Resistance spot welding is the principal method of welding sheet steel products. In practice, the manufacture of welds of acceptable quality depends on the definition of optimum welding parameters and the implementation of suitable controls to ensure constant weld quality over a long production run. The ability to make a weld is best defined by a weldability lobe outlining the available manufacturing tolerances between minimum and maximum limits. Both two- and three-dimensional weldability lobes exist defined in terms of weld time, welding current and electrode force. Production variables influencing weld growth are discussed, particularly the effect of electrode diameter. The importance of welding machine characteristics relative to weld growth is highlighted. In particular, the rigidity of the machine coupled with the weight and frictional effects developed in the electrode head assembly are shown to be important factors influencing weld growth. Also important are the electrical characteristics of the machine, including transformer configuration current waveform and current ‘off’ time in the nonconducting part of the waveform. A reliable control philosophy is an essential requirement of any inprocess feedback system if high quality spot welds are to be produced in high volume. Various model simulations indicate that changes, with time, in electrode/sheet and sheet/sheet interfacial resistances control weld nugget formation and growth. The relative contributions of these resistances are discussed. Heat generation and temperature distribution in the weldare determined by the current and force distribution across these interfaces. One-, two- and three-dimensional models have been developed to describe the temperature distribution in the weld zone and weld nugget growth. These models have limited application due to inadequate input data to describe the transient conditions appertaining in the weld zone. Current waveform, inductance effects, and friction/rigidity of the electrode head assembly, are not considered. Neural networks and fuzzy logic control have shown promise in classifying weld quality into predetermined groupings. The way forward is to adopt a multidisciplinary approach, taking into account the various interactions between the thermal, electrical, mechanical and metallurgical phenomena developed during the welding process. Models describing these phenomena should be interlinked to simulate heat generation and growth in the weld zone. The resulting model could be coupled with experimentally developed trends to optimise inputs to a neural network, the output of which is used, through a fuzzy logic controller, to take appropriate corrective action to ensure the required weld quality. It is stressed that any mathematical simulation or control system must take into account changes that occur at the welding electrodes as a consequence of electrode wear. The latter are discussed in Part 2 of this review.

Review of resistance spot welding of steel sheets Part 1 Modelling and control of weld nugget formation

The failure mechanisms of electrode/solid electrolyte (SE) interfaces in solid‐state lithium metal batteries (SSBs) involve multiscale and multiphysical field coupling. Various in situ observation technologies and corresponding theoretical approaches have been used to investigate the degradation mechanism of SSBs. Based on the experimental and theoretical results, well‐established solutions are explored to construct stable electrode/SE interfaces in SSBs.

Electro–Chemo–Mechanical Issues at the Interfaces in Solid-State Lithium Metal Batteries

A contact tip suitable for electric arc welding has a consumable electrode. The contact tip has a body which defines a bore through which the electrode is able to pass to enable electric current from a welding power supply to be transferred from the body to the electrode. The body, in part of the length of the bore between an inlet end and an outlet end, has at least one region (herein referred to as a primary contact region) at which the body is adapted to enable primary electrical contact with the electrode, and along a remainder part of the length of the bore, the body is adapted such that any secondary contact between the body and the electrode along the remainder part does not substantially short circuit the primary electrical contact in the primary contact region of the bore.

Consumable electrode arc welding

Analysis of Al-steel resistance spot welding process by developing a fully coupled multi-physics simulation model

Characterization of electrical contact conditions in spot welding assemblies

An important input property in the development of process models for resistance spot welding is electrical contact resistance A model for the pressure and temperature dependence of electrical contact resistance was developed from established concepts of contact resistance The key to developing the desired relationship is determining surface roughness characteristics, which is experimentally problematic To overcome this difficulty the electrical resistance of contacting interfaces was measured as a function of the pressure applied across the interfaces Using known information about the temperature dependence of bulk resistivity and mechanical properties, a curve fitting procedure was used to establish the desired relationship of contact resistance to pressure and temperature This empirical model agrees well with experimental measurements in the regime of low applied pressure At high pressures, predictions underestimate contact resistance, and this was attributed to strain hardening of asperit

J.W. Cohron

Papers

Empirical model of effects of pressure and temperature on electrical contact resistance of metals