Understanding WAAM: A Complete Guide to its use in Metal 3D Printing

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Wire Arc Additive Manufacturing (WAAM) is a subset of Directed Energy Deposition (DED) 3D printing. DED is a metal 3D printing process where a metal substance in either powder or wire form is deposited via a nozzle attached to a multi-axis arm. To melt the metal and create the part one layer at a time, a focused energy source such as a laser, electron beam, or plasma is used. In WAAM’s case, an electric arc serves as the heat source, drawing inspiration from arc-welding techniques.

WAAM technology operates on the principle of various automated welding techniques using robotics: metal-inert gas (MIG) or metal-active gas (MAG), tungsten-inert gas (TIG) or plasma arc-wire (PAW) welding. Cold Metal Transfer (CMT) welding process, which is a subcategory of MIG and was created by Fronius in 2004, is also used. WAAM is compatible with various metals, including titanium, aluminum, nickel, and steel alloys, among others.

Applications for WAAM 3D Printing

Like with other DED processes, WAAM is often used to repair equipment and reproduce parts that are no longer manufactured, in order to maintain older machines. However, the technology can also be used to manufacture complete parts. WAAM is used in particular in the aeronautics, aerospace, automotive, energy and defense sectors. It is used to manufacture prototypes, molds, single parts and small series. Its use for mass production is still under review, however, though it is particularly well-suited to the creation of large, metal parts.

For example, in the aerospace sector, Naval Group used WAAM technology to manufacture a propeller for the mine-hunting ship Andromède. In the energy sector, Vallourec used WAAM to produce the first sealing ring to ensure the safety of EDF Hydro’s hydroelectric installations, measuring one meter in diameter and weighing 100 kg. In the robotics sector, MX3D also used the technology to produce a structural steel connector. MX3D also uses WAAM to manufacture pipe connectors for the oil and gas industry, as well as gears and custom components for large machines. MX3D even built a bridge in Amsterdam using the WAAM process! Moreover, Relativity Space used this technology to build its Terran 1 light launcher. The production of molds for the plastics industry is another common application.

WAAM 3D printing offers many advantages. First and foremost, printing speeds are high, which has a positive impact on production times. Costs are also lower than for machines using powder-bed fusion technologies, in particular Selective Laser Melting (SLM). WAAM technology also stands out for its ability to produce extremely large parts. As already mentioned, a wide range of compatible metals is also available.

Limitations of the Technology

The WAAM process also has its limitations. Since it allows faster printing, the detail and dimensional accuracy of the parts are less well reproduced than with powder-bed fusion technologies. Parts manufactured using WAAM technology can have defects such as internal porosities, which can degrade the mechanical properties of the part, either statically or in fatigue (when the part is subjected to various forces, resulting in damage). This is particularly true of aluminum parts.

Residual stresses are another anomaly that can occur with WAAM technology. They can lead to deformation of the part’s dimensions and/or shape, notably through curling, warping or delamination. All these phenomena are characterized by deformation on the layers of the printed part, be it the top, bottom or, in the case of delamination, all the layers. These deformations are caused by the very high working temperature and the technical nature of the materials. They will result in the part holding up poorly when forces are exerted on it.

Vallourec uses WAAM technology for power plants (photo credits: Vallourec)

To reduce the occurrence of defects in the Wire Arc Additive Manufacturing (WAAM) process, it is crucial to understand and accurately set all the WAAM parameters. These parameters like unwinding speed, feed speed, current, voltage, layer thickness, protective gas flow rate, and bead spacing are key to ensuring a consistent molten metal deposition and constant heat supply.

There are also technical solutions that can help mitigate these anomalies, such as mechanical work-hardening or rolling. This technique involves applying pressure on the weld bead using a roller during the cooling phase, which effectively reduces porosity. Preheating the material is another method that can be used to minimize residual stresses. It is also important to note that certain materials and alloys, such as aluminum-copper, aluminum-titanium, and aluminum-iron alloys, are more prone to cracking or delaminating than others.

Like other additive manufacturing technologies, the WAAM process also requires a substantial amount of post-processing. This is usually done through a traditional machining process, however, for some WAAM applications, this machining can also be done during the printing phase using a secondary robot.

WAAM 3D Printer Manufacturers

An MX3D 3D printer using WAAM technology (photo credits: MX3D)

Manufacturers of 3D printers using WAAM technology include Prodways, whose 3D printers work with the WAAM-TIG process, Norsk Titanium and its in-house Rapid Plasma Deposition (RPD™) process, GEFERTEC, MX3D, WAAM3D and Lincoln Electric, among others.

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