Welding Metallurgy of

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processing heat treatments to improve the mechanical properties of the parts. An important aspect that still hinders this technology is certification and nondestructive testing of the parts, and this is discussed. Finally, a general perspective of future advancements is presented.

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

Fiber lasers have seen progressive developments in terms of spectral coverage and linewidth, output power, pulse energy, and ultrashort pulse width since the first demonstration of a glass fiber laser in 1964. Their applications have extended into a variety of fields accordingly. In this paper, the milestones of glass fiber laser development are briefly reviewed and recent advances of high-power continuous wave, Q-switched, mode-locked, and single-frequency fiber lasers in the 1, 1.5, 2, and 3 μm regions and their applications in such areas as industry, medicine, research, defense, and security are addressed in detail.

Fiber lasers and their applications [Invited]

Cold metal transfer (CMT) technology - An overview

There is an increased requirement in the automotive, food and medical equipment industries to weld heat-sensitive materials, such as thin sheets, coated thin plates, stainless steel, aluminium and mixed joints. Nevertheless, relevant innovations in arc welding are not widely known and seldom used to their maximum potential. In the area of gas metal arc welding welding processes, digitalisation has allowed integration of software into the power source, wire feeder and gas regulation. This paper reviews developments in the arc welding process, particularly the effect of the set-up of the welding process parameters on waveform deposition. It is found that good weldability, good mechanical joint properties and acceptable process efficiency can be obtained for thin sheets through advanced power source regulation, especially over short circuiting, controlled polarity and electrode wire motion. The findings presented in this paper are valuable for waveform and deposition prediction. The need is furthermore noted for an algorithm that integrates gas flow parameters and wire motion control, as well as a variable sensor on the tip of the electrode, permitting flexibility of control of the current and the voltage waveform.

Advanced gas metal arc welding processes

Transportation industries are obliged to address concerns arising from greater emphasis on energy saving and ecologically sustainable products. Engineers, therefore, have a responsibility to deliver innovative solutions that will support environmental preservation and yet meet industries’ requirements for greater productivity and minimised operational costs. Aluminium alloys have successfully contributed to meeting the rising demand for lightweight structures. Notable developments in aluminium welding techniques have resolved many welding related problems, although some issues remain to be addressed. The present study attempts to give an overview of the key factors related to the formation of defects in welding methods commonly used with aluminium alloys. First, a concise overview of defects found in friction-stir welding, laser beam welding and arc welding of aluminium alloys is presented. The review is used as a basis for analysis of the relationship between friction-stir welding process parameters and weld defects. Next, the formation and prevention of the main weld defects in laser beam welding, such as porosity and hot cracking, are discussed. Finally, metallurgical aspects influencing weld metal microstructure and contributing to defects are tabulated, as are defect prevention methods, for the most common flaws in arc welding of aluminium alloys.

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Investigation of weld defects in friction-stir welding and fusion welding of aluminium alloys

Shielding gases are of considerable significance in the protection of molten metal from atmospheric contamination during welding processes. These gases play an important role in a number of aspects of welding, including arc characteristics and the microstructure of weldments. Understanding of the influence of welding shielding gases on different materials is consequently important, and extensive studies and experiments have been performed by numerous researchers. Based on previous studies, the objective of the current study is to collate and summarize the most important findings and approaches of earlier research. This paper provides analysis of the influence of different combinations of process gases on welding of commonly used materials in manufacturing. The results presented can be used as guidelines to achieve higher quality and efficiency in welding practices. This study provides a good foundation for learning and creates enhanced awareness of shielding-gas-related issues among metal industry actors, permitting objective evaluation of welding productivity and quality.

Influence of shielding gases in the welding of metals

Dissimilar welding of aluminium (Al) and copper (Cu) has many applications in the electric power, electronic and piping industries. The weldments in these applications are highly valued for their corrosion resistance, heat and electricity conducting properties. The Al-Cu joints are lighter, cheaper and have conductivity equal to that of copper alloys. Much research has investigated dissimilar welding of Al-Cu by solid-state welding and fusion welding processes with the aim of optimising the properties and strength of such dissimilar joints. The main aim of the study is to critically review the factors influencing the properties of the Al-Cu joint. The study mainly discusses about the effects of intermetallic compounds (IMC) on the properties of Al-Cu joint and their effect while in service. The effects of joining aluminium alloy 1060 with pure copper by laser welding, friction stir welding and brazing have been reviewed and compared. The review shows that the various intermetallic compound formations in the joint have both beneficial and detrimental effects. The characteristics of these intermetallic compounds vary according to the location of the phase formed. Comparison of processes and parameters for welding of Al 1060 with pure Cu shows that the formation of the intermetallic compounds and their effects on the weld properties are mainly influenced by the welding speed, heat input, the thermal properties of the base metals and the filler metal as well as the dilution between the base metal and filler metal.

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Factors influencing Al-Cu weld properties by intermetallic compound formation

Technical innovations in robotic welding and greater availability of sensor-based control features have enabled manual welding processes in harsh work environments with excessive heat and fumes to be replaced with robotic welding The use of industrial robots or mechanized equipment for high-volume productivity has become increasingly common, with robotized gas metal arc welding (GMAW) generally being used More widespread use of robotic welding has necessitated greater capability to control welding parameters and robotic motion and improved fault detection and fault correction Semi-autonomous robotic welding (ie, highly automated systems requiring only minor operator intervention) faces a number of problems, the most common of which are the need to compensate for inaccuracies in fixtures for the workpiece, variations in workpiece dimensions, imperfect edge preparation, and in-process thermal distortions Major challenges are joint edge detection, joint seam tracking, weld penetration control, and measurement of the width or profile of a joint Such problems can be most effectively solved with the use of sensory feedback signals from the weld joint Thus, sensors play an important role in robotic arc welding systems with adaptive and intelligent control system features that can track the joint, monitor in-process quality of the weld, and account for variation in joint location and geometry This work describes various aspects of robotic welding, programming of robotic welding systems, and problems associated with the technique It further discusses commercially available seam-tracking and seam-finding sensors and presents a practical case application of sensors for semi-autonomous robotic welding This study increases familiarity with robotic welding and the role of sensors in robotic welding and their associated problems

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Paul Kah

Papers

Advanced gas metal arc welding processes

Investigation of weld defects in friction-stir welding and fusion welding of aluminium alloys

Influence of shielding gases in the welding of metals

Factors influencing Al-Cu weld properties by intermetallic compound formation

Robotic arc welding sensors and programming in industrial applications