Kyu-Yeol Park

Micro-forming characteristics of a Zr-based amorphous alloy with a gear-like mold

The amorphous alloy Zr62Cu17Ni13Al8 exhibits a supercooled liquid state over a wide temperature range under high temperatures. In this present paper, the authors studied the micro-forming ability of the alloy by compressing specimens under a miniature pattern mold with a micro-gear shape. Micro-compressive formation is a formation method in which the surface of specimens of the Zr62Cu17Ni13Al8 amorphous alloy is compressed under conditions of dead loads and high temperatures and maintained for a given period for the fabrication of miniature patterns with a micro-gear shape. All the experiments were carried out under a vacuum environment to prevent the specimens from suffering deleterious effects, such as air traps in the miniature patterns and oxidation at the surface of the Zr62Cu17Ni13Al8 amorphous alloy. The characteristics of micro-compressive formation were investigated at temperatures higher than the glass transition temperature with different experimental parameters of loads and times. In addition, the micro-forming characteristics of the gear-like shape were investigated by means of scanning electron microscopes and a 3-D surface profiler system.

Microforming of superplastic 5083 aluminum alloy

Abstract The mechanical behavior of superplastic 5083 aluminum alloy during microforming process was investigated by finite element analysis. A micro V-groove die was modeled to analyze the effects of forming time, load and temperature on the microformability of the 5083 aluminum alloy. First, the microformability of the 5083 aluminum alloy was estimated using a microformability index. The simulation results show that the microformability increases with the forming load, time and temperature increasing. Superplasticity of the 5083 aluminum alloy during microforming using the V-groove die was also investigated in terms of the effective strain rate. The results show that the superplasticity of the 5083 aluminum alloy occurs in a specific part of the material for a specific period during the microforming process depending on the forming conditions and the microformability index.

Development of Monitoring Process of Friction Stir Spot Welding of Aluminum Alloys using Acoustic Emission

대표적인 경량화 소재인 알루미늄(Al) 합금은 최근 자동차 산업에서 강하게 일고 있는 경량화 추세와 맞물려 자동차 차체 샤시 분야에의 응용이 빠른 속도로 확산되고 있다. 그러나 알루미늄 합금은 용융용접 시 고온균열 및 용접변형 등이 발생하기 쉽다는 취약점을 가지고 있다. 특히 차체 샤시 제조의 주요 공정으로서 부품간의 Lap 접합이 사용되고 있음을 고려할 때 알루미늄 합금의 낮은 용접성은 자동차 산업에서 알루미늄 합금의 보급 확대를 위해서 반드시 극복해야 할 문제점이라고 할 수 있다. 알루미늄 합금의 낮은 용접성을 극복할 수 있는 대표적인 신기술로서 주목 받고 있는 고상접합공정인 마찰교반용접((Friction Stir Welding: FSW)

A study on the micro electric discharge grinding characteristics of WC-Co-relationship between surface integrity and dielectric conditions-

In this paper, wire electric discharge grinding(WEDG) method for machining a micro shaft was introduced and the machining characteristics was investigated. From the experimental results, it was concluded that high surface integrity could be obtained by use of dielectric fluid spray method and small capacitive condenser. KeyW ords : Wire Electric Discharge Grinding, Micro Electric Discharge Machining, Dielectric Spray Method, Dielectric Stream Method

Potential of fuel stratification for reducing pressure rise rate in HCCI engines fueled with DME/n-Butane

This study investigated the effect on reducing the pressure rise rate(PRR) in HCCI Engine by the variation of mixing ratio in the pre-mixture of DME and n-Butane that has different auto-ignition characteristics. In addition to measure of gas pressure in the engine cylinder, chemiluminescence image using the optical accessible engine and numerical analysis with multi-zones model were used to assess the combustion at each local area in the combustion chamber. The maximum PRR changes depending on mixing condition of DME and n-Butane. When DME is stratified and n-Butane is distributed uniformly, maximum PRR becomes lowest which is about 0.25MPa/ms and it corresponds to 5deg. retarding of CA50.

Recent Developments in Monitoring of Friction Stir Spot Welding Process Using Acoustic Emissions

부재나 구조물이 외부 혹은 내부에서 작용하는 하중에 의해 변형 또는 내부 균열의 발생과 성장에 따라 부재 내부에 에너지가 축적되고, 축적된 에너지는 파면형상에너지, 열에너지, 격자변형에너지 등의 형태로 공극의 형성과 더불어 급격한 해방에 의해 탄성응력파를 발생시킨다. 이때 발생한 탄성응력파는 부재나 구조물을 따라 사방으로 진동해가며, 압전 센서에 의해 전기적인 신호로 계측 변환된 후 증폭되고 공학적으로 분석하여 응용하게 되는데, 이러한 기술을 음향방출법(AE법) 이라고 한다. 주로 마찰이나 마모 거동을 이해하기 위한 연구의 목적으로 이용되고 재료나 기계의 변화 상태를 지속적으로 감지하는 진단 기술로도 활용되고 있다

Potential of Fuel Stratification for Reducing Pressure Rise Rate in HCCI Engines Fueled With DME/n-Butane

We investigated the efficacy of fuel stratification in a pre-mixture of Di-methyl ether and n-Butane, which have different auto-ignition characteristics, for reducing the pressure rise rate of homogeneous charge compression ignition engines. A new chemical reaction model was created by mixing DME and n-Butane and compared to existing chemical reaction models to verify the effects. The rate of maximum pressure rise depends on mixture ratio. When DME was charged with stratification and n-butane was charged with homogeneity, the maximum pressure rise rate was the lowest. The calculations were performed using the SENKIN application of CHEMKIN-II.

Effects of Loading Type And Cavity Position On The Pattern Height In Micro‐manufacturing of Al5083 Superplastic Alloy And Zr62Cu17Ni13Al8 Metallic Glass

Vibrational micro‐forming of pyramidal shape patterns was conducted for an Al superplastic alloy, Al 5083 and a Zr‐based bulk metallic glass, Zr62Cu17Ni13Al8. A vibrational micro‐forming system was specially designed for generating vibrational load by combining a PZT actuator with a signal generator. Si micro dies with wet‐etched pyramidal patterns were used as master dies for vibrational micro‐forming. The micro‐formed pattern height was increasing with increasing the frequency of the vibrational load. In particular, the vibrationally‐microformed pattern height is similar or even higher than the statically‐microformed pattern height when the load frequency exceeded about 125 kHz. It was also observed that the crystal grains affect the surface quality of the microformed pattern and the distribution of the pattern height in the die cavity array.Vibrational micro‐forming of pyramidal shape patterns was conducted for an Al superplastic alloy, Al 5083 and a Zr‐based bulk metallic glass, Zr62Cu17Ni13Al8. A vibrational micro‐forming system was specially designed for generating vibrational load by combining a PZT actuator with a signal generator. Si micro dies with wet‐etched pyramidal patterns were used as master dies for vibrational micro‐forming. The micro‐formed pattern height was increasing with increasing the frequency of the vibrational load. In particular, the vibrationally‐microformed pattern height is similar or even higher than the statically‐microformed pattern height when the load frequency exceeded about 125 kHz. It was also observed that the crystal grains affect the surface quality of the microformed pattern and the distribution of the pattern height in the die cavity array.

Estimation of Micro-Formability and FEM Simulation of Micro-Forming Process of a Zr-Based Bulk Metallic Glass

Micro-forming is considered to be a suited technology to manufacture very small metallic parts (several μm~mm). Zr-based bulk metallic glass, Zr62Cu17Ni13Al8, has been expected to be a promising metallic material for micro-forming process due to their isotropy, low flow stress in a wide supercooled liquid region and good stability of amorphous matrix. Therefore, one can expect that micro-forming of Zr62Cu17Ni13Al8 might be feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, micro-formability of Zr62Cu17Ni13Al8 bulk metallic glass was investigated for micro-forging of U-shape pattern. Microformability was estimated by comparing Rf values (=Af/Ag), where Ag is corss-sectional area of U groove, and Af the filled area by material. Micro-forging process was also simulated and analyzed by applying the finite element method. The micro-formability of Zr62Cu17Ni13Al8 was increased with increasing load and time in the temperature range of the supercooled liquid state. In spite of the similar trend in the variations of Rf values, FEM simulation results showed much higher Rf values than the experimental Rf values. This disagreement was analyzed based on the stress overshoot phenomena of bulk metallic glasses in the supercooled liquid region. FEM simulation of the microstamping process was applicable for the optimization of micro-forming process by carefully interpreting the simulation results.

Micro forming characteristics of A15083 superplastic alloy

Micro forming is a well suited technology to manufacture very small metallic parts, in particular for mass production, as they are required in many industrial products resulting from micro technology. A15083 superplastic alloy have a great advantage in achieving deformation under low stress compared to conventional plastic deformation. This paper describes the basic characteristics of micro forming of A15083 superplastic alloy. Self-designed micro forging system with (100) silicon dies used to micro forming characteristic test of A15083 superplastic alloy.