Development of Super Processing Center

-Basic Concept and Possibility of Turn-Grinding Method-

Daisuke Yoshii1, a *, Takeshi Nakano1, Yuki Tsukuda1

Minoru Ota1,b, Kai Egashira1, and Keishi Yamaguchi1 1Kyoto Institute of technology, Matsugasaki, Sakyo-ku, Kyoto, Japan

a yoshii.kit@gmail.com, b m-ota@mech.kit.ac.jp

Keywords: processing center, prototyping, multi-functional unit, process integration, turn grinding

Abstract. Ultra‒Agile Advanced Manufacturing System (U‒AMS) has been proposed for an agile

prototyping system of research and development, and Super Processing Center (SPC) has been

developing as a core machine tool of U‒AMS. In this report, basic concept and development status

of SPC is described. SPC has a high accuracy, a high rigidity, various functions and

process‒integration performance. SPC base machine has a double column structure based on a

vertical precision machining center. Hydrostatic oil guides and hydro static/dynamic hybrid oil

bearing were used in the base machine. A linear motor drive having 0.01 μm resolution was used for

positioning system. Moreover, SPC has various processing functions by mounting various processing

units such as a laser processing unit, an electrical discharge machining unit, a micro forming unit and

a high speed spindle unit to spindle head. On the other hand, the authors devised turn‒grinding

method to expand the versatility of SPC. In this method, a grinding wheel is set on the main spindle

and a cylindrical workpiece is held on a horizontal rotary table. Therefore, cylindrical grinding using

SPC will be carried out, and it is expected to integrate the processing steps of prototyping requiring

cylindrical grinding by employing the turn‒grinding method.

Introduction

The Ultra-Agile Advanced Manufacturing System (U-AMS) has been proposed as an agile

prototyping system for research and development, and a Super Processing Center (SPC) is being

developed as a core machine tool of the U-AMS. In this report, the basic concept and development

status of the SPC are described. In addition, a turn-grinding method which realize cylindrical grinding

by a vertical machine tool and extends the versatility of the SPC is described. SPC realizes a

process-integration performance of prototype requiring cylindrical grinding and has a diversity of

processing by employing the turn-grinding method.

Basic concept of SPC

The base machine of the SPC is based on a precision microfabrication machine (Zµ3500, Komatsu

NTC Co, hereinafter referred to as Zµ3500) to provide high rigidity and accuracy. The SPC has

various functions and realizes process-integration performance by a multifunctional processing unit.

As shown in Fig. 1, even parts such as pulleys, requiring multiple steps in their fabrication and

machining with many different machine tools in the conventional are expected to be realized by

ultrarapid processing by using the SPC to consolidate processes. The concept of the SPC is shown in

Fig. 2. The basic specifications of the SPC base machine are as follows. The machine has a double

column structure hiving a high rigidity based on a vertical precision machining center. It has control

axes of X, Y, Z, C, which are controlled by an NC rotary table (simultaneous control of four axes) and

an another axis. The amounts of movement along the X, Y, and Z axes are 500×700×300 mm for

small parts. Hydrostatic oil guides are used in the guide surfaces. Hydrostatic/dynamic hybrid oil

bearings, are used in the main spindle, which can perform milling, turning, and grinding. A linear

motor drive having 0.01 µm resolution is used for the positioning system. In addition, by mounting

multifunctional processing units that are mounted on the SPC base machine, it can realize a

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Proceedings of the 20th International Symposium on Advances in Abrasive Technology 3-6 December, Okinawa, Japan

process-integration performance, a multifunctional processing, versatility, flexibility, high accuracy,

and high rigidity. As shown in Fig. 2, the processing functional units include, for example, the small

electric discharge machining function units, the laser machining function unit, the micro forming unit,

and so on. The small electric discharge machining function unit is shown in Fig.3(a) and has been

developed for processing high hardness materials, narrow holes which are 0.3 to 3 mm in diameter,

deep holes with 500 aspect ratios. The laser machining function unit is shown in Fig.3(b) and has been

developed for expanding uses (which are cuttings, welds, heat-treatments, and so on.) by increasing

variations of laser oscillators. The Micro forming unit is shown in Fig.3(c) and has been developed for

plastic processing of free form surfaces [1][2]. Furthermore, the SPC makes it possible to perform more,

varied and high-accuracy processing by installing a high-speed truing device and a tool /

workpiece-measuring device.

Pro

du

ct

Ra

w M

ate

ria

l

Ultra-Agile Manufacturing Process

Super Processing Center

Conventional Process

NCTurning

VerticalMilling

SplineMachining

GrooveMilling

HardMilling

HardTurning

CylindricalGrinding

AngularGrinding

Ball GrooveGrinding

Heat-Treatment

Fig. 1 Ultra-Agile Advanced Manufacturing System

④Ultra High-speed Spindle

⑤Small Electrical

Discharge Machining Unit

⑥Laser Machining Unit

⑦Micro Forming Unit

⑧Fixed-Abrasive

Finishing Unit

⑨Small Honing Unit

⑩Ultra-sonic Vibration Spindle

High-speed Truing Equipment

Tool and Workpiece

Measuring Device

①Milling

②Turning

③Grinding

Super Processing Center

Scale FB Linear

Motor Drive

Hybrid Oil Bearing

Main Spindle

Universal

Rotary Table

Completely Oil

Static Pressure Guide

Multifunctional Processing UnitUltra Precision and High Rigidity Base Machine

Fig. 2 Basic concept of Super Processing Center

(a) Small electrical discharge

machining unit

(c)Micro forming unit(b) Laser machinig unit

Fig. 3 Multifunctional processing units

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Processing experiment using Zµ3500

A fine-cutting experiment on turning by

Zµ3500 was performed to determine the

microfabrication performance by the SPC base

machine. The condition of the experiment is

shown in the Fig. 4(a). The turning experiment

was performed by using a monocrystal diamond

turning tool to process V-shaped grooves on the

outer circumferential surface of the cemented

carbide rollers plated with electroless

nickel-plating with a groove depth of 1 µm and a

pitch of 4 µm. After the experiment, the groove

shape was measured using a laser microscope

(VK-X200, KEYENCE Co., Ltd.), the result of

which is shown in Fig. 4(b). It can be seen that

V-shaped grooves were formed at interval of 4

µm. The groove depth has a submicron

inclination, which was caused by thermal

displacement.

Dressing experiment for turn-grinding method

A turn-grinding experiment was performed

using a grinding cBN wheel (BN200L125VE4A,

A.L.M.T. Corp.) with Zµ3500. The shape and

dimensions of the grinding wheel are shown in

Fig. 5. First, as shown in Fig. 6, the dressing

experiment was performed to adjust the initial

shape of the grinding wheel and to dress the grains of its by rotary dresser (SD#100-C125-M64,

A.L.M.T. Corp.) with a diameter of 50 mm referring papers [3][4] about truing of small-diameter CBN

grinding wheel. The rotary dresser was set on a table and positioned at an angle of about 45° via a jig.

The end face of the grinding wheel was dressed the top of the rotary dresser. As shown in Fig. 6, the

dressing was performed from an outer to an inner peripheral edge of the grinding wheel along the

normal. Here, a single cut of 2 µm was made, the grinding wheel speed was 8,333 rpm, the dresser

speed was 5,000 rpm, and the dressing lead was 0.015 mm/rev. Also, the shape of the grinding wheel

became inclined as a result of one-way dressing. Then, as shown in Fig. 6, after the dressing reached

the inner peripheral edge of the grinding wheel, the dressing was performed with reversing the feed

direction and 2 µm cutting. By repeating this processing, the dressing was continued up to a total

dressing amount of 32 µm which is approximately the average grain diameter of the grinding wheel.

Micro form roller

Roller holder

Diamond bite

NC rotary table Digital microscope

Bite holder

(a) Photograph of processing situation

Hei

ght

[µm

]

Scan length [µm]

A A’

(b) Laser microscope view and cross-sectional

profile

Fig. 4 Micro grooving with turning

Fig. 6 The dressing experiment Fig. 7 The transcription of the grinding trace

8

20 100

10

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Then, as shown in Fig. 7, the grinding trace of the grinding wheel was transcribed on the soft steel

(SS400) surface by grinding to grasp the end face of it. The transcription was performed under the

condition that main spindle was rotated at 15,000 rpm, the depth of cutting was 20 µm, and the feed

speed was 0.06 µm/min. From this, when the transcription was performed, the condition follows the

above it. The result of transcription was observed using a coherence scanning interferometer

(NewView 8200, Zygo Corporation, hereinafter referred to as NewView 8200), and is shown in Fig. 8.

Unlike in general dressing, the speeds of the grinding wheel in the outer and inner peripheral edge are

different. The ratios of the dresser speed to the grinding wheel speed are 1.50 and 3.75 at the outer and

inner peripheral edge of the grinding wheel, respectively. According to the result, the difference in the

speed ratio has little effect on the grinding trace. The above dressing conditions were used in the

grinding experiment, because the transcribed surface was near the plane and dressed.

Fig. 8 Photograph of the transcription and the surface roughness

Cylindrical grinding by turn-grinding method

The experimental condition of turn-grinding is shown in Fig. 9. The grinding wheel was set on the

main spindle and ground the step part of the stepped round bar set on the NC rotary table. First, the

vibration of workpiece was removed by grinding for preparing initial condition. Vibration of 30 µm

was measured at the workpiece tip by a lever type dial test indicator when the workpiece was first set

on the NC rotary table. Then, the workpiece was ground to a diameter of 40 µm, where the speed of

main spindle was 15,000 rpm, the speed of the spindle on the NC rotary table was 120 rpm, the cutting

was 2 µm in the radial direction per pass and the feed speed was 20 mm/min. Also, the grinding

direction was changed at the center of the grinding wheel. Under these conditions, the grinding

direction changed down-cutting to up-cutting. Also, the grinding experiments below were performed

under the above conditions. After removing the vibration of the workpiece, it was removed from the

NC rotary table to observe the surface. Then, the surface at the center of the workpiece’s step part

was observed by the NewView 8200. Also, the

diameter was measured by a digital micrometer.

The measurement positions were the tip, the

center, and near the shaft of the workpiece’s

step, and the three measurement points were

located at equal intervals on the outer periphery

of the workpiece. The workpiece was set on the

NC rotary table once again and the vibration of

its tip was set to 6 µm. Then, one hundred passes

were performed in the grinding experiment.

Here, the diameter of the workpiece was

measured every 10 passes for the first 50-passes.

Then, the surface was observed and the diameter

was measured after 50, 75, 100 passes in the

grinding experiments.

Fig. 9 Photograph of processing situation

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Result of turn-grinding experiment

The photograph and optical micrograph, using

optical microscope (STM6-LM, OLYMPUS), of

the workpiece after 100-passes grinding are

shown in Fig. 10. The surface was processed with

almost a mirror surface. Also, comparing the

diameter of the tip and near the shaft of the

workpiece’s step, the diameters are 24.504 mm

and 24.509 mm, respectively. It is considered that

this tapered shape is caused from deflection by

cantilever support. The actual amount of grinding,

calculated from the diameter of the grinding

wheel, and the set amount of grinding are shown

in Fig. 11. The actual amount of grinding and the

set amount were almost the same up to 50-passes.

The surface of the soft steel, on which the

grinding wheel surface was transcribed, is shown

(a) After removing the vibration of workpiece

and (b) After 100-passes grinding experiment in

Fig. 12. Comparing Fig. 8 and Fig. 12, grinding

abrasion was observed near the outer and the

inner peripheral edge part of the grinding wheel.

Also, the fine unevenness observed on the profile

becomes finer from Fig. 8 to Fig 12(a). It is

considered that the inclination of the grinding

abrasion was caused by the difference of the

grinding wheel peripheral speed. The observation

of the workpiece surface (a) before grinding (b)

after removing the vibration of workpiece (c)

after 100-passes grinding experiment are shown

in Fig. 13. And those surface roughness is Sa

0.227 µm, Sa 0.066 µm and Sa 0.051 µm,

respectively. Finally, it is confirmed that a mirror

surface was obtained. Also, a periodic pattern

was observed on the workpiece surface in the

direction of grinding wheel feeding and in the

direction of workpiece rotation. The periodic

pattern in the direction of workpiece rotation has

a period of about 0.63 mm intervals, which

matches the amount of rotation of the workpiece

per revolution of the grinding wheel. The

periodic pattern in the direction of grinding

wheel feeding also has a period of about 0.17 mm,

which matches the feed of the grinding wheel per

revolution of the workpiece. It is also considered

that the shape of the grinding trace was

transcribed on the workpiece surface. These

observations indicate that the periodic pattern

can be controlled by controlling the grinding

conditions.

Fig. 10 Photograph and optical micrograph view of

the workpiece

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

0 10 20 30 40 50

Gri

nd

ing a

mo

unt

[µm

]

Processing passes

actual grinding amount

set grinding amount

(4 µm in diameter per pass)

Fig. 11 The actual and set grinding amount

(a) After removing the vibration of workpiece

(b) After 100-passes grinding experiment

Fig. 12 The surface roughness of grinding trace

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Proceedings of the 20th International Symposium on Advances in Abrasive Technology 3-6 December, Okinawa, Japan

(a) Before grinding

(b) After removing the vibration of workpiece

(c) After 100-passes grinding experiment

Fig.13 The surface roughness of the workpiece and cross-sectional profile by turn-grinding

Summary

The basic concept of the SPC, which is the core of the U-AMS agile prototyping system, was

examined in terms of its feasibility and the following results were obtained:

(1) Fine outer circumferential grooves were formed by super-precision turning using a precision

microfabrication machine (the base machine of the SPC) and a fine processing performance was

confirmed.

(2) The processing characteristics of the turn-grinding method were examined and roughness of Sa

0.051 µm was obtained.

(3) On the basis of the above processing experiments, it was proved that the precision

microfabrication of shaft objects can be realized with a single machine tool based on the concept

of the SPC.

In the future, authors will evaluate the performance of each processing unit and aim to realize the

concept that the SPC has various functions and realizes process-integration performance by a

multifunctional processing unit.

Reference

[1] J. Tomita, S. Ymao, M. Ota, K. Egashira, K. Yamaguchi and Y. Uehara, Micro cyclic structuring on metal foil surface

using Micro Form Rolling, proceeding of The 15th International Conference on Precision Engineering (2014), 78-82.

[2] T. Nakano, K. Maeda, M. Ota, K. Egashira, K. Yamaguchi and Y. Uehara, Developed Micro Ball Forming device to

produce microtexture on curved surface, proceeding of The 16 th International Conference on Precision Engineering,

[3] O. Fukuyama and J. Takagi, Truing of small-diameter CBN grinding wheel by corner end of PCD rotary truer 1ST

Report:Application of new truing method for quills 3-0.6 mm in diameter, Journal of the Japan Society for Abrasive

Technology Vol.59 No.8 2015 AUG. 453-458.

[4] O. Fukuyama and J. Takagi, Truing of small-diameter CBN grinding wheel by corner end of PCD rotary truer 2ND

Report:Generation mechanism of micro cutting edges formed by truing, Journal of the Japan Society for Abrasive

Technology Vol.59 No.11 2015 NOV. 637-642.

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