A Sampling of Speed: Some Fast Machining Centers

Gary S. Vasilash

Although people often talk about the flexibility of machining centers, one aspect that shouldn't be overlooked is that some of them offer the ability to go fast. Here are some of them. None are particularly exotic, but they surely can be productive.

There isn’t a single company— OEM or supplier—that probably isn’t interested in doing things faster. The fact that product life cycles are decreasing regardless of what the product is drives this need for speed. To help accommodate this acceleration, equipment manufacturers have been working to provide machinery that is fast. Exceedingly fast with regard to such things as spindle speeds and axis movement.

That said, however, many of these equipment manufacturers, even those that offer fast machines, provide a caution. They correctly argue that what needs to be taken into account when making a decision about machinery and associated equipment is throughput, not sheer velocity in one aspect or another. At the end of the day (or shift or cycle or whatever it is that you use as a metric) what really matters is how many machined parts you’ve produced, not how quickly the machine was able to perform one aspect or another of its operations.

Still, just as we like to consider the performance of cars that go fast, so to there is a fascination with machinery that operates at blistering rates. Which brings to mind a story that was once told to me by the editor of one of the automotive buff books. He was talking about the Acura NSX, the aluminum-bodied sports car that’s now equipped with 290-hp engine and is capable of getting up in the 175 mph vicinity. And he said that of all of the sports cars in the world, the only one that he’d willingly drive through a desolate landscape would be the NSX because he was confident of its fundamental reliability as a machine. In other words, here was something that while unlike, say, an Accord in most characteristics other than both being Hondas, was something that would get the job done. So is the case with the machining centers we’ve collected here*. Fast, yes. But useful, too.

Heller Machine Tools (Troy, MI) has a lineup of horizontal machining centers that includes the MC 16 (630 x 630 x 630-mm cube) and the MC 25 (800 x 800 x 800-mm cube). These machines can provide a spindle speed up to 24,000 rpm. The spindle acceleration of 1 G brings the tool up to 8,000 rpm in 0.5 seconds. Chip to chip time is 1.8 seconds for tools 6-in. in diameter or less. Changing a loaded pallet can be accomplished in 9 seconds. All of which means that it is about keeping the tool in the cut longer rather than waiting for things to happen.

The NV5000 vertical machining center from Mori Seiki (Irving, TX) offers a spindle with a maximum speed of 12,000 rpm. What’s important to note about it is that, because it uses what’s called DDS—Direct Drive Spindle—a gearless mechanism, the machine is able to provide its full power—22 kW over 15 minutes; 18.5 kW, 30 minutes/continuous—at all speeds, which helps boost productivity. The spindle can go from 0 to 12,000 rpm in 0.97 seconds. It decelerates from 12,000 rpm to 0 in 0.91 seconds. Chip-to-chip toolchange can be accomplished in 3.1 seconds. The rapid traverse rate for all three axes is 42 m/in; the X-axis gets up to rate at 0.43 G; Y-axis acceleration is 0.39 G; and Z-axis acceleration is 0.74 G. One of the things that Mori Seiki engineers did was to benchmark their previous-generation vertical and then set about to trump it.

The DMP 60 V linear vertical machining centers from Deckel Maho Seebach [Germany] GmbH (DMG America) makes use of a linear drive on its X-axis so that it has a rapid traverse rate of 80 m/min. The rapids in the Y- and Z-axes are both 65 m/min. Axes acceleration is performed at 1 G. The 25-kW integrated motor spindle provides 18,000 rpm and a torque of 94.9 lb.-ft. So not only is there speed, but also high material-removal capability. There is a clever toolchanger, that has a modified double-gripper design, that synchronizes the turning and lifting motions when in action so that there is a chip-to-chip time of just 1.8 seconds. Look for more linear motors on various machines from DMG. The company is committed to using them where they make sense—like on this machine.

Designed to make quick work of things like aluminum cylinder heads, the BZ 500L from Grob Systems (Bluffton, OH), a horizontal-spindle machining center equipped with linear motors, provides an X, Y, Z-axis speed of 120 m/min. The 500-mm pallet machine accelerates to get there rather quickly, as well: 10 m/sec2 for the X- and Y-axes and 34 m/sec2 for the Z-axis. The top end for spindle speed is 18,000 rpm. And the chip-to-chip toolchange is 3.1 seconds. Although the machining center can be equipped with ballscrews, for those who are really seeking speed, this is the way to go.

Designed particularly for suppliers, the a51 horizontal machining center from Makino (Mason, OH) is a 400-mm pallet machine with a spindle that provides up 12,000 rpm. The a51 has a rapid traverse rate of 50 m/min and a cutting feedrate of 40 m/min. The axes travels are 560 mm for X and Y and 500 mm for Z. The tool-to-tool change time is a mere 0.9 seconds and the chip-to-chip time is 2.3 seconds. The index table rotates at 47 rpm. Makino has engineered this machine and others in its line to be not only affordable, but seriously capable.

Although the HMC 95 (500 x 400-mm pallets) and HMC 135 (630 x 500-mm pallets) horizontal machining centers from Giddings & Lewis (Fond du Lac, WI) are specifically designed for high-production environments (e.g., they’re built with a solid cast-iron design), there is a recognition of the importance of doing things rather rapidly in those places, so they’ve developed what they’re simply calling the “Speed Package” for these two machines. What this includes is a 16,000-rpm spindle that’s driven by a 35-kW motor. The drives have been pumped up such that the rapid traverse rate is 70 m/min. for the X- and Z-axes, and 60 m/min. for Z. The acceleration: 1 G. The package provides a chip-to-chip toolchange time of 2.7 seconds. For those looking for extra performance, the Speed Package is a must.