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ADDITIVE MANUFACTURING
Wire AM – A new additive technology Additive manufacturing is a field where groundbreaking innovations are emerging all the time. One particularly promising new technique is wire-fed additive manufacturing, writes Alex Kingsbury. Metal additive manufacturing (AM) has certainly taken the world by storm. With the ability to create shapes not previously thought possible, this revolutionary, Industry 4.0-enabling technique has backers from a range of different industries all over the globe. However, when metal AM is mentioned, the first thought is usually of a laser-powered machine fusing metal powders layer by layer. Certainly, this has been the predominant technique with a vast amount of machine sales dedicated to laser powder bed fusion (LPBF) since the advent of commercially available AM. But new and intriguing metal AM technologies have been making headway of late and offering a point of difference to the commonly accepted LPBF systems. One such technique is wire-fed additive manufacturing. The concept is very simple: it is based on traditional welding, but rather than welding components together, a weld bead is laid upon another weld bead. This process is repeated until there is a series of weld beads welded successively, such that they create a threedimensional shape. The process is controlled by a robotic arm and the shape is built up on a substrate material (a base plate) that the part can be cut from once finished. The shape is considered a ‘nearnet shape’: it is close to the final part shape but usually requires additional machining to achieve final part shape and tolerance. This process has many benefits over both LPBF and more traditional manufacturing techniques such as casting, machining and forging.
Wire feedstock As the name suggests, welding wire is the sole feedstock for wirefed AM, meaning established supply chains can provide a feedstock source. Numerous certified alloys are readily available to build parts with. Often this means that moving to wire AM from a traditional manufacturing process does not need to involve a change of alloy, as the same alloy of the exact specification can be sourced through a global supply network. If an alloy can be welded, it can be used in a wire AM process. Operationally, using wire as a feedstock makes life in the workshop much easier. Changeover time between alloys is straightforward as a new wire is inserted and there is minimal clean-up after the previous build. Additionally, working with wire is inherently safer than other AM feedstocks such as powders. It is not reactive, nor can it be inhaled or irritate the skin.
Properties Parts made via wire AM have been proven to be stronger than parts made via forging or casting. As the wire feedstock is a 100% dense input material, there is negligible porosity induced in the fabrication process, leading to a very dense final part. Additionally, the wire AM process enables better control over deposition rates, and therefore has better control of cooling rates, enabling processing to be tailored to the working alloy. Improved material properties mean parts that once had to be constructed of solid material can be built as thinwalled parts. This reduces material consumption, improving the cost basis and overall competitiveness with traditional techniques such as casting. For parts of medium complexity that are forged and machined, wire-fed AM can be an excellent alternative process. Typically, a wire AM part undergoes a final machining step to remove surface irregularities and ensure a smooth surface. The material machined away usually amounts to 2% to 10% of the total material deposited. Compared with high ‘buy-to-fly-ratio’ parts – where in some cases
AMT OCT/NOV 2019
up to 90% of the original starting material must be machined away – this presents a significant material and cost saving. This is especially true for high-value materials that are difficult to machine such as titanium and nickel superalloys. Like most AM processes, wire AM is most suitable for low to medium-volume production, as set-up and tooling costs are minimal. This lack of tooling also increases speed to market as lead times are significantly reduced. Increased speed to market assists with product development, allowing in-field testing to feedback to further design iteration, which the wire AM process can very flexibly accommodate. This lack of tooling can also assist with reduction of lead time for critical spares. Using wire AM, lead time can be reduced from months to days, meaning a business no longer needs to maintain large inventories of critical spares. Using wire AM, part size becomes virtually unlimited. The process is only constrained by the size of the workshop and the reach of a robotic arm. As the process utilises a gas shroud, reactive materials such as titanium and aluminium can be easily processed. Of course, just because you can, does not mean you should. Exceptionally large items (in excess of 2m) tend to require excessive fabrication times and can make wire AM uncompetitive. Likewise, very small items (less than 20cm) tend not to be cost-competitive. However, like most manufacturing technologies, this is material and part-requirement dependent. Wire AM has a sweet spot where the technology is best put to use; usually for medium size parts of medium complexity. This applies across all metals and part functions.
Made in Australia by AML3D Andy Sales knows this value only all too well. With a background in welding technology, Sales went to Cranfield University in the UK to complete his Masters in 2012. Cranfield had been developing a wire AM process and this inspired Sales to return to Australia to establish AML3D, a service bureau based on wire AM technology. In addition to commissioning its own wire AM-based system,