• Current Optics and Photonics
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• 제1권4호
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• pp.364-371
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• 2017

Compared to one made of glass, an aluminum mirror features light weight, compact design, low cost, and quick manufacturing. Reflective mirrors and supporting structures can be made from the same material, to improve the athermal performance of the system. With the rapid development of ultraprecise machining technologies, the field of applications for aluminum mirrors has been developed rapidly. However, most of them are rotationally symmetric in shape, and are used for infrared applications. In this paper, the design and manufacture of an off-axis aluminum mirror used for a three-mirror-anastigmat (TMA) optical system at visible wavelengths is presented. An optimized, lightweight design provides a weight reduction of more than 40%, while the surface deformation caused by earth's gravity can meet the required tolerance. The two pieces of an off-axis mirror can be diamond-turned simultaneously in one setup. The centrifugal deformation of the off-axis mirror during single-point diamond turning (SPDT) is simulated through the finite-element method (FEM). The techniques used to overcome centrifugal deformation are thoroughly described in this paper, and the surface error is reduced to about 1% of the original value. After post-polishing, the form error is $1/30{\lambda}$ RMS and the surface roughness is better than 5 nm Ra, which can meet the requirements for visible-light imaging.

• 한국생산제조학회지
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• 제22권5호
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• pp.824-830
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• 2013

In ultra-precision machining, the inside temperature should be controlled precisely. The important factors are environmental conditions (outside temperature, humidity) and temperature conditions (cutting heat, spindle heat). Thus, in this study, an environmental control cell for the ultra-precision machine that could control the inside temperature and minimize effects of the surrounding environment to achieve a thermal deformation of less than 400nm of a specimen was designed and verified through C.F.D. Further, a method that could control the temperature precisely by using a blower, heat exchanger and heater was evaluated. As a result, this study established a C.F.D technic for the environmental control cell, and the specimen temperature was controlled to be within $17.465{\pm}0.055^{\circ}C$.

• 한국기계가공학회지
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• 제19권9호
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• pp.15-23
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• 2020

Spline is a machine component using transmits rotating energy with grooves on internal of boss and external periphery of shaft. Internal spline is generally produced by machining process. However, to reduce manufacturing cost and save time, plastic deformation process such as backward extrusion is gradually adapted for spline production. In plastic deformation process, forming load, stress on tools and flow flaws should be taken into account to have sound products. For this purpose, kinematically admissible velocity fields for Upper Bound Method in backward extrusion of internal spline has been suggested, then forming load and relative pressure have been calculated. Internal spline forming experiments have been con-ucted under hydraulic press and the calculated forming load well predicts the load of experiment.

• 한국정밀공학회지
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• 제20권9호
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• pp.55-62
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• 2003

This paper investigates the micro-cutting of cemented carbides using PCD (polycrystalline diamond) and PCBN (polycrystalline cubic boron nitride) cutting tools are performed with SEM direct observation method. The purpose of this study is to make clear the cutting mechanism of cemented carbides and the fracture of WC particles at the plastic deformation zone in orthogonal micro-cutting. And also to achieve systematic understanding, the effect of machining parameter on chip formation and machined surface was studied, including cutting speed, depth of cut and various tool rake angle. Summary of the results are shown below. (1) Three type of chip formation process have been proposed by the results of the direct observation in orthogonal micro-cutting of cemented carbide materials. (2) From the whole observation of chip formation, primary WC particles are crushed and/or fine grained in the shearing deformation zone. A part of them are observed to collide directly with a cutting edge of tool by following the micro-cutting. (3) Surface finish, surface morphology and surface integrity is good to obtain by cutting with PCD cutting tool compared with PCBN. (4) The machined surface has the best quality near the low cutting speed of 10${\mu}m$/sec with a cutting depth of 10 ${\mu}m$ using 0$^\circ$ rake angle and 3$^\circ$ flank angle in this condition, but it was found that excessively low speed, for example the extent of 1 ${\mu}m$/sec, is not good enough to select for various reason.

• 한국기계가공학회지
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• 제15권4호
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• pp.101-108
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• 2016

Endmill fillet cutting at the corner was conducted with the online measurement of cutting forces and tool deflection by a tool dynamometer and an eddy current sensor system. The profile of the machined surface was also compared with the CAD profile with a Coordinate Measuring Machine (CMM) and CALYPSO software. It was found that the end mill cutter with four blades has a better surface profile than that with two blades, and the cutting forces and tool deformation were increased as the cutting speed was increased. When the tool located at the degree $45^{\circ}$ corner was found to conduct the maximum cutting force than started to the point of the workpiece. As it was compared with the CMM and ANOVA analysis result in the case that the cutting force and tool deformation was the maximum, it was found that the result was affected by the spindle speed and the number of blades.

• 한국정밀공학회지
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• 제19권1호
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• pp.56-64
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• 2002

Machine tools are engineered to give high dimensional accuracy in machining operation. However, errors due to thermal effects degrade dimensional accuracy of machine tools considerably, and many machine tools are equipped with thermal error compensation function. In general, thermal errors can be generated in the angular directions as well as linear directions. Among them, thermal errors in the angular directions contribute a large amount of error components in the presence of offset distance as in the case of Abbe error. Because most of thermal error compensation function is based on a good correlation between temperature change and thermal deformation, angular thermal deformation is often to be the most difficult hurdle for enhancing compensation accuracy. In this regard, this paper investigates the effect of thermal bending to total thermal error and gives how to deal with thermally induced bending effects in thermal error compensation.

• 반도체디스플레이기술학회지
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• 제18권2호
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• pp.38-43
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• 2019

In this study, a hydraulic press structure has been investigated in order to enhance the precision machining and the productivity, which are generally damaged by the structural deformation from the pressure and the vibrations originated from the centrifugal forces from the rotating parts of the machine. Computer simulation based on the finite element method has been utilized for the analysis of static and dynamic characteristics to investigate each component's critical points, and to further improve the static and dynamic stabilities of a hydraulic press structure. The result shows that the deformations and the vibrations of the machine could be reduced 35% without increasing the weight of the machine.

• 반도체디스플레이기술학회지
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• 제18권1호
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• pp.112-116
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• 2019

This study was carried out by structural analysis using finite element method for designing high rigidity structure of multi - functional automatic lathe bed. As a result of comparison, it was confirmed that the weight was designed to be higher than the maximum deformation amount. The shape and dimensions of the main pillars and walls of the bed were changed to derive the most suitable design for the multifunction automatic lathe bed. A model of structural design was derived with the goal of minimizing the maximum deformation amount of $20{\mu}m$ or less and the weight of the bed. As a result of applying the derived design improvement proposal to the multifunctional automatic lathe bed, 57.4% weight reduction and maximum principal stress decreased by 45.0% than the initial design model. It is expected that the optimum design that meets these design conditions will reduce the weight of the structure as well as improve the safety of the structure and reduce the machining error in the operation of the machine tool.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.572-579
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• 2001

본 연구에서는 유한요소해석을 통한 와이어 방전가공기의 설계검증을 위하여 두 모델을 선정하여 CAD 패키지 I-DEAS를 이용하여 3차원 유한 요소모델을 모델링한 후 상용 유한요소해석코드인 ABAQUS로 각 모델의 가공위치에 따른 해석을 수행하였다. JW-35A와 JW-60A 두 모델의 상호 비교 타당성 여부를 확인하기 위하여 ${\eta}-factor$ 개념을 이용하였다. 이어 공리적 설계 개념을 도입하여 오차보정을 위한 설계변수들의 선택과 방법이 적절함을 보이고 두 모델의 유한요소해석 결과를 상호 비교하여 구조물의 설계를 검증하고 변형 예측식을 유도하였다. 본 연구를 통해 유도된 변형 예측식 (5)-(6) 형태의 접근방법은 비단 방전가공기 뿐만 아니라 이와 유사한 형태의 공작기계에도 적용 할 수 있을 것이다.

• 한국생산제조학회지
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• 제7권1호
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• pp.75-81
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• 1998

We have studied internal quality including chemical compositions, microscopic structure and nonmetallic inclusion of test materials. We have analyzed tensile strength value, hardness value, impact value etc. In analyzing internal quality, all of the test materials showed typical ferrite+pearlite structure. But nonmetallic inclusion showed oxide and sulfide inclusions in medium carbon steels, and sulfide inclusion is S-free cutting steels. In ca+ S-free cutting steels, the calcium aluminate and sulfide complex inclusion had low-melting points as deformation of sulfide and oxide inclusion is existed. It was found that tensile strength and hardness give maximum value in medium carbon steels, where as minimum in Ca + -free cutting steels. But values of elongation, reduction of area impact are reverse. Fracture surface of impact specimen is ductile in free cutting steels but brittle in medium cabon steels.