A New Technique of Dressing and Conditioning Resin Bonded Superabrasive Grinding Wheels

A New Technique of Dressing and Conditioning Resin Bonded Superabrasive Grinding Wheels R. Komanduri and W. R. Reed, Jr.. General Electric Co., Schenectady. NV 12301 Sunrnary:

- Submitted by B. F. von Turkovich (1)

A new technique o f dressing and c o n d i t i o n i n g a r e s i n bonded superabrasive (diamond or cubic boron

n i t r i d e ) g r i n d i n g wheel i s presented.

I t comprises c o n t a c t i n g the surface of the wheel w i t h a w e t t i n g l i q u i d ( i n

t h i s case a s u i t a b l e l u b r i c a n t ) , forming a f i l m on the surface o f t h e r e s i n , and using the r e s u l t i n g wetted wheel surface t o g r i n d a hot pressed s i l i c o n carbide or s i l i c o n n i t r i d e ceramic alongside the workpiece o f i n t e r e s t . The r e s u l t i n g t h i n ceramic chips (whose surfaces are extremely a c t i v e as they a r e f r o s h l y generated) adhere t o t h e wetted r e s l n face forming a t h i n

SlUrry

l a y e r . Such a l a y e r i f r e j u v i n a t e d p r o t e c t s the r e s i n bonding m a t e r i a l from

thermal and/or mechanical degradation or damane and t h e superabrasive from premature p u l l o u t , thus i n c r e a s i n g t h g r i n d i n g wheel l i f e . INT9ODUCTION

A g r i n d i n o wheel i s t r u e d by removing small amounts o f

i s t o r e m v e the unwanted r e s i n m a t e r i a l on the wheel surface

m a t e r i a l from the surface o f a r o t a t i n a wheel t o maintain con-

f o r adequate c h i p clearance without d i s l o d g i n q the superabra-

c e n t r i c i t y . Otherwise, due t o unbalance, the wheel c h a t t e r s

s i v e g r i t s . The above techniques produce d i f f e r e n t surface

a t h i g h o r i n d i n g speed and unsatisfactory performance r e s u l t s .

toooflranhical features on the g r i n d i n g wheel surface and the

Dressing i s a much f i n e r operation than t r u e i n g because the t i p s

degree o f success depends upon the extent o f g r i t p r o j e c t i o n

o f the abrasives a r e subjected t o d e l i c a t e microcleavage f r a c -

from t h e bond, t h e void space f o r c h i n clearance and t h e s e l f

t u r e t o provide sharp f r a c t u r e facets which then remove m a t e r i a l

sharpening action. The topographical features e x h i b i t e d by

e f f i c i e n t l y i n subsequent g r i n d i n g by the sharp c u t t i n ? a c t i o n

some o f t h e above techniques w i l l be reported elsewhere [ 1

3.

o f the g r i t s . I n t h i s paper, a new and simole technique f o r achieving

I n o r e c i s i o n nrindina, i t i s necessary t o dress the face

the same goal i s described. B r i e f l y , t h e method comprises

of t h e g r i n d i n g wheel t o i n s u r e proper shape o f t h e p a r t t o be

generating t h i n s i l i c o n carbide chips by grindino, forming

ground (as i n the case o f form g r i n d i n g ) and t o prepare or res-

a s l u r r y w i t h t h e l u b r i c a n t and c o a t i n g a t h i n l a y e r on t h e

t o r e the surface o f t h e p r i n d i n p wheel ( a l s o known as c o n d i t i o n i n g ) t o optimize i t s c u t t i n g a b i l i t y and t o ins\.,re t h a t the q u a l i t y o f f i n i s h imparted t o t h e workpiece i s high. The techniques used f o r dressing and c o n d i t i o n i n g v i t r i f i e d bonded g r i n d i n g wheels a r e d i f f e r e n t from those used f o r r e s i n bonded wheels. This i s due D a r t l y t o the d i f f e r e n c e i n t h e g r i t bond i n t e r f a c e s t r e n g t h and p a r t l y t o the d i f f e r e n c e i n t h e v o i d space f o r c h i p clearance. This paper i s concerned only w i t h a dressing and c o n d i t i o n i n g technique f o r r e s i n bonded g r i n d i n g wheels. Conventionally, r e s i n bonded diamond or cubic boron n i t r i d e

Fig: 1 ( a ) S i l i c o n carbide brake f o r t r u e i n g a r e s i n bonded g r i n d i n g wheel.

g r i n d i n g wheels are t r u e d and p e r i o d i c a l l y dressed by a combinat i o n of techniques. Usually, t r u e i n g of a r e s i n bonded wheel i s c a r r i e d out w i t h a s i l i c o n

carbide brake composed o f a bonded

s i l i c o n carbide wheel (Fig. l a )

or by means o f a t r u e i n g t o o l

c o n t a i n i n g diamond g r i t s i n a metal m a t r i x (Fig. l b ) . Dressing,

on t h e o t h e r hand, i s c a r r i e d out by means o f a f i n e g r a i n a l u minum oxide abrasive dressing s t i c k i n a s o f t v i t r e o u s bond, e i t h e r h e l d by hand o r clamped t o t h e machine table. A l t e r n a t e ly. dressing i s c a r r i e d o u t by means o f a r o t a r y w i r e brush o r by g r i n d i n g on a s o f t s t e e l work m a t g r i a l . The o b j e c t i v e here

Fig: 1 ( b ) Trueing t o o l containing diamond g r i t s i n a metal m a t r i x .

Annals of the CIRP Vol. 29/1/1980

239

r e s i n p o r t i o n o f the g r i n d i n g wheel t o p r o t e c t the r e s i n and t o anchor t h e superabrasive g r i t s .

The idea was conceived w h i l e

f i n i s h g r i n d i n g a hot pressed s i l i c o n carbide r i n g w i t h a r e s i n bonded diamond wheel f o r a d i f f e r e n t study.

The r e s u l t s o f

t h i s experiment w i l l be presented f i r s t followed by t h e g r i n d i n g r e s u l t s obtained using t h e new technique o f t r u e i n g and c o n d i t i o n i n g t h e r e s i n bonded diamond wheel [ 2

3.

EXPERIMENTAL RESULTS Figure. 2 shows t h e arrangement used on a l a t h e f o r f i n i s h g r i n d i n g a hot pressed s i l i c o n carbide r i n g using a r e s i n bonded diamond g r i n d i n g wheel.

Fig: 2

The workpiece was h e l d

??tun on a l a t h e f o r f i n i s h g r i n d i n g 6.f a h o t pressed s i . icon carbide r i n g using a r e s i n bonded diamond g r i n d i n g wheel.

i n a three jaw chuck and the h i g h speed g r i n d i n g spindle was nmunted on t h e cross s l i d e o f t h e l a t h e .

Grinding conditions

and o t h e r d e t a i l s a r e given i n Table I . TABLE 1 Work material Grinding wheel

: Hot pressed s i l i c o n carbide : Resin bonded diamond wheel, 2.54 un

diameter x 6.3 mn wide SD 100 - N 100 8 68 3

-

Wheel speed

4

: 900 t o 3050 m/min -

Work speed Grinding f l u i d Downfeed/ pass

i

: 3 m/min I

: water s o l u b l e o i l (Annix)

Kx)o

I

2ooo

: 38 bm

Grinding wheel speed was v a r i e d from 900 t o 3050 m/min t o optimize t h e wheel speed f o r nuximum g r i n d i n g r a t i o (G-ratio.

Fig: 3

I

-

Moo

WHEEL SPEED ( Y E T E R I Y I N I

4000

V a r i a t i o n o f g r i n d i n g r a t i o with wheel speed.

Fig. 5 i s an e l e c t r o n micrograph of an area around a diamond

which i s t h e r a t i o of t h e volume o f work ground t o the volume

g r i t a t higher magnification.

of wheel worn). A s o l u b l e o i l (Annix) was used throughout as

g r i t by t h e s i l i c o n carbide l a y e r surrounding i t . Stereo p a i r s

the g r i n d i n g f l u i d t o cool t h e g r i n d i n g wheel and t o c a r r y

of p o r t i o n s of t h e g r i n d i n g wheel surfaces c l e a r l y i n d i c a t e d

t h e g r i n d i n g debrls.

showing anchoring o f the diamond

t h a t the wheel was n o t loaded and t h e g r i t s p r o j e c t e d w e l l above the s i l i c o n carbide l a y e r . Also, t h e s l u r r y

Figure. 3 shows t h e v a r i a t i o n o f g r i n d i n g r a t i o w i t h wheel speed. I t can be seen t h a t t h e & r a t i o increases w i t h speed, reaching a maximum o f over 900 a t a wheel speed o f

l a y e r was found t o be very coherent (Fig. 6) as a r e s u l t o f p l a s t i c deformation and subsequent surface a t t r a c t i o n (as the chips a r e f r e s h l y generated) o f numerous t h i n s i l i c o n carbide

about 1980 m/min. With f u r t h e r increase i n wheel speed, a drop chips (Fig. 7 ) . i n the G - r a t i o was observed. During these t e s t s , t h e wheel never r e q u i r e d any dressing, and sharp c u t t i n g a c t i o n was observed throughout t h e g r i n d i n g operation. This i n d i c a t e s t h a t

From the above observations. i t i s c l e a r t h a t t h e high wheel l i f e i s due t o :

t h e s e l f sharpening a c t i o n o f t h e diamond g r i t s i s being proformation of a t h i n l a y e r o f s i l i c o n carbide on t o p vided continuously by microcleavage f r a c t u r e o f t h e g r i t s of t h e r e s i n bond. which provided a s h i e l d a g a i n s t w h i l e grinding. Also, t h e h i g h q r i n d i n g r a t i o ( > 900) i n d i thermal degradation and/or mechanical scouring, cates very l i t t l e wheel wear due t o bond erosion and/or g r i t p u l l o u t . The g r i n d i n g f l u i d used was found t o reach t h e grind-

anchoring o f t h e diamond g r i t s , thereby reducing

i n g zone e f f e c t i v e l y . Note t h e w h i t e p a r a b o l i c shape o f t h e

c o s t l y g r i t p u l l o u t , and

l u b r i c a n t f l o w a t t h e wheel work i n t e r f a c e i n Fig. 2. continuous microcleavage f r a c t u r e o f t h e diamond To i n v e s t i g a t e t h e reasons f o r t h e h i g h wheel l i f e . the

g r i t s w h i l e conditioning, thereby p r o v i d i n g s e l f

g r i n d i n g wheel was examined p e r i o d i c a l l y i n a Scanning E l e c t r o n

sharpening a c t i o n t o the g r i n d i n g wheel. High hard-

Microscope (SEM). Fig. 4 i s an e l e c t r o n micrograph o f a p o r t i o n

ness together w i t h t h e chemical i n t e r a c t i o n o f t h e

o f t h e g r i n d i n g wheel surface showing a t h i n l a y e r o f s i l i c o n

work m a t e r i a l (hot pressed s i l i c o n c a r b i d e ) w i t h

carbide on t o p o f the r e s i n surface o f the g r i n d i n g wheel.

diamond a r e a t t r i b u t e d here as t h e reasons f o r the

240

s u p e r i o r s e l f sharpening a c t i o n , although f u r t h e r work i s needed t o v e r i f y t h i s hypothesis. Yheel wear due t o g r i t p u l l o u t and bond e r o s i o n accounts f o r major l o s s o f wheel l i f e .

Since bonding between super-

abrasives ( w i t h o r w i t h o u t metal c o a t i n g ) and t h e r e s i n i n a g r i n d i n g wheel i s g e n e r a l l y mechanical, t h e r e i s a need t o improve t h i s s t r e n g t h e i t h e r i n d i r e c t l y o r d i r e c t l y i n o r d e r

t o improve wheel l i f e .

B e t t e r anchoring o f t h e g r i t s and pro-

v i s i o n o f a thennal/mechanical s h i e l d on t o p o f the r e s i n bond can c e r t a i n l y improve wheel l i f e .

Based on t h e above obser-

vations, a t h i n c o a t i n g o f s i l i c o n c a r b i d e formed c o n t i n u o u s l y d u r i n g g r i n d i n g may be one way o f accomplishing t h i s goal. J u s t s p r a y i n g w i t h micron s i z e d p a r t i c l e s o f s i l i c o n carbide w i l l n o t accomplish t h i s goal as t h e surfaces o f t h e g r i t s a r e

n o t as a c t i v e as t h e h e a v i l y deformed, f r e s h l y generated, t h i n c h i p s c r e a t e d by g r i n d i n g h o t pressed s i l i c o n c a r b i d e .

The

c h i p s generated w i l l form a s l u r r y w i t h t h e l u b r i c a n t and a t h i n l a y e r w i l l be deposited on t h e r e s i n s u r f a c e o f t h e wheel. G r i n d i n g t e s t s were conducted t o v e r i f y t h i s concept under t h e c o n d i t i o n s given i n Table 11. TABLE I1 Work m a t e r i a l

:

Steel ( A I S I 1045)

-

Carbide (94", WC

and 6' Co) combination 50:50

G r i n d i n g wheel

:

Resin bonded diamond g r i n d i n g wheel, 12.7 cm diameter x 0.5 cm wide

Abrasive

:

100/120 g r i t , n i c k e l coated blocky diamond ( C S G 11)

!Jheel speed

:

1370 m/min

Table speed

:

15.25 m/min

Cross feed/ pass

: 0.6 m

Down feed/pass

:

Lubricant

: water s o l u b l e o i l ( T r i m s o l )

12.7

3111

I n t h e i n i t i a l s e r i e s of t e s t s , t h e g r i n d i n g wheel was f i r s t t r u e d and c o n d i t i o n e d once by g r i n d i n g on a h o t pressed s i l i c o n c a r b i d e o r s i l i c o n n i t r i d e c o n d i t i o n i n g p i e c e i n presence o f a g r i n d i n g f l u i d u n t i l a t h i n l a y e r was formed on t h e wheel periphery. The amount o f c o a t i n g was determined e m p i r i c a l l y by observing t h e t r e a t e d wheel surface through a magnif y i n g glass o r a s t e r e o microscope. The wheel was then used t o g r i n d t h e s t e e l - c a r b i d e combination. Tests were conducted a t d i f f e r e n t removal r a t e s b u t t h e a m u n t o f m a t e r i a l removed was kept constant i n a l l cases. For comparison, conventional g r i n d i n g t e s t s were a l s o conducted b u t w i t h o u t t h e s i l i c o n c a r b i d e / s i l i c o n n i t r i d e treatment. The g r i n d i n g r a t i o was measured i n a l l cases t o e v a l u a t e t h e r e l a t i v e e f f e c t i v e n e s s o f t h e new technique.

Table 111 l i s t s t h e g r i n d i n g r a t i o s obtained i n

various t e s t s w i t h and w i t h o u t t h e s i l i c o n c a r b i d e / s i l i c o n n i t r i d e treatment on t h e wheel surface. A s i g n i f i c a n t improve-

241

m n t i n the G-ratio can be noted using t h e new technique o f

accomplished by c o n d i t i o n i n g the wheel p e r i o d i c a l l y or continu-

c o n d i t i o n i n g and dressing t h e r e s i n bonded superabrasive

ously by p l a c i n g a h o t pressed s i l i c o n c a r b i d e / s i l i c o n n i t r i d e

g r i n d i n g wheel.

c o n d i t i o n i n g oiece i n jUXtaP0SitiOn TABLE

Test

111

sides) t o t h e

Grinding r a t i o

Remarks

[ e i t h e r on one o r on both

work m a t e r i a l . I n t h i s way the wheel i s a l t e r -

n a t e l y conditioned and ground. Figs. 9 ( a ) and ( b ) show schem a t i c a l l y two such arrangements. I n a l l cases, the s i z e o f the c o n d i t i o n i n g p i e c e ( s ) should be such t h a t , when a l a y e r i s

No treatment

67

ground, t h e r e I s an adequate number o f chips t o form a t h i n

H

137

No treatment

183

No treatment

360

wheel t r e a t e d w i t h S i c

431

wheel t r e a t e d w i t h S i c

379

wheel t r e a t e d w i t h Sic

347

wheel t r e a t e d w i t h silicon nitride

36 1

wheel t r e a t e d w i t h silicon nitride

s l u r r y c o a t i n g w i t h t h e l u b r i c a n t on t h e g r i n d i n g wheel surface. DISCUSSION Since conducting t h i s work, another technique o f dressing r e s i n bonded diamond wheels, developed recently, was brought t o the a t t e n t i o n o f the authors [ 3

1.

That technique b a s i c a l l y

involves t h e a p p l i c a t i o n of a dresser composed o f abrasive

__-

p a r t i c l e s such as alumina and a f r i c t i o n meltable organic poly-

Since the s i l i c o n c a r b i d e / s i l i c o n n i t r i d e l a y e r depletes w i t h time during grinding, i t i s necessary t o r e p l e n i s h i t

meric m a t e r i a l against the r o t a t i n g g r i n d i n g wheel surface causing the dresser t o melt and t o form a dressing s l u r r y on

p e r i o d i c a l l y . Otherwise, i t s e f f e c t i v e n e s s w i l l decrease and

t h e surface o f the wheel, then pinchinq t h e s l u r r y between the

even vanish. One can observe t h i s e f f e c t by increasing the

wheel and t h e work m a t e r i a l . While t h e technique appears some-

removal r a t e a f t e r c o n d i t i o n i n g t h e wheel w i t h s i l i c o n carbide

what s i m i l a r t o t h e one presented i n t h i s paper. i t d i f f e r s

once. Fig. 8 shows the v a r i a t i o n o f removal r a t e .

grinding r a t i o with

I t can be seen t h a t t h e d i f f e r e n c e i n p e r f o r -

m n c e between the untreated and t r e a t e d wheel narrows down as

f z

r

involvps t h i n s i l i c o n based ceramic chins which a r e canable of chemical i n t e r a c t i o n w i t h t h e diamond o r i t s nroducino an enhanced sharnenino action. I n a d d i t i o n , the s i l i c o n carbide o r s i l i c o n n i t r i d e chips may be

m r e s t r o n o l y attached t o the

r e s i n surface because o f the r e a c t i v i t y o f t h i n f r e s h l y oenerated s u r f aces.

i

110

from t h a t o f t h e present i n v e s t i g a t i o n i n t h a t the new method

\ RESIN BONDED DIAMOND GRINDING WHEEL 100

200

100

400

GRINDING R A T 0

500

600

-

700

-

HOT PR CONDIT

SIC LAYER ON THE RESIN BOND

Fig: 8 V a r i a t i o n o f m a t e r i a l removal r a t e w i t h g r i n d i n g r a t i o .

WORK MATERIAL

the removal r a t e i s increased. Examination o f t h e t r e a t e d wheel a f t e r g r i n d i n g a t t h e higher removal r a t e s showed considerable

loss o f c o a t i n g a f t e r a c e r t a i n l e n g t h o f time. The t r e a t e d

L-=4 GRINDING TABLE

wheel from then on i s p r a c t i c a l l y the same as t h e untreated wheel. So, a t higher removal r a t e s and/or w i t h prolonged g r i n d ing, i t i s necessary t o f r e q u e n t l y r e p l e n i s h t h e coating on t h e wheel surface f o r t h i s technique t o be e f f e c t i v e . This can be

242

Fin. 9 ( a )

SPRINGLOADED HOT PRESSED SIC CONDITION I NG PIECE

U.S.

[ 3

1

Patent pending.

Bonnice, P.E.,

' Grinding Wheel Dressing Method"

U.S. Patent No. 4068416 dated Jan 17, 1978. ' G r i n d i n g Wheel Dresser' U.S.

Patent No. 4098253 dated J u l y 4, 1978. ' G r i n d i n g Wheel Dressing Method'

U.S.

Patent No. 4027648 dated June 7, 1977.

'llethod For Improving Surface F i n i s h o f Morkpieces Ground With Abrasive Wheels' U.S.

%&sic

1

+WORK

Patent No. 3990192 dated Nov. 9, 1976.

LAYER ON THE RESIN BOND

MATERIAL

Figs: 9(a) & ( b ) Two arrangements f o r e f f e c t i v e c o n d i t i o n o f a r e s i n bonded superabrasive g r i n d i n g wheel.

CONCLUSIONS

A new technique o f c o n d i t i o n i n g and dressing a r e s i n bonded superabrasive g r i n d i n g wheel by p r o v i d i n g a t h i n l a y e r of s i l i c o n carbide o r s i l i c o n n i t r i d e on t h e wheel surface i s e f f e c t i v e i n i n c r e a s i n g the wheel l i f e and consequently the g r i n d i n g r a t i o . However, a t higher removal r a t e s and/or prolonged grinding, i t i s necessary t o r e p l e n i s h the c o a t i n g cont i n u o u s l y by p l a c i n g a h o t pressed s i l i c o n c a r b i d e / s i l i c o n n i t r i d e c o n d i t i o n i n g p i e c e i n j u x t a p o s i t i o n t o t h e work material. ACKNOWLEDGEMENTS The authors thank Ors. D.G.

Flom and A.W.

Urquhart of

G.E.'s CRD f o r t h e i r i n t e r e s t i n t h i s work.

REFERENCES

[ 1 ]

Kmanduri, R e t a l . ,

' On the methods o f dressing and

c o n d i t i o n i n g r e s i n bonded superabrasive g r i n d i n g wheels

-

An SEH study o f the wheel surface topographical

f e a t u r e s ' . (1979) t o be published

[ 2

3

Komanduri, R and Y.R.

Reed, Jr.,

' Dressing and con-

d i t i o n i n g r e s i n bonded diamond g r i n d i n g wheel'

243