• 제목/요약/키워드: Globular Microstructure

검색결과 62건 처리시간 0.024초

반용융 단조를 위한 소재의 유도 가열 (Induction Heating of a Billet for Semi-Solid Forging)

  • Park, J.C.;Park, H.J.;Kim, B.M.
    • 한국정밀공학회지
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    • 제14권8호
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    • pp.15-20
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    • 1997
  • Semi-solid forging is a compound forging technology to develop conventional forging process. Among several steps of semi-solid forging process, the heating step of a billet prior to semi-solid forging step is necessarily required to obtain globular microstructure. For the forming operation to work properly, it is also important to heat the billet uniformly for the uniformity of solid-liquid distribution. To satisfy these requirements, induction heating has been generally used for a long time. This paper presents the method to find heating condition and the temperature distribution inside a billet with a induction heating apparatus by comparing the computer simulation with experiment for aluminium alloys A12024 and A356.

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반융용알루미늄재료의 재가열공정 (Reheating Process of Semi-Solid Aluminum Alloy)

  • 강성수;도영진;강충길
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
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    • pp.16-27
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    • 1997
  • A semi-solid forming has a lot of advantages compared to the die casting, squeeze costing and convenctional forging, therefore, semi-solid forming process are now becoming of industial interest for the production of metal components and metal matrix composites. However, the material behaviour in the semi-solid temperature range is not sufficiently known although it controls the whole process through forces and geometry evolutions bcause the behaviour of metal slurries is complex. The semi-solid materials(SSM) fabricated under electric-magnetic stirring condition is necessary to be applicate in forming process. A reheating conditions were studied with the reheating time, holing time and reheating temperatures. The microstructure of SSM (which specimen size:d 40${\times}$i60) on condition of heating time 10min and heating temperature 590$^{\circ}C$ is most globular and finest one. The microstructure of SSM(specimen size:d75${\times}$i60) reheated under the three step reheating conditions is most globular and finest.

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반용융 알루미늄재료의 단조공정조건이 기계적 성질에 미치는 영향 (The effect of forging process conditions of semi-solid aluminum material on mechanical properties)

  • 강충길;강동우
    • 대한기계학회논문집A
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    • 제21권9호
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    • pp.1400-1413
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    • 1997
  • Semi-solid forging(SSF) process of A356 aluminium alloy has been studied to assess the effect of process variables on the component integrity. Semi-solid material(SSM) was fabricated by mechanical and electro-magnetic stirring process. The fabricated SSM by using mechanical stirring process has been carried out on cooling rate of 0.022.deg. C/sec 0.0094.deg. C/sec and stirring speed n=600, 1000 rpm, respectively. The fabricated SSM by using electro-magnetic stirring process is supplied by Pechiney. The holding time and temperature in the semi-solid state before forging also affects the globular microstructure of alloy. Therefore, the influence of these two parameters is discussed in terms of the microstructure of alloy. The SSF process has been conducted with three different die temperatures($T_{die}$=250.deg. C, 300.deg. C, 350.deg. C) and two kinds of gate types(straight gate and orifice gate). This paper is to investigate the influence of gate shapes of die on filling phenomena in SSF process more deeply. The mechanical properties of forged components were also investigated for variation of process conditions such as die temperature, gate shape and SSM.

유도가열에 따른 SKH51의 반응고 미세조직 특성 연구 (The Characteristics of Microstructure in the Semi-solid State of SKH51 at High Frequency Induction Heating)

  • 이상용
    • 열처리공학회지
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    • 제25권3호
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    • pp.126-133
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    • 2012
  • Semi-solid forming of the high melting point alloys such as steel is a promising near-net shape forming process for decreasing manufacturing costs and increasing the quality of the final products. This paper presents the microstructure characteristics of SKH51 (high speed tool steel) during heating and holding in the mushy zone between $1233^{\circ}C$ and $1453^{\circ}C$, which has been measured by differential scanning calorimetry (DSC). The results of heating/holding experiments showed that the grain size and the liquid fraction increased gradually with temperature up to $1350^{\circ}C$. The drastic grain growth occurred at heating above $1380^{\circ}C$. The strain-induced melt-activated (SIMA) process has been applied to obtain globular grains in the billet materials. Working by mechanical upsetting and successive heating of SKH51 into the temperatures in the mushy zone resulted in globular grains due to recrystallization and partial melting.

임의 형상의 다이를 이용한 반용융 단조 공정의 유한요소해석 (A Finite Element Analysis of Thixoforging Process by using Arbitrarily Shaped Dies)

  • 강충길;김남석
    • 한국정밀공학회지
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    • 제16권9호
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    • pp.123-134
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    • 1999
  • A new forming technology has been developed to fabricate near-net shape components by using aluminum alloys with globular microstructure. The estimations of filling characteristic in the forging simulation with arbitrarily shaped dies of SSM are calculated by finite element method with proposed algorithm. The proposed model and various boundary conditions for arbitrarily shaped die are investigated with the coupling calculation between the liquid phase flow and the solid phase deformation. The simulation processes with arbitrarily shaped dies are performed on the isothermal conditions and axisymmetric problems. To analyze the forging process simulation with SSM, new stress-strain relationship for semi-solid behaviour is described, and forging the liquid flow. Furthermore, For the purpose of getting net shape of SSM, it is important to be obtain a solid fraction in forging process with arbitrarily shaped dies. To produce a automotive part which have good mechanical properties, the filling pattern in accordance with die velocity and solid fraction distribution has to be estimated for arbitrarily shaped die.

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SKH51의 반응고 상태에서의 가열 및 성형에 의한 부품 제조 (Fabrication of a Part by Heating and Forming in the Semi-solid State of the SKH51 Material)

  • 이상용
    • 열처리공학회지
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    • 제27권3호
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    • pp.127-132
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    • 2014
  • The semi-solid metal forming process has been applied to realize a near-net shape fabrication of a high speed tool steel. A complicatedly shaped part out of SKH51 was successfully manufactured by introducing pertinent materials, tooling and processing conditions. A SKH51 billet with globular grains was heated at temperatures between 1300 and $1350^{\circ}C$ using high frequency induction heater to get semi-solid microstructure before high rate injection of mushy metal into a die cavity for the forming process. It was necessary to control the preheating of dies between 300 and $400^{\circ}C$ to maintain the homogeneous microstructure during the semi-solid metal forming process. Significant defects such as pores, high fraction of liquid fraction and segregation could be removed from the part by using air vents.

전자교반시스템에서 Sleeve 의 크기가 유동특성과 미세조직에 미치는 영향 (The effect of the primary particle of the A356 Alloy according to different wall thickness of the sleeve of die-casting by electromagnetic stirrer)

  • 고재홍;서판기;강충길
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2004년도 추계학술대회 논문집
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    • pp.660-663
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    • 2004
  • Recently in the automotive industries, light and high quality material is strongly required because of emissions regulation issues. In the electromagnetic stirring process, it has many merits that are the exact control ability about material processing and a good point of the protection of environment. In this paper, the morphology of the change of primary Al phase in A356 alloy by electro magnetic stirrer was investigated to obtain the globular structure. The parameters are the current, stirring time, pouring temperature and cooling rate of different wall thickness; 5mm, 15mm, 25mm respectively. By proper selection of the processing parameters, globular primary particles can be obtained by electromagnetic stirrer.

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Thixoforming을 위한 재가열용 유도코일 설계의 최적화 (Optimization of Induction Coil Design for Reheating in Thixoforming Process)

  • 김남석
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 1999년도 춘계학술대회논문집
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    • pp.165-168
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    • 1999
  • The coil design of induction heating systems and their optimization are of paramount importance for semi-solid processing(SSP) The authors of this paper present the coil design and optimization of a 60 Hz induction heating system for ALTHIX 86S (Al-6%_Si-3%Cu-0.3%Mg) alloy. An objective function on the basis of the optimization process for the coil design is proposed by introducing an optimization technique. Finally the results of the optimal coil design are also applied to the induction heating process to obtain a fine globular microstructure. The proposed new objective function based on the computational techniques would contribute to obtaining the thixoformed components with good mechanical properties and reducing lead time.

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수평식 전자교반을 이용한 A356 합금의 결정립 제어 (The Grain Size Control of A356 Aluminum Alloy by Electromagnetic Stirring)

  • 고재홍;서판기;최우식;강충길
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2004년도 추계학술대회논문집
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    • pp.111-114
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    • 2004
  • It is many devices to obtain the globular structure because the globularity of the structure is the key to the low apparent viscosity and also to good rheological properties. In this study, the morphology of the change of primary Al phase in A356 alloy by electro magnetic stirrer was investigated to obtain the globular structure. The parameters are the current, stirring time, pouring temperature individually. The greater current and longer stirring time was to get the finer the primary however in case of over the 80A of current and 60sec of stirring time, the primary Al was merged together and was increased. The effect of pouring temperature has an important effect on the size of primary phase. About the $675^{\circ}C$, the primary Al was very fined.

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반용융 알루미늄 재료의 압축성형시 변형율속도가 미시적 거동에 미치는 영향 (The Effect of Strain Rate on Macroscopic Behaviour in Compression Forming of Semi-Solid Aluminum Alloy)

  • 강충길;김기훈
    • 소성∙가공
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    • 제6권4호
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    • pp.338-345
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    • 1997
  • The behaviour of alloys in the semi-solid state strongly depends on the imposed stress stage and on the morphology of the phase which can vary from dendritic to globular. To optimal net shape forging of semi-solid materials, it is important to investigate for material behaviour for variation of strain rate. Therefore, to investigate the effect of compression speed on deformation of aluminum alloy with globular microstructure, the compression test for semi-solid aluminum alloy with controlled solid fraction is perform by material test system which is attracted with furance. The behavior of semi-solid aluminum alloy were discussed for the various solid fraction and die speed. The material constants in stress-strain were are also proposed.

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