• Journal of Welding and Joining
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• v.28 no.2
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• pp.47-53
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• 2010

According to the research report for the recent a few years, the dissimilar welding of Cu and STS 304 alloy have been presented that a weldability is very poor. This article present a study on Lap joint by Electron beam welding dissimilar materials. The weld metals was constituted between pure copper and STS 304 steel. The experiment was performed with 125mA welding current, 520mA focusing current. The Vacuum condition of chamber is 5${\times}$10-5torr and welding speed is 300mm/min. Showing the bead shape of weld metal, the thickness of the stainless 304 using as the protect materials is 3mm and the thickness of a copper is 15mm. The analysis about the microstructure were carried out in which it was observed with SEM. The results showed that complex heterogeneous fusion zone microstructure characterized both by rapid cooling and mixing of the molten metal, however the liquation crack was formated in the fusion line.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.49-57
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• 2001

In this study, the residual stress fields of multi-pass welded were analyzed by FEA under various geometrical conditions. In order to estimate the effects of pipe geometries on residual stress distribution, welding processes of each model were performed under the same heat cycles. And then, the influence of cutting off the weld bead on the residual stress redistribution was also estimated. From the results, in the range of t/D=0.05, axial residual stresses on the outer surface of the welded pipe were linearly decreased with pipe diameter increase. On the other hand, hoop residual stresses were not influenced by them. And both axial and hoop residual stresses on the outer surface of the welded pipe were increased with pipe diameter increase. But, when t/D was smaller than 0.05, they were converged in the nearly same value. The maximum residual stresses were generated at around HAZ. It in therefore necessary to consider them in welding design, strength evaluation, and analysis of fracture characteristics.

• Journal of Welding and Joining
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• v.32 no.1
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• pp.102-107
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• 2014

SCR(Thyristor) type $CO_2$ welders have widely used for the welding process of heavy industries such as shipbuilding and plant. Since the industrial fields of shipbuilding and plant are usually exposed to severe welding condition with lots of dust, extreme temperature, high humidity and vibration, it is not recommended to use inverter type welder despite its state-of-the-art technology. Many sophisticated functions in the inverter welder may not work due to malfunction of its sensitive components. Hence this study focused on digitalization of SCR $CO_2$ welder by making use of microprocessor for SCR phase control. By this application, fine control of output of the $CO_2$ welding systems is achieved. Also pulse output mode of operation is realized and its verification is carried out with aluminum sample welding. The experimental results showed sound weld bead. The front operation panel provide user with numerical parameter settings and monitors. It will help precise weld process monitoring and control with digital value.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.120-125
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• 2004

Fatigue life of welded joints are governed by the propagation of multiple collinear surface cracks distributed randomly along weld bead. These cracks propagate in mutual interaction and coalescence of them. To estimate the fatigue life, the influences of above two mechanisms on the fatigue life should be taken into account. These two mechanisms appear through the stress intensity factors disturbed mutually. However, it is difficult to calculate the stress intensity factors of multiple surface cracks located in vicinity of weld toe. The stress intensity factors are calculated normally by using the Mk-factors, but such Mk-factors are very rare in literature. In this study, the Mk-factors were obtained from a parametric study on crack length and depth, in which a finite element method is used. A fatigue test for a cruciform welded joint was conducted. The fatigue life of the tested specimen was estimated through present method with the informations obtained from the test, e.g. the number, size and locations of the cracks. The estimated and measured fatigue life showed a good agreement.

• Journal of Welding and Joining
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• v.17 no.2
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• pp.66-75
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• 1999

Weld bead quality in tailored blank(TB) is critically affected by edge preparation of sheets. The edge quality of prepared sheets for TB can be classified into straightness and the cross section quality of sheared plane such as a ratio of shear face, shear plane angle, etc. In order to have a good edg quality for butt-welding sheets, precision shearing will be recommended. In this paper, the feasibility of a conventional mechanical shearing as the edge preparation for tailored blanks is studyied. It reveals that fine shearing may not be the unique solution as it is generally accepted. To obtain the good shearing condition with a conventional mechanical shearing, experiments were carried out using Tahuchi method. The major parameters affecting a sheared contour are the clearance between upper blade and lower blade, and shear angle. The optimal shearing condition yields a very good straightness along the entire length of the cut, which gives a butt joint gap less than 10% of the base material thickness. The good cross section of sheared plane is also achieved in the optimal shearing condition such as a ratio of the shear face above 65%, a cross section's shear plane angle above 85%, little burr, which is providing finally good weld beads.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.627-631
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• 2005

In this study, low fatigue behavior of laser welded sheet metal were investigated. Before welding, the cross section of butt joint was prepared only by fine shearing without milling process. Specimens were same sheet metal and welding condition that using automobile manufacturing company at present. Butt joint of cold rolled sheet metal was welded by $CO_2$ laser. It is used that welding condition such as laser welding speed was 5.5m/sec and laser output power was 5kW for 0.8mm and 1.2mm sheet metal. The laser weldments were machined same or different thickness and same or different material. In order to mechanical properties of around welding zone, hardness test was performed. Hardness of welding bead is about 2 times greater than base material. We performed the low cycle fatigue tests for obtaining fatigue properties about thickness and the weld line direction of specimen. The results of strain controlled low cycle fatigue test indicate that all specimens occur cyclic softening, as indicated by the decrease in stress to reach a prescribed strain.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.525-534
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• 2002

During laser spot welding of the braun tube electron gun, phenomena such as serious spattering and oxidative reaction, etc. were occurred. The spatter occurred from weld pool affects the braun tube, namely it blocks up a very small hole on the shadow mask and causes short circuit between two roles of the electron gun. We guessed that high power density and oxidative reaction are main sources of these problems. So, we studied to prevent and to reduce spatter occurring in spot welding of the braun tube electron gun using pulsed Nd:YAG laser. The characteristics of laser output power was estimated, and the loss of laser energy by optical parameter and spatter was measured by powermeter. The effects of welding parameters, laser defocused distance and incident angle, were investigated on the shape and penetration depth of the laser welded bead in flare and flange joints. From these results, the laser peak power was a major factor to control penetration depth and to occur spatter. It was found that the losses of laser energy by optic parameter and sticked spatter affect seriously laser weldability of thin sheets. The deepest penetration depth is gotten on focal position, and a "bead transition" occurred with a slight displacement of focal position relative to the workpiece surface and the absorption rate of the laser energy is affected by the shape factor of the workpiece. When we changed the incident angle of laser beam, the penetration depth was decreased a little with increasing of the incident angle, and the bead width was increased. The spattering was prevented by considering laser beam energy and incident angle.ent angle.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.55-62
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• 1998

While excellent joint quality has been obtained using dry chamber underwater welding methods, the size limitations imposed by this process restrict its use for underwater construction work. The wet underwater shielded metal-arc welding eliminates this restriction but suffers from poor weld properties by the 1-pass bead-on-plate welding due to the excessive diffusible hydrogen. On the other hand, in the wet underwater welding, it is well known that the quantity of diffusible hydrogen in multi-pass welded parts reduce to less than that in 1-pass welded parts. Therefore, in this paper, welding experiments are made the 3-pass bead-on-plate welds by using TMCP and normalized steel plates and E4301 and cellulose coated electrode. After that, The amounts of the hydrogen absorbed into the 3-pass welded area were measured according to the JIS Z 3118 specification. The microstructural changes as well as the microhardness distribution after the underwater 3-pass welding were also investigated using Vickers microhardness tester and S.E.M and O.M. The results indicated that the quantity of diffusible hydrogen in 3-pass welded areas was reduced little less than a half of one of that in 1-pass welded areas at the specific welding condition. As a result, the cold cracking of 3-pass welded areas decreased by reduced effect of diffusible hydrogen. In the underwater 3-pass welding, the micrography of cold cracking fracture surface showed mainly the cleavage of hydrogen embrittlement.

• Journal of Welding and Joining
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• v.24 no.1
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• pp.56-63
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• 2006

The characteristics of $CO_2$ or Nd:YAG laser welded 600MPa ade TRIP steel was investigated. He or Ar gas was used as a shield gas in case of $CO_2$ laser welding, but the shield gas was not used in case of Nd:YAG laser welding. Bead on plate welding was performed with various welding conditions. Defects in the joints of both welding type occurred at 1.8m/min but were not observed over the welding speed of 2.1m/min in case of Nd:YAG laser welding. However, porosity occurred in $CO_2$ laser welding and the tendency of decreasing with the increase of welding speed. The hardness was the highest at heat affected zone near fusion zone as well as at the fusion zone and decreased on approaching the base metal. In a perpendicular tensile test to the weld line, all specimens that have been welded at optimum conditions were fractured at the base metal, and the tensile properties showed the rather higher than those of raw material. In a parallel tensile test, the strength of the joints was higher than that of the base metal. Elongation was found to be lower than that of the raw material. Forming height by Erichsen test and elongation were deeply related with the ratio of base metal/weld metal and the maximum hardness of the weld metal. Also porosity induced to decrease the strength and the elongation. The maximum formability was recorded at approximately 80% as compared with that of the raw material with the optimum condition.

• Journal of Welding and Joining
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• v.24 no.3
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• pp.27-33
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• 2006

Structural stress approach is well known as a mesh-size insensitive fatigue assessment method by using finite element analyses. It is, however, difficult to estimate the structural stress (SS) at weld end points due to stress singularities when shell elements are used. In this study, fatigue evaluations with longitudinal load carrying box fillet weldment under out-of-plane bending load have been performed by using virtual node method (VNM) in order to avoid the problem, which is called the weld end effect. Various combinations of virtual node parameters, such as reference point and virtual node locations, are investigated for the estimation of proper structural stress values applying VNM in a systematic manner. The appropriate guidance of virtual node parameter has been offered for the fillet weldment considered in the study. The structural stress values obtained by VNM have also been validated by comparing the result with finite element model including weld bead. Moreover, the fatigue strength of the fillet weldment based on the equivalent structural stress is shown to be consistent with the master S-N curve.