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TECHNICAL PAPERS

Modeling and On-Line Estimation of Electrode Wear in Resistance Spot Welding

[+] Author and Article Information
Wei Li

Department of Mechanical Engineering,  University of Washington, Box 352600, Seattle, WA 98195

J. Manuf. Sci. Eng 127(4), 709-717 (Dec 20, 2004) (9 pages) doi:10.1115/1.2034516 History: Received May 01, 2004; Revised December 20, 2004

Electrode wear is inherent in the resistance spot welding process. It determines the electrical and mechanical contact condition and thus strongly affects the resistance spot weld quality. A practical approach to minimizing the electrode wear effect is to compensate the welding current as the electrodes wear. However, the existing methods for welding current compensation rely on either a predetermined stepper schedule or an expulsion detection algorithm. These methods are not reliable since the welding current is not determined based on the contact condition for each weld made in the welding process. This paper presents an on-line electrode wear estimation approach to determining the contact condition and the welding current needed to make every weld a good weld during the entire life of the electrodes. In the study, an incrementally coupled finite element simulation was first formulated to analyze the contact area behavior in the resistance spot welding process. A lumped parameter model was then developed to characterize the contact area change with the dynamic resistance measurement. A calibration and an estimation algorithm were subsequently devised for on-line applications. The proposed approach has been validated with experimental data. The results have shown that the estimation algorithm is robust under various process conditions including both welding current and electrode force.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Contact areas in resistance spot welding process

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Figure 2

The finite element simulation model: (a) the model and boundary conditions and (b) the incrementally coupled simulation procedure

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Figure 3

A comparison between the simulation and experimental results: (a) a result from the finite element simulation model and (b) the cross section of a weld nugget (thickness of the sheet is 1.2mm)

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Figure 4

Contact pressures at S/S and E/S interfaces: (a) contact pressures at the S/S interface and (b) contact pressure at the E/S interface

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Figure 5

Finite element simulation of contact area change during the welding process (contact area at the E/S interface is shown in diamonds and that at the S/S interface in squares)

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Figure 6

The lumped parameter model: (a) the model structure and (b) the dynamic resistance model

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Figure 7

Underlying mechanisms of the dynamic resistance curve

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Figure 8

Three stages of the dynamic resistance curve

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Figure 9

The on-line electrode size estimation algorithm

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Figure 10

Experimental setup

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Figure 11

Relationship between re and pressure

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Figure 12

Recursive contact diameter estimation

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Figure 13

Validation test of the electrode size estimation method

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Figure 14

Dynamic resistance curves at different welding currents

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