• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.83-89
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• 1999

In this paper an experimental study on the development of the shielded metal are welding(SMAW) optimization technique for the dissimilar materials SS41 and STS304 of Auto-Lifting Magnet core plate was carried out. It was confirmed that the optimum welding heat input range was 37.5 to 45 kj/cm by considering on the strength and fatigue life of the welded joints more than 100% joint efficiency. And the quantitative relationship empirical wquation between the strength toughness adn fatigue life and the weld heat input was obtained.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.41-41
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• 2010

에어컨용 냉매 압축기, 냉장고용 냉매압축기 및 자동차 샷시 부품들은 주로 겹치기 필릿용접을 GMAW 으로 실시하고 있다. 그러나 용접 시 스패터 발생으로 인한 추가공수가 요구되며 작업환경 또한 열악한 실정이다. 따라서 저가의 고생산이면서 용접비드의 외관이 미려하고 스패터, 소음 그리고 Fume 이 발생되지 않는 청정한 TIG 용접이 있지만, 용접속도가 수십 cpm 이하로 제한되어 생산성이 낮다는 기술적 모순을 가지고 있다. TIG 용접에서 생산성을 증가시키기 위해 모재와 와이어를 고속 용융 시키려면 전류를 높여 입열량을 증가시켜야 하지만, 증가된 전류로 인하여 상승된 아크력이 험핑비드와 언더컷이 발생되는 물리적 모순을 가진다. 또한 필러와이어를 사용한 기존의 TIG 용접에서 필러 와이어는 주로 원형 단면 와이어를 사용하게 되는데 와이어의 직경이 증가함에 따라 비표면적은 감소하여 용융효율이 낮아지므로 $\Phi$1.2 이하의 필러와이어를 송급하여 용접하였다. 그러나 요구되는 용착량이 큰 경우 필러 와이어를 고속으로 송급하게 되는데 이 경우 필러 와이어 용융이 곤란하거나 송급상의 문제가 자주 생겨 용접속도를 고속으로 하기 곤란하였다. 따라서 필러와이어를 사용한 TIG 용접에서 용착금속의 용융효율을 높게 함으로서 전류를 크게 증가시키지 않으면서도 용접속도를 높일 수 있는 용접 공정개발이 필요한 실정이다. 본 연구에서는 비표면적을 증가시켜 용착금속의 높은 용융효율을 얻을 수 있도록 개발된 와이어와 기존의 $\Phi$3.2 일반와이어 및 를 이용하여 BOP TIG 용접에 비교 실험하였으며, 개발된 와이어와 기존의 $\Phi$1.2 필러와이어를 이용하여 필릿용접부에 적용 실험하여 비교하였다. 그 결과 개발된 와이어의 경우 적절한 비드를 형성하였으나 3.2 일반와이어의 경우 과도한 볼록비드와 불용착부의 문제가 발생하였고, 필릿용접 비교실험에서는 각각 200cpm과 50cpm에서 적절한 비드가 형성되어 더 높은 용착금속 용융효율을 얻을 수 있었다.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.30-30
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• 2010

고강도강의 용접성은 저온균열 저항성으로 대변되는데, TMCP강과 HSLA강 등이 개발되면서 고강도강의 저온균열저항성이 크게 향상되어 무예열 용접성이 확보되었다. 그러나 용접재료 측면에서는 그에 상응하는 재료의 개발이 지연되어 강재 개발로 인한 우수한 성능을 충분히 발휘하지 못하고 있으며 용접부의 건전성 문제가 심각하게 인식되고 있다. 이로 인해 고강도강에 적용시킬 수 있는 무예열 용접재료의 필요성이 대두되어 개발이 진행되고 있으며 상용화를 앞두고 있다. 이러한 용접재료의 개발단계에서 합금설계는 가장 중요한 항목으로 합금 조성에 따라 용착금속의 강도 및 인성에 상당한 변화를 가져오기 때문이다. 합금원소 중 Al은 강재의 탈산을 돕기 때문에 가능한 많은 양의 첨가를 요구하지만 적정량 이상을 초과하게 되면 오히려 용착금속의 저온인성 특성에 부정적인 영향을 미치게 된다. 본 연구에서는 고강도 GMA 용착금속의 Al함량을 단계적으로 변화시켜 용착금속 내 최적의 Al의 함량을 찾고자 하였다. 또한 높은 비용 및 많은 시간을 필요로 하는 와이어로드를 제작하지 않고도 Al함량을 조절 할 수 있는 방법을 고안하고자 하였다. 실험의 모재는 HSLA-100강을 사용하였으며 용접재료는 ER120S-G급의 GMA용접 재료를 사용하였다. 모재 성분과의 희석을 방지하기 위해 V-Groove 가공 후 6패스 Buttering 용접을 실시하였고, 다시 Buttering용접부에 V-Groove 가공을 하여 최종 용접을 실시하였다. 이 때 Al함량을 조절하기 위해 최종 용접 개선부 밑면에 홈을 판 후 Al fiber(직경 0.3mm)를 깔고 용접(입열량 20kJ/cm)하여 Al함유량을 총 3가지(0.003~0.04% Al)로 제어하였다. 용접 후 각각의 시편에 대해 미세조직, 충격시험, O/N분석, 성분분석 등의 시험을 수행하여 저온인성과의 상관관계를 알아보았다.

• Journal of Welding and Joining
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• v.15 no.6
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• pp.57-65
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• 1997

A study was undertaken to determine the influence of welding variables such as shielding and plasma gases, torch standoff, travel speed and heat input, etc. on the quality of plasma arc welds in Zircaloy-4 sheet, 2mm thick. Effect of shielding gases and their flow rates on the mechanical properties of Zircaloy-4 welds by plasma arc welding were determined in terms of tensile, bardness and bend tests. The microstructure and fracture surface of Zircaloy-4 welds were investigated by optical and scanning electron microscopies. In addition, the causes of porosity and undercut in plasma arc welds of Zircaloy-4 were also investigated. Zircaloy-4 weld bead width and depth by helium shielding gas showed a wider and deeper than those by argon. It was found that Zircaloy-4 welds with shielding gas of helium did dxhibit a little smoother and uniform weld beads than those with shielding gas of argon. It was also found that the optimum gas flow rates for Zircaloy-4 welding were 0.45l/min for plasma gas with Ar and 4.5 - 6 l/min for shielding gas with He. In addition, there was no big difference in the microstructure and fracture surface of the weld metals made by either Ar shielding gas or He shielding gas.

• Journal of Welding and Joining
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• v.2 no.2
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• pp.54-61
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• 1984

Construction of welding structure is greatly dependent upon welding heat cycle. Fracture toughness is decreased remarkablely due to coarse grained HAZ and inequal residual stress of three dimensions to originate in welding. Post weld heat treatment(PWHT) is carried out to increase the fracture toughness of HAZ and to remove the residual stress. There occur some problem such as toughness decrement and stress relief cracking(SRC) in the coarse grained HAZ subject to the effect of tempering treatment. Therefore, in this paper, the effect of heat inputs affecting cooling rate and PWHT under the no stress on fracture toughness were evaluated by crack opening displacement (COD), SEM and micro-hardness test. Experimental results are as follows; 1. Fracture toughness of weld HAZ is dependent upon weld heat cycle and it is decreased with increment of heat input, but the degree of improvement of fracture toughness after PWHT was linearly increased with heat input. 2. Hardness of the parent metal is not changed, but the softening of coarse grained HAZ is remarkable due to PWHT. 3. Fracture surface of as-weld show the perfect brittle fracture with the cleavage fracture, but after PWHT they appear the ductile fracture surface with dimple.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.2
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• pp.133-142
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• 1984

With the weld-joined compact tension specimens compared with each other, that is, transverse and lengthwise about the crack propagation direction, high and low in the input heat level, same as and lower than the base metal in the strength of weld material, the fatigue test were performed. With these data, the log-log curves between the fatigue crack propagation rate ${\frac{da}{dN}}$ and the transition range of the stress intensity factor ${\Delta}K$ ahead the crack tip were drawed. These curves were compared and estimated among each compared specimens, among each zones, that is, the base metal, the heat-affected metal and the weld-mixed metal, and between this study and the past studies. Basically, Little difference in the slope of the $da/dN-{\Delta}K$ relation was showed in all the welded directions, all the input heat levels and all the zones. But, First, to comparison with in the past studies about the base metals, it was showed that da/dN started in the much later rate, increased faster and stoped in the little faster rate. Second, it was showed that, near the time the crack's going from the heat-affected zone to the weld-mixed metal da/dN decreased a little for a while. Third, in the lengthwise weld compared with the transverse weld, in the high input heat weld compared with the low input heat weld in the case used the weld material of the same strength as the base metal, in the opposite case in the case used the one of the lower strength than the base metal, in the case used the weld material of the same strength as compared with the lower strength than the base metal beside the high input heat and the lengthwise weld, it was showed that the crack occured earlier in lower ${\Delta}K$ and later da/dN, the curves went with the same slope. Forth, in the lengthwise weld compared with the transverse weld in the low input heat weld, in the low input heat weld compared with the high input heat weld, it was showed that da/dN went with the lower level.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.7-7
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• 2009

TIG 용접에서는 후판 용접의 경우 용입의 한계 때문에 깊고 넓은 그루브 가공을 하여 다층 용접을 한다. 이 때, 그루브를 채우는 용착금속에 의한 응고 수축과 과대한 입열로 인한 변형이 문제시 되고 있다. 변형을 줄이기 위해서는 용착금속의 양과 입열량을 줄여야 한다. 이러한 문제를 해결하기 위해 그루브의 루트패이스를 두껍게 하고 그루브각을 줄여서 용착량을 줄인다. 이때, 좁은 그루브에서 두꺼운 루트패이스를 완전 용입할 수 있는 용접 프로세스가 필요하다. 비드가 좁고 깊은 용입 특성을 가지는 Plasma welding(PAW) 경우에는 좁은 그루브 속에 토치가 접근하기 어려워 적용하기 어렵다. 따라서 접근성이 용이한 TIG 용접에서 높은 용입형상비를 가지는 용접공정 개발이 필요하다. 선행연구로 높은 용입 형상비를 가지는 Active flux Tungsten Inert Gas(ATIG) 용접이 연구되었다. ATIG의 용입 증가 메커니즘으로는 Marangoni effect, 음이온들로 인한 아크 수축 효과, 절연 플럭스에 의한 아크 수축효과 등으로 알려져 있다. 또한 선행연구에서 ATIG에서 Ar가스에 He 또는 $H_2$ 가스를 첨가하면 용입이 더욱 증가하는 것을 확인하였다. 본 연구에서는 A-TIG에 He 가스를 적용하고 아크길이 0.5mm, 1.0mm, 2.0mm와 전극 선단각 30도, 60도, 90도에 따른 용입 형상비와 변형량을 검토하기 위해 실험을 하였다. 실험 결과는 아크길이가 감소할수록 전극 선단각이 증가할수록 용입 형상비는 증가하였고, 변형량은 감소하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1560-1565
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• 2005

Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for 304 stainless steel plates changing several process parameters such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar plates, etc. The following conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.3 s.180
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• pp.47-55
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stress-strain behavior and the hardness of the welded metal are investigated. From the results of the investigation, it has been shown that the optimal voiding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• Journal of Industrial Technology
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• v.21 no.A
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• pp.329-336
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• 2001

In this study, a series of fatigue tests are carried out in order to estimate quantitatively the characteristics of fatigue crack growth rate for high strength steels of SM570, POSTEN60, and POSTEN80 steel, that is, the influence on fatigue crack growth rate according to the welding line, the characteristics of fatigue crack growth according to the welding method and the kinds of steel, and the characteristics of fatigue crack growth for base metal, heat affected zone and weld metal. From the test results, in case that the notch if parallel to welding line, it knows that the retardations of fatigue crack growth rate in crack tip at early stage increase remarkably than in case that the notch is perpendicular to welding line due to compressive residual stress. And the characteristics of fatigue crack growth rate according to welding method are that the dispersion of fatigue crack growth rate in case of FCAW method is smaller than that of SAW method. Also, it knows that the fatigue crack growth rate converges in high stress intensity factor range.