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“I keep hearing about advances in additive manufacturing with metals.  How does the arc welding based additive manufacturing process differ over other methods?”

The good news for welders and the welding industry is that we’ve been adding metal to manufacture objects since the beginning of the industry.  Certain metal artists are experts at this technique as their primary medium to create sculptures using nothing but a welding machine and filler metal.  (The opposite of additive manufacturing is subtractive manufacturing where we cut parts or remove material by machining processes; imagine the artist chiseling an object from a block of stone or carving it out of wood.)  As welders we typically will be cladding a surface, building up the edge of a plate, and occasionally other pieces of base metal get in the way, and we end up sticking two or more pieces together to make a welded fabrication.  

Additive manufacturing is a collection of methods to create objects through building up layers.  The ASTM lists seven different categories of these technologies, but only four of these are capable of creating metallic objects:  Binder Jetting (which uses a metal powder and includes a non-metallic binding agent or glue), Powder Bed Fusion (typically using a laser beam to fuse objects from metallic powders), Sheet Lamination (one variation uses Friction Stir Welding to fuse layers of metallic sheets), and Directed Energy Deposition (which uses a welding process, including GMAW, to deposit successive layers).

Within the past few years, the use of a welding robot and Gas Metal Arc Welding (GMAW) has started to stand out as a key industrial scale Directed Energy Deposition (DED) additive manufacturing process.  Since this process uses a welding electrode filler wire, this method has taken the acronym WAAM (Wire Arc Additive Manufacturing).  This method has several key advantages over the alternatives listed above:

• WAAM is based upon arc welding, a process where industries have many decades of familiarity. 

• WAAM can produce deposition rates of up to 10x greater or potentially even higher.

• An arc welding robotic cell has significantly lower capital costs for an operating machine versus a large laser-based system.

• The wire-based process has more widely available and less expensive feedstock materials for a wide variety of engineering alloys.

• There are fewer safety hazards for personnel working with a solid welding feedstock wire as compared to very fine metallic powders which can present an inhalation or explosion hazard.

• With the wire-based method, there is better control over the deposited alloy composition and subsequent properties.

Large objects, 100’s of kg in mass, are being printed right now with the WAAM method for ships, pressure vessels, aerospace, and large structural components.  One company in Amsterdam, Netherlands has even printed an entire 12-m long stainless-steel pedestrian bridge with a mass of 6,000 kg!  Any metal that can be arc welded is a candidate material for the WAAM process.

For several years Conestoga College welding technology students and faculty have been developing methods to create large objects from 3D CAD models using their robotic welding lab.  Important aspects of developing this technology are to experiment with the many welding process parameters and their effects on the print programs, trying various alloys and combinations of alloys, developing destructive and non-destructive testing methods, calculating the production rate, estimating production costs, and evaluating the resulting mechanical properties of the material produced.  Steel objects with superb strength, ductility, and notch toughness have been produced and experiments with aluminum alloys have begun.

In the demonstration object shown, Conestoga Manufacturing Engineering Technology – Welding & Robotics students Scott McElhone & Jackson Macor designed and printed the light-weight structural steel column (double-wall with internal corrugations).  This object was designed in CAD as a solid model, followed by ‘slicing’, and then generating the robotic path using off-line programming (CAD to Print).  This column has a mass of ~3 kg per 100 mm in height and takes approximately 2.5 hrs. (per 100 mm) to print. 

The WAAM process is relatively new, and there are many challenges in integrating advanced welding automation with a precisely controlled welding process and understanding the metallurgy, however, welding experts are uniquely placed to lead the way for bringing this process to wide-spread use.  In some ways this is similar to developing a new welding procedure, with the major benefit that we don’t have to worry about the base metal heat affected zone unless we’re attaching the object to another component.  

Just imagine that no one had ever produced metal castings or forgings before, and we must think about all the variations, alloys, metallurgical effects, product designs, costs, tooling, post-processing, inspection and quality control, and production procedures to make it successful for industry.  That is the emerging state of the very promising WAAM process in 2024.

Jim Galloway is a Professor of Welding Engineering Technology at Conestoga College in Cambridge, Ontario.  Jim also volunteers on several CSA Technical Committees related to welding safety, electric welding machines, and welding filler metals.

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