Solutions cover all aspects of precision aerospace machining
By Jim Lorincz
There doesn’t seem to be any lack of information about or interest in manufacturing the newest generation of materials required for aerospace and commercial aircraft applications. Knowledge ranges from the properties and machining characteristics of the newest toughest metals and carbon-fiber reinforced plastics (CFRP composites) to information about the machine technology, tooling, controls, and coolant and ancillary systems required to produce quality precision-machined parts. Applications range from structural components to jet engine turbine components. At the Tier levels there is an opportunity to expand manufacturing capacity and capability to meet demands of the aircraft industry, which is enjoying a boom period.
In general, aerospace components drive innovation in cutting tools, machine tools and all other aspects of the manufacturing processes, according to Michael Standridge, aerospace industry specialist, and Ronald Talarico, CAM programmer, Sandvik Coromant US (Fair Lawn, NJ). "OEMs are continuing to partner with material producers to develop new material recipes to address four key areas in aircraft manufacturing: strength, weight, corrosion resistance, and cost of manufacturing. As a result, aircraft designers continue to engineer aircraft that are lighter in weight, yet retain the proper strength required in either heat resistance or torque resistance, and flexibility. The focus now is on fuel efficiency, reducing the buy-to-fly ratio, increasing carrying capacity for persons or ordnance, and even passenger comfort. We see this continuing to expand the use of composite materials, heat resistance superalloys, aluminums, and titanium," Standridge and Talarico say.
Expanding Tier Supply Chain
As OEMs have reduced their manufacturing capabilities, they are relying more on outside resources. As a result, they say, "the trend seems to be that the tier suppliers are taking on much more of the manufacturing role and investing in people, material, and equipment, and subcontractors are relying on their tooling and machine suppliers to assist and support manufacturers in areas where they need support." Sandvik Coromant, for example, has invested in its internal capabilities by enhancing its product and service offered with a new Aerospace Application Center, which includes a number of programming and engineering resources.
According to Daniel Martinez and Mark Haydock of Siemens Industry Inc.‘s Aerospace Center of Competence, the use of composite material technology has moved into mainstream commercial applications. "Both the Boeing 787 and the Airbus A350 claim extensive use of carbon fiber. At the same time, the use of titanium has increased because of the material’s compatibility with composites. That said, let’s not forget that aluminum alloys are still the bread and butter for the industry. New aluminum alloys are coming out that may give composite materials a good run for the money. Both Boeing’s 737MAX and Airbus A320Neo--the most popular models in the market—are mostly made of aluminum alloys and take advantage of a supply chain that knows those products well."
"Next-generation aircraft will continue rolling off assembly lines built with a much higher percentage of high-strength titanium alloys and carbon-fiber-reinforced polymer (CFRP) composite parts, driven by new aircraft developments like the Boeing 787, Airbus A350 XWB, Bombardier C-Series, and years of backlog," states Randy Von Moll, director, technical sales, MAG (Erlanger, KY). Roughly 50% of the total aircraft weight of the Boeing 787 and the Airbus A350 XWB are manufactured from composite materials. Composites parts are very strong and corrosion resistant when used with titanium. These two materials provide the qualities aircraft manufacturers are looking for in new defense and commercial aircraft parts, such as wing skin panels, fuselage barrels and panels, vertical and horizontal stabilizers, floor beams and engine cowlings.
Materials Vying for Supremacy
"Composite materials will continue to displace components currently produced from aluminum; however, both the competing wide body aircraft developments, 787 and A350, still have aluminum wing ribs. These complex-shaped parts will be candidates for composites in the future. It will be interesting to watch what happens with Boeing on the future 737 replacement aircraft—currently there have been no decisions on large structures, such as fuselage and wing, as to whether these will be aluminum or composites. Aluminum material continues to be readily available, and worldwide tier suppliers have a good understanding of how to efficiently produce aluminum aerospace parts," Von Moll continues.
MAG offers an extensive line of aerospace machining centers, precision boring mills, vertical turning centers, profilers, and composite machine tools. Recently, MAG introduced its multi-patented cryogenic machining system, which delivers liquid nitrogen at -321° F (-196° C) through the spindle and through the tool directly to the point where the tool meets the cutting surface. The process, which is called Minimum Quantity Cryogenics (MQC), literally "refrigerates" the heat away, acting as a heat sink and removing heat generated during the cutting process. MQC has been approved by the US government for standard roughing operations in production of titanium parts for the Lockheed Martin F-35 Lightning II Stealth Fighter.
Vince Trampus, vice president, Heller Machine Tools LP (Troy, MI), says: "I can see aluminum to be more competitive in the future when it comes to fuselages, but there is an offset compared to composite material in cost and availability. Aircraft builders will have to factor in the specific characteristics of all three – composite-aluminum-titanium.
"Aluminum is typically machined with high cutting speeds. The overall machining process is very mature. The quality level of the machined parts is typically a function of the volumetric accuracy of the machine tool. Robust machining of composites, on the other hand, is a matter of optimizing the process with regard to feed rate selections, cutting tool geometries, and the choice of dry and /or lube-assisted machining. Titanium-machining creates higher chip volume, and utilizes higher cutting forces and elevated cutting temperatures. To be effective machining titanium, metalcutting machine tools must exhibit dynamic stiffness paired with thermal stability and high volumetric accuracy," Trampus explains.
Heavy-Duty Machining Delivered
When the material choice is composite and titanium, Heller’s machining center characteristics are well-suited to this type of challenge. Heller’s MCH-C and F Series HMCs are designed for heavy-cutting, high precision, and high performance with five-axis contouring. Gear-driven spindles with options for high-speed as well as high-torque operation are well-matched to the demands of aerospace machining, based on material to be machined. Heller machines feature high dynamic stiffness, high torque curves, absolute temperature control in all axes, vibration damping bed and column design, powerful controllers with adaptive control and customized options to guarantee finish-machining with speed and precision reliably and cost-effectively.
"We’ve been successful with our fixed-spindle large 2.5-m trunnion machines for machining parts to 120" [3 m] in titanium and tougher steel alloys for flap tracks," says Scott Walker, president, Mitsui Seiki USA (Franklin Lakes, NJ). "There is no doubt that for structural components, as the 787 program ramps up, titanium is leading the way and the amount of tonnage of titanium will increase substantially across the board. The predominant grades are 5-5-5-3, 10-2-4, and 6-AL-4. Also, titanium material requirements will be increased as the Airbus 320 program comes on line, and even the new 737 program where the rate is about 34 aircraft a month. Boeing has said that they are planning to increase that rate to 60 a month. In fact, we just finished the installation of the gearbox line for that rampup out in Portland. The 737 is having quite a few upgrades with new engines put on it. There’s a larger content of titanium for engine mounts, and some of structural components are going to move away from aluminum into titanium for longer life. At the job shop level, more and more of the job shops are moving into the titanium area, which is becoming a much larger piece of their business. Aluminum usage will increase, too, just because aircraft rates are going up."
Titanium Processing Capacity Needed
With the economics about producing titanium changing, new machines like the T-Series with ADVANTiGE technologies from Makino Inc. (Mason, OH) have been introduced specifically for processing titanium. Mark Larson, titanium R&D manager, points out that "with the current demand for titanium part production exceeding available capacity, there is ample opportunity for manufacturers to invest in a strong and profitable market segment. But there are challenges in processing these materials.
"The same characteristics that make titanium ideal for aircraft parts also lead to challenges in the machining process, including poor thermal conductivity, strong alloying tendency and chemical reactivity with cutting tools. By effectively addressing rigidity, vibration damping, spindle power chip management and cooling concerns, these technologies have enabled manufacturers to overcome these cutting challenges with four times the productivity and four times the tool life of conventional machining platforms. "
Still More Composite Growth Ahead
While the fuselage of airplanes will primarily be constructed of composite material, aluminum will still play a major role in the construction of airplanes. Jochen Reichert, technical sales manager, Methods Machine Tools, Inc. (Sudbury, MA) explains: "Composites have not yet reached their full potential from a design standpoint, confirming the necessity of aluminum in plane construction. At this time, aluminum alloys are still more cost-effective and have a lower risk factor than composite materials. Aluminum manufacturers are producing more advanced aluminum alloys which are beneficial to the commercial aircraft industry such as 7085 and aluminum lithium.
"Titanium use will increase with the increased production of greener, larger more fuel efficient engines. There is a trend to use composites to reduce the structural weight of the aircraft, and due to the problematic nature of galvanic corrosion between the fibers of the composites and the aluminum, it will be necessary to use more titanium alloys when moving forward with composite designs. The machining of titanium and high temperature alloys requires stable machine structure and vibration dampening characteristics as well as a high- torque, low-rpm spindle." Methods offers the Matsuura MAM72-100H five-axis HMC for cutting challenging materials, including titanium, for large-sized, complex parts. Equipped with a high-torque 50-taper spindle, the 100H has built-in automation for unattended machining and storage for up to 360 tools. The table can accommodate a weight capacity of 1720 lb (780 kg); workpieces can have a diameter of 39.37" (1 m) with a height of about 31" (787 mm). Parts can be machined and moved automatically with the pallet changer.
"Machining processes for machining hard metals rely on a complete system consisting of optimal components: machine, CNC system, tooling and CAD/CAM/post. Each of these is an important part of the machining system and needs to be the best selection for the application to result in an ideal production solution," says Rick Schultz, aerospace program manager, FANUC FA America (Hoffman Estates, IL). "To machine hard metal or any metal, you’ve got to look at the whole system. Especially if you’re making the investment to make a part for a decade or more—you need optimal performance and reliability.
"Today, airframe manufacturers are looking for metals with the best strength-to-weight ratio. Titanium 5553 is a particular alloy I see more often in aerospace. To machine this, you have to have a rigid machine combined with an advanced CNC, tooling and properly configured CAD/CAM/post system. For hard metal work, I’ve seen a recent trend toward large trunnion-style machines. Because of their mass and rigidity, trunnion-style machines make a good platform for five-axis hard metal work," says Schultz.
"In general, for your CNC you want the fastest, most accurate CNC you can get, the most responsive and accurate servos, and the smoothest tool path possible," says Schultz. "With FANUC you have some of the most responsive servos out there when it comes to loop closure, and you also have advanced algorithms that will smooth your path for you. If you look at the traditional programming process, you have CAD, CAM, post processor, and then CNC. FANUC has advanced algorithms with the Nano Smoothing and AiCC functions that will take approximations made by the CAM system and convert them back to a smooth spline curve for really smooth motion through the cut. That’s what produces a better part, reduces cycle time, and extends both tool and machine life."
"We expect to see a lot more use of composites and titanium, because their lighter weight is becoming increasingly more attractive to the aerospace industry, and new grades of each are being released frequently," says Kevin Farwick, production manager, Dynomax Inc. (Wheeling, IL). "Composites are evolving daily. Every day they are coming out with a new grade to test. Although we anticipate an increase in composites and titanium use, we don’t see aluminum consumption diminishing. The use of composites and titanium in aerospace machining is a challenge because they have a higher sheer and tensile strength than steel and aluminum. This creates a little work-hardening as you cut, which affects the cut and your cutter, and your speeds and feeds will need to change. Harder metals equal slower cycle times and more tool wear."
Based on his company’s long association with the aerospace industry, Robert Komljenovic, president, Hermle Machine Co. (Franklin, WI) sees the industry moving toward a greater use of titanium: "We see a decline in the use of aluminum and aluminum alloys in favor of titanium and composites. While this poses challenges to the cutting tool industry, the fact remains that machining such substances, especially meeting the challenges of titanium and Inconel, requires a strong and stiff machine structure. The kinematic design of Hermle machines gives our customers the advantage of being able to machine larger components in a smaller footprint. Further, our line has now expanded to a wider range of sizes, all of which can incorporate various modes of automation. Typical parts produced on Hermle machining centers include blisks, impellers, turbine blades and spool housings." ME
This article was first published in the March 2012 edition of Manufacturing Engineering magazine. Click here for PDF.