Drilling of Composite Material Using Vibration

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Composite materials are used in many structures since there are high strong-to-weight ratio and easy formational. Composite materials are usually assembled and joined together for large size structure. Therefore, secondary machining process such as drilling, sawing etc. are often required for assembling and joining composite components. When composite materials are machined, delamination occurs at adhesive layer between laminated layers. It is required to prevent delamination during machining in industry. From view point of vibration, it is possible to cut hard materials using relatively small vibrational load during cutting and to improve precision of machined surface. However, study on cutting composite material using vibrational load has not been published.In this study, preventing method of delamination of composite material during drilling using vibration is proposed. In this method, it is enough to generate small vibrational load and to use small shaker or ultrasonic vibrator. He … More nce, the proposed method is expected to be practical.First, the proposed method is examined by some experiments. Composite material is supported onto the supporting device and shaken during drilling using a small shaker. For some conditions of excitation frequencies, tool materials, tool diameters and tool revolutions, occurrence of delamination is measured. Excitation frequencies are determined by considering frequency response function of the specimen. The power spectral density function of response of the specimen subjected to white noise excitation is measured. Frequencies at which power spectral density function has peaks are chosen as excitation frequencies. For comparison, some specimens are machined without vibrational load. Delamination is examined by surface roughness of machined surface. After drilling, the specimens are cut by a diamond cutter through center of holes. Center line average height roughness of machined surface is measured.From the experiments, it is found that surface roughness of composite material machined with vibration is less than that without vibration for many conditions for each condition. Hence, when composite materials are machined with vibration, occurrence of delamination becomes less.Finally, results of experiments are examined by a theoretical method. Adhesive layer is considered to be damping component. Dissipated energy in adhesive layer is obtained and condition where delamination occurs is derived. Less