• Journal of Welding and Joining
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• v.29 no.1
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• pp.74-79
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• 2011

Three different welding wires were used to study the effects of Al content on weld metal toughness and porosity formation in self-shielded arc welding. Weld metal microstructure showed that while wire with 1.3% Al content contains coarse $\delta$-ferrite, wires with less than 0.5% Al content showed no such phase. In addition to the microstructural differences, cleanliness in weld metal was also different among wires. It showed that weld metal toughness was influenced by the $\delta$-ferrite formation, cleanliness and Ni addition. Even though wires with less than 0.5% Al content showed higher weld metal toughness, they showed relatively poor workability, forming porosities in weld bead in lower arc voltages.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.196-196
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• 2000

Formation of the weld defect, such as a blowhole and a pit in lap-jointed fillet arc welds has been a serious problem in arc welding of Zn-coated steel sheet. In this study, the relationship among welding conditions, welding materials and defect formation was investigated in order to minimize these defects in the CO₂ welds. In addition, the arc stability of the commercial welding wires was evaluated for revealing their effects on defect formation. Main conclusions obtained are as follows:1) There was no difference between shear tensile strength of the sound welds and that of the welds with blowholes whose diameters are less than 0.5mm. However, the welds with blowholes whose diameters are equal or larger than 0.5mm and pits exhibited tensile strength 10~20% and 30~40% lower than that of the sound welds respectively.2) The optimum welding condition to effectively prevent or reduce the weld defects formation are as follows:- The welding variables of 220A-23V-100cm/min and 120A-190V-30cm/min were recommended for minimizing the weld defects.- The gap between the two sheets at the lap-joint should be controlled to more than 0.2mm- Solid wire was less susceptible to the formation of the weld defects than the flux-cored wire.- The low welding current condition produced less weld defects than the hihg welding current condition.3) One of the reason why the amount of the defect was reduced at the low welding current was the gas discharging by the active agitation of the molten pool, due to an increasing in the number of the short circuit. (Received September 27, 1999)

• Journal of Welding and Joining
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• v.18 no.2
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• pp.69-76
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• 2000

Formation of the weld defect, such as a blowhole and a pit in lap-jointed fillet arc welds has been a serious problem in arc welding Zn-coated steel sheet. In this study, the relationship among welding conditions, welding materials and defect formation was investigated in order to minimize these defects in the CO₂welds. In addition, the arc stability of the commercial welding wires was evaluated for revealing their effects on defect formation. Main conclusions obtained are as follows: 1) There was no difference between shear tensile strength of the sound welds and that of the welds with blowholes whose diameters are less than 0.5mm. However, the welds with blowholes whose diameters are equal or large than 0.5mm and pits exhibited tensile strength 10∼ 20% and 30∼40% lower than that of the sound welds respectively. 2) The optimum welding condition to effectively prevent or reduce the weld defects formation are as follows: -The welding variables of 220A-23V-100cm/min and 120A-19V-30cm/min were recommended for minimizing the weld defects. -The gap between the two sheets at the lap-joint should be controlled to more than 0.2mm. -Solid wire was less susceptible to the formation of the weld defects than the flux-cored wire. -The low welding current condition produced less weld defects than the high welding current condition. 3) One of the reason why the amount of the defect was reduced at the low welding current was the gas discharging by the active agitation of the molten pool, due to an increasing in the number of the short circuit.

• Journal of Welding and Joining
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• v.26 no.2
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• pp.62-68
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• 2008

Effects of gravitational orientation on gas tungsten arc welding (GTAW) for 304 stainless steel were studied to determine the critical factors for weld pool formation, such as weld surface deformation and weld pool shape. This study was accomplished through an analytical study of weld pool stability as a function of primary welding parameters (arc current and arc holding time), material properties (surface tension and density), and melting efficiency (cross-sectional area). The stability of weld pool shape and weld surface deformation was confirmed experimentally by changing the welding position. The arc current and translational velocity were the major factors in determining the weld pool stability as a function of the gravitational orientation. A 200A spot GTAW showed a significant variation of the weld pool formation as the arc held longer than 3 seconds, however the weld pool shape and surface morphology for a 165A spot GTAW were 'stable', i.e., constant regardless of the gravitational orientation. The cross-sectional area of the weld (CSA) was one of the critical factors in determining the weld pool stability. The measured CSA ($13.5mm^2$) for the 200A spot GTAW showed a good agreement with the calculated CSA ($14.9mm^2$).

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.143-148
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• 1998

A dynamic electrical parameter monitoring device was designed to simultaneously record the instantaneous value of voltage, current, power, and resistance during spot welding. The data obtained using this technique have been analyzed in term of the relationships of these parameters to the phenomena occuring during the formation(surface break-down, nugget formation and mechanical collapse) of spot weld. Finally, a database implementation is undertaken to develop techniques for improving weld quality of the resistance spot welder.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.79-87
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• 1996

SMC(Sheet Molding Compound) is made of unsaturated polyester resin and other additives reinforced with randomly distributed chopped fiberglass strands. Because of its higher stiffness per unit mass, SMC was used as a substitute for steel for automotive steel outer panels. Thus, understanding of flow characteristics during fabrication of SMC is of importance since the formation of weld line depends on material flow. In the present study, SMC compression molding simulations in the flat and T-shape molds were accomplished. During simulations, the preferential the preferential flow occurred at the low mold closing speed while plug flow was observed for the higher mold closing speed. When the preferential flow was observed, the weld line was seen at the final stage. For simulations, rigid-viscoplastic finite element method was applied. Self-contact algorithm was also applied in order to predict the formation of the weld line. Simulation results were compared to the experimental results available in the literature.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.531-536
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• 1992

In GMA welding processes, monitoring and control of weld quality are extremely difficult problems. This paper describes a neural network-based method for monitoring and control of weld pool sizes. First, weld pool sizes are estimated via a neural estimator using multi-point surface temperatures, which are strongly related to the formation of weld pool, and then controlled using the estimated pool sizes. Two types of controllers using the pool size estimator are designed and tested. To evaluate the performance of the designed controllers, a series of simulation studies was performed.

• Journal of Welding and Joining
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• v.19 no.3
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• pp.317-324
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• 2001

This study deals with high power Nd:YAG laser welding of thin steels for small pressure vessels. Full penetration welding at the overlap joint was performed so as to assure sufficient weld strength. Results showed that mid-depth weld size reduced drastically with increasing the travel speed. Position of focus had little effect on the bead formation even though short focal system was used. However, the shape factor and the bead width had closely related with the position of focus. Based on the microstructural inspection, acceptable weld was obtained when the overlap clearance was controlled up to 20% of the base metal thickness. In the case that the joint contained more clearance than the critical value, both the tensile shear strength and the tear strength were reduced. Results also demonstrated that shielding gases were proved to play a key role as far as the bead formation characteristics was taken into consideration. Blowing dry air through 5mm in diameter nozzle produced narrower bead cross-section than that of argon or nitrogen shielding.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.91-96
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• 2000

Characteristics of the weld defect, such as a blowhole and a pit in lap-jointed fillet Co₂ welds of Zn-coated steel sheet were studied in order to make clear the sequence of the blowhole formation during welding. Main conclusions obtained are as follows: 1) Blowhole, wormhole and pit were found in fillet welds, although the optimum welding condition of 200A-23V-100cm/min was applied. 2) Zn was only detected at the solidification boundary at the early stage of the blowhole formation. 3) Most of the blowholes was started to form at lap-joint by the Zn vapor. With increasing of the Zn vapor and its pressure, the blowhole was develope to th bed surface until the completion of weld solidification. 4) The behavior of the blowhole in growth was similar to that of the columnar dendrite during welding.

• Laser Solutions
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• v.1 no.1
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• pp.30-38
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• 1998

This study includes the efface of shielding gas types on $CO_2$ laser weldability of low carbon automotive galvanized steel. The types of shielding gas evaluated are He, $CO_2$, Ar, $N_2$, 50%Ar＋50%$N_2$. The weld penetration, strength, formability(Erichsen test) of Laser weld are found to be strongly dependent upon the types of shielding gas used. Further, the maximum travel speed and flow rate to form a keyhole weld is also dependent upon types of shielding gas. The ability of shielding gas in removing plasma plume and thus increasing weld penetration is believed to be closely related with ionization/dissociation potential, which determine the period of plasma formation and disappearance. Further, thermal conductivity and reactivity of gas with molten pool also give strong effect on penetration and porosity formation which in turn affect on the formability and strength.