Advanced aerospace engine production: expertise and manufacturing methods

December 4, 2013 7:17 am

increasingly difficult-to-machine materials, complex geometries, exacting specifications and constant time restraints, the manufacture of aerospace parts has many limitations; still, production rates are set to increase
Aerospace is one of the most technically demanding industries in the world. With increasingly difficult-to-machine materials, complex geometries, exacting specifications and constant time restraints, the manufacture of aerospace parts has many limitations; still, production rates are set to increase.
Total component expertise is the key to success in such a competitive manufacturing landscape. These and other challenges dictate a production environment with complicated four- and five-axis machines driven by CAM solutions. Choosing an industry partner that has the experience and resources to support all aspects of individual component development, including both the physical tool and the processing knowledge is crucial in this highly competitive industry.
Total solution support should encompass spindle interface, tool holder selection, programming methods, insert grade and geometry, and surface integrity – all of the parameters that will produce the highest-quality parts. Aligning and optimising these factors will help you compete on a global scale.
A look at aero engine components The aerospace industry specifications, the nature of the materials and the component configurations all create some of the most challenging machining operations. These components are made up of some of the most difficult-to-cut materials and complex shapes, requiring extensive tool reach and the right tool path.
These high-temperature operations create demands for materials that are harder, stronger, tougher, stiffer and more resistant to corrosion or oxidation, such as nickel alloys, high-strength titanium, high-alloy steels and composites. These materials have much lower machinability than other, more common materials, and require a great deal of processing knowledge. You can optimise machining productivity with the right combination of cutting tools, cutting conditions and machine tools.
Engine components are demanding workpieces due to their complex geometries. They are often extremely large in size, with critical strength and weight restrictions. This is achieved with thin walls, intricate geometries, and complex shapes – all presenting new challenges in machinability.
Here we take a look at the machining challenges of certain aero engine components, and then show how combining the latest application and process knowledge with the best possible tooling solutions can be the key to success.
Component: Turbine DiscThe turbine disc is a complex turned part machined from difficult alloys such as Inconel 718, Waspalloy and Udimet 720. This component usually features profiled pockets with difficult clearance requirements.
Tooling Solution: The modular SL70 tooling systemDue to tough material, accessibility and productivity, round inserts offer the best method for both roughing and finishing. The large radius of these round inserts means a reduction in the entering angle without reducing the depth of cut, therefore increasing productivity. The modular SL70 tooling system is designed with blades to fit restricted pocket features without the need for special or modified tools. The range of adapters and blade alternatives for the tool gives it the flexibility to build many different tools from a limited tool inventory. These blades include the required radial and axial clearances for blades reaching deep into angled grooves with high-pressure coolant supplied through the tool to the cutting edge. Having built-in dampening for ensuring performance at extended tool reach, these blades turn features in deep grooves often at higher feed rates causing less vibration and increased tool life. In addition, the Coromant Capto interface provides excellent stiffness even in long overhangs and against high cutting forces.
Application: Trochoidal TurningTrochoidal turning is a productive method for removing material in deep slots and grooves. By breaking the part into manageable pieces, trochoidal turning uses a roll-into-cut approach to reduce engagement on the insert. When producing grooves by turning, chip evacuation is always a critical factor. Because the material is being highly sheared, generating narrow chips is often more demanding, and requires a balance between the most suitable insert geometry and feed rate. It also maximises straight line movements, which enables max feed rates for optimal productivity. This approach involves changing the cutting direction at the end of every pass. Alternating the direction of the cut makes the insert last longer because it never leaves the material. Trochoidal turning minimises chip jamming, vibration tendencies and residual stress, and is well suited to remove a large amount of material efficiently and securely. 
Component: Turbine CasingThe turbine casing is typically machined from challenging materials such as Inconel or Waspalloy. The structure of these components poses significant problems during milling due to the large amounts of material that must be removed. These components require a significant number of mill-turn and 5 axis operations to remove large amounts of material, resulting in very long cycle times.
Tooling Solution: Ceramic Grade CC6060Ceramic cutting tools have a much higher resistance to heat than carbide tools and have low reactivity with workpiece materials. Ceramic grade CC6060 is optimised for large-diameter components with long cutting lengths that allow it to cope with higher feed rates and longer continuous cuts, making it ideal for milling operations on turbine casing components. Excellent resistance to notch wear allows for higher depth of cut than other ceramic grades, for optimal productivity in medium to roughing operations in first- and intermediate-stage machining. The grade is also the first choice for pocketing and profiling operations.
Application: Ceramic turn milling between bossesOn average 75 per cent of the total turbine casing machining is spent on removing material using mill-turn operations between the bosses. Mill-turning involves cutting with a rotating milling tool while the workpiece is also rotating. This operation is ideal for turned parts that require high metal removal and have obstructions such as ignition bosses. Turbine casing bosses are located around its cylindrical perimeter. Turn-milling with ceramic inserts reduces notch wear, increases feed rates and achieves higher metal-removal rates – it is the most productive way to remove material between bosses.

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