The current state of research of wire arc additive manufacturing (WAAM): a review

Wire arc additive manufacturing is currently rising as the main focus of research groups around the world. This is directly visible in the huge number of new papers published in recent years concerning a lot of different topics. This review is intended to give a proper summary of the international state of research in the area of wire arc additive manufacturing. The addressed topics in this review include but are not limited to materials (e.g., steels, aluminum, copper and titanium), the processes and methods of WAAM, process surveillance and the path planning and modeling of WAAM. The consolidation of the findings of various authors into a unified picture is a core aspect of this review. Furthermore, it intends to identify areas in which work is missing and how different topics can be synergetically combined. A critical evaluation of the presented research with a focus on commonly known mechanisms in welding research and without a focus on additive manufacturing will complete the review

Development of surface coatings for high-strength low alloy steel filler wires and their effect on the weld metal microstructure and properties

The lightweight construction of steel structures is often limited by the mechanical properties of the weld metal. The strength values of modern base materials are not achieved in the weld metal. There is a considerable need to develop welding consumables that allow the processing of modern fine-grained structural steels without limiting their potential. The Physical Vapor Deposition (PVD) coating of welding wire electrodes can increase the strength of the weld metal of a Mn4Ni2CrMo welding wire electrode by up to 30%. By using different coating elements, the Hall–Petch relationship can be exploited and such an increase in strength can be achieved. Especially by applying titanium, vanadium, and yttrium coatings, the strength of the weld metal can be increased. Due to a multilayer structure of the coating, the weld metal and the process can be influenced independently of each other. The effects of mono-element coatings and multi-component coatings on the weld metal and the process are discussed. PVD coatings allow welding wire electrodes to be individually adapted to the requirements

Re-melting behaviour and wear resistance of vanadium carbide precipitating Cr27.5Co14Fe22Mo22Ni11.65V2.85 high entropy alloy

High entropy alloys (HEAs) are among of the most promising new metal material groups. The achievable properties can exceed those of common alloys in different ways. Due to the mixture of five or more alloying elements, the variety of high entropy alloys is fairly huge. The presented work will focus on some first insights on the weldability and the wear behavior of vanadium carbide precipitation Cr27.5Co14Fe22Mo22Ni11.65V2.85 HEA. The weldability should always be addressed in an early stage of any alloy design to avoid welding-related problems afterwards. The cast Cr27.5Co14Fe22Mo22Ni11.65V2.85 HEA has been remelted using a TIG welding process and the resulting microstructure has been examined. The changes in the microstructure due to the remelting process showed little influence of the welding process and no welding-related problems like hot cracks have been observed. It will be shown that vanadium carbides or vanadium-rich phases precipitate after casting and remelting in a two phased HEA matrix. The hardness of the as cast alloy is 324HV0.2 and after remelting the hardness rises to 339HV0.2. The wear behavior can be considered as comparable to a Stellite 6 cobalt base alloy as determined in an ASTM G75 test. Overall, the basic HEA design is promising due to the precipitation of vanadium carbides and should be further investigated

Beneficial use of hyperbaric process conditions for welding of aluminium and copper alloys

The joining of components with as few weld layers as possible is an important aspect of weld seam design due to the resulting reduced manufacturing effort and reduced influence of thermal cycles on the base material as well as reduced distortion. For materials with good thermal conductivity, this is not easily possible. The energy density of the arc has been found to be the core parameter for determining the penetration. In the present work, it is shown how the use of a hyperbaric process environment (2 to 16 bar) allows an increase of the energy density of the arc and thus an increase of the penetration depth for selected aluminium and copper alloys. Furthermore, the effects of this novel approach on weld metal metallurgy are presented. It is shown that the penetration depth can be doubled by increasing the ambient pressure. Furthermore, a statistical model for the prediction of the penetration depth depending on the welding parameters will be presented

Wire and arc additive manufacturing of a CoCrFeMoNiV complex concentrated alloy using metal-cored wire: process, properties, and Wear Resistance

The field of complex concentrated alloys offers a very large number of variations in alloy composition. The achievable range of properties varies greatly within these variants. The experimental determination of the properties is in many cases laborious. In this work, the possibility of using metal-cored wires to produce sufficient large samples for the determination of the properties using arc-based additive manufacturing or in detail wire and arc additive manufacturing (WAAM) is to be demonstrated by giving an example. In the example, a cored wire is used for the production of a CoCrFeNiMo alloy. In addition to the process parameters used for the additive manufacturing, the mechanical properties of the alloy produced in this way are presented and related to the properties of a cast sample with a similar chemical composition. The Characterization of the resulting microstructure and wear resistance will complete this work. It will be shown that it is possible to create additively manufactured structures for a microstructure and a property determination by using metal-cored filler wires in arc-based additive manufacturing. In this case, the additively manufactured structure shows an FCC two-phased microstructure, a yield strength of 534 MPa, and a decent wear resistance

Micromagnetic properties of powder metallurgically produced Al composites as a fundamental study for additive manufacturing

Resource-efficient manufacturing with a high degree of freedom in terms of component shape can be realised through additive manufacturing. The focus can lie not only on the manufacturing process in terms of geometrical correctness, stability, etc., but also on the targeted development of specific material properties. This study shows the development of hybrid material systems made of aluminium and the ferromagnetic particles iron, cobalt, and nickel. The aim is to use the ferromagnetic properties as sensor properties to enable the easy sensing of material properties such as the microstructure, fatigue, or occurring stresses. To easily adopt different compositions, hot isostatic pressing was selected for the characterisation of the material composites Al-Fe, Al-Ni, and Al-Co with regard to their magnetic properties. Subsequently, transfer to the additive manufacturing process of wire and arc additive manufacturing gas metal arc welding was carried out by mixing the powder separately into the weld pool. The study shows that it is possible to prevent a complete transformation of Ni and Co into intermetallic phases with Al by adjusting the influencing variables in the HIP process. Magnetic properties could be detected in the composites of Al-Co and Al-Fe. This work serves as a preliminary work to realise additive components made of hybrid material systems of Al-Fe, Al-Co, and Al-Ni with the GMA welding process

Real-time measurement of temperature and volume of the weld pool in wire-arc additive manufacturing

The quality of the material deposition and contour accuracy produced by WAAM (Wire Arc Additive Manufacturing) depends on process parameters such as the temperature and the volume of the weld pool. The control of the welding process can be substantially improved by obtaining real-time signals of the weld-pool temperature and volume. In this paper, we present a new optical sensor that can measure the quantities through the welding arc. We have developed a ratio pyrometer with narrowband filters that suppresses the radiation from the plasma. We present our new sensor in this paper and demonstrate its capability to measure the weld-pool temperature pyrometrically and the weld-pool area by digital image processing as a real-time signal through the arc. In addition, we estimate the weld-pool volume from its area and the known material inflow

Potenziale neuartiger Schweißdrahtbeschichtungen in der Prozessgestaltung

Durch Nutzung höchstfester Stähle in der Konstruktion steigen die Anforderungen an Schweißzusätze und Prozessführung. Nachfolgend werden erste Untersuchungen zu den Potentialen von gezielt beschichteten Massivdrähten zur Prozessbeeinflussungund dem Einfluss der Beschichtung auf die mechanisch-technologischen Eigenschaften des Schweißgutes dargestellt. Es zeigen sich dabei deutliche Einflüsse der Beschichtungselementeauf die Prozesscharakteristika wie Einbrandverhalten und Gefüge des Schweißgutes sowie signifikante Einflüsse auf die mechanischen Eigenschaften

Influence on the weld strength of high-strength fine-grained structural steels by thin-film-coated GMA welding electrodes

The increasing demand for high-strength fine-grain steels for the purpose of reducing the weight of steel structures and increasing payloads, is driving forward the development of fine-grain steels. However, with the currently available welding consumables, it is not possible to achieve the strengths of modern fine-grain steels with a grade of S1300QL in the weld metal. As a result, there is a need for novel welding consumables, which guarantee high-strength joints. The application of thin, functional layers on GMA welding electrodes by a PVD coating process makes it possible to influence the mechanical-technological properties to an extent which cannot be achieved by state-of-the-art technology. The sputtering of different elements on the substrate material of GMAelectrodes and the layer thickness has an influence on the welding process and the welding metal. Especially, the influence on the microstructure by a niobium coating of different layer thickness is presented. Furthermore, the changes in the mechanical properties of the weld metal depending on the layer thickness or rather the niobium content are shown. In particular, the fine-grain and carbide-forming effect of niobium and the influence on the mechanical properties are presented. Here niobium contents between 0.5 wt.-% and 1.5 wt.-% are in the focus of investigations

Liquid metal embrittlement in resistance spot welding and hot tensile tests of surface-refined TWIP steels

Automotive industry strives to reduce vehicle weight and therefore fuel consumption and carbon dioxide emissions. Especially in the auto body, material light weight construction is practiced, but the occupant safety must be ensured. These requirements demand high-strength steels with good forming and crash characteristics. Such an approach is the use of high- manganese-content TWIP steels, which achieve strengths of around 1,000 MPa and fracture strains of more than 60%. Welding surface-refined TWIP steels reduces their elongation at break and produces cracks due to the contact with liquid metal and the subsequent liquid metal embrittlement (LME). The results of resistance spot welds of mixed joints of high-manganese- content steel in combination with micro-alloyed ferritic steel and hot tensile tests are presented. The influence of different welding parameters on the sensitivity to liquid metal embrittlement is investigated by means of spot welding. In a high temperature tensile testing machine, the influence of different parameters is determined regardless of the welding process. Defined strains just below or above the yield point, and at 25% of elongation at break, show the correlation between the applied strain and liquid metal crack initiation. Due to the possibility to carry out tensile tests on a wide range of temperatures, dependencies of different temperatures of the zinc coating to the steel can be identified. Furthermore, the attack time of the zinc on the base material is investigated by defined heating periods