It all started in 1996 when Fanuc came out with a new control specification that was capable of transferring data as a geometry set rather than a bunch of points in the X, Y, Z space. By doing so, the door was opened to transferring NURBS (Non-Uniform Rational B-Splines) as NURBS, basically a free-form curve and not a linear set of data points. Which translated, for part makers everywhere, into parts made with better surface finishes in a shorter amount of time.

Of course, that spec was for three-axis machining, and the advent of high-speed five-axis machining prompted Fanuc to introduce a multi-axis specification a couple of years ago that can accommodate five axes and beyond.

“This is bleeding edge type stuff we are talking about here,” says Makino CAD/CAM Engineer Jeff Wallace. “Only a few are beta testing five-axis NURBS machining, but there are a lot of bugs to be worked out.”

Before you can generate a multi-axis program, you have to be able to define the kinematics of the machine. Unless something strange and dramatic happens in the machine tool industry, machine kinematics differ from builder to builder—and sometimes even from machine to machine.

This means software makers have the dubious task of trying to create CAM programs with mathematical formulas. These will either take such variables in kinematics into account or generate CAM programs that are specific to the machine tool builder.

The problem with the first option is that a software program that would attempt to take on all of the kinematic variables of every machine tool would be so large and so cumbersome that neither the post-processor nor the control could handle it. So, the second option is definitely much more feasible.

There are also the kinds of ticks and bugs that occur when you finally have a control, a machine and the software interacting that are anticipated but never defined until it is actually run all together. These occur on nearly every machine, no matter what software or hardware system is incorporated into it, which is why there is a testing cycle before a machine is delivered to a user. As the beta testing cycle on high speed machining of five-axis NURBS progresses, the bugs and ticks will become more predictable, and will be worked out by the hardware, software and machine tool makers.

While harnessing five-axis NURBS does not give users the ability to program and machine more complex parts than they can now, it probably will give them the ability to machine complex parts faster and with better surface finish. Another potential benefit will most likely be a reduction in part program size, which may simplify post-processing.

Copyright © 2001 - 2008 by Makino, Inc. All rights reserved.