Evaluation of drill bit performance for carbon-fiber composites
Ever since composite materials have been used in the aerospace industry, there have been problems with cutting and machining them. One of the reasons for this problem was the dearth of available tooling to machine composites. As research in composites progressed and as composites found wide application in the aerospace industry, efforts have been made to develop good and efficient tools to machine them. Nevertheless, this effort is still ongoing to develop better tools, as the problems faced during machining have not been totally eliminated. Of the different machining operations performed on composite materials, drilling is the most common. The major problems faced during the drilling of composite materials are delamination and fibers pull out. Delamination reduces the strength of the composite. Another problem that persists is the effect of excess cutting temperatures on the quality of the drilled hole. Excess cutting temperatures affect the dimensional accuracy of the drilled hole and deteriorate its surface finish. Excess cutting temperatures during drilling may melt the matrix and char the drilled hole. Research and experiments conducted on drilling of composite materials have shown that as the cutting edges of the drill bit wear out, the heat generated and the thrust force produced increases. Increase in thrust force gives rise to delamination. Also tool geometry plays a big role in producing a hole with an acceptable quality. Hence, it is important to thoroughly investigate the performance of the drill bit in terms of producing a good hole quality. The objective of this research work was to evaluate the performance of drill bits when drilling carbon-fiber composites. Drill bits were evaluated for temperature, Hole oversize, surface roughness, roundness, thrust force, torque, damage area, and tool wear. By conducting experiments using different drill bits, the drill bit performance was determined for every parameter in question. Based on the results of these experiments, it was possible to determine which drill bit performs optimally for the different parameters investigated in this research work. Also by evaluating the Hole oversize, roundness, and surface roughness, it was be possible to study the effect of speed and feed rate on these parameters. Also tool wear analysis was carried out as a part of this research work.
Wichita State University, College of Engineering, Dept. of Mechanical Engineering
Includes bibliographic references (leaves 167-169)