Development of Plasma Arc Spot Welding Process and Finite Element Method Analysis Model for Predicting Fracture Strength: Part 1—Development of Plasma Arc Spot Welding Process

Geonho Lee,Hansol Kim,Jongho Jeon,Sangjun Han,Sang-Woo Han,Jung Ho Cho 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.1

Resistance spot welding is widely used in automobiles and ships, and especially, it accounts for 70% of the body welding process. However, resistance spot welding is limited when welding the closed structure of a vehicle body. As welding is performed by placing a spot gun in a closed structure, a passage is required for the insertion of the spot gun. This passage is called a “passing hole”, and the structural design of the passing hole and the cover that is installed to block the passing hole is complicated, resulting in durability problems as the weight of the vehicle body increases. This study aims to develop a plasma arc spot welding (PASW) process that can replace resistance spot welding. “Part 1 - Development of Plasma Arc Spot Welding Process” determines whether this process can replace the resistance spot welding process through experiments by adjusting the existing process variables of the plasma arc welding process as well as additional process variables. The experimental results of applying the PASW process are then applied to the development of a finite element analysis model for predicting the fracture strength of the PASW process in Part 2.

중첩된 구리 판재의 전기저항가열 표면마찰 점용접(RSFSW)에 관한 연구

순샤오광(Xiao-Guang Sun),진인태(In-Tai Jin) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.2

Copper sheets has been used widely in electric and electron industry fields because they have good electric and heat conduction property of the material. And, in order to bond copper material, a kind of soldering process is generally used. But, because it is difficult to bond by soldering between overlapped thin copper sheets, so, another kind of brazing bonding process can be used in that case. But, because the brazing process needs wide bonding area, it needs heat treatment process in electric furnace. Generally, for spot welding of sheets, a conventional electric Resistance Spot Welding process(RSW) has been used, it has welding characteristics using contact resistance heating induced by electric current flow between sheets. But, because copper sheets has the low electric resistance, it is difficult to weld by electric resistance spot welding. So, in this study, an electric Resistance heated Surface Friction Spot Welding process(RSFSW) is suggested and is testified for the spot welding ability of thin copper sheets. It is known from the experimental results and simulation that the suggested spot welding process will be able to improve the spot welding ability of copper sheets by the combined three kinds of heating generated by surface friction by rotating pin, and conducted from heated steel electrode, and generated by contact resistance of electricity.

Recent Research Trend of Resistance Spot Welding Quality Monitoring Technology in Korea

Young-Min Kim,Insung Hwang,Jason Cheon 대한용접접합학회 2023 대한용접·접합학회지 Vol.41 No.2

Resistance spot welding is a simple welding process with high welding speeds and one of the most economical and productive welding processes. It is applied in various industries such as automobile, aircraft, and home appliance; thus, the demand for monitoring welding quality is increasing. Owing to the nature of the resistance spot welding process, there are several factors that can be monitored, such as the dynamic resistance value, which can be determined using current and voltage measurements, the displacement of welding electrodes, and the indentation that occurs after welding. These process features can be monitored using cameras, LVDT sensors, and deep learning techniques and used for predicting weld quality. In this paper, we introduced the recent trends in resistance spot welding quality monitoring techniques in Korea using various sensors and techniques.

전류 파형 제어를 적용한 마그네슘 합금의 저항 점 용접 특성

최동순,황인성,김동철,류재욱,강문진,Choi, Dong-Soon,Hwang, In-Sung,Kim, Dong-Cheol,Ryu, Jae-Wook,Kang, Moon-Jin 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.2

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.

AZ31 마그네슘 합금 판재의 전기저항 이중 스폿용접 특성

순샤오광(Xiao-Guang Sun),진인태(In-Tai Jin) 한국기계가공학회 2022 한국기계가공학회지 Vol.21 No.3

In this study, an electric resistance dual-spot welding process using a copper electrode inserted in a heating electrode is suggested for the spot welding of AZ31 magnesium sheets. This spot-welding process involves two heating methods for welding at the interfacial zone between the magnesium sheets, one of which is the heating method by thermal conduction from the heating electrode heated by the welding current induced to the steel electrode, and the other heating method uses the electric resistance between the contacted surfaces of the two sheets by the welding current induced to the copper electrode. This welding process includes the welding variables, such as the current induced in the heating electrode and the copper electrode, and the outer diameters of the heating electrode. This is because the heat conducted from the heating electrode can be maintained at a higher temperature in the welding zone, which has a slow cooling effect on the nugget of the melted metal after the welding step. The pressure exerted during the pressing of the magnesium sheets by the heating electrode can be increased around the nugget zone at the spot-welding zone. Thus, it not only reduces the warping effect of the elastoplastic deformation of sheets, but also the corona bond can make it less prone to cracking at the welded zone, thereby reducing the number of nuggets expelled out of the corona bond. In conclusion, it was known that an electric resistance dual spot welding process using the copper electrode inserted in the heating electrode can improve the welding properties in the electric resistance spot welding process of AZ31 magnesium sheets.

차체용 1.2GPa급 초고장력 TRIP강판의 저항 점 용접부 너겟 지름 예측에 관한 연구

신석우(Seok-Woo Shin),이종훈(Jong-Hun Lee),박상흡(Sang-Heup Park) 한국산학기술학회 2018 한국산학기술학회논문지 Vol.19 No.3

최근 자동차 산업에서는 연비향상 및 안전규제 강화에 따라 차량 경량화가 필수적으로 요구됨에 따라 DP강(Dual Phase steel), CP강(Complex Phase steel), MS강(Martensitic Steel), TRIP강(Transformation Induced Plasticity steel), TWIP강(Twinning Induced Plasticity steel) 등과 같은 인장강도 700MPa 이상인 초고장력강(Ultra High Strength Steel)의 적용이 증가하고 있다. 초고장력강을 차체에 적용하기 위해서는 용접공정이 필수적이며, 원가 측면에서 유리한 전기저항점용접(Resistance Spot Welding, RSW)이 차체 용접에서 80%이상으로 가장 많이 적용되고 있다. 초고장력강은 강도향상을 위해 합금원소 함량을 늘이기 때문에 일반적으로 용접성이 열악한 것으로 알려져 있다. 이러한 초고장력강의 저항점용접의 경우 적정 용접조건 영역이 축소되고 용접부에서 계면파단 및 부분계면파단이 발생하는 것으로 보고되어 있어 결함 및 품질을 실시간으로 예측할 수 있는 용접품질 판정 연구가 활발히 진행되고 있다. 이에 따라 본 연구에서는 저항 점 용접을 수행할 때 검출되는 2차 회로 공정 변수를 이용하여 용접부의 동저항을 모니터링하고, 이 동저항 패턴에서 용접 품질 판단에 필요한 인자들을 추출하였다. 추출한 인자들을 상관분석하여 용접 품질과의 상관성을 파악하였으며, 상관성이 높은 인자들을 이용하여 회귀분석을 실시하였다. 이를 근거로 현장 적용이 가능한 회귀 모델을 제시하였다. In the automobile industry, in order to increase the fuel efficiency and conform to the safety regulations, it is necessary to make the vehicles as light as possible. Therefore, it is crucial to manufacture dual phase steels, complex phases steels, MS steels, TRIP steels, and TWIP from high strength steels with a tensile strength of 700Mpa or more. In order to apply ultra-high tensile strength steel to the body, the welding process is essential. Resistance spot welding, which is advantageous in terms of its cost, is used in more than 80% of cases in body welding. It is generally accepted that ultra-high tensile strength steel has poor weldability, because its alloy element content is increased to improve its strength. In the case of the resistance spot welding of ultra-high tensile steel, it has been reported that the proper welding condition area is reduced and interfacial fracture and partial interfacial fracture occur in the weld zone. Therefore, research into the welding quality judgment that can predict the defect and quality in real time is being actively conducted. In this study, the dynamic resistance of the weld was monitored using the secondary circuit process variables detected during resistance spot welding, and the factors necessary for the determination of the welding quality were extracted from the dynamic resistance pattern. The correlations between the extracted factors and the weld quality were analyzed and a regression analysis was carried out using highly correlated pendulums. Based on this research, a regression model that can be applied to the field was proposed.

구리와 알루미늄 이종금속 판재간의 전기저항가열 표면마찰 스폿용접 특성

순샤오광,진인태 한국기계가공학회 2022 한국기계가공학회지 Vol.21 No.8

In this study, an electric resistance-heated surface friction spot-welding process was proposed and tested for the spot-welding ability of copper and aluminum dissimilar metal sheets using electric resistance heating and surface friction heating. This process has welding variables, such as the current value, energizing cycles, rotational speed, and friction time. The current value and energizing cycle can affect the resistance heat, and the rotational speed of the rotating pin and friction time influence frictional heat generation. Resistance heating before friction heating has a preheating effect on the Cu–Al contact interface and a positive effect on preventing friction heat loss during the friction stage. However, because resistance preheating can soften the copper sheet and affect the contact stress and friction coefficient, it has difficulties that may adversely affect frictional heat generation. Therefore, the optimal combination of welding variables should be determined through simulations and experiments of the spot-welding process to determine the effects of electric resistance preheating on the suggested process. Through this procedure, it is known that the proposed spot-welding process can improve the welding quality during the spot welding of Cu–Al sheets.

New Methods of Resistance Spot Welding Using Reference Waveforms of Welding Power

유지영 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.10

The use of high strength steels in car bodies has increased gradually in recent years, contributing to lighter weight vehicles. In general, the resistance spot weldability of high strength steels is poor when compared to that of low-carbon steels due to a number of factors including narrow welding range (weld lobe), irregular occurrence of expulsion, high resistivity of base metals, and zinc coating. To improve the weldability of high strength steels, technologies such as adaptive resistance spot welding and optimization of welding conditions have been developed and applied within the automotive industry. This study focuses on developing two methods of resistance spot welding with the aim of improving the weldability of high strength steels. The first method is reference welding, which uses the reference power waveforms obtained from preliminary welding. The second is modified reference welding, which uses modified power waveform from the reference welding method. The features and effects of these welding methods were evaluated through a tensile shear test, analysis of welding signals, and an investigation into the frequency of expulsion. Both welding methods showed high tensile shear strength results and reductions in expulsion over a wide variety of different steel types including GI coated steels.

EVALUATION OF THE FINITE ELEMENT MODELING OF A SPOT WELDED REGION FOR CRASH ANALYSIS

J. H. SONG,H. HUH,H. G. KIM,S. H. PARK 한국자동차공학회 2006 International journal of automotive technology Vol.7 No.3

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.

용융아연도금 강판 저항 점 용접 시 정전류 및 적응제어 적용에 따른 연속타점 특성 평가 및 고찰

서정철,최일동,손홍래,지창욱,김치호,서성부,서진석,박영도,Seo, Jeong-Chul,Choi, Il-Dong,Son, Hong-Rea,Ji, Changwook,Kim, Chiho,Suh, Sung-Bu,Seo, Jinseok,Park, Yeong-Do 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.2

With using adaptive control of the resistance spot welding machine, the advantage on electrode life time for galvanized steels has been addressed. This study was aimed to evaluate the electrode life time of galvanized steels with applying the constant current control and the adaptive control resistance spot welding process for a comparison purpose. The growth in diameter of electrode face was similar for both the constant current and the adaptive control up to 2000 welds. The button diameter was decreased with weld numbers, however, sudden increase in button diameter with use of the adaptive control after 1500 welds was observed. The peak load was continuously decreased with increasing number of welds for both the constant current and the adaptive control. The current compensation during a weld was observed with using the adaptive control after 1800 welds since the ${\beta}$-peak on dynamic resistance curve was detected at later weld time. The current compensation with adaptive control during resistance spot welding enhanced the nugget diameter at the faying interface of steel sheets and improved the penetration to thinner steel sheet.