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Article Dans Une Revue Modelling and Simulation in Materials Science and Engineering Année : 2001

Thermal stresses and distortion in dies of die casting processes: a new normalized approach

Résumé

A general approach to thermal stresses in die casting dies has been attempted with a simple slab geometry. The approach consists of finding the proper normalization parameters, which enables one to summarize the thermal and thermo-elastic equations into a single expression whatever the variables, such as the thermal conductivity of the die, its Young's modulus, its expansion coefficient, its thickness, the maximum heat flux density transferred through the moulding surface and the duration of this maximum heat transfer. Provided that the heat flux density entering the die can be seen as a square function of maximum phi (max) and duration tau, corresponding to the time spent between filling the cavity and the air gap formation, the evolution of the normalized thermal stresses on the moulding surface versus the normalized time can then be summarized with one single figure, instead of a chart of curves. This shows that the heat flux density is a parameter for the thermal stress problems, which replaces the more classical pair (heat transfer coefficient and temperature difference). The same trend applies for the evolution of the normalized distortion of the die (expressed in terms of a radius of curvature). These two curves follow a reference curve that was obtained from a step function from zero to the maximum heat transfer. The duration tau appears to be the key process parameter, along with the heat flux density, that controls the normalized maximum stresses and temperature. In contrast, the heat transfer coefficient at the rear surface has an insignificant influence on the maximum temperature and stresses. In a complex shaped die the key parameter varies from one location to another. Therefore a sensitivity study has been performed from high-pressure die casting data. The sensitivities are at their highest when the duration tau is short. It is possible for the stress sensitivity to reach zero. The temperature sensitivity then tends towards a low asymptotic value. These conditions correspond to a situation where the heat wave has enough time to reach the rear face of the die. It illustrates the close interaction between the transient heat transfer and thermal stresses.
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Dates et versions

hal-01703127 , version 1 (07-02-2018)

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Citer

Gilles Dour. Thermal stresses and distortion in dies of die casting processes: a new normalized approach. Modelling and Simulation in Materials Science and Engineering, 2001, 9 (5), pp.399-413. ⟨10.1088/0965-0393/9/5/305⟩. ⟨hal-01703127⟩
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