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This study investigates the dynamic temperature behaviour around a melt pool in metal-based powder bed fusion using a laser beam (PBF-LB/M) to clarify the influence of the associated morphological changes of the metal powder experimentally. Gas-atomized 18Ni (300-grade) maraging steel powders were processed by PBF-LB/M while high-speed photography with a two-colour radiometric thermal imaging system that was employed to correlate the temperature with melt pool behaviour. In addition, the cooling rate of the melt pool was measured directly using the dynamic temperature distribution. The temperature distribution of the melt pool was influenced by the morphological changes of the metal powder induced by physical and thermal interactions, and the melt pool exhibited an asymmetric temperature distribution in the direction parallel to the laser scan. The significant factors were droplet cohesion at low melt pool temperatures, remaining heat energy from previous laser beam irradiation, and the heat conduction inside the melt pool. The laser beam incident on the metal powder was primarily characterized by two modes: direct heating induced by laser beam irradiation and heat conduction through the single track, droplets, and substrate. In addition, the dynamic temperature behaviour provided a direct explanation for the cooling rate, the values of which ranged from 0.1 to 0.9 × 106 K/s owing to the self-cooling induced by PBF-LB/M.

This study is the first attempt of applying thermal stress cleavage to a single-crystal round sapphire bar having a morphologically continuous circumference surface. Previously, thermal stress cleavage was only applied to brittle material substrates or wafers owing to the crack propagation behaviour induced by thermal stress distribution. To overcome this issue, a V-shaped groove was prepared on the circumference as an initial point for crack propagation, and a continuous-wave carbon dioxide (CO2) laser was used as the heat source. The thermal stress behaviour was simulated via finite element analysis, and the effect of the initial crack morphology on the thermal stress behaviour was evaluated. In addition, the crack propagation was monitored using an acoustic emission sensor, and the separation mechanism of the round sapphire bar was investigated. Results indicated that the thermal stress cleavage using the CO2 laser beam allowed the complete separation of the round sapphire bar with the V-shaped groove without any final edge remaining. The crack propagation behaviour was determined from the relationship between the thermal stress distribution and morphology change during crack propagation. The fabricated sharp V-shaped groove improved the quality of the cleaved surface, and the high aspect ratio of the groove enabled a high-quality cleavage. The initial crack propagation immediately after the start of laser beam irradiation was affected by the tip of the V-shaped groove, and the crack propagation direction could be controlled through the tip morphology of the V-shaped groove.

This paper pertains to the thermal and strain behaviour in laser consolidation of metal powders by additive manufacturing. The temperature and strain induced in the substrate during the laser consolidation process were theoretically estimated by the thermal-structure interactive analysis with two-dimensional finite element method, and experimentally evaluated in order to investigate the influence of thermophysical and mechanical properties on the resistance to thermal deformation in the consolidated structure. Additionally, the effects of different ferrous-based materials on the deformation were also investigated. The results reveal that the deformation of the consolidated structure was mainly caused by the thermal expansion and shrinkage induced by the laser beam which was repeatedly irradiated to the deposited powder. The deformation direction varied depending upon the temperature gradient which was induced inside the structure and stiffness of the consolidated structure which was added on the substrate. The analytical results obtained coincided well with the experimental results. The coefficient of thermal expansion was one of the most effective factors in restraining the thermal deformation, and the thermal deformation was reduced by combining the materials in which the coefficient of linear expansion was similar. In addition, the deformation was minimized by adjusting the temperature gradient induced by the laser beam irradiation.

It is necessary to strengthen glass surfaces to protect mobile electric devices from unexpected scratches and breakages, and various strengthening methods are available to this end. However, strengthened glass is difficult to cut and finish owing to the high compressive stress on the glass surface. In this work, chemically strengthened glass was separated using a fracture control technique. The initial crack for the crack propagation was generated through a thermal shock induced by laser beam irradiation, and the thermal stress distribution inside the strengthened glass was simulated via a finite element analysis. In addition, the influence of the laser conditions on the cleavage characteristics was evaluated experimentally, and a groove was fabricated via a short-pulsed laser to improve the quality of the cleaved surface. The thermal stress induced by the laser beam irradiation was affected by the stress distribution inside the strengthened glass, and the depth of the initial crack was required to exceed that of the compressive stress layer to realize the crack propagation through laser beam irradiation. The minimum energy density required for the thermal stress cleavage decreased with the increase in the initial crack depth, and the energy density required for the thermal stress cleavage was large when the compressive stress on the surface was high. The compressive stress layer on the surface helped reduce the lateral crack at the tip of the initial crack, and the tensile stress inside the specimen helped realize high-quality cleavage. In addition, the groove fabricated using the short-pulsed laser acted as the initial point for the crack propagation and helped prevent the thermal damage induced by the laser beam irradiation applied as the heat source.

This study describes the characteristics of separating a silicon wafer with a moving Nd:YAG laser beam by using a thermal stress cleaving technique. The applied laser energy produces a thermal stress that causes the wafer to split along the irradiation path. The wafer separation is similar to crack extension. In this study, the micro-groove was prepared at the leading edge of the silicon wafer to facilitate the fracture. In order to study the thermal effect in the separating process, the temperature at the laser spot was measured by using a two-color pyrometer with an optical fiber, and the mechanism of crack propagation was observed by using an acoustic emission (AE) sensor. The influence of the micro-groove length and depth was also examined. Thermal stress distribution was calculated using the finite-element method (FEM) by considering the temperature from the experimental result. The result indicates that the wafer separation occurred in two stages, fracture initiation and intermittent crack propagation. A higher temperature resulted in faster fracture initiation and higher repetition of the crack propagation signal. The wave mark on the cleaved surface was consistent with the AE signal. The influences of laser power, temperature and the groove parameters to the fracture initiation, crack propagation and cleaved surface features are explained based on the experimental results, while the thermal stress condition is clarified with FEM analysis.

This paper looks at the gas permeability of the porous structure of an injection-moulding die fabricated by selective laser sintering (i.e., additive manufacturing), and how this is affected by the laser conditions used. The metal powder used is a mixture of alloy steel, copper phosphorous and nickel powders with an average particle diameter of 25 μm. A fibre laser (wavelength 1070 nm) is used to consolidate the metal powder, thus making any differences in the consolidation of the metal powder strongly related to the energy density under which it is irradiated; varying from fully melted to a fully sintered condition with decreasing energy density. The permeability of compressed gases is found to increase with porosity, but no gas escapes when the porosity is below 6%. The tensile strength of the porous structure is also found to be related to its porosity, decreasing due to a combination of pores inside the structure.

This study describes a finishing performance of cooling channel with a face protuberance inside a molding die with free abrasive grains. A fluid flow in the cooling channel is calculatedly simulated, and the effect of internal face protuberance which is spirally arranged on the finishing performance is experimentally investigated. The molding die used in the experiment is fabricated with layered manufacturing equipment. The internal face of cooling channel is finished by the fluid flow with free abrasive grains which are passed through the cooling channel. The results showed that the fluid flow with the face protuberance is flowing spirally according to the face protuberance on the internal face, and the velocity distribution inside the molding die was quite small. The internal face roughness in the cooling channel was improved significantly up to the early finishing time by the removal of unstable powder, such as the stain, the partially molten powder and the adhered powder. The application of the face protuberance on the internal face was quite effective for the improvement of the alloyed face in the cooling channel.

This paper deals with a finishing method for the internal face of a cooling channel located in an injection mold that makes use of free abrasive grains. The injection mold is fabricated by layered manufacturing equipment using a ferrous based metal powder. When the internal pressure is loaded to the hydraulic cylinder, the solution containing the free abrasive grains is passed through the cooling channel. The internal face is then finished by the free abrasive grains. The effects of various conditions on finishing characteristics are investigated experimentally. The results showed that the internal face roughness of the cooling channel improved significantly during the first 1000s of finishing. The significant improvement achieved during the initial stages of finishing is due to the removal of the aforementioned unstable powders. Free abrasive grains are employed to remove the unstable powder on the internal face rather than to polish the alloyed face. The high-speed flow of the free abrasive grains results in an increase in their kinetic energy, thereby increasing the force with which they collide with the internal face and resulting in an improvement of the surface roughness. The internal face finishing was effective for the improvement of the thermophysical properties in the cooling channel.

This study describes the consolidation characteristics of chromium molybdenum steel (SCM) based powder used for rapid tooling. The laser beam used was a Yb:fiber laser with a spot diameter of 45 μm and a maximum power of 40 W. In order to investigate the influence of irradiation conditions on the maximum temperature at the focal area, a two-color pyrometer developed by the authors was used. In addition, the cross section of the consolidated structure was analyzed with an electron probe microanalysis, and the cutting force was measured with a dynamometer. The result showed that the maximum temperature at the focal area was related to the consolidation characteristics of the metal powder. The main parameters which affected the consolidation characteristics were laser power and scan speed of the laser beam. The deposited powder and the plate surface were melted with generated heat and alloyed in the process of the solidification. The specific cutting force was greatly influenced by the consolidation conditions. The highest value of a specific cutting force was obtained when the melting of the powder and the solidification of the molten powder were performed repeatedly and the structure was consolidated linearly.

This paper describes an experimental investigation on the cutting mechanism of laser sintered material using small ball end mill focusing on the temperature of the cutting edge. Sintered material was produced by irradiating a laser beam on a layer of loose fine SCM–Ni–Cu powder. Bulk carbon steel AISI 1055 was selected as reference steel. The influence of cutting conditions, tools diameter and unsintered metallic powder on the cutting edge temperature were examined. Comparison of the cutting edge temperature between the peripheral and surface milling were investigated. Investigations of the tool life and wear mechanisms in cutting the sintered material and AISI 1055 were also carried out. Results indicated that the cutting edge temperature for sintered material was higher than for bulk AISI 1055. Cutting at the outer surface of sintered material produced higher temperature than at the inner surface. The temperature of the cutting edge was greatly influenced by the cutting speed followed by depth of cut and feed per tooth. Cutting temperature for different tool's diameter was almost similar under the same rotational speeds and cutting conditions. Cutting tool temperature in peripheral milling was higher than in surface milling. Adhesion of the work material and chipping were the main wear mechanisms of the ball end mill in cutting sintered material.