This paper presents an overview of resistance spot welding control. The presentation of the physical background of the resistance welding process is followed by the description of the main problems concerning the appurtenant control theory. Solutions to these problems are presented primarily according to the measured signals used and to the type of control strategies.

The emerging of the fourth industrial revolution, also known as Industry 4.0 (I4.0), from the advancement in several technologies is viewed not only to promote economic growth, but also to enable a greener future. The 2030 Agenda of the United Nations for sustainable development sets out clear goals for the industry to foster the economy, while preserving social well-being and ecological validity. However, the influence of I4.0 technologies on the achievement of the Sustainable Development Goals (SDG) has not been conclusively or systematically investigated. By understanding the link between the I4.0 technologies and the SDGs, researchers can better support policymakers to consider the technological advancement in updating and harmonizing policies and strategies in different sectors (i.e., education, industry, and governmental) with the SDGs. To address this gap, academic experts in this paper have investigated the influence of I4.0 technologies on the sustainability targets identified by the UN. Key I4.0 element technologies have been classified to enable a quantitative mapping with the 17 SDGs. The results indicate that the majority of the I4.0 technologies can contribute positively to achieving the UN agenda. It was also found that the effects of the technologies on individual goals varies between direct and strong, and indirect and weak influences. The main insights and lessons learned from the mapping are provided to support future policy.

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The present paper presents the influence of welding current shape on weld strength of resistance spot welds of zinc coated mild steel sheets. The influence is analysed at different levels of the electrode wear. Welding currents with different peak values and different RMS (root mean square) values were used in the experiment. The results show that welding current with high peak values implies higher weld strength.

Audible sound signals detected during the resistance spot welding (RSW) of zinc coated steels were investigated in order to assess their suitability for estimating the strength of the weld. A new sonic emission indicator was introduced and compared to a commonly used emission count indicator. A new method of spot weld strength estimation based on the two indicators is presented. The advantage of the method is that it makes it possible to establish the stage when the electrode is worn out. The method enables the development of improved RSW process control algorithms.