Moon-Jin Kang

Resistance Spot Welding Characteristics of Mg Alloy Using Process Tape

Abstract Recently, studies about application of magnesium alloy sheet to automotive bodies are on the increase. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Electrode life of resistance spot welding of magnesium alloy is very short due to sticking of magnesium alloy to copper alloy electrode. To increase electrode life, most effective method is inserting cover plate between electrode and magnesium sheet. But application of cover plate to actual process is difficult and decreases welding productivity. Process tape supplied automatically as cover plate can minimize lose of productivity and increase welding quality. In this study, resistance spot welding of magnesium alloy is carried out with applying process tape. Acceptable welding current region according to electrode force and welding time is determined. Key Words : Resistance spot welding, Mg alloy, Process tape, Cover plate, Electrode life 1. 서 론

A Study on Distributions of Electromagnetic Force of the Dissimilar Metal Joining in MPW Using a FEM

Recent trends of welding system have been focused on the development of new process in order to achieve better quality, higher productivity and friendly to the environmentally in welding process. The Magnetic Pulse Welding(MPW) process is based on the principle of a tremendous amount of energy compressed and discharged for an extremely short period of time. The purpose of this paper is to investigate welding characteristics according to the distributions of an electromagnetic force on the weldment using a finite element method and to find the optimal process parameters such as input current and frequency. To successfully accomplish this objective, a 2-dimensional axisymmetric electromagnetic numerical model has firstly been developed. The equation was solved using a general electromagnetic mechanics computer program, ANSYS code. The comparison between the calculated and measured results has been carried out to verify the developed system.

Electrode Life Test of Resistance Spot Welding on Mg Alloy Using Dome Type Electrode

Abstract Magnesium alloy is used on parts of aircraft and electronic equipment because of the highest specific strength among the common metal materials. Recently, studies about appling magnesium alloy sheet to automotivebodies are on the increase rapidly. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Magnesium alloy has low boiling point, so getting sound bead shape is difficult when appling varies welding processes. Resistance spot welding is also particular about setting optimum welding conditions because of spatter generation, pores and cracks occurrence in nugget. And life of electrodes is very short because of alloying with copper that main materialof electrodes. This requires frequent dressing and replacement of electrodes and decrease in productivity of resistance spot welding on magnesium alloy. Therefore in this study, for effective analysis of changes in tensile shear load and nugget size during electrode life test, evaluate detail characteristics of resistance spot welding on magnesium alloy sheet using dome type electrode.Key Words : Resistance spot welding, AZ31, Mg alloy, Dome type electrode

Principle and Application of Magnetic Pulse Welding

최근 금속가공산업은 자동차, 조선 기계, 전자 등의 부품소재 제조에 있어 핵심적인 산업으로 자리하고 있다. 특히 가장 많은 비중을 차지하고 있는 용접산업은 저임금을 바탕으로 한 중국기술의 추격과 선진국의 고품질화에 직면하고 있으며 이러한 문제를 해결하기 위하여 친환경 공정기술의 개발과 신기술을 통한 제품의 부가가치 제고가 요구된다. MPW는 자기장에 의한 전자기력을 사용하므로 물리적인 접촉 없이 금속을 가공하는 방법으로서, 용접(brazing과 soldering 포함), 금형 및 소성가공공정에서 환경오염 발생원인 용접재료, 가스, 용가재, 플럭스, 윤활유 및 세척유 등이 필요 없이도 고품질의 제품을 생산할 수 있는 친환경적인 공정기술이다. 그 외에도 도금된 상태에서 작업이 가능하여 기존의 공정에서 결함이 발생되었을 때 재도금을 실시하는 후공정이 생략되어 도금공정에서 배출되는 오염물질도 줄일 수 있고, 작업이 수 μs 하에서 이루어지기 때문에 전력소모가 매우 적으며 작업시간을 절약할 수 있는 장점을 갖고 있다

Development of Push-pull Type Arc Welding Wire Feeder

Abstract It is difficult to feed welding wire stably, when the distance between welding wire feeder and welding torch is far enough. In order to solve this problem, arranging a extension wire feeder between them could be one of useful methods. However, the welding wire could be twisted up in the extension cable between extension and terminal wire feeders in the case that RPM of extension wire feeding motor is higher than that of terminal motor. In this study, feeding problem of normal push-pull wire feeding system occurred at low welding current range less than 250A. In order to solve the problem, two new wire feeding systems of push-pull type were introduced. Welding wire feeding tests were preformed in the range of 150A to 400A with the developed push-pull feeding system. In addition, weldability test was performed at the welding current of 200A, 300A, and 400A. The welding wire twisting problem that was observed in the normal feeding system did not occur in the new push-pull wire feeding system.Key Words : Arc welding, Welding wire, Wire feeder, Push-pull type feeder, Welding torch

Effects of Electrode Shape on Electrode Life of Resistance Spot Welding of Mg Alloy

According to weight lightning trend of automobile body, necessity of resistance spot welding (RSW) of Mg alloy on automobile industry is increasing rapidly because of the highest specific strength among commercial metals. Mg alloy has low electric resistance and high thermal conductivity like as Al alloy, so that needs applying high current in short time when welding. Thick oxide film of Mg alloy pollutes the electrodes and makes partial current carrying paths when on welding. Partial current carrying paths signify excessive concentration of current. There can initiate expulsion easily and reduces electrode life rapidly. Generating partial current carrying paths and expulsions are influenced by shapes of electrode. Therefore, electrode life also influenced by shape. In this study, we perform life test of RSW electrode of radius type. Measure tensile shear load and nugget size every spot alternately. As a result, radius type electrode can extend life over twice as dome type electrode.

Resistance Spot Welding Characteristics of Mg Alloy Applying Current Waveform Control

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.

Wear Resistance Evaluation of Contact Tip according to Flux Cored Wire

Abstract The contact tip for flux cored arc welding has important functions to transmit the welding current to the wire and to guide the wire to molten pool. A damaged contact tip causes a productivity reduction and a welding quality problem. In this study, the welding experiments for the wear resistance of contact tip regarding flux cored wire types were performed. With two fold type and a seamless type flux cored wires, the wear rates of contact tips were compared. In addition, the wear rate was checked according to the contact tip position.Key Words : Wear resistance, Contact tip, Flux cored wire, Wear rate, Fold type, Seamless type 1. 서 론 콘택트 팁의 주된 역할은 용접 전류를 와이어에 전송하는 역할과 용융풀로 와이어를 유도하는 역할을 한다. 이러한 기능을 하는 콘택트 팁이 손상되면 용접 결함제거 및 콘택트 팁 교체 등으로 인하여 용접 생산성을 저하시키는 원인이 된다. 그리고 콘택트 팁을 장시간 사용하면 팁 중앙에 가공된 구멍이 확장되어 와이어 선단에 지향하는 위치를 벗어나게 되므로 아크가 불안해져 용접 품질에도 문제가 발생하게 된다. 그러므로 콘택트 팁 내마모성은 용접 생산성과 용접 품질에 밀접한 관계가 있다. 이러한 이유로 콘택트 팁의 내마모성에 대한 신뢰성 및 수명에 대한 연구가 진행되어 왔다. Villafuerte은 콘택트 팁의 마모기구는 고온에서의 마찰마모(abrasion)와 전기적 에로존(electrical erosion)이 주된 손상기구라고 제안하였다