“We can now do these noise excitation
optimized modifications — NEO modifications,”
Mehr says. “That means we create
a defined waviness to reduce noise in
a high-frequency whining noise. These
modifications are not new. You can make
them on the old Maag gear grinders,
where they do generate grinding with
indexing in a single flank contact. But
these machines have completely gone
away from the market.
“Now, Liebherr developed the mathematics
and the machine dressing and
machine movements to bring this correction possibility into the continuous
generating grinding process. That was the
trick — and that is absolutely brand new.
Maag machines, which were prominent
in the 1970s and 80s, have all but
vanished from the market in present
times as modern machines have gotten
faster and more efficient.
“There are still a few old ones kicking
around, but they are tremendously slow,”
says Scott Yoders, Liebherr’s vice president
of sales. “The cycle times are like
one hour — I’m sorry, one day — for a
part. But [when it comes to NEO modifications]
it’s the same principle.”
Instead of letting a possibly groundbreaking
innovation die with the old
Maags, Liebherr dusted off the decades
old process developed by its very own
Dr. Gerd Sulzer and applied it to cuttingedge
technology.
And what they discovered was a revelation
to modern generating gear grinding.
The situation is that we can now apply
[the NEO modifications] to generating grinding, says Yoders. “And that is really
state of the art.”
Idle Time is the Devil’s Workshop
Türich, vice president of product management
- grinding solutions, of Gleason
Corporation (Rochester, NY), has also
been working on conquering his own
burdensome list of gear grinding problems.
One of which, like Liebherr, has
been noise reduction.
“We have a slogan — which is a bad
slogan — but we say, ‘Singing gears are
happy gears,’” Türich says. “But nobody
wants to hear the gears in the gearbox
because it’s a terrible noise. So noise
issues are an important factor.”
Another concern, though, is shortening
grinding time, a point that brought
the conversation tangentially back to
both Cubitron II and Liebherr.
“To speed up the process is a neverending
story,” Türich says. “Every time
we think, ‘Wow, this must be the pinnacle,’
someone else is coming on the
market with a new grinding material and
you can once again increase your productivity.
“One important point here is the grinding
material Cubitron II, and I’m quite
sure [Mehr] over at Liebherr also told
you about it, because they are heavily
advertising this technology as well — and
they are right, it’s really something that is
maybe a game changer.”
But grinding time, according to
Tuerich, isn’t the only thing that matters.
“It’s not everything,” he says, “because
at the end what counts is the cycle time.
You also have to add non-productive idle
time, which is loading and unloading. If
you’re doing gear grinding, you have to
index your parts in order to mesh them
together with the grinding wheel. If you
can grind faster and faster but you’re not
working on your idle time, then your
idle time, in proportion, will get higher
and higher. This is something that customers
don’t like.
“This is something that we’ve recently
worked on. Our latest development is
a new grinding machine called 200GX,
which is a new double-spindle grinding
machine. There are two work spindles,
and on one spindle we are doing
the grinding cycle, while on the second
spindle — it’s the non-productive spindle
— we are exchanging the workpieces
and clamping and indexing the workpieces,
to minimize the idle time.
“This is our latest machine development,
although I should say this is nothing
really new to the market since there
is already some competition on the market
for a couple of years.”
Among those competitors are
Reishauer, which introduced their double-
spindle concept several years ago,
and Star-SU LLC (Hoffman Estates,
IL), a company that prides itself on the
uniqueness of its gear grinding machines
and its ability to consistently produce
products “equal or better” than anything
else on the market, according to president
David Goodfellow.
“We have a lot of gear grinding equipment
in both the horizontal and vertical
environment,” says Mark Ritchie,
Star-SU’s vice president of sales - engineering.
“Right now we’re promoting the
G 250, which is our vertical twin-table
machine, which is capable of being converted
into a single table machine up to
450 mm parts. In conjunction with our ability to contour dress and bias grind
we also have technology in our control
that manages all transmission errors that
are known to cause noise issues in a gear
set. We have also developed technology
that allows us to manage the surface pattern
and roughness of the gear surface to
further reduce the noise of the gears and
increase the surface toughness.
“For us, that’s kind of a unique thing
where it gives us a little bit more modularity,
if you will. We’re using the same
machine for various part sizes. We do
have some very interesting technology
that is available on the G 250 that we
don’t see on a lot of our competitors. We
have the ability to use threaded wheels
with an outside diameter of 110-90 mm
for special applications.
“We also have a spindle multiplier that
we use with very small CBN wheels that
allows us to do higher production, difficult-
type parts up to 24,000 RPM. These
are some of the unique features of the G
250.”
The G 250 machine, which debuted
at EMO in 2011, is based on the established
concepts of the Samputensili S
250/400 G machine — so consider it the
latest evolution of a product line that has
long been considered one of the industry’s
standard bearers.
“The vertical machines are more orientated
toward the automotive industry,”
Goodfellow says. “Very high-volume
production, and of course the trend
today in automotive transmission boxes
is going away from hob and shaved to
hob and ground gears. This leads us,
therefore, to the promotion of the G 250
double-spindle machine, which takes
cycle time out of the machine. It can
change the part very quickly and we’re
grinding parts down in about 10 seconds.
“So you need to change the workpiece
from the ground piece you just did to the
next piece in less than two or three seconds.
Otherwise, if you have a five second
cycle time between workpieces, then
50% of your grinding cycle is in your
workpiece changing.
“Everyone is in a fight now to take the
idle time out of the grinding process.
That’s the reason for the double spindles.”
Interestingly enough, for a company
that routinely throws out the
“unique” designation when speaking of
its machines, Goodfellow surprisingly
downplayed the notion that there’s much
of a difference between what companies
such as Reishauer, Kapp, Gleason,
Liebherr and Star-SU are doing in terms
of gear grinding.
“There’s nobody that has a super special,
unique thing that is so different
that nobody else can do it,” he says. “It’s
always about who has the faster loadunload;
whose got the more reliable
machines; whose got the latest technology;
whose got the best accuracy.
“I believe we are equal or better than
anybody else that’s out there.”
Goodfellow paused briefly after that
confident declaration, and then added:
“You also often don’t know what
somebody else has got on the drawing
board. But it will certainly be worth visiting
us at EMO Milan to see what new
technology advancements we’re coming
out with.”
Carrying the Load
Twenty-five years ago, Liebher’s Sulzer
had one of the busiest drawing boards in
the industry.
Among several processes Sulzer patented
while at Liebherr was one for a
form of polish grinding that created a
fine surface finish on cylindrical gears.
“It’s an old concept,” Mehr says. “It was
from the same guy: Dr. Sulzer. He had a
very creative brain. He patented the process
in 1988 based on an electroplated
CBN tool for roughing and finishing and
a resin bonded wheel for super finishing
mounted on one arbor … nobody wants
to have it. Twenty-five years running this
patent, nobody asks. Now the patents are
over and everybody wants to have it.
“Therefore, we had to [change the
process a little bit] due to the new abrasives
[on the market] — for example,
roughing with Cubitron II to get a fast
roughing process, then maybe we make
a finishing with a finer grit size, and at
the end [we use] the resin bonded, synthetic,
elastical polishing worm.”
Liebherr’s polish grinding process is
past testing and is close to going into
production, Mehr says.
According to Reishauer, polish grinding
is a final machining sequence performed
on a manufacturer’s existing gear
grinding machines that consists of one
polish grinding pass with a resin bonded
section joined to a vitrified bonded
threaded grinding wheel, said Walter
Graf, marketing manager for Reishauer
AG, during a presentation on polish
grinding at the CTI Symposium held in
May in Novi, MI.
According to Graf, the aim of polish
grinding is a reduction in surface roughness
without altering the gears’ macro
geometry, the gears’ flank topography
and the material surface structure. The
polishing process has to remove the peak
surface roughness, reduce the core roughness,
but leave intact some of the peak
valley roughness such that transmission
oil films continue to adhere to the transmission
gears. Because the surface roughness
of a polish ground gear is substantially
reduced, it will cause less friction in
a transmission and, consequently, would
offer increased load-carrying capacity
and a reduction in power loss.
“The reason for [polish grinding] is
that some customers want to increase
the load carry capacity on the gear
flank,” Mehr says. “You also can get a
better efficiency out of the transmission,
because you can change the transmission
oil; you can make it more liquid so
that the slipping wear when the gears are
running through the oil can be reduced.
“It’s possible, but not the biggest aim
for the customer to reduce gear noise
with this. It’s really load carrying capacity
of the asymmetric gears and the efficiency
of the transmission — those are
the two big aims.”
For more information:
Gleason Corporation
www.gleason.com
Liebherr USA
www.liebherr.us
Reishauer AG
www.reishauer.com
Star-SU LLC
Phone: (847) 649-1450
www.star-su.com
About Author
Erik Schmidt, Assistant Editor, has a Bachelor’s degree in journalism from Marquette University. He has a decorated writing history that includes stops at various journalistic enterprises in the Chicagoland area where he covered sports and hyperlocal news. He joined the staff of both Gear Technology and Power Transmission Engineering in 2014.
