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Research Papers

Resistance Spot Welding of Ultra-Thin Automotive Steel

[+] Author and Article Information
YanSong Zhang

e-mail: zhangyansong@sjtu.edu.cn
Shanghai Key Laboratory of Digital
Manufacture for Thin-walled Structures,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, PRC

XinMin Lai

State Key Laboratory of Mechanical,
System and Vibration,School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, PRC

Pei-Chung Wang

Manufacturing Systems Research Laboratory,
General Motors R&D Center,
Warren, MI 48090

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the Journal of Manufacturing Science and Engineering. Manuscript received May 21, 2012; final manuscript received December 27, 2012; published online March 22, 2013. Assoc. Editor: Wei Li.

J. Manuf. Sci. Eng 135(2), 021012 (Mar 22, 2013) (10 pages) Paper No: MANU-12-1156; doi: 10.1115/1.4023367 History: Received May 21, 2012; Revised December 27, 2012

One of the major challenges in spot welding of ultra-thin gage steel (e.g., <0.6 mm) is the short cap life. Because of the elevated temperature developed at the electrode/sheet interface, the electrodes often require dressing or replacement within a fraction of the time when welding more traditional automotive gage steel (>0.75 mm). In this study, the method of inserting flexible strips between the electrode and workpiece in resistance spot welding of 0.4 mm thick galvanized SAE1004 steel sheet has been adopted in order to reduce electrode tip temperature and improve weld quality. The effect of the inserted strips on the Joule heat generation and temperature distribution has been analyzed analytically. Then, because of the difficulties in measuring the experimental electrode tip temperature, a finite element model has been employed to estimate temperature distributions within the weld zone. The effects of the process variables (i.e., strip material and thickness) on the cap temperature and weld quality were modeled. Experiments were also conducted to validate the modeling results. Test data and modeling results showed that the presence of the strip significantly facilitated weld initiation and growth and decreased the rate of electrode degradation. Of the materials investigated, the desirable strip for resistance spot welding 0.4 mm thick galvanized SAE1004 steel was determined to be 0.12 mm thick Cu55Ni45 alloy.

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Figures

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Fig. 1

(a) Schematic and (b) experiment setup of resistance welding with inserted flexible strips

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Fig. 2

Heat generation during RSW process

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Fig. 3

(a) Geometric model and (b) boundary conditions for modeling of resistance welding of thin gage steel

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Fig. 4

Distribution of (a) contact pressure and (b) current density at the sheet/sheet interface

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Fig. 5

Typical temperature contours at the instant that current is terminated (a) without strips under welding current of 6.5 kA, (b) with 0.10 mm thick AISI304 strips under welding current of 5.7 kA and (c) temperature at the electrode surface versus welding time, and (d) temperature distribution from the weld center to the electrode at the end of welding along the Y-axis

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Fig. 6

(a) Contact pressure at sheet/sheet interface and (b) temperature at the weld center under different electrode force

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Fig. 7

Calculated effect of the resistivity of the strip material on temperature distribution along the (a) Y-axis and (b) X-axis in resistance welding of 0.4 mm thick galvanized SAE1004 steel

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Fig. 8

(a) Calculated effect of Cu55Ni45 alloy strip thickness on temperature distribution and (b) electrode tip temperature/temperature at sheet/strip interface versus strip thickness relationship

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Fig. 9

Top view and typical cross section of spot welded galvanized 0.4 mm thick SAE1004 steel (a), (b) without strip under 5.7 kA, 160 ms, 1.8 kN, (c)–(h) with 0.10 mm thick AISI304 strip under 5.7 kA, 160 ms and (c), (d) 1.8 kN, (e), (f) 1.4 kN and (g), (h) 2.2 kN

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Fig. 10

(a) Effect of strip on the weld formation and cross section of spot welded galvanized 0.4 mm thick SAE1004 steel, (b) with 0.10 mm thick AISI304 strips, and (c) without strips under the weld condition of 1.8 kN, 5.7 kA and 160 ms

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Fig. 11

Effect of the inserted strip on the (a) electrode profiles and (b) growth in electrode surface diameter during electrode wear test under the weld condition of 1.8 kN, 5.7 kA and 160 ms

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Fig. 12

SEM observation and EDS analysis of the electrode after 600 welds, (a), (b) without strip; (c), (d) with 0.10 mm thick AISI304 strip and (e), (f) with 0.12 mm thick Cu55Ni45 strip in resistance welding of 0.4 mm thick galvanized SAE 1004 steel

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