NEW PRODUCTCNC Cylindrical Grinder GL4-SⅢ PREMIUM
The GL4-S III PREMIUM is a high accuracy CNC
cylindrical grinder optimal for the high accuracy
machining of automobile components associated withimproved fuel consumption, as well as high precisionrolls which manufacture aircraft components and medicalcomponents made from difficult-to-cut and new materials,
batteries for EV automobiles, and solar panels.

1) Stable dimension accuracy that lasts from the initial
workpiece· Sharp decline in dimensional changes from cold startdue to total temperature control of heat generatingparts
2) High shape accuracy· Improved wheelhead positioning accuracy throughfluid film lubrication and full closed loop control
3) High grade grinding· Higher grinding surface grade due to low vibration· Improved roundness due to higher rigidity

2. Structure
2. 1 Total temperature control of heat generating parts
Heat sources such as the wheel spindle, motor,
servo motor, and hydraulic pump exist on a grinder.
Temperature changes in these heat sources cause complex
thermal displacement to occur at each part of the grinder.
Thermal displacement can lead to changes in workpiecemachining accuracy.
We have suppressed thermal displacement in thismachine to the very minimum by implementing
temperature control for seven parts ranging from the staticpressure wheel spindle bearing to the motor, and in all
nine heat generating parts.

T h i s h a s a c h i eve d s u p p r e s s i o n o f wo r k p i e c edimensional changes to u3 μm at continuous 8-hour
grinding from cold start (Fig. 1).

Dimensions, umm

1. Features

44.49544.48544.47544.465
44.45544.44544.435

Following morning
Cold start

Cold start

8910111213141516171819Time

Fig. 1 Results of indirect auto-sizing plunge machining

2. 2 Improvement of wheelhead feed positioning accuracy
The slide surface of the wheelhead employs fluid film
lubrication applying the principles of static pressure
bearings, enabling long-lasting smooth feed without stickslip and improving positioning accuracy.
Furthermore, full closed loop control through a linear
scale and a low-lead ball screw are utilized for the feed,
achieving high positioning accuracy.
Figure 2 is an example of five-step 1 μm (u2 μm)
difference grinding on a cylindrical workpiece. All steps
were automatically ground using an ordinary grinding
program, achieving and step grinding of exactly 1 μm
(u2 μm).

Present point

Base point

Difference
Delta
Delta
STRt selection

1 µm (5 places)
u40
15300

1 µm
1 µm
1 µm
1 µm 1 µm

Fig. 2 Fully automatic micro step machining

HOUKO CO.,LTD
96

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

NEW PRODUCT
Figure 3 shows the grinding of a crowning-shaped
workpiece using a wheel with concave R-shape dressing
applied through simultaneous 2-axis control.
Generally, when the wheelhead feed direction changes
at the crowning peak, shape deformation can easily occur
due to backlash. This is called “quadrant protrusion.”
The GL4-S III PREMIUM achieves extremely smooth
grinding without shape deformation.

Grinding shape
Target crown quantity: 0.02mm

Expansion of crowning inflection point
1 µｍ
0.0218ｍｍ

No quadrant protrusion

Fig. 3 Simultaneous 2-axis crowning

2. 3 Improved grinding surface grade through lowvibration
The relative motion between the wheel and workpiece
greatly contributes to workpiece shape generation
during machining. Therefore, if vibration occurs within
the wheelhead or wheel spindle, it is transferred to theworkpiece during machining, causing deterioration ofsurface quality.
The following measures have been taken against theconventional machine in order to thoroughly eliminate
wheelhead vibration within this machine.
(1) Separation of wheel spindle pump and motor (changedto floor type)(2) Lower center of gravity to inhibit wheel shaking(3) Low vibration through obtainment of dynamic balanceof the wheel spindle motor and drive system
Dynamic balance was thoroughly obtained for eachindividual component of the wheel spindle motor
including the rotor, shaft, and pulley, particularly forthe main cause of vibration, listed in (3). Through thesemeasures, wheelhead vibration was reduced to 1/3 that of
the conventional machine.

2. 4 High rigidity
The rigidity of the workhead and footstock of theGL4-S III PREMIUM has been improved considerably
over that of the conventional. This has achieved betterroundness and high accuracy machining without
chattering, as the workpiece is able to be grinded while
held more firmly in the grinding center. In addition,
the wedge type taper adjusting device mounted on thefootstock enables precise cylindricity adjustment.
We have revised the installation mechanism of thewheel dresser to secure over twice the rigidity of theconventional product. This achieves high grade wheel
dressing in which neither escape nor hitting of the
diamond occur during wheel dressing, improving thequality of the grinding surface.
Figure 4 shows the results of fully automatic mirror
finishing.
A roundness of 0.07 μm and surface roughness of 20
nmRa were achieved with wheel grain size #80.

×100 000

Scale: 0.1 µm/Graduation

Roundness: 0.07 µm

Surface roughness 20 nmRa (0.02 µm)

Fig. 4 Fully automatic mirror finishing

HOUKO CO.,LTD
JTEKT ENGINEERING JOURNAL English Edition No. 1012E (2015)97