This paper focuses on the effect of the drill geometry on the drilling of woven Carbon Fiber Reinforced Polymer composite (CFRPs). Although different geometrical effects can be considered in drilling CFRPs, the present work focuses on the influence of point angle and wear because they are the important factors influencing hole quality and machining forces. Surface quality was evaluated in terms of delamination and superficial defects. Three different point angles were tested representative of the geometries commonly used in the industry. Two wear modes were considered, being representative of the wear patterns commonly observed when drilling CFRPs: flank wear and honed cutting edge. It was found that the crossed influence of the point angle and wear were significant to the thrust force. Delamination at the hole entry and exit showed opposite trends with the change of geometry. Also, cutting parameters were checked showing the feed’s dominant influence on surface damage.
This paper focuses on the analysis of tool wear mechanisms in finishing turning of Inconel 718, one of the most used Ni alloys, both in wet and dry cutting. Cemented carbides, ceramics and CBN tools are suitable for machining Ni alloys; coated carbide tools are competitive for machining operations of Ni alloys and widely used in industry. Commercial coated carbide tools (multilayer coating TiAl/ TiAlN recommended for machining Ni alloys) were studied in this work. The feasibility of two inserts tested for dry cutting of Inconel 718 has been shown in the work. Experimental test were performed in order to analyze wear patterns evolution. It was found great influence of side cutting edge angle in tool wear mode.
A fast fiber-optic two-color pyrometer operating on the optical communication bands is designed for temperature measurements in machining processes. Off-the-shelf low-loss fiber-optic demultiplexers and optoelectronics equipment are used in order to obtain a cost-effective sensing solution while reducing both the temperature measurement error and the minimum measurable temperature. The system is capable of measuring highly localized temperatures without using collimation lens. The designed pyrom-eter allows measuring temperature in the range from 300 to 650 °C, achieving a full-scale temperature error as low as 4%. Factors in-fluencing the temperature measurements are studied in order to identify the sensor limitations, such as a possible damage on the end of the optical fiber, the spectral loss attenuation and responsivity, or the distance between the fiber end and the target. Finally, this pyrometer is applied in a turning process, using a fiber-optic sensor embedded on a standard tool holder. Temperature measurements on the Inconel 718 are reported showing a good agreement with the simulations.
This paper focuses on the influence of the step drill bit geometry on the damage induced during drilling Carbon Fiber Reinforced Polymer materials (CFRPs).Step geometry designed with the aim of avoiding composite damage in CFRPs drilling, is compared to conventional twist configuration. Despite the reduction of thrust force and torque observed when using the step drill, the delamination was only reduced at low feed rates. A numerical model developed for the step geometry was validated with experimental data demonstrating its ability to predict thrust force and delamination for different values of feed rate and cutting speed. Numerical model allowed the development of a parametrical study. Finally, using a response surface methodology a mechanistic model and surface diagrams have been presented in order to help in the selection of optimum variables minimizing drilling induced damage.
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