In-process range-resolved interferometric (RRI) 3D layer height measurements for wire+ arc additive manufacturing (WAAM)

In this work a range resolved interferometry (RRI) instrument for absolute distance measurements is integrated into a wire + arc additive manufacturing (WAAM) system to provide in-process monitoring of layer height, and prospects for volume and profile monitoring are discussed. In this experiment titanium feedstock was used to create a 150 mm long, 13.5 mm high wall comprised of 11 WAAM deposited layers. The RRI in-process measurements are in very good agreement ($\lt$0.05 mm) with both mid-process, on-machine micrometre measurements taken by hand after each WAAM deposition, and post-process laser scanning measurements of the completed wall. The high depth of field allows direct referencing of the layer height measurements to the build plate making the measurement independent of the motion system and build plate bending, considerably lowering uncertainties. This, together with the capability for cost-effective in-process measurements in harsh environments, should make the proposed approach very interesting for routine use in WAAM systems.