• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1047-1053
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• 2016

In this study, welding of pure titanium was carried out by using a continuous wave fiber laser with a maximum output of 6.3 kW. Because brittle regions form easily in titanium as a result of oxidation or nitriding, the weld must be protected from the atmosphere by using an appropriate shielding gas. Experiments were performed by changing the type and the flow rate of shielding gases to obtain the optimal shielding condition, and the weldability was then evaluated. The degree of oxidation and nitriding was distinguished by observing the color of beads, and weld microstructure was observed by using an optical microscope and a scanning electron microscope. The mechanical properties of the weld were examined by measuring hardness. When the weld was oxidized or nitrified, the bead color was gray or yellow, and the oxygen or nitrogen content in the bead surface and overall weld tended to be high, as a result of which the hardness of the weld was thrice that of the base metal. A sound silvery white bead was obtained by using Ar as the shielding gas.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.701-706
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• 2015

In this study, experimental and computer simulation results are compared and analyzed. Three-dimensional (3D) fabricated matrices from an MJM 3D printer were joined with poly-acetate thermoplastic polymers using a diode laser. A power range of 5-7 W was used to irradiate the boundary of two polymers. The heated polymers flowed into the matrices of the 3D fabricated structure, and reliable mechanical joining was achieved. Computer simulation showed the temperature distribution in the polymers, and flow direction was estimated based on the flux and temperature information. It was found that the more than the minimum energy threshold was required to effectively join the polymers and that two scans at low-speed were more effective than four scans at high speed.

• Korean Journal of Optics and Photonics
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• v.10 no.1
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• pp.73-79
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• 1999

Semiconductor optical switch modules of 1$\times$2, 1$\times$4, and 4$\times$4 types for 1550 nm optical communication systems were fabricated by using laser welding technique, embodying in 30-pin butterfly package. For better coupling efficiency between switch chip and optical fiber, tapered fibers of 10~15mm lens radii were used, which provided up to 60% optical coupling efficiency. With the help of new laser hammering process, we could recover the lost optical power almost completely up to average 82% of initially obtained power. The fabricated optical switch modules showed good thermal stability of less than 5% degradation even after 200 times thermal cycling test. The 2.5 Gbps optical transmission characteristics of the 4$\times$4 switch module showed low sensitivities of less than -30dB for all possible switching paths. The transmission penalties of 1$\times$2 switch module at $10^{-10}$ BER were 0.6dB and 0.7dB for 50Xm and 90 Km optical fibers, respectively.

• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.297-304
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• 2010

The microstructure and hardness of $CO_2$ laser welds were investigated in the Ti-stabilized ferritic stainless steel 409L. The observed specimen was welded in a fully penetrated condition in which the power was 5 kW and the welding speed 5 m/min. The grain structure near the bond line of the laser welds was produced by epitaxial growth. The grain size was the largest in the fusion zone, and HAZ showed nearly the same grain size as that of the base metal. The HAZ microstructure consisted of subgrains and precipitates that were less than 100 nm in size and that were located along the subgrain boundaries. On the other hand, the hardness was the highest in the fusion zone due to the large amount of small precipitates present. These were composed of TiN, Ti(C,N) and $TiO_2$+Ti(C,N). The hardness decreased continuously from the fusion zone of the base metal. The HAZ hardness was slightly greater than that of the base metal due to the existence of subgrains and precipitates in the subgrain boundary.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.5
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• pp.608-619
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• 2017

In this paper, the effects of parameters related to the residual stress induced due to laser shock peening process to determine mitigation of the initial tensile residual stresses are discussed, such as the maximum pressure, pressure pulse duration, laser spot size and number of laser shots. In order to estimate the influence of the initial tensile residual stresses, which is generated by welding in 35CD4 50HRC steel alloy, the initial condition option was employed in the finite element code. It is found that $2{\times}HEL$ maximum pressure and a certain range of the pressure pulse duration time can produce maximum mitigation effects near the surface and depth, regardless of the magnitudes of tensile residual stess. But plastically affected depth increase with increasing maximum pressure and pressure pulse duration time. For the laser spot size, maximum compressive residual stresses have almost constant values. But LSP is more effective with increasing the magnitudes of tensile residual stress. For the multiple LSP, magnitudes of compressive residual stresses and plastically affected depths are found to increase with increasing number of laser shots, but the effect is less pronounced for more laser shots. And to conclude, even though the initial tensile residual stresses such as weld residual stress field are existed, LSP is enough to make the surface and depth reinforcement effects.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.286-291
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• 2015

LLC resonant converter is used to control laser output power in Nd:YAG laser. Zero voltage switching (ZVS) is implemented to minimize the switching loss which is adopting the LLC resonant converter. In the spot welding processing of metal thin films, the processing quality is decided by the laser beam output energy of single pulse. We decide to the 50 [J] as the single pulse laser beam energy. Laser output power is investigated and experimented by changing the output current. That current is controled by the charging voltage of capacitor. From those results, we obtained the maximum laser output of 58.2 [J] and the conversion efficiency of 2.52% at the discharge voltage of 620V and the discharge current of 861 [A] and the pulse repetition rate of 1 [Hz] at the charging capacitor of 12,000 [${\mu}F$].

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1367-1372
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• 2014

As the awareness of the environmental crisis has recently increased around the world, numerous studies in the transport industry have been conducted to solve this problem through lightweight car bodies. The hot-stamping process has been presented as solution to achieve a light weight. Hot-stamping is a method that is used to obtain ultra-high strength steel (1,500 MPa or greater) by simultaneously forming and cooling boron steel in a press die after heating it to a temperature of $900^{\circ}C$ or above. This study involved a, fundamental examination of laser parameters to investigate the laser weldability of boron steel. As a result, the following optimum parameters for the shielding gas were found: Q = 20 l/min, ${\alpha}=40^{\circ}$, d = 20mm, and l = 0 mm. The hardness of butt weldment increasesed sharply as a result of martensite formation at the fusion zone.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.402-407
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• 2002

Laminate tooling process is a fast and simple method to make metal tools directly for various molding processes such as injection molding in rapid prototyping field. Metal sheets are usually cut, stacked, aligned and joined with brazing or soldering. Through the joining process, all of the metal sheet layers should be rigidly joined. When joining process parameters are not appropriate, there would be defects in the layers. Among various types of defects, non-bonded gaps of the tool surface are of great importance, because they directly affect the surface quality and dimensional accuracy of the final products. If a laminate tool with defects has to be abandoned, it could lead to great loss of time and cost. Therefore a repair method for non-bonded gaps of the surface is essential and has important meaning for rapid prototyping. In this study, a rapid laminate tooling system composed of a CO2 laser, a furnace, and a milling machine was developed. Metal sheets were joined by furnace brazing, dip soldering and adhesive bonding. Joined laminate tools were machined by a high-speed milling machine to improve surface quality. Also, repair brazing and soldering methods of the laminates using the $CO_2$ laser system have been investigated. ill laser repair process, the beam duration, beam power and beam profile were of great importance, and their effects were simulated by [mite element methods. The simulation results were compared with the experimental ones, and optimal parameters for laser repair process were investigated.

• Laser Solutions
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• v.16 no.3
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• pp.1-10
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• 2013

In this study, Al-Si coated boron steel(1.2 mm) were laser welded by $CO_2$ laser and hot-stamping was applied to the laser joints. Tensile properties and microstructures of the joints were investigated before and after hot-stamping. Tensile and yield strengths of the as welded specimen similar with base metal and fracture occurred base metal of boron steel. Although, in case of heat treated specimen, fracture occurred fusion zone that Al segregated zone near the bond line. These could be explained by the existence of ferrite, in the Al segregated zone near the bond line and base metal of boron steel. Before hot-stamping, hardness of base metal is lower than fusion zone and heat affected zone in spite of exist Al segregation zone($Fe_3$(Al,Si)). So fracture occurred base metal. Although, after hot-stamping, microstructure of base metal and welds zone transformed to martensite and bainite except in Al segregation zone near the bond line that $Fe_3$(Al,Si) transformed to a-ferrite. So fracture occurred Al segregation zone near the bond line.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.1
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• pp.92-99
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• 2013

The ratio of mobility handicapped was 12,110,000 in late 2009 about 24.4% of total population. The number of handicapped population is increasing continuously due to traffic accidents and industrial disasters. Therefore, the purpose of this research is to suggest a design for passengers on wheelchairs to get into and off to raise handicapped or elderly people's right of mobility. The scope of this research is mobility handicapped especially wheelchair passengers who use vans, small buses, and trains. The ramp design of vans is module form. The ramp is moved with screw jack and guides are installed on each side to increase stability. Moreover, a bridge was installed for smooth getting in and off of the van. The ramp design for small bus is lowed by 200m in order not to have obstacle such as speed bump when getting in or off. In order to reduce vulnerable environment and administration, air slide cylinder was chosen. Lastly, for the ramp design of train, the principle of link was used that the simpler structure made the weight lighter and installation in the train became easier. If we look at the conjugation condition of heterogeneous materials to produce a ramp, proper welding condition for cold steel plate and stainless plate is 3kW output and 3-5m/min of welding speed using laser beam seems proper.