Diamonds Advance Composites Drilling

Carbon fiber reinforced polymers (CFRP), alone or stacked with titanium and aluminum plates, are widely used in aerospace industries worldwide for their high strength weight ratio and stable material properties in demanding environments. Boeing’s Dreamliner 787, for example, has 80% composites by volume, equivalent to 50% of its weight, eliminating 1,500 aluminum sheets and up to 50,000 fasteners. This achieves 20% better fuel efficiency compared to the Boeing 767. Currently, connection technologies such as gluing or welding are still under question, so fixturing with rivets is still a dominating practice. Due to the substantially different mechanical properties of carbon fibers and metals, drilling fastener holes efficiently challenges cutting tools by requiring high wear resistance as well as optimum tool geometries.

Poly-crystalline diamond (PCD) shows great potential for improving machining efficiency compared with traditional tungsten-carbide cutting tools in machining advanced aerospace materials. Brazed PCD drills are being developed and offered by some leading metal cutting tool manufacturers. Such tools combine the PCD as the cutting edges onto a solid carbide drill body. The carbide drill body provides the rigidity and the dimensional accuracy to maintain hole qualities while enabling spiral internal coolant holes and helical flutes to improve cooling and chip evacuation necessary for drilling. The functional cutting edges are PCD, which provides the wear resistance to enhance machining efficiency.

Optimum tool design is critical to generate good hole quality in machining advanced aerospace composites. Many essential factors in the course of tool dimensional design play important roles in affecting hole qualities, such as sharper edge radius and larger rake angle to generate lower cutting forces. Other factors include a smaller point angle to reduce thrust force and fiber delamination, and optimized edge design to improve burr height control. Machine tools, spindle and setup rigidity, tool adaptor, internal or flood coolant, and workpiece materials that the drill enters and exits are also important factors to be considered in tool design. In many cases, customized tools are required to meet various customers’ needs in a timely manner.

From: http://www.onlineamd.com/amd0214-machining-poly-crystalline-diamonds.aspx