In the directed energy deposition (DED) process, significant empirical testing is required to select the optimal process parameters. In this study, single-track experiments were conducted using laser power and scan speed as parameters in the DED process for titanium alloys. The results of the experiment confirmed that the deposited surface color appeared differently depending on the process parameters. Cross-sectional view, hardness, microstructure, and component analyses were performed according to the color data, and a color suitable for additive manufacturing was selected. Random forest (RF) and support vector machine multi-classification models were constructed by collecting surface color data from a titanium alloy deposited on a single track; the accuracies of the multi-classification models were compared. Validation experiments were performed under conditions that each model predicted differently. According to the results of the validation experiments, the RF multi-classification model was the most accurate.

Bimetallic structures manufactured by direct deposition have a defect due to the sudden change in the microstructure and properties of dissimilar metals. The laser metal deposition (LMD)-wire arc additive manufacturing (WAAM) process can alleviate the defect between two different materials by depositing the functionally graded material (FGM) layer, such as a thin intermediate layer using LMD and can be used to fabricate bimetallic structures at high deposition rates with relatively low costs using WAAM. In this study, the LMD-WAAM process was performed, and the microstructure of the fabricated bimetallic structure of IN625-SUS304L was investigated. The microstructure of the FGM zone of the LMD-WAAM sample was mainly fine equiaxed dendrite morphologies. In contrast, coarse columnar dendrite morphologies constituted the WAAM zone. The composition of the major alloying elements of the LMD-WAAM sample gradually changed with the height of the deposited layer. The microhardness of the LMD-WAAM sample tended to increase with an increasing Inconel content. In the case of the LMD-WAAM sample, the fracture occurred near the interface between 25% IN625 and 0% IN625; in the WAAM sample, the final fracture occurred in SUS304L near the interface. The tensile strength of the LMD-WAAM samples was inversely proportional to the laser power. The results showed that the LMD-WAAM samples had 8% higher tensile strength than the samples fabricated using only WAAM.

The Machining of titanium alloys is challenging because of their high strength, low thermal conductivity, high chemical reactivity, and high stresses at the cutting tool edges. Laser-assisted machining is an effective way to improve the machinability of titanium alloys. This paper presents an experimental investigation of the machinability of cutting force and surface roughness in laser-assisted end milling of titanium alloy Ti-6Al-4V. The absorptivity of Ti-6Al-4V was determined by conducting preheating experiments using a high-power diode laser with a wavelength of 940–980 nm. A thermal analysis was performed using the finite element method to predict temperature distribution. The depth of cut was determined where tensile strength decreased sharply, and the predicted surface temperature is presented in the analysis results. The experiments were performed with conventional machining and laser-assisted machining. Surface roughness, tool wear, and cutting force were evaluated. In contrast to the results of conventional end milling, laser-assisted end milling improved surface roughness. Moreover, laser-assisted end milling proved more effective than conventional end milling in terms of cutting tool damage. Our results proved that heat assistance significantly influenced the magnitude of the cutting forces—while the actual reduction in forces varied slightly depending on the force component, cutting tool, and cutting conditions, force components showed a reduction of roughly 13–46%.

Wire arc additive manufacturing (WAAM) is being extensively used in various industrial fields. In WAAM, if a bead is deposited without considering the central angle, its shape may collapse with increasing number of layers. To address this problem, a new method for optimizing the bead geometry using a support vector machine (SVM) classifier was established in this study. The ranges of the optimal deposition conditions were determined using the SVM classifier and verified by experiments. Geometric data of deposited beads were extracted using a laser profiler, and an SVM binary classifier was used to predict suitable ranges of the deposition conditions. Data were extracted through 20 single-layer basic experiments, classification was performed based on 4°, and the appropriateness of SVM classification was found through 8 single-layer and 3 multi-layer verification experiments.

Additive manufacturing (AM) has the advantages of reducing material usage and geometrical complexity compared to subtractive manufacturing. Wire arc additive manufacturing (WAAM) is an additive manufacturing process that can be used to rapidly manufacture medium-and large-sized products. This study deals with the path-planning strategy in WAAM, which can affect the quality of deposited components. It aims at suggesting effective path planning to reduce the height error of intersection parts. A comparative analysis of the bead width and height at the intersection parts was performed to verify the effectiveness of the proposed path. The initial parameters were determined through single-layer deposition experiments, and multi-layer deposition experiments were performed. The resultant height error in the intersection part was 0.8%, while that in the non-intersection part was absent at the maximum height. Path planning is considered to be an effective method.

High-entropy alloys (HEAs) are composed of 5–35 at% of five or more elements, have high configurational entropy, do not form intermetallic compounds, and have a single-phase face-centered cubic structure or body-centered cubic structure. In particular, refractory HEAs (RHEAs), based on refractory materials with excellent mechanical properties at high temperatures, have high strength and hardness at room temperature and excellent mechanical properties at low and high temperatures. In this study, the Ti-Nb-Cr-V-Ni-Al RHEAs were deposited using direct energy deposition (DED). In the microstructure of Ti-Nb-Cr-V-Ni-Al, the sigma, BCC A2, and Ti2Ni phases appeared to be different from the BCC A2, BCC B2, and Laves phases predicted in the phase diagram. This microstructure was similar to that of the casted Ti-Nb-Cr-V-Ni-Al and had a constructed fine grain size. It was found that the growth of these microstructures was due to the DED process, which has a fast solidification rate. The fine grain size caused high hardness, and the microhardness of the Ti-Nb-Cr-V-Ni-Al was measured to be about 900 HV. In addition, in order to analyze the thermal properties of Ti-Nb-Cr-V-Ni-Al composed of the refractory material, the heat-affected zone (HAZ) was analyzed through a preheating test. The HAZ was decreased, owing to the high thermal diffusivity of Ti-Nb-Cr-V-Ni-Al.