Additive manufacturing (AM) is an alternative manufacturing method to conventional processes, such as casting and subtractive machining. This technology has gained considerable attention in the aerospace and automotive industries due to its many potential benefits, such as rapid prototyping, near-net-shape processing, component mass reduction, and geometric freedom. Initially developed around polymeric materials, the advancement of AM technology has pushed AM of high-density metallic materials to use a variety of high-power laser and welding-based technologies [1
Metal-based AM processes often fit within two distinct principles of operation: powder bed fusion or direct energy deposition. The AM processes also differ by the heat source (e.g., laser, electron beam, and arc) and materials (e.g., powder, and wire) used in the deposition. In essence, almost all of the AM processes for the deposition of metallic materials are fundamentally repetitive welding processes.
The primary and universal principle of AM technologies involves the direct production of 3D objects from computer-aided design (CAD) data. These CAD data can be analyzed and converted into an additive manufacturing file format. From this, tool paths are then calculated and created from the slicing routine, and process parameters are derived, which are then uploaded to the specific AM equipment.
In a powder bed fusion system, material is distributed across the work area to form a thin metal powder layer. A programmed energy source transmits energy to the surface of the bed, thereby melting the powder to form the desired shape. After the additional powder is raked across the bed area, the process is repeated until desirable geometry is created. While powder bed fusion systems have the benefit of producing internal passages, high-resolution features, and maintaining dimensional accuracy, they suffer from disadvantages such as complicated set-ups, expensive equipment, and post-processing cleanup requirement [4
In direct energy deposition systems, two basic strategies are used for depositing metal that is powder feeding and wire feeding. In powder feed systems, metallic powders are conveyed through a nozzle onto the build surface. The powders are then met by the energy source, melting a monolayer or more of the powder into the desired shape. This process is then repeated until the component is built. There are two possible configurations of the powder feed system. In one configuration, the workpiece remains stationary while the deposition head moves. In the second configuration, the deposition head remains stable and the workpiece is moved. The benefits of this type of system include larger build volumes and the ability to be used to refurbish damaged components. Drawbacks include expensive equipment such as laser and robotic systems, and post-processing cleanups [6
In wire feed systems, the energy source may include electron beam, laser beam, or plasma arc. Typically, the plasma arc utilizes welding processes to generate the energy source. The material deposited is in the form of wire. A single bead of metal is deposited, and subsequent passes are built upon to develop a three-dimensional structure. The benefits of wire feed systems include a high deposition rate, huge build volumes, and less expensive equipment. When compared to traditional machining and subtractive manufacturing, the wire arc additive manufacturing (WAAM) systems can reduce fabrication time by 40–60% and post-machining time by 15–20% depending on the component size [8
]. When comparing with powder bed fusion systems, the main drawbacks of WAAM systems are lower dimensional accuracy, difficulty in building complex geometries, and need for more extensive machining [6
Gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), or plasma arc welding (PAW) processes are usually used in wire arc additive manufacturing (WAAM). GMAW consists of a welding process in which an electric arc forms between a consumable metal inert gas (MIG) wire electrode and the workpiece metal. The formation of the electric arc heats the metal, causing it to melt and join. GTAW is a welding process that utilizes shielding tungsten inert gas (TIG) and a non-consumable tungsten electrode to produce the arc. PAW is a welding process similar to TIG; the critical difference from GTAW is that here the positioning of the electrode is within the body of the torch, and the plasma arc can be separated from the shielding gas.
Typically, WAAM systems utilize sophisticated robotic equipment to mobilize the torch component on a fixed workpiece and some use expensive CNC equipment to move the workpiece precisely into the desired positions. The central concept of WAAM is to produce a metallic part by melting a wire material using an electric arc in a layer-by-layer format [6
Several researchers around the world have studied WAAM processes. In many cases, researchers have deployed WAAM systems through the use of GMAW processes due to their popularity, affordable welding equipment and, semi-automatic wire feed system [11
]. For example, Rosli et al. developed a WAAM system by using MIG welding equipment [13
]. The GTAW system provides some advantages over GMAW. The researchers at the University of Kentucky used a GTAW system to control the size and frequency of deposited droplets to improve deposition accuracy [14
]. A GTAW system was also incorporated into a robotic arm to deposit material into specific geometric shapes and then with a five-axis CNC machine to smooth all surfaces [15
]. Variations of these designs have been used in other systems. For instance, a six-axis welding robot, instead of CNC, allowed improved precision with larger travel movements [16
]. The advantage of using GTAW can range from the variety of materials that can be deposited, finer weld beads, less heat input, less porosity, better mechanical properties and better surface finish [17
]. Anzalone et al. also developed a low cost WAAM system by using delta bot and GMAW equipment [19
Different metallic alloys can be used in WAAM systems; Williams et al. explained the usage of aluminum, titanium and steel parts that are mainly used in aviation industries such as landing gear assemblies, spars, wing ribs [20
]. Gu et al. studied on different strategies such as cold working and heat treatment to increase strength in copper alloys [21
]. Yan studied low thermal expansion coefficient Invar alloy composite mold tool repair with WAAM process [22
WAAM-fabricated components are often comparable to their conventionally processed counterparts in terms of mechanical properties. However, WAAM processing may introduce some critical defects, such as porosity, residual stress and cracking. Defects in WAAM can result from a number of factors, including thermal deformation due to heat accumulation, an unreliable programming strategy, an unstable welding pool, and contamination from the environment. There is typically severe oxidation in titanium alloys, porosity in aluminum alloys, poor surface roughness in steel, and severe deformation and cracks in nickel alloys [5
The safety issues of WAAM systems are similar to those of traditional welding processes. Therefore, good ventilation, protective equipment against metal fumes and excessive heat and light are required [23
In this study, a low-cost wire-arc additive manufacturing (WAAM) system is designed that offers an alternative solution to develop and repair high-value metallic components. The applications include repair and manufacturing of parts such as fittings, implants, heat exchangers in aviation, automobile and medical industries [24
]. The system incorporates an open-source 3D printer and gas tungsten arc welding (GTAW) process. The system costs around $
1000 and includes open source fused deposition modeling (FDM) 3D printer parts, microcontroller, TIG welder, and specially designed and produced parts, such as a torch holder, among other components. The computer and gas container were excluded from this cost estimate. This design approach eliminates the use of expensive equipment, such as a robotic arm, thus reducing the price of the machine drastically. This low-cost AM machine also implements an open-source architecture.
It was demonstrated that a standard 3D gantry system which is widely used in fused deposition modeling (FDM) 3D printers can be modified to build a WAAM metal 3D printer. Special fixtures, such as a torch holder and wire feeding system, were designed. The proposed design offers an affordable system for 3D printing metallic components that can be of particular interest for repair applications.
The main limitations of the designed system are the dimensional limitation of the repaired or fabricated part, the absence of additional axis movements of the torch and sample, and the limited environmental protection of the solidified metal from the atmosphere. Some of these restrictions can be addressed by using the larger frame and using an additional enclosed inert gas filled shielding chamber to isolate the hot metal from the air. Although there is no serious risk to the operator, due to its fully automatic remote operation, the protective chamber will also increase the safety of the operator by blocking the extremely bright and hot arc. It is also worth noting that WAAM should be performed in a well-ventilated area to protect the operator from metal vapors.
Nevertheless, the proposed system together with proper process parameters can be used with many metallic alloys that can be processed by GTAW and WAAM, with less effort and lower cost compared to the expensive powder-bed systems [5
]. Some examples of the alloys that can be processed include titanium alloys, aluminum alloys, nickel-based superalloys, cobalt-based superalloys, and low alloy steels.
In this work, design and build of a simple, affordable, and effective wire arc additive manufacturing (WAAM) machine was presented. This inexpensive system was made with a budget of approximately $1000 by integrating a GTAW welding machine into a cartesian gantry. The open-source architecture allowed the implementation of different methods to manipulate and control the additive manufacturing process. Open-source software Repetier was utilized to control all aspects of the machine, providing the flexibility to manipulate movements of mechanical components through a laptop computer. Preliminary testing was conducted to learn how the custom made WAAM machine would behave when depositing engineering alloys. Adjustments to the system were incorporated to make the machine more reliable. Even though WAAM systems are candidates to replace conventional methods of manufacturing metal components, a substantial need for research still exists to make this revolutionary manufacturing process acceptable for industrial applications.
Although some challenges still could not be solved due to the nature of the WAAM process and designed system characteristics, the most frequently seen problems during design were addressed with their related suggested solutions. Nevertheless, there is still a need for automatic distance adjustment between the torch tip and the work piece to achieve more consistent results. The angles and distances between wire tip, torch tip, and work piece should be precisely adjusted and kept fixed throughout the process. These demands may be fully satisfied by the deployment of a closed-loop control system in future works. The design presented here proves the potential of a cost effective WAAM system developed by using FDM printer frame and open source software after applying the recommended additions.