Wire and arc additive manufacturing : Opportunities and challenges to control the quality and accuracy of manufactured parts

Wire and arc additive manufacturing (WAAM) is an additive manufacturing (AM) technology that uses wire-form materials and arc discharges as the energy source. AM techniques can fabricate complicated shapes that cannot be obtained via conventional processing. Building lattice structures inside components enables weight reduction while maintaining high strength. Strut shapes must be constructed to form these lattice structures using WAAM. For fabricating strut shapes with high accuracy, the process parameters should be optimized. However, the relationship between layer geometry and process parameters is not clear. Therefore, in this study, struts were fabricated under various process conditions to investigate the influences of process parameters on the built object geometry. The results showed that fabrication of strut shapes depends on the heat input condition. Moreover, it was found that the arc discharge time had the highest influence on the layer height and diameter. The inclination angle of an overhanging shape had little influence on the dimensional accuracy of the built object. In addition, computer-aided manufacturing (CAM) system was developed for the fabrication of lattice structures, and the lattice structures were successfully built using WAAM. The build accuracy was measured using an x-ray computed tomography (CT) scanner; the deviation in the structures designed using the CAM system and the actual fabricated structures measured using the CT scanner was lower than approximately ±2.3 mm.

Layer geometry control for the fabrication of lattice structures by wire and arc additive manufacturing

Wire Arc Addtive Manufacturing (WAAM) is a promising direct energy deposition technology to produce high-value material components with a low buy-to-fly ratio. WAAM is able to produce thin-walled structures of large scale and also truss structures without any support. To manufacture complex parts, process reliability and repeatability are still a necessity and this often leads to long developing times. In this paper, a method is proposed to automatically manufacture complex truss structures with point by point arc additive manufacturing and a six axis robot. Computer aided manufacturing (CAM) software is designed to manage (i) material deposition at intersections and (ii) collisions between the part under construction and the torch. Because it is difficult to model the deposition process, the bead geometry is monitored using video imaging. Image treatment program detects the contour of the deposit and computes its current position. With this position, the CAM software corrects the geometry of the part for future deposition. Simple case studies are tested to validate the algorithm. Two solid free form geometries designed by topology optimization are manufactured with this skeleton arc additive manufacturing process.

Skeleton arc additive manufacturing with closed loop control

One of the challenges in additive manufacturing (AM) of metallic materials is to obtain workpieces free of defects with excellent physical, mechanical, and metallurgical properties. In wire and arc additive manufacturing (WAAM) the influences of process conditions on thermal history, microstructure and resultant mechanical and surface properties of parts must be analyzed. In this work, 3D metallic parts of mild steel wire (American Welding Society-AWS ER70S-6) are built with a WAAM process by depositing layers of material on a substrate of a S235 JR steel sheet of 3 mm thickness under different process conditions, using as welding process the gas metal arc welding (GMAW) with cold metal transfer (CMT) technology, combined with a positioning system such as a computer numerical controlled (CNC) milling machine. Considering the hardness profiles, the estimated ultimate tensile strengths (UTS) derived from the hardness measurements and the microstructure findings, it can be concluded that the most favorable process conditions are the ones provided by CMT, with homogeneous hardness profiles, good mechanical strengths in accordance to conditions defined by standard, and without formation of a decohesionated external layer; CMT Continuous is the optimal option as the mechanical properties are better than single CMT.

https://www.mdpi.com/1996-1944/11/8/1449/pdf

Analysis of Favorable Process Conditions for the Manufacturing of Thin-Wall Pieces of Mild Steel Obtained by Wire and Arc Additive Manufacturing (WAAM).

Over the past years, the demand for the wire arc additive manufacturing (WAAM) is potentially increased, and it has become a promising alternative to subtractive manufacturing. Research reported that the wire arc additively manufactured (WAAMed) material’s mechanical properties are comparable to wrought or cast material. In comparison with other fusion sources, WAAM offers a significant cost saving and a higher deposition rate. However, there are significant challenges associated with WAAM such as undesirable microstructures and mechanical properties, high residual stresses, and distortion. Thus, more research is still needed to handle the above challenges by optimizing the process parameters and post-deposition heat treatment. In line with the above, this paper attempts to fill the gap by presenting a comprehensive review of WAAM literature including stagewise development of WAAM, metals and alloys used, effects of process parameters, methodologies used by various researchers to improve the quality of WAAM component. Besides, this work proposes the areas that could be used as avenues for future research.

Wire Arc Additive Manufacturing: A Comprehensive Review and Research Directions

WAAM (Wire-Arc-Additive-Manufacturing) is a metal additive manufacturing process using arc welding to create large components with high deposition rate. The workpiece quality and the process productivity are strongly dependent both on the process parameters (wire feed speed, voltage and current) and on the selected deposition path. Currently, the CAM (Computer-Aided-Manufacturing) software dedicated to WAAM rely on a multi-pass strategy to create the component layers, i.e. each layer is built overlapping multiple welding passes. However, since WAAM can create wide layers, a single pass strategy can improve the process efficiency when dealing with thin walled components. This paper proposes CAM software dedicated to WAAM, using a single pass strategy. The proposed solution uses a midsurface representation of the workpiece as input, to generate the deposition toolpath. A feature recognition module is proposed, to identify the critical features of the part, such as free end walls, t-crossings, direct-crossings and isolated tubulars. A specific strategy is developed and proposed for each one of the selected features, with the aim of minimizing the geometrical errors and to ensure the required machining allowances for the subsequent finishing operations. The effectiveness of the proposed strategy is verified manufacturing a test case.

Francesco Bandini

Papers

Feature based three axes computer aided manufacturing software for wire arc additive manufacturing dedicated to thin walled components