Evaluation of GRCop-84 for use as a resistance spot welding electrode material through experimental and analytical techniques

Electric resistance spot welding has been extensively used for many years in the automotive and aerospace industry for joining body sheet components. Compared to other welding processes such as arc welding process, resistance spot welding is fast, easily automated and easily maintained. Accurate thermal analysis of spot welding electrode could permit critical design parameters to be identified for improved electrode life. It is a complex process where coupled interactions exist between electrical, thermal and mechanical phenomena. On the other hand, finite element method (FEM), which can deal with nonlinear behaviors and complex boundary conditions, provides a powerful tool for studying these interactions and has become the most important method for the analysis of resistance spot welding. In this study, a 2-D finite element model has been developed to predict the transient thermal behavior of spot welding electrodes. The model included heat transfer analysis, electrical field analysis and phase change during melting or solidification and temperature dependant material properties, and also their inter-dependence. The contacts at faying surface and at electrode – work interface, with temperature dependant contact resistances were modeled. Three types of electrode shapes – flat, pointed and dome nose were analyzed. Temperature distribution on each electrode shape was obtained from the finite element analysis. Maximum temperature of 2876 ºC was observed in dome nose electrode in 0.2 seconds of welding time. Dome nose electrode requires a minimum weld time of all the other electrode shapes to get the required nugget size, resulting in the least power consumption. Nugget size was predicted for each electrode shape. Experimental results obtained were in good agreement with the finite element analysis results.

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Modified Recurrence Plot for Robust Condition Monitoring of Electrode Tips in a Resistance Spot Welding System

Applied Sciences ◽

10.3390/app10175860 ◽

2020 ◽

Vol 10 (17) ◽

pp. 5860

Author(s):

Wonho Jung ◽

Hyunseok Oh ◽

Dong Ho Yun ◽

Young Gon Kim ◽

Jong Pil Youn ◽

...

Keyword(s):

Condition Monitoring ◽

Resistance Spot Welding ◽

Spot Welding ◽

Welding Process ◽

Recurrence Plot ◽

External Noise ◽

Dynamic Resistance ◽

Resistance Spot ◽

Welding Electrode ◽

Welding System

Degraded electrodes in a resistance spot welding system should be replaced to ensure that weld quality is maintained. Welding electrodes are subjected to different environmental and operational loading conditions during use. When they are replaced with a fixed interval, replacement may occur too early (raising maintenance costs) or too late (leading to quality issues). This motivates condition monitoring strategies for resistance spot welding electrode tips. Thus, this paper proposes a modified recurrence plot (RP) for robust condition monitoring of welding electrode tips in resistance spot welding systems. The overall procedure for the proposed condition monitoring approach consists of three steps: (1) transformation of a one-dimensional signal to a two-dimensional image, (2) unsupervised feature extraction with LeNet architecture-based convolutional neural networks, and (3) health indicator calculation. RP methods convert dynamic resistance waveforms to RPs. The original RP method provides an image with binary-colored pixels (i.e., black or white) that makes this method insensitive to the change of the waveform signal. The proposed RP method is devised to be sensitive to the change of the waveform signal, while enhancing robustness to external noise. The performance of the proposed RP method is evaluated by examining simulated aperiodic waveform signals with and without external noise. A case study is presented to examine the proposed method’s ability to monitor the condition of resistance spot welding electrodes. The results show that the proposed method outperforms handcrafted, feature-based condition monitoring methods. This study can be used to accurately determine the lifetime of welding electrodes in real time during the spot welding process.

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