Heat evolution and nugget formation of resistance spot welding under multi-pulsed current waveforms
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ORIGINAL ARTICLE
Heat evolution and nugget formation of resistance spot welding under multi-pulsed current waveforms Yaqiong Wang 1 & Zhenghua Rao 1 & Fengjiang Wang 2 Received: 8 July 2020 / Accepted: 29 October 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract The pulsed current waveform is essential for the precise control of nugget size in resistance spot welding (RSW). Understanding this link may enable high-quality RSW for the emerging materials. To shed light on this issue, a 3D electrical-thermal-mechanical coupled model is developed to simulate transient multi-physical fields and nugget shapes in RSW. The effects of pulsed current waveforms on the heat evolution and nugget formation are elaborated. The model is validated by calculating nugget size and weld indentation well consistent with the experimental measurements. The results show that with the same energy input, although the continuous and pulsed currents can provide acceptable nugget sizes, the “ramp-up” pulsed current with a high initial current can well match the variations of temperature-dependent electric resistance and lead to an enlarged nugget size. The electrode temperature maintains at a low level with an extended electrode life. This work will provide a better understanding of the heat evolution and nugget formation during RSW process under different multi-pulsed current waveforms, and thus can help to select a proper current waveform. Keywords Multi-pulsed current waveform . Heat evolution . Nugget formation . Resistance spot welding . Electrical-thermal-mechanical coupled model
Nomenclature cp Specific heat f0 Yield stress F Electrode force h1 Convective heat transfer coefficient h2 Radiative transfer coefficient hc Heat transfer coefficient of cooling water hcom Heat transfer coefficient combined with convection and radiation H Latent heat I Welding current j Current density k Thermal conductivity coefficient Kij Jacobian matrix
P qconv qrad re ri RT Ru Rφ t T Ta TL TS U
* Zhenghua Rao [email protected]
Greek symbols α Coefficient of thermal expansion εe Elastic strain εp Plastic strain εth Thermal strain ρ Density σ Stress σb Electrical conductivity of base material
1
School of Energy Science and Engineering, Central South University, Changsha 410083, Hunan, China
2
Provincial Key Laboratory of Advanced Welding Technology, Jiangsu University of Science and Technology, Zhenjiang 212003, Jiangsu, China
Pressure Heat flux of convective heat transfer Heat flux of radiative heat transfer External radius of top surface of electrode Internal radius of top surface of electrode Thermal vector Mechanical vector Electrical vector Welding time Temperature Ambient temperature Liquidus temperature Solidus temperature Displacement
Int J Adv Manuf Technol
σc σe φ Δl Δt ΔT Δu Δφ
Electrical contact conductivity of faying surface Total electrical conductivity Electrical potential Typical element dimension Time increment. Corrections of incremental temperature Corrections of incremental displacement Corrections of incr
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