April 2012 / Volume 64 / Issue 4|
Cutting noncut time
By Alan Richter, Editor
Most horizontal machining centers have a rotary B-axis in addition to the X, Y and Z axes. Traditionally, B-axis tables are indexing or NC rotary-type ones. On the a51nx and a61nx horizontal machining centers from Makino Inc., the B-axis rotation is accomplished by a direct-drive (DD) table, explained Dave Ward, horizontal product manager for the machine tool builder. “A key technology on our DD tables is Inertia Active Control (IAC), which can optimize the rotational acceleration to reduce noncut time,” he said, noting that the DD rotary table uses an integral motor and provides 0.0001° resolution—3.6 million positions.
Ward explained that because machine tool builders have no idea how much weight a customer is going to put on a pallet, they set the B-axis acceleration/deceleration default speed at the worst-case, maximum-weight, maximum-inertia scenario to ensure accuracy. That’s effective, for instance, when a tombstone-mounted pallet has workpieces at the outer edges, creating a high-inertia condition. In that case, the motor has to work hard to rotate the pallet. However, if that weight is concentrated near the center, IAC automatically increases the acceleration/deceleration speed accordingly because there is less inertia during rotation.
Courtesy of Makino
In addition to cemented carbide, suitable workpieces include hardened steel, glass and silicon carbide.
“More and more high-volume manufacturers are getting squeezed on their piece-part pricing,” Ward said. “IAC is a tool we can provide to our customers that allows them to get potentially thousands of additional parts produced on each horizontal machining center per year.”
With a typical four-sided tombstone, IAC can reduce noncut time during B-axis indexing 14 to 18 percent compared to the default value, according to Ward. “The more B-axis rotations the customer’s parts have, the more they’re going to benefit from this,” he said.
The technology’s foundation lies in the DD table’s ability to provide inertia feedback from the B-axis motor to the machine’s control. During the teach mode, the IAC rotates the pallet back and forth plus or minus 45°, senses the energy consumed to do that rotation and extrapolates from that how much inertia is on the pallet, Ward explained.
The 400mm-pallet and 500mm-pallet represent the largest segments of the horizontal market, according to Ward. “The a51nx and a61nx provide this key market with IAC capability, and we’re evaluating what’s the next model that would benefit from this technology.”
For more information about Makino Inc., Mason, Ohio, call (800) 552-3288 or visit www.makino.com. CTE
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