• Journal of Welding and Joining
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• 제26권5호
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• pp.74-78
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• 2008

The laser welding of the car body and components has been spread in the automotive industry. The Nd:YAG laser welding system could be used in 3D welding with robot. However, this system cannot efficiently reduce the welding cycle time according to various welding sequences because the robot's moving time is same that of the resistant spot welding system. But the remote welding system with high power $CO_2$ laser and scanner makes it possible welding cycle time much faster than the robot laser welding system. In the $CO_2$ laser remote welding system, laser beam can be rapidly transferred to a workpiece by moving mirrors of scanner system. So, it makes reducing the cycle time of welding process and shaping various welding patterns easily. Therefore, in this paper, the characteristic of weld strength according to patterns of weld bead on $CO_2$ laser welding was investigated. Also, the relationship between shape of weld bead and value of tensile load was studied. Finally, the optimum remote welding condition for car bumper was investigated.

• 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.

• Journal of Welding and Joining
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• 제11권2호
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• pp.27-41
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• 1993

The estimation of nugget sizes was attempted by utilizing the artificial neural networks method. Artificial neural networks is a highly simplified model of the biological nervous system. Artificial neural networks is composed of a large number of elemental processors connected like biological neurons. Although the elemental processors have only simple computation functions, because they are connected massively, they can describe any complex functional relationship between an input-output pair in an autonomous manner. The electrode head movement signal, which is a good indicator of corresponding nugget size was determined by measuring the each test specimen. The sampled electrode movement data and the corresponding nugget sizes were fed into the artificial neural networks as input-output pairs to train the networks. In the training phase for the networks, the artificial neural networks constructs a fuctional relationship between the input-output pairs autonomusly by adjusting the set of weights. In the production(estimation) phase when new inputs are sampled and presented, the artificial neural networks produces appropriate outputs(the estimates of the nugget size) based upon the transfer characteristics learned during the training mode. Experimental verification of the proposed estimation method using artificial neural networks was done by actual destructive testing of welds. The predicted result by the artifficial neural networks were found to be in a good agreement with the actual nugget size. The results are quite promising in that the real-time estimation of the invisible nugget size can be achieved by analyzing the process variable without any conventional destructive testing of welds.

• Journal of Welding and Joining
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• 제26권2호
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• pp.75-84
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• 2008

With the development of surface roughness textured steel for automotive body-in-white assemble, one of key issues is to understand the role of the surface roughness in textured steel sheets. To investigate effect of surface roughness on weldability in prepared steels, electrode force was varied. Steel sheets (T-H) with high surface roughness ($Ra\;=\;1.94\;{\mu}m$) reduced electrode life. It was attributed to the higher contact resistance at the electrode-sheet interface in the presence of the high surface roughness. The increased electrode diameter decreased current density, therefore reducing weld electrode life due to small weld button size. When an increased electrode force was used, a significant increase in the electrode life was observed in welding of high surface roughness steel sheet. This study suggested that contact resistance at the electrode-sheet interface was the dominant factor, as compared to the sheet-sheet interface for determining electrode life in welding of surface roughness textured steel.

• Journal of Welding and Joining
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• 제34권6호
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• pp.28-34
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• 2016

Galvannealed(GA) steels are now generally used in car body manufacturing for corrosion resistance. In this study, the weldability and joint mechanical behavior of a newly developed 1.2GPa grade GA ultra high strength TRIP(transformation induced plasticity) steel was investigated for three joining processes, such as adhesive bonding, resistance spot welding and weldbonding. Under both shear and peel stress conditions, the failure mode of the adhesive joints were the mixture of the adhesive cohesive failure, adhesive interface failure and coating layer failure. It means that the adhesion strength of GA coating onto the base metal was similar to that of adhesive bonding onto the GA coating. Under the shear stress condition, the weldbonding exerted to expand the optimal spot welding condition of 1.2GPa GA TRIP steel because the strength of adhesive bond overwhelmed that of the resistance spot weld. Under the peel stress condition, the weldbonding also exerted to expand the optimal spot welding condition of 1.2GPa GA TRIP steel by inducing the tear fracture mode rather than the partial plug fracture mode.

• 한국재료학회지
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• 제19권7호
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• pp.369-375
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• 2009

The spot weldability of dissimilar metal joints between stainless steels (AISI316) and interstitial free (IF) steels were investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensileshear strength, hardness, and microstructure. The fracture surface was investigated by using a Scanning Electron Microscopy (SEM). The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the STS316 sheet was larger due to the higher bulk-resistance. The microstructure of the fusion zone was fully martensite. In order to evaluate the microstructure further, dilution of stainless steels were calculated and imposed onto the Schaeffler diagram. The predicted microstructure from the Schaeffler diagram was martensite. In order to confirm the predicted microstructure, XRD measurements were carried out. The results showed that that initial weld nugget was composed of austenite and martensite.

• 대한조선학회논문집
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• 제42권4호
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• pp.388-395
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• 2005

A numerical procedure is proposed as a mesh-size insensitive structural stress definition that gives a stress state at a weld toe with relatively large mesh size. The structural stress values obtained using different finite element types, i.e. shell element and solid element, are examined for typical weld structures. The calculation procedures are performed using the balanced nodal forces and moments obtained from finite element solutions. A consistent formulation based on work equivalent argument has been implemented to transform the balanced nodal forces and moments from shell to line force and line moments at each nodal position. The mesh-insensitivity, the effect of distance $\delta$(where the stress is calculated) and the potential limitations of the structural stress method are examined for various types of weldments. Based on the results from this study, it is expected to develop a more precise stress estimation technique for fatigue strength assessment of welded structures.

• 한국정보통신학회논문지
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• 제5권1호
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• pp.144-149
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• 2001

산업현장의 열악한 작업중의 하나인 용접작업을 자동화하기 위한 방법으로 본 논문은 비접촉식 센서인 Fiber Sensor를 이용하여 용접선을 1차적으로 추적하고, 추적한 데이터를 텍스트 파일로 저장함과 통시에 2차적으로 추적한 용접선을 X-Y 로봇의 좌표값으로 다시 출력하여 용접을 하도록 하고 있다. Fiber Sensor를 통하여 읽어 들인 데이터는 Delphi Version 3.0을 이용하여 만들어진 프로그램을 통하여 처리하였고, I/O 입출력은 16 채널의 Relay Actuator 출력과 16 채널의 opto-isolated 입력이 가능한 PC의 ISA슬롯에 직접 삽입하여 사용하는 카드를 통해서 이루어졌다. 본 실험에서 용접선 추적은 직선, 기울기를 가진 직선 및 곡선에 관하여 추적을 행하였고, 추적한 데이터를 토대로 인버터 $CO_2$ 용접기를 사용하여 용접을 행하여 보았다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 추계종합학술대회
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• pp.558-561
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• 2000

산업 현장의 열악한 작업중의 하나인 용접작업을 자동화하기 위한 방법으로 본 논문은 비접촉식 센서인 Fiber Sensor를 이용하여 용접선을 1차적으로 추적하고, 추적한 데이터를 텍스트 파일로 저장함과 동시에 2차적으로 추적한 용접선을 X-Y 로봇의 좌표값으로 다시 출력하여 용접을 하도록 하고 있다 Fiber Sensor를 통하여 읽어 들인 데이터는 Delphi Version 3.0을 이용하여 만들어진 프로그램을 통하여 처리하였고, I/O 입출력은 16 채널의 Relay Actuator 출력과 16 채널의 opto-isolated 입력이 가능한 PC의 ISA 슬롯에 직접 삽입하여 사용하는 카드를 통해서 이루어졌다. 본 실험에서 용접선 추적은 직선, 기울기를 가진 직선 및 곡선에 관하여 추적을 행하였고, 추적한 데이터를 토대로 인버터 CO2용접기를 사용하여 용접을 행하여 보았다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.1117-1124
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• 2009

Under frame side sill of rolling stock structure is designed for preventing corrosion in order to meet mechanical requirements. However during long operation time more than 20 years, there are corrosion in the under frame side sill caused by environmental effect, vibration and etc. So, detection and evaluation of the corrosion ill the under frame nondestructive is one of important issues to extend their life time. Most of nondestructive methods are not easy to apply for detecting corrosion in the under frame side sill, since the under frame side sill consist of there layered with different material (stainless steel - stainless steel - mild steel) and each layer is connected by spot weld and plug weld. Fortunately, pulsed eddy current method claimed that it can be measured not only thickness change but also corrosion under their insulation layers. So, in this study, we have investigated performance of pulsed eddy current testing method by measuring thickness variation of fabricate of mock-up specimens. The investigation results obtained from mock-up specimens and the corrosion evaluation results of the aged rolling stocks will be presented.