Ritsuko Higashino

Effect on beam profile of Ti alloy plate fabrication from powder by sputter-less selective laser melting

Titanium alloy (Ti-6Al-4V) ,which has a crystal orientation of α+β type, are clinical employed for an artificial bone and a hard tissue implant for human body because of light, nonmagnetic, weather resistance and biocompatibility, but it is difficult to form a complicated structure, as a bionic structure, owing to a difficult-to-cut machine material. Thus, titanium alloy plates were fabricated by selective laser melting (SLM) in vacuum. Melting and solidification process were captured with high speed video camera, it was found that sputter was depended on the surface roughness. The sputter-less fabrication for SLM in vacuum was developed to minimize the surface roughness to 0.6μm at the laser scanning speed of 10mm/s. It was also determined that crystal orientation was evaluated with X-ray diffraction (XRD). It was recorded from the powder peaks of α (1011), α (0002), α (1010), and α (1012) that the crystal orientation is composed mainly of martensitic alpha by XRD analysis. Diffraction peaks corresponding to β (110) were detected in vacuum SLM processed samples.

Synchrotron x-ray induced real time observations of CoCr alloy layer formation by micro laser cladding

The direct injection type laser cladding system using combined multi lasers, which supplies a clad powder from a center nozzle, was developed for realize of low dilution area and micro cladding. A fiber coupled diode laser was employed. The six-diode lasers were guided to focusing head with every optical fiber, which core diameter is 100 μm. Beam profile at focal point of the combined six lasers was set a spot diameter of 300 μm by CCD camera. Here, A cobalt-chromium alloy (CoCr-alloy) called by Stellite, which has excellent properties such as wear resistance, corrosion resistance and resistance to environment, was used as a cladding material. The focusing head has a function to supply a CoCr-alloy powder at a focal point from a center nozzle. When the laser irradiation and powder supply are simultaneously performed toward to a stainless steel 304 substrate, the CoCr-alloy powder was melted and solidified on the substrate to form a cladding layer. The melting and solidification process for CoCr-alloy was observed in real time using synchrotron radiation imaging technique at BL22XU in SPring-8. From results, it was clarified that the CoCralloy melt-solidification phenomenon greatly differs for laser output power. At the output power of 60W, it was found that a minimum amount of molten pool was formed and then solidified to form the cladding layer.

Development of laser metal deposition technology with IR and blue diode lasers (Conference Presentation)

Laser cladding, which is one of laser metal deposition (LMD) technologies, is an effective metal surface coating technique capable of increasing component lifetimes, in which an additive material such as a powder or a wire is melted by a laser beam and deposited on the substrate surface. We developed a multi-beam processing head with six high intensity infrared (IR) diode lasers, which was based on multi laser combining method, in order to realize a high quality cladding layer having a dense, fine and purity. An IR diode laser light with the power of 50 W was output from an optical fiber. Total laser power on the base plate was 300 W since six laser beams were overlapped. A nozzle to supply the powder was in the center of the processing head. The processing head was installed in a machine tool (simultaneous 5-axis machining). Hardness and abrasion resistances of blade edge and shaft made from stainless steel were improved by cladding of cobalt-base alloy powder, which was one of the applications with the machine. We also designed a multi-beam processing head with high intensity blue diode lasers for cladding of copper powder. We have developed a high intensity blue diode laser with the power of 100 W. The blue laser light was output from an optical fiber whose core diameter and NA were 100 m and 0.22, respectively. The three blue diode lasers would be installed to the processing head to obtain the power of 300 W on the base plate

In-situ x-ray observation of molten pool dynamics while laser cladding with blue direct diode laser

A blue direct diode laser cladding system, which uses multi laser combining method, was developed in order to realize a high quality cladding layer having a dense, fine and purity. In order to clarify the mechanism of copper layer formation, the layer formation process when forming a copper layer using a blue direct diode laser was observed using in situ X ray observation. The six-blue diode lasers were guided to focusing head with every optical fiber, which core diameter is 100 μm. Beam profile at focal point of the combined six lasers was set a spot diameter of 400 μm. The focusing head has a function to supply a pure copper powder at a focal point from a center nozzle. As the results, it was found that the stainless steel 304 substrate was melted and generate some bubble in molten pool at laser fluence of 1221 kJ/cm2, and output power of 92W. At laser fluence of 407 kJ/cm2, the bubble was not appeared because only a slight molten pool was formed on the surface of the substrate. It was found that amount of bubble and penetration depth was depended on the laser fluence with blue direct diode laser. By controlling the amount of input energy, the copper coating was produced minutely with no weld penetration.

Copper film formation on metal surfaces with 100 W blue direct diode laser system

In laser cladding, in the wavelength range of blue, light absorptivity of copper is much higher than that in the wavelength range of infrared. The authors developed the laser cladding system with the continuous wave blue direct diode laser (blue DDL). The system consists of a number of fiber-coupled blue DDLs with a maximum power of 20 W at a wavelength of 445 nm, a focusing lens, and a powder feeding nozzle. In this study, the authors investigated the fundamental characteristics of the multiple blue DDL system and formed copper film on 304 stainless steel plate using the system.In laser cladding, in the wavelength range of blue, light absorptivity of copper is much higher than that in the wavelength range of infrared. The authors developed the laser cladding system with the continuous wave blue direct diode laser (blue DDL). The system consists of a number of fiber-coupled blue DDLs with a maximum power of 20 W at a wavelength of 445 nm, a focusing lens, and a powder feeding nozzle. In this study, the authors investigated the fundamental characteristics of the multiple blue DDL system and formed copper film on 304 stainless steel plate using the system.

Development of high intensity blue diode laser system for materials processing (Conference Presentation)

High intensity blue diode laser system has been developed for materials processing of especially difficult processing material such as copper. A blue diode laser has an advantage in materials processing of copper since it has a higher absorption rate than traditional lasers whose wavelengths are in infrared region. A blue laser light with the power of 100 W and wavelength of 445 nm could be output from an optical fiber whose core diameter and NA were 100 m and 0.22 since high efficiency coupling of blue lasers emitted from laser diodes using an optical fiber with the core diameter of 100 m was achieved in this system. The intensity of 1.3 x 106 W/cm2 on the substrate was easily obtained at the output power of 100 W and the laser spot diameter of 100 m. The blue laser has already been applied to welding and additive manufacturing. In thermal heat welding, welding of a thin copper plate and a stainless steel pipe was completed. Laser metal deposition (LMD), which was a technology of additive manufacturing, with pure copper powders was performed using the blue laser. The blue laser was also installed in a 3D printing equipment using copper powders based on selective laser melting (SLM) method of additive manufacturing. The performance of the blue laser in materials processing experiments of welding, LMD and SLM in addition to its characteristics and the difference between those experimental results with the blue laser and the traditional infrared diode laser are reported.

Development of 100W class blue direct diode laser coating system for laser metal deposition

Laser cladding technique is widely used for industrial application such as oil, energy industry, and aircraft and so on because it is able to repair and to form a near net shape. This process have been employed infrared lasers with wavelength of 0.8-10.6μm since output power of these lasers have over 1000W. Metal processing efficiency was, however, low in these wavelength, because the absorption was low. Thus, we developed the laser cladding system with blue direct diode laser at the wavelength of 445nm. 6 blue diode lasers was combined on the focusing spot to reach the output power of 100W by a lens, which one blue diode laser module was maximum output power of 20W. By using this laser cladding system, a pure copper film coating on a SUS304 stainless steel plate was demonstrated from a copper powder. As the result, the copper layer was formed on SUS304 stainless steel plate at the width of 322μm and thickness of 534μm was formed on the substrate.

Welding and forming of thick steel plates with a high power density diode laser

Diode lasers offer the advantage of higher conversion efficiency than conventional CO2 and YAG lasers, but their beam properties are very poor. Nevertheless, they can be focused into a spot 0.96mm in diameter at a laser power of 2kW. The feasibility was thus examined of welding and forming thick steel plates using a diode laser with a high power of 2kW and a high power density of 236kW/cm2. Steel plates ranging from 0.5mm to 10mm in thickness were successfully welded without porosities or cracks. The diode laser beam’s top hat shape was found to be suitable for welding. Laser forming of thick steel plates with a high power density diode laser was also investigated. A 5mm thick steel plate was bent at an angle of about 9.23° by scanning it 50 times with a 4mm diameter beam at a power of 1kW and a scanning speed of 1.5m/min. Even though the diode laser has a short focusing length, it was found to be suitable for laser forming because it does not require the melting of specimen’s surface.Diode lasers offer the advantage of higher conversion efficiency than conventional CO2 and YAG lasers, but their beam properties are very poor. Nevertheless, they can be focused into a spot 0.96mm in diameter at a laser power of 2kW. The feasibility was thus examined of welding and forming thick steel plates using a diode laser with a high power of 2kW and a high power density of 236kW/cm2. Steel plates ranging from 0.5mm to 10mm in thickness were successfully welded without porosities or cracks. The diode laser beam’s top hat shape was found to be suitable for welding. Laser forming of thick steel plates with a high power density diode laser was also investigated. A 5mm thick steel plate was bent at an angle of about 9.23° by scanning it 50 times with a 4mm diameter beam at a power of 1kW and a scanning speed of 1.5m/min. Even though the diode laser has a short focusing length, it was found to be suitable for laser forming because it does not require the melting of specimen’s surface.