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Research Papers: Heat Transfer in Manufacturing

A Microscopic Approach to Determine Electrothermal Contact Conditions During Resistance Spot Welding Process

[+] Author and Article Information
P. Rogeon1

Laboratoire d'Études Thermiques Energétiques et Environnement, Université de Bretagne Sud, rue de Saint-Maudé, BP 92116, 56321 Lorient Cedex, Francephilippe.rogeon@univ-ubs.fr

R. Raoelison, P. Carre

Laboratoire d'Études Thermiques Energétiques et Environnement, Université de Bretagne Sud, rue de Saint-Maudé, BP 92116, 56321 Lorient Cedex, France

F. Dechalotte

PSA Peugeot Citroën, Centre Technique de Vélizy, Route de Gisy, 78943 Vélizy Villacoublay Cedex, France

1

Corresponding author.

J. Heat Transfer 131(2), 022101 (Dec 29, 2008) (11 pages) doi:10.1115/1.3000596 History: Received February 09, 2008; Revised September 08, 2008; Published December 29, 2008

This study deals with resistance spot welding process modeling. Particular attention must be paid to the interfacial conditions, which strongly influence the nugget growth. Imperfect contact conditions are usually used in the macroscopic model to account for the electrical and thermal volume phenomena, which occur near a metallic interface crossed by an electric current. One approach consists in representing microconstriction phenomena by surface contact parameters: The share coefficient and the thermal and electrical contact resistances, which depend on the contact temperature. The aim of this work is to determine the share coefficient and the contact temperature through a numerical model on a microscopic scale. This surface approach does not make it possible to correctly represent the temperature profiles, with the peak temperature, observed in the immediate vicinity of the interface and thus to define, in practice, the contact temperature correctly. That is why another approach is proposed with the introduction of a low thickness layer (third body) at the level of the interface the electric and thermal resistances of which are equivalent to the electrical and thermal contact resistance values. In this case, the parameters of the model are reduced to the thickness of the arbitrarily fixed layer and equivalent electric and thermal conductivities in the thin layer, the partition coefficient and the contact temperature becoming implicit. The two types of thermoelectric contact models are tested within the framework of the numerical simulation of a spot welding test. The nugget growth development is found to be much different with each model.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of thermoelectric contact conditions in the model through surface contact parameters

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Figure 5

Comparison between the thermal fields in the models (with contact parameters and with thin layers and equivalent conductivities) and the thermal fields in the reference model, in the case of steel/copper contact (a) and in the case of steel/steel contact (b)

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Figure 6

Experimental evolution of TCR versus temperature under pressure of 80 MPa for the contact DP6G-Cu (a). Experimental evolutions of ECR versus temperature under pressure of 80 MPa for the contacts DP6G-Cu and DP6G-DP6G and comparison with the evolution of the DP6G sheet electrical resistance versus temperature (b).

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Figure 7

Comparison, during the welding stage (t<0.26 s), between calculated temperature evolution at the faying interface with the surface contact parameters approach and with the volume contact approach (a) and during the first period (t<0.02 s) (b)

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Figure 8

Numerical nugget sizes at the end of the welding stage (13th cycle), with the surface contact parameters approach (a) and with the volume contact approach (b). Comparison with the experimental nugget size (dashed lines).

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Figure 9

Macrographic cuts at different periods presenting the experimental nugget growth (dashed lines)

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Figure 2

Geometries and meshing of the reference model with constriction, without asperity (h=0) (a), and with asperity in the medium 2 (h=5 μm) (b)

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Figure 3

Thermal fields simulated with both types (microscopic and macroscopic models) along the symmetry axis in the case of steel/copper contact (a) T1=T2=0°C, (b) T1=10°C, T2=0°C, (c) T1=100°C, T2=0°C, and in the case of steel/steel contact (d) T1=T2=0°C, (e) T1=0°C, T2=10°C), (f) T1=0°C, T2=100°C

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Figure 4

Electrothermal contact conditions in the models with surface contact parameters (a) and with two thin contact layers and equivalent conductivities λE and σE (b)

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