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.

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.

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.

자동차 차체용 1.2GPa급 TRIP 강의 Weld-bond부 너깃경에 따른 인장전단특성에 관한 연구

최일동,박지연,김재원,강문진,김동철,김준기,박영도,Choi, Ildong,Park, Jiyoun,Kim, Jae-Won,Kang, Mun-Jin,Kim, Dong-Cheol,Kim, Jun-Ki,Park, Yeong-Do 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.2

High strength steels have been continually being developed to improve in fuel economy in automotive and ensure safety of passengers. New bonding and welding methods have been required for improving weldability on high strength steels. In this study, resistance spot welding and Weld-bond with nugget diameters of 4.0mm, 5.0mm, 6.0mm and 7.0mm were produced and tested, respectively. In order to confirm the effect of nugget diameters on tensile shear characteristic of the Weld-bond, tensile shear characteristics of Weld-bond were compared with those of resistance spot welding and adhesive bonding. Peak load of Weld-bond were increased as the nugget diameter increases. After appearing maximum peak load continuous fracture followed with second peak owing to load being carried by resistance spot weldment. Fracture modes of the adhesive layer in Weld-bond fractures were represented by mixed fracture mode, which are cohesive failure on adhesive part and button failure at resistance spot welds. The results showed that the tensile shear properties can be improved by applying Weld-bond on TRIP steel, and more apparent with nugget diameter higher than 5${\surd}$t.

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.

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.

충돌 해석에서의 점용접부 모델링에 관한 연구

송정한(Junghan Song),허훈(Hoon Huh),김홍기(Honggee Kim),박성호(Sungho Park) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Simulation of vehicle crashes using the finite element method has made major advances in the last several years. Every major automotive company now uses CAE to perform virtual crash tests. Designers can mow quickly adjust the structural performance before performing a physical crash test. Compared to physical crash tests, the virtual simulation is less costly and faster which allows manufactures to reduce costs and vehicle development time. In order to produce more efficient and precise simulations, it is needed to adopt the dynamic property of materials and the failure modeling of resistance spot weld. The resistance spot weld in most current finite element crash models are characterized as a rigid beam at the location of the weld. The role of this rigid beam is simply to transfer the load across the welded component. The spot weld elements is design to be failed by some failure criteria which is function of axial and shear load at the rigid beam. For this reason, the calculation of the load at the rigid beam is important to predict the failure of the spot weld. In this paper, the numerical simulations are carried out to evaluate the calculation of the load at the rigid beam. The first study conducted is to examine the effect of mesh size on the load at the rigid beam. The effect of element shape on the welded components is, then, investigated. Finally, the location and the number of welded constrains is changed for the correct prediction of the load on the spot weld element. The analysis results demonstrate that the correct prediction of the load on the spot weld element is achieved by the change of the element shape on the welded component s and the location of welded constrains.

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.

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.

차체용 1.2㎬급 초고장력 TRIP강판의 저항 점 용접 강도 예측에 관한 연구

신석우(Seok-Woo Shin),이종훈(Jong-Hun Lee),박상흡(Sang-Heup Park) 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.1

Recently, in the automobile industry, it has become necessary to increase the fuel efficiency and the safety regulations to make the vehicle lightweight. Therefore, it is necessary to manufacture the dual phase steel, the complex phase steel, the MS steel, the TRIP steel, and TWIP have been increasingly applied to high strength steel with a tensile strength of 700MPa or more. In order to apply ultra high tensile steel to the body, welding process is essential. Resistance spot welding, which is advantageous in terms of cost, is applied more than 80% in body welding. It is generally known that ultra high tensile strength steel has poor weldability because it increases the alloy element content to improve strength. In the case of 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. In order to overcome such problems, researches on welding quality judgment that can predict the defect and quality in real time are actively conducted. In this study, the dynamic resistance of the weld is monitored using the secondary circuit process variables detected during resistance spot welding, and the factors necessary for welding quality determination are extracted from the dynamic resistance pattern. Using the analyzed factors, a regression model that could estimate weld strength was developed. Two regression equations of model were suggested depending on the factors, and it was showed that the model developed by backward elimination method was effective one for weld quality estimation. Based on this, a regression model that can be applied to the field was suggested.