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More Profitable Toolpaths

Kip Hanson
By Kip Hanson Contributing Editor, SME Media
A high-speed milling application using a Sandvik Coromant Plura end mill. (Provided by Sandvik Coromant)

Adaptive Milling. Dynamic Motion. hyperMILL. Profit Milling. VoluMill. Waveform machining. If you’re one of the lucky people who machines parts for a living, chances are about 50-50 that you’re using one of these or a comparable high-performance programming technology to generate chip thinning, continuous engagement, high-axial and low-radial depth of cut toolpaths for your shop’s machining centers.

We’re not going to weigh in on the benefits of one CAM system vs. another, because all of them are pretty darned good—much better, in fact, than what was available even a decade ago (as is true with most everything in the machining industry). That said, give them a chance and each CAM provider will list a handful of features that make their software the best, with ease-of-use, greater productivity, and toolpath accuracy among the benefits. Which one is right? The answer is quite simple: it depends.

No Argument Here

Again, we won’t attempt to settle the argument today. Only carefully constructed test cuts or perhaps years of daily use will end this often-heated discussion, and even then, your mileage may vary. A more important question is this: are you applying the technology correctly? Is your chosen CAM package providing the greatest benefits possible to its users, or is it being held back by poor cutting tool selection, wimpy workholding, tired toolholders, or even the machine tool itself?

There are some very good reasons to find out. John Giraldo, aerospace engineer at Sandvik Coromant Co., Fair Lawn, N.J., said a Tier II aerospace manufacturer he worked with recently increased machining productivity by 198 percent on a Waspaloy LPT (low-pressure turbine) component after adopting a high-efficiency toolpath strategy using one of Sandvik Coromant’s Plura HFS end mills. And a Tier IV motorsports supplier used a similar approach to double tool life and triple throughput when machining titanium wheel hubs.

“There’s been growing demand in the aerospace industry for high-feed side milling in titanium and nickel-based alloys,” he said. “Traditional toolpaths don’t perform well in these hard-to-machine materials, thus the need for development of new programming strategies that not only maintain efficiency and productivity but also reduce any negative impacts on tool wear.”

It’s more than airplane and spaceship manufacturers that are on the hunt for novel and more effective toolpaths, though. Giraldo noted that the automotive industry continually pushes its suppliers to reduce production costs, a push that trickles down to cutting tool suppliers and CAD/CAM providers alike. And while suppliers have largely risen to the challenge, it’s often difficult for shops to adapt these advanced machining technologies to older equipment, never mind finding the time to test and validate new processes.

Exploring the Synergies

Jay Ball, North American product manager for solid milling at Seco Tools LLC, Troy, Mich., agreed. He said that at least half of all shops remain faithful to their tried-and-true, now decades-old programming methods, either because they’re not yet believers in today’s programming techniques, or their equipment is simply unable to achieve the significantly higher feed rates needed to implement them.

“It’s a real shame when you get a call from someone who read a magazine article or watched a video on high-efficiency machining and they’re excited about trying it, but then you arrive at the shop and find that their CNC equipment is antiquated, their toolholders are ten years old, and you know there’s little chance of effectively applying one of these strategies,” he said. “Worse, maybe you give it a shot anyway and it leaves the customer disappointed, and they’ll avoid trying it again once they do get a new machine.”

The co-dependent relationship involving the toolpath, cutting tool, toolholder, and machining center is one that many in the industry overlook, although everyone interviewed for this article agreed that it’s quite real. Despite this, pressure is high to develop novel, effective toolpaths. Ball said “pretty much any CAM provider” today has some form of high-efficiency machining within its offering and that they can’t compete without it, making it necessary for Seco Tools and its competitors to develop equally high-performing cutting tools.

For Ball, this comes in the form of flute counts well beyond the traditional four-flute end mills, with five-, six-, seven-, or nine-fluted versions readily available. High-speed, high-feed, high-efficiency, and high-performance cutters designed and optimized for advanced milling strategies are also increasingly common, often with variable pitch, variable helix designs to reduce the chatter-producing harmonics that might occur when cutting through steel and superalloys at hundreds of inches per minute.

Scaling Up

Despite Ball’s suggestion that a sadly-large percentage of shops have yet to jump on the high-efficiency bandwagon, he affirmed that these strategies are becoming more popular as machinists and programmers grow comfortable with the concept and how to apply it. “More and more people are being exposed to the technology every day, and once they recognize that cycle time reductions of 40 percent or more are fairly typical, you’ll see even more of them getting on board.”

Someone who knows all about it is Ben Mund, senior market analyst for Mastercam developer CNC Software Inc., Tolland, Conn. He said the Dynamic Motion technology in Mastercam mentioned earlier continues to grow in popularity and capability, adding that “we’ve introduced a broad variety of new toolpaths along with refinements of existing ones over the past year, all aimed at either increasing metal removal rates or improving our blending and surfacing capabilities.”

Seco Tools’ six-flute S638R ramping into a 4140 steel workpiece at a feed rate of 100 ipm and 4,000-rpm spindle speed. (Provided by Seco Tools)

Mund noted that productivity boosts are always available regardless of a machine’s age and the style of cutter being used, and he stated that Dynamic Motion is almost universally applicable. “It’s not going to falter because you’re using a less expensive cutting tool or lower-end CNC machines, but the benefits will definitely scale downwards as the setup becomes less than optimal.”

Over a Barrel

He was quick to point out that, while his statement holds true when using Dynamic Milling for roughing, 2D machining and 3D semi-finishing work, Mastercam’s “accelerated finishing” is another situation entirely. In that scenario, the toolpaths typically require a specific cutter geometry if they’re to achieve the desired results.

One example of this is barrel cutting, also known as circle-segment tool cutting. Mund noted that Mastercam has worked aggressively with cutting tool manufacturers to define and test these and other “shaped cutters” for use in moldmaking, medical machining, and aerospace finishing applications. These tools give users the ability to produce “really high-precision finishes in shorter amounts of time” than traditional surfacing methods.

He explained that this open door policy extends to all of Mastercam’s software products. “For example, we also worked with a leading cutting tool provider a few years ago when developing our Dynamic Motion toolpath engine,” he said. “We were having problems with chip control and getting to depth quickly during some internal testing, so we suggested they make some tweaks to their cutter geometry.”

As it turned out, the cutting tool supplier ended up adding a high-speed tip to its chatter-free line of end mills. Mund and his team learned a few things as well, which they’ve since incorporated into Mastercam features. “These are both great examples of the synergies that exist between hardware and software providers, where each participant ends up with a much better product as a result,” said Mund.

The Great Back and Forth

Thomas Raun, national product manager for milling at Iscar Metals Inc., Arlington, Texas, is another firm believer in partnerships between companies making complementary products.
“There should be a continuous back and forth,” he said. “Sometimes it’s the capabilities of their software that drives our development as a cutting tool manufacturer, and sometimes it’s the other way around. Either way, we’re completely open to working with CAM developers and machine tool builders alike if it means improving productivity for our customers.”

As Seco’s Ball mentioned, Raun said that one of the more recent developments in cutting tool geometry—more flutes—sprang directly from trochoidal milling’s light radial engagement and high feed rates. Iscar has taken this idea one step further by offering solid-carbide end mills with one flute for every millimeter of diameter, tools that in classic “chicken or egg” fashion are for the most part only effective with trochoidal milling.

“Of course, once you’ve taken that first step into high-efficiency milling, the next thing you’ll be looking for is greater axial engagement, so as to maximize metal removal,” he said. “Because of this, we’re seeing end mills with cut lengths of four and six times the diameter—these tools were available before but were primarily for niche applications. Now they’re fairly common. The challenge here, though, is that the chips might be several inches in length; they pile up really fast and are difficult to clear from the machining zone, so we’ve had to develop end mills with notched flutes, which split chips into manageable pieces.”

Iscar is working with software developers in other ways as well. Raun pointed to the creation years ago of libraries containing tool geometries and cutting parameters for inclusion into a variety of popular CAM packages. This places important application data a few mouse clicks away, he said, and because there’s no longer a need to manually key in these values, it essentially “poka yokes” the process of tool selection and feed and speed determination.

Despite this, Raun suggested taking these values with a grain of salt. “Programmers generally understand the higher feed rates needed for high-efficiency milling, but tend to overlook the potential for increased surface speeds,” he said. “A good rule of thumb is to double the recommended cutting speed when using a 10 percent stepover, and even triple it at 5 percent. Of course, that depends on the machine tool, because a lot of them can’t actually achieve the feed rates needed to maintain proper chip thickness at these higher spindle speeds, especially on smaller parts and complex geometries. In this situation, you’ll end up underfeeding the tool, which leads to rubbing and premature wear.”

Going Bonkers

When it comes to buying machine tools based solely on their feed rates and rapid traverse speeds, it pays to look beyond the spreadsheet, according to Wade Anderson, product specialist manager for Okuma America Corp., Charlotte, N.C. He said Iscar’s Raun is absolutely correct about feed rates, which is why it drives him “absolutely bonkers” when machine tool buyers base their purchasing decisions solely on a chart that compares values such as maximum feed rate and rapid traverse speeds. “You cannot, under any circumstances, prove what machine tool is best by looking at a spreadsheet,” he said.

Granted, comparing equipment specifications is an essential step in the machine tool evaluation process, but it’s not until the chips start flying that a machine’s mettle can truly be tested. This is only possible through realistic test cuts, preferably using your material, although not necessarily with your cutting tools and toolpaths. Unless your shop is fully up to speed on the high-efficiency milling curve, any machine demo will likely (and hopefully) introduce programming methods, toolholding, and cutting tools that your shop may be unfamiliar with—technologies that are absolutely necessary if you’re to be successful.

You can think of it as a triangle, Anderson explained, with the machine builder, CAM system, and cutting tools as three equally important components. “Obviously there are other variables like workholding and cutting fluids that enter the machining equation, but it’s these three that tend to spark innovations that the others must then chase and ultimately surpass,” he said.

For any application that utilizes high feed rates, chip thinning, and trochoidal milling strategies, Anderson recommends a machining center that has a superior spindle design with dual-contact taper and face connection, a machine structure with the proper mass and chip evacuation characteristics needed for high rates of metal removal, and a control capable of supporting extreme processing speeds.

This last part reiterates what Raun alluded to earlier, that just because you program a certain feed rate doesn’t mean the machine tool will ever achieve it. “For Okuma, it’s important that we provide a platform able to handle whatever innovations the CAM and cutting tool providers bring to market,” Anderson said. “This means a machine control and servo systems capable of handling the huge amounts of data that come with dynamic motion control, and advanced acc/dec and jerk curves that allow the machine to reach its maximum potential.”

There’s also longevity to consider. It’s one thing to see a dynamic high-speed milling demonstration; it’s quite another to handle this type of work over the course of several years. Said Anderson, “If the machine doesn’t have enough mass, or the spindle connection isn’t correct, or the control can’t keep up, the results will be less than optimal. All the variables must be in balance to fully realize the potential of the latest technologies, and do so for the long haul.”

Hello Old Friend

Having the right machine tool also opens the door to cutting tools once considered suitable only for specialty applications. Martin Dillaman, manager of applications engineering and a project manager at Greenleaf Corp., Saegertown, Pa., said ceramics fall into this category.

“Just last week we were discussing how, over the last five to ten years, machine tools have finally caught up with ceramic cutting tools,” he said. “Thanks to higher spindle speeds and greater machine rigidity, we can apply these tools more effectively than we could in the past. So not only are more shops now able to use our products, we also have the opportunity for additional development.”

Dillaman pointed to several of these developments, many of which were spawned through Greenleaf’s work with its customers and their CAM providers. These include phase-toughened ceramics that can better absorb the shock associated with milling operations, high-shear indexable cutters, a line of fine-pitch Excelerator end mills being released later this year, and even a foray into carbide cutting tools with the company’s Hushcut chatter-reducing geometries.

“We’re definitely seeing an increase in the number of customers moving towards high-performance milling strategies, and we are working to support them in any way we can,” he said. “We’ll sit down with their programmers and machinists to help them develop the best machining approach for whatever material they’re cutting and whatever software they’re using, even if that means asking our engineering department for a custom solution. A lot of shops are pushing the envelope these days, and it’s our job to give them the greatest success possible.”

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