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TECHNICAL PAPERS

Influence of Machine Specific Instantaneous Current Wave Form on Resistance Spot Welding Process

[+] Author and Article Information
A. De

 Mechanical Engineering Department, IIT Bombay, Mumbai, Maharashtra, Indiaamit@iitb.ac.in

K. Momeni, L. Dorn

 Institute for Joining and Coating Engineering, TU Berlin, Berlin 10587, Germany

M. P. Thaddeus

 Mechanical Engineering Department, IIT Bombay, Mumbai, Maharashtra, India

J. Manuf. Sci. Eng 128(3), 668-676 (Dec 02, 2005) (9 pages) doi:10.1115/1.2164507 History: Received June 05, 2005; Revised December 02, 2005

The influence of the machine specific instantaneous current wave forms on weld nugget dimensions and weld strength is investigated over six spot welding machines. It is observed that the nature of the real-time current wave forms corresponding to a common rms value can vary in different ac spot welding machines. The variations exist in the values of peak current and in the current-on and -off times in every ac cycle. It is observed that real-time current wave form involving higher peak current leads to slightly larger weld nugget diameter compared to wave form with smaller peak current even if the overall rms value remains similar. The real-time current wave form from a medium frequency dc confirms to a fast rise to the set weld current and remains steady for the complete weld time. A detailed experimental study has depicted that the real-time ac wave forms especially with high peak values and sharp rise characteristics offer a relatively smaller permissible range of weld currents compared to the wave forms with relatively flatter characteristics. The steady instantaneous current wave form confirming to the medium frequency dc machine has facilitated a larger permissible range of weld current. A numerical analysis of the spot welding process based on finite element process is carried out using both the instantaneous current wave forms and the corresponding rms values of weld current. The predicted weld dimensions using instantaneous current wave forms have showed slightly better agreement with the corresponding measured weld dimensions.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Real-time current wave forms from four different spot welding machines at a similar weld current setting (≈6.8kA→ rms value) (electrode force =2.6kN): (a) zoomed for first 20ms, (b) zoomed for last 20ms

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Figure 2

Real-time current wave forms from four different spot welding machines at a similar weld current setting (≈8.0kA→ rms value) (electrode force =3.0kN): (a) zoomed for first 20ms, (b) zoomed for last 20ms

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Figure 3

Real-time current wave forms from dc four different spot welding machines at a various weld current settings (electrode force =3.0kN): (a) zoomed for first 20ms, (b) zoomed for last 20ms

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Figure 4

Permissible range of weld currents in various spot welding units (a) electrode force = 2.2kN; weld time = 200ms, (b) electrode force = 3.0kN; weld time = 200ms

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Figure 12

Growth of computed weld nugget diameter and sheet-sheet contact zone with weld time. Instantaneous current wave form from machine M3 for a corresponding rms value of 8.85kA are used for computation.

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Figure 11

Growth of computed weld nugget diameter and sheet-sheet contact zone with weld time. Instantaneous current wave form from machine M3 for a corresponding rms value of 7.73kA are used for computation.

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Figure 10

Schematic picture of weld nugget, electrode-sheet contact zone and sheet-sheet

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Figure 9

Comparison of measured and computed weld nugget diameter at electrode force of 2.6kN corresponding to various spot welding units: (a) M1; (b) M2; (c) M3; (d) M4

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Figure 8

Comparison of computed and measured weld nugget dimensions (M1) at electrode force = 3.0kN and weld time = 200ms. Weld current: (a)7.0kA (rms value) and (b)8.85kA (rms value). Measured weld diameters are (a)3.8mm; (b)4.9mm.

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Figure 7

Schematic presentation of in-process growth of the sheet-electrode and sheet-sheet contact zone

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Figure 6

Elemental plot of the analysed sheet-electrode section

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Figure 5

Analyzed section of the sheet-electrode system along with elemental plot

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