• Title/Summary/Keyword: Preheating Temperature

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An Analytical Study on the Preheating Effect of Flat Workpiece in Thermally Assisted Machining by Multi Heat Sources (다중열원 보조가공을 위한 평판 시편의 예열 효과에 관한 해석적 연구)

  • Moon, Sung-Ho;Lee, Choon-Man
    • Journal of the Korean Society for Precision Engineering
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    • v.33 no.8
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    • pp.629-634
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    • 2016
  • Laser-assisted machining (LAM) is one of the most effective methods of processing difficult-to-cut materials, such as titanium alloys and various ceramics. However, it is associated with problems such as the inability of the laser heat source to generate an appropriate preheating temperature. To solve the problem, thermally assisted machining with multiple heat sources is proposed. In this study, thermal analysis of multiple heat sources by laser and arc is performed according to power, heat source size, and leading heat source position. Then, the results are analyzed according to each condition. The results of this analysis can be used as a reference to predict preheating temperature in thermally assisted machining with multiple heat sources.

Analysis of Moving Heat Source for Laser Assisted Machining of Plate by Feed Rate Control (이송속도 조절에 의한 평판 레이저 보조가공의 이동 열원해석)

  • Kim, Kwang-Sun;Lee, Choon-Man
    • Journal of the Korean Society for Precision Engineering
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    • v.28 no.12
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    • pp.1341-1346
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    • 2011
  • Currently, many researches are carried out for laser assisted machining, which is one of the important fields in materials difficult to process. However, a prediction of heat source is difficult because of moving heat source. In this paper, a thermal analysis of laser assisted machining of plate by change of heat source size is performed, and preheating temperature by adjusting the feed rate is controlled. It was recognized that the maximum preheating temperature increases according to the decrease in heat source size, and feed rate need to adjust as high speed. The results of this analysis can be used as a reference for preheating temperature prediction in laser assisted milling.

Study of High Speed Steel AISI M4 Powder Deposition using Direct Energy Deposition Process (DED 기술을 이용한 고속도 공구강 M4 분말 적층에 관한 연구)

  • Lee, E.M.;Shin, G.W.;Lee, K.Y.;Yoon, H.S.;Shim, D.S.
    • Transactions of Materials Processing
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    • v.25 no.6
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    • pp.353-358
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    • 2016
  • Direct energy deposition (DED) is an additive manufacturing technique that involves the melting of metal powder with a high-powered laser beam and is used to build a variety of components. In recent year, it can be widely used in order to produce hard, wear resistant and/or corrosion resistant surface layers of metallic mechanical parts, such as dies and molds. For the purpose of the hardfacing to achieve high wear resistance and hardness, application of high speed steel (HSS) can be expected to improve the tool life. During the DED process using the high-carbon steel, however, defects (delamination or cracking) can be induced by rapid solidification of the molten powder. Thus, substrate preheating is generally adopted to reduce the deposition defect. While the substrate preheating ensures defect-free deposition, it is important to select the optimal preheating temperature since it also affects the microstructure evolution and mechanical properties. In this study, AISI M4 powder was deposited on the AISI 1045 substrate preheated at different temperatures (room temperature to $500^{\circ}C$). In addition, the micro-hardness distribution, cooling rates, and microstructures of the deposited layers were investigated in order to observe the influence of the substrate preheating on the mechanical and metallurgical properties.

A Study on Laser Assisted Machining for Silicon Nitride Ceramics (I) - Preheating Characteristics and Oxidation Behaviors of Silicon Nitride Ceramics with Machining Parameters - (질화규소 세라믹의 레이저 예열선삭에 관한 연구 (I) - 공정변수에 따른 질화규소의 예열특성 및 산화거동 -)

  • Kim, Jong-Do;Lee, Su-Jin;Shu, Jeong;Lee, Jae-Hoon
    • Journal of Welding and Joining
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    • v.28 no.4
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    • pp.61-66
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    • 2010
  • Silicon nitride is widely used as an engineering ceramics because it has high strength, abrasion resistance and corrosion resistance even at high temperature. However, machining of silicon nitride is difficult due to its high hardness and brittleness. Laser assisted machining(LAM) allows effective cutting using CBN tool by locally heating the cutting part to the softening temperature of YSiAlON using the laser beam. The effect of preheating depending on process parameters were studied to find out the oxidation mechanism. If silicon nitride is sufficiently preheated, the surface is oxidized and $N_2$ gas is formed and escapes from the material, thereby making the cutting process more advantageous. During laser preheating process before machining, high temperature results in strong oxidation which makes the bloating, silicate layers and micro cracks. Using the results of these experiments, preheating characteristics and oxidation behavior were found out.

The Effects of Centrifugal Casting Conditions on the Structure and Mechanical Properties in Fabrication Development of Super Heat-Resisting Steel Pipe of HP Alloy Modified with Nb (Nb을 첨가한 HP 초내열강관의 제조개발에 필요한 원심주조 조건이 조직과 기계적성질에 미치는 효과)

  • Choi, Sang-Ho
    • Journal of Korea Foundry Society
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    • v.14 no.6
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    • pp.566-575
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    • 1994
  • The effects of varying the pouring temperature and the die preheating temperature in producing centrifugally cast HP alloy modified with Nb was evaluated on the basis of the resultant macrostructure, microstructure and hardness of these castings. Increased die preheating temperatures and pouring temperatures resulted in an increase in the thickness of the columnar dendritic zone, the primary and secondary dendrite arm spacing and the thickness of the zone of porosity at the casting I.D.(inner diameter). Lower die preheating temperature and pouring temperatures result in increased grain fineness and an increased zone of equiaxed grains. A higher hardness was achieved toward the casting O.D.(outer diameter) compared to the casting I.D., attributable to alloy segregation toward the casting I.D. and segregation differences resulting from reduced solidification cooling rates toward the casting I.D. Also, a higher hardness was realized at the cold end of the casting attributed to a more uniform distribution of carbides.

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Performance Analysis of Solid Oxide Fuel Cell/Gas Turbine Hybrid Systems for Different Cell Inlet Preheating Methods (셀 입구 예열방법에 따른 고체산화물 연료전지/가스터빈 하이브리드 시스템의 성능해석)

  • Yang, Won-Jun;Kim, Tong-Seop;Kim, Jae-Hwan
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.1664-1669
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    • 2004
  • Design analysis of the solid oxide fuel cell and gas turbine combined power system is performed considering different methods for preheating cell inlet air. The purpose of air preheating is to keep the temperature difference between cell inlet and outlet within a practical design range. Three different methods are considered such as a burner in front of the cell, a preheater in front of the cell and recirculation of the cathode exit gas. Analyses are carried out for two maximum cell temperature differences. The greater temperature difference ensures higher efficiency. The cathode exit gas recirculation exhibits better performance than other methods.

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Finite Element Analysis of Effect of Preheating on the Residual Stress in 304 Stainless Steel Weldment (304 스테인레스강 용접부 잔류응력에 미치는 예열 효과의 유한요속 해석)

  • 장경복;김하근;강성수
    • Journal of Welding and Joining
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    • v.16 no.5
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    • pp.67-75
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    • 1998
  • This study aimed at he experimental and finite element analytic investigation of the effect of preheating on he residual stress of weldment. In this study, an autogenous arc welding was used on type 304 stainless steel and MARC as F.E.M. common code was utilized in analysis The analyses include transient and moving heat source and thermal properties as function of temperature. During welding, the thermal cycles of four locations in the weldment were recorded to investigate of the behavior of thermal stress and residual stress. The experimental and analytic results had good coincidence and show that there are two factors influencing the formation of welding residual stress in preheat process. One is the elevation of welding equilibrium temperature and the other is the increase of amount of heat input. The former decrease welding residual stress and the latter increase welding residual stress. Therefore, the cumulative effects result in the welding residual stress not being improved significantly with preheating in 304 stainless steel.

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A study on the tensile strength of flow-soldered joint using low residue flux (저잔사 플럭스를 사용한 플로 솔더링부의 인장특성 연구)

  • 장인철;최명기;신영의;정재필;서창제
    • Journal of Welding and Joining
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    • v.17 no.1
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    • pp.77-81
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    • 1999
  • Through-hole PCB(Printed Circuit Board) was soldered by flow soldering process using cleaning or noncleaning fluxes. Preheating temperature and conveyor speed were changed in the range of 323∼413K and 0.3∼2m/min respectively. The soldered joints were tensile tested in order to evaluated bonding strength. As experimental results, relatively high tensile fracture load, 120∼140N, were obtained in case of preheating temperature of 383K, and conveyor speed was 0.6∼1.0 m/min. Fractured surfaces of higher tensile strength show some dimple area, while those of lower tensile fracture load show brittle fracture.

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Preparation and Properties of Magnesia-Alumina Spinel by SHS (SHS 법에 의한 Magnesia-Alumina Spinel 제조와 특성)

  • 최태현;전병세
    • Journal of the Korean Ceramic Society
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    • v.33 no.2
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    • pp.235-241
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    • 1996
  • Self-Propagating high temperature synthesis(SHS) technique was used to synthesize the spinel phase of MgAl2O from MgO and Al powder. Processing factors such as mixing time preheating temperature and ignition catalyst were varied to determine the optimum condition to form MgAl2O4 phase. The reaction products were heat treated at the temperature range of 120$0^{\circ}C$ and 150$0^{\circ}C$. to observe phase transformation of unreacted materials. Processing factors such as 48 hrs-mixing 80$0^{\circ}C$-preheating and 20wt% KNO3-ignition catalyst were effective of the formation of MgAl2O spinel. An activation energy 49.7kcal/mol. was calculated to form a MaAl2O4 spinel from unreacted materials.

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Determination of Preheating Temperature for Box Girder Welding (강교용 박스거더의 용접예열 온도 선정에 관한 연구)

  • Cho, Jae-Hun;Moon, Seung-Jae;Yoo, Hoseon
    • Plant Journal
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    • v.7 no.1
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    • pp.49-55
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    • 2011
  • This study analyzed causes and status of cracks to suggest preventives for welding cracks generated on fillet welding zone of atmosphere corrosion resisting steel box girder. Penetrant testing, a sort of non-destructive testing, was conducted for inspection of crack status on welding zone. As a result of test, welding cracks were found on the point of start, center and end to fillet welding zone of 32 mm-thickness. The result of carbon equivalent composition of materials was 0.452%. According to welding specification, to preheat prevent welding crack, preheat temperature of $100{\sim}200^{\circ}C$ should be kept before welding execution. It was failed to keep preheat temperature because it had been executed on winter season and the structure of box girder had wide heat transfer area. As a result of examination of time varying preheating temperature of 32mm-thickness material, it was understood that preheat temperature of above $230^{\circ}C$ on both 130mm-long sides of welded joint can prevent welding crack.

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