YAGレーザによる硬脆材料の加工とその応用に関する研究

取得学位：博士(工学)，学位授与番号：博甲第778号，学位授与年月日：平成18年3月22日,学位授与年：200

Investigation of laser consolidation process for metal powder by two-color pyrometer and high-speed video camera

This paper deals with the measurement of surface temperature on metal powder during the laser consolidation process with two-color pyrometer. Additionally, the aspect of selective laser sintering (SLS) and selective laser melting (SLM) of metal powder is visualized with high speed video camera. As a result, the surface temperature during the laser irradiation was ranged 1520-1810 °C and the consolidation phenomena was classified according to the melting point of metal powder. The metal powder at the heating process cohered intermittently to the melt pool although the laser beam was continuously irradiated to the powder surface. © 2013 CIRP

Study on Laser Consolidation of Metal Powder with Yb fiber laser : Temperature Measurement of Laser Irradiation Area

金沢大学理工研究域　機械工学系The layered manufacturing technique is one of the most effective processes for the manufacture of prototypes, tools and functional end products. Selective Laser Sintering (SLS) and Selective Laser Melting (SLM), in particular, are two of the most versatile techniques, able to cover a wide range of materials such as polymer, ceramic and metal powder. In this study, the monitoring method of processing temperature at laser irradiation area by two-color pyrometer is applied. In order to in-vestigate the consolidation characteristics of chromium molybdenum steel (SCM) based powder with a Yb:fiber laser, the maximum temperature at the irradiation area of a laser beam was measured under various experimental conditions. The influence of the scan conditions of a laser beam on the maximum temperature was evaluated. As a result, it was revealed that the maximum temperature during laser irradiation changed under the influence of laser power and scan speed of a laser beam. The maximum temperature increased with the increase of laser power, and decreased rapidly to al-most at room temperature for 20 ms after the laser beam passed the center of the target area. More than the unit length 5 mm, the maximum temperature during laser irradiation was not influenced by the previous laser scan

Study on laser assisted milling of ferrous based consolidated material

金沢大学理工研究域機械工学系This study deals with the laser beam assisted milling to improve the machinability of a consolidated structure formed by layered manufacturing processes. The laser beam used is a continuous CO2 laser with a maximum output power of 100 W. The metal powder for layered manufacturing is a ferrous-based mixture. To investigate the influence of laser conditions on the machinability, specific cutting force, tool wear and tool temperature of the flank face are measured. The results showed that the specific cutting force of the consolidated structure was decreased by the effect of energy input on the structure surface. The progress of wear on the flank face assisted by the laser beam was 20% slower due to the softening of the consolidated structure and the melting of the powder which remained on the structure surface. The dimensional accuracy and surface finishing of the consolidated structure were influenced by the rise of the tool temperature on the flank face. © KSME & Springer 2010

Study on reduction of residual stress induced during rapid tooling process: Influence of heating conditions on residual stress

金沢大学理工研究域機械工学系This paper deals with the reduction of residual stress induced during the selective laser melting with a mixture of ferrous based metal powder. To evaluate the residual stresses induced during layered manufacturing processes, a strain gauge is attached on the bottom face of the base plate. The residual stress within the consolidated structure is calculated from the amount of strain change measured by the strain gauge when the consolidated structure is cut with an end mill. The influences of base plate thickness and consolidated structure height on the residual stresses are investigated. In addition, the effect of pre-heating and post heating by a laser beam irradiation are evaluated. The results showed that the deformation of the base plate increased with the increase of the consolidated layer and the decrease of base plate thickness, and the deformation was flattened when the consolidated structure was completely removed with the end mill. The deformation was related to the induced residual stresses. The residual stress distribution within the consolidated structure in the z direction was extremely large at the top layer of the structure and the boundary between the base plate and consolidated structure. The residual stress at the first layer of the structure decreased when the base plate was heated before consolidating the deposited powder. The residual stresses decreased when each of the consolidated layers was repeatedly heated by the laser beam irradiation. © (2010) Trans Tech Publications

Study on thermal and strain behaviour in selective laser sintering process

This paper investigates thermal and strain behaviour in the selective laser sintering process with a mixture of SCM, Cu and Ni metal powder. In-process monitoring of strain change and temperature at the base plate is proposed in order to investigate thermal and strain behaviour induced by selective laser sintering. A strain gauge was attached to the bottom surface of the base plate while a thermocouple was inserted at a distance of 2 mm from the top surface of the base plate. Changes in the strain and the base plate temperature were observed using an oscilloscope during the laser sintering process. The results showed that the development of strain within the sintered structure was affected by the processing temperature. Besides that, after the laser sintering process was completed, the strain value increased gradually and became constant as it reached room temperature. This strain value was found to correspond with the test model\u27s deformation. In addition, the effects of laser scanning direction and laser energy density during the process were observed. Measurement of the test model\u27s deformation was also carried out to discover its relationships to strain change and processing temperature. The results showed that the sintered structure produced by laser scanning of a sector along the width induced less residual strain, which resulted in less deformation. In contrast, both residual strain and deformation were found to be higher when the laser scanning was carried out along the length. Furthermore, when a low laser energy density was used, less deformation of the sintered structure could also be obtained. © (2012) Trans Tech Publications

Thermal conductivity of metal powder and consolidated material fabricated via selective laser melting

Selective Laser Melting (SLM) is a direct fabrication of part through layer by layer powder deposition and successive laser beam irradiation based on Computer Aided Design (CAD) data. One of the important properties in SLM is thermal conductivity of metal powder. This is because the ability of metal powder to conduct heat will affect the consolidation process during SLM. In this paper, thermal conductivity of metal powders with different particle diameters and their mixture was analysed. Other than that, thermal conductivity of consolidated materials fabricated via SLM process was also studied. In order to measure the thermal conductivity of metal powder, a theoretically verified method which was previously developed by the authors was used. Determination of thermal conductivity of consolidated material was analysed using laser flash technique. It was found that the thermal conductivity of powder metal was influenced by bulk density and particle diameter of metal powder. In this study also, metal powders of different particle diameters were mixed with various volume ratios, and its effect was discussed. Thermal conductivity of the consolidated materials was also examined, and its relation to porosity was elaborated. © (2012) Trans Tech Publications, Switzerland