Calibrated Heat Flow Model for Determining the Heat Conduction Losses in Laser Cutting of CFRP
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Laser machining has great potential regarding automation in fabrication of CFRP (carbon-fiber-reinforced plastics) parts, due to the nearly force and tool-wear free processing at high process speeds. The high vaporization temperatures and the large heat conductivity of the carbon fibers lead to a large heat transport into the sample. This causes the formation of a heat-affected zone and a decrease of the process speed. In the present paper,an analytical heat flow model was adapted in order to understand and investigate the heat conduction losses. Thermal sensors were embedded in samples at different distances from the kerf to fit the calculated to the measured temperatures. Heat conduction losses of up to 30% of the laser power were determined. Furthermore, the energy not absorbed by the sample, the energy for sublimating the composite material in the kerf, the energy for the formation of the HAZ, and the residual heat in the sample are compared in an energy balance.Keywords:
Vaporization
The lifetime curves of a single droplet impinging on heated surfaces of ceramics and stainless steel were investigated. The experiments were carried out while concentrating mainly on the temperature region in which the time for vaporization could be shortened. We observed and examined thoroughly the behavior of the droplet, taking photographs with a 16 mm high-speed camera and recording on videotapes. For materials such as ceramics having low thermal conductivity and a characteristic surface, the vaporization modes were different from those on stainless steel or other metal surfaces. The significant difference between them was in the existence of the wide temperature range yielding minimum vaporization times and short lifetimes. The ceramic surface facilitates rapid vaporization of a droplet over a wide temperature range.
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Thermal conductivity measurement
Thermal effusivity
Volumetric heat capacity
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Vaporization
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The mechanism for the vaporization of ZnO from powders of (Zn0.2Co0.8)O⋅1.1Al2O3 and (Zn0.2Ni0.8)O⋅1.1Al2O3 spinels was studied at 1335° to 1500°C in vacuum of 3×10-5 to 10-4 Torr. The vaporization of ZnO occurred in two stages-vaporization of constant rate at the first stage and of decreasing rate at the second stage. The observed fractions of ZnO vaporized deviated from the calculated values at higher temperatures. The results were interpreted with the assumption that the exsoluted corundum layer at the powder surface sintered more densely at higher temperatures causing the decrease in vaporization surface area. The ratio of the concentration of ZnO at the surface to the initial concentration at the time the vaporization mechanism changed from the first to the second stage was approximately 0.9 and independent of temperature.
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Vaporization
Thermogravimetric analysis
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Abstract Abstract – Adiabatic spray vaporization is investigated by analyzing the coupled problem of the vaporization of an ensemble of droplets in a gaseous medium whose properties are continuously being modified by the vaporization process. A criterion on the mixture properties for achieving complete spray vaporization is established. By further showing that the droplet emperature rapidly approaches a constant, characteristic, value after vaporization is initiated, simplified solutions are obtained for the transport of monodisperse, as well as polydisperse, sprays in quasi-one-dimensional chambers.
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Anisotropic solids possess thermal conductivities ranging from among the highest found in nature, as in the in-plane thermal conductivity of graphite, to the lowest, as in the cross-plane thermal conductivity of disordered layered crystals. Though these extremes of thermal conductivity make anisotropic materials attractive for diverse applications such as thermal management and thermal insulation, the microscopic physics of heat conduction in these materials remain poorly understood. In this review article, we discuss the recent advances in our understanding of thermal phonon transport in anisotropic solids obtained using new theoretical, computational, and experimental tools.
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