Laser-aided additive manufacturing is used for complex shapes and Ni-based superalloy parts. This study aimed to optimize the additive manufacturing process of Hastelloy X alloy to obtain its excellent mechanical properties without pores or cracks in the additively manufactured parts. The additively manufactured Hastelloy X was analyzed by comparing porosity, microstructure, and mechanical properties in as-built and post-heat treatment conditions. In addition, the pores existing inside the as-built specimen considerably decreased after the hot isostatic press (HIP) treatment. Furthermore, cell/columnar microstructures were observed owing to a fast cooling rate in the as-built condition. However, after heat treatment, dendrite structures disappeared, and recrystallized equiaxed grains were observed. The tensile test results showed that there was mechanical anisotropy along the vertical and horizontal directions, and as the microstructure changed to equiaxed grains after heat treatment, the mechanical anisotropy decreased, and the high-temperature properties improved.

In additive manufacturing (AM), the powder properties and laser powder bed fusion (LPBF) process parameters influence the quality of materials and building parts. However, the relationship between the size of the powder, LPBF process parameters, and mechanical properties is not well-established. In addition, Hastelloy X (HX) is attracting attention for its excellent high-temperature properties, but it is difficult to process, such as by cutting and milling, because of its high hardness and high ductility. This can be overcome by applying the AM process. We compared the LPBF window process maps for two HX powders of different sizes. Despite their small difference of 19.7% in particle size, it was confirmed that the difference in laser power was more than 40 W, the difference in scan speed was more than 100 mm/s, and the difference in energy density was more than 20% under the optimal process conditions. The as-built specimen had a larger molten-pool size as the energy density was higher, which resulted in the differences in mechanical properties at room temperature and high temperature (816 °C). We considered the control of the size of the powder to obtain the properties required for each temperature condition. The microstructures and mechanical properties of the as-built LPBF specimens were also investigated and compared with those of cast HX. Because of the rapid melting and solidification processes in LPBF, the as-built HX exhibited nano-sized dendrite structures and large internal strain energy. This resulted in the as-built LPBF exhibiting a higher room-temperature tensile strength than the cast material. Under high-temperature conditions, the grain boundary of the as-built LPBF acts as a sliding path, and the as-built LPBF HX showed significantly better high-temperature tensile strength characteristics than the cast HX.

We present a fundamental study on the development of trimming dies at room temperature for the hot-stamping process using directed energy deposition. Specimens of G and F materials were fabricated by machining 3D-printed blocks. The hardness of G-layered specimens was slightly higher than that of F-layered specimens, reaching approximately 700 HV at the surface. The G-layered specimens consisted of columnar and equiaxed dendrites, whereas the F-layered specimens mainly consisted of equiaxed dendrites. Spherical pores were observed inside the layered cross section, whereas relatively large irregular-shaped cavities were observed in layered boundaries. The tensile strengths of the G-layered and F-layered specimens were approximately 1800 and 1650 MPa, respectively. During bonding strength tests on an area bonded with S45C base metal, a fracture occurred in one case because of the lack of fusion at the boundary, and the F-layered specimens showed a lower strength than the G-layered ones. During wear tests on a quenched 1.5 GPa-grade aluminized steel plate, the F-layered specimens showed lower wear loss. However, the G-layered specimens showed better wear resistance during wear tests on a 1.5 GPa-grade electrogalvanized steel plate. These findings serve as fundamental data for additive manufacturing processes using tool steels of high-strength materials with high melting points.

Additive manufacturing (AM) has recently been receiving global attention. As an innovative alternative to existing manufacturing technologies, AM can produce three-dimensional objects from various materials. In the manufacturing industry, AM improves production cost, time, and quality in comparison to existing methods. In addition, AM is applied in the fabrication and production of objects in diverse fields. In particular, metal AM has been continuously commercialized in high value-added industries such as aerospace and health care by many research and development projects. However, the applicability of metal AM to the mold and die industry and other low value-added industries is limited because AM is not as economical as current manufacturing technologies. Therefore, this paper proposes an effective solution to the problem. This study examines a method for using direct energy deposition and heterogeneous materials, a heterogeneous material additive-manufacturing process for metals used to optimize the cooling channels and a key process in manufacturing hot-stamping dies. The improvements in the cooling performances and uniform cooling were evaluated by heat-flow analysis in a continuous process. Finally, trial products were fabricated using the proposed method, and a trial for hot stamping was conducted to examine the possibility of it being used in commercial applications.

The most common screening techniques to diagnose a patient’s illness are blood collection and intravenous procedures. To find a collection or injection site, conventional blood collection support tools, such as latex tubing and buckle-type tourniquets, are generally used to compress the patient’s blood vessels. This conventional passive method has significant problems such as latex allergy, vulnerability to site contamination and potential bloodstream infection, and physical damage due to improper use. To overcome the disadvantages of conventional blood collection support tools, an automatic tourniquet with a high-elasticity biocompatible strap was constructed. The automatic tourniquet is designed to automatically adjust the strap length using a motor to control the pressure according to the body dimensions of patients. In order to evaluate the performance of the automatic tourniquet, blood flow characteristics were analyzed using an ultrasound measurement system. The results demonstrated that the automatic tourniquet showed better performance compared with those of other blood collection support tools.

Unpredicted sheet forming failures of dual-phase (DP) steels can occur in regions of high curvature and with little apparent necking. Such failures are often referred to as “shear fractures”. In order to reproduce such fractures in a laboratory setting, and to understand their origin and the inability to predict them, a novel draw-bend formability (DBF) test was devised using dual displacement rate control. DP steels from several suppliers, with tensile strengths ranging from 590 to 980 MPa, were tested over a range of rates and bend ratios (R/t) along with a TRIP (transformation induced plasticity) steel for comparison. The new test reliably reproduced three kinds of failures identified as types 1, 2, and 3, corresponding to tensile failure, transitional failure, and shear fracture, respectively. The type of failure depends on R/t and strain rate, and presumably on the initial specimen width, which was constant in this study. Two critical factors influencing the lack of accurate failure prediction were identified. The dominant one is deformation-induced heating, which is particularly significant for advanced high strength steels because of their high energy product. Temperature rises of up to 100 deg. C were observed. This factor reduces formability at higher strain rates, and promotes a transition from types 1 to 3. The second factor is related to microstructural features. It was significant in only one material in one test direction (of 11 tested) and only for this case was the local fracture strain different from that in a tensile failure. Alternate measures for assessing draw-bend formability were introduced and compared. They can be used to rank the formability of competing materials and to detect processing problems that lead to unsuitable microstructures.