An experimental investigation into tool wear in micro-drilling of aluminium, aluminium/copper metal alloys and carbon fibre reinforced composites

Abstract

Limitation of conventional machining equipment has become a growing concern over the past two decades due to the demands for greater machining accuracy in today’s manufacturing. The development of micro-machining has therefore attracted significant attention; it signifies the advancement of national economy as well as the level of accuracy manufacturing industry could achieve. While the connection between tool lifespan, cost of machining and throughput is well established, the factor of tool lifespan appears to have more significance since the miniaturization of tool could lead to further performance concerns such as its lack of strength and durability. On the other hand, raising feed rate and spindle rotation speed are the two common approaches for increasing manufacturing throughput. Such approaches tend to cause an increase in the thrust force subjecting the tool to greater stress, which is the main cause of tool wear and even tool failure. Through literature review and preliminary experiments, it was found that spot-drill is often done prior to micro-drilling since it prepares a pre-drill countersunk hole that helps the alignment of tool for subsequent micro-drilling. Although such pre-drill step does improve the micro-drilling operation, the fundamental issue of tool diameter difference still remains. Often the tool used for pre-drill has a bigger diameter than the one for micro-drilling although a significant difference is always something to be avoided. This is because the difference has to be picked up by the tool used for micro-drilling and is directly linked to the wear caused by increased thrust force. In this research the operation of micro-drilling is investigated via mathematical models. Such operation is further broken down into various steps and stages so more detailed description can be achieved. The findings are then further enhanced by simulation based on the 3D model of micro-drilling. Three materials were selected for this research: Al 6061T, Al/Cu metal alloy panel and Carbon fibre reinforced composites. Such a selection enables the study of individual characteristics of different materials and the variation in respective thrust forces. Finally, Conclusions present the summary of the main findings from micro-drilling process analysis based on research and investigation shown in earlier chapters. By combining actual measurements on micro-drilling and mathematic model this research hopefully would improve the understanding towards micro-drilling processes.