PARK RIDGE, Ill. Linear motors and digital controls will take a significant step forward in industrial automation Wednesday when Cincinnati Machine rolls out a high-speed machining center at the International Manufacturing Technology Show in Chicago. The new machine, which relies on an advanced electronic controller to guide it, could transform the way aircraft manufacturers build their airframes.
The Hyper-Mach horizontal machining center is said to be about five times faster than state-of-the-art machining centers and 10 times faster than conventional systems. Its high speed and high power hold special interest for airframes, potentially allowing allowing manufacturers to create enormous single-piece, monolithic structures simply by hogging them out of huge billets of aluminum.
That would be a tremendous step forward for aircraft makers, who have talked for decades about how monolithic parts could remove hundreds of hours of labor from the process of building aircraft floor beams, wing ribs, fuselage frames and other large sections of a plane.
"The whole industry wants to move in the direction of monolithic parts," said George Neilson, an associate technical fellow in Boeing's manufacturing research and development center. "Labor is so expensive today that we're all looking for ways to take it out of the manufacturing process."
Currently, structural items such as floor beams, wing ribs and other parts are built as an assembly of hundreds of pieces, including rivets, bolts, plates, channels and steel angles.
Given the cost advantages, some engineers believe that Hyper-Mach's combination of linear motors and electronic controls could signal the beginning of a machine-tool industry trend. "Over the years, we haven't seen many linear-motor-based machines," said Randall Von Moll, project manager for Cincinnati Machine. "But this could be a breakthrough year."
The technology to build ultrafast machining centers has long existed, engineers say, but they hesitated to use it because they didn't believe it could achieve the required accuracy. "Anyone can make a machine go fast," Von Moll said. "It's a matter of making it go where you want it to go. We could have built a high-speed machine like this one five years ago. But I doubt we could have achieved our accuracy goals."
To maintain accurate motion even in the face of exceptionally high speeds, Cincinnati Machine employed a Sinumerik 840D computer numerical control (CNC) from Siemens Energy & Automation (Elk Grove Village, Ill). The Sinumerik controller ultimately will use a 500-MHz Pentium III processor (prototype versions use a 266-MHz Pentium II) to monitor the position feedback loop, which compares the actual position of the machine's cutting head to its commanded position.
Data is stored in a 2.5-Mbyte memory or in a 2-Gbyte hard drive contained in the CNC. Each machine axis also employs its own digital signal processor to monitor the velocity loops and current loops at each axis.
Cincinnati Machine engineers say the controller is the key to maintaining a low "following error" the parameter that describes the difference between the system's actual and commanded positions.
"Linear motors and digitized drives allow you to run a higher gain, which effectively shrinks your following error," Von Moll said. "That's necessary for a high-speed system, because if you have a wide following error, your system is never where the controller 'thinks' it is."
Cincinnati Machine first considered the idea of building such a machine after a call from Boeing in 1994. "Boeing engineers wanted to make monolithic parts, and they knew they would have to work with us to make it happen," Von Moll said. The two companies collaborated on the design for five years before producing a working prototype in 1999.
The result, which will be officially unveiled for 120,000-plus IMTS attendees next week, is a machine that is unusual not only in its use of technology, but also in appearance. Hyper-Mach, said Von Moll, is "designed more like an airplane than a machine tool."
The Hyper-Mach consists of a cutting head on a movable truss. The cutting system, which connects to a massive steel wall, moves at extraordinary speeds: up to 2,400 inches per minute (40 inches/second) during contours and 4,000 inches/minute while moving in a straight line.
Electric motors on the truss move the cutting head in five axes two horizontal, one vertical, one tilt and one "wrist roll." Using a very high-power spindle, the machine cuts preprogrammed patterns into thick billets of solid aluminum and thus creates structural shapes.
The unconventional part of the machine, however, is its use of linear motors supplied by Anorad Corp. (Hauppauge, N.Y.). Linear motors, until now used only sparingly in machine tools, employ no mechanical linkages or gear boxes to produce linear motion. Instead, they use a rotor and a so-called "linear stator," which is similar to a conventional stator except that it is slit axially and then peeled back and laid flat. Using this configuration, the motor's rotor actually moves linearly along the stator instead of rotating within it, as it would on a conventional motor.
Engineers say that this simple technique is responsible for producing high speeds and huge acceleration forces in the new machining center. The key, they say, is the elimination of the gear box and ball screw, which converts rotary motion to linear in conventional systems.
"The ball screw is always the limiting factor in terms of velocity," said Tom Bullock, president of Industrial Controls Consulting (Fond du Lac, Wis.). "Ball screws wobble and they shake the machine. If you really want to achieve high speeds, you have to get rid of them and use a linear motor."
Cincinnati Machine engineers say that Hyper-Mach's speeds of 2,400 inches/minute are far greater than the fastest systems on the market today. Conventional systems, they claim, operate at 100 to 200 inches/minute, while state-of-the-art models achieve 500 inches/minute.
Similarly, Hyper-Mach's acceleration rates are exceptional, they say. It accelerates at 800 inches per second squared (about 2 g's), against 15 inches/s2 on normal machining centers.
In beta-test applications, Hyper-Mach is said to have milled out a thin-walled, honeycomb-shaped part from a solid billet of aluminum in under 30 minutes. Engineers say the same process would take approximately three hours on the best state-of-the-art high-speed machines or up to eight hours on a conventional mill.
Engineers say they don't expect Hyper-Mach technology to spread quickly throughout the industry. "Not everyone needs a linear-motor-based machine," said Chip Storie, aerospace industry market director for Cincinnati Machine. "But there are markets where this technology will be very important."
Among them: the machining of molds and dies. "The machine-tool industry and its customers are conservative," Von Moll said. "But if this technology can help them cut their costs, they'll find ways to use it."