Aerospace: Taking flight: Drilling Performance

Mission-critical aerospace components, such as engine and landing gear parts, turbines and blisks, must be made from materials that can withstand extreme temperature and stress. Those workpiece materials include heat-resistant superalloys and titanium alloys, whose composition and properties make them effective for demanding applications but also create challenges when machining them.

One requirement when machining superalloys and titanium is adequately pulling heat from the cutting zone, said Bill Durow, manager of global engineering for aerospace at Sandvik Coromant Co. in Mebane, North Carolina.

High-pressure coolant helps achieve that need because just applying a stream of coolant or flooding the zone with coolant is insufficient. Creating a parallel hydrolaminar flow with high-speed, high-pressure coolant also can assist with chip formation, said Brent Godfrey, machine integration product specialist at Sandvik Coromant.

“When the coolant nozzle is positioned correctly on the cutting tool,” he said, “you can get the flow of coolant to act almost like a power wedge to curl the chip and help to mechanically break the chip in some materials. In materials like titanium, you can effectively break chips with high-pressure coolant, which is a good problem-solver on those materials.”

Machining aerospace materials can be difficult, but tools and techniques are available to help. Image courtesy of Sandvik Coromant

The minimum pressure on a standard high-pressure pump on many machine tools is about 69 bar (1,000 psi), Godfrey said, but pumps are available, such as on some vertical lathes, that go to 172 to 207 bar (2,500 to 3,000 psi).

The tool manufacturer reports that when it developed the first version of the Jetbreak high-pressure coolant system several decades ago, the Coromant Capto modular quick-change tooling system was the basis for that development and was designed with an internal coolant supply for pressures up to 138 bar (2,000 psi). Coromant Capto is a machine tool interface with a tapered polygon design that transmits torque.

Godfrey explained that Capto’s self-centering coupling proves beneficial when machining aerospace materials.

“You just mount it into the tooling block and align the polygon to the other polygon that’s in the tooling block,” he said, “and the clamping unit and cutting edge is on center right away.”

Durow added that the high level of repeatability for the modular quick-change system is essential for efficiently machining aerospace parts.

“Just taking the tool out, for instance, is an easy plug-in place for customers,” he said, “especially when they deal with highly critical, highly valuable components.”

Another major benefit of the modular system is that it provides a significant amount of pull force on the cutting tool, Godfrey said, noting that a Capto tool has a ground contact face and the polygon to provide two methods of contact for the coupling.

“It translates to very high rigidity, very high strength, very good bending stiffness of the cutting tool,” he said.

Cutting tool geometries, including a positive cutting geometry and a comparatively open chipbreaker on indexable inserts, play a substantial role when machining exotic metals for aerospace parts.

“We have geometries specific for aerospace materials with special chipbreakers on them that are also designed to handle the high-pressure coolant,” Godfrey said.

In addition, Durow said the toolmaker designs the insert top geometry expressly for aerospace materials.