• 소성∙가공
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• 제24권4호
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• pp.256-263
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• 2015

Electric resistance spot welding has been used to join overlapped steel sheets in automotive bodies. Recently to reduce weight in automotive vehicles, non-ferrous metals are being used or considered in car bodies for hoods, trunk lids, doors parts, etc. Various welding processes such as laser welding, self-piercing rivet, friction stir welding are being used. In the current study, a new electric resistance heated friction stir spot welding is suggested for the spot welding of non-ferrous metals. The welding method can be characterized by three uses of heat -- electric resistance heating, friction stir heating and conduction heating of steel electrodes -- for the fusion joining at the interfacial zone between the two sheets. The welding process has variables such as welding current, diameter of the steel electrodes, revolutions per minute (rpm) of the friction stir pin, and the insert depth of the stir pin. In order to obtain the optimal welding variables, which provide the best welding strength, many experiments were conducted. From the experiments, it was found that the welding strength could be reached to the required production value by using an electrode diameter of 10mm, a current of 7.6kA, a stirring speed of 400rpm, and an insert depth of 0.8mm for the electric resistance heated friction stir spot welding of 5052 aluminum 1.5mm sheets.

• 소성∙가공
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• 제18권6호
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• pp.465-470
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• 2009

The frictional behaviors of Cermets/Cr-Ceramics and Cu-Al coatings of piston ring were investigated. Friction tests were carried out by pin-on-disk test and materials properties of coating layer were analyzed by nano indentation tester. The effect of surface roughness of cylinder liner on the friction coefficient was analyzed. This study provided tribological data of hard and soft piston ring coatings against cylinder liner. The surface roughness does exert an influence on the average friction coefficient, with smoother surfaces generally yielding lower friction coefficients. In case of hard-coating, the scratch depth, width and pile-up height had close relationship with hardness. So the scratch width, depth and pile-up height increases with decreasing friction coefficient. But in case of soft-coating, the friction coefficients are strongly dependent on the morphological characteristics such as, scratch depth, width, pile-up height and elastic modulus.

• Tribology and Lubricants
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• 제10권3호
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• pp.18-28
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• 1994

Sliding friction between a spherical pin of 8mm in diameter and flat (disk) substrates coated with vacuum-deposited thin film was measured under ultra high vacuum pressure for various materials, various rates of film supply (8~210 nm/min), various sliding velocities (1.5~67.0 mm/s). It was found that the most effective lubrication was obtained when the adhesion between $Si_3N_4$ pin and SUS440C disk was high and that between $Si_3N_4$ pin and $Si_3N_4$ disk was low. When In film was used as a lubricant between $Si_3N_4$ pin and stainless steel disk, the friction coefficient had a value as low as 0.04. In this case, the normal load W and the sliding speed V were expressed as 10N and 24 mm/s for $10^{-6}Pa$. The dependence of $\mu$ on the thickness h of the Ag film, which was used as a lubricant between $Si_3N_4$ pin and SUS440C (Q) disk was expressed as $\mu$=0.12 for W=10N and V=24mm/s when the film was thicker than 100nm. A brief discussion on these relations is presented from the viewpoint of the real contact area.

• 한국기계가공학회지
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• 제11권6호
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• pp.16-21
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• 2012

Magnesium alloy has been focussed as lightweight material owing to its high strength even though low density with aluminum alloy, titanium alloy and plastic material. Friction stir welding technique was performed by rotating and plunging a shouldered tool with a small diameter pin into the joint line between two butted plates and useful to join magnesium alloy. In this paper, the experiments of friction stir welding were done to investigate the joint characteristics of AZ31 magnesium alloy. For its evaluation, the orthogonal array method$(L_{27}(3^{13}))$ was applied with four factors of pin diameter, shoulder diameter, travel speed and rotation speed of tool and also three levels of each factor. Nine tools were worked through shoulder diameter of 9, 12, 15mm and pin root diameter of 3, 4, 5mm. In addition tensile tests were excuted for the assessment of mechanical properties for joint conditions. From the results, pin diameter, shoulder diameter, and rotating speed of tool influenced on the tensile strength meaningful, but welding speed did not influence on that by the variance analysis. Beside of that, optimum condition of tensile strength was estimated as following ; shoulder diameter:15mm, welding speed:200mm/min, rotating speed:200rpm.

• 한국유체기계학회 논문집
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• 제13권5호
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• pp.43-53
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• 2010

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a $180^{\circ}$ turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in $180^{\circ}$ turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2002년도 춘계학술대회논문집
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• pp.153-160
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• 2002

This paper shows the possibility of performing Lap joint using the friction stir welding and the determination of tool's dimensions for FSW in Milling machine. This research also is reported on obtaining the tensile-shear strength, 9.319 ( kgf/mm$^{2}$) and the energy absorption, 2,682 (kgf-mm) under this experiment. The optimal tool's dimensions and method for Lap joint in 2tmm aluminum alloy plate using FSW is as follows; The diameter of shoulder and pin are 9 $\phi$mm and 3$\phi$mm, the length of pin is 3.6mm. The conditions of shoulder of tool is not pressed into original base metal.

• 한국철도학회논문집
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• 제12권4호
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• pp.512-517
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• 2009

알루미늄합금 철도차량의 차제를 조립하기 위하여 적용하는 용접방식으로는 가스 메탈 아크용접과 가스 텅스텐 아크용접이 주로 적용되고 있다. 그러나 알루미늄합금은 강재에 비해 용접성이 불리하며, 용접결함을 제어하기 위하여 보다 엄격한 용접조건과 용접설비의 작업환경이 요구된다. 따라서 선진국을 중심으로 비 용융 고상접합 방식인 마찰교반용접(FSW)이 널리 상용화 되고 있다. 본 연구에서는 대형 중공형 알루미늄합금 차량에 적용되는 압출재 A6005 소재의 마찰교반용접 시 용접변수에 따른 용접부의 기계적 특성을 평가하고, 적용 공구에 대한 최적의 용접조건을 파악하고자 하였다.

• 대한기계학회논문집A
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• 제33권7호
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• pp.693-699
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• 2009

This paper shows mechanical properties and behaviors of macro- and micro-structures on friction stir welded specimen with 6061-T6 aluminum alloy plate. It apparently results in defect-free weld zone jointed at welding conditions like the traverse speed of 267mm/min, tool rotation speed of 2500rpm, pin inserted depth of 4.5mm and tilting angle of $2^{\circ}$ with tool dimensions such as tool pin diameter of 5mm, shoulder diameter of 15mm and pin length of 4.5mm. The tensile stress ${\sigma}_T=228MPa$ and the yield point ${\sigma}Y=141MPa$ are obtained at the condition of traverse speed of 267mm/min and tool rotation speed of 2500rpm. With the constant rotation speed, the higher traverse speed become, the higher tensile stress and yielding point become. Vickers hardness for welding zone profile were also presented.

• 한국해양공학회지
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• 제14권4호
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• pp.79-85
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• 2000

Press-fit pin connection is the solderless interference-fit between pins and plated through holes(PTH) in the printed curcuit board(PCB). Because of not only its simple assembly and absence of problems associated with soldering, but also its good mechanical and electrical characteristics, the press-fit pin connection technology has quickly gained wide acceptance in the telecommunications and computer industries. In this paper, the contact stress characteristics of the domestic CPF pin when inserted into the friction coefficients were compared and the stress variations of the compliant part of the pin, which have an influence on the performance, were displayed with the time and arc length after complete connected. It is supposed that the results will provide useful data to improve the performance of the pin-PCB interconnection mechanism.

• 한국산업융합학회 논문집
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• 제23권6_2호
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• pp.917-926
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• 2020

Friction mechanisms is a very important role in the industrial machinery. However, many experiments have been conducted to reduce the loss of energy resources and parts used due to friction because the friction force adversely affects parts, efficiency, noise, and the like of the power unit. Therefore, in this study, the friction coefficient according to the characteristics of the lubricant was measured to find out which Grease Lubricant maintains the low friction coefficient without being most affected by external conditions. A total of five grease lubricants were tested in this study: GHP CAL 301, GHP EP 2, GHP KG 10, GHP HPG 2, and GHP HTG 2. And the friction coefficient was conducted by changing the load conditions (2, 4, 6, 8, 10N) and rotational speed (24, 48, 67, 86, 105, 124, 143, 162vrpm) using a pin-on-disk wear test system. Also, duty number were calculated. As a result, it was confirmed that in all grease lubricants, the speed did not significantly affect the friction coefficient, and it was confirmed that in all lubricants, the size of the friction coefficient decreased as the load increased from a small load to a large load. In addition, it was determined from the experimental results that GHP EP 2 is the most suitable as a grease lubricant and GHP CAL 301 is not the most suitable.