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http://pib.sagepub.com/ Manufacture Engineers, Part B: Journal of Engineering Proceedings of the Institution of Mechanical http://pib.sagepub.com/content/226/3/553 The online version of this article can be found at: DOI: 10.1177/0954405411423574 originally published online 21 December 2011 2012 226: 553 Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture B Guo, Q-L Zhao and M J Jackson materials Ultrasonic vibration-assisted grinding of micro-structured surfaces on silicon carbide ceramic Published by: http://www.sagepublications.com On behalf of: Institution of Mechanical Engineers can be found at: Manufacture Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Additional services and information for http://pib.sagepub.com/cgi/alerts Email Alerts: http://pib.sagepub.com/subscriptions Subscriptions: http://www.sagepub.com/journalsReprints.nav Reprints: http://www.sagepub.com/journalsPermissions.nav Permissions: http://pib.sagepub.com/content/226/3/553.refs.html Citations: What is This? - Dec 21, 2011 OnlineFirst Version of Record - Mar 7, 2012 Version of Record >> at UQ Library on November 6, 2014 pib.sagepub.com Downloaded from at UQ Library on November 6, 2014 pib.sagepub.com Downloaded from

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Page 1: Ultrasonic vibration-assisted grinding of micro-structured surfaces on silicon carbide ceramic materials

http://pib.sagepub.com/Manufacture

Engineers, Part B: Journal of Engineering Proceedings of the Institution of Mechanical

http://pib.sagepub.com/content/226/3/553The online version of this article can be found at:

 DOI: 10.1177/0954405411423574

originally published online 21 December 2011 2012 226: 553Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture

B Guo, Q-L Zhao and M J Jacksonmaterials

Ultrasonic vibration-assisted grinding of micro-structured surfaces on silicon carbide ceramic  

Published by:

http://www.sagepublications.com

On behalf of: 

  Institution of Mechanical Engineers

can be found at:ManufactureProceedings of the Institution of Mechanical Engineers, Part B: Journal of EngineeringAdditional services and information for

   

  http://pib.sagepub.com/cgi/alertsEmail Alerts:

 

http://pib.sagepub.com/subscriptionsSubscriptions:  

http://www.sagepub.com/journalsReprints.navReprints:  

http://www.sagepub.com/journalsPermissions.navPermissions:  

http://pib.sagepub.com/content/226/3/553.refs.htmlCitations:  

What is This? 

- Dec 21, 2011OnlineFirst Version of Record  

- Mar 7, 2012Version of Record >>

at UQ Library on November 6, 2014pib.sagepub.comDownloaded from at UQ Library on November 6, 2014pib.sagepub.comDownloaded from

Page 2: Ultrasonic vibration-assisted grinding of micro-structured surfaces on silicon carbide ceramic materials

Ultrasonic vibration-assisted grinding of micro-structured surfaces on silicon carbide ceramic materialsB Guo1,2*, Q-L Zhao1, and M J Jackson2

1Center of Precision Engineering, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin,

People’s Republic of China2Center for Advanced Manufacturing, Purdue University, West Lafayette, Indiana, USA

The manuscript was received on 18 August 2011 and was accepted after revision for publication on 25 August 2011.

DOI: 10.1177/0954405411423574

Abstract: Precision grinding of silicon carbide ceramic micro-structured moulds is becomingmore common in the area of the moulding of glass materials. However, in micro-structuredgrinding of super-hard and brittle materials, problems frequently occur in terms of chippingand rounding of micro-structural edge features. In order to overcome these technological con-straints, a promising method using ultrasonic vibration of workpiece materials is proposed.The design of a novel ultrasonic vibration apparatus and the experimental investigation ofultrasonic vibration assisted grinding of SiC micro-structures are presented. The experimentalresults show that the application of ultrasonic vibration can enhance the ground surface qual-ity and improve the edge features of micro-structures.

Keywords: ultrasonic vibration assisted grinding, micro-structured surfaces, silicon carbide

(SiC) ceramic, edge

1. INTRODUCTION

Micro-structured optical elements made of glass are

generally replicated by hot pressing with super-hard

materials, such as silicon carbide (SiC) and tungsten

carbide (WC). These materials are now widely used

in glass moulding owing to their excellent character-

istics, such as high wear resistance, high tempera-

ture strength, excellent chemical resistance, high

thermal conductivity, and thermal shock resistance

[1]. For efficient manufacturing of these moulds, the

precision grinding (PG) of super-hard materials

micro-structured moulds is a stringent requirement

[2–5]. However, the grinding of these micro-struc-

tures is very difficult because of the super hardness

and high brittleness, which results in chipping and

rounding of micro-structured edges and surface

roughness [6–8].

Ultrasonic vibration assisted grinding (UVAG)

methods are suitable to machine difficult materials

precisely, especially for ceramics. In contrast to PG,

the advantages of UVAG are that ultrasonic vibrations:

(a) improve the ground surface quality [9, 10];

(b) decrease the grinding forces [11, 12];

(c) reduce the subsurface damage induced by

grinding processes [13, 14].

These previous researches focused on continuous

surfaces, such as a plane and spherical surface.

However, few works have been carried on the UVAG

of micro-structured surfaces because of the interfer-

ence between the vibration path and functional

structure of the ground surface.

In this paper, a new PG method for micro-struc-

tured surfaces, that applies ultrasonic vibration to

improve the surface quality and protects the edges

and tips of micro-structured surfaces, is presented.

Machining surface quality of the novel grinding

approach for SiC ceramic microgroove generation was

evaluated using an ultraprecision planar grinder

*Corresponding author: Center of Precision Engineering, School

of Mechatronics Engineering, Harbin Institute of Technology,

Harbin, People’s Republic of China

email: [email protected]

SHORT COMMUNICATION 553

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integrated with the devised ultrasonic vibration table.

The effects of vibration amplitude, feedrate on surface

roughness, and edge radius were studied. The mor-

phology of surface and microgroove edges was exam-

ined with a scanning electron microscope (SEM), while

the surface roughness was measured by a laser interfe-

rometer. In addition, a contact probe profilometer was

used to assess the radius of micro-structured edges.

2. EXPERIMENTAL APPARATUS

The structure and shape of the ultrasonic table were

designed using finite element analysis as shown as

Fig. 1. In order to avoid the interference between

machined micro-structural features and vibration

tracks, a high frequency and low amplitude ultraso-

nic vibration was superimposed on the movement

of the workpiece. The axial vibration mode was

selected and the vibration direction of the table was

parallel to the wheel feed direction. The table used

the rectangular section with double vibration nodal

plane support design for increasing the grinding

stiffness. The vibration amplitude was amplified by

the booster and the dumb-bell-shape vibration table

and transmitted to the workpiece attached to the

middle of the table. The vibration frequency was

34.3 kHz, while the amplitude was designed to be

adjustable in the range of 0 mm and 10 mm.

The grinding experiments were performed using

a CNC grinder (MUGK7120X5, Hangzhou Machine

Tool Group Co. Ltd, People’s Republic of China).

Within this work an UVAG process for the struc-

tured surfaces exhibiting an Echelle grating (a type

of diffraction grating that is characterized by a rela-

tively low groove density, but is optimized for high

diffraction orders) mould has been developed. A

universal table was used under the workpiece in

order to control the angle between the workpiece

and wheel, as well as adjust the direction of vibra-

tion. The schematic illustration and photograph of

the experimental set-up for micro-structured sur-

face grinding is shown in Fig. 2.

In the experiments, in order to reduce the edge

wear of grinding wheel, a bigger diamond grinding

wheel (Ø200) compared with typical micro-struc-

tured surface PG was employed. Considering the

spindle power and vibration character with a bigger

grinding wheel, a lower spindle speed (2000 r/min)

was used. The machining parameters are summar-

ized in Table 1. The tests were carried out for both

UVAG and PG with the same instrument. During the

PG the ultrasonic table was switched off.

3. EXPERIMENTAL RESULTS AND DISCUSSION

The surface and edge morphology formed by PG

and UVAG (A = 4.5 mm and f = 34.3 kHz) at the same

grinding parameters (n = 2000 r/min, ae = 300 mm,

vf = 1 mm/min) are shown in Fig. 3, respectively.

Compared with PG, the ground surface was smooth-

er with fewer cracks than with ultrasonic vibration.

The SEM examination results proved that ultrasonic

vibration would lead to ductile material removal

and better surface quality in the grinding process.

Furthermore, the grain traces were obviously

reduced on ground surfaces using UVAG. The

micro-structure edges were more integrated when

using ultrasonic vibration, as shown in Fig 3. The

ground edge by UVAG not only had less fragmenta-

tion caused by cracks, but also had less spurs and

build-up bulges than that demonstrated using PG.

Apparently, one of the reasons for these improve-

ments is the change of the grinding process, which

increases the critical ductile grinding depth of cera-

mic [15]. Accordingly, there are improvements in

the surface quality and a reduction in brittle

Fig. 1 Ultrasonic vibration table with piezoelectricactuators (frequency: 34.3 kHz)

Fig. 2 The schematic illustration and photograph ofthe experimental set-up (reproduced with per-mission of Harbin Institute of Technology)

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fragmentation. The other reason is the high-fre-

quency repetitive finishing on ground surfaces by

the grinding wheel due to the change of the

kinematic path of the grinding wheel relative to the

workpiece, which results in the removal of spur and

build-up bulge on edges, the reduction of grain

traces and the decrease of surface roughness.

The average three-dimensional surface roughness

(SRa) values of ten measured points were measured

by means of a laser interferometer (Olympus,

OLS3000, Japan) on the ground surface, as shown in

Fig. 4. The top of the bar means maximum surface

roughness value, while the bottom of bar means

minimum value. The average value of roughness

SRa was 452 nm when using traditional grinding,

while it was improved to 178 nm by induced ultraso-

nic vibration. A contact probe profilometer (Form

Talysurf PGI 1240, Taylor Hobson Ltd, UK) was used

to assess the edge radius R of micro-structured

Table 1 Major machining parameters

Grinding wheel Ø200, resin-bond, D25, 100 %CWorkpiece SiC ceramic (grain size: 4–10 mm)Feedrate, vf 0.2–0.5–1–2 mm/minSpindle speed, n 2000 r/minDepth of cut, ae 300 mmUltrasonic vibration

frequency, f34.3 kHz

Ultrasonic vibrationamplitude, A

0–3–4.5–6.5–8.5 mm

Coolant Water–oil emulsionDressing tool D25 grit size diamond block

Fig. 3 SEM photographs of micro-structured surface and edge: (a) ground surface by PG; (b)ground edge by PG; (c) ground surface by UVAG; (d) ground edge by UVAG

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surface (the radius of the profilometer’s probe is

1 mm). For PG, the fragmentation of edge had a sig-

nificant impact on the increase of edge radius, the

average edge radius R by five measures using the

contact probe profilometer was more than 3.2 mm,

while the average R of UVAG was about 2.1 mm. The

results of the experiment show that lower surface

roughness and sharper edges will be obtained due

to ultrasonic vibration.

The effect of feedrate and vibration amplitude on

surface roughness and edge radius were studied.

Fig. 5 shows the SEM photographs of surface mor-

phology formed by different feedrates. Experiments

were carried out at n = 2000 r/min, ae = 300 mm,

f = 34.3 kHz, and A = 4.5 mm. When feedrate, vf, was

less than 1 mm/min, the ground surfaces show that

Fig. 4 Surface roughness of PG and UVAG (A = 4.5 mmand f = 34.3 kHz)

Fig. 5 SEM photographs of ground surface with different federate: (a) vf = 2 mm/min; (b) vf =1 mm/min; (c) vf = 0.5 mm/min; (d) vf = 0.2 mm/minde

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low-damage grinding had been achieved, although

some cracks were observed on the surface of micro-

structures. The ground surfaces were formed pri-

marily by the ductile material removal process. The

grain traces reduced with the decrease in feedrate.

Fig. 6 shows the SEM photographs of micro-struc-

tureal edges at vf = 2 mm/min and at vf = 0.2 mm/

min, respectively. The edge radius at the feedrate of

0.2 mm/min was sharper than that at 2 mm/min.

The effect of feedrate vf on surface roughness

SRa values and edge radius R of micro-structures

are shown in Fig. 7. The results show surface

roughness and edge radius were both improved

when the feedrate decreased, which is consistent

to SEM observations. The reason is that a slow

feedrate not only reduces the depth of cut per rev-

olution, as well as for conventional grinding, but

also enhances the repetitive finishing effect. At

the feedrate of 2 mm/min, the largest average SRa

value of 272 nm, and R value of 2.5 mm was

obtained. Decreasing the feedrate from 2 mm/

min to 0.2 mm/min resulted in the smallest SRa

value of 128 nm and R value of 1.5 mm.

The SEM photographs of surface morphology

formed by different vibration amplitudes A at n =

2000 r/min, ae = 300 mm, vf = 2 mm/min, and f =

34.3 kHz is shown in Fig. 8. The results show that

on the ground surface, the cracks caused by the

brittle removal process were decreasing when A

increased in the range of 3 mm to 6.5 mm. However,

the bigger amplitude of 8.5 mm produces no benefit

beyond 6.5 mm. This may indicate that there is a

threshold beyond which no additional benefit

occurs.

The surface roughness SRa and edge radius R of

micro-structural features as a function of A are

shown in Fig. 9. First, the surface roughness

decreases with increasing amplitude, and then

shows an increased tendency after 8.5 mm ampli-

tude, which corresponds to the observed results of

SEM examinations. The effect of amplitude on edge

radius is the same with that on surface roughness.

Setting the amplitude A of 6.5 mm resulted in the

best micro-structured surface with the smallest SRa

of 146 nm and sharpest R of 1.8 mm.

According to the experiments results, the Echelle

grating was ground on SiC ceramic using UVAG at

n = 2000 r/min, ae = 300 mm, vf = 0.2 mm/min, f =

34.3 kHz, and A = 6.5 mm, as shown as Fig. 10. The

average edge radius R was 1.6 mm, and the average

surface roughness SRa was less than 106 nm.

Fig. 6 SEM photographs of edges with different feedrate: (a) vf = 2 mm/min; (b) vf = 0.2 mm/min

Fig. 7 The effect of vf on SRa and R

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4. CONCLUSIONS

A novel UVAG of SiC ceramic micro-structured sur-

faces was proposed. Experimental results showed

that the application of ultrasonic vibration leads to

significant improvements of the surface roughness

and edges of micro-structures compare with tradi-

tional PG processes. In addition, the effect of feedrate

and vibration amplitude on ground quality was also

investigated. The surface roughness and edge radius

were both reduced when the feedrate decreased. As

the amplitude increased in the range of 3 mm to

6.5 mm, the ground surface was improved first.

However, there is likely to be a threshold beyond

which higher amplitudes would produce no addi-

tional advantage. Finally, an Echelle grating of SiC

Fig. 8 SEM photographs of ground surface with different amplitude: (a) A = 3 mm; (b) A = 4.5 mm;(c) A = 6.5 mm; (d) A = 8.5 mm

Fig. 9 The effect of A on SRa and R

558 B Guo, Q-L Zhao, and M J Jackson

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with surface roughness of 106 nm and edge radius of

1.6 mm was obtained.

For future research, the focus on investigating the

amplitude threshold, the grinding force, and the

effects of ultrasonic vibration on the integrity of

micro-structural surfaces will be conducted.

FUNDING

This work was supported by National Natural

Scientific Foundation of China [grant number

51075093]; and Chinese State Key Project of NC (04)

Technology [grant number 2009ZX04001-101].

ACKNOWLEDGEMENTS

The authors would like to thank the Joint

Laboratory for Ultra-Precision Grinding Technology

(JLUPG) of Harbin Institute of Technology and

Hangzhou Machine Tool Group Co., Ltd. The

authors would also like to thank Purdue University

for hosting the first two authors as visiting scholars

in the Center for Advanced Manufacturing.

� IMechE 2011

REFERENCES

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Fig. 10 SEM photographs of Echelle grating

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