A multi-beam type laser metal deposition (LMD) system equipped with two blue diode lasers (B-LMD) was developed to form a three-dimensional object production of a pure copper rod. Beams output from the two blue diode lasers are combined at the focal point, and pure copper powder is supplied there, the processing head is moved in the vertical direction to continuously melt and solidify the pure copper. A 100 mm long pure copper rod was formed in 25 seconds with multibeam LMD system using two 100 W-class blue diode lasers. The long side of the formed pure copper rod was 780 μm and the short side was 600 μm, which was larger than the spot at the focal point. Observation with a high-speed video camera showed that the pure copper rod was formed with a thin molten layer at a position 300 µm away from the focal point ( Z = 300 μm). When the laser profile at Z = 300 μm and the cross section of the pure copper rod were overlapped, the size of the pure copper rod coincided with the laser irradiation.
We developed several blue diode lasers and applied laser metal deposition one of the additive manufacturing technologies. This system has two laser modules, a focusing head, a powder feeder and a XYZ stage. Fiber couple direct diode laser module was guided to focusing head by optical fiber, which core diameter is 400 μm. In case pure copper layer formation with blue diode laser, the laser output power is 80 W, a scanning speed is 10 mm/s. A powder feed rate was varied from 14 to 80 mg/s. The stage was moved to the X direction. And In case pure copper rod formation with blue diode laser, the laser output power is 80 W and a scanning speed is 4 mm/s. A powder feed rate was varied from 14 to 80 mg/s. The stage was moved to the Z direction. Layer thickness was linearly increased to 40ms in all powder feed rate and the layer formation rate was gradually decreased over 40ms. An average slope Δspeed = 4 mm/s at 40 ms is obtained. From this, it is considered that pure copper rod can be formed by pulling upward at 4 mm/s. Based on the results obtained from copper layer, pure copper was stacked upward (direction Z) to form a pure copper wire. The result as expected was obtained by raising the speed at 4 mm/s. And since a thin molten pool was formed only in a limited area, it was observed that the molten pool was piled up without melting. It was confirmed that the flying powder adhered without melting. And thereafter, it was melted to form a rod. It was confirmed that there were no pore in pure copper rod.
In order to clarify the influence of light absorption characteristics and thermal conductivity of the substrate in forming a pure copper layer using multi-laser cladding system, a pure copper layer was formed on two type substrates. Two lasers were combined at a focal point to set a spot diameter of 507 μm. At the same time, pure copper powder having an average particle size of 34 μm was supplied from a center nozzle. The powder melted and solidified to form a pure copper layer on the substrate surface. The copper coated samples were cut with a micro-cutter, and cross section was observed with the microscope to investigate layer thickness, penetration depth and material organization. As a result, it was confirmed that the copper layer became larger as the laser input energy increased. And compared with the substrates of stainless steel and copper alloy, it was found that the input energy of copper alloy substrate required about 3 times more energy than that of stainless steel substrate. Therefore, it was revealed that the laser input energy depended on the thermal conductivity of the substrate.
Recently along with the advancement of EV shift in the automobile industry and the advancement of lithium ion batteries accompanying the advancement of mobile devices, expectations for laser welding of pure copper are increasing. In the laser welding, although a fiber laser, disk laser and direct diode laser with the wavelength of near infrared ray (IR) are generally, employed, it is difficult for pure copper to weld because of its low light absorption rate to copper. Thus, we have developed a high brightness blue diode laser system with absorption rate about 6 times that of IR laser, and demonstrated for it possible to form a weld bead of pure copper. The intensity of 1.3 × 106 W/cm2 on the substrate was easily obtained at the output power of 100 W and the laser spot diameter of 100 μm. In this study, the copper micro bead formation was investigated with respect to the height, penetration depth and contact angle to the substrate by in situ high speed x ray imaging in order to analysis the fusion bonding. As the results, it was found that the bead thickness was depended on the contact angle to the substrate while the laser irradiation. The interfaces between a pure copper and substrate were joined well without cracks or pores.
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
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.
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.
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.
In this Paper, laser cutting of super abrasive thin stick stone (SATSS) whose grains are CBN and diamond using Nd:YAG laser is studied. We have investigated cutting characteristics of SATSS and strength of the heat affected zone (HAZ) on the surface cut with laser. As a result, SATSS of 3 mm in thickness can be cut off with the width of 0.2 mm in maximum, and there is no chipping at the edge of the surface cut with laser. In the case of CBN stick stone, cutting time with laser is 2.5 times faster than that with diamond blade, and 15 times faster in the case of diamond one. There is a HAZ with a thickness of 0.05 mm. In this HAZ, the abrasive grains are oxidized and their crystal structures are changed by the heat of laser irradiation. However, laser is absorbed effectively by the HAZ, and the HAZ raises the strength of SATSS because the pores inside of the HAZ are closed by the re-solidified vitrified bond. From these results, it is shown that laser cutting can apply to the manufacturing of the SATSS and improve the productivity and the quality.
Recently, industrial products parts and components are being made smaller to reduce energy consumption and save space, creating a growing need for micro-welding of thin foil less than 100 mm thick. For this purpose, laser processing is expected to be the method of choice because it allows more precise heat control compared wih arc and plasma processing. In this report, the practicability of welding thin stainless steel foil with a direct diode laser system was investigated. The elliptically shaped laser beam of the direct diode laser enabled successful butt-welding of thin stainless steel foil 100 μm and less in thickness. Foil as thin as 50 μm could be successfully welded with a narrow bead width of 150 μm at a high speed of 18.0m/min. No spatter or plasma plume was observed when welding without an assist gas. The tensile strength of the weld bead was nearly the same as that of the base material.
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