Showing papers by "Dai Gil Lee published in 2002"

Cure Cycle for Thick Glass/Epoxy Composite Laminates

Abstract: Duringthe curingprocess of thick glass/epoxy composite laminates, substantial amounts of temperature lagand overshoot at the center of the laminates is usually experienced due to the large thickness and low thermal conductivity of the glass/epoxy composites, which require a long time for full and uniform consolidation. In this work, the temperature profiles of a 20mm thick unidirectional glass/epoxy laminate duringan autoclave vacuum bag process were measured and compared with the numerically calculated results. For the calculation of distributions of the temperature, degree of cure, resin pressure, exothermic heat and required time for full consolidation by three-dimensional finite element analyses, the effects of convective heat transfer coefficient and geometry of mold and bagging assembly on the temperature profiles were taken into consideration. Based on the numerical results, an optimized cure cycle with the coolingand reheatingsteps was developed by minimizingthe objective function to reduce the te...

High stiffness composition tool bar

Abstract: The present invention is to provide a machining tool bar in which mechanical machining properties are improved by using high stiffness composite material. According to the present invention, the tool bar includes an adaptor (110) constructed to be coupled to a driving device, a body (120) constructed to be mounted with cutting tools and a tip (130) constructed to be supported by a workpiece, said body (120) is constructed to be mounted with one or more cutting tools, wherein the adaptor (110) and tip (130) are made of metal material, the body (120) is made of composite material having high stiffness, the composite material constructing the body (120) is formed to surround at least a portion of the adaptor (110) and at least a portion of the tip (130), and the metal material constructing the adaptor (110) and tip (130) and the composite material constructing the body (120) are securely joined to each other in an interface therebetween.

Thrust Bearing Design for High-Speed Composite Air Spindles

Abstract: Composite air spindles are appropriate for the high-speed and the high-precision machining as small hole drilling of printed circuit board (PCB) or wafer cutting for manufacturing semiconductors because of the low rotational inertia, the high damping ratio and the high fundamental natural frequency of composite shaft. The axial load and stiffness of composite air spindles fur drilling operation are determined by the thrust ben ring composed of the air supply part mounted on the housing and the rotating part mounted on the rotating shaft. At high-speed rotation, the rotating part of the thrust bearing should be designed considering the stresses induced by centrifugal force as well as the axial stiffness and the natural frequency of the rotating shaft to void the shaft from failure due to the centrifugal force and resonant vibration. In this work, the air supply part of the thrust bearing was designed considering the bending stiffness of the bearing and the applied load. The rotating part of the thrust bearing was designed through finite element analysis considering the cutting forces during manufacturing as well as the static and dynamic characteristics under both the axial and con trifugal forces during high-speed rotation.

Robust design of a composite air spindle

Abstract: If the spindle shaft of an air spindle system is made of high-stiffness carbon fiber composite material, the spindle system will be dynamically robust because the maximum rotating speed of a spindle (or rotor) system is usually restricted by the critical whirling vibration frequency of the spindle shaft, which is proportional to (EI/m) 0.5 (E: Young's modulus, I: 2nd moment of inertia of shaft cross section, and m: mass per unit length of spindle). In this paper, a composite air spindle system composed of a high-modulus carbon fiber composite shaft, powder-containing epoxy composite squirrel cage rotor, and aluminum tool holder is introduced. For the optimal design of the composite air spindle system, the stacking sequence and thickness of the composite shaft were determined by considering the fundamental natural frequency and deformation of the system. Then the dynamic characteristics of the composite spindle system were compared with those of a conventional steel air spindle system.

Design and Manufacture of Composite High Speed machine Tool Structures

Abstract: Abstract The high transfer speed as well as the high cutting speed of machine tools is important for the productivity improvement in the fabrication of molds/dies because non-machining time, called the air-cutting-time, amounts to 70% of total machining time with complex shape products. One of the primary reasons for low productivity is large mass of the moving parts of machine tools, which cannot afford high acceleration and deceleration encountered during operation. Moreover, the vibrations of the machine tool structure are among the other causes that restrict high speed operations. In this paper, the slides of high speed CNC milling machines were designed with fiber reinforced composite materials to overcome this limitation. The vertical and horizontal slides of a large CNC machine were manufactured by joining high-modulus carbon-fiber epoxy composite sandwiches to welded steel structures using adhesives and bolts. These composite structures reduced the weight of the vertical and horizontal slides by 34% and 26%, respectively, and increased damping by 1.5–5.7 times without sacrificing the stiffness. Without much tuning, this machine had a positional accuracy of ±5 μm per 300 mm of the slide displacement.