• Journal of Advanced Marine Engineering and Technology
• /
• v.31 no.8
• /
• pp.961-969
• /
• 2007

The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• Laser Solutions
• /
• v.9 no.2
• /
• pp.1-9
• /
• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range $({\Delta}K)$ region and faster in high${\Delta}K$ region than that of the base metal specimens. The slant crack angle slightly influenced the crack propagation of the TB specimen of 2.0+2.0mm thinkness.

• 제어로봇시스템학회:학술대회논문집
• /
• 2000.10a
• /
• pp.292-292
• /
• 2000

Since high-power CO$_2$ Laser can be make a high densed energy to Local processing area, manufacturing processes using the laser can be processed for very Localized areas at a very fast rate with minimal or no distortion. Accordingly, the laser has been widely used in the fields of thermal manufacturing processes such as welding, fusion cutting, grooving, and heat treatment of metals. In particular, interest in the laser heat treatment process has grown tremendously in the past few years. In this process, maintaining the uniform hardening depth is important problem to obtain good quality products and to reduce heat induced distortion and residual stress. For achieving this objective, we introduced a new design technique of a fuzzy logic controller that greatly simplified the design procedure by defining several simplified design parameters. In the design procedure, the major design parameters of the controller are characterized by identifying several common aspects. From a series of simulation results, we found that the proposed design technique can be effectively used to design of a fuzzy logic controller for the LASER surface hardening process.

• Journal of Institute of Control, Robotics and Systems
• /
• v.20 no.2
• /
• pp.218-222
• /
• 2014

In this paper, we introduce an autonomous calibration method for a 2D laser displacement sensor (e.g. laser vision sensor and laser range finder) by matching a single point on a flat structure. Many arc welding robots install a 2D laser displacement sensor to expand their application by recognizing their environment (e.g. base metal and seam). In such systems, sensing data should be transformed to the robot's coordinates, and the geometric relation (i.e. rotation and translation) between the robot's coordinates and sensor coordinates should be known for the transformation. Calibration means the inference process of geometric relation between the sensor and robot. Generally, the matching of more than 3 points is required to infer the geometric relation. However, we introduce a novel method to calibrate using only 1 point matching and use a specific flat structure (i.e. circular hole) which enables us to find the geometric relation with a single point matching. We make the rotation component of the calibration results as a constant to use only a single point by moving a robot to a specific pose. The flat structure can be installed easily in a manufacturing site, because the structure does not have a volume (i.e. almost 2D structure). The calibration process is fully autonomous and does not need any manual operation. A robot which installed the sensor moves to the specific pose by sensing features of the circular hole such as length of chord and center position of the chord. We show the precision of the proposed method by performing repetitive experiments in various situations. Furthermore, we applied the result of the proposed method to sensor based seam tracking with a robot, and report the difference of the robot's TCP (Tool Center Point) trajectory. This experiment shows that the proposed method ensures precision.

• Proceedings of the KWS Conference
• /
• 2006.05a
• /
• pp.59-61
• /
• 2006

The $CO_2$ laser cladding was conducted on an AC2B alloy with feeding Fe-based powders. A powder feeding rate (PFR) and a travel velocity were related with the cracks adjacent to the Fe/Al interface. Preheating temperature was varied to study the interface crack. Preheating to $250^{\circ}C$ during the laser cladding suppressed the interface crack ratio (ICR). The ICR was limited for the single pass clad and the reciprocating test for the slide wear was conducted on an overlay cladding experiment. Comparing with no overlap overlay, the overlay clad with 50% overlap showed better wear resistance.

• Journal of Welding and Joining
• /
• v.11 no.1
• /
• pp.73-79
• /
• 1993

The phenomenon of metal transfer has been investigated for different transfer modes using a digital high speed motion analyzer and an arc shadow-graphing system based on a laser source and related optical system. It was observed that the pinch instability phenomenon did not occur for the globular transfer mode, since the liquid globule was then spherical rateher than a cylindrical liquid bar. On increasing the ratio of carbon dioxide to argon, the transition current from globular to spray transfer generally increased, but it is interesting that the transition was observed to occur at the lowest current in a 5% CO$_{2}$-95% argon gas mixture. For pure carbon dioxide and helium shielding gases, the drop frequency increased slowly with increasing current. At high currents or an argon based shielding gas, the length of liquid bar decreased as the carbon dioxide content increased. The acceleration of a droplet within the arc was determined using the gas drag force theory and was found to be greater than the experimental results.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.2
• /
• pp.26-32
• /
• 2012

In this paper, the effects of irregular bead shapes on fatigue life were investigated. A modified S-N curve method was used to estimate the fatigue life, which considered the inherent multiaxiality caused by the geometrical feature produced by the welding process. The point method of the critical distance method was used to determine the fatigue effective stress. Three types of fillet joint models were tested in the fatigue experiments. For each model, real bead shapes were collected using a 3D laser scanner, and finite element analyses were performed. The results of the analyses with actual bead shapes were compared with those using an idealized bead shape model. The results of the present analytical methods showed good agreement with the experimental results.

• Journal of the Korean Society for Precision Engineering
• /
• v.3 no.2
• /
• pp.102-104
• /
• 1986

최근 레이저 가공에 대한 관심이나 인식이 높아지고 재료가공분야에서 급속한 기술혁 신이 추진되고 있다. 여러 종류의 재료 가공 분야중 용접분야의 기술발전은 용접을 할때 사용되는 열원의 발전에 크게 영향을 받아 왔다. 현재 공업적으로 용접에 이용되고 있는 가장 발전 된 열원으로는 레이저 빔과 전자 빔이 있으나, 전자 빔 용접은 작업 환경과 피용 접물의 조건에 제한이 있으므로 레이저 빔 용접에 비하여 불리하다. 레이저 용접은 1960 년대에 전자부품의 용접에 적용된 이후 기술적으로 상업적으로 미약하던 레이저 용접 응용 과 1971 년 Brown과 Banas에 의해 수kw급 $Co_2$ 레이저로 심층 침투 용접이 발표된 이후 크게 증가하였다. 레이저 빔의 특성을 이용하여 전자 빔만으로 할 수 있었던 특수 정밀용접 을 해야하는 용접하기 어려운 재료의 용접에 레이저 빔을 이용하는 많은 실험이 행해져 오고 있다. 여기서는 레이저 용접의 특징, 용접 품질에 영향을 미치는 각 변수들, 레이저 용접의 응용사례에 대하여 개설하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.1
• /
• pp.53-62
• /
• 1987

High power lasers provide a controllable and precise energy source in surface transformation hardening. A careful control of the process is needed in order that the surface layer of the material reaches the austenizing temperature, but that it does not melt. In order to achieve this the results of theoretical and experimental studies on the laser surface hardening of a medium carbon steel are described. A two-dimensional computer program, which can be used generally for the determination of transient temperature distributions in welding and heat treatment, was established on the basis of the finite element method. For the confirmation of the accuracy of the numerical analysis, a medium carbon steel (SM 45C) of 5mm thickness was heat-treated with a 1kW CW CO$_{2}$ laser machine, while the traverse speed and the distance from the focal point (defocused distance) were varied. Experimental and numerical results showed a similar tendency in correlations between the hardened zone shape and the process parameters. With increasing beam spot diameter the width and depth of the hardened zone increased for relatively small beam spot diameters, but decreased rapidly after reaching the maximum value, while with increasing traverse speed the width and depth of the hardened zone decreased monotonously. Too small beam spot diameters are to be avoided, since the surface melting would lower the surface hardness and produce an uneven surface which may be unacceptable because of the possible requirement for subsequent machining. It could be observed that for a given traverse speed and laser power input there exists a optimal range of the beam spot diameter, which produce a large width of the hardened zone but no melting on the surface.

• Journal of Korea Foundry Society
• /
• v.18 no.4
• /
• pp.389-397
• /
• 1998

회주철 모재의 표면에 감압 플라즈마 용사법으로 실리콘 분말을 피복시킨 후 $CO_2$ 레이저를 이용하는 표면 합금화로 고온 내스케일성이 향상된 표면 개질층을 제조하였다. 실리콘의 표면 합금층에는 응집상의 흑연(chunky graphite)이 $Fe_5Si_3$로 구성된 망상의 화합물 기지속에 정출하는 조직특성을 보였다. 대기 분위기에서 18.0ks동안 열중량측정(TG)한 결과 실리콘 표면 합금층의 무게 증가율은 회주철 모재에 비하여 923K에서는 약 1/3, 1098K에서는 약 1/10을 나타내었다. 그리고 1098K에서 18.0ks동안 유지시킨 주철모재 시편에서 원래의 모재표면을 기준으로 다공성의 외부스케일과 편상흑연을 따라 생성된 내부스케일로 구성된 두께 $60{\sim}70\;{\mu}m$의 두꺼운 산화스케일이 생성되었으나, 실리콘의 표면 합금층에서는 두께 $3{\sim}5\;{\mu}m$의 치밀한 외부 산화스케일만이 생성되었다. 실리콘 합금층의 단면 미소경도값은 MHV $300{\sim}1100$으로 그 변동폭이 심하였으나, 진공분위기에서 열처리(1223K, 18.0ks)한 경우 미소경도값의 편차는 MHV $300{\sim}500$으로 개선되었다.