There is a popular misconception that powder based additive manufacture is superior to the wire alternative. This impression has been created largely through aggressive marketing and by the technical press preferring the more glamourous powder method used for creation of body implants.
Whilst it has to be conceded that the relatively delicate powder deposition process is excellent for producing small components, often requiring no further machining, in terms of speed and cost-effectiveness the wire option wins hands-down.
Wire and Arc Additive Manufacture (WAAM), is performed by laying down progressive beads of metal under computer numerical control to create a shape. The alternative version uses a laser or electron beam as the heat source in conjunction with metal powder, Direct Metal Laser (or Electron Beam) Sintering (DMLS or DMEBS).
Let’s look at the characteristics in a little more detail.
Cost of Equipment
Powder deposition technology requires a substantial metal enclosure within which is situated, all the operating system including laser (or electron beam) heat source, computer numerical control equipment and powder dispensing. A typical cost of a production system is $750,000.
Wire deposition is undertaken with standard arc welding equipment coupled with a 5-axis articulated robot costing a total of $120,000.
Cost of Consumables
Only a limited number of metallic alloy systems are currently available for additive manufacturing using powders principally Ti-6Al-4V, some stainless steels, Inconel 625/718, and Al-Si-10Mg. The cost for most stainless steel is in the region of $400/kg.
Few problems remain when it comes to fusion welding and consequently an extensive variety of wire electrodes is available, most of which can be used for arc deposition. Because of the quantity of wire manufactured the cost is not high. Typically, stainless steel filler wire is readily available for $30/kg.
Powder deposition rates are very low and average 0.1 kg/hr. With advancing technology this may well increase but at the present time this severely restricts applications.
The wire arc process is capable of laying down 10 kg/hr of a wide range of metal alloys.
Protection of the Deposit
Molten metal needs to be protected against oxidation and contamination during the deposition process and this is a common feature of both powder and wire processes.
The electron beam technique is undertaken in vacuum and this obviates the need for any additional shielding. Inert gas such as argon is used with both the laser powder and arc wire techniques. Since the laser procedure is undertaken inside a metal enclosure the enclosed volume can be purged with inert gas. With arc wire deposition the welding torch provides a protective flow of inert gas, but a much better method is to contain the torch and manipulation system and special flexible enclosures have been developed for this purpose.
Where inert gas is used for protective purposes there exists a need for gas quality control and sensitive instruments are available that can detect as little as 10 ppm oxygen.
The integrated laser and electron beam techniques are very expensive and require special purpose and sophisticated equipment. Arc Wire techniques employ readily available gas tungsten arc welding plant coupled with a standard computer numerically controlled system such as a multi-axis robot.
In terms of applications for the powder and arc metal processes the welding version is most suitable for heavier and larger products whilst the powder alternative is best applied where smaller, delicate objects are required. In other words, welding is essentially a bulk deposition technique and powder is a precise and highly controlled process.
Significant welding applications have been found in the maritime and aerospace sectors whereas powder had been used for the production of body implants and specialist precision components as evidenced by the publications below.
Advances in Laser Materials Processing, Woodhead Publishing Series in Welding and Other Joining Technologies, 2018, Pages 507–539 Laser-Based Additive Manufacturing Processes
Hybrids accelerate adoption of laser additive manufacturing, Ken Vartanian, Industrial Laser Solutions, September 2015
RobotWorx, 370 W. Fairground St. Marion, OH 43302
Lincoln Electric Company, St. Clair Ave. Cleveland, OH 22801
Gratschmayr P, IMT Conference, Chicago Sept 2016
World’s first class approved 3D printed propeller. International Institute of Marine Surveying May 2017
Design for Wire and Arc Additive Layer Manufacture. J. Mehnen et al. 20th CIRP Design Conference, Nantes April 2010.
Surgical implant to replace ribcage. Metal AM, February 2018
Mechanical behaviour of additive manufactured, powder-bed laser-fused materials. Mower et al Materials Science and Engineering: Volume 651, 10 January 2016, Pages 198-213
Wire & Arc Additive Manufacturing, S. W. Williams et al, Materials Science & Technology 2016 Vol 32.
Cranfield University complete additive manufacture of a 6-metre-long aluminium alloy aircraft wing spar using the arc wire process.
Multi-axis robot system inside large flexible enclosure, for manufacturing large Titanium structures by additive manufacturing with the WAAM process.
Simple xyz axis manipulation system in a vertical enclosure for research into additive manufacturing by the WAAM process.
By Dr. Michael J. Fletcher M.Sc. Metallurgy
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