• Title/Summary/Keyword: Spot welding

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Ultimate and Fatigue Strength of Ship Hopper Knuckles (선체 호퍼너클 구조의 최종강도 및 피로강도)

  • 김영한;정장영;백점기;김하수;김도현
    • Journal of Welding and Joining
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    • v.18 no.1
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    • pp.77-82
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    • 2000
  • The aim of the present study is to investigate the characteristics of ultimate the fatigue strength of hopper knuckles in merchant vessels carrying bulk cargo or LNG/LPG/ The ultimate strength test is undertaken on the hopper knuckle model, subject to end tip load. A series of fatigue tests are carried out on the hopper knuckle models varying the level of the nominal stresses. The elasto-plastic finite element analysis is performed to examine the distribution of hot spot stresses near weld toe and also the progressive collapse behavior of the test model. S-N curves are developed based on the fatigue test results.

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Laser Cutting Characteristics of Cold Rolled Steel Sheets (레이저를 이용한 박강판의 절단특성)

  • 이기호;김기철;이종훈
    • Journal of Welding and Joining
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    • v.13 no.4
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    • pp.113-121
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    • 1995
  • This study deals with the quality and the optimum range of laser cutting process. Cold rolled steel sheets for automobile application were cut by a high power CO$_{2}$ laser system with beam quality of TEM$_{\infty}$ mode. Both process parameters such as travel speed and assist gas pressure, and quality factors were considered to optimize the laser cutting. It was revealed that the thinner the sheet thickness, the less effect of oxidation energy for contributing the cutting process. High speed photographs demonstrated that molten spot on the cut surface moved in a random and vigorous manner according to its viscosity and the flowing direction of assist gas, which resulted in so called striation. Laser cutting produced a very smooth surface of average roughness(Ra) about less than 1.5.mu.m at the optimum range. It was also shown that the characteristics of dross formation was influenced by the flowing durection of assist gas and the fluidity of molten metal drop..

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Asay of the fabrication technology of the KSTAR vacuum vessel mockup (KSTAR 진공용기 시작품 제작관련 기술분석)

  • 조승연
    • Journal of the Korean Vacuum Society
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    • v.8 no.4A
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    • pp.391-396
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    • 1999
  • KSTAR vacuum vessel mockup was fabricated by Korea Heavy Industries. The fabrication technology chosen for the mockup is introduced and assessed in this paper. KSTAR vacuum vessel is a huge vacuum chamber of 52 cubic meters never built in this country. Through the experiency of the KSTAR mockup fabrication, welding methods for obtaining both ultra high vacuum and structural integrity of the large vacuum chamber are extracted. The fabrication and assembly techniques for the complicated structure composed of reinforced ribs, double walls and various ports are also developed. A nondestructive test on the welding spot was performed and the results show that no major leaks violating the criterion were found. The one of the main objectives of the mockup fabrication is to measure the dimensions of the structure before and after fabrication, which plays an important role in the fabrication and the assembly. By assaying the problems occurred during mockup fabrication, the KSTAR mockup will provide the techniques for the fabrication of the main vacuum vessel.

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Fatigue Life Evaluation on Compressive & Tensional Residual Stress Induced Materials and Residual Stress Measurement using Hole Drilling Method (HDM을 이용한 잔류응력측정과 압축·인장 잔류응력이 인가된 재료의 피로수명평가)

  • Baek, Seung Yeb
    • Journal of Welding and Joining
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    • v.31 no.2
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    • pp.43-48
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    • 2013
  • This paper Investigated the characteristics of residual stress in weld is composed of typical specimens, are investigated by using three dimensional thermal elasto-plastic FEM analysis. Numerically calculated residual stresses in the gas welds were then compared with experimental results obtained by the hole-drilling method. Using the stress amplitude (${\sigma}a$)R at the hot spot point of gas weld, the relations obtained as the fatigue test results for typical specimens having various dimensions and shapes were systematically rearranged to obtain the (${\sigma}a$)R-Nf relationship. It was found that more systematic and accurate evaluation of the fatigue strength of plug- and ring-type gas-welded joints can be achieved by using (${\sigma}a$)R.

Pendulum Impact Tests for 16by16 Through Welded Spacer Grids with Optimized H type Springs (선용접방법으로 제작된 $16{\times}16$ 최적화 H형 스프링 지지격자에 대한 진자식충격시험)

  • Kim, J.Y.;Yoon, K.H.;Song, K.N.
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.1803-1806
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    • 2007
  • The General roles of a spacer grid(SG) are providing a lateral and vertical support for fuel rods, promoting a mixing of coolant and keeping guide tubes straight so as not to impede a control rod insertion under any normal or accidental conditions. To evaluate the impact characteristics of a SG such as impact velocity, critical buckling strength and duration time, a few types of impact tests for SGs have been conducted. In a previous study, a new welding method, a through-welding method, was proposed to increase critical buckling strength of a SG without any design change or material change and was verified by impact tests with $7{\times}7$ partial SG specimens.In this paper, the effect of through-welding method in case of a $16{\times}16$ full-size SG is investigated by pendulum impact tests with $16{\times}16$ SG specimens. And the increase of critical buckling strength for full-size SGs is measured by comparison with impact results of spot-welded and through-welded SGs.

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A Study on the Vision Sensor System for Tracking the I-Butt Weld Joints (I형 맞대기 용접선 추적용 시각센서 시스템에 관한 연구)

  • Bae, Hee-Soo;Kim, Jae-Woong
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.9
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    • pp.179-185
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    • 2001
  • In this study, a visual sensor system for weld seam tracking the I-butt weld joints in GMA welding was constructed. The sensor system consists of a CCD camera, a diode laser with a cylindrical lens and a band-pass-filter to overcome the degrading of image due to spatters and arc light. In order to obtain the enhanced image, quantitative relationship between laser intensity and iris number was investigated. Throughout the repeated experiments, the shutter speed was set at 1-milisecond for minimizing the effect of spatters on the image, and therefore most of the spatter trace in the image have been found to be reduced. Region of interest was defined from the entire image and gray level of searched laser line was compared to that of weld line. The differences between these gray levels lead to spot the position of weld joint using central difference method. The results showed that, as long as weld line was within $^\pm$15$^\circ$from the longitudinal straight fine, the system constructed in this study could track the weld line successful1y. Since the processing time reduced to 0.05 sec, it is expected that the developed method could be adopted to high speed welding such as laser welding.

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A Study on a Vision Sensor System for Tracking the I-Butt Weld Joints

  • Kim Jae-Woong;Bae Hee-Soo
    • Journal of Mechanical Science and Technology
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    • v.19 no.10
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    • pp.1856-1863
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    • 2005
  • In this study, a visual sensor system for weld seam tracking the I-butt weld joints in GMA welding was constructed. The sensor system consists of a CCD camera, a diode laser with a cylindrical lens and a band-pass-filter to overcome the degrading of image due to spatters and arc light. In order to obtain the enhanced image, quantitative relationship between laser intensity and iris opening was investigated. Throughout the repeated experiments, the shutter speed was set at 1/1000 second for minimizing the effect of spatters on the image, and therefore the image without the spatter traces could be obtained. Region of interest was defined from the entire image and gray level of the searched laser stripe was compared to that of weld line. The differences between these gray levels lead to spot the position of weld joint using central difference method. The results showed that, as long as weld line is within $\pm15^{o}$ from the longitudinal straight line, the system constructed in this study could track the weld line successfully. Since the processing time is no longer than 0.05 sec, it is expected that the developed method could be adopted to high speed welding such as laser welding.

Effect of Pulse Shapes on Weld Defects in Pulsed Laser Welding of Stainless Steel

  • Kim, Jong-Do;Kil, Byung-Lea;Kim, Young-Sik
    • Journal of Advanced Marine Engineering and Technology
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    • v.28 no.8
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    • pp.1270-1278
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    • 2004
  • This paper describes the effectiveness of laser pulse shaping in eliminating weld defects such as porosity, cracks and undercuts in pulsed Nd:YAG laser welding. A large porosity was formed in a keyhole mode of deeply penetrated weld metal of any stainless steel. Solidification cracks were present in STS 310S with above 0.017%P and undercuts were formed in STS 303 with about 0.3%S. The conditions for the formation of porosity were determined in further detail in STS 316. With the objectives of obtaining a fundamental knowledge of formation and prevention of weld defects, the fusion and solidification behavior of a molten puddle was observed during laser spot welding of STS 310S through a high speed video photographing technique. It was deduced that cellular dendrite tips grew rapidly from the bottom to the surface, and consequently residual liquid remained at the grain boundaries in wide regions and enhanced the solidification cracking susceptibility. Several laser pulse shapes were investigated and optimum pulse shapes were proposed for the reduction and prevention of porosity and solidification cracking.

Characteristics of the Nd:YAG laser Spot Welding in $Cu_{54}Ni_{6}Zr_{22}Ti_{18}$ Bulk Metallic Glass Alloy ($Cu_{54}Ni_{6}Zr_{22}Ti_{18}$ 벌크비정질 합금의 Nd:YAG 레이저 점용접 특성)

  • Kim, J.H.;Lee, J.H.;Shin, S.Y.;Bae, J.C.;Lee, C.H.
    • Laser Solutions
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    • v.8 no.2
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    • pp.13-20
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    • 2005
  • Weldability is largely dependent on the phase evolution and the microstructure of the weld. For the weldability of the $Cu_{54}Ni_6Zr_{22}Ti_{18}$ bulk metallic glass, the crystallization affects the sensitivity of the weld to the brittle failure. In order to suppress the irreversible crystallization, Nd:YAG laser welding was chosen. The pulsed Nd:YAG laser was irradiated onto the BMG plate and the effects of the pulse shape [peak power intensity and pulse duration time] on the crystallinity were evaluated.

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High power pulse source

  • 안수길
    • 전기의세계
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    • v.11
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    • pp.14-17
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    • 1963
  • 정확하게 control된 pulse의 용도는 과학과 공업이 발달될수록 날로 많아져 가고 있는데 그의 일부는 대전력을 취급하는 경우로서, Radar에 대한 응용을 들 수 있다. 한편, 요지음 gallium-arsenide등 반도체 diode를 사용해서 Laser action을 일으킬 수 있다는것이 발견되어 G.E. 및 IBM등에서 개발되고 있다. 이 경우에, continuous emission도 가능하지만 흔히, intermittent operation을 시켜야 할 때가 많기 때문에 timed pulse source가 필요하게 된다. 또 한편, spot welding의 경우에도 이러한 pulse source가 필요하게 된다. 이들을 크게 나누어 source를 AC로 할 경우와 DC로 할 경우가 있는데, 전자의 경우는 thyratron을 사용할 경우가 많게 될 것이다. DC의 경우나 AC의 경우에나 잘 shape되고 time된 pulse source를 만들어 놓으면 진공관이나 thyratron이나 같은 모양으로 drive할 수 (thyratron의 경우는 trigger)있을 것이기 때문에, 이러한 pulse source를 만들 필요가 있게 된다.

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