Optimization of Process Parameters and Microstructure for Wire Arc Additive Manufacturing of ER70S-6 for Repair-Based Applications Using Response Surface Methodology

Additive manufacturing (AM) is a transformative approach in modern manufacturing, enabling efficient component fabrication while reducing material waste, production cost, and lead time. This study investigates direct energy deposition via wire and arc additive manufacturing (WAAM) using gas metal arc welding (GMAW) on a semi-automatic 3D welding machine (SA3DWM), with emphasis on repair applications where dimensional accuracy and functional integrity are critical. The effects of welding voltage, wire feed rate, and carbon dioxide shielding gas flow rate on material waste were evaluated using Response Surface Methodology (RSM) with a Box–Behnken Design (BBD), supported by analysis of variance (ANOVA), where material waste was quantified after secondary machining of deposited 3D blocks. The optimized welding condition was subsequently examined for microstructural characteristics using Optical Microscopy and Field Emission Scanning Electron Microscopy (FESEM). Practical applicability was validated through repair trials on two components: a tool holder body and a slot-cutting insert. Successful restoration was achieved after secondary finishing, with the slot-cutting insert treated as a critical load-bearing functional region. The repaired parts met the original dimensional requirements, and the repaired tool holder’s functional performance was further verified through lathe-machining tests involving the removal of an aluminium round bar.