Aerofoil machining and polishing combined into a single automated process

Citation

(2004), "Aerofoil machining and polishing combined into a single automated process", Aircraft Engineering and Aerospace Technology, Vol. 76 No. 5. https://doi.org/10.1108/aeat.2004.12776eab.005

Aerofoil machining and polishing combined into a single automated process

Aerofoil machining and polishing combined into a single automated process

Keywords: Machining, Aerospace industry, Aerospace technology

An innovative demonstration of “on-the-fly”, adaptive five-axis reverse-engineering and machining of complex aerospace compressor blades were demonstrated at the recent Famborough Air Show following the high technology partnership established between StarragHeckert UK of Brackley and TTL of Aylesbury.

The combination of TTL's adaptive machining technology and StarragHeckert's expertise in multi-axis machining of complex forms is said to enable blade reprocessing time to be cut by half, with production of a more consistent aerofoil surface. This process technology will now be applied to a wide range of industry applications including gas turbine, blisk, impeller and nozzle guide vane repair, compressor blade and turbine component machining.

On the joint exhibition stand, TTL demonstrated how the geometric data of the component involving topography, twist and angle, is captured from the aerofoil surface of a refurbished welded compressor blade. This is achieved using a touch-trigger probe on the latest StarragHeckert STC 100 Dixieland high speed 40,000 revs/min, five-axis vertical machining centre. The machining program is then prepared through TTL's adaptive machining software and the blade re-machined and polished in a single hands-off automated cycle.

Normally inconel 718 and titanium components that have been reclaimed by weld build-up on the blade tips are fettled and polished by hand in a bid to restore a technically acceptable aerofoil profile. However, this process has numerous drawbacks, which TTL has addressed, such as total lack of consistency from blade to blade, health and safety issues attributed to repetitive strain injury and “white finger” problems experienced by the highly skilled manual operators. In addition, aircraft engine “off-wing” time has become an increasingly key issue in the industry.

TTL believes that through its adaptive machining techniques, the reverse engineering process can be performed with less likelihood of scrap or rejected blades. And, by eliminating inconsistency from blade to blade, quality and performance issues are addressed with the ability to re-machine within a tolerance window of 0.03 mm. The company states that the complete re-machining and polishing cycle, depending on the size of the component, can be completed in as little as 8 min which provides a significant saving in cycle time against traditional manual techniques.

In the demonstration, TTL's process used a laptop computer to take over the executive control of the Heidenhain/TNC 530 control system on the STC 100 machining centre via ethernet connection. This established the desired protocol transfer program, incorporates tool data and remotely communicates the variables derived from the component.

The infrared touch-trigger probe captures the topography of the blade to be processed and presents the scanned information for the software to calculate the “best fit” and relative datum position to the root form of the blade.

From the data captured, an individual five-axis toolpath is generated through TTL developed algorithms using parametric techniques that can be utilised for both milling and final polishing in the same floor-to-floor production cycle. Incorporated within the process program is the precise control over speed from the 8kW, 40,000 revs/min STC 100 spindle and axis feed rates to ensure the correct pressure and oscillation rates of the abrasive grinding wheel during final polishing. Following the single-cycle scanning, machining and final polishing process, the component is ready for any subsequent processing.

Key elements in the construction of the StarragHeckert STC 100, allowing the combined machining process, is its inherent rigidity and stability through the monobloc machine bed, with moving column and longitudinal slide which fully supports the vertical slideway and headstock. It has an X-axis stroke of 400 mm, Y-axis of 220 mm and Z-axis of 350 mm. A 360° rotary table creates the A-axis and a separate swivel axis enables +110°-15° movement. This is all achieved within a compact floor space requirement of 2.1 m by 1.65 m and the process can be further automated with an integrated multiple pallet and fixturing set up.

Details available from: StarragHeckert UK Ltd. Tel: +44 (0) 1280 705482; E-mail: sales@starraaheckert.co.uk; Web site: www.starragheckert.co.uk; and TTL. Tel: +44 (0) 1296 395215; Web site: www.ttl-solutions.com