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ticle
Gear Production Technology on Display
Makers of gear generation equipment are incor****ating machining
concepts long employed on machining centers into their products
Gear generation has not been immune from the trends affecting general
metalcutting. Like other manufacturers, gear producers are looking for
ways to cut their products ever better, faster, and cheaper. They need
flexible machines and tools designed to accommodate smaller lots,
squeeze out idle time during changeovers, and process jobs quickly.
They want machines that, in some ways, resemble general-purpose
machining and turning centers.
The more than 30 exhibitors in this year's Gear Generation Pavilion
have responded to this demand. They will be showing a variety of
products that have adapted concepts that began appearing in machining
and turning centers more than a decade ago. High-speed cutting and
quick changeovers will be im****tant themes.
In its booth, for example, Liebherr Gear Technology (Saline, MI) will
show a hobber capable of cutting as fast as 7000 rpm and 1700 m/min.
Using language common among machine tool builders, the company says
that this machine can load a new workpiece in 4.4 sec chip-to-chip. It
also relies on such things as quick-change grippers and fixtures to
streamline changeovers.
Spindle speeds between 5000 and 10,000 rpm will be a recurring theme
for cylindrical-gear production, because builders have been busy
designing new machines that get the most from the latest generation of
hobs. Like other cutting tool manufacturers, hob producers have
learned to exploit the latest coatings and substrate materials, as
they become available for an increasingly larger number of
applications.
The most im****tant development in this field has been the various
chromium nitride coatings that will stick to high-speed steel and
tungsten-carbide hobbing tools. Chromium nitride has a unique mix of
heat resistance and lubricity that makes it the coating of choice for
these tools. "The coatings are allowing people to run faster," says
Kent Yunker, director of R&D and new product development at Gleason
Works (Rochester, NY).
He also re****ts that he and his competitors have been experimenting
with ceramic blends, because ceramic is a substrate that can maintain
its strength and integrity at the very hot temperatures generated at
even higher hobbing speeds. Consequently, it's possible that you will
see some ceramic prototypes at the show. No one is promising to bring
any, but hopefully a vendor or two will bring some to show off a bit,
and to lay the groundwork for their introduction once saleable
versions are developed.
Although chipping of these materials has been a concern in the past,
manufacturers have found ways around this problem. "We avoid chipping
in ceramics the same way that we do it on carbide," says Yunker. "We
are rounding the edge a little." Others are developing manufacturing
processes that boost the toughness of these historically brittle
materials.
For the production of large gears with coarse pitches, the trend has
been a marked increase in the popularity of hobs and ga****ng cutters
using indexable carbide inserts, according to Scott Yoders at
Liebherr. For this reason, many tool suppliers will be showing
expansions to their indexable lines.
Although the initial investment is much higher than that needed for
conventional tools, gear manufacturers using indexable tools can reap
productivity gains in large-batch production similar to those that
other manufacturers enjoy from using indexable drills and mills.
Inserts allow the tool to cut at higher speeds and feeds.
The new coatings and substrates are freeing machine builders to design
and build faster machines. Not only will this generation of machines
be stiff, but it also will have precisely built spindles that will not
vibrate at the higher speeds characteristic of this new equipment.
"The runout usually has to be twice as good," says Gleason's Yunker.
The alignments of the spindles and outboardsup****t mechanisms also
must be better in these machines.
This higher speed and greater accuracy translate into better finishes
and accuracy, a result that is transforming hobbing into a fini****ng
process. Historically, hobbing has been a semifini****ng process that
usually required shaving, and perhaps grinding or honing, to follow
after heat treatment. With these new machines and tools, subsequent
operations are often unnecessary. Although this performance has been
true for specialty machines built for high production for a while now,
builders are expecting it to become more mainstream.
Another way that gearcutting machines are eliminating subsequent
operations is to adopt the multitasking concept that has become
popular among other genres of machines. Now that the automation and
control technology necessary to combine operations onto one platform
has become sophisticated enough to apply to specialized processes like
gear making, builders are incor****ating a number of gearcutting
technologies into their products. Gleason, for example, is developing
a machine for cutting cylindrical gears that will be able to do some
turning and milling before it goes into hobbing mode.
Liebherr has developed two ways to add chamfering and deburring to its
hobbers. The first involves adding a parallel-processing unit, such as
roll deburring for high-volume jobs, or an end-mill-type chamfering
unit for flexible production. The second approach relies on a
combination tool from LMT-Fette Inc. (Cleveland). Called ChamferCut,
the tool contains a hobbing cutter on one end and a profile cutter for
chamfering on the other. Software in the controller adjusts the feed
of the tool to put the correct end in the cut at the appropriate time.
Although the tool system is expensive, because it must be made as a
special for the application, it can more than pay for itself by
eliminating a subsequent operation. "You don't have to remove the
workpiece after hobbing," explains Yoders. "Chamfering is done in the
same station."
Besides multitasking, another way that builders are boosting the
flexibility of their products is to design gear grinders that can use
a variety of wheels. Yoders points to the new line of gear grinders
that his employer will be showing. These machines can do generating
and profile grinding with both nondressable CBN and dressable aluminum
oxide. Induction sensors and fast loading devices cut the idle times
for loading and me****ng in half, making series production with
grinding much more practical.
Another im****tant trend in gear generation has been greater interest
among automotive manufacturers in making bevel gears at angles other
than 90=B0. The interest began when European governments passed laws
reducing the height of the front of cars in an attempt to improve
pedestrian safety. "The drive shafts can't be in line because it would
make the front of the vehicle too high," explains Yunker at Gleason.
"So with the lowering of engines, there has come a need for a new
angular gear set in the automotive industry." For this reason, he says
that attendees will see a variety of new testing machines that will be
able to inspect gear sets made at these angles. =97 James Koelsch
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