1,720,969 research outputs found
Composite machine tool structures for high speed milling machines
No full textTo maximize the productivity in machining molds and dies, machine tools should operate at high speeds. However, the productivity of mold manufacturing has not increased significantly because CNC milling machines have massive slides, which do not allow rapid acceleration and deceleration during the frequent starts/stops encountered in machining molds and dies. This paper presents the use of composites for these slides to overcome this limitation. The vertical and horizontal slides of a large CNC machine were constructed by bonding high-modulus carbon-fiber epoxy composite sandwiches to welded steel structures using adhesives. These composite structures reduced the weight of the vertical and horizontal slides by 34% and 26%, respectively, and increased damping by 1.5 to 5.7 times without sacrificing the stiffness. Without much tuning, this machine had a positional accuracy of +/- 5mum per 300 mm of the slide displacement
Superconductivity and electric field effect of 90 degree grain boundaries in YBa2Cu3O7-x thin films
No full textthree terminal devise was fabricated by depositing YBa2Cu3O7-x (YBCO) thin films containing 90 degree grain boundaries which was covered with a SrTiO3 gate layer and an Au gate electrode. YBCO thin films were grown by bi-epitaxial process on LaSrGaO4(100) substrate. The resistance versus temperature curve of the YBCO microbridge containing 90 degree grain boundaries showed double resistive transitions. This result was interpreted by the weak link effect of 90 degree grain boundaries in YBCO thin films. A large electric field effect on 90 degree grain boundaries was observed. The superconducting transition temperature of the 90 degree grain boundaries was modulated up to 11.4% by applying an electric field of 4 x 10(4) V/cm.We would like to thank Dr. E.-H. Lee for his consistent support. This work was supported by Ministry of Information and Communications, Rep. of Korea
Plasma surface treatment for the composite bipolar plate of polymer electrolyte membrane fuel cells
No full textCubic Y-Ba-Cu-O thin films by high speed pulsed laser deposition
No full textThe crystal structure and properties of YBa2Cu3Ox (YBCO) thin films on LaSrGaO4 (100) substrate have been investigated as a function of deposition rates in the range of 0.1-12.2 nm/s using different repetition rate of pulsed laser. At a given substrate temperature of 700 degrees C, when the Nm was deposited at low deposition rate of 0.1 nm/s, c-axis oriented orthorhombic YBCO thin film growth was observed. However, at high deposition rate of 12.2 nm/s, cubic YBCO thin film growth was observed. This demonstrates that the shortening of interval time between the vapor pulses is important for the cubic YBCO thin film growth. The cubic YBCO thin film growth under high deposition rates was explained by the cation kinetics. (C) 1998 Published by Elsevier Science B.V. All rights reserved.We would like to thank Dr. E.-H. Lee for his
consistent support. This work was financially supported
by the Ministry of Information and Communications,
Republic of Korea
Damping characteristics of composite hybrid spindle covers for high speed machine tools
No full textIn order to improve the vibration characteristics of a spindle cover made of 2 mm thick steel plate for high speed machine tools, the cover was reinforced with carbon fiber epoxy composite material. Considering the mounting conditions and the vibration mode shape of the spindle cover, the stacking sequence and the thickness of the reinforced composite laminate were determined through finite element analysis. The relationship between the loss factor and the stacking sequence was also investigated. The steel-composite hybrid spindle cover was fabricated by co-cure bonding in an autoclave and its dynamic characteristics were tested. From the tests, it was found that damping improvement of the composite hybrid spindle cover was substantial over a wide frequency range. (C) 2001 Elsevier Science B.V. All rights reserved
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