Making the grade: Turning Performance

In addition to 5-axis machine tools, manufacturers of aerospace parts must have the appropriate cutting tools for an application to remain competitive. Rather than choosing a standard tool grade for the spectrum of materials being machined and sacrificing productivity, these manufacturers are benefiting from the increasing amount of material-specific grades toolmakers are developing.

Sandvik Coromant Co. is one of the toolmakers that “completely optimized tools” for specific workpiece materials and machining techniques, according to William Durow, global engineering project office manager for the Mebane, North Carolina, company. For example, the toolmaker engineers solid-carbide endmill grades with geometries designed for cutting titanium while following a trochoidal toolpath.

In addition, machining heat-resistant superalloys (HRSA) is common in aerospace applications but challenging, nonetheless. To assist when finishing nickel-base superalloys, Durow said Sandvik Coromant developed the S205 turning grade for indexable inserts. The inserts have a second-generation Inveio coating for high wear resistance and long tool life, and are enhanced with a post-treatment technology that alters mechanical properties, the company reports. The Inveio layer features tightly packed, unidirectional crystals, which create a strong protective barrier around the insert to maximize thermal protection, improve crater wear and better resist flank wear.

Sandvik Coromant developed the S205 grade for intermediate and last-stage turning of heat-resistant superalloy aerospace engine components. Image courtesy of Sandvik Coromant

Because cutting a HRSA sends heat back into the tool rather than being primarily carried away with the chips, HRSA-specific grades are harder than other grades, Durow added. With light DOCs typically employed, the grades also have sharper geometries to shear rather than rub the material, creating less heat at the tool/workpiece interface.

Also helping to dissipate heat is high-pressure coolant streamed through channels that are targeted directly where it’s needed, he notes. “If you have flood coolant, usually what happens is there’s so much heat generated in the cut, you’re just vaporizing coolant in the cutting zone. Also in some applications, it helps move the chip off the top of the insert, so you’ll avoid crater wear on the top of the insert.”

Not only can the workpiece material be difficult-to-machine, but features found in many aerospace components present challenges, Durow said. These include disks, blisks and IBRs. “If you think about the ton of machining that goes into those, any little issue is going to create a very expensive scrap part.”