• Journal of Welding and Joining
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• 제12권2호
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• pp.39-48
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• 1994

In comparison to the conventional brazing, laser welding of ceramics has advantages of direct bonding without filler material, which causes the thermal stress due to the differences of thermal expansion coefficients. In pulse-mode, laser welding of dispersion ceramic having high thermal resistance is possible at relatively low preheating temperature of $1300^{\circ}C$ In CW-mode, alumina can be welded at high preheating temperature $1500^{\circ}C$ under the condition of low feed rate of 500 mm/min, respectively. Further studies on developing mechanism of pores in the bead during laser welding of ceramics is required.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2750-2753
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• 2008

This paper introduce the CFD analysis for predicting the heat transfer at the Ultrasonic horn. Approximately Ultrasonic horn separates two part. One is preheating part and the other is cooling part. Temperature of preheating part rise up by $260^{\circ}C$ that make it possible to attach a chip to a semiconductor. Also there is a piezo material in the cooling part. When piezo work, it generates heat of $100^{\circ}C$. It can stand by $150^{\circ}C$. But the high temperature conducted from the preheating part has a bad affect on the piezo. These situation make it necessary cooling at piezo. Previously except of the piezo, all of them are composed of the SUS440c that has good thermal conductivity. This study shows way that not only cooling the piezo but also cutting off the conduction between preheating part and cooling part by using the Ti and Duralumin that have low thermal conductivity compare with the SUS440c. Conclusion of CFD analysis that the heat coming from the piezo can't be transferred the horn cause of the Ti and Duralumin.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.124-124
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• 2009

We observed the changes of crystal structure of Rubrene (5,6,11,12-tetraphenylnaphthacene) polycrystal thin films at various in situ substrate temperature and process by scanning electron microscope(SEM), x-ray diffraction (XRD) and near-field microwave microprobe (NFMM). Amorphous rubrene thin film was initially obtained on 200 nm thick $SiO_2/Si$ substrate at 35 $^{\circ}C$ in a vacuum evaporation but in situ long time postannealing at the temperature 80 $^{\circ}C$ transformed the amorphous phase into crystalline. Four heating conditions are followed : (a) preheating (b) annealing (c) preheating, annealing (d) preheating, cooling(35 $^{\circ}C$), annealing. We have obtained the largest polycrystal disk in sample (c). But the highest crytallity and conductivity of the rubrene thin films were obtained in sample (d).

• Journal of Welding and Joining
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• 제15권4호
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• pp.99-108
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• 1997

Analytical model for the temperature distribution and the cooling rate of weld in dual beam laser welding is presented for investigating the possibility of controling the cooling rate. The model is based on the solutions to the problem of heat flow due to the distributed and line heat sources for preheating and welding respectively in plates with finite thickness. The effects of beam power, beam distribution parameter, interbeam distance, and welding speed on the resulting temperature distribution and cooling rate are presented. The cooling rates of dual beam laser weld at the weld centerline under the investigated conditions are reduced to as one third of those of welds which were produced by single beam laser. And it appeared that the cooling rate of dual beam laser weld is strongly dependent on the process parameters of preheating laser beam power and welding speed.

• 소성∙가공
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• 제8권3호
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• pp.289-289
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• 1999

This paper describes the investment casting of TiAl alloys. The effects of mold material and mold preheating temperature for the investment casting of TiAl on metal-mold interfacial reaction were investigated by means of optical micrography, hardness profiles and an electron probe microanalyzer. The mold materials examined were colloidal silica bonded ZrO₂, ZrSiO₄, A1₂O₃and CaO stabilized ZrO₂. When compared with conventional titanium a1loy, the high aluminum concentration of TiAl alloys helps to lower their reactivity in the molten state. The A1₂O₃mold is a promising mold material for the investment casting of TiAl in terms of the thermal stability, formability and cost. Special attention need to be paid to thermal stability and mold preheating when developing the investment calling of TiAl alloys.

• Journal of Mechanical Science and Technology
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• 제14권8호
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• pp.851-860
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• 2000

Temperature field and cooling rate are important parameters to influence the properties of clad layer and the heat affected zone. In this paper the temperature field and cooling rate of laser cladding are studied by a two-dimensional time-dependent finite element model. Experiment has been carried out by Nd:YAG laser cladding with wire feeding. Research results indicate that at the beginning of cladding, the width and depth of melt pool increase with cladding time. The cooling rate is related to position, cladding time, cladding speed, and preheating temperature. The temperature near melt pool changes rapidly while the temperature far from melt pool changes slowly. With the increase of cladding time, cooling rate decreases. The further the distance from the melt pool, the lower the temperature and the slower the cooling rate. The faster the cladding speed, the faster the cooling rate. The higher the preheating temperature, the slower the cooling rate. The FEM results coincide well with the experiment results.

• 한국결정성장학회지
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• 제14권5호
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• pp.187-192
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• 2004

We try to use isopropanol which has low boiling point to prepare ZnO thin films at low temperature. ZnO thin films were prepared by sol-gel spin-coating method using zinc acetate dehydrate-isopropanol-monoethanolamine (MEA) solution. The c-axis preferred orientation and optical properties of ZnO films with preheating temperature have been investigated. ZnO thin films were preheated at 200 to $300^{\circ}C$ with an interval of $25^{\circ}C$ and post-heated at $650^{\circ}C$. The ZnO film preheated at $275^{\circ}C$ and post-heated at $650^{\circ}C$ was highly oriented along c-axis (002) plane, and the surface with homogeneous and dense microstructures was formed having nano-sized grains. The optical transmittance was above 90 % in the visible range and exhibited absorption edges at 368 nm wavelength.

• 한국생산제조학회지
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• 제21권6호
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• pp.988-997
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• 2012

Laser surface hardening is one of core technologies to enhance various characteristics such as the strength, hardness, toughness, abrasion resistance, and fatigue resistance for the mold material. This paper focuses on testing characteristics of the laser heat treatment according to the preheating parameters in case of the SM45C medium carbon steel. In this paper, we assume that the power and travel speed of the laser are 1,800W and 0.5m/min, respectively, and the range of the preheating temperature is $50^{\circ}C{\sim}300^{\circ}C$. From the result of the test, we observed that the hardness width and depth are enhanced as the temperature is increased. Also, the best average hardness was 751.7Hv for the temperature of $100^{\circ}C$.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.163-167
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• 2007

은 촉매는 과산화수소 촉매분해에 많이 사용되지만, 상온에 시동이 어렵고 높은 온도에 적용하기 곤란하다. 본 논문에서는 은이 가지고 있는 단점을 극복하기 위해 기화기와 고온 촉매 베드로 구성된 이원 촉매 베드에 대한 연구를 수행하였다. 백금을 기화기 촉매로, perovskite 구조를 가지는 촉매를 고온 촉매로 선정하였고, 가스발생기를 이용한 시험을 통해 상온에서 예열이 없이도 시동이 가능함과 고온에서 안정적으로 작동함을 보여주었다.

• 한국주조공학회지
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• 제22권2호
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• pp.75-81
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• 2002

The main objectives were to investigate the suitability of CaO crucible for melting TiAl alloys and to develop investment mold for investment casting of TiAl alloys. TiAl alloy specimen were prepared by plasma arc furnace under argon atmosphere. After melting of TiAl alloy using CaO crucible, the results showed that there is little contamination of oxygen in the TiAl bulk. Conventional vacuum induction furnaces can be readily adaptable to produce cast parts of TiAl without high skilled techniques. The determination of optical metallography and microhardness profiles in investment cast TiAl alloy rods has allowed the gradation of the relative thermal stability of the oxides examined. The molds used for the present study were $ZrO_2$, $Al_2O_3$, CaO stabilized $ZrO_2$ and $ZrSiO_4$. Even although high temperature of mold preheating, $Al_2O_3$ mold is a promising mold material for investment casting of TiAl alloys in terms of thermal stability, cost and handling strength. It is important to take thermal stability and preheating temperature of mold into consideration for investment casting of TiAl alloys.