickly and allows us to get an idea on the stability of the process.Keywords: Hydroforming process, metamodels, random, forming limit curve (FLC), failure mode, finite element.

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