• 한국자동차공학회논문집
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• 제8권3호
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• pp.110-118
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• 2000

For reasonable fatigue design and estimation of fatigue durability considered fatigue strength and stiffness of the automotive body structure, many fatigue data must be insured according to the shapes, materials, and welding conditions of the spot welded lap joints. However, because it is actually difficult problem, there is need to establish a new method to be able to predict its fatigue life without any additional fatigue tests. Therefore, In order to improve such problems, in this study, the maximum stress function presenting the $\delta\sigma_{1max}―\delta P$ relation was defined form the relation between $\delta\sigma_{1max}-N_f$ and ${\delta}P-N_f$. By using the fatigue data on the IB type spot-welded lap joints previously obtained from the fatigue test results, fatigue life of the spot-welded lap joint previously obtained from the fatigue test results, fatigue life of the spot-welded lap joint having a certain dimension was tried to predict without any additional fatigue tests. And, its result was verified by ${\delta}P-$N_f$ curves. Obtained conclusion are as follows, 1) a maximum stress function considered the relation of the maximum principal stress, fatigue load, and the effects of geometrical factors of the IB type spot-welded lap joint was suggested. 2) the fatigue life predicted by the maximum principal stress function and the relation of $\delta\sigma_{1max}-N_f$ was well agreed with the fatigue life obtained through the actual fatigue test result. 3) the fatigue life of the IB type spot-welded lap joint having a certain dimension is able to be predicted without any additional fatigue tests from the fatigue life prediction method by the maximum principal stress function.

• 한국산학기술학회논문지
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• 제22권2호
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• pp.794-801
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• 2021

이 연구는 electric resistance element spot welding 프로세스를 도입하여 알루미늄 합금-강철의 이종 접합부의 기계적 강도 및 내식성을 향상시키기 위해 수행되었다. SPFC980Y 강철과 Al5052-H32가 각각 모재로써 적용되었고, S20C 강철은 리벳 element로써 음각과 양각의 형상으로 구분되며, Al5052-H32에 전기 저항 스폿 용접을 위해 리벳팅 되어 6.5 kA의 전류와 250 kgf/㎠의 가압력으로 접합되었다. 그 결과, 음각된 S20C element는 스폿 용접 공정 후 불안정한 너깃이 형성되는 반면, 양각된 S20C의 경우, 구조적으로 건전한 접합부로 건전한 내식성 및 탁월한 기계적 특성이 얻어졌다. FEM 시뮬레이션의 도입으로, 음각과 양각의 계면의 접합 특성이 수치적으로 밝혀졌으며, 시뮬레이션 결과는 미세조직 발달 양상을 수치적으로 뒷받침하였다. 이 연구는 element 스폿 용접된 H32-A5052 이종 접합부의 기계적 강도 및 부식 신뢰성에 대해 체계적으로 분석되었으며, 이 공정은 금속재료뿐만 아니라, 경량 비전도성 비철/비금속계 재료에도 적용 될 수 있기 때문에, 차세대 차체 경량화의 양산 기술로 확장 될 수 있다.

• Journal of Advanced Marine Engineering and Technology
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• 제12권1호
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• pp.37-45
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• 1988

A calculating method of transient temperature distribution due to spot welding of thin plates is studied in this paper. Considering the contact stress between upper and lower plate and temperature-dependence of specific resistance and elastic limit of base metal, the model of calorific density of heat source was decided. Using 2-dimensional polar coordinates system, the governing equation of heat transfer was developed. The thermal cycles of various points were recorded using C-A thermocouples during spot welding procedure for mild steel plates of 1mm thickness, and those results were compared with the results of calculations presented in this paper.

• Journal of Welding and Joining
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• 제30권2호
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• pp.76-80
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• 2012

In this study, the effect of the welding current on the hardness characteristics and microstructure in the resistance spot welding of 1GPa grade cold-rolled DP steel was investigated, Also, correlation between the hardness and microstructure was discussed. In spite of the change in the welding current, the hardness distributions near weld was similar. the hardness in the HAZ and the fusion zone was higher than that of the base metal and the hardness in the fusion zone was variated with the location. Especially, the hardness of HAZ adjacent to the base metal showed maximum value, and softening zone in the base metal adjacent to HAZ was found. With the increasing of welding current, there were no difference in maximum hardness and average hardness in the fusion zone were, but the hardness of the softening zone reduced. The difference in the hardness in each location of weld due to grain size of prior austenite. The softening of the base metal occurred by tempering of the martensite.

• Journal of Welding and Joining
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• 제29권5호
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• pp.99-105
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• 2011

In this study, effect of Si content on nugget diameter in electric resistance spot welded dual-phase(DP) steel was investigated. The cold rolled DP steels with different Si content (0.5, 1.0, 1.5, 2.0 wt.%) were used and thickness of those sheet was 1.2mm. With increasing Si content, nugget diameter was increased at the same welding current. This is attributed to increase of heat input result from high resistivity. Also, nugget diameter was increased with an increase in Si content for the same heat input. For this reason, the melting point of DP steel is lowered with an increase in the Si content. And solid DP steel can easily be transformed to a liquid phase because the low melting point. Finally, a prediction formula for the nugget diameter(N.D.) could be obtained in terms of heat input(Q) and melting point(M.P) as follows: N.D.(mm) = 0.11Q(J) - 0.0031 M.P.($^{\circ}C$) + 0.32.

• Journal of Welding and Joining
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• 제32권2호
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• pp.70-75
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• 2014

In automotive industry, applying of Mg alloy to autobody has been issued recently as a light metal. But poor resistance spot weldability of Mg alloy is blocking commercialization. So studies on improving resistance spot weldability of Mg alloy is increasing continuously. For reduce loss of heat input during welding, inverter DC power source is considered because of short rise time to target welding current. But rapid rising of welding current can increase temperature rapidly in nugget and oxide film between electrode and base metal, and that causes generating expulsion on low welding current range. In this study, for increase optimum welding current range and prevent generating expulsion, applicate various types of welding current waveform controls during resistance spot welding. For analysis effects of each current waveform control, acceptable welding current regions according to electrode force and welding time is determined and lobe diagram is derived. In result, pre heat is proposed as optimum type of welding current waveform control.

• Journal of Welding and Joining
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• 제35권2호
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• pp.52-57
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• 2017

In this study, resistance spot weldability of lightweight steel with high Al contents was evaluated using various electrode shapes. The six types of electrode shape were prepared with different electrode face diameter and radius. The tensile shear tests were carried out to investigate the failure behaviors. Also, the nugget size and hardness were measured and compared with various electrode shapes. The experimental results show that the acceptable weld current region for low density lightweight steel could be obtained with 10mm electrode face diameter and 76mm electrode face radius.

• Journal of Welding and Joining
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• 제19권6호
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• pp.622-629
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• 2001

The aim of this experiment is to establish the method that obtains symmetrically two nuggets in microresistance series spot welding. The sheets of austenite stainless steel STS304 applied to various electronic parts were experimented by the inverter welding power source of polarity controllable type and by the twin head for left and right electrode force to be controlled separately. The experimental results were obtained as follows : 1) When series spot welding was carried out by DC 1 pulse as welding current with same electrode force at left and right, the asymmetry of nuggets was resulted from the larger nugget of the (-) pole because of the Peltier effect. The dynamic resistance of weld spot at left and right was appeared differently according to the growth of nuggets. 2) When AC 1 cycle by welding power source of polarity controllable type was applied, the nuggets were almost symmetrically formed. 3) In a twin head, if the electrode force of (-) pole was larger than that of (+) pole, the diameters of two nuggets became to same. It was confirmed that the dynamic resistance of (-) pole was decreased to the same level as it of (+) pole. 4) Although the forces of left and right electrode were same, and only DC 1 pulse was applied, symmetric nuggets were obtained if the conductivity of (+) pole was lower than it of (-) pole.

• Journal of Welding and Joining
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• 제19권1호
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• pp.112-117
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• 2001

The factor affecting on the fatigue strength of spot welded specimen have been studied. To analyze and predict crack initiation position and propagation directions on the spot welded area are very important for strength design of the automobile body structure. In fact, there are a various of loads in running automobile but, it is impossible to replay like an actual conditions in the laboratory. So, in this study tensile-shear type and in-plane bending type specimens were used in fatigue test and includes an analysis of fatigue crack initiation position and propagation directions about earth specimens. The results obtained in the present study are summarized as follows: 1. In tensile-shear type fatigue test, the region of fatigue crack initiation position was affected by out-of-plane bending deformation due to bending angle. 2 In in-plane bending type fatigue test, the behavior of fatigue crack initiation position and propagation derections due to angle between upper plate and lower plate was dominated by magnitude of in-plane bending moment.

• 한국자동차공학회논문집
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• 제14권2호
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• pp.174-183
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• 2006

The resistance spot-welded region in most current finite element crash models is characterized as a rigid beam at the location of the welded spot. The region is modeled to fail with a failure criterion which is a function of the axial and shear load at the rigid beam. The role of this rigid beam is simply to transfer the load across the welded components. The calculation of the load acting on the rigid beam is important to evaluate the failure of the spot-weld. In this paper, numerical simulation is carried out to evaluate the calculation of the load at the rigid beam. The load calculated from the precise finite element model of the spot-welded region considering the residual stress due to the thermal history during the spot welding procedure is regarded as the reference value and the value of the load is compared with the one obtained from the spot-welded model using the rigid beam with respect to the element size, the element shape and the number of imposed constraints. Analysis results demonstrate that the load acting on the spot-welded element is correctly calculated by the change of the element shape around the welded region and the location of welded constrains. The results provide a guideline for an accurate finite element modeling of the spot-welded region in the crash analysis of vehicles.