Newest designs will run hotter, burn cleaner for fuel efficiency, limit carbon emissions
By Jim Lorincz
There’s nothing like a healthy commercial aviation industry to spur capital investment, expand one of the most successful US export product categories and challenge engine designers to increase fuel efficiency and reduce air-polluting carbon emissions. Recent studies indicate that profitability of the airlines (in years when there is any) can be traced to controlling fuel costs in a wildly fluctuating oil market. The airline industry could face the very real threat that landing fees in the world’s major metropolises could be charged based on carbon emissions, which can be measured in tons per round trip per airliner.
The challenges of fuel efficiency and emission control have been clear enough to send the major engine manufacturers back to their CAD station drawing screens to develop new innovative and efficient engine designs featuring heat-resistant materials that can operate at higher temperatures. Engine programs like the CFM LEAP engine and Pratt & Whitney Pure Power Geared Turbo Fan engine are being developed for retrofitting on Boeing 737 and Airbus A 320 airliners, as well as being installed on the new Airbus A 320neo and the Boeing 737 MAX airliners.
“These new programs involve all-new components, new designs and new strategies for fuel efficiencies in operation,” said Scott Walker, president, Mitsui Seiki (USA) Inc. (Franklin Lakes, NJ). “The Pratt & Whitney gear fan strategy is designed to use high-nickel base alloys for hot stage components and make the engine diameter smaller, make it burn hotter, and drive the fan with a planetary gear system that’s more efficient at slower speeds. The LEAP strategy is to make the hot and cold stage components smaller in diameter and run them hotter and faster, using a totally new proprietary blade design.
How Much Machining Capacity Will Be Needed?
A good question might be how many spindles are going to be required and purchased for machining integrally bladed rotors (IBR) and blisks (bladed disk) and related components required for the engine programs. The answer is a substantial number with capital investment outlay for high-precision five-axis machining centers topping an estimated $100 million for these engine programs alone. That doesn’t even take into account the impact of the Boeing 787 and Airbus A380 and A350 programs that are already well underway.
As much as 40% of the engine machining is going to be outsourced to a supply chain that is quietly consolidating. “What I see happening is that the large Tier 1 public companies have been on a buying spree, acquiring second-tier shops, putting them in the position to go to an OEM and say they can do it all, supply the castings, materials, do the machining, and ship assemblies with all the tools needed to complete the job in assembly,” said Walker. “It’s JIT, almost like automotive assembly. The comment that I often hear: ‘I don’t need parts faster, I need them at a consistent production rate’ sounds just like the automotive industry. At Boeing, for example, that translates into 98.7% uptime for machine availability that is expected.”
Complex Airfoil Designs Challenge Machining
“All the engine manufacturers have run their hot gas path temperature to well above 2000° F [1093° C],” said Larry Marchand, vice president, United Grinding Technologies (Miamisburg, OH). “Ceramics are used for coatings and base material and are difficult to machine, as are alloys with exotic elements like chrome, tungsten and nickel that are used for the increasingly complex investment castings for blade vanes and shrouds. In addition, castings feature complex three-dimensional airfoil design making them that much harder to machine.
“There has been a shift in what our aerospace customers expect from us,” said Marchand. “The mix of turnkeys required has shifted from 25% 10 years ago to 75% today. Our customers want us to design it, build it, debug it, troubleshoot, and run off systems, activities that would have been done internally in the past.”
“There’s a definite trend toward flexibility in engine machining, requiring quick response to engineering changes. We use the term multitasking to describe this flexibility when we talk about our toolchanging grinding centers like the Magerle MFP 50 grinding center. It’s a five-axis toolchanging machine which can do milling, turning, and drilling, as well as grinding. If you have a part with a lot of milling, obviously it’s going to be cheaper to mill it, because they’re mass produced. But if you have a part that is 80% grinding that has a couple of holes that have to be drilled, which is very common with turbine vanes, or slots and keyways, the multitasking grinding center is a good way to eliminate the need for secondary milling and fixturing,” said Marchand.
Matching Processes to New Materials
“The machining solutions for higher efficiency engines that are designed to achieve higher by-pass ratios and higher combustion temperatures must deal with more exotic alloys and more exotic cooling solutions in the turbine stage,” said Greg Hyatt, vice president and chief technical officer, DMG / Mori Seiki USA (Hoffman Estates, IL). “The newest blisk and blade designs can’t be machined with older four-axis machines. All of the new designs require five-axis machining capability and processes that can handle difficult-to-machine materials.”
To meet these uniquely challenging machining requirements, DMG / Mori Seiki has developed new processes for machining heat-resistant materials like titanium aluminide, sintered nickel-based alloys, and carbon fiber for structural components for its machining center technology. “Pinch milling for machining the larger stage fan blades that are designed for higher by-pass ratios overcomes the tendency of the blades to deform under more cutting force,” said Hyatt.
“Pinch milling is available on any of our mill-turn machines, preferably with the Siemens 840D control as well as the DMG machining centers. The zero-chip process is a technique we use to vacuum dust and swarf through the tool and through the spindle away from the work zone when machining carbon fiber. Zero-chip machining is available on NMV machines and the NVX machines that are currently being used for production of some of the carbon-fiber components in the wing box for the 787,” said Hyatt.
Special machining packages for heavy cutting of difficult-to-machine alloys have also been developed by DMG Mori Seiki. “For example, new designs for integral bladed rotors [IBR] are being used more frequently in new stages of the engines. We’re seeing tandem blisks for IBRs, where two or three stages are machined from a single piece of material. For those applications, direct-drive of the rotary axis on the NMV and Mono Block machines is faster, more accurate with a longer service life than gear-driven rotary tables,” said Hyatt.
Choosing a vertical or horizontal machine is important in terms of the floor space requirements and the size of the workpiece. “Typically the heavier components tend to go on the horizontals and the lighter components tend to go on the vertical machining centers,” said Hyatt. “With a heavy workpiece, it’s unattractive to be rotating an extremely massive workpiece centrifugally. You want to leave the workpiece static and rotate the spindle and bring the spindle to the workpiece. With the workpieces that are low in mass, it’s advantageous to do just the opposite. Blisks and impellers tend to go on the vertical based five-axis machines,” said Hyatt.
Critical Cooling Holes Get at Production Speed
For machining critical cooling air holes and shaped diffuser holes in blade and vane segments, Makino (Mason, OH) has introduced its new EDBV3 (electrical discharge blade and vane) fast hole drill EDM. “The EDBV3 is designed to provide aerospace manufacturers with the speed, flexibility and reliability to produce a wide range of hole shapes and sizes within a single setup, reducing required tool variety and overall cycle times.” said Brian Pfluger, Makino EDM product line manager.
Forced air cooling, special coatings and higher heat-resistant metals are increasingly being used to overcome the effects of increased aero-engine temperatures that are beyond the melting pointt of the base materials. “Holes range from typical straight through-hole sizes between 0.020–0.030″ [0.5–0.76 mm] diameter with relatively shallow depths of 0.040–0.080″ [1–2 mm] to diffuser holes with funnel or fan-shape geometry that can vary from a simple cone to an elongated rectangle,” said Pfluger. “The purpose of diffuser holes is to control the airflow and effective cooling of the inner and outer surfaces of the hollow cast engine detail. Often the final through-hole of a diffuser isn’t centered to the outer funnel geometry and is offset to one side to direct or change air flow.”
Design of the EDBV3 is aimed at production EDM hole drilling. “To facilitate the processing of complex 3D parts, the machine is configured with an integrated two-axis rotary table that is used for positioning of the workpiece, and the remaining four machine axes are used to position the electrode and die guide to the proper machining location. Typically, we use a palletized tooling mechanism from EROWA or System 3R to hold and chuck the part into and out of the machine,” said Pfluger. The standard configuration of the EDBV3 includes a 24-station tool carousel system and 24 holder assemblies to fully tool up the machine. The tool carousel can also be exchanged as a palletized magazine for extended hours of automated operation.
Critical process issues address machining speed as well as breakthrough detection. “As you drill through the outer skin and you break into a hollow cavity, you have to avoid machining the interior back wall of that cavity. That’s called back striking. If an adjacent cavity feature is machined, it will change the air flow and affect cooling effectiveness. Special machine generator circuitry has been developed that can detect breakthough within one second or 0.040″ [1 mm],” said Pfluger.
EDM drilling on the EDBV3 is performed fully submerged under water for higher part quality, improved stability and up to 10 times faster processing speed compared with conventional technologies. To improve productivity, the EDBV3 uses a single-electrode processing approach, which avoids the high cost of custom multi-electrode holders and standardizes the tool holders with a flexible and cost-efficient system.
For untended burning of varying cooling hole diameters, the EDBV3 features a combined automatic tool change (ATC) and automatic guide change (AGC) system. The patented electrode toolholders combine the electrode holder and die guide together into a common assembly, providing ATC and AGC exchanges in 30 seconds. In addition, changing to a different brass electrode diameter is simplified.
Makino developed the EDBV3 fast hole drill EDM for production drilling of critical cooling air holes and shaped diffuser holes in blade and vane segments.
Machining Choices for Other Components
Capacity for machining structural titanium and related components has also expanded the investment in advanced machining technology. Aerospace Dynamics International Inc. (Valencia, CA), increased its titanium machining capacity approximately 40% to support Airbus A350 and Boeing 787 programs by acquiring eight five-spindle, five-axis MAG XTi profilers from MAG IAS LLC (Erlanger, KY) in a $36 million machinery purchase. The XTi profilers join ADI’s extensive portfolio of MAG machines including two three-axis XTi profilers and two MAG U5 portal mills and two MC 1600 boring mills acquired in a 2011 plant expansion. The 40 spindles of the five-axis XTi profilers are carried on eight individually controlled gantries that span 6 m with a Z-axis depth of 711 mm, providing a work envelope between each pair of rails of 1300 m2 for roughing and finishing the largest titanium workpieces.
For machining both titanium and aluminum structural components, Valent Aerostructures (Kansas City, MO) recently acquired Vortex 1060V/8 simultaneous five-axis vertical machining centers from Mazak Corp. (Florence, KY). Valent is a supplier to major aircraft builders like Boeing, Spirit Aerosystems, Lockheed Martin and Gulfstream. Valent’s strategy is to create two separate fully automated machining lines using Mazak’s Palletech system. Both machining lines will allow untended operation and are modular so that Valent will be able to easily and cost-effectively expand as more machines are added to both lines. The titanium machining line features two Vortex 1060V/8 machines with hard metal machining packages and a two-level system with 24 pallets and a load/unload station. The high-speed machining line will incorporate four Vortex 1060V/8 machines and a Palletech system.
The Vortex machines at Valent illustrate how aerospace shops can obtain lowest possible cost of ownership through standard machines. Mazak offers both high-speed and high-torque versions of the Vortex, so Valent can process its aluminum and titanium parts with the same model machine. And together with the standard Palletech automation system, Valent further increases productivity.
Mazak’s portfolio of machines for the aerospace industry will soon be captured in an industry-specific brochure featuring what President Brian Papke calls small and large-part machining capability for virtually every facet of aerospace machining. “The larger Integrexes are used virtually by every landing-gear manufacturer in the world. On the engine side of the business, machine solutions include e-vertical Integrex machines, 800-mm vertical turning centers, five-axis machining centers, and multitasking machines,” said Papke.
At IMTS, Mazak introduced the Mega 8800 horizontal machining center with high torque and horsepower for heavy-metal machining requirements like titanium machining. “We have a full range of general-purpose machines, but we also provide machines that meet the needs of specific industries like off-highway equipment, energy, medical as well as aerospace applications,” said Papke.
“Aerospace manufacturers need high repeatability and accuracy when machining large, heavy, challenging aerospace parts,” said Dale Hedberg, Feeler product manager, Methods Machine Tools Inc. (Sudbury, MA). Manufacturers are increasingly relying on vertical turning lathes to accommodate their larger and heavier parts, said Hedberg. “The new Feeler FVT-600 is equipped with heavy-duty, roller-type linear guideways, resulting in high rigidity when making heavy cuts. To minimize thermal deformation and vibration, and increase positioning accuracy, the FVT-600 features rugged construction and precision ballscrews that are directly coupled with highly responsive AC servomotors.”
The Feeler vertical turning lathe offers a high-precision and high-rigidity spindle which is supported by two double-row cylindrical roller bearings and duplex angular thrust bearings. This enables the lathe to endure heavy cutting in both radial and axial directions, resulting in high accuracy during long cutting cycles. The FVT-600 design permits coolant to flush chips to an extra-wide conveyer where the chips are immediately evacuated. To facilitate automating processes, the Feeler FVT-600 is available in left-side and right-side versions, allowing automation to be strategically stationed between the lathes for high-volume production applications. ME
This article was first published in the March 2013 edition of Manfacturing Engineering magazine. Click here for PDF.
Published Date : 3/1/2013