Gear Cutting and Grinding
Machines and Precision
Cutting Tools Developed forGear Manufacturing for
Automobile Transmissions
MASAKAZU NABEKURA* 1

MICHIAKI HASHITANI* 1

YUKIHISA NISHIMURA* 1

MASAKATSU FUJITA* 1

YOSHIKOTO YANASE* 1

MASANOBU MISAKI* 1

It is a never-ending theme for motorcycle and automobile manufacturers, for whom the Machine Tool Division of
Mitsubishi Heavy Industries, Ltd. (MHI) manufactures and delivers gear cutting machines, gear grinding machines
and precision cutting tools, to strive for high precision, low cost transmission gears. This paper reports the recent
trends in the automobile industry while describing how MHI has been dealing with their needs as a manufacturer ofthe machines and cutting tools for gear production.
process before heat treatment. A gear shaping machine,
however, processes workpieces such as stepped gears andinternal gears that a gear hobbing machine is unable toprocess. Since they employ a generating process by aspecific number of cutting edges, several tens of micronsof tool marks remain on the gear flanks, which in turncauses vibration and noise. To cope with this issue, agear shaving process improves the gear flank roughness
and finishes the gear tooth profile to a precision of microns while anticipating how the heat treatment will
strain the tooth profile and tooth trace. After heat treatment, it was usual only to finish the portion of the gearthat accommodates a bearing.

1. Gear production process
Figure 1 shows a cut-away example of an automobiletransmission. Figure 2 is a schematic of the conventional, general production processes for transmission
gears. The diagram does not show processes such asmachining keyways and oil holes and press-fitting bushes
that are not directly relevant to gear processing. Normally, a gear hobbing machine is responsible for the

2. Recent trends in gear production1
As described above, gear tooth finishing based on thepredicted distortion due to heat treatment takes place
conventionally before the heat treatment process. The
recent stringent requirements for higher precision, however, prompts processes such as gear grinding and honing
to finish the gears to take place more frequently after
heat treatment. Since sophisticated processing techniques such as gear shaving have not readily taken rootoverseas, gear grinding is more often the choice.

Fig. 1 An automobile transmission

Material

Material

Turning

TurningGearcuttingGearcuttingHeat
treatment
ShavingHard
turning

CompleteHardturning

Complete

Fig. 2 Conventional production processes for transmission gears.
Normally up to the gear hobbing process. Gears requiring high-precision call for the shaving process.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)*1 Machine Tool Division1Material

TurningGearcutting

Material

TurningGearcutting

Material

TurningGearcuttingHeat
treatment
GearshavingHard
turningGeargrindingHard
turningGeargrindingHard
turningGearhoningCompleteGearhoningComplete

Complete

Fig. 3 Recent production processes for transmission gears
Gears requiring high-precision call for finishing processes after heat treatment. Gears of conventional accuracy end
at the shaving process.

Figure 3 shows recent gear production processes. The
honing process improves gear flank roughness and creates a three-dimensional tooth profile. However, sincefinishing after heat treatment pushes up production costs,
attempts to reduce the total cost are in progress. Since
each gear in a transmission is separately responsible forvibration and noise, each calls for its own optimal finishing method regarding precision and cost. For example, agear undergoing the grinding process calls for improved
hobbing precision instead of eliminating the shaving process. Another example is that the honing process calls
for shaving before heat treatment to save tool costs whilestabilizing the pre-process precision and reducing themachining allowance. Plastic processes such as die forging are also recent choices that increasingly employ amonoblock forging method to produce clutch teeth among
others. The following summarizes the recent trends intransmission gear production.
(1) Employing dry cutting
To improve productivity of gear cutting by highspeed cutting.
To reduce tool costs by making tool life longer.
To reduce cutting oil costs by employing dry cutting.
(2) Skipping shaving process
To skip the shaving process if tooth grinding comes
after heat treatment.
(3) Employing a monoblock forging process for clutchteeth
To use plastic processes (eliminating machine cutting processes).
To make gears compact.
(4) Developing gear production overseas and operators
being less skilled
To call for machine tools with ease of operation andmaintenance.
To enhance and improve operator support softwareand pre-services.
(5) Employing optimal processes for workpieces
To provide various machine tools to satisfy eachmethod of processing.

environmentally friendly but also reduces costs. To
this end, MHI has developed the world's first dry gear
cutting system. 2 More specifically, the developmentof cutters protected by Super Dry Coating as well asgear hobbing machines suitable for dry cutting has
realized dry gear hobbing. MHI's gear shaper also
employs the dry cutting method.
During hob cutting, the tip of the hob cutter reaches
a high temperature which makes it wear quickly. Hobcutters protected with Super Dry Coating have improved thermal strength. Since this enables the cutting
speed to be increased from the conventional 100 to 120
m-- min-1 to as high as 200 m-- min -1 while suppressing
tool tip wear to double the tool life, productivity has
improved considerably.
Figure 4 compares the changes in the coat compositions between Super Dry Coating and the conventional
TiN coating. When exposed to high temperatures, theTiN coating has its Ti oxidized and is transformed intoa brittle structure. Super Dry Coating, on the other
hand, is considered to have its aluminum selectively
oxidized to form a strong, hard layer.
Recently, MHI has developed the Super Dry II Coating with its high temperature oxidization
characteristics enhanced even further to realize acutting speed as high as 250 m-- min-1. The Super Dry
II Coating also demonstrates high anti-oxidization
characteristics at the high temperature of 1,200oC.

.
..
.
.
.
.
.
.

O
50
Ti
N
0

3. Precision cutting tools(1) Coating for dry cutting
Getting rid of coolant from workshops is not only100
Ti oxideComposition (%)

Composition (%)

100

1

2

3

4

5

6

Al oxide

50

N
AI
O Ti

0

1

2

3

4

Depth from surface

Depth from surface

TiN coat (thickness

TiAlN coat (thickness

5

6

Fig. 4 Comparison of coat compositionso
800 C, in atmosphere, maintained for 5 hours

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

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Quantity machined/cutter
re-sharpening(2) Carbide hob cutters for finishing after heat treatment
Finishing by a carbide hob cutters is gaining acceptance for small diameter gears such as steering
pinions because they are difficult to process on a gear
grinding machine after heat treatment due to the interference of the grinding wheel. MHI offers carbide
hob cutters for finishing that are a combination ofultra-fine particles, carbide alloy and a coating.
(3) Surface-treated shaving cutters
The shaving process accounts for the most of thegear finishing process. Surface treatment raises thesurface hardness of the shaving cutter to extend thetool life which in turn reduces the tool cost. Combined with the high rigidity design that takes theelastic deformation of teeth into account, the tool life
Fig. 5
actually improves 1.2 to 2 times (Fig.
5).

5 080

6 000
4 280

5 000
4 000

2 440

3 000
2 000
1 000
0

Other makeof cutter

High-rigidity High-rigidity design
design cutter cutter + super coatFig. 5 Improving life of shaving cutterssures against noise.
(3) Improving ease of operation and maintenanceImprovement in operator support systems and measures against operators being less skilled.
(4) Unification of line concept
Establishing a unified, total concept from hobbing
machines, gear shapers, shaving machines, gear
grinding machines to cylindrical grinding machines.
(5) Compatible with flexible production
Organizing major units into packages and modules
to make line configuration and re-configuration easy.
These developments have involved striving for customer satisfaction and implementation of CFT activities
comprising the marketing, design, assembly and service
functions. The standard specifications incorporate pastcomplaints and defects, customers' requirements andspecifications in an organized manner.
The development design thoroughly mobilized the 3DCAD system while a full design review for ease ofoperation and better workability took place in addition
to FEM analysis. MHI also strives to develop servo technology that has resulted in the NC guide gear shaper ST
series, synchronous shaving machines and synchronous
honing machines. Figure 6 lists MHI's lineup of gear

4. E series gear cutting and grinding machines
To answer the needs of the automobile industry as
described in Section 2 of this paper, MHI has integrated
the gear cutting and grinding machines such as gear
hobbing, gear shaping and gear shaving machines into
the E series along with the development of cutting tools.
The newly developed ZE series of gear grinding machines
for the generating process are also available. The letter"E" of the E series stands for being ecological, economicand excellent. The following concepts are the basis of
the developments.
(1) Global standard
Clearly defining the standard specifications compatible with development of production overseas.
(2) Thorough measures for energy saving and the environment
Standardization of energy-saving circuits and mea-

Gear production process
Lathe

Broach

Hobbing
machineGear shaping
machineChamfering Shaving
Heatmachinemachine treatment

Full dry cut
GE15A
GE20A
GE25A
GD10
Machine
tools

SE25A

ME20

GT06R (Hobbing +Chamfering + Rolling)Geargrinding machine

Gearhoning machine

Production cylindrical
grinding machine

Generating gear
grinding machine

Synchronous gear
honing machine

PD32

ZE15A

ZS25A

PD23

ZE24A

General-purposecylindrical grinding
machineForm gear
grinding machine

Cylindrical
grinding machine

FE30A
Synchronous gear
shaving machine

SD15

Helical guide-lessgear shaping
machine

SD25

ST25

RD23

ZG400

SC40

ST40

RD32

ZG1000RC45

Shaving cutter
grinding machine

GD20
GD30

FS30A

GD50
GB63

SC63

GB100

SC100
ZA30A

GBH18
Tools

SplinebroachShaving
cutterFig. 6 Lineup of MHI's gear processing machines and gear cutters

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)3

integration type shown in Fig. 7 that can later hookup with the modular-designed gantry loader with anarrowed width.
This machine is capable of machining a workpiece
as shown in Fig. 8 at a cutting speed of 250 m-- min -1
for a cycle time of 14.3 seconds, reducing the cost by
approximately 45%. Figure 9 shows the benefits ofintroducing this machine. If equipped with a coolant
unit, the machine becomes capable of conventional wet
cutting.
4.2 Dry cutting gear shaper SE25A
Figure 10 shows the newly developed E series gear
shaper model SE25A. With the structure around thespindle redesigned for high-speed dry cutting, the machine improves the maximum spindle stroke speed from1,500 min-1 to 1,800 min-1 and the cutting speed from 90
m-- min -1 to 130 m-- min -1 . To suppress vibration duringhigh-speed cutting, which is an issue with the gear
shaper because of the reciprocating motion of the cutter,
the SE25A has a new model balancer shaft. The arrangement successfully suppresses the vibration duringhigh-speed cutting to 1/6 or less of conventional models.

processing machines. By manufacturing and marketing
gear processing machines such as gear hobbing, shaping
and shaving machines, various gear grinding machines,
cylindrical grinding machines and cutting tools and evencommercially producing actual gears in quantity, MHI
is a total gear processing system manufacturer unparalleled in the world.
4.1 GE series gear hobbing machines compatible withdry cutting
To be compatible with dry cutting, the E series gear
hobbing machines incorporate the following features.
(1) Discharging chips: A cover provided in the machine
prevents chips from scattering. A steeply sloped covermade of stainless steel smoothly discharges chips outof the machine.
(2) High-speed operation: Adopting a spindle and tablespindle structure compatible with a cutting speed of
250 m-- min-1.
(3) Heavy cutting: Improving the machine rigidity andemploying large-capacity spindle motors.
The GE15A is available for choice in either the
standard type with a conventional layout or the line-

Workpiece specifications
1.4
ModuleGantry loader
Control box
installed onleft side ofmachine lessens
machine width.

34
Number of teeth
25 mm
Face widtho
17.5
Pressure angleoHelix angle
22.5 RH
Tool specifications
Type
Solid hobOutside diameter
58 mm
Starts4
Flute16
Coating
Machining parameters
Machining method
Climb cutGantry loader
can be installed later.

Control box

Hob rotational speed
Cutting speed
Axial feed rate
Cycle time

Index ration compared with conventional machine

Fig. 7 General view of GE15A(compatible for line integration)

1

Electricity
cost

0.9
0.8

Coolant
cost

0.55

0.5

0.2

After machining

Cutting tool cost:
40 % reduction
Coolant cost:
100 % reduction
Electricity cost:
33 % reduction

0.09

0.6

0.3

Before machining

Fig. 8 Actual processing data

45% reduction

1
0.06

0.7

0.4

1 370 min-1
250 m/min
2.0 mm/rev
14.3 sCutting
tool cost
0.85

Electricity
cost 0.04
Coolant Cutting
cost 0tool cost
0.51

0.1

Fig. 10 General view of gear shaper
model SE25

0Conventional machine

GE hobbing machine

Fig. 9 Case example: Benefits of introducing dry cutting

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

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Stroke width 21 mm, module 2.5, diameter 75 mm, spur gear
Stroke speed 760/1 200 min-1, cutting speed 50/80 m-min-1
Cycle time 49 seconds (conventional machine 73 seconds, production efficiency improvement 1.5 times)
Tooth profile error
500X
ROOT
FF
R1
R2
R3
R4

4
4
4
4

MEAN 3

TIP
FFA
FA
4
0
3
2
4
0
4
4
2
1

BIAS

FF: F

5

total profile
deviation

4.0X
ROOT
FF

L1

0

L2

0

L3

10

L4

10

MEAN 0

TIP
FFA
FA
3
7
3
6
3
9
3
8
3
7

BIAS

FA: FH profile
slope deviation

Tooth lead error

JIS class N6
BOTTOMFQ

BOTTOM

MEAN 4
BIAS

1

1

FQ: F

total helix
deviation

R2
R3
R4

profile form
deviation

44
4
4JIS class N4

4.0X

FH
FQA
4
1
4
2
3
2
4
2
4
2

R1

4

FFA: FF

500X
TIP

FQ
L1

2

L2

3

L3

3

L4

2

MEAN 1
BIAS

TIP

FH
FQA
-3
2
2
1
1
2
-1
2
0
1

2

4

FH: FH helix slope
deviation

FQA: FF helix form
deviation

Fig. 11 Example of machining by SE25A

Workpiece specifications
2.5

ModuleOBD diviation in continuously
dry machining

Machining parameters
Stroke speed(min-1)

40

600/1 000

Cp=3.13

20

Cutting speed(m-min-1)

Number of teeth

2.8

Diameter(mm)

75Face width (mm)15

Radial feed
(mm/str)0.009/0.01

Spur gear

Cycle time

90s

Helix angle

30

40/66

Circumferential feed 2.618/1.1122(mm/str)

10
0
-10
-20
-30
-40

0

5

10 15 20 25 30 35 40
Quantity

Fig. 12 OBD variation at continuously cutting

Figures 1
1 and 12 show case examples of machining
11
by SE25A. Restricting vibration results in stable, favorable machining accuracy. The thermal deformation that
could be a problem with dry cutting remains low while
the over ball diameter during continuous machining is
also stable. As with the GE15A, the SE25A is also capable of both dry and wet cutting.
4.3 Gear shaving machine FE30A
Figure 13 shows the newly developed model FE30A.
Reviewing the column and saddle structures using FEM
analysis improved their rigidity. The operation panel
has a large color graphics display to ensure easier operation and maintenance. The feature for monitoring
the spindle load currents helps to establish the machining parameters. In addition, data entry on the NC
screens alone allows tapers and the crowning amount tobe corrected. Figures 14 and 15 illustrate the principle
and actual data samples, respectively.
4.4 Gear grinding machines
Grinding gears after heat treatment to reduce vibrationand noise from transmission gears and improve final accuracy is drawing attention. As the E series gear grinding
machines, MHI has developed models ZE15A/24A3 to meetthese needs. These machines have the following features.

Fig. 13 General view of FE30A(1) Use of threaded, general grinding wheels and the shift
grinding method realizes stable, high precision grinding and reduces the tool cost.
(2) Use of built-in motors on the grinding and tablespindles realizes high-speed, high-precision grinding.
(3) With the dresser mounted on the ring loader, dressing while being clamped by the Hirth coupling realizes
high precision dressing on the machine.
(4) Use of the standard 8-axis NC system and various
machining support software offers ease of operationand maintenance.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

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Face width

Face width

K

K

CutterCutter facecDistance
between d'centers

Z

Taper

K

a

d

Workpiece

Workpiece
width

b

c
d
d'

b'
b

a

b'
Face widthc'a'Face width

Conventional
crowning method

With table at extreme left end

Guide rail
With table at center

Center of oscillation
Allowable table feed lengthWith table at extreme right end

Fig. 14 Taper/crowning principle

Machining example

Data
entry
(mm)

A simple data entry on the operation display can revise crowningand taper/crowning.
Zero setting

Tooth trace correction

Crowning

Taper/crowning

Amount of crowning

0.0

0.0

0.03

0.03

Axis A compensation

0.0

0.02
0.0

0.0

0.0
0.02

Amount of taper

0.0

0.0

Tooth trace accuracy

Fig. 15 Revised of taper and crowning

4.5 High-speed, high-precision synchronization
Placing emphasis on developing a high-speed, highprecision synchronous system, MHI has been the world
leader in developing the NC guide gear shapers and synchronous shaving machines.
(1) NC guide gear shaper
When machining a helical gear, a gear shaper uses
a device called a guide to make the cutter have a spiral motion along the tooth trace. Since a dedicatedguide that matches the lead of each cutter is necessary, a skilled operator has to change the guides whenusing cutters with different leads. MHI's ST series
gear shapers numerically control the spiral motion.
Figure 19 illustrates the guide structure.
These machines are capable of machining a twostep gear with different helix angles by a single
chucking as shown in Fig. 20
20.
(2) Synchronous gear shaving machine
In general, a gear shaving machine drives the cutter while the workpiece trails it. With no control
exercised over the workpiece in its direction of rotation, conventional shaving machines are unable toFig. 16 Gear grinding machine model ZE15A

While an operator conventionally has to fine tune thedresser to correct the pressure angle of a gear tooth, thesemachines, as shown in Fig. 18
18, only require data entry
on the NC screens to easily correct the gear tooth pressure angle, which in turn contributes to a considerable
improvement in workability and stable gear quality.
Figures 16 and 17 show the general machine view andan example of grinding parameters, respectively.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

6Grinding wheel specifications
Outside diameter 300 mm
Number of threads 3
Overall length 125 mm

Gear specificationsoModule 3, number of teeth 31, pressure angle 20 ,helix angle 20o (RH), outside diameter 105 mm, face witdth 40 mm

Dressing parameters
Grinding wheel revolution speed 70 min-1
Dresser revolution speed 3 260 min-1
Dressing time: 3 minutes 43 seconds
Tooth profile error

Grinding parameters
Grinding wheel revolution speed 2 580/3 800 min-1,
axial feed 0.8/0.4 mm/rev,
radial depth of cut 0.25/0.8 mm, climb/conventional
Tooth lead error

JIS class N1

500X
ROOT
MAX MIN
FQ

TIP
FH
FQA

4.0X
ROOT
MAX MIN
FQ

500X
TIP
FH
FQA

TOP

TOP

5
R1

0
5

-2
5

5
L1

0
6

5
R2

0
5

-2
5

5
L2

0
6

1
5

1
1

5
R3

0
5

-1
5

5
L3

0
6

2
5

-1
1
0
1
MEAN 1

1
1

4
R4

0
5

0
5

5
L4

0
6

2
5

1
1

5 0
MEAN 5-1
5

5 0
MEAN 6

1
5

0
BIAS

2

BIAS

2

BIAS

1

0
2

2
-2

L1

0

-1
1

1
1

0
R2

0
2

1
-1

L2

0

-1
2

1
1

1
R3

0
2

2
-1

L3

0

-1
1

2
R4

0
2

2
-1

1
MEAN
BIAS
0

0
2

2
-1

1

L4

FH
FQA

JIS class N1

1.0X
BOTTOM
MAX MIN
FQ

FH
FQA
1
5

2
R1

0

BOTTOM
MAX MIN
FQ

Cycle time:
78 seconds

Fig. 17 Example of gear grinding by ZE15A

Correction right + 3/left +1

0.5Standard (right -2.7/left -0.9

Correction right -10/left -10

Right 0.5

Right -14
-14.0

-2.7
Aiming at-2.7-10=-12.7

Aiming at-2.7+3=0.3

0.5

m)

Left 0.5

Left -12.3-0.9

Aiming at-0.9+1=0.1-12.3

Aiming at-0.9-10=-10.9

Fig. 18 Pressure angle correction
Conventional
machineSpindle motor
Crank

Crank

ST25CNC
Spindle motor

Helical guide (male)
Helical guide (female)

SpindlePinion cutter

Servomotor
for helix
angle control

Fig. 19 Illustrated explanation of guide structure

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)7

(1) Accuracy distribution after hobbing
10: L cumulative pitch: R cumulative pitch: Tooth run-out

8
6
4
2
0

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100(2) Accuracy after conventional gear shaving with workpiece trailing
12
10
8
6
4
2

Fig.20 Machining two-step gears

0

improve the pitch accuracy. This has moved MHI todevelop the synchronous gear shaving machine model
FS30A. 4 Figure 21 shows how much this machine
improves the pitch accuracy. While the synchronous
shaving finishes the teeth with the workpiece rotating in one direction only, the conventional machines
have to change the cutter rotation between the forward and reverse directions. Eliminating theswitching between the two directions contributes toreducing the cycle time. In addition, since the synchronous control maintains the correct positional
relationships between the cutter and the workpiece,
the cutter can copy its tooth profile correctly on theworkpiece. It has been reported that this makes thetool life control easy and has a favorable effect on extending the tool life.

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Almost no pitch accuracy improvement.

(3) Accuracy after synchronous gear shaving
14
12
10
8
6
4
2
0
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Pitch accuracy improves.

Fig. 21 Improvement in pitch accuracy by synchronous gear
shaving machine

5. Conclusions
As a comprehensive manufacturer of gear processing
systems producing both machine tools and cutting tools,
MHI has developed the dry cutting system, E seriesmachine gear grinding machines, among others, while
anticipating the future trends of the automobile industry. While continuing to develop product systems that
anticipate the need of customers, MHI is also willing tooffer the comprehensive services including remote monitoring of production lines, implementation of pre-services
and enhancing production support systems.
References(1) Hashitani, Dry Cutting System and Gear Finishing Process,Japan Society for Abrasive Technology Special Symposium
2004.1.19(2) Kage et al., Dry Hobbing of Gear, Japan Society of Mechanical Engineers Mechanical Engineering Congress Review 2003
VIII p.177(3) Hashitani et al., ZE15A Gear Grinding Machine for economical hard gear finishing of quiet, small gears, Mitsubishi Heavy
Industries Technical Review Vol.42 No.2 (2005)(4) Nabekura et al., The Synchronous Gear Shaving Machine
Aimed at Low-Noise Gear, Mitsubishi Juko Giho Vol. 39 No.4
(2002)

Masakazu NabekuraMichiaki Hashitani

Yukihisa Nishimura

Masakatsu Fujita

Yoshikoto Yanase

Masanobu Misaki

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 3 (Sep. 2006)

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