Hole diameter variation and roundness in dry orbital drilling of CFRP/Ti stacks

The inevitable problem of machining accuracy that follows accelerated tool wear deters severely the drilling of carbon fiber reinforced plastics/titanium (CFRP/Ti) stacks and is attributed to the cutting mechanism inherent to drilling and drill geometry. This paper develops orbital drilling of this stacked material by use of a special cutter under a dry machining condition and analyzes the characteristics of the variation in hole diameter and roundness. The influence of spindle speed for both CFRP and Ti alloy segments, and the bore and tool diameter ratio on these indexes with progressive tool wear is further studied. The experimental results show that the hole diameter at the CFRP exit always maintained the maximum value; spindle speed when machining different segments can improve or decrease these hole accuracy indexes, and the ratio of bore and tool diameter has greater influence on the roundness of the CFRP layer than that of the Ti alloy layer.