By Colleen DeJong
Some high-speed machining operations are becoming old hat. High-speed milling of aluminum, for example, is an application that's about 15 years old. But high-speed applications on other, tougher metals is still relatively new. As the capability to cut faster has evolved, machine tool builders claimed—perhaps justifiably so—that failure to achieve maximum feedrates were the fault of cutting tool makers not providing tools that could get the job done. Cutting tool manufacturers have been working hard to develop new technologies and materials to combat this image, bringing out cermets, ceramic tools, diamond tools, and a plethora of coatings and substrates. With all of the advances cutting tool manufacturers have made, one would think they've finally "caught up" to machine tool capabilities. Yet the great debate continues: Who can go faster?
How Fast Is Fast?
There are several challenges to getting to the bottom of this issue, not the least of which is trying to define "high-speed." It depends on the material, the type of machine, the type of insert, the type of application, etc. Perhaps the best definition comes from Lee Reiterman, product development manager at Valenite, Inc. (Madison Heights, MI). He put it this way: "Any speed above conventional for any material." That's as specific as it gets. One can assume that conventional is any speed you've been using thus far.
While the geometry issue has not gone completely untouched, there haven't really been significant advances. Especially in regard to depth of cut and the type of cut, where rake, angle, and other geometric considerations determine how a workpiece will be machined (and in some cases, how well it will be machined).
Among machine tool builders, the prevailing attitude is that there need to be more coating options, especially for the new exotic metals. Perhaps even made from some of these exotic metals. Dr. A.T. Santhanum, manager of carbide insert product development at Kennametal, Inc. (Latrobe, PA) seconds this, saying that cubic boron nitride (CBN) tool coatings could be the next great breakthrough. But first, scientists need to figure out how to get the CBN to adhere to the substrate material.
However, Neil Desrosiers, application engineer at machine tool builder Mazak, waves a cautionary flag, pointing out that there are already a lot of exotic substrates and coatings available, and perhaps there needs to be more education before there is more creation. "There are a lot of different coatings for exotic metals," Desrosiers says. "The problem is that we don't know much about them. They could have capabilities we don't even know about. We need a lot more information from cutting tool makers."
Machine tool builders also agreed that there were some parts of the machine tool that could use some work. Joe Kraemer, corporate accounts manager at Mazak and Desrosiers both cite axis drives as components with room for improvement. They are still much too sensitive to vibration, as are spindles, which have a tendency to go out of whack at higher speeds. "There are self-balancing spindles out there," says Kraemer. "But they are much too expensive to be used on a large scale."
Anything else? Microprocessors. Both cutting tool makers and machine tool builders agree that they can make products capable of cutting at extremely high speeds, but what's the point if the microprocessor can't process blocks fast enough to accommodate the desired speed.
Taking the Brakes Off Productivity
The Cutting Tool Story
Realizing a long time ago that advancing cutting tool technology meant acknowledging the growing synergy between cutting tools and machine tools, cutting tool makers began exploring new tool materials and coating materials that fit the machining needs of specific materials and specific applications. As they advanced, the machine tool builders did also, not wanting to stay behind for very long. This industrial "leap frog" game has been pushing rpms to ever higher rates. And, it appears that neither side is sitting still. Reiterman already sites areas of improvement for cutting tool technology. "We really haven't taken a good hard look at geometry yet," he says. "That'll be the next big area of exploration."
Eis Brake Parts (Berlin, CT) had been looking for a solution to bottlenecks in finish milling operations in the CNC cells that make hydraulic master cylinders from gray cast iron. Like every other company, Eis realized they needed to upgrade the system without dropping loads of capital on new equipment. Based on earlier success with retooling grooving applications, Eis brake manufacturing and tooling engineer, Warren David, asked cutting tool manufacturer Sandvik Coromant (Fair Lawn, NJ) to investigate and recommend a solution.
What Sandvik's team found was that operators were forced to reduce speeds and feeds in order to finish mill the cylinders. With a depth of cut of only 0.80 to 0.100 in., the operators had to be very careful not to take too much metal off the already thin cylinder walls.
The recommendation from Sandvik was to switch from a conventional, five-tooth, zero-rake shell facemill to a 45°, ten-tooth facemill. The inserts were changed to high-positive milling inserts designed specifically for cast iron. The ten-tooth configuration provides a tighter pitch, enabling higher, more accurate metal removal rates, while the inserts' geometry contributes to the higher metal removal rates, and provides a better finish quality than required.
The end results of the tooling upgrade were feeds increased by 3:1, speeds 20 to 30% faster, and a 15 to 18% net throughput improvement. Unexpected benefits for Eis include a 40% tool life boost over the old tooling, and reduced tooling costs.
But are the operators running full-tilt through these finishing operations? Not quite. To run at full potential now would mean that the finishing operations are completed faster than the rest of the cell can keep up. To keep a good balance within the production cycle, David has been running the machines at improved, but conservative speeds. At least they'll be able to upgrade the rest of the machines without worrying about future finishing bottlenecks.
Thinking about adding high-speed machining to your bag of tricks? Dr. A.T. Santhanum, manager of carbide insert product development at Kennametal, Inc. (Latrobe, PA) suggests you ask yourself a few questions:
1. Will high-speed machining fit into your total production process?
2. What will you be gaining by switching certain operations to high-speed?
3. What will you be sacrificing? Will you loose accuracy (and therefore, part quality)?
4. Are the parts you plan to machine at higher speeds amenable to the process? Really big and really small parts are excluded from high-speed machining by their very nature, take a good look at the type of parts you make.
5. Do you have the proper equipment? This may sound like a ridiculous question, but Dr. Santhanum points out that you can't just retrofit a machine's spindle and run at high speeds. A good high-speed machine will have a rigid base and a good control.
6. Do you have adapters and workholding devices capable of holding workpieces in high-speed applications?
7. Do you have a proper coolant delivery system? It should be flexible enough to handle various coolant types, and to be repositioned as jobs change.
And the Users?
With all of the work to be done bringing cutting tools and machine tools to higher speeds, users shouldn't just stand in the middle of the road waiting to reap the benefits. Cutting tool makers and machine tool builders can only do so much to make the most out of new technologies and faster speeds. Those using cutting tools should be actively participating in moving cutting tool technology forward. According to Joe Kraemer, many companies already have this philosophy. "People doing high-speed machining, especially of alloy metals, are very successful," says Kraemer.
Cutting tools, he says, are probably being taken to new heights of speed every day, thanks to highly creative research and development teams. Tool blanks, cutter grinders, and an open mind are all that they need to create their own "brew" of tools. But (there had to be a "but" in here somewhere) very few will ever hear about it. "They keep their success to themselves. It's their competitive edge." Good point. How many individual companies out there are cutting at amazing speeds using cutting tools they created themselves? And how many would be willing to share this information with the rest of the world?
It is also up to users to keep up to date with all of this new technology. Kennametal's Santhanum, recommends that users take the time to learn what's going on. "To use tools properly, you must acquire a good understanding of the general mechanical and chemical properties of substrate and coating materials being used," suggests Santhanum. "It will be easier to choose the right cutting tool when you know how it will interact with the workpiece."
Most cutting tool companies have manuals, training seminars, or web sites that are designed to teach people how to take full advantage of technologies as they are introduced. Several manufacturers indicated that more users should take advantage of these learning tools.
So, Who's Faster?
Well, it depends on what material you're running, and what machine tool you're using, and what cutting tool you're using, and how stable the factory floor is, and—well, you get the idea. So many factors are involved in achieving higher machining speeds that it is nearly impossible to come up with a clear-cut winner. Cutting tools have definitely caught up to machine tools, especially up to the 40,000 to 50,000 rpm range (again, depending on various factors).
At the end of the day, this means that products can be made better, faster. So the real winner must be the user.