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The powder bed fusion (PBF) technique is a metal-based additive manufacturing (AM) method in which metal powder is deposited on a substrate and melted by selective laser-beam irradiation. Given that the process and parameters of metal-based AM are complicated, there are various problems in high-precision fabrication. One of these is that although metal-based AM can be used for fabrication of high-density parts, pores can easily form inside the fabricated structure owing to process instabilities. Pore formation degrades the mechanical strength of the fabricated structure. Therefore, this study investigated the pore formation mechanism inside a structure fabricated by PBF. Pore suppression by controlling the substrate temperature was also evaluated. Small- and large-sized pores with diameters of 10 μm and more than 50 μm, respectively, were found. Furthermore, differences in pore formation in the cross-section of the fabricated structure were observed owing to a variation in the volume-specific energy density and substrate temperature. At a substrate temperature of 25°C, the number of pores decreased more at the upper position than at the lower position owing to repeated melting and solidification under the laser-beam irradiation. At a substrate temperature of 200°C, the number of pores decreased significantly more than at 25°C. Furthermore, as the substrate temperature increased, the wettability of the molten metal improved, resulting in smaller contact angles of the fabricated structure in the single-line track. In PBF, multiple lines are fabricated in each layer. At low substrate temperatures, interstices were formed between the lines owing to the low wettability of the molten metal. These interstices acted as the origins of pores when the next layer was fabricated. Heating the substrate made the surface of the structure smooth owing to the high wettability of the molten metal and a reduction in the number of pores. Therefore, the formation of large pores could be reduced by controlling the substrate temperature.

In this study, the tool performance of two types of binderless diamond tools – single-crystal diamond (SCD) and nano-polycrystalline diamond (NPD) – is investigated in the high-speed cutting of titanium alloy (Ti-6Al-4V) with a water-soluble coolant. The NPD tool allows for a larger cutting force than the SCD tool by dulling of the cutting edge, despite NPD being harder than SCD. This large cutting force and the very low thermal conductivity of NPD yield a high cutting temperature above 500°C, which promotes the adhesion of the workpiece to the tool face, thereby increasing tool wear. Based on the morphology of the tool edge without scratch marks and the elemental analysis by energy-dispersive X-ray spectroscopy (EDX) of both the flank face and the cutting chips, diffusion-dissolution wear is determined to be the dominant mechanism in the diamond tool. A thin TiC layer seems to be formed in the boundary between the diamond tool and the titanium alloy at high temperatures; this is removed by the cutting chips.

Side milling tests of CFRP (carbon fiber reinforced plastics) containing thermosetting resin are carried out by TiAlN/AlCrN-coated, H2-free DLC (diamond-like carbon)-coated, and CVD diamond-coated carbide end mills without coolant. Two types of end mills having different helix angles of 30° and 60° are used. The film thickness and surface smoothness are varied for the DLC-coated end mills. The cutting characteristics are evaluated by tool wear and surface integrity (i.e., 3D profiles of the machined surface, generation of fluffing, delamination, and pull-out of the carbon fibers). The cutting force and tool flank temperature are also examined for the two types of CFRP composites and the helix angle of the end mill. “Inclination milling,”in which the end mill is tilted so that the resultant cutting force acts parallel to the work surface, is proposed as a novel technique to be used with a high-helix angle end mill. This unique approach enables the reduction of tool wear and improves the surface integrity of machined CFRP surfaces.

This study was conducted to investigate the effects of tool edge geometry on cutting temperature in the continuous cutting of case hardened steel. The tool edge temperature was measured using a two-color pyrometer with an optical fiber. The tool flank temperature increased with the negative land angle. When the flank wear VB was 0.05 mm, the tool flank temperature was only a little higher than with a new insert. However, when the flank wear VB was 0.1 mm, the tool flank temperature was dramatically higher. A horned insert resulted in higher tool flank temperature than when an insert without a horned edge was used. The tendency was remarkable at larger negative land angles and wider flank wear widths. Tool flank temperature increased with an increase in the nose radius of inserts. When comparing inserts with the same nose radius, the insert with the wiper edge caused higher tool flank temperatures than did the insert without the wiper edge.

Burring is a vital factor in metal cutting processes, since it may cause production-line problems that add unwanted time and cost required for deburring. We found that laser hardening of workpieces before face milling efficiently prevents burr formation. Our purpose here is to study optimum laser hardening conditions and cutter paths. Where no burring occurs, minimal chipping such as in chamfering is seen at the martensite layer on the workpiece exit face. The martensite layer thickens with laser power density, increasing chamfer height. The larger the exit angle, the more difficult it is to form a chamfer-like edge. Even for relatively small exit angles, the lower the feed rate, the more difficult it becomes to form a chamfer-like edge.

With laser-based dental treatment coming into increasing use, we introduce in-process monitoring using a two-color pyrometer and spectroscopic measurement ensuring safe treatment. Sound level monitoring is proposed for detecting hard-dental-tissue removal based on the relationship between tissue removal and sound.