Numerical study on heat and mass transport phenomena during a multilayer cladding process for direct laser deposition

During the direct laser deposition (DLD) manufacturing process, complicated cladding process, and multiple thermal cycles lead to changeable transport phenomena and solidification behavior in the melt pool, which significantly affect the evolution of the structure and properties of part. Clarifying the process mechanism of the DLD process is of great value for further promoting its application service, and the development of an accurate and robust layer cladding model is obviously the key point. In this study, a three-dimensional numerical layer cladding model consisting of coupled heat transport and fluid flow, layer cladding and interface capture is developed and validated. Then, the heat and mass transfer characteristics, as well as its formation mechanism in multilayer cladding process are investigated in depth. Results show that a smooth, continuous, equal height, and common width cladding layer is formed in any cladding layer. Under the effect of the asymmetric evolution in scanning direction, the sub-layer reverse scanning strategy can effectively improve the surface roughness reducing at the end of previous layer. Besides, the front layer residual heat has significant influence on the multilayer cladding process. When the melt pool expands, the maximum temperature and velocity increase sharply, but the average energy decreases. Furthermore, the layer evolution will enter quasi-steady state as the heat input and dissipation reach dynamic balance.