Ceramic end mills help optimize aerospace component machining

With components made from nickel-based alloys becoming increasingly prevalent across the aerospace industry, the demand for optimized cutting tools continues to grow. For common operations such as shoulder and face milling, the machining of nickel-based materials remains challenging. Although offering excellent performances, these materials exhibit poor machinability due to their low thermal conductivity, the potential for adhering to cutting tools and the presence of abrasive particles within the alloy structure.

Due to these issues, productivity with carbide tools tends to be low. In addition, part complexity means that some components demand extended reach, while process flexibility is another factor high on the wish list of many aerospace manufacturers. Here, new ceramic end mill technology has emerged to help meet these requirements, offering the potential to optimize the machining of aero-engine parts and provide significant competitive gain.
There are many challenges facing those tasked with producing aerospace engine components. Most such parts are manufactured from HRSAs/nickel-based alloys, which place a particular set of demands on production engineers looking to manufacture components like spools, turbine disks, combustion casings and blisks.

Up to 30 times more speed

Although many manufacturers use conventional solid-carbide end mills, such tools have their limitations in terms of performance when it comes to nickel-based alloys. In a highly competitive global arena, aerospace machine shops are looking for next-level technologies capable of delivering a step-change in factors such as productivity and/or tool life. Ceramic end mills can provide that very leap, offering up to 20-30 times more machining speed in comparison with solid-carbide tools for operations such as shoulder and face milling. Such impressive gains can be achieved largely because ceramic cutters retain their hardness at the high temperatures which arise when machining nickel-based alloys.

The brazed ceramic CoroMill® 316 exchangeable-head end mill for roughing operations is a productive solution for aerospace engine applications in ISO S materials. In the first instance, the exchangeable head concept facilitates inherent process flexibility. Available is a six-flute version with a straight corner radius that delivers highly productive side milling operations, and a four-flute version designed to boost face milling thanks to its high-feed face geometry.

The brazed ceramic CoroMill 316 end mill is optimal for difficult reachability conditions, or to take advantage of the exchangeable head system flexibility.

The ceramic substrate of the end mills allows for a different cutting process in comparison with traditional solid-carbide tools. Importantly, the unique S1KU SiAlON grade is purpose-designed for the superior machining of nickel alloys, and is supported by negative geometry that provides a tough cutting edge. The latter also features a T-land for stable operations.

SiAlON carries a chemical composition of aluminium oxide and silicon nitride (Al203+Si3N4), a combination that promotes high wear resistance, even at elevated temperatures.

Stable machining

A stable set-up is advised in all cases, and always without coolant application; machine shops should use pressurized air instead as coolant would simply burn at the high temperatures involved. In addition, the use of coolant promotes thermal shocks and has a negative effect on tool life. Importantly, high spindle speeds are required, of at least 13000 rpm. Further recommendations include the use of down milling, as well as a programmed tool path that keeps the tool in constant contact with the material.

Good chip evacuation

High cutting speed increases the cutting temperature, making the chips highly sheared. In fact, the process generates dust-like chips, which is good for chip evacuation using pressurized air.

Ceramic end mills retain their hardness at the high temperatures which arise when machining HRSA materials, making them especially suitable for blade machining of aerospace blisks.

No white layer

Of particular note, no white layer formation has been observed when using the ceramic end mills from Sandvik Coromant. Tests have been conducted for a wide range of cutting speeds between 375 and 900 m/min (1230 to 2953 ft/min) without any evidence of this unwanted effect. White layer, which is thought to encourage cracks, is associated with temperature created on the surface of a workpiece followed by quick cooling.

Beyond shoulder milling and face milling, the ceramic end mills can also be used for pocket milling, helical interpolation, ramping and slot milling. CoroMill 316 is part of the Sandvik Coromant Optimized solutions offer within the company’s solid round tools range.

The CoroMill 316 Ceramic ball nose end mill has a brazed ceramic on carbide interface, which provides both strength and flexibility, and the ball nose geometry ensures an easier, faster profiling.

The series also includes a ceramic ball-nose version of CoroMill 316 for blisk machining. This profile-milling solution is suitable for both roughing and finishing operations.