Gear Grinding Processing
Developed for High-Precision
Gear Manufacturing
YUKIHISA NISHIMURA*1

YUJI ASHIZAWA*1

TOSHIFUMI KATSUMA*1

YOSHIKOTO YANASE*1
KOICHI MASUO*1

In recent years, many industries have been trying to introduce gear grinding machines, backed by the increasing demands forlow-noise gears in automotive transmissions and for high-precision large gears in construction machines, gearbox for wind turbine
systems, and printing machines. To address these demands, Mitsubishi Heavy Industries, Ltd. (MHI) has developed and added to its
product line-up two gear grinder products: the ZE series for mass production of small gears and the ZG series for medium and large
sized gears. This document describes the features of these products from the technical standpoint and explores the future prospects ofgear grinding because it is anticipated that more manufacturers will adopt this machining technique.

1. Introduction

Wheel spindle
Multi-thread
grinding wheel

In recent years, from mass -produced small gears to
medium and large sized gears, gear finishing technologies
are used after heat treatment to reduce vibrations and noisefrom automotive transmissions or to improve the efficiency
and reduce the size of wind power generators. As for thetechniques for finishing gears after heat treatment, gear
grinding is commonly used in addition to carbide hobbing
and honing.
To add ress t he d iversi f ied gea r- g r i nd i ng needs ofcustomers, MHI offers two lines of gear grinder products: theZE series for mass production of small gears and the ZG series
for medium and large sized gears. The following describes
the features of these products.

TangentialfeedWorkpiece

Axial feed

Work spindle

2. Features of the ZE series gear grinding machine
2.1 Diagonal grinding
Gear grinders introduced into an automotive transmission
gear manufacturing line must satisfy productivity and tool
cost requirements in addition to machining accuracy. To
attain this, in ZE series gear grinding machines, we adopted
the continuous generating-grinding technique using a multithread grinding wheel. The use of diagonal grinding in
conjunction with the synchronized high-speed and highprecision control of the wheel and work spindles realizes
high-accuracy and high-efficiency grinding.
Figure 1 shows a schematic diagram of diagonal grinding.
Diagonal grinding is a grinding technique in which thegrinding wheel is fed into the workpiece in an axial direction
while being shifted along the tangential feed axis. Thisg r inding technique has advant ages in prevent ing thewear of the grinding wheel and improving the grinding
efficiency with stable precision, because the workpiece isFig. 1 Schematic diagram of diagonal grinding
Grinding wheel is fed axially into workpiece while
being shifted in a tangential direction.

constantly ground by new abrasives. ZE series grinders
provide the functionality to automatically dress the multithread grinding wheel using the rotary dresser and perform
diagonal grinding while sequentially shifting the portion of
the grinding wheel that grinds the workpiece. Figure 2 shows
the transition of the tooth profile pressure angle when thegrinding wheel ground 40 workpieces between dressing
cycles. According to the graph, the variation on both theright and left flanks is 2 μm or less, which means that themachine provides stable grinding precision even in highvolume gear production. Moreover, ZE series grinders canfinish approximately 8,000 gears per grinding wheel because
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)*1 Machine Tool Division

33

Profile angle deviation ( m)5

Correction
result A: Deviation on right flank : 1.6 m: Deviation on left flank : 1.7 m

0Measurement
resultRight flank 0.5 m
Left flank 0.5 m

Correction
result B

Right flank −2.7 m
Left flank −0.9 m

Right flank −14.0 m
Left flank −12.3 m-5Correctioninput value

Correction
input value-10

Right flank+3 m

Right flank−10 m

Correction

Correction

Left flank+1 m

Left flank
−10 m

-15

1611

16

21

26

31

36

No. of gears groundFig. 2 Transition of profile angle deviation between dressing cycles
Transition of pressure angle when 40 workpieces were groundcontinuously between dressing cycles.

Fig. 4 Example of pressure angle correction
Correction amount is entered based on result of accuracy measurement.

it allows the dressing interval to be set to as many as 40workpieces. This means that the cost of grinding can be
reduced to as low as 12 to 13 yen per workpiece.
2.2 Modification of tooth profile pressure angle
In the ZE series, to obtain a high-accuracy tooth profile,
the rotary dresser is set to almost the same position as thatof the workpiece so that the grinding wheel is dressed on
the machine in the same position and posture as when aworkpiece is ground. Because the dresser is set and adjusted
by an operator, there is a possibility of a setting error, which
in turn causes a profile pressure angle deviation. Although,on competitors’ machines, the correction of the pressure
angle is accomplished manually by fine-adjusting the dresser
position, to help inexperienced operators, we developed
a functionality that completes this adjustment by simply
entering NC data. The process of fine-adjusting the dresser
position is to change the relative positional relationshipwith the grinding wheel and this is achieved by using theNC system to move each axis to correct the grinding wheel
position with the dresser fixed. Figure 3 is a schematic
diagram that illustrates this function. Figures 3 (a) and 3 (b)show the relative positions of the wheel and dresser spindles

before and after pressure angle correction, respectively. To
develop this function, we analyzed the relative positional
relationship between the two spindles when correcting thepressure angle.
Figure 4 shows an example of correcting the pressure
angle by entering the required correction amounts forboth tooth flanks into the NC system. It can be seen thatthe correction results almost reflect the input values. Thisfunction is becoming indispensable for customers in Japan
where the number of experienced operators is decreasing
and in overseas manufacturing plants without experts.
2.3 Machining simulation technologies
In developing the ZE series, we created a machining
simulation program based on the theory of meshing between
threaded grinding wheel and workpiece and the existing
simulation technologies. A simulation example is shownin Fig. 5. The figure represents the shapes of both toothflanks at three points along the face width when the leads
are crowned. These are biased flank shapes in which thetooth profile pressure angle changes in the direction of theface width. The simulated data was very close to the actualmachining data collected from the grinders, so we decided touse the program to simulate various machining applications.

(a) Before pressure angle correction
m : Wheel spindle
zzPlane 2Plane 1yym
I : Dresser spindle
o2 Io1Dx Plane 1 Plane 2 : yz planez y: Axis angle
x(Grinding wheel side) (Dresser side)

Tooth profile

Crowning
10 μ(b) After pressure angle correction
m’ : Wheel spindle: Swivel angle
zz Plane 2’
Plane 1’m’ yy m’ is located on Plane 1’I’
I’ is located on Plane 2’o2o1xx Plane 1’ and Plane 2’
are parallel(Grinding wheel side) (Dresser side) (with same normal vector)

Lead: Locus of grinding points(points of contact)

Fig. 3 Pressure angle correction

Fig. 5 Simulation of generating grinding

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)34

2.4 Machining example of automotive transmission
gears (ZE24A)
Using the ZE24A grinder, we finished a final gear (moduleof 2.5, number of teeth 74, and face width 25 mm) with acycle time of 1.5 minutes and the accuracy of the finishedgear was JIS N1 grade for the tooth profile and lead and JIS
N3 grade for the pitch, respectively. The machining result isshown in Fig. 6.

Tooth profile correction patterns

Machining example using ZE24
Tooth profile accuracy

Lead correction patterns
1. Straight

2. Crowning

3. Relief

4. Side crowning

Fig. 7 Tooth profile and lead correction patterns
Tooth profile and lead can be entered and corrected in an easy,
conversational manner.

Lead accuracy

Workpiece (Gear)CZ

Lead25

Tooth profile
Workpiece specificationsModule
2.5
No. of teeth
74
Face width25 mm
Pressure angle
20°Helix angle
30° RH

Measuring probe XFig. 6 Machining result
An automotive final gear was finished in 1.5 minutes to JIS N3-grade
accuracy.
Fig. 3 Result of thermal analysis of spindle

3. Features of ZG series gear grinding machines
3.1 Tooth profile and lead correction
ZG series grinding machines use vitrif ied grinding
wheels, which can be dressed into any shape on the machinefor complex tooth prof ile correction. Moreover, thesegrinders can correct the lead of gear teeth by controllingthe amount of radial infeed of the grinding wheel. ZG
series grinders provide the standard tooth profile and leadpatterns shown in Fig. 7 and allow the operator to specify
the preferred tooth profile and lead in an easy, conversationalmanner.
3.2 On-machine measurement
For medium- and large-sized gear grinding machines on

Fig 8 On-machine measuring system and measurement result
Tooth profile, lead, pitch can be measured.

which the replacement and measurement of the workpieceis time-consuming, there is a strong demand for the onmachine measuring capability. In addition to the on-machinemeasurement function, ZG series grinders also provide
the ability to calculate the correction amount automatically
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)35

Qw’ (mm 2/s)=ΔX (mm) × F (mm/min)/60
Where,ΔX (mm): Amount of radial infeed
F (mm/min): Axial feedrate
Using the above formula, optimal radial infeed amountand feedrate values are set for each cycle. Next, the cuttingvolume limit is set according to the grinding wheel in use,
and then the dressing interval is calculated automaticallyfrom the cutting conditions as follows.
Dressing interval =Cutting volume limit (mm3/mm)/Amount of removed flank(mm3/mm)
Using the above formula, an optimal dressing interval
is set based on the specifications of the grinding wheel
and workpiece. Figure 10 shows an example of how thegrinding conditions are set automatically.

from the measurement result in an effort to automate jobs
that require operator experience. Figure 8 shows theappearance of the measuring system and an example of ameasurement result.
3.3 Bias modification
In profile grinding, the grinding wheel makes a line
contact with the workpiece and its direction is different fromthe locus of the points of contact in generating grinding. This
also appears as a difference in the flank shapes. Particularly,
when you crown a helical gear, generating grinding andprofile grinding produce opposite trends of biased f lank
shapes. Because many customers want to modify biased
flank shapes as desired, in profile grinding, we provide theability of flank shape modification that controls the contactlines and machine operations. On the ZG series, biasmodification is accomplished by the motion of the additionaltangential wheel feed axis during grinding. Figure 9 shows
an example of bias modification and its simulation result.

(Set value)
Cutting
Q'w
volume limit(mm3/mms) (mm3/mm)
Total radial infeed
0.826 (mm)5.0600
Rough grinding
Amount2.0300Semi-finish grindingof radial infeed
Finish grinding
1.5300()(Grinding conditions)
Amount No. ofDressingof radial grinding Feedrateinterval
infeed cycles (mm/min) Grinding pass
(No. of teeth)(mm)(times)
Before bias modification

After bias modification

Simulation of profile grinding

Before bias
modification

Roughgrinding

0.121

62 479Conventional/
Climb

15

Semifinishgrinding

0.06

1

2 000

Conventional

30

Finishgrinding

0.04

12 250Conventional

45Fig. 10 Automatic calculation of grinding conditions

After bias modification

Fig. 9 Example of bias modification
Tooth profiles were made almost equal at top, middle, andbottom of face width.

3.5 Machining example (1)Figure 11 shows an example of grinding a large gearusing the ZG1000 grinder.
We finished a large gear (module 5, number of teeth
162, face width 95 mm, grinding stock in tooth thickness
0.45 mm) with a cycle time of 3 hours 45 minutes, and theaccuracy of the finished gear was JIS N2 grade (JIS N0 grade
for the cumulative pitch).
3.6 Machining example (2)In gear grinding, as with other types of grinding, thesurface roughness is also an important factor in addition
to the accuracy of the tooth profile and lead. Since, in gear
lubrication, the oil film parameter λ (= film thickness/surfaceroughness) is closely related to the lubrication effects anddamage to the flank surface, the improvement of the surface
roughness has a large impact on the improvement in the3.4 Machining support software
In order to grind the tooth flanks of the workpiece withhigh accuracy, it is important to set grinding and dressing
conditions. In particular, in profile grinding, the operator
needs to speci f y t he d ressi ng i nter va l appropr iately
because a grinding cycle may include several dressing
cycles. Therefore, ZG series grinders provide the ability toautomatically calculate grinding conditions in the formula asshown below as a means to assist unskilled operators.
Regarding the grinding conditions, the recommended
conditions are calculated automatically based on the specificcutting rate Qw’ and the grinding stock as follows:

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)

36

left

JIS
Tip

performance and life expectancy of a gear. On these points,
the Mitsubishi ZG1000 gear grinder has achieved a surface
roughness of Ra 0.3 μm in large gear grinding. Figure 12
shows a machining example.

rightPROFILE20m

Tooth profile error
Left flank 2.9
Right flank 2.4(JIS N1 grade)

Va500:1
Vb2:1

4. Development of future gear grinding technologies

5mm

4.1 ZE15/24A (Generating gear grinding machine)(1) Bias grinding
As mentioned above, even in generating grinding,crowning a gear tooth causes the tooth profile to bebiased. However, in response to today’s customer
needs, we find it necessary to develop technologies tocontrol this bias.
(2) Improvement in grinding speed
To accomplish high productivity and cost reduction,
there is a strong demand for high-speed grinding.
Although the grinding speed V has been approximately
60 m/s -1 conventionally, it is now approximately 75
m/s -1 in practical use. In the future, it is anticipatedthat this will be increased to as high as 90 m/s -1. The
reduction of the non-cutting time in a grinding cycle isalso a requirement.
4.2 ZG400/1000 (Profile gear grinding machine)(1) Line-up of large gear machines
In the market of gearbox for wind turbine systems,
there is an increasing need for gear machines that
can handle a workpiece diameter of φ1,000 mm orlarger to support the target workpiece diameter ofapproximately 1.5 to 2.5 m.
(2) On-machine measuring system with higher precisionand higher speed
On a large gear gr inding machine, unloading
and then reloading a workpiece is time-consuming.
Therefore, it is becoming more important to develop anon-machine measuring system improved in accuracy
and speed.
(3) Adoption of a direct drive technology
It is c onsidered ne c es s a r y t o adopt a d i re c t
drive technology because high-precision control isimpossible if any clearance exists in each axis.
(4) Ease of workpiece centering
For large gears, facilitating the centering of theworkpiece is an important technology because it isdifficult and time-consuming.
(5) Development of production support systems
T here is an increasing demand for production
support systems that assist customers in simulating
the tooth profile, estimating the grinding accuracy,
automatically calculating the grinding conditions, andmore.

RootleftToprightLEAD

20m

Lead error
Left flank 1.7
Right flank 2.5(JIS N1 grade)

Va500:1
Vb0.5:1
20mm
Hottom
JISPitch error
Single pitch error
Left flank 2.6(JIS N2 grade)
Cumulative pitch error
Left flank 5.0(JIS N0 grade)

Tooth to tooth spacing fp lett

20 m
500:1

Tooth to tooth total accumulative Fpleft

20 m
500:1

Tooth to tooth spacing fp rightSingle pitch error
Right flank 1.9(JIS N1 grade)

20 m
500:1
Tooth to tooth total accumulative Fp

rightCumulative pitch error
Right flank 5.9(JIS N0 grade)

20 m
500:1

Workpiece specifications
ModuleNo. of teeth
Pressure angle

5mm
16220°

Helix angle
15.4°
Outer diameter 850 mm
Face width95 mm

Fig. 11 Machining example of a large gear (Machining result)
Finished gear was finished to a machining accuracy of JIS N2grade.

Left flank
0.24 mRoughness curve
Evaluation length 4.0 mm
c=0.8 mm×5×2K

Right flank
0.21 mRoughness curve
Evaluation length 4.0 mm
c=0.8 mm×5×2K

RaRa×20
Vertical
5.0 m/cm
Horizontal 500.0 m/cm

×20
Vertical
5.0 m/cm
Horizontal 500.0 m/cm

5. Conclusion
For gears used in automobiles, construction machines,
wind turbine systems, and general industrial machinery,
there is an increasing need for high accuracy and customers

Fig. 12 Machining example of a large gear (surface roughness)

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)37

are seeking high-precision, easy-to-use, and low-cost gear
grinding machines. To address this, for the grindingof relat ively sma l l gea rs (φ25 0 m m or less) used forautomobiles, we developed gear grinders that feature highefficiency, high precision, and low running cost by adding
diagonal grinding and other capabilities to conventional
generating gear grinding techniques. As a result, more
automobile gear manufacturers are introducing our machines
into their manufacturing lines. On the other hand, for thegrinding of φ500 mm or larger gears used in construction
machines, wind turbine system, and so on, we offer a lineup of profile gear grinding machines with additional tooth
prof ile/lead cor rect ion and on-machine measurement
capabilities to improve operability and more customers areintroducing them into their gear machining facilities. We
will continue to offer gear grinding machines that feature
higher efficiency, higher precision, lower running cost, andeasier operation.

Yukihisa Nishimura

Yuji Ashizawa

Yoshikoto Yanase

Koichi Masuo

Toshifumi Katsuma

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)38