Directed energy deposition using laser beam and wire feed is a critical technology in high-productivity metal additive manufacturing, enabling precise deposition and fabrication of components with high quality and deposition rates. The interaction between the laser beam and metal is highly temperature-sensitive, affecting metal transfer, melting, solidification, and phase transformations. Effective control of heat input is crucial for influencing the geometry, microstructure, and overall integrity of the fabricated parts. This study investigates the correlation between the melt pool top surface boundary contour and the immediate solidification temperature, utilizing machine vision and radiation pyrometer measurements. The research highlights the significance of melt pool length as an indicator of temperature variations during deposition. System identification techniques were employed to develop a predictive model of the dynamic relationship between melt pool length and temperature, aimed at enhancing process control strategies. Our approach substitutes off-axis pyrometry with a cost-effective coaxial vision camera integrated into the laser head. By incorporating a vision camera without active illumination, the study offers a compact, omnidirectional solution. Comparative analysis of melt pool length and area measurements demonstrates the superiority of length-based correlations with temperature data. This work addresses the challenges of heat-input control in directed energy deposition laser beam wire processes and suggests future research directions in various metal alloys, complex geometries, and advanced sensing and automatic control methodologies.

Effective thermal management is essential in metal additive manufacturing to ensure process stability and desirable material properties. Directed energy deposition using a laser beam and wire (DED-LB/w) enables the production of large, high-performance components but remains sensitive to adverse thermal effects during multi-layer deposition due to heat accumulation. While prior studies have investigated interlayer temperature control and substrate preheating in DED modalities, including laser-powder and arc-based systems, the influence of substrate preheating in DED-LB/w has not been thoroughly examined. This study employs substrate preheating to simulate heat accumulation and assess its effects on melt pool geometry, wire–melt pool interaction, and the microstructural evolution of Alloy 718. Experimental results demonstrate that increased substrate temperatures lead to a gradual expansion of the melt pool, with a notable transition occurring beyond 400 °C. Microstructural analysis reveals that elevated preheat temperatures promote coarser secondary dendrite arm spacing and the development of wider columnar grains. Moreover, Nb-rich secondary phases, including the Laves phase, exhibit increased size but relatively unchanged area fractions. Observations from electrical conductance measurements and coaxial visual imaging show that preheat temperature significantly affects the process dynamics and microstructural evolution, providing a basis for advanced process control strategies.

Laser energy absorption plays an important role in determining process stability and energy efficiency in wire Directed Energy Deposition using a laser beam. However, the combined influence of wire geometry, beam positioning, and temperature-dependent optical properties on absorbed laser power remains insufficiently understood. This work presents an analytical framework for predicting the absorptance and absorbed power during the processing of Inconel 718. The model combines Monte Carlo ray tracing, Fresnel reflection theory, and a temperature-dependent Drude formulation in which the optical properties are related to electrical resistivity. A parametric investigation was conducted to evaluate the effects of wire-feeding angle, beam-wire offset, melt pool temperature, and wire temperature. The results showed that increasing the wire feeding angle altered the incidence-angle distribution of laser rays on the wire surface, resulting in non-monotonic variations in wire absorptance and absorbed power despite increasing beam interception. Furthermore, the interaction between wire and melt pool temperatures revealed three operating regimes governing the response of absorbed power to beam-wire offset. When the wire absorptance was lower than that of the melt pool, absorbed power increased with increasing offset, whereas the opposite trend occurred when the wire absorptance exceeded that of the melt pool. Between these regimes, a compensation condition was identified in which absorbed power remained nearly independent of beam-wire offset. This behavior occurred when the wire absorptance approached that of the melt pool, minimizing the influence of laser-energy redistribution between both surfaces. For the investigated geometry and optical assumptions, the compensation condition was associated with an approximately constant electrical-resistivity ratio and a constant relationship between the compensation wire temperature and melt pool temperature.