Enhancing Heat and Mass Transfer at the Alternating Interface of Additive/Subtractive Hybrid Manufacturing Using a Variable Powder Layer Strategy

Additive/subtractive hybrid manufacturing (ASHM), which enables in-situ machining to alleviate tool interference issues and improve surface quality during additive manufacturing, holds significant potential for fabricating complex, high-performance components. However, due to the differing characteristics of machined and additively built surfaces, variations in powder spreading, melt pool flow, and solidification behavior make the alternating interface a weak point in interlayer fusion quality. This study investigates the influence of substrate surface condition and powder layer thickness on melt pool behavior during laser powder bed fusion (LPBF) of GH3536 powder. The thermal-flow behavior under varying substrate surface conditions was simulated using a Computational Fluid Dynamics (CFD)-based model and validated by single-track laser scanning experiments. Peak temperature and melt pool lifetime were used to assess thermal behavior. The results showed that rough substrates promoted continuous and stable melt tracks, while smooth substrates were prone to defects such as necking and balling. For smooth substrates, increasing the powder layer thickness to 8 μm significantly improved thermal behavior, with the peak temperature and melt pool lifetime increasing by 15.65% and 43.89%, respectively, compared to the 4 μm layer used for rough substrates. To enhance interlayer fusion quality and microstructural uniformity at the interface, a variable powder layer thickness strategy was proposed. This study provides practical guidance for determining layer thickness in ASHM to improve interfacial quality.