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Aero-style machining coming to auto: as the auto industry turns to materials that are certainly more exotic than the cast iron and aluminum that are familiar, the sorts of processes associated with aerospace manufacturing--albeit kicked up several notches--will find greater application.

There used to be a big gulf between the processes and materials in auto and aero. And it used to be, more or less, that aero would borrow processes or practices from auto for the simple reason that auto had managed to come up with approaches that were, in order to be done in automotive volumes, more or less optimized, or at least dialed in to the extent that would make them cost-effective enough to perform mass production. Aero, where things are generally done at a more leisurely pace (no 60-per-hour airframes) and with a significantly more advanced materials. After all, the budgets are not only bigger, but the conditions, rigors and requirements are greater.

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But now things are changing, says Greg Hyatt, vice president of the Mori Seiki Machining Technology Laboratory (www.moriseikius.com). "As automotive is pursuing higher and higher fuel economy, they're driving up the combustion temperatures, and we're starting to see the use of materials normally associated with turbo machinery and jet aircraft," he says. Among the materials are stainless alloys, nickel-based alloys, and titanium. "The cutting conditions used for those materials in aerospace are completely inappropriate for automotive production. They're extremely slow."

But Hyatt points out that the fundamental processes are being modified so that there is applicability in automotive: comparatively speaking, they become "high-speed machining." As he observes, "High speed is relative. Machining titanium valves and stainless manifolds is not high speed relative to aluminum machining, but it is high speed relative to the aerospace industry. But to get costs under control and to get parts produced for a price consumers are going to accept we need more aggressive cutting conditions than have been the case in aerospace."

Here are four developments from aerospace that are being brought to automotive. And while the cutting speeds aren't necessarily "high" as regards the RPMs and the traverse rates typically found in what's become "high-speed machining," Hyatt points out that what is becoming more relevant is high productivity rather than high speed: Getting more parts out more quickly than just operating machinery at higher speeds and feeds.

Grinding Rather Than Machining.

It's called "VIPER grinding," which is an acronym for either Very Impressive Performance Extreme Removal or Vitreous Improved Performance Extreme Removal. This technology was developed at Rolls-Royce aircraft engine operations (www.rolls-royce.com) along with Tyrolit (www.tyrolit.com), the Austrian grinding wheel manufacturer. Hyatt says that in the process, extremely porous vitrified grinding wheels are used--so porous "they're more air than wheel." The reason: the wheel is flooded with coolant, and it acts like a reservoir and consequently puts massive quantities of coolant right in the cut. "For difficult-to-machine alloys," Hyatt says, "we can actually rough grind the material and have higher material rates than we could with milling or turning." He says that parts made with stainless or those with a high nickel content are well suited to the process. It should be noted that they are not performing the grinding on a traditional grinding machine, but they are integrating the grinding into a conventional machine tool so that any additional turning, milling or drilling can be performed in the same setup.

Spinning and Turning.

Here it is a case where parts like titanium valves can be produced. Hyatt admits, however, that even the gains made by this process--he cites a 300% increase in cutting speed "as a starting point"--aren't what they might seem to be: "Ten times normal productivity for producing titanium parts is getting close to the normal productivity that Detroit is used to." Essentially, this is a development that comes from both Kennametal (www.kennametal.com), a cutting tool manufacturer, and Mori Seiki. In the process, both the round insert and the workpiece is rotated. Not only is the cutting speed increased, but so too is the feed per revolution, also about three times the norm. But because of the radius of the tool, good surface finish can be attained. Hyatt says that it is possible to machine with the minimum quantity lubrication (MQL) approach that's being pursued by more companies because the spinning tool brings the coolant into the cutting zone such that it is "much more effective than static lathe tools." Again, this process is being performed on standard machines, like the Mori Seiki NZ series of turning machines that include multiple turrets and integral motors to drive the tools.

Speed-Feed Grinding.

You may be familiar with creep-feed grinding, wherein the workpiece is moved in the direction of grinding wheel rotation very slowly. But because of that creeping, the depth-of-cut is significant. Speed-feed grinding is just the opposite. The wheel is reciprocated across the workpiece-it works best on cylindrical surfaces (e.g., valve stems) rather than prismatic parts--at an extremely high velocity. Hyatt explains, "There is a shallow depth of cut and the high feed, so the heat generated is distributed across a wide area." Because of this, there is no thermal damage to the workpiece. "With the high acceleration and traverse rates of modern machining centers," he observes, "we can do this on a modified standard machine." Mori Seiki is working with Tyrolit on developing this process.

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Grind Hardening.

This is a process that is being used in lower-volume applications-like producing high-performance parts for race cars or components for agricultural equipment-and the metal removal speed isn't particularly fast, but the total processing time for the parts are greatly minimized compared to conventional processing methods. Again, Mori Seiki is working with Tyrolit on what is certainly an unconventional approach. "We've done everything wrong intentionally," Hyatt says. Whereas the normal process of machining some medium carbon steel components is to machine, take the parts out of the machine and induction-flame-harden the surface, then put it back into a machine for finishing. What they're doing "wrong" in the grind hardening process is machining the part in its annealed state, then using the grinding process to put so much heat into the workpiece ("The material is glowing," Hyatt notes) that it is hardened. Then it can be finished with hard turning or grinding. This helps reduce the throughput time as it isn't necessary to move the part into a secondary heat-treating area. Because this process eats up the tools rather quickly, they're using their Hydrogage system, which uses the coolant in a way analogous to air in air gaging, but this is being performed in process. They are able to achieve a submicron resolution--better than the repeatability of the machine--and the measured results allow them to provide closed-loop control and tool compensation.

High-speed Mold Machine

With a 30,000-rpm high-frequency spindle and axis acceleration rates of up to 1.2 g, the Mikron HSM 300 MoldMaster is designed for high precision applications in the tool and mold industry. The machine from GF Agie Charmillles (www.gfac.com/us) features a pallet changer that permits multi-shift operation. Its travels are 14.97-in. X, 15.35-in. Y, and 10-in. Z. High resolution glass scales are used on all axes. The toolholder is an HSK E 40 type. It has a polymer-concrete base with high damping properties. Control is via the Heidenhain iTNC530 control.

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Robust Milling Cutter

Looking for a robust cutter that can operate at speeds that help optimize the performance of tipped polycrystalline diamond (PCD) inserts for aluminum machining and cubic boron nitride (CBN) inserts for other metals? Check out the VFlash mill from Valenite (www.valenite.com), which can operate at speeds of up to 20,000 surface feet per minute (sfm). It features a closed wedge-lock pocket design that protects 75% of the insert body, thereby permitting the absorption of high centrifugal forces. Because there is direct mounting of the inert, the clamping system is compact, which permits a more aggressive pitch and higher insert density, which permits the high feed and metal-removal rates. Diameters range from 2 to 12 in.

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Near-Net Means Less Machining

William Durow, milling specialist at Sandvik Coromant (www.coromant.sandvik.com) says that within the past few years, more castings are being produced with a near-net shape, which consequently means that there's less material to be removed ... which leads directly to highspeed machining. And he says that this is a common approach that's being taken by companies now. But more than high-speed machining, he says that a better approach is "high-productivity machining," which can also involve higher feeds rather than just faster rotational speeds. One thing that he is seeing is the development of inserts and toolholders that have the needed levels of hardness and locking to handle the rigors of the metal removal. He cites, for example, the company's recently introduced CoroMill 690 long edge cutter that was developed for titanium milling for aerospace, but which has applicability in automotive on aluminum, stainless steel and other materials. The cutter, available in diameters of 50 to 100 mm, features the iLock interface that keeps the inserts rigid for accurate machining. It can be used with the company's GC1030 inserts, which are TiAIN coated via the physical vapor deposition (PVD) process. Durow notes that PVD is becoming more prevalent, and it is allowing the production of inserts that have thin coating layers, which minimize such issues as crack propagation that can occur with thicker coatings.

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RELATED ARTICLE: High Speed or High Output?

Remember when discussion of acceleration in terms of g-forces was all the rage? Greg Hyatt, vice president of the Mori Seiki Machining Technology Laboratory, explains that that whole movement became a "victim of diminishing marginal utility." To push the axes faster and faster it became costlier and costlier and the benefits became lower and lower because there would be a decreasing amount of parasitic time to be eliminated.

Similarly, it was once the case where the cutting tool manufacturers would produce stronger, more durable tools that could run faster and faster. Hyatt suggests that if you look at the strides that were made in cutting tools up until the mid-point of the 20th century, they were "spectacular" as compared with what has happened since. He says that generally, the year-on-year improvement for cutting speeds of late is on the order of 3%. "Improvements are being made," he admits, but adds, "but not breakthroughs."

In his view: "We're realizing that the remaining breakthroughs are in the system. The whole processing strategy must change. We are no longer at a point where the enhancements are pursued unilaterally by the cutting tool manufacturer or the machine tool builder. The enabling technology must come from multiple partners."

by Gary S. Vasilash

* EDITORIAL DIRECTOR
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Title Annotation:FEATURE
Author:Vasilash, Gary S.
Publication:Automotive Design & Production
Date:Apr 1, 2009
Words:1765
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