• 한국기계가공학회지
• /
• 제14권1호
• /
• pp.123-129
• /
• 2015

In general, recent critical studies of five-axis machine have tended to center on the question of effective machining to realize complex shape parts. However, the hydrostatic bearing and journal bearing, both of which are involved in the complex process of dividing the processing of internal precision-shape machining, must be optimized. Although the angle head is designed to machine the internal shape as it approaches the inner diameter of the work piece, research on the angle head in five-axis machining has received only minimal attention in domestic industries. In this study, an angle head which is optimized for effective internal shape machining is developed. In pursuit of this purpose, 3D and 2D designs of the angle head for five-axis machining are devised. Reliability is secured through static performance tests and machining accuracy evaluations of the angle head in keeping with the machining accuracy standard of 0.2mm for hydrostatic bearings.

• 대한기계학회논문집A
• /
• 제36권10호
• /
• pp.1131-1137
• /
• 2012

해저배관은 부력과 외부 충격을 방지하기 위하여 1.2~4m의 매설 깊이로 설치되어 운영된다. 해저배관은 수압과 토하중에 의한 외압으로부터 소성붕괴에 대한 저항성을 가져야한다. 해저배관에 수압과 토하중으로 발생하는 원주응력을 유한요소해석으로 파악하여 배관의 건전성에 미치는 영향을 평가하였다. 내압은 외압에 의한 소성붕괴 저항성을 향상시켜 소성붕괴 발생 깊이를 증가시켰다 동일 수심에서는 매설 깊이 증가에 따라 원주응력은 증가하나, 동일 매설 깊이에서는 수심이 증가함에 따라 배관에서 발생하는 원주응력은 감소한다.

• 한국정밀공학회지
• /
• 제31권8호
• /
• pp.715-720
• /
• 2014

Recently, surface texturing technologies have been widely used in lots of industries to increase the machinery efficiency. In this research, the lubrication characteristics of a crank shaft pin turner bearing with dimples were studied. When increasing the dimples, the load carrying capacity due to the increased pressure was increased because those have sealing effects. Also, the run-out error of the bearing was decreased. Therefore, it is important to consider the depth, the number and the distribution of dimples when designing the hydrostatic journal bearing.

• 한국산학기술학회논문지
• /
• 제19권11호
• /
• pp.230-236
• /
• 2018

최근 국내에서도 규모 5.0 이상의 지진이 발생하여 구조물의 내진 안전성에 대한 관심이 증가하고 있다. 특히, 물을 저장하는 시설은 지진에 의해 손상 및 파손이 될 경우, 누수로 식수 및 용수가 부족하게 될 뿐만 아니라 화재 진압의 어려움이 야기되므로 지진에 대한 안전성을 만족하여야 한다. 본 연구에서는 기초와 탱크사이에 납고무받침을 고려하여 지진에 대한 물탱크의 내진성능을 향상시키고자 한다. 이를 위해 기존 콘크리트 기초에 설치 가능하도록 납고무받침을 설계하였다. 물탱크에 대하여 유체-구조물 상호작용을 고려하기 위하여 ANSYS를 활용하여 모델링을 수행하였으며 정수압과 4개의 지진파를 이용한 동수압을 고려하였다. 만수위 2.5m의 정수압이 작용하는 경우에 대하여 정적 해석을 수행한 결과, 면진 적용여부와 상관없이 동일한 응력이 발생하였다. 정수압과 동수압을 동시에 고려했을 때, 면진 물탱크는 전반적으로 지진력 감소가 이루어졌지만 일반적인 구조면진과 비교했을 때 감쇠율이 다소 낮은 것으로 나타났다. 이는 물탱크 중량이 면진 강성보다 매우 작아서 나타난 결과로 판단되며, 향후 물탱크 내진성능 평가에 기초 자료로 활용될 것으로 기대된다.

• Tribology and Lubricants
• /
• 제33권5호
• /
• pp.187-201
• /
• 2017

This paper presents the impact of couple stress lubricant on performance of slot-entry hydrostatic/hybrid journal symmetric/asymmetric bearings. Reynolds Equation using Finite Element Technique has been solved for the flow of couple stress and Newtonian lubricants in bearings. The results have been computed for concentric design pressure ratio(${\beta}^{\ast}=0.5$), slot width ratio (SWR = 0.25) and chosen parameters of couple stress lubricant ${\bar{l}}=5$, 10, 15. It is observed that numerically simulated outcomes for slot-entry journal bearings, considering the influence of couple stress lubricant indicate a substantial improvement in the performance of the bearing.

• 한국정밀공학회지
• /
• 제14권3호
• /
• pp.82-88
• /
• 1997

In this paper, the development of a precision CNC lathe prototype for mirror surface machining is presented. To obtain high precision machining accuracy, a hydrostatically supported precision spindle and a sliding guideway with turcite pad are adopted as the motion elements. The machining accuracy of the prototype machine, and the motional accuracy of its motion elements are tested and evaluated to confirm the validity of the application of these elements on the prototype. The hydrostatic spindle shows 0.09 .mu. m of rotational accuracy and the guideway shows about 0.8 .mu. m/170mm of horizontal straightness. The sur- face roughness of cupper and aluminium cylinder machined by the prototype machine with diamond tool are 0.07 .mu. m and 0.10 .mu. m Rmax respectively. From these results, it is verified that the prototype lathe is avail- able for high precision machining.

• 대한기계학회논문집A
• /
• 제31권12호
• /
• pp.1173-1179
• /
• 2007

In recent years, research to machine large-surface micro-features has become important because of the light guide panel of a large-scale liquid crystal display and the bipolar plate of a high-capacity proton exchange membrane fuel cell. In this study, in order to realize the systematic design technology and performance improvements of an ultra-precision machine for machining the large-surface micro-features, a structural characteristic analysis was performed using its virtual prototype. The prototype consisted of gantry-type frame, hydrostatic feed mechanisms, linear motors, brushless DC servo motor, counterbalance mechanism, and so on. The loop stiffness was estimated from the relative displacement between the tool post and C-axis table, which was caused by a cutting force. Especially, the causes of structural stiffness deterioration were identified through the structural deformation analysis of sub-models.

• Tribology and Lubricants
• /
• 제12권3호
• /
• pp.85-91
• /
• 1996

An analysis for turbulent hybrid beatings with fluid inertia and swirl injection effect was derived for studying static characteristics of swirl-controlled hybrid journal. The swirl-controlled hybrid journal beating is considered to have more freedom in stability control in high speed rotating machinery. Current analysis is compared with experimental results with 3-recess hydrostatic journal bearing. The analysis revealed that the fluid momentum exchange at orifice discharge could produce pressure rise inside the recess region which can control the shear flow induced by journal rotation. The analysis also shows that the swirl-controlled hybrid journal beating has a capability of controlling load carrying capacity and stability by manipulating supply pressure and injection angle.

• 한국정밀공학회지
• /
• 제30권12호
• /
• pp.1327-1333
• /
• 2013

Air bearings are widely used in precision stages because of low friction and high motion accuracy, however, they suffer from low stiffness in comparison with rolling bearings or hydrostatic bearings. So, several preloading methods using weight, magnet and vacuum force, and opposing pads have been used to increase the stiffness of the air bearings. In this paper, pressure distributions of the vacuum preloaded porous air bearings are calculated using the proposed method. And then, the load capacity and stiffness are analyzed. For the vacuum preloaded air bearings, the stiffness is increased owing to reduced bearing clearance by vacuum force. The simulation results indicate that variation of vacuum pressure with clearance in the vacuum pocket gives rise to low stiffness, so the vacuum pocket should be designed for pressure to be constantly maintained regardless of the bearing clearance by means of large effective pumping speed.

• Journal of Mechanical Science and Technology
• /
• 제19권2호
• /
• pp.682-691
• /
• 2005

This paper describes the design, fabrication, and testing of a microturbine developed at Seoul National University. Here, the term 'microturbine' refers to a radial turbine with a diameter on the order of a centimeter. Such devices can be used to transmit power for various systems. The turbine is designed using a commercial CFD code, and it has a design flow coefficient of 0.238 and work coefficient of 0.542. It has 31 stator blades and 24 rotor blades. A hydrodynamic journal bearing and hydrostatic thrust bearings counteract radial and axial forces on the rotor. The test turbine consists of a stack of five wafers and is fabricated by MEMS technology, using photolithography, DRIE, and bonding processes. The first, second, fourth, and fifth layers contain plumbing, and hydrostatic axial thrust bearings for the turbine. The third wafer contains the turbine's stator, rotor, and hydrodynamic journal bearings. Furthermore, a turbine test facility containing a flow control system and instrumentation has been designed and constructed. In performance tests, a maximum rotation speed of 11,400 rpm and flow rate of 16,000 sccm have been achieved.