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 three-dimensional 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 ‘near-net 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 wire-fed 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 thin-walled 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 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, AML3D has also developed a software package that integrates material-processing parameters with its robotic cell. These sets of material-specific parameters have been developed in-house by AML3D, and the team has been rigorous in ensuring they can achieve repeatability and reliability in their process.
But far from being content with that, Sales has ambitious global plans for AML3D. The company is planning a production facility in Singapore in the near term, with the ability to further expand that capability. This is driven by demand from the Singapore marine hub, as the location is a strategic hub for commercial shipping routes.
Sales recognised the applicability of wire AM for shipping early on. Ten months after establishing AML3D in Adelaide he secured certification from Lloyd’s Register, the global shipping industry accreditation body. Being a certified provider gives customers the assurance that work is being performed to stringent quality standards. With certification in place, AML3D was quick to deliver its first part to a marine customer: a set of martensitic stainless steel wear rings.
The rings were normally fabricated via a forging process, but this required an additional heat treatment post-processing step. The total lead time was six-to-eight weeks, which as a long lead item was either held in a spares inventory or replaced prematurely. Using wire AM, AML3D was able to manufacture the rings for the same cost, but was able to reduce the lead time to a few days. This is a real game-changer for ships in dock for a limited time.
In addition to the marine sector, AML3D is also engaged with Boeing. For the aerospace industry, reducing material wastage is key to profitability, particularly with expensive, high-value material such as titanium, where as much as 80% of the starting material ends up as chips or swarf – a low-value titanium waste stream. Boeing in particular has had a long-standing interest in pursuing wire AM, and has been working with Norsk Titanium, a company that uses a wire AM process that employs plasma as a heat source. Working with Boeing, Norsk Titanium has received Federal Aviation Administration (FAA) certification for two structural aircraft parts in the US.
An aluminium jet engine cover plate manufactured by AML3D for an unnamed client showcases the benefits of wire AM when compared with machining. The cover plate was ordinarily machined from a 30kg billet and took four days of non-stop machining to produce. Using wire AM, a final machine of the near-net shape took just six hours to finish. Likewise, an aluminium wing rib, machined from plate, saw a 70% reduction in waste and a 60% reduction in cost. With those figures it’s hardly surprising that aerospace players across commercial and defence sectors are taking note of wire AM.
A new machine
To address the need for onsite production, especially in remote locations where spares inventories can be a real pain point for companies in the resources sector, Sales has created a packaged wire AM turnkey solution. Being guided by Industry 4.0 principals, the system integrates wire AM with machining and is controlled via AML3D software developed specifically for this hybrid solution. It means that customers can develop a digital inventory and produce a fully finished part onsite in days if not hours.
Selling this system, and the wire to be used in it, eases the pressure on the AML3D facilities in Adelaide and Singapore, and optimises the manufacturing-on-demand capabilities of wire AM. The machine is the first of its kind to be offered on the market.
Despite the outstanding possibilities of wire AM, AML3D is part of only a handful of wire AM-based businesses around the globe. RAMLAB in the Netherlands is the only other active service bureau, notable for its wire AM-produced ship propeller. MX3D, also in the Netherlands, uses a similar concept and in 2015 showcased an eyecatching demonstration of a robot 3D printing a bridge in mid-air. Norsk Titanium and Sciaky Inc. both produce wire AM systems – the former with a plasma-based process, Sciaky with an electron beam solution.
Like any new technology, it takes time for applications to develop and the benefits to proliferate through industry. Yet it is encouraging to see a small company in Australia with global connections taking the lead. No other wire AM companies around the world have made quite the progress that Sales and the team at AML3D have, with an established global presence, high-profile partnerships in place, and a business model poised for growth. Australia is fortunate to have a company right on our doorstep taking on this next frontier of additive manufacturing.
Alex Kingsbury is an Additive Manufacturing Industry Fellow at RMIT University.