Supplying thrust for the future

Aero engine designers and manufacturers face a number of challenges when it comes to supplying the latest components. There is the constant demand from OEMs and airlines to produce more fuel efficient, reliable engines, ever tightening environmental initiatives, such as Clean Sky 2 to reduce noise and pollution emissions and added to this predicted ramp up rates, particularly in the civil sector, meaning more rapid methods of production are required throughout the supply chain.

François Arrien (pictured top) is vice-president for business development at Canadian robotic finishing specialist AV&R Aerospace. The company is a leading developer of automated technology designed to increase the production of turbine blades/vanes in aero engines.

He believes there are still areas where engine design can achieve efficiencies but new manufacturing technologies will have to be implemented to achieve them.

“Increasing fuel burn efficiency allows a significant reduction of CO₂ and NOx emissions and represents tremendous fuel savings for airlines. One of the main methods to achieve this goal is to improve aerodynamics on compressor blades and vanes by using more complex 3D shapes and tighter tolerances on leading and trailing elliptical edges. Tolerances on newer engines are around 37μm and are planned to go to 25μm. With these new requirements manual profiling is no longer sustainable. Aspects such as labour costs reduction, difficulty to find skilled operators and eliminating injuries also point to automating this operation.”

Peter Smith CEO and chairman of the UK's Nasmyth Group, which produces many parts for the aerospace industry, believes longer term more radical design solutions may be required.

“Clean Sky and new developments in Clean Sky 2 appear to be hitting the mark and delivering results on Low Pressure Ratio Fan/Variable area fan nozzles, Low Weight/Low Drag fixed or rotating structures, nacelles and high power gearbox. If we are focusing on reducing CO₂, NOx and noise emissions then we should be working on hybrid engines, if not 100% electrically powered.”

Metal matters 

Leaner and consequently hotter engines of the future will demand new sophisticated heat resistant super alloys (HRSA) with new machining challenges. Smith is also conscious that costs will be a major consideration.

“HRSA fall into three groups, nickel-based, iron-based and cobalt-based. The physical properties and machining behaviour of each varies considerably, due both to the chemical nature of the alloy and the precise metallurgical processing it receives during manufacture. Whether the metal is annealed or aged is particularly influential on the subsequent machining properties. Alloys designed to reduce the use of rhenium, a rare metal that has increased tenfold in price in recent years as demand has increased, will be a likely next step. Advances in coatings utilising Plasma APS and EB-PVD are intended to provide improved wear resistance in the engine.”

So what are the challenges when it comes to machining and working with advanced alloy materials, particularly when it comes to increasing cutting tool life?

Smith continues: “All machine shops should have a real time coolant management system. Alkaline levels, PH testing, bacteria content and oil/water percentage mix are critical to the life of cutters whilst machining harder materials. Nasmyth Group has on-site testing to check all of the above criteria.

“The cutting tool industry has a huge part to play in the development of new coatings. Titanium Nitride coatings and in particular ceramic inserts are playing a vital role in prolonging tool life. Further developments are however still required to match the desire of design engineers to run and develop hotter engines and hence use more exotic materials. Other improvements that are becoming more prevalent are the use of specific CAD/CAM strategies designed for harder materials.

“Additionally Viper grinding in particular has led the way in multi-axis grinding with fir tree grinding and profile grinding becoming the norm.”

Both Smith and Arrien believe that automation and robotics will have an increasing role in aero engine manufacturing as demand continues to rise.

“If we consider high volume blades or larger components a Flexible Manufacturing System (FMS) process is required,” Smith says. “The robot can utilise a rail system to move in between the machines to deliver the parts if numerous machines are in operation, or a pallet transfer FMS can be introduced that negates the need for robotics.

“World class FMS systems can expect to achieve 98% uptime when truly optimised, compare this to traditional efficiencies where 75% would be considered amongst the best performers.”

When it comes to the specific field of blade profiling Arrien explains: “Besides the fact that robotic systems can work 24/7, precision levels required by new jet engine designs are not attainable manually. Using robots, AV&R Aerospace's automated blade edge profiling system creates high precision elliptical profiles on blades and variable vanes. To achieve these tight tolerances, AV&R's systems use adaptive and closed-loop capabilities coupled with final leading and trailing edge inspection. On turbine blades, these technologies can also blend the casting injection pins and polish the blades. This system is a perfect example of automation allowing jet engine manufacturers to achieve the precision levels required by new environmental initiatives and reducing labour costs.”

Coping with composites 

So how do developments such as composite/titanium fan blades impact on the manufacturing process?

“Automation suppliers will have to adjust their technologies to the new materials used in jet engines,” Arrien continues. “Titanium leading edges for composite fan blades require long amounts of manual polishing operations. We have developed a titanium polishing robotic solution to do this operation automatically with much more repeatability.”

Smith believes composites have their advantages but these may not apply to every component.

“A composite engine casing reduces weight by up to 1,500lb per aircraft, the equivalent of carrying seven more passengers at no cost. However, the impact on utilising composites in large volumes is not as ‘easy' as first predicted. It is yet to be proven if high volumes on large products can meet the demand.

“Without doubt traditional blade manufactures will have to evolve and change with new manufacturing techniques and perhaps undertake a relatively lengthy learning curve.”

Aero engines, although reliable, demand expensive servicing and MRO costs that will need to be kept to a minimum in future for highly cost conscious airline operators.

Smith observes: “New and improved alloys, coatings, improved quality of product through improved machining and tooling strategies, moving away from welding and fabrication towards one piece manufacturing add to extending service intervals. With Finite Element Analysis software to underpin the designer's theories, engineers can predict with greater accuracy the failure rate or life of any given part.”

AV&R Aerospace's technology specifically means that longer turbine and fan blade life can be achieved during engine overhauls.

“Our automated profiling system is a natural fit to address the high levels of variations found in MRO parts,” Arrien explains. “Today, MRO compressor blades are mostly blended and re-profiled manually. By using an adaptive robotic system instead, the robot will greatly improve the aerodynamics of the blade. Better aerodynamics reduces turbulences around the blade increasing its life. Since the profiling system only removes the minimum amount of material required, it also reduces significantly the number of blades scrapped during manual repair.”

I ask what impact the much lauded additive manufacturing (AM) process will have on engine production.

“Additive manufacturing has the advantage to create complex 3D shapes within very high precision, but unfortunately it generates poor surface finish,” Arrien notes. “During manual polishing operations, the operator improves the surface finish but often compromises the shape of the part. By its consistency a robotic polishing system can polish without compromising the shape done by the additive process.”

Smith concludes: “For the next five years, additive manufacturing has a small part to play in the rotative area of the engine. However, certification is problematic because of the issues surrounding the powder from which the parts are sintered; with the manufactures struggling to produce identical sized particles that are free from inclusions that in turn reduce the standard and accuracy of each individual part.

“The future for traditional subtractive manufacturing must be based on improved performance, faster removal rates - based on improved software technology, (CAD/CAM) improved feeds and speeds through motion enhancements, digital technology regarding feedback units, look ahead speed and processing speed of controllers.

“I predict casting will come under a greater pressure from AM compared to precision machining. Difficult and complex shapes lend themselves to casting and this is also an area where AM excels.”

www.nasmythgroup.com

www.avr-aerospace.com