Effect of temperature step on selection strategy of deposition head lift height and manufacturing stability during the direct laser deposition process

Abstract

Based on the layer by layer cladding characteristics of the direct laser deposition (DLD), the optimal selection strategy of deposition head lift height is one of the effective methods to maintain the manufacturing process stability, improve product quality, and reduce complex post-process. However, owing to the temperature step caused by changeable layer residual temperature, the selection of deposition head lift height becomes extremely complex. In this paper, to clearly analyze the effect of temperature step on selection strategy of deposition head lift height for the DLD multilayer deposition process with a 1.85 kW fiber laser and a coupled coaxial four-channel nozzle, a semi-theoretical model considering the main physical phenomena involved in DLD process is proposed, validated, and applied. Here, working plane position, deposition head lift height, and step of residual and preheating temperature are considered as input process variables while manufacturing stability and error are determined as process responses. Results show that without considering the temperature influence, the final manufacturing stability can be achieved by ensuring that the distance between the deposition head and the initial working plane is less than the maximum relative distance corresponding to the selected deposition head lift height. When the layer residual temperature is considered, the single-layer cladding height steps positively, which makes the extreme working plane position positively migrated, and the manufacturing stability is also further enhanced. However, due to the migration of the finally stable working plane position, the manufacturing errors are also conditionally changed. Finally, in order to obtain an optimal manufacturing process, for any DLD process where the initial working plane position has been determined, the deposition head lift height should be selected slightly smaller than the single-layer height corresponding to that determined plane under residual temperature condition (hTr,Si), otherwise the manufacturing process will gradually lose stability and lead to fabrication failure.