How to Make Machine Tools More Sustainable
If you maximize spindle utilization and don’t use energy to run pumps when a machine is idle, you’ll make more (parts and money). So explains Adam Hansel of DMG MORI.
The University of California-Davis (ucdavis.edu) is just west of Sacramento, about 15 miles. If you were to take I-80 southwest from the campus and connect with Highway 12, within the hour you’d find yourself on Hwy 29 and traveling north through the Napa Valley. According to the university’s website, UC-Davis is:
• 1st among national universities in number of faculty papers written in the field of ecology and the environment, agriculture, entomology, food science and nutrition, and plant and animal sciences (ScienceWatch)
This emphasis on ecology and the environment, given its location, is not surprising. But about three miles east of the center of campus, there is something that is surprising. It is called the Digital Technology Laboratory (DTL). That sounds somewhat expected for the locale, being northern California. But it is the DTL of DMG MORI (www.dmgmori.com), one of the world’s leading machine tool manufacturers. And literally across the parking lot from the DTL is a $50-million, 200,000-ft2 manufacturing plant opened in 2012, where DMG MORI manufactures machine tools.
Adam Hansel is a graduate of UC-Davis. No, not from the College of Agricultural and Environmental Sciences, but from the College of Engineering. And Hansel is now the product managing director at DMG MORI Manufacturing USA. He joined the company in 2000. Hansel recalls that back then, he and some of his grad school colleagues worked to convince company head Dr. Masahiko Mori that it would be a good idea to set up a research facility in Davis. Clearly, one good idea led to another, and there are more than 80 researchers in the DTL today.
But there must be something to the influence of the ecology and the environment in the area, because Hansel says that they are keenly aware of sustainability in both how they make things at the plant and how the machines they build can help contribute to the sustainability of those who use them.
At a base line, Hansel points out that the MORI part of the company is headquartered in Japan (the DMG is European, with its roots in Gildemeister Aktiengesellschaft; the companies have been partners since 2009), and “Japanese culture is not wasteful.” So there is a cultural basis of the importance of sustainability. What’s more, he points out that after the 2011 Tōhoku earthquake in Japan, there was a mandatory 25% energy reduction across the country, which resulted in a rethinking of energy use across DMG MORI as a whole, even in its California facilities.
Hansel says that there tends to be two sides of the sustainability debate, with one side being as green as the other is skeptical. But he sees a coming together of the two in the arena of manufacturing for the simple reason that “being more productive, making more parts per unit of time, is a huge improvement for sustainability practices, and it also means more money in the pockets of even those who don’t care about sustainability.”
That’s right: more productive machines are more sustainable. He explains that generally, the “vast majority” of power use is not in the actual machining of metal but “all of the parasitic losses, like pumps, electronics, and hydraulic units” that occur when the machine isn’t machining parts. He says that studies at UC-Berkeley show that the amount of power being consumed for no productive reason is on the order of 40 to 60%. In addition to which, you have to calculate into the non- cutting time of the machine the overhead for the plant lighting, HVAC, etc.
“Getting the non-running times down to a minimum makes the machines far more sustainable,” he says. “So if we can use a five-axis machine or a mill-turn, where we can do everything on a single platform and the spindle is cutting the whole time, we can show dramatic decreases in energy use.”
He acknowledges that while people are familiar with their computers and smartphones going into energy-saving “sleep mode,” this is something that is just becoming part of machine tool functionality, with pumps turning off and electronics powering down after a user-specified period of non-use. When, as he points out, it is likely that standard job shops may have just 50% spindle utilization, that sleep mode can make a big difference on energy use.
But in higher-volume production, big differences can be realized in energy savings via small things. Hansel points to an automatic toolchanger for a machining center. While a toolchange can be made in two seconds, he says that if they are able to reduce that by 0.1 second, “it may seem like nothing, but over the course of a year in a production environment, that adds up to a huge amount of time that the machine would otherwise be idle.” And wasting energy.
They’re using inverter control to vary the output of motors to an on-demand state. “If we only need 10% coolant flow, then we’re running the motor at 10% of its capacity.” The previous norm is to have synchronous motors that are either running or not, so if you needed 10% coolant flow, the motor would still run at 100%.
He says they’re looking at spindle speeds in relation to axis travel. That is, say there is a long traverse before cutting commences and the spindle needs to be running at 10,000 rpm for machining. Typically today, the spindle is run up to that speed as the axis motors are bringing the spindle to where it needs to be for machining. So what they’re doing at DMG MORI is calculating the time for both the time it takes to get the spindle up to speed and the time it takes for the spindle to be positioned for the cut, and then adjusting accordingly: “If the spindle gets to maximum rpm half way through the rapid movement, then we slow the spindle down to save energy
without affecting the cycle time in any way.” That is, the spindle isn’t running at 10,000 rpm when it is still on its way to getting to where it needs to be.
Similarly, when it comes to face milling, Hansel points out that when the face mill clears the workpiece, the machining is over. “But,” he points out, “ordinarily, the feedrate is constant until the entire face mill not only clears the surface, but moves a distance past the workpiece. If we can calculate the edge of the workpiece, as soon as the face mill is halfway over the edge and it is done cutting, we can go to a rapid feed and pick up a couple of tenths of a second for every pass. It adds up over time.”
“Anything we can do to shorten cycle time,” Hansel says, makes the machine more sustainable.”
And that’s a good thing for everyone.