Critical aerospace engine turbine fan blades and high-bypass turbines produce much of an aircraft’s forward thrust. In the past, precision-forged blades needed only light finishing operations to achieve the tolerances required. Today, with growing demand for greater fuel efficiency, tighter tolerances are required, and many manufacturers have responded by machining oversize forgings to final net shape.
Typically machined from titanium alloys, newer blade materials include aluminium and carbon-fibre composites. Carbon-fibre blades attach titanium leading edges to the relatively brittle composite material – a design element that minimises damage should an engine ingest foreign objects.
Titanium aluminide used for blades in the low-pressure sections of some new engines is brittle, but provides high heat resistance. Futuristic materials and the complex shapes required to securely unite them into a single turbine blade need equally futuristic machining processes, particularly when it comes to machine movement.
To meet the standards of aerospace manufacturers, the machine must also be able to produce a high-quality finished blade that requires minimal polishing and less bench work than a blade processed on a general application machine. GF Machining Solutions’ Liechti Turbomill 1400 g airfoil machining platform has been designed to handle these challenges. The machine’s configuration means that blades are clamped at each end and rotated between centres, while a milling tool performs cutting operations. This motion facilitates the creation of complex aerofoil contours, allowing the machine to perform heavy-duty roughing and dynamic finishing for the aerofoil, root form and shroud.
Complex profiles can be rapidly created on the leading and trailing edges of the blades that control airflow into the engine, while maintaining the tight tolerances that maximise fuel efficiency.
Acceleration and deceleration at 1 g generates significant force, strong enough to topple the machine if it is not securely anchored to the floor. The Liechti Turbomill 1400 g uses its large size, weight and rigidity to resist these forces. Machine ways are engineered with the strength to handle extreme momentum and inertia. The X axis moves via a linear drive, the Y and Z axes on ball screws, while direct-drive motors power the rotary B and A axes.
Aimed at OEMs and large tier-one manufacturers involved in high-volume turbine blade production, the Liechti Turbomill 1400 g is able to machine blades twice as fast as conventional or multi-purpose machines, says the company.
