Publication: Tool conditioning monitoring using vibration and acoustic detection for composite drilling application
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Date
2023-07
Authors
Kang, Zhi Wei
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Abstract
Drilling operations on Carbon Fiber Reinforced Plastics (CFRP) and Glass fibre reinforced polymers (GFRP) have become crucial in the aerospace industry. Tool wear is the most unfavourable aspect of machining processes because it severely affects tool life, which is crucial in metal cutting due to its direct influence on the dimensional accuracy and surface quality of the machined surface as well as the economics of machining operations. Tool condition monitoring (TCM) systems are widely sought after for drilling operations in the aircraft manufacturing industry because of the poor machinability of composite materials. In order to prevent the composite material from being harmed by a blunt drill bit, it is crucial to promptly change the drill bit. As a result, the TCM system offers a convenient method for tracking, managing, and optimising the use of drill bits which will indirectly raise machining quality. According to a variety of different perspectives, the drill bits are currently disposed of in the industries after a specific number of cycles. Some of the drill bits that can still produce holes without delamination even after being used for a certain number of cycles are wasted. Researchers have conducted numerous experiments to link tool wear with process variables including cutting force, thrust force, vibrations, spindle current, acoustic emission and etc. in order to monitor the tools' state. In this study, the impact of drill bit sharpness on air drill vibrations, sound generated during drilling and hole quality will be investigated. To quantify the vibrations of the air drill in this experiment, three accelerometers were fastened to the spindle, the center and a place close to the handle. The sounds made throughout the drilling operation were recorded using a microphone that was situated about a meter distance from the jig. The air drill's vibrations and the sound it makes while drilling under various drill bit conditions are analysed and contrasted. The result demonstrates that vibrations detected by an accelerometer placed closest to the spindle are more responsive to changes in drill bit condition. For CFRP plates, the maximum air drill vibration amplitude increases from sharp to no drill bit to dull to chipped off. For GFRP plates, the maximum air drill vibration amplitude goes from no drill bit to blunt to chipped off to sharp. In addition, the rapid Fourier Transform of the vibration signals from this accelerometer reveals the existence of a distinct collection of frequencies with notable peaks under various drill bit conditions. During
CFRP plate drilling, the maximum amplitude of air drill vibration increases with drill bit condition, from sharp to no drill bit, dull to chipped off. However, while drilling GFRP plates, the air drill's maximum vibratory amplitude increases in the following order: no drill bit, dull, chipped off, and sharp.