Five-Axis Machines Grow in Popularity
Technology chases complex parts machining in a variety of industries
By James Lorincz
The growing popularity of five-axis machining shouldn’t be a surprise. Manufacturers are becoming increasingly aware of the advantages of 3+2 positional or simultaneous five-axis machining of complex small and large parts. They have a wider selection of advanced machine platforms to choose from evidenced by the offerings of machine tool builders and distributors at IMTS.
Five-axis machining capability goes right to the heart of how parts as diverse as aerospace parts and a host of medical, and energy oil/gas parts can be efficiently processed with the highest accuracy and superior surface finishes. Parts designers can incorporate more features and functionality into parts working in materials ranging from titanium, Inconel, stainless steel to superalloys, as well as hardened steel and aluminum.
Five-axis machining in both vertical and horizontal machines continues to add a dimension to process engineering that complements mill/turn and multitasking technology. In addition to better geometric accuracy and complete to near complete processing in minimum setups, five-axis machining offers simplified workholding compared with traditional four-axis horizontal machining centers, and is capable of more aggressive roughing cuts. In addition, five-axis machines lend themselves to being readily handled in robotic, multiple pallet, and cellular configurations. Here’s a selection of recent five-axis machining developments:
Mitsui Seiki USA Inc. (Franklin Lakes, NJ) has developed the Vertex 550-5XB five-axis CNC vertical machining center specially designed for the production of aerospace and power generation turbine blades from forgings, castings, bar stock, or solid billets of titanium, and stainless steel. Introduced at IMTS 2012, the machine meets design criteria suggested by manufacturers that include the ability to rough and finish parts in competitive cycle times with improved part accuracy and surface finish. According to Tom Dolan, Mitsui Seiki vice president, that adds up to “a total machining center package that had to be smaller, faster, more accurate than what they had been using—all at an affordable price.”
Specification highlights of the Vertex 550-5XB include an X-Y-Z working envelope of 550 × 600 × 500 mm, rapid traverse rates in all linear axes of 48 m/min in a 65 ft² (6-m²) footprint. A and B axes are in a rotating/tilting table; A axis tilts from +45 to −90° angles and the B axis features infinite positioning points. According to Dolan, a new non-traditional approach to engineering the rotary axes enhances manual and automatic load/unload operations, such as the integration of a robot and cellular manufacturing capability. The Vertex spindle is designed for cutting hard titanium and stainless steel under control of the latest Fanuc CNC. The Vertex 550-5XB features a cast bed and a “box in a box” design for rigidity and stiffness that typically isn’t available in a machine of this size. All guideway mounting surfaces are hand-scraped after machining and grinding in Mitsui Seiki’s temperature-controlled factory.
Five-Axis Can Take Heavy Cuts
Kyle Klaver, five-axis product specialist at Okuma America (Charlotte, NC), says that as engineers put more features and functionality into larger parts, it’s increasingly difficult to machine these components using standard three-axis or even four-axis horizontal machining centers. “Mill/turns with a B axis like our Multus or MacTurns are great alternatives, but sometimes there is a greater need for milling and that’s where the five-axis machining center still has its strengths. It takes heavier cuts,” says Klaver. At IMTS, the MU-10000H, the largest of the Okuma MU range of five-axis high-speed HMCs, made its world debut. The machine features a 1-m square pallet that can handle a 1.5-m diameter by 44" (1.1-m) high workpiece, weighing 5500 lb (2495 kg).
“The MU-10000H is a new design of a horizontal machine for applications like large aerospace, energy, and heavy equipment applications,” says Klaver. “We’re seeing companies that have never been five-axis customers taking advantage of being able to buy off-the-shelf equipment for these large workpieces, as well as other applications. The initial offering is intended for titanium, Inconel, 15-5 stainless, and high-temperature heat-resistant alloys, and it can cut aluminum as well.” Two spindles, one with standard torque and a high-torque version, are available depending on customer requirements, and the machine is equipped with a two-pallet changer.
”Aircraft parts have very elongated aspect ratios like a rib and require a huge amount of X axis relative to Y and Z axes.”
Also introduced to the US at IMTS, Okuma's VTM-1200YB vertical turning CNC lathe has simultaneous five-axis machining capability. “It’s a 1.2-m chuck machine VTL with a B-axis head with a Y axis that is able to process parts on this machine in two operations,” Klaver explains. “Typical parts include large cylindrical housings that require a lot of milling and a lot of angled holes and features. It changes the way you process parts. You’re no longer thinking that you have to run parts on a large lathe and then take it over to the mill and set it up two times. Now you can do a turning operation, flip the part over and then finish it.”
Structural Parts Get New Fixturing Process
DMG / Mori Seiki (Hoffman Estates, IL) has devised what it calls “pinch fixturing” to virtually eliminate deflection in five-axis milling of asymmetric structural parts on a mill/turn machine. “Basically, we’re doing five-axis machining with a nine-axis machine and drawing some dramatic benefits doing it,” explains Greg Hyatt, chief technology officer. “It’s an all milling application, and no turning is involved. By using the mill/turn and putting robotic clamping units on the lower turrets, we run the lower turret up and clamp on the workpiece, where we want to, when we want to. As we move from pocket to pocket in typical structural parts, we’re completely unconstrained by any traditional fixture.”
At IMTS, DMG / Mori Seiki demonstrated the pinch-fixturing technique on an NT 4300 machining a large workpiece that resembled a wing rib from a Boeing 737. “Because we’re putting this solution on a mill/turn machine, we can handle a structural part 6-m long on an NT 6600, for example,” says Hyatt. “That’s part of the beauty of this system. Aircraft parts have very elongated aspect ratios like a rib and require a huge amount of X axis relative to Y and Z axes. The mill turning envelope is well suited to typical aircraft structural parts like rib spars, stringers, segments, flap tracks, and landing gear components.”
Hyatt credits the technique with overcoming the tendency of fixtured forgings that have residual stress to spring back after cutting and being unclamped, requiring multiple machining cuts to get an accurate part. “Using this method and having no fixture and avoiding the problem of overconstraining the part, we use the lower turret to support the part while we’re cutting the pocket. We can immediately release it and let the part spring, reclamp the part, semifinish or finish a pocket on the opposite side, release it, reclamp. We can consolidate multiple operations into a single operation, working all the way around the part and allowing us to relieve all of that residual stress without all the operator intervention of multiple refixturing and indicator checks,” Hyatt explains.
Don’t Want to Go Back After Five-Axis
AT IMTS, Methods Machine Tools Inc. (Sudbury, MA) introduced its new Matsuura MAM72-100H five-axis horizontal machining center with a large capacity work envelope offering the ability to cut challenging materials in complex aerospace and energy industry parts. The MAM 100H can handle 360 tools on the machine, starts with two pallets and is expandable to a six-pallet system or FMS. “We are noted for our multi-pallet systems, whether standalone or in an FMS environment,” explains Michael Minton, Methods Machine national application engineering manager.
“Once our customers move into five-axis machining, they rarely if ever go back, because workholding becomes so much simpler and cost effective. Rather than having eight parts on a horizontal tombstone, they’re machining one part just as fast as they did the eight parts, if not faster, with simpler workholding. Our engineers are raving about one product called the Raptor fixture with a simple dovetail design in a low profile system. It allows you to get to five sides of the part with minimal fixturing interference on any five-axis platform,” says Minton.
“The biggest advantage with five-axis machining is geometric accuracy, because you can get to five sides of that part in one setup,” according to Dave Lucius, Methods vice president-sales. These systems really shine when customers are being pushed for tighter and tighter tolerances. Applications in aerospace, power generation, and for turbine applications include blades and blisks, and include blades and impellers in land-based diesel engines.”
Having the ability to process workpieces vertically or horizontally on five-axis machines can yield important gains in accuracy. “Depending on how you process the part, you have the opportunity to put precision bores in vertically and do a lot of the milling horizontally, and you can flip around the processes to gain accuracy. When you bore vertically, you are more accurate than boring horizontally. You have flexibility by combining two types of machine geometries into one machining platform to further enhance your process and part geometric accuracy,” Lucius explains.
Methods Machine Tools offers its five-axis Matsuura machines with a CAMplete post processor software which shows what the machine will do based on the program and will optimize the toolpath. “To take any mystery out of five-axis machining we offer a bimonthly, complimentary three day course to our customers. When customers come to our technology center, we can show them how easy five-axis machining is rather than spending time to try to familiarize themselves with the platform itself,” says Lucius. “We have great success in making people comfortable moving from a traditional vertical or a horizontal machining center into five-axis machining.”
Compact Five-Axis Meets Precision Needs
Five-axis machining is increasingly taken to the extremes in processing small parts in small footprint platforms for medical device manufacturing, and larger machines for aerospace applications, according to Marc Jagoda, applications manager, Mazak Corp. (Florence, KY). At IMTS, Mazak introduced its Vertical Center Nexus Compact, which is available in three and five-axis versions for medical applications and its Vertical Center Universal 400 five-axis machine.
The VCN Compact features a 25-hp (18.6-kW), 12,000-rpm CAT 40 spindle and X-Y-Z axis travels of 19.69 × 16.93 × 20" (500 × 430 × 510 mm). With its 40-taper spindle, it is designed for five-axis machining of tough materials, such as stainless steel, Inconel, and titanium used in medical and other applications. The machine’s three linear axes reach high-speed rapid traverse rates of 1417 ipm (36 m/min) and fast feed rates of 315 ipm (8 m/min). Five-axis machining is rigid and precise on a rotary/tilt table constructed with high-speed roller drive technology, allowing the table to rotate and tilt at speeds of 100 rpm and 75 rpm, respectively.
Mazak also demonstrated its VCU 400-5X advanced technology for machining high-precision small-parts for various industries, including medical, aerospace, electronics, and automotive. Based on a modular design platform, the machine is easily configured as a three-axis fixed table or five-axis rotary/tilt table model. Both machines share the same small footprint and table size of 15.7 × 15.7" (399 × 399 mm), allowing them to fit into almost any manufacturing facility. Each machine’s linear X-Y-Z-axis travels measure 19.6 × 15.7 × 20" (498 × 399 × 508 mm) and attain rapid traverse rates of 945 ipm (24 m/min). Both models are equipped with 10,000-rpm, 15-hp (11-kW), 40-taper spindle for machining materials, including steel, aluminum, and cast iron.
High-Speed Gantry For Aerospace Materials
For machining large composite or nonferrous aerospace parts, Triumph Aerostructures Vought Commercial Division has ordered two Precision Mill/Trim (PMT) gantry systems for installation in 2013 on existing X-axis rails at its Hawthorne, CA, plant. The two high-speed PMT gantries will be used to produce aluminum wide-body fuselage skins for next-generation commercial aircraft. The modular PMT is a five-axis gantry machine tool for high-speed multiprocessing of large nonferrous components, such composite structures, aluminum skins and fabrications, molds, patterns, and post-cure cutouts in foam and sandwich structures. In addition to machining, the highly configurable PMT is designed to use various special heads, such as waterjet, sawing and other finishing tools, including a system for precision control of countersink depth.
The machine’s unlimited X axis is accompanied by its configurable Y axis of 2–6 m; Z axis of 1, 1.5 or 2 m; feed rates up to 60 m/min; five-sided part access; and optional precision scale feedback. The compact dual-axis rotary spindle head is powered by direct-drive torque motors with encoder feedback, providing 220° of A-axis tilt and standard 550° of C-axis rotation. The PMT’s rail-type configuration allows a variety of workholding systems to be adapted, including MAG’s Flexitool universal workholding system. The Flexitool system consists of modular table sections equipped with programmable vertical actuators tipped with swiveling vacuum end effectors that adjust to almost any part shape, so nests of various part shapes can be machined in multiple workzones. Five different motorized spindles are available beginning with a standard 22,000 rpm/20 kW and ranging up to 30,000 rpm/42 kW. ME
This article was originally pubished in the October 2012 issue of Manufacturing Engineering magazine. Click here for a PDF of the original article.