Unlike automobiles, machine tools stand to become more energy-efficient when they move faster. High speed machining offers real potential for reduced energy costs. That’s because, in addition to the direct energy costs of removing material, the machining cycle also has indirect energy costs associated with the machine’s fan motors, pumps, lights and so on. A shorter cycle reduces the amount of time these components spend drawing power. Therefore, technology for faster machining delivers not only productivity, but also energy savings.
Paul Webster of GE Fanuc (Charlottesville, Virginia) says his company has been giving increased attention to the energy impact of machine tool control systems—in part as an extension of GE’s “Ecomagination” campaign. Mr. Webster, a product manager for servo technology, notes various points in the control system where advanced technology can save on indirect costs. Those aspects of the control system include:
Motor core and power density. The servomotor core can be designed to minimize inertia, he says, while permanent magnet synchronous motors provide high power density and excellent acceleration. Motor windings. Dual windings allow one motor to perform like two. A low speed winding lets the machine deliver high torque at lower rpm values, while switching to the high speed winding extends the constant power range to let the machine accelerate to higher speeds more quickly. Close Control loops. The company’s HRV (High Response Vector) closes the motor control loops at a rapid rate and adjusts the control commands based on the load and speed of the motor. Quickly responding to deviations in the system in this way allows the control to achieve high acceleration without sacrificing accuracy.
The choice of control system technology also affects direct energy costs, Mr. Webster says—specifically by reducing the amount of energy wasted as heat. For example, dynamic control of the motors can optimize the amount of torque produced for a given current. Even more significant is power source regeneration, which lets the decelerating motor act as a generator by putting some of the braking energy back into the system instead of wasting it. Power source regeneration can be the number-one contributor to energy savings in a CNC machine tool’s design.
The machining center shown above combines technologies for both direct and indirect energy savings. Savings such as these are worth considering when a new machine is evaluated, Mr. Webster says. In short, consider how much it will cost to run that machine.