Numerical analysis of thermal accumulation and cooling design in SCAC-assisted wire-arc directed energy deposition: coupled effects of copper-block length and heat-transfer conditions

Thermal accumulation limits stability and productivity in directed energy deposition–arc with metals (DED-Arc/M), commonly referred to as wire-arc directed energy deposition (WA-DED). This study numerically examined thermal accumulation in WA-DED with solid-contact active cooling (SCAC) and the coupled effects of cooling-block length and heat-transfer conditions for a short-tracking SCAC configuration. A three-dimensional transient heat-conduction model for AZ31 magnesium-alloy thin walls was calibrated using substrate-temperature histories and melt-pool lengths from previous experiments conducted with water-cooled copper blocks covering the full wall length. The so-called volume-averaged stored-thermal-energy density was introduced to evaluate thermal accumulation in the substrate and the deposited wall. The model reproduced continuing temperature increase under natural cooling (NC) and early thermal stabilization under SCAC. Despite its shorter interpass times, SCAC maintained the volume-averaged stored-thermal-energy density at levels comparable to or lower than those during late NC. A parametric study was conducted for a short block tracking the heat source during 24-pass deposition. Block length and the wall–block and block–water heat-transfer coefficients were each varied at three levels. Increasing these factors reduced both the late-stage accumulation rate and final accumulation level. However, stronger water-side cooling had a limited effect under low wall–block heat transfer. Thermal accumulation continued for a 5 mm block even under the strongest heat-transfer conditions, nearly stabilized for a 10 mm block, and slightly decreased for a 20 mm block. The lowest final accumulation level was approximately 94% below the maximum across 27 conditions. Numerical results indicate that short-tracking SCAC requires sufficient wall–block heat transfer, appropriate block length, and water-side heat rejection.