TECHNICAL REPORT

Development of the GC20Mi CBN Cam Grinder
E. FUKUTA

The GC20Mi CBN cam grinder was developed to meet the need for technological innovativeness, highproductivity, and high accuracy stability in CBN cam grinders for grinding automobile camshafts. The GC20Mi is
belt-driven, with wheel diameter specifications of u350-120 m/s, u100-60 m/s and u150-80 m/s, and supports directdrive with wheel diameter specifications of up to u350-160 m/s. This enables users to choose the equipment best
suited for the target camshaft type. Furthermore, this grinder is equipped with the latest technological elements,
and was developed with careful consideration to operability and safety, as well as environmental friendliness.
Key Words: cam grinder, reduction of heat distortion, stable accuracy, operability, safety

1. Introduction

2. Aim of the development

In recent years, as needs for fuel-efficient and lowcost cars grow, automakers have been bringing a series of
new products that respond to the needs to market. Whileelectric vehicles (EV) and hybrid vehicles (HV) arereceiving attention, cars downsized for fuel efficiency andequipped with a highly efficient engine still represent themajority.
Due to these backgrounds, there is an increasing needfor high productivity, stable machining accuracy, andhigh machining surface quality from carmakers andmanufacturers specializing in camshafts. To respond to
this need, we have developed the GC20Mi CBN cam
grinder (this machine) as a successor of the conventional
machine GC20M so that CBN wheels and transfer units
can be newly developed and equipped, in cooperation
with JTEKT group companies. The overview of thismachine follows (Fig. 1).

JTEKT released the GC20M-63 CBN cam grinder in2005 under the concept of “optimal equipment suitablefor camshaft grinding” and has gained a high reputationin the market. More than 8 years have passed, however,since the machine was developed, and it is losing its edge
against competitors’ machines.
This machine adopts the basic unit, for which highreliability has been proven with GC20M-63. We have
improved its raw performance by implementing the latest
technological elements and utilizing CAE analysis andgiven it a facelift to achieve a texture consistent with itsquality. Since machines other than high surface speed andhigh output machines are conventionally used, customers
need to prepare maintenance parts for each machine. We
have developed this machine with an aim to maintain its
superiority over competitors’ machines by incorporatinghigh surface speed and high output functions.

3. Features of this machine

Fig. 1 GC20Mi CBN cam grinder

80①High accuracy and no need to compensate dimensions
In camshaft grinding, workpieces are grinded bysimultaneously controlling two axes that advance/retract
the wheelhead and rotate the spindle (workpiece).
In order to grind cams with high accuracy, thewheelhead needs to follow the workpiece rotation without
delay. As a wheelhead feed mechanism for this machine,
we have adopted a system driven by a linear motor
consisting of a static pressure slide without friction,achieving high tracking performance, eliminating theneed for feed screws and bearings, and securing longterm stability.

JTEKT ENGINEERING JOURNAL English Edition No. 1012E (2015)

−Development of the GC20Mi CBN Cam Grinder−

Workpiece dimensional change, uµm

Furthermore, the ribs of the bed, a machine base,have been optimally arranged based on CAE analysis,
minimizing the effects of thermal displacement of theworkpiece support point and grinding wheel position as
much as possible.
In addition, by cooling the heat generated by grindingand quickly releasing the heated coolant without keeping
it in the bed, thermal displacement has been reduced
by approximately 40% per shift (8 hours) comparedwith the conventional machine (Fig. 2). Dimensions
are conventionally compensated in the production line
during a quality check as necessary, but this machine
only requires an initial product check, thus improving
productivity.
②High productivity
As a grinding wheel spindle drive system, thismachine employs a belt drive system, which has been
conventionally used, with a wheel surface speed of 120
m/s. As an optional specification, a direct drive system
featuring a built-in motor with a wheel surface speed of
160 m/s is provided so that workpieces can be grinded
in optimal grinding conditions according to workpiecematerials.
The wheel spindle of the direct drive system has acompact and high output motor with an instantaneous
maximum output of 85 kW for high efficiency. In
addition, the motor is optimally arranged utilizing CAE
analysis to suppress the distortion of the wheel spindle
caused by the motor heat (Fig. 3).

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Grinding performance that suppresses the effects ofthe vibration caused by the wheel rotation frequency has
been achieved through a low vibration bed and “ToughVi-F” (Fig. 4), a CBN wheel developed by JTEKT groupcompany Toyoda Van Moppes Ltd., that has balanced
cutting quality and service life, achieving high efficiency(approximately 60%) and cycle time reduction (▲approximately 15%).
③ Operability and safety
JTEKT started to develop control units in the 1970s andhas made a series of improvements so that machines will
be easy to use and achieve full performance as control units
made by a machine manufacturer. GC20Mi is equipped®
with a newly developed TOYOPUC -GC70, achieving
5 times faster calculation speed and 10 times fastercommunication speed, with a substantial reduction in size.
In addition to the conventional easy-to-use touch panelsystem, global specifications including icons that enableintuitive operation and language settings that can beeasily changed allow the smooth start-up of a production
line abroad, etc.
There are functions for safety. Specifically, when themachine is manually operated by the handle, the motion
direction is displayed before the operation to prevent
erroneous operation, and when the initial workpiece isgrinded after a workpiece setup change, the wheelhead
slows down near interference objects to assist in checking
the operation through the grinding of the initial workpiece(Fig. 5).

Transition of dimensional change during no-load
continuous operationConventional machineu69 µm100

Developedmachine
Conventionalmachine

Developed machine
u43 µm−10−20−30

Front bearing
portionLoad(max. grinding force)−40

Rear bearing
portionMotor temperature: 120°C−50−60(Allowable temperature)
060

120

180

240

300

360

420480Friction loss in bearing portion

Time, min.

Fig. 3 CAE analysis of wheel spindle

Fig. 2 Transition of dimensional change of workpiece

Improvement in truing intervals

Air hole
Newly developed bond

3.0
2.5
2.0
1.5
1.00.50.0

Conventional
product

Newly developedproductTwice as better

050100150Grinding times, index

200(Index)
200

Marginal grinding efficiency

Grain

Surface roughness（mmRz）
3.5Wheel structure

160150100

100500Conventional
product

Newly developedproductFig. 4 Tough Vi-F CBN wheel

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Inching/handle mode

[Initial product automatic cycle]• Moves slowly near theinterference area when theinitial workpiece is grinded
after data change.

[Manual handle operation]• Moves slowly near theinterference area
(speed limit).

Footstock
Displays the traveldirection before operation

Fig. 5 Safety operation function

SupplySupply

Grinding
point

Grindingpoint

Circulation
filtering circuit
Anti-settlingagitation circuit

Anti-settlingagitation circuit

Collection

ReturnP

Anti-settlingagitation circuit
PPPP

ReturnSquare tank(clean tank)

Circular tank
Circular tank
Circular tankHigh cleanliness coolant feed system

54

3.95
3.2

3280 ppm

30 ppmInstallation space, m2

Energy consumption, kW

Conventional coolant feed system

5.0
4.5
4.1
4.0
3.5

3.5
3.080 ppm

30 ppmFig. 6 High cleanliness factor coolant feed system④ Energy conservation
A coolant supply unit is required for a grinder toremove the heat generated by grinding, discharge cutting
chips from the machine, and dispose of them. Stockremoval is significant in camshaft grinding, resulting
in a large amount of chips, therefore if chips are notproperly disposed of, problems including the scratchingof workpieces, inaccuracy caused by entangled chips
when a workpiece is clamped, overflow of coolant due toaccumulated chips in the machine, and failure of devices
may occur. A system that circulates coolant to a magnetic
separator using a circular tank of the coolant supply

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unit is conventionally used, but GC20Mi has adopted ahigh cleanliness factor coolant feed system with a newmagnetic circuit developed by JTEKT (Fig. 6). This has
substantially reduced residual foreign particles in coolant
from 80 ppm to 30 ppm. High cleanliness with 30 mg offoreign particles per liter of coolant has been achieved,
reducing scratches and greatly extending the coolant
replacement intervals. Moreover, the new system isenergy-saving and environmentally-friendly as the pumpused for the conventional circulation system is no longer
necessary.

JTEKT ENGINEERING JOURNAL English Edition No. 1012E (2015)

−Development of the GC20Mi CBN Cam Grinder−

4. Specifications
The specifications of GC20Mi are shown in Table 1.
Table 1 Main specifications
Item

Unit

GC20Mi-35

GC20Mi-63

Distance between centers

mm

350

Swing over table

mm

u320

Center heightmm

1 120630mm

u10〜u300

Outside diametermm

u350 [u100, u150]

Max. diametermm

Grinding diameter

CBN wheel

20Wheel diameter u350 ‒ Belt drive speciﬁcation: 120 [80][Wheel diameter u350 ‒ DD wheel spindle speciﬁcation: 160 & 120]

Surface speedm/s

Bearing system−

Drive system−

Feed system−

Rapid feed rate

m/min

u40

Min. input increment

mmu0.0001[Wheel diameter u100 : 60][Wheel diameter u150 : 80]

Wheel spindle

Wheelhead
feed
Wheelhead
traverse feedWorkhead

Feed system

Motor[DD drive (u350)]
Static pressure square slide, linear motor

V-ﬂat slide, ball screw
m/minMin. input increment

mm0.0001

Type−

Live spindle

Center20ー

MT No. 4

Max. rotation speed

min−1250

Min. input increment

Degree0.0001−

Hydraulic type [NC center adjustment type]

Center−MT No. 4StrokemmHydraulic stroke 60 [NC stroke 190]

Wheel spindle

kW22 [30]Wheelhead feed

kW

9.8

Wheelhead traverse feedkW

2.9Spindle

kW

2.5Truing unit

kW0.75 (2P)

Wheel spindle pumpkW

3.7 (4P)

Hydraulic oil pumpkW

0.75 (4P)

Lubricant pumpkW

0.4 (4P)

V200

Power supply voltage
Bearing oil
Tank capacity Hydraulic oil
Lubrication oil
Net mass

Belt drive u350 [u100, u150]

Rapid feed rate

TypeFootstock

Static pressure bearing

L70

L

25L

40kg

11 000JTEKT ENGINEERING JOURNAL English Edition No. 1012E (2015)83

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5. Machine layout
The standard layout of this machine is shown in Fig. 7.
2 77500

R600

710
2 540

227690R7044 955

R8Fig. 7 Machine layout drawing

6. Conclusion
We have developed this GC20Mi with consideration
to stable high accuracy, high productivity, improved
operability, safety, and the environment. As newtechnologies and needs continue to emerge, we willembrace them and endeavor to develop equipment thatpleases customers.

E. FUKUTA**84Machine Tools Development Dept., Machine Tools &Mechatronics Operations Headquarters

JTEKT ENGINEERING JOURNAL English Edition No. 1012E (2015)