Directed Energy Deposition using a laser beam and metallic wire (directed energy deposition using a laser beam with wire (DED-LB/w)) is a promising additive manufacturing technique known for its high deposition rates, low material waste, and suitability for applications such as the repair of high-value components, rapid prototyping, and low-volume production. As a layered manufacturing process, it builds metal structures by melting and depositing wire in successive beads and layers. While DED-LB/w offers significant advantages, including potential cost and lead time reductions, especially when automated, its complex thermal and geometric dynamics present major challenges for process stability and part quality. Achieving consistent outcomes requires real-time, non-intrusive monitoring solutions capable of capturing critical process parameters, such as the temperature of the deposit, which significantly influences bead geometry, microstructure, and overall mechanical properties.

The setup used in this study consisted of a vision camera and a pyrometer, with the vision camera potentially replaceable by a pyrometer. The proposed measurement approach enables reliable estimation of the immediate solidification temperature and serves as a compact and flexible alternative to conventional pyrometers, which often suffer from a limited field of view and alignment challenges.

This leads to a solution that is industrially practical, low-cost, and robust, and that can be easily installed to existing DED-LB/w systems.   The results revealed the effectiveness of the proposed temperature estimation method, showing strong correlations between the melt pool’s top-surface length and the immediate solidification temperature. Temperature variations (increasing and decreasing, and how fast it reacts to the changes in laser power) during multi-layer deposition can be tracked using in-situ melt pool length measurements. Comparative analysis of the melt pool’s top-surface length and area revealed that melt pool length is a better representative of temperature variations, and it can be used for controlling energy input in multi-layer depositions in DED-LB/w.

In another set of experiments, the influence of preheat temperature on melt pool behavior, melt pool-wire interaction, and microstructure of as-deposited beads was presented, using vision and high-speed cameras and resistive preheating of the feedstock wire. The results of these experiments showed that higher preheat temperatures reduce the thermal gradient between the melt pool and substrate, resulting in larger melt pool volume. Beyond a threshold around 400°C preheat temperature melt pool width showed a gradual increase, larger melt pool volumes resulted in bigger cross-section of liquid bridge and better flow of free electrons from wire to melt pool therefore a jump in electrical conductance values. Higher preheat temperatures shortened and thickened the liquid bridge. A hotter substrate reduces the temperature difference between melt pool and incoming wire, enabling faster and more uniform melting upon contact. The wire reaches melting conditions over a shorter distance while the sustained molten state maintains a thicker transfer region with greater metal flow. The bead cross-section measurements showed a sharp increase in depth and total area of the beads. Microstructural analysis revealed coarser solidification features at higher preheat temperatures caused by reduced cooling rates.

Overall, this work contributes to the advancement of in-situ monitoring in DED-LB/w by demonstrating the feasibility and benefits of vision-based temperature estimation and the suitability of electrical sensing as a feedback variable for closed-loop control of heat input. By quantifying the effects of thermal history and validating predictive models, the study lays the foundation for future development of closed-loop control strategies in wire-based additive manufacturing.