By Dr Michael J Fletcher of Delta Consultants for Huntingdon Fusion Techniques HFT®

An acronym for Wire Arc Additive Manufacturing, WAAM is one of several prominent 3-D printing techniques where significant advances have been made in the last five years. Already established as an alternative production process in the airframe industry WAAM is now making an impact in other manufacturing sectors.

Already attracting massive investment across the world, a recent estimate from the International Data Corporation indicates that global spending on 3-D printing will grow to $23.0 billion by 2022. This is an increase of over 23% from 2018. China, the UK and the USA spearhead the drive to exploit the potential for 3-D printing but Australia, India and the rest of Europe are also actively examining applications.

Essentially, 3-D printing involves the progressive deposition of material under computer control to generate a three-dimensional structure. Because the material source is very small and control is extremely accurate the process offers the potential to produce near-finished complex shapes that are difficult if not impossible to create by any other technique.

Wire Arc Additive Manufacturing employs an electric arc as a heat source and metal as the deposition material. Standard arc welding equipment coupled with readily available filler alloys coupled with a routine multi axis robot means that a system can be purchased for little over $100,000.

The concept of metal deposition using arc welding is not new. Over 50 years ago the process was used for cladding operations in which thick coatings were added to low alloy steels to improve corrosion or wear resistance. WAAM employs the same arc welding processes (GTAW, GMAW or PAW) but under much more precise computer control.

Previously focused on aerospace there is now growing interest from the automotive, marine, motor sport, renewable energy, oil and gas, and nuclear sectors. At Cranfield University in the UK for example there are more than 60 ongoing projects, totaling more than £3.5 million, involving almost 30 staff and MSc / PhD students; some are in collaboration with other universities such as Manchester, Birmingham and Nottingham. The work is in part funded by organisations such as Airbus, BAE Systems, United Technologies Research Centre and Lockheed Martin.

The WAAM process promises to make a reduction in the cost of parts by reducing material wastage and time to market, as well as offering the benefits of increased freedom of design and part complexity, and customisation. Thanks to low capital and operating costs, WAAM is a much cheaper process when compared with other 3-D techniques such as laser, electron beam wire or powder-based additive manufacturing.

A recent major additive manufacturing conference in Detroit included 150 sector experts on processes, applications, materials and research. They highlighted how these 3D technologies can cut costs, reduce time to market, produce stronger and lighter parts, improve efficiency and create complex geometries without sacrificing strength. A case study of a 2.1m tall additively manufactured excavator arm with a final error of 1mm was introduced.

Aerospace Applications
The early application areas have been in aerospace and several prominent examples are available to illustrate the dramatic developments.

One of the largest 3D metal titanium parts in the UK has been produced by Cranfield University. Measuring 1.2m in length. The part forms a main structural element (Fig 1) of an aircraft wing structure and took just 37 hours to build from a digital model, where previously this process would have taken weeks. An even larger aluminium wing part measuring over 2.5m in size has also been produced in less than one day.

The world’s largest and fastest metal 3D printer to date has been manufactured by Titomic Ltd in Australia and is capable of making complex aircraft wing parts of up to 9m in length. It can also print metal bicycle frames in around 25 minutes. The company is also using the additive manufacturing process to produce wear-resistant coatings for the mining industry.

Spirit AeroSystems recently began installing the Boeing 787’s first titanium structural component, made by Norsk Titanium (Fig 2). Feedback from Boeing notes that the real wins won’t involve just material reduction; they will include part weight, reduction in assembly time by consolidating systems into single 3D-printed forms, and faster time-to-market as a result of reducing the number of manufacturing steps.

Marine Applications
Casting is the traditional method used to create marine propellers, but it requires long lead times since the process involves making a mould, casting it, and then processing it. Most forging and casting companies are no longer located in Europe, which means even more time is needed to obtain parts. Additionally, most of those companies require orders for quantities larger than one part, which means warehousing a large stock of components that may never be used.

Automotive Applications
WAAM affords the possibilities of producing complex parts for vehicles that may not be possible with traditional manufacturing techniques. This is particularly attractive in sectors such as motor sport and specialist road vehicles where production runs are limited and cannot take advantage of cost reductions that come with volume manufacture. The process even offers the opportunity to produce prototypes on a one-off basis quickly and cost-effectively.

Car manufacturer Audi is taking advantage of the benefits of metallic 3D printing in collaboration with SLM Solutions Group AG. (Fig 4)

Limitations on further application of WAAM

Deposition Rates
Early uses of metal additive technology were restricted to small components because of the very low deposition rates and the resultant long and therefore expensive manufacturing times.

Rapid development by the WAAM industry generally has led to current rates of 15 kg/hr being realised with many metals. Whilst this may not appear noteworthy it brings the process into line with alternative manufacturing methods whilst at the same time offering opportunities for producing complex shapes in small runs and this is now leading to exploitation by an ever-widening industrial arena.

Component Size
Limited availability of large dimension 3-D computer numerical control equipment has restricted growth of direct metal deposition but recent developments, particularly by the aerospace industry, have expanded the scope considerably. Work at Cranfield University has achieved a milestone by depositing a 6-metre long spar using the WAAM process and an aerospace-grade aluminium alloy. The 300-kg, double-sided spar was built at the university’s 10-metre deposition facility. This trend seems likely to continue with similar facilities in Australia, USA and Spain.

Precision
Whilst the early applications of WAAM included the use of multi-axes robots, the positioning accuracy falls well short of that available with specialist computer numerical control equipment. A typical robot can offer precision of between 0.5 and 2 mm whereas a cnc facility might claim to be ten times more accurate. The final decision will be one of cost and space – robots are much cheaper and more compact.

Protection Against Oxidation
The use of high metal deposition rates brings with it the problem of protection of the metal from oxidation during the fusion and cooling cycles. Local protection using standard shields is often inadequate but specialist equipment suppliers have developed flexible enclosures capable of providing an inert gas environment. Fabricated from engineering plastics and using advanced sealing technology these enclosures can be large enough to accommodate a complete WAAM system (Fig 5) and provide a gas environment with an oxygen content as low as 20 parts per million – more than adequate to protect even the most sensitive materials from oxidation.

Lack of Awareness
The success of 3D printing generally has been publicised widely but the emphasis has been almost exclusively on a phrenetic outpouring of the more exciting applications such as those in the medical and biomedical sectors.

Despite success in the demanding aerospace industry, full engineering potential has so far gone largely unrecognised.

The proven application of WAAM in the aerospace, automotive and marine industries should now be grasped eagerly. The process promises to make significant reductions in the cost of parts by reducing material wastage and time to market, as well as offering the benefits of increased freedom of design and part complexity, and of customisation.

Sources of further information
Additive Manufacture of Large Structures. Bandfari et al. Welding Engineering and Laser Processing Centre, Cranfield University MK43 0AL,

Welding Makes Major Impact on 3D Printing Technology. Fletcher. Huntingdon Fusion Techniques White Paper WP 197. huntingdonfusion.com

What Is the Role for Additive Manufacturing in Aircraft Structural Components? Zelinski. Additive Manufacturing. March 2019

Video: WAAM Casts Away Traditional Large Manufacturing Methods.Heimgartner. Engineering.com. April, 2018

This technical article is authored by Dr Michael J Fletcher of Delta Consultants for Huntingdon Fusion Techniques HFT®. The views, thoughts, and opinions expressed in this article belong solely to the author.