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Weld defect detection is a crucial aspect for improving the productivity and quality of the welding process. Several non-destructive methods exist for the identification of defects post weld deposition. However, they only help assess the quality of the component and offer no inputs while the welding process is being performed. Real-time or in situ weld defect detection aids in the detection of defects during the welding process, allowing to take corrective measures or halt the welding to avoid further wastage of time and material. The current paper provides a brief description of various types of weld defects and the commonly used non-destructive testing (NDT) techniques used for identifying weld defects. It then proceeds to provide a detailed review of various methods available for in situ weld defect detection, classifying them based on their input signals. It also classifies the methods based on the type of algorithm used, along with an intuitive explanation of the commonly used algorithms in weld defect detection. The methods covered in this manuscript make use of different input signals that include audio, welding current and voltage, and optical signals also highlighting methods that use a combination of the abovementioned signals for in situ prediction of weld defects. A critical analysis of the efficacy, advantages, and drawbacks of each method is presented. Further, this work highlights a few research gaps identifying avenues for future research in this area.

Weld bead forming rule is very important during double-pulsed gas metal arc welding (DP-GMAW) process, and this process has more advantages than that of conventional arc welding process. This work employed grey rational analysis to explore the weld bead forming rule. Since the latest twinpulse XT DP control process was employed, the parameters adjustment was easier than that of conventional operation. The grey relational analyses between five main process parameters, which were average welding current, welding speed, twin pulse relation, twin pulse frequency together with twin pulse current change in percent, and three key characteristic parameters, which were bead width, bead height and penetration, were conducted to explore the weld bead forming rule. To accurately calculate the grey relational degree, the negative relevancies were transformed to positive ones. According to calculations and corresponding analyses, it can be concluded that the effects of average welding current and welding speed on the weld bead forming and key characteristic parameters of the weld bead were higher than that of other process parameters. Moreover, the relevancies between key characteristic parameters of the weld bead, and process parameters which included twin pulse relation, average welding current and twin pulse current change in percent were positive, while the relevancies between key characteristic parameters and other two process parameters were negative. The work can supply a new method to evaluate the effects of process parameters during the DP-GMAW process on the weld bead forming or other process characteristics, and references for parameters selection and process optimization.

Material welding failure considerably influences the electrical lifetime and reliability of low current switching devices. However, relevant studies on methods for calculating the threshold welding current and welding area under milli-Newton scale load forces are very limited. In this paper, the welding characteristics of metal material, including the threshold welding current, welding area and welding force are studied by using theoretical calculations and experiments. The comparison between the theoretical calculation and experimental results shows the accuracy of the built model. Further, the effects of mechanical load force and load current on welding force and welding area of representative metal materials are investigated. It is found that the anti-welding ability of metal materials depends not only on the exerted load force and current, but also the electrical resistivity, the thermal conductivity, the tensile strength, and the melting temperature of the materials.

The welding process itself is a non-linear, multivariable, coupled physical metallurgical process that is easily perturbed. Improper welding parameter selection and welding process conditions will interfere with the welding process and affect the final welding quality. This study aims to identify and locate two types of welding interference, insufficient shielding gas and unremoved oxidation film on the base metal surface, during the Pulse Multi-Control Gas Metal Arc Welding (PMC GMAW) process of aluminum alloy. The Characteristic Intrinsic Mode Function (IMF), which is closely related to the short circuit transition process, was obtained by applying the Complementary Ensemble Empirical Mode Decomposition (CEEMD) method to the welding current signal measured during the welding process. Time and frequency domain analysis of the acquired characteristic IMF was then performed. The experimental results demonstrated that for a stable welding process, the frequency of the characteristic IMF is concentrated within a narrow range. The frequency spectrum of the characteristic IMF exhibits distinct variations under different types of welding interference. Based on this, the chronological arrangement of characteristic IMF components’ frequency spectrum allows for locating welding interferences by analyzing their abnormal signals within the reconstructed signal sequence.

To improve the mechanical properties of resistance spot–welded 780-MPa-grade lightweight steel, post-weld heat treatment (PWHT) through the application of a second welding current and using a furnace was performed after resistance spot welding. It was not possible to obtain satisfactory mechanical properties of the weld through the application of a second welding current. In the case of the PWHT by a furnace, the required loads were satisfied when PWHT was applied at temperatures of less than 300 °C for more than 30 min, and at more than 300 °C for 15 min or more. Due to the softening of martensite by PWHT, the resistance to fracture progression during tensile test was increased, and mechanical properties could be improved.

This paper investigates the influence of the submerged arc welding (SAW) process parameters (welding current and welding speed) on the microstructure, hardness, and toughness of HSLA steel weld joints. Attempts have also been made to analyze the results on the basis of the heat input. The SAW process was used for the welding of 16 mm thick HSLA steel plates. The weld joints were prepared using comparatively high heat input (3.0 to 6.3 KJ/mm) by varying welding current (500–700 A) and welding speed (200–300 mm/min). Results showed that the increase in heat input coarsens the grain structure both in the weld metal and heat affected zone (HAZ). The hardness has been found to vary from the weld centre line to base metal and peak hardness was found in the HAZ. The hardness of the weld metal was largely uniform. The hardness reduced with the increase in welding current and reduction in welding speed (increasing heat input) while the toughness showed mixed trend. The increase in welding current from 500 A to 600 A at a given welding speed (200 mm/min or 300 mm/min) increased toughness and further increase in welding current up to 700 A lowered the toughness. Scanning electron microscopy of the fractured surfaces of impact test specimen was carried out to study the fracture modes. Electron probe micro analysis (EPMA) was carried out to investigate the variation in wt.% of different elements in the weld metal and HAZ.

Resistance spot welding (RSW) process is the major joining technique in the automobile industry due to its high speed and relatively low cost. Although RSW is widely used, it is difficult to ensure the consistency of joint quality in real production, a common phenomenon in resistance spot welding is expulsion, characterized by the ejection of molten metal during welding linked to excessive current densities. To determine the spot weldability of steels the available welding current range is evaluated. This range is defined by the maximum current without splash and the minimum current still giving an acceptable size of the weld diameter. Previous studies show that the static and dynamic behaviors of spot welders have complex influences on the resistance welding process and weld quality. A criterion of dynamic stiffness has been established here to explain why the welding current range of a given steel grade can depend on the structural stiffness of spot welding machine.

The CMT welding technology is adopted to solve the difficulties in full-position welding of circular pipes, and a robotic arm is controlled to achieve automatic full-position welding. The characteristics and laws of weld formation are studied by adjusting technology parameters like welding current, angle, and speed. The results show that once the welding current increases, the fusion depth and width of the weld simultaneously increase. However, as the welding speed increases, the depth and width of fusion decrease. Root welding experiments indicate that the optimal morphology of the root weld is achieved under the welding current of 200 A at the 0.2 m/min welding speed. In the weld filling experiment, both the left and right passes use the welding current of 260 A at the 0.2 m/min welding speed, which can fill the weld with two passes and achieve complete well formation.

Pipe end surfacing represents a standard welding technique employed in the fabrication of bimetallic mechanical composite pipes. This study investigates the application of cold metal transfer (CMT) welding technology for pipe end surfacing of bimetallic composite pipes. The effect of CMT welding parameters, including welding current, welding speed, weave width, weave frequency, and dwell time, on the weld width, weld height, heat-affected zone (HAZ) width, and fusion ratio was analysed. The results show that the main factors affecting welding forming are welding current, welding speed and weave width, which basically determine both the width and height of the weld. The orthogonal test shows that the more suitable welding parameters are 120 A welding current, 3.28 mm/s welding speed, 5 mm weave width, 3 Hz weave frequency, and 0.05 s dwell time on both sides. To improve welding efficiency and ensure arc stability, the adjusted surfacing welding parameters are 120 A welding current, 5.12 mm/s welding speed, 5 mm weave width, 2 Hz weave frequency, and 0.05 s dwell time on both sides. The lap surfacing weld was well formed.

Selecting an economically suitable welding technique and optimizing welding parameters to obtain high joint quality is considered a challenge for expanding the 5xxx aluminum alloy series in various industrial applications. This work aims to investigate the effect of applying different welding techniques, tungsten inert gas (TIG) and metal inert gas (MIG), as fusion welding processes compared to friction stir welding (FSW), a solid-state joining process, on the joint performance of the produced 5 mm thick similar AA5083-H111 butt weldments at different welding conditions. Different methods were used to evaluate the quality of the produced joints, including visual inspection, radiographic testing (RT), and macrostructure evaluation, in addition to hardness and tensile tests. The fracture surface of the tensile-failed specimens was also investigated using a scanning electron microscope (SEM). Furthermore, the current study ended with an economic analysis of the welding techniques used. The results showed that, for the friction stir-welded joints, the radiographic films revealed defect-free joints at the two applied travel speeds of 100 mm/min and 400 mm/min and a constant tool rotating speed of 400 rpm. In addition, only one joint was welded by MIG at a welding current of 130 Amp, with a 19 L/min flow rate of pure argon. In contrast, the radiographic films showed internal defects such as lack of fusion (LOF), lack of penetration (LOP), and porosity (P) for the two joints welded by TIG and one joint welded by MIG. The hardness of the welded joints was enhanced over the AA5083-H111 base material (BM) by 24–29, 31–35, and 46–50% for the MIG, TIG, and FSW joints, respectively. The maximum ultimate tensile strength was obtained for the FSW joint welded at a 400 mm/min travel speed. Adopting FSW in shipbuilding applications can further produce the AA5083-H11 joints with higher quality and efficiency than fusion welding techniques such as MIG and TIG processes. In addition, time and cost comparisons between TIG, MIG, and FSW were performed for five-millimeter-thick and one-meter-long AA5083-H111.