Hybrid Analytical-numerical Modeling of Surface Geometry Evolution and Deposition Integrity in a Multi-track Laser-directed Energy Deposition Process

Abstract

Modeling multi-track laser-directed energy deposition (LDED) is different from single-track deposition. There is a temporal variation in the deposition geometry and integrity in a multi-track deposition which is not well understood. This paper employs an analytical model for power attenuation and powder catchment in the melt pool in conjunction with a robust fully-coupled metallurgical-thermomechanical finite element (FE) model iteratively to simulate the multi-track deposition. The novel hybrid analytical-numerical approach incorporates the effect of pre-existing tracks on melt pool formation, powder catchment, geometry evolution, dilution, residual stress, and defect generation. CPM 9V steel powder was deposited on the H13 tool steel substrate for validating the model. The deposition height is found to be a function of the track sequence but reaches a steady-state height after a finite number of tracks. The height variation determines the waviness of the deposited surface and, therefore, the effective layer height. The inter-track spacing (I) plays a vital role in steady-state height evolution. A larger value of I facilitates faster convergence to the steady-state height but increases the surface waviness. The FE model incorporates the effects of differential thermal contraction, volume dilation, and transformation-induced plasticity. It predicts the deposition geometry and integrity as a function of inter-track spacing and powder feed rate. The insufficient remelting of the substrate or the preceding track can induce defects. A method to predict and mitigate these defects has also been presented in this paper.