In-process path replanning and online layer height control through deposition arc current for gas metal arc based additive manufacturing

Wire Arc Additive Manufacturing (WAAM) is recently receiving increasing attention as it offers a way to produce parts on a meter scale with high deposition rates and low production and capital costs. A major challenge in WAAM is the inherently variable layer height, which causes geometric inaccuracies in the final product. This paper proposes an on-line layer height control and in-process toolpath replanning for Gas Metal Arc (GMA) WAAM system, which enables better geometric accuracy when depositing tall shell parts. Deposition arc current and voltage were considered as control variables for layer height control. Arc current proved to be a more suitable control variable due to its higher sensitivity and higher correlation with changes in the contact tip to work distance. Different types of layer height controllers were developed and evaluated by depositing 30-layer high thin walls. Additionally, a re-slice algorithm was developed and implemented in the system controller. It compares the deposited section of the part to the CAD model after each layer has been built. The algorithm replans (re-slices) the toolpath to ensure better geometric accuracy of the finished part when the deviation exceeds the maximum allowable threshold. A 160 mm high case study part was manufactured and 3D scanned to demonstrate the novelty of the developed system. Results show that the layer height control keeps distance between the welding torch and the part surface during the deposition. Re-slice control, combined with layer height control, enables the manufacture of parts with correct final geometry