by Kip Hanson
Exploring the impressive grinding technology behind cutting tool manufacturing
Provided they work as advertised, most of us tend to take cutting tools for granted. End mills and drills, taps and inserts—these are just a few of the high precision hunks of carbide or high speed steel (HSS) that can either make machining operations productive and profitable or unpleasant enough to consider early retirement. Thanks to increasingly capable grinding equipment and specialized machine software, most cutting tools are falling into the first category.
Bjorn Schwarzenbach, communications coordinator for CNC tool grinding machine manufacturer Rollomatic Inc., explains that much of this advanced capability is due to some fairly recent developments in machine tool technology, starting with linear drive motors.
“Granted, linear drives have been around for a couple decades or so in the tool grinding industry and aren’t exactly new, but we’ve taken the technology one step further by combining them with hydrostatic guides,” he says. “Our GrindSmart 830XW six-axis tool and cutter grinder is an excellent example of this. It offers an exceptionally high degree of rigidity and dampens the vibrations that occur during grinding operations.”
This increases grinding wheel life significantly, but also guarantees the extremely fine surface finishes and sharp cutting edges that give cutting tool users a competitive advantage, adds Schwarzenbach. As well, the combination of hydrostatic guides and linear motor technology offers additional advantages, such as non-contact, non-stick and friction-free slide movements together with reduced maintenance costs.
The company has also taken the interesting and apparently quite effective approach of using the same oil for the hydrostatic slides, spindle lubrication, and as a cutting fluid during grinding. “This allows the machine to be kept at a constant temperature and provides a remarkably high level of thermal stability, both during setup and grinding,” says Schwarzenbach.
ANCA CNC Machines is another grinding equipment manufacturer that has made the switch to linear motors. Global marketing manager Lucas Hale notes that these offer substantially higher traverse speeds, but their primary attribute is increased accuracy. “Even the best ballscrew in the world will have some small amount of localized errors along its length,” he says. “You can try to compensate for those errors with laser measurement of the various machine axes, or through the use of linear scales, but you’ll still see some of those artifacts on the actual surface of the tool once it’s been ground. The linear motors in our entire range of tool grinders eliminate all that.”
Stick to it
Aside from faster, more accurate grinders, ANCA, Rollomatic, and indeed most machine tool builders are meeting the increased call for automation by shops looking to run unattended. Both companies offer wheel changing systems, in-process laser measurement, integrated tool handling, and automated “sticking” of the wheel to remove build-up, all of which serve to increase efficiency.
“Some shops prefer to stick the wheel by hand based on operator experience, so we continue to support that option, but ANCA and others have found through testing that automated sticking delivers more consistent results, and does a better job of opening up the wheel,” Hale says. “This in turn leads to more consistent tool accuracy, so we’ve developed a software function that triggers the machine to re-stick the wheel when the load exceeds a certain threshold or at specific intervals.”
The demand for more capable machine tools extends well beyond automation. Hale and Schwarzenbach agree that grinding shops of all sizes are always trying to produce more accurate tools with higher quality surface finishes, a task that falls to tool grinders to complete. Much of this challenge is addressed with the improvements in machine construction already mentioned, but other steps must be taken to further reduce process variability.
For example, ANCA is using its patented “integral spring” technology to apply more consistent draw force on the workholding collet system, reducing tool runout.
And Rollomatic has developed an “ultra-efficient synchronous spindle motor” for some of its machine models that provides consistent rotational speed and torque regardless of the motor load. These and other machine builders are also promoting their own versions of Industry 4.0, offering advanced data collection and analysis functions that promise to increase machine uptime and improve throughput.
Both companies continue to develop smarter, more user-friendly software as well, a feature that’s especially important as skilled machine operators become more difficult to come by, and the cutting tool world grows more demanding.
“Using variable pitch, variable helix end mills as just one example, cutting tool geometries are becoming exceedingly complex,” says Hale. “We’ve developed software that not only makes the programming of these tools easier, but offers simulation to calculate and compensate for the cutter imbalance inherent with variable flute cutting tools.”
Schwarzenbach agrees, pointing to the need for reduced setup time as a key concern—as with much of the manufacturing industry, batch sizes are becoming smaller and smaller for many tool grinding shops, making the percentage of setup time proportionately larger.
“This is why we are continually working on ways to reduce blank scraps,” he says. “Our intelligent software assists the operator by making a 3D model of the part together with a machine animation, eliminating the need for a dry run—together with improved wheel dressing and other machine enhancements, this often makes it possible to produce a good tool on the first attempt.” SMT