Chemical machining with oxalic acid to improve surface quality of wire arc additively manufactured titanium for jewellery and interior design

Wire-arc additive manufacturing (WAAM) provides numerous benefits, including high deposition rates, cost-effective equipment, efficient material usage, and environmental sustainability. These characteristics render WAAM a suitable technology for applications in fashion and jewellery production. Nevertheless, achieving complete protection from oxygen poses challenges, leading to surface characteristics that differ from those of the bulk material. The presence of thermal oxide and alpha case layers increases brittleness, limiting suitability for direct application or aesthetic treatments such as anodization. Although chemical treatments efficiently remove oxides from complex-shaped titanium components, they frequently rely on highly polluting acids. This study investigated the feasibility of using oxalic acid, a naturally occurring organic acid, for the chemical machining of Ti6Al4V samples produced via WAAM. The efficacies of organic solutions at 60 °C, 75 °C, and 90 °C were evaluated and compared with those of conventional treatments based on hydrofluoric and nitric acids. Oxalic acid treatment at 90 °C for 24 h completely removed the oxide and alpha case layers, whilst the conventional treatment achieved the same result in 30 min, resulting in a thickness reduction of approximately 4% in both cases. Although the organic treatment increased the surface roughness by 5 µm, no substantial variation was detected in the sample profiles, with the initial geometry being preserved. These results demonstrate that organic treatments are an effective alternative to conventional methods, although further optimisation remains necessary to produce components with reduced surface roughness.