Automotive Gears and Their Opportunities and … Gears and Their Opportunities and Challenges ... gear sets, composed of a set of ... Liebherr has also developed a new gear grinding

May 2016 | AdvancedManufacturing.org 61

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Automotive Gears and TheirOpportunities and Challenges

Bruce MoreyContributing Editor

Business is booming, but that

doesn’t mean it’s simple or easy

It’s a good time to be supplying the automo-

tive powertrain sector,” said David Goodfellow,

CEO of Star SU (Hoffman Estates, IL), reflect-

ing the impact of record setting vehicle sales in

2015. Gears are Star SU’s business. The com-

pany provides cutting tools, machine tools, and

servicing for practically any industry needing gears.

“About 50% of our business today is supplying the

automotive powertrain sector,” he said, not includ-

ing off-highway customers.

While business is good, it does not mean it

is easy. “The trends in the automotive sector are

achieving higher performance and better fuel

economy,” he explained. He has observed high

horsepower engines in the 300- to 500-hp range

mated to transmissions boasting up to 10 speeds.

More speeds translate into better fuel economy

by allowing the engine to operate at its most ef-

ficient load point more of the time. There is also

an increasing demand for all-wheel drive, which

means more transfer cases with even more gears.

Machines such as those

available from Mazak that cut

gears as part of multitasking

machine are ideal for low to

medium volume applications,

according to the company.

62 AdvancedManufacturing.org | May 2016

Competitive pressures require all these

gears to be quiet and robust over a long

time. That puts pressure on machine

tool makers to deliver machines that cut

gears faster to an almost unbelievable

tolerance level.

A good example are automatic trans-

missions. These often use planetary

gear sets, composed of a set of ring,

sun, and pinion gears. “We’re produc-

ing some of these pinion gears in four or

five seconds today,” he said. “Ten years

ago, they were being produced in a

minute or two.” That translates into ob-

vious savings for the customer, requiring

fewer machines. Faster cutting means a

much more rigid machine tool combined

with efficient automation and associ-

ated gaging. “Robust, noise-free gears

mean cutting them to a very tight tolerance,” he said. Where

even just a few years ago the industry spoke of tolerances in

the thousandths of an inch, today it is expected to be 3–5 μm,

according to Goodfellow. “That is a pretty dramatic change in

the fundamentals of gearcutting,” he said.

Process Changes, Quality Gears Made Cleaner

Another dramatic change in the process itself is the move

away from first hobbing a gear, then shaving it and then heat

treating it. Hobbing is a multipoint cutting process that rotates

both tool and workpiece in precise relations to each other.

It is used to rough cut multiple gear teeth at once. “Today,

automakers are hobbing gears, heat treating them and then

grinding them post-heat treat. This provides a harder, more

robust gear. Post-heat treat finishing of these gears eliminates

distortion or changes of geometry in that gear set. The toler-

ance requirement after grinding is pretty critical,” he said.

The push for environmentally friendly factories is adding yet

another challenge for machine tool builders—eliminating poten-

tially toxic coolants. “Nowadays, everybody wants to machine

dry to get rid of oil, contamination, smoke, and the potential

harm to operators as well as simply keeping a clean shop floor,”

Goodfellow said. Towards that end, Star SU partner Sampu-

tensili (Bentivoglio, Italy) introduced a new dry grinding machine

in October, 2015, in response to the pressure to eliminate the

mess and bother of coolants while grinding after heat treating.

Called the SG160 Sky Grind, it features two spindles, one for


A gear that has just been hobbed (cut) on the Kashifuji KE201 Gear Hobber,

available through Involute Gear & Machine.


skiving hobbing and the other for generating grind-

ing. Generating grinding is becoming a common

process for gears post heat treating. The grinding

tool resembles a worm gear with a grinding coat.

Like hobbing, both the tool and the workpiece rotate

rapidly in precise relation to one another.

Speed and Cost

“Cost is always a concern with automakers,” said

Loyd Koch, vice president and founder of Bourn and

Koch (Rockford, IL), citing another challenge amidst

the boom. Bourn and Koch supplies a wide range

of machine tools under 25 different brands, includ-

ing gear shaping machines. “Each time they add a

speed to the transmission, that translates into them

buying a lot more machine tools and may require

setting up a new plant to make those transmis-

sions,” he said. However, he stressed that even after a contract

is awarded, there is usually a cost improvement rate written in

requiring incremental year-over-year reductions. “They figure

once you get out of the engineering stage and into production,

you should be able to get better tools, better tool materials,

better coatings, and faster machines. We try to accommodate

them by building ever faster machine tools,” he said.

Star SU is a supplier of the cutting tools used by gear

shapers like the Fellows 10-4 that Bourn and Koch supplies.

“From our standpoint, the shaping end of it, they are looking

for high speeds, but the tools have a big impact on that. It

does not make any sense for the machine to go faster than

the tool can tolerate. As tool life improves, then that pushes

the speed of the machines,” explained Koch. To make

advanced machines that can drive the improved tools, he

explained, it is important to have linear motors replace ball

screws. Using advanced CAE tools to provide the lightest yet

strongest machine movements is just as vital. “It is impor-

tant to not overdesign gear shaping machine tools. That is

especially true with linear motors. Those devices are fast and

they do not like having to move a lot of weight,” he said. He

compares today’s machine tools to designing an airplane,

with honeycombs and special shapes to reduce weight.

Lighter Gears, Better Fuel Economy

Most of the original processing methods and innovations for

gear manufacturing date to the early 1900s (or before), accord-

ing to Scott Yoders, vice president of sales for Liebherr (Saline,

MI), including the invention of hobbing, shaping, and skiving.

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GMTA provides accurate gear cutting through their trademark scudding

process, described as a cross between hobbing and shaving by the company.


sions. As noted above, improved tooling and grinding wheels

have made some processes economical only recently. Other

techniques seem truly revolutionary and Yoders believes now is

the time for automotive to consider them.

One example is lightweighting. “In recent years, to reduce

weight, manufacturers have reduced the face width of their

transmission gears,” he said. This makes the chamfer on the

teeth ends, that runs the length of the involute, especially critical

as manufacturers reduce the width of the face. The common

way of producing that chamfer was to plastically deform the

sharp edge with a roll/press process. “A better way to engineer

that chamfer is through cutting, but that can eat into cycle

time without the right process. Lost seconds are real money in

automotive,” he said. Starting in 2014, Liebherr began offering

a method of both hobbing and precisely cutting the end relief

chamfer simultaneously while roughing the gear tooth. Offered

on the LC ChamferCut series of machines, Yoders describes

this as a parallel operation. “We believe it is five times cheaper

than the roll/press method when all tooling and expenses are

included,” he said. He noted that the method was developed in

conjunction with LMT-Fette, with its ChamferCut tooling solu-

tion, highlighting the need for a cutting tool that can keep up

with machine speeds.

Fuel Economy with Better NVH

While engineered chamfers are important for weight,

Liebherr has also developed a new gear grinding technology

that improves fuel economy and NVH directly. Gear manufac-

turers are increasingly designing asymmetric gear teeth—dif-

ferent pressure angles from left-flank to right-flank. To the

layman’s eye, these appear to be misshapen examples of

gears, but in fact account for different loadings in power

transmission on one flank of a tooth compared to the other;

drive-flank compared to coast-flank. “This increases load

carrying capacity while reducing NVH,” said Yoders.

The challenge, according to him, was developing a gen-

erating grinding process that specifically addressed dressing

of the grinding worm and the complex machine movements

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to accurately grind asym-

metrically. “We believe we

are the first to market to do

this for asymmetric gears,”

he said. Available on the

Liebherr LCS- and LGG-

platforms, he also noted

that these machines can

also provide the completely

new development called

generated end-relief (GER).

Until now, end relief in gear

grinding was only available

with the much slower profile

grinding method, where

each tooth is ground indi-

vidually. The GER grinding

has a similar effect—gears

can now be designed with

shorter face widths (i.e.,

lighter weight) but still carry

the same loads.

Perhaps the most

exciting new technology

for addressing NVH is what

Yoders describes as Noise

Excitation Optimization, or

NEO, developed in a part-

nership with the Technical

University of Munich “This

is similar to noise cancel-

lation in that we grind into

the teeth a specific wave-

length and amplitude of

the form error, both in lead

and profile direction on the

gear tooth,” he explained.

This introduces, on pur-

pose, a defined and engineered “waviness” in the profile form

deviation (commonly defined as ffα) and lead form deviation

(commonly defined as ffβ). Yoders presented audio data in

an interview with SME that dramatically demonstrated a gear

with significantly less gear whine after NEO correction.

Other gear manufacturing equipment suppliers have

noticed the increasingly stringent technical requirements in

automotive. “I think if you were to speak to an automotive

engineer about transmissions, they would say the difference

between the quality of the transmission [today] and one from

seven or eight years ago is something like 500%,” said Scott

Knoy, vice president of sales for German Machine Tools

of America (GMTA; Ann Arbor, MI). A unique process from

GMTA that helps provide that accuracy is their trademark

scudding process.

What is scudding? “Think of it as a cross between hob-

bing and shaving,” explained Knoy: A continuous generat-

ing process using a multipoint tool that eliminates issues

such as the spacing error known as drop tooth. “There are

no idle strokes on the machine tool, as you get with the

gear shaping process,” he said. He also noted that it prob-

ably will not completely replace shaving, since it requires

a cross-axis angle that prevents the process from getting

as close to a shoulder as shaving. “It is especially useful in

increasing the quality of the green machining, so that after

heat treating you do not have to do as much honing or

grinding,” Knoy said. “Presenting a more accurate part after


Gear manufacturers are increasingly designing asymmetric

gears, allowing higher loads with less NVH. Liebherr developed

a generating grinding process that solves the complex machine

movements needed to grind such gears.


heat treat keeps costs down.” Knoy also

hinted that hard scudding might be avail-

able in the near future, replacing a grinding

or a honing operation after heat treating and

further reducing costs while producing higher

quality, lighter gears.

There are a number of applications where

it could be the process of choice, includ-

ing ring gears, sliding sleeves, and annulus

gearing. Synchronizer parts and hubs are

also ideal, according to Knoy. For internal ring

gears, he notes that a special advantage of

scudding is in making lead corrections along

the face or flank of the tooth. “You can crown.

You can taper. This is something that the in-

dustry hasn’t been able to do with broaching,

which was the major way of making internal

ring gears for 40 years. In some instances, we

are replacing broaching,” he said.

Special Applications

The search for a quality finish is, in some cases, lead-

ing automotive manufacturers to look at honing after heat

treating and grinding gears, or as an alternative to grinding.

“We are seeing some desire for honing after gear grinding,”

explained Rodney Soenen of Involute Gear and Machine

(Chesterfield, MI), though he observes it is more popular

in aerospace. Involute is a provider of gear hone tools and

accessories, as well as a distributor of gear hobbing and

gear inspection machines. “We have seen some companies

experimenting with honing a shaved gear to increase quality,

or in some cases to repair gears. They may have a thousand

gears that perhaps for whatever reason were slightly below

expectations” and honing brings them back into compliance,

he said. He also noted that honing is popular for finishing

pinions and sun gears, critical and numerous gear parts in

automatic transmissions. “The honing process can be very

fast, depending on the style, and improved surface finish cor-

relates to increased durability,” he explained.

Machines that provide multitasking operations is another

niche area of gear and spline cutting. “Multitasking is aimed

at low- to medium-volume production,” explained Mike Finn

development engineer at Mazak Corp. (Florence, KY). Multi-

tasking machines that power skive gears and splines using

the synchronized rotation of a multitasking machine’s milling

spindle and C axis, as is done on some Mazak machines,

offers a lot of flexibility for low-to medium-volume production

The Fellows 10-4 Gear Shaper available through Bourn and Koch boasts an

infinitely variable stroking range of 50 to 1300 strokes/minute.



runs. “This would be useful for building prototype parts and

aftermarket applications, as well as off-road equipment,” said

Finn. “We successfully did that with crankshaft prototypes

many years ago and the same mind set could be made

towards gearcutting.”

For its skiving process development,

Mazak offers its Integrex Series Multi-

Tasking machines, according to Finn.

“Many machines can cut gears, de-

pending on the gear type, but our most

popular models are the Integrex series of

machines, ranging from the Integrex 100,

200, 300, 400, and e420,” he remarked.

“These cut gears and splines from 1 to

12" [25.4–304.8 mm] in diameter.”

Mazak is currently developing cutting

processes for power skived gears and

splines of all sizes and types, both OD

and ID in either straight and angled teeth

patterns, said Finn. “These machines

allow for easy part and tool changeover

with the toolchanger the tilting B-axis

milling spindle to accommodate different

cross-axis angles,” he said. He noted

that flexibility is the key advantage of a

multitasking machine. The same mul-

titasking machine that power skives a gear one day can ma-

chine completely different, nongeared components the next.

The same machine can also cut the part’s mating surfaces on

the same machine that cuts the gear teeth.

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Mazak859-342-1700 / www.mazakusa.com/

Star SU LLC847-649-1450 / www.star-su.com/

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Automotive Gears and Their Opportunities and … Gears and Their Opportunities and Challenges ... gear sets, composed of a set of ... Liebherr has also developed a new gear grinding