Phase Change Effects on Transport Processes in Resistance Spot Welding

ABSTRACTThe effects of distinct properties during phase change on mass, momentum, energy, species, and magnetic field intensity transport in workpieces and electrodes in the course of heating, melting, cooling and freezing periods in AC (alternative current) resistance spot welding are realistically and extensively investigated. Resistance spot welding has been widely used in joining thin workpieces due to its light weight and easy manufacturing. This study accounts for electromagnetic force, heat generations at the electrode-workpiece interface and faying surface between workpieces, and dynamic electrical resistance taking the sum of temperature-dependent bulk resistance of the workpieces and contact resistances at the faying surface and electrode-workpiece interface. The contact resistance is a function of hardness, temperature, electrode force, and surface condition. Instead of dealing with specific materials, this work is a general dimensionless investigation of resistance spot welding of materials with different specific heat and thermal conductivity ratios subject to realistic working parameters. The computed results show that nugget formation is delayed and heat transfer is reduced by increasing solid-to-liquid thermal conductivity and liquid-to-solid specific heat ratio. The corresponding thermal fields and flow patterns are also presented.

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Modeling Dynamic Electrical Resistance During Resistance Spot Welding

Journal of Heat Transfer ◽

10.1115/1.1370502 ◽

2000 ◽

Vol 123 (3) ◽

pp. 576-585 ◽

Cited By ~ 43

Author(s):

S. C. Wang ◽

P. S. Wei

Keyword(s):

Electrical Resistance ◽

Resistance Spot Welding ◽

Spot Welding ◽

Transport Processes ◽

Dynamic Resistance ◽

Resistance Curve ◽

Bulk Resistance ◽

Resistance Spot ◽

Faying Surface ◽

Stage 4

Dynamic electrical resistance during resistance spot welding has been quantitatively modeled and analyzed in this work. A determination of dynamic resistance is necessary for predicting the transport processes and monitoring the weld quality during resistance spot welding. In this study, dynamic resistance is obtained by taking the sum of temperature-dependent bulk resistance of the workpieces and contact resistances at the faying surface and electrode-workpiece interface within an effective area corresponding to the electrode tip where welding current primarily flows. A contact resistance is composed of constriction and film resistances, which are functions of hardness, temperature, electrode force, and surface conditions. The temperature is determined from the previous study in predicting unsteady, axisymmetric mass, momentum, heat, species transport, and magnetic field intensity with a mushy-zone phase change in workpieces, and temperature and magnetic fields in the electrodes of different geometries. The predicted nugget thickness and dynamic resistance versus time show quite good agreement with available experimental data. Excluding expulsion, the dynamic resistance curve can be divided into four stages. A rapid decrease of dynamic resistance in stage 1 is attributed to decreases in contact resistances at the faying surface and electrode-workpiece interface. In stage 2, the increase in dynamic resistance results from the primary increase of bulk resistance in the workpieces and an increase of the sum of contact resistances at the faying surface and electrode-workpiece interface. Dynamic resistance in stage 3 decreases, because increasing rate of bulk resistance in the workpieces and contact resistances decrease. In stage 4 the decrease of dynamic resistance is mainly due to the formation of the molten nugget at the faying surface. The molten nugget is found to occur in stage 4 rather than stage 2 or 3 as qualitatively proposed in the literature. The effects of different parameters on the dynamic resistance curve are also presented.

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Effects of electrical current on transport processes in resistance spot welding

Science and Technology of Welding & Joining ◽

10.1179/136217110x12693513264295 ◽

2010 ◽

Vol 15 (6) ◽

pp. 448-456 ◽

Cited By ~ 10

Author(s):

P. S. Wei ◽

T. H. Wu

Keyword(s):

Resistance Spot Welding ◽

Spot Welding ◽

Electrical Current ◽

Transport Processes ◽

Resistance Spot

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Analyses of Nugget and Expulsion Formation Process during Resistance Spot Welding between Aluminum Alloy and Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.859.7 ◽

2013 ◽

Vol 859 ◽

pp. 7-10 ◽

Cited By ~ 1

Author(s):

Nan Nan Wang ◽

Ran Feng Qiu ◽

Fang Fang Liu ◽

Man Zhang ◽

Qing Qing Xuan

Keyword(s):

Aluminum Alloy ◽

Resistance Spot Welding ◽

Spot Welding ◽

Surface Condition ◽

Softening Temperature ◽

Growth Stages ◽

Resistance Spot ◽

Surface Breakdown ◽

Nugget Growth ◽

Nugget Formation

In this paper, nugget growth stages during resistance spot welding between aluminum alloy and steel, such as surface breakdown, asperity softening, temperature rising, molten nugget formation, nugget growth and mechanical collapse, was analyzed according to resistance dynamic variation during welding. The effects of work pieces surface condition and electrode force on the occurrence of inter-expulsion and surface expulsion was discussed during resistance spot welding.

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Factors Affecting Nugget Growth With Mushy-Zone Phase Change During Resistance Spot Welding

Journal of Heat Transfer ◽

10.1115/1.2910613 ◽

1991 ◽

Vol 113 (3) ◽

pp. 643-649 ◽

Cited By ~ 25

Author(s):

P. S. Wei ◽

F. B. Yeh

Keyword(s):

Mushy Zone ◽

Phase Change ◽

Resistance Spot Welding ◽

Spot Welding ◽

Maximum Velocity ◽

Temperature Fields ◽

Factors Affecting ◽

Resistance Spot ◽

Nugget Growth ◽

Cooling Effects

An unsteady, axisymmetric model is first proposed to investigate extensively effects of the physical, thermal, and metallurgical properties and welding conditions on nugget growths with mushy-zone phase change during resistance spot welding. The electromagnetic force, joule heat and interfacial heat generation, and cooling effects of electrodes are taken into account. Fluid patterns, temperature fields, and solute distributions in the liquid, solid, and mushy zones are determined. Results show that the computed nugget growths and temperature fields are consistent with experimental data. Variations of properties strongly affect the nugget growth. The maximum velocity in the weld nugget is found to be small and around 5 mm/s.

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