Wire Arc Additive Manufacturing (WAAM)
The invention of wire arc-additive manufacturing (WAAM) is driven by the demand for better manufacturing efficiency in engineering constructions, presently called a direct energy repositioning arc (DED-arc). Its ability to produce very close to the net form provides the potential for significant cost and lead times reductions without needing complex tools, moulds or dies, increasing materiel efficiencies, improved component performance and a reduced inventory and logistics cost by local, on-demand production.
Working of WAAM
The WAAM is an arc welding process used to print metal components of 3D and is a version of direct energy deposition technology. WAAM operates by melting metal wire utilising electric arc as thermal source, as opposed to the most popular metal powder Additive Manufacturing techniques. A robotic arm controls the process and the shape is formed on a material substrate (a base platform) which can be cut out from the finished object. The wire is extruded to the substrate surface as perls when melted. When the beads stick together, a metal layer is created. Then, layer by layer, the process is repeated until the metal section is completed.
Robotic WAAM System
As a mechanism of motion, most WAAM systems use an industrial articulated robot. There are two different designs of the system. The first design has an inert gas protection environment similar to laser Power-Bed Fusion (PBF) systems using an enclosed chamber. The second concept uses local gas protection mechanisms, existing or specifically designed, with the robot positioned on a linear rail for increasing the overall working surround. It can build up to several metres of dimension very large metal structures.
Materials used in WAAM
The materials that can be welded can be used in WAAM for example Titanium, Nickel, Stainless steel, and their alloys.
1 Titanium Alloys
Because of its high strength-to-weight ratio and naturally high material cost, titanium alloys have been extensively explored for use in aircraft components using additive manufacturing. There is growing desire for more efficient and cost-effective alternatives to subtractive manufacturing, which has relatively low fly-to-buy ratios for many component designs. The WAAM technique has numerous commercial applications, particularly for large-scale titanium components with complicated architectures.
2 Aluminum Alloys and Steel
Although fabrication trials for a variety of aluminium alloy series, including Al-Cu (2xxx), Al-Si (4xxx), and Al-Mg (5xxx), have been successful, the commercial value of WAAM is primarily justified for large and complex thin-walled structures, because the cost of manufacturing small and simple aluminium alloy components using conventional machining processes is low. Although steel is the most commonly used engineering material, using WAAM to fabricate it is unpopular for the same reason. Another reason for WAAM’s limited commercial application in aluminium is that some series of aluminium alloys, such as Al 7xxx and 6xxx, are difficult to weld due to turbulent melt pools and weld defects that frequently occur during the deposition process.
In general, as-deposited additively manufactured aluminium alloy parts have poorer mechanical properties than billet-machined parts. Most as-deposited aluminium parts are subjected to post-process heat treatment to refine the microstructure in order to achieve higher tensile strength.
3 Nickel-based Superalloys
After titanium alloys, nickel-based superalloys are the second most popular material studied by the additive manufacturing research community, owing to their high strengths at elevated temperatures and high fabrication costs using traditional methods. Because of their outstanding strength and oxidation resistance at temperatures above 550 °C, nickel-based superalloys are widely used in the aerospace, aeronautical, petrochemical, chemical, and marine industries. Various nickel-based superalloys, such as Inconel 718 and Inconel 625 alloy, have been studied after WAAM processing to date.
LIMITATIONS OF WAAM
1 Residual Stress and Deformations
Distortion and residual stress are inherent in the WAAM process, as they are in all additive manufacturing processes, and cannot be completely avoided. The residual stress can cause part distortion, loss of geometric tolerance, layer delamination during deposition, and deterioration of fatigue performance and fracture resistance in additively manufactured components. As a result, cooling must be considered in the process.
2 Porosity
WAAM raw materials, including as-received wire and substrate, frequently have surface contamination, such as moisture, grease, and other hydrocarbon compounds, which can be difficult to remove completely. These contaminants can easily be absorbed into the molten pool, resulting in porosity after solidification.
3 Some materials require shielding
Shielding is important to generate an inert atmosphere when employing specific materials, such as titanium, to guarantee the correct building conditions. The procedure must therefore be carried out in an inert gas chamber. The inert gas chamber nevertheless limits the size of components which may be made using this system and increases the equipment cost when establishing such a chamber.
ADVANTAGES OF WAAM
1 Ability to 3D Printed Large Metal Parts
WAAM is well suited for the production of metal parts of massive size. This is in opposition to metal AM technologies used for Powder Bed Fusion (PBF), which usually create smaller, high definition components. In contrast to the limited PBF AM machines, a WAAM robotic arm has more flexibility of movement, such that the size of a component is not limited to space but only via the distance the robotic arm is able to reach. This enables the fabrication of larger parts that with PBF methods would not be viable.
2 Cheaper Process and Materials Cost
The welding wire used for WAAM printing is considerably lower than the metal powder used for PBF in terms of the material expenses. The reason is that WAAM technology is based on welding, a proven production process. WAAM gear generally comprises off-shelf welding equipment that is cheaper than several on the market metal 3D printers. Furthermore, wire is usually simpler to handle than powder, and particular protection equipment needs to be used.
3 Quality of products is relatively higher
WAAM-made parts have high density and robust mechanical qualities, which can be compared with parts produced using traditional production processes. Because the wire feedstock is 100% dense input, zero porosity results in a dense final phase of the manufacturing process.
4 Suitable for Repair Operations
WAAM is also a good option for specific components like turbine blades, as well as moulds and dietary operations. WAAM can be used to repair workout or damaged parts by depositing new material onto the surface. This can lead to significant cost savings because the need for a new part to be produced is eliminated.