• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.187-192
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• 2002

Applicability of laser micro welding process to the fabrication of medical devices was investigated. Austenitic stainless steel wire (SUS304) was spot melted and crosswise welded, which is one of the most possible welding process for the fabrication of medical devices, by using a Nd-YAG laser. Effects of welding parameters on the microstructure, tensile strength and corrosion resistance were discussed. In the spot melting, melted metal width decreased with decreasing the input energy and pulse duration. Controlling the laser wave to reduce laser noise which occurred in the early stage of laser irradiation made reasonable welding condition wider in the welding condition of small pulse duration such as 2ms. The microstructure of the melted metal was a cellular dendrite structure and the cell size of the weld metal was about 0.5~3.5 ${\mu}{\textrm}{m}$. Tensile strength increased with the decrease of the melted metal width and reached to a maximum about 660MPa, which is comparable with that for the tempered base metal. Even by immersion test at 318K for 3600ks in quasi biological environment (0.9% NaCl), microstructure of the melted metal and tensile strength hardly changed from those for as melted material. In the crosswise welding, joints morphologies were classified into 3 types by the melting state of lower wire. Fracture load increased with input energy and melted area of lower wire, and reached to a maximum about 80N. However, when input energy was further increased and lower wire was fully melted, fracture load decreased due to the burn out of weld metal.

• International Journal of Automotive Technology
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• 제7권3호
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• pp.329-336
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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 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. At first, the load on the spot-welded region is calculated with the precise finite element model considering the residual stress due to the thermal history during the spot welding procedure. And then, the load is compared with the one obtained from the model used in the crash analysis 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.

• 대한금속재료학회지
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• 제46권8호
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• pp.495-505
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• 2008

With the high proportion of zinc coated steels in body-in-white assembly, newly developed surface roughness textured galvannealed steel sheets have been introduced. In this study, zinc coated and surface roughness textured steel sheets were welded by resistance spot welding to investigate its weldability including electrode wear test. Based on the results of tensile-shear test, nugget diameter changes, and electrode tip growth test, it was clear that both surface roughness textured steels (GA-T and GA-E) showed good weldability. Also, there was no large difference in weldability and electrode wear behavior between GA-T and GA-E steels which have different surface roughness morphology. An analysis of electrode degradation showed Fe and Zn penetration through the electrode tip surface at 2400 welds reached $55{\sim}60{\mu}m$ and $75{\sim}80{\mu}m$, respectively. Therefore, there is no significant effect of surface roughness morphology on spot weldability of surface roughness textured galvannealed steel sheets. However, slight difference in thickness of alloying layers existing on electrode tip was found between GA-T and GA-E steels.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 추계학술발표대회 개요집
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• pp.219-221
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• 2004

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년도 춘계 학술대회 개요집
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• pp.124-126
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• 2006

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 춘계학술발표대회 개요집
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• pp.207-210
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• 2002

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2003년도 추계학술발표대회 개요집
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• pp.162-164
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• 2003

Spot welding, a kind of electric resistance welding, has been used in many fields such as automobile, aircraft, and appliance industry. This paper is to investigate the relationship between tensile shear strength and indentation depth under various welding conditions. The tensile shear strength increases with increasing the welding current in the range of 6-l3kA. The optimum welding conditions were 200∼250kg welding force and 10∼15 cycles welding time at 9kA welding current for EZNCEN. The indentation depth for optimum welding condition was 0.6mm at 9kA welding curent and 200kg welding force, 0.17mm at 9kA welding current and 300kg welding force, 0.19mm at 9kA welding current and 10cycle, 0.17mm at 9kA welding current and 15cycle welding time, respectively.

• Journal of Welding and Joining
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• 제33권2호
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• pp.18-22
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• 2015

The importance of emotional quality of car is getting higher in these days. Noise takes great portion in emotional quality because it is detectable problem with just a few rides. The sources of car noise during operation are various and the related technical issues are vast. Sometimes weldments of auto body are referred as the source of noise and the suspicious weldment shows unsatisfactory welding quality in most cases. In this research, cases of noise making weldments are investigated to figure out the solution for welding quality improvement. They are categorized into several groups in according to the inferred types of the error source then appropriate solutions are suggested. Auto body has weldments of resistance spot welding and gas metal arc welding in general. Therefore the solutions are suggested as adjustment of welding process variables and related machineries. Inevitable error source is also referred which is originated from thermal expansion rate difference between ultra high strength steel and mild steel. This new approach is validated through simple calculation then more concrete investigation with numerical analysis is remained as further works to be done.

• 대한금속재료학회지
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• 제48권1호
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• pp.71-76
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• 2010

The use of advanced high-strength steels (AHSS) in automotive applications has steadily increased over the past few years. Two different failure modes are generally observed in shear-tension tests for resistance spot welds of AHSS. interfacial fractures and full button pullout. Despite high load-carrying capacity. the resistance spot welds in AHSS cue prone to interfacial fractures. To improve the load carrying ability of welds during shear-lap and cross tension tests. the tip surface of the electrode was grooved in a round shape. The electrode tip surface was modified so as to concentrate the current now in the central and circumferential portion of the electrode force. The results showed that the interfacial fracture was suppressed in welds using the modified electrode. In a comparison of failure mode during mechanical tests. the welds made with the modified electrode showed a higher tendency to fail via full button pullout fracture.

• 대한기계학회논문집A
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• 제25권11호
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• pp.1713-1719
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• 2001

Estimation of fatigue strength on the spot welded joint is very Important for strength design of spot welded steed sheet structures. In this paper, the effect of residual stress on the fatigue life of resistance spot weldment was studied. Residual stress fields of weldment were calculated by using thermo elastic plastic finite element analysis and equivalent fatigue stress considering residual stress effect was obtained. And then we predicted fatigue life, which included the effect of the residual stresses and the actual loading stresses. The calculation and experimental results were in good agreement. Therefore, the proposed calculated model can be considered to be sufficiently powerful for the prediction of fatigue life.