Over the last 20 years, Heller machine tools have become 70–80% more productive yet use 30% less energy. Much of these savings have come from improving the energy efficiency of controls, drives and switches.
Today, however, the largest user of energy in a machine tool is the coolant system and chip conveyor, consuming about 40% of the total energy used in producing a part. Hydraulics, controls and drives, and cooling are each about 20%. Further reductions in the energy costs of operating a machine tool will reduce its life cycle cost to the benefit of machine tool users.
Machining centers in single-shift shops typically have about 2750 productive hours a year out of 4000 "on" hours—1250 hours are stand-by or sleeping, which still uses some energy. According to Prof. Dr.-Ing. Alexander Verl, Institute Director at Fraunhofer IPA (Institute for Manufacturing Engineering and Automation) and ISW (Institute for Control Engineering of Machine Tools and Manufacturing Units), the energy costs of a machine tool amount to about 20% of its life cycle cost. We have found, however, that controlling the peripheral devices in a machine tool according to actual needs can produce meaningful energy savings.
Improving energy efficiency starts with needs-based design of systems in the machine tool. Ways to achieve efficiency include progressive shutdown of the control by means of standby mode, low-watt valves, and operating just one cooling system in the overall machine. Collaboration with other manufacturers of machines and components to optimize peripheral equipment including hydraulics and coolant or refrigeration units also yields positive results.
Each new machine tool should be delivered to the user with ideas on optimizing energy use including individual regulation of chip conveyors or pressure regulation during coolant unit runtimes and run-on times.
There are other strategies for reducing energy use, too: Motors can be adjusted to the machine cycle requirements. Drive modules with lower power ratings can be used. There are also machine tools available that incorporate control systems capable of storing or even regenerating electrical brake energy, made almost exclusively by German manufacturers.
Further, using simulation technology, it’s possible to reduce moving masses and consequently the electrical energy required for generating highly dynamic movements. As a result, process stability increases and cycle times decrease while power requirements are reduced. A thermally stable machine design yields tremendous energy savings while minimizing thermal growth, reducing warm-up times and eliminating the need for extensive plant heating.
In single-shift operation, energy savings of up to 6% can be achieved simply by reducing the warm-up phase. Significant savings potentials also result from standby strategies, such as spindle deactivation and recognition of non-operation, resulting in switch-off as well as stop-at-end-of-shift and warm-up functions. Machining may also be optimized through a control override for adjusting feed override and a tuning cycle for adapting the machining operation to the process by means of defined cycles.
A great deal of energy can be saved by optimizing the changeover between full-load and part-load operation or idle state. For this purpose, Heller provided a machine to WZL (Laboratory for Machine Tools and Production Engineering) at RWTH Aachen University for extensive trials before and after a changeover. The energy efficiency benefits can now be proved.
However, with needs-oriented project-planning and optimized machining processes, savings potentials should be even higher.
Operation of the machine also needs to be customized. Factors to be considered include two- or three-shift operation, breaks, continuous operation or unmanned shifts as well as automation solutions. Process design also contributes to energy savings. This includes harmonization of component material and cutting material and choice of machine size, spindle power, torque and table size appropriate to the application.
Environmental awareness and the responsible use of natural resources are driving the need to develop technical standards in the machine tool industry for energy consumption. And political pressure on companies to become more involved in environmental protection is growing. Add cost pressure on machine tool users due to rising energy and commodity prices and you have all the reasons you need to improve energy efficiency. ME
This article was first published in the March 2013 edition of Manufacturing Engineering magazine. Click here for PDF.