Welding Metallurgy of

Asymmetric single point incremental forming of sheet metal

Wire-feed additive manufacturing (AM) is a promising alternative to traditional subtractive manufacturing for fabricating large expensive metal components with complex geometry. The current research focus on wire-feed AM is trying to produce complex-shaped functional metal components with good geometry accuracy, surface finish and material property to meet the demanding requirements from aerospace, automotive and rapid tooling industry. Wire-feed AM processes generally involve high residual stresses and distortions due to the excessive heat input and high deposition rate. The influences of process conditions, such as energy input, wire-feed rate, welding speed, deposition pattern and deposition sequences, etc., on thermal history and resultant residual stresses of AM-processed components needs to be further understood. In addition, poor accuracy and surface finish of the process limit the applications of wire-feed AM technology. In this paper, after an introduction of various wire-feed AM technologies and its characteristics, an in depth review of various process aspects of wire-feed AM, including quality and accuracy of wire-feed AM processed components, will be presented. The overall objective is to identify the current challenges for wire-feed AM as well as point out the future research direction.

Wire-feed additive manufacturing of metal components: technologies, developments and future interests

A review of the wire arc additive manufacturing of metals: properties, defects and quality improvement

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)

Weld deposition-based rapid prototyping: a preliminary study

It is well documented that applying mechanical vibration to the mold during solidification has a profound effect on the microstructure and mechanical properties of castings. However, it is still not well understood how mechanical vibration change the resulting microstructure. Most of the available studies are qualitative and provide little quantitative information that can be used by the casting industry. In this work, mechanical mold vibration is applied to an Al–Si eutectic (Al–12.5% Si) alloy at a frequency of 100 Hz and variable amplitudes in the range of 18–199 μm. It is shown that the silicon morphology was strongly influenced by the level of vibration amplitude. Generally, increasing the vibration amplitude tends to reduce the lamellar spacing and change the silicon morphology to become more fibrous. However, exceeding a critical value of vibration amplitude tends to coarsen the silicon. The corresponding changes in mechanical properties are also investigated. It is shown that the maximum elongation is more influenced by vibration than the tensile strength for the range of conditions tested here.

Silicon morphology modification in the eutectic Al-Si alloy using mechanical mold vibration

Automated system for welding-based rapid prototyping

Due to its popularity and high crack sensitivity, 6061 aluminum alloy was selected as a test material for the newly developed double-sided arc welding (DSAW) process. The microstructure, crack sensitivity, and porosity of DSAW weldments, were studied systematically. The percentage of fine equiaxed grains in the fully penetrated welds is greatly increased. Residual stresses are reduced. Porosity in the welds is reduced and individual pores are smaller. It was also found that the shape and size of porosity is related to solidification substructure. In particular, a weld metal zone with equiaxed grains tends to form small and dispersed porosity, whereas elongated porosity tends to occur in columnar grains.

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Improved microstructure and properties of 6061 aluminum alloy weldments using a double-sided arc welding process

This study explores an improved method of welding austenitic stainless steel. The method uses two series connected arcs to weld the workpiece simultaneously from opposite sides. Owing to this arc configuration, the welding current is forced to flow from one arc to the other through the workpiece. It is known that such current flow concentrates the arcs and thus improves the penetration capability. Also, the current flowing through the workpiece generates fluid flow within the weld pool. In addition, owing to the use of the two opposite arcs, the heating tends to be symmetric. In addition to the increased penetration, the use of this method for welding austenitic stainless steel results in improved microstructure in the resultant welds because of an increased columnar to equiaxed transition and a decreased angular distortion, which sometimes induces solidification cracking.

A. T. Male

Papers

Weld deposition-based rapid prototyping: a preliminary study

Silicon morphology modification in the eutectic Al-Si alloy using mechanical mold vibration

Automated system for welding-based rapid prototyping

Improved microstructure and properties of 6061 aluminum alloy weldments using a double-sided arc welding process

Welding of austenitic stainless steel using double sided arc welding process