Important Results on External Cylindrical Plunge Grinding with Unusual Workpiece Peripheral Speeds and Speed Ratios q in the Range of -0.2 to -20 000

Important Results on External Cylindrical Plunge Grinding with Unusual Workpiece Peripheral Speeds and Speed Ratios q in the Range of -0.2 to -20 000 E. Salje ( l ) , H. Teiwes, H. Heidenfelder

The s p e e d r a t i o g i s d e f i n e d a s q u o t i e n t of c u t t i n g s p e e d v and workDiece p e r i p h e r a l speed v a t t h c p r i n c i p l e p o i n t D. The s p e e d r a t i o map be g e g a t i v e o r p o s i t i v e ( u p - g r i i & i n g o r down-grinding)

.

The g r i n d i n g p r o c e s s i s i n f l u e n c e d by t h e s p e e d r a t i o . The c u t t i n a t r a c e s of t h e s i n q l e g r a i n s a r e n e a r l y c i r c i l l a r f o r h i g h s p e e d r a t i o s and c a n b e e x t r f m e l v c y c l o i d i c f o r l o w speed r a t i o s . Speed r a t i o s q between $0 and 1 0 0 a r e n o r m a l l v used fo; most e x t e r n a l p l u n g e grinding operations. I m p o r t a n t c h a r a c t e r i s t i c q u a n t i t i e s of t h e g r i n d i n g p r o c e s s l i k e w o r k p i e c e r o u g h n e s s , c u t t i n g forces, q r i n d i n g t e m p e r a t u r e and wheel wear a r e p r e s e n t e d a s f u n c t i o n s of t h e s p e e d r a t i o . For t h e f i r s t t i m e t h e s p e e d r a t i o was v a r i e d between 0 . 2 and 2 0 0 0 0 . The wheel s p e e d and t h e m e t a l removal r a t e were c o n s t a n t . The i n v e s t i g a t i o n s were made w i t h aluminium o x i d e w h e e l s and w i t h a CBN-wheel i n c r e e p f e e d g r i n d i n g .

I r h r o d u c t iou G r i n d i n y p r o c e s s e s can b e d e s c r i b e d by c h a r a c t e r is t i c v a l u e s . Among o t h e r c h a r a c t e r i s t i c s t h e speed ral-io q and t h e r e l a t i v e s p e e d vrel a r e i m p o r t a n t . The r e l a t i v e s p e e d r e s u l t s from t h e g e o m e t r i c sum of p e r i p h e r a l s p e e d of t h e g r i n d i n g wheel and workpiece.

and vs speed vft

v

principal

60

ft

=

1 *-*v

-q

(1)

s

The c a s e of a c o n s t a n t p e r i p h e r a l vft

In u s u a l y r i n d i n g p r o c e sse s t h e speed r a t i o q lies between 20 and 100 / 1, 2 / . This a l s o applies t o

-

15 m/s. The w o r k p i e c e p e r i p h e r a l h a s a n e g a t i v e s l o p e f o r a double-logar i t h m i c scale and f o l l o w s t h e € u n c t i o n :

m/a

In e x t e r n a l c y l i n d r i c a l p l u n g e g r i n d i n g t h e

p e r i p h e r a l s p e e d of t h e w o r k p i e c e is t h e f e e d motion

s p e e d vg is c o n s t a n t . f o r example vs

ripheral

and

a

changing

workpiece

speed

p e r i p h e r a l w h e e l s p e e d v s is

also t h i n k a b l e b u t s h a l l , however, n o t b e d i s c u s s e d here.

h i g h s p e e d gr i n d i n g . For some y e a r s c r e e p f e e d g r i n d i n g is i n u s e .

This process c a n b e a p p l i e d for c o n t i n u o u s and d i s c o n t i nuous y r i n d i n g . C r e e p f e e d g r i n d i n g is c h a r a c t e r iz e d by s p e e d r a t i o s , which l i e o v e r 1000, sometimes up t o 20000. T e s t r e s u l t s f r o m c r e e p f e e d g r i n d i n y are well known and p u b l i s h e d i n l i t - e r a t u r e

The r a d i a l i n f e e d f r h a s a p r o p o r t i o n a l b e h a v i o u r Lo t h e s p e e d r a t i o q , a c c o r d i n g t o e q u a t i o n ( 3 ) . The p r o d u c t of r a d i a l i n f e e d f r and w o r k p i e c e p e r i p h e r a l s p e e d vft g i v e s t h e constant material remov a l r a t e p e r u n i t wheel w i d t h Q ' The r e l a t i v e s p e e d vrel

.

r e s u n s from:

/ 3 , 4 , 14 e t a l . / . Up(q
.,r- -

I

With t h e g r i n d i n g r e s u l t s shown h e r e it w a s a t t e m p Led

f o r t h e f i r s t t i m e t o enter i n t o other regions

of s p e e d r a t i o s q. T h i s is e x p l a i n e d i n f i g . 1. F i g u r e l a shows a n a r r a n g e m e n t of w o r k p i e c e and g r i n d i n g w h e e l w i t h t h e t w o v e c t o r s of t h e g r i n d i n g w h e e l p e r i p h e r a l s p e e d vg and t h e w o r k p i e c e p e r i p h e r a l s p e e d vCt (vw). A c c o r d i n g t o IS0 t h e wheel p e r i p h e r a l s p e e d is c a l l e d vc. Only i n t h e case of t h e c y l i n d r i c a l g r i n d i n g w h e e l examined h e r e , vc c o r r e s p o n d s t o v . The e x p e r i m e n t s were c o n d u c t e d under t h e p r e m i s e t h a t t h e material removal r a t e p e r u n i t w h e e l w i d t h

Q' and t h e g r i n d i n g w h e e l p e r i p h e r a l s p e e d vs and t h e r e f o r e t h e equivalent grinding thickness h reeq mained c o n s t a n t ( h -Q'/vs). 99 F i y u r e l b shows t h e

development

of

the

--c-

grinding

w h e e l p e r i p h e r a l s p e e d v : ~ ,t h e w o r k p i e c e p e r i p h e r a l s p e e d v T L , Lhe r e l a t i v e s p e e d vrel and t h e r a d i a l speed ratto - q

i n f e e d f r as a func-tion of t h o s p e e d r a t i o q . As u p - g r i n d i n g is u s e d , t h e s p e e d ratio y is n e g a t i v e . l o q a r i t h m i c s c a l e was c h o s e n t o b e a b l e t o show t h e whole r a n g e of t h e s p e e d r a t i o q.

-

A

F i g u r e 1:

G r i n d i n g wheel- and w o r k p i e c e p e r i p h e r a l speed,

In t h e c a s e c o n s i d e r e d h e r e t h e g r i n d i n g w h e e l

Annals of the CIRP Vol. 32/1/1983

pe-

r e l a t i v e s p e e d and r a d i a l i n f e e d

as a f u n c t i o n of t h e s p e e d r a t i o .

241

For speed r a t i o s Iql-, t h e r e l a t i v e speed vrel r u n s a g a i n s t vs a s y m p t o t i c a l l y and for speed r a t i o s lql-0 asymptotically against v f r . Only for speed r a t i o s q610 t h e r e l a t i v e speed v r e l d i f f e r s n o t i c e a b l y from t h e g r i n d i n g wheel p e r i p h e r a l speed v s . T h i s c o r r e s p o n d s t o t h e "new range" examined for t h e f i r s t time

10rEK60Kbke CkLSN

fad =

I

O.Lmm

The c o n d i t i o n s f o r q = -1 a l s o appear t o be i n t e resting. For a c o n s t a n t material removal r a t e Q ' t h e r a d i a l i n f e e d f r corresponds t o t h e e q u i v a l e n t yrinding thickness h

as t h e g r i n d i n g wheel p e r i -

eq'

p h e r a l speed vs is i d e n t i c a l t o t h e workpiece p e r i p h e r a l speed v f t . The t e s t s wheels i n

-

speed rotio - q I

OD1

were conducted w i t h aluminium o x i d e t h e whole range of t h e speed r a t i o men-

tioned. I n t h e range of c r e e p f e e d g r i n d i n g CBNg r i n d i n g wheels were a l s o t a k e n i n t o c o n s i d e r a t i o n .

0.1

1 10 rodial infeed 1,

I

300wO

1000 pm 10000

30

300

3

0.3

workpiece peripheral speed v,,

16977 0

Figure 2 :

3000

mmh

100

C a l c u l a t e d and r e a l geometric and matic c o n t a c t l e n g t h t h e speed r a t i o .

kine-

a s a f u n c t i o n of

SDeed R a t i o an-d Conditions of Contact between Grine i n a Wheel and Wor kDiece The speed r a t i o q is t h e q u o t i e n t of t h e wheel

pe-

r i p h e r a l speed and t h e workpiece p e r i p h e r a l speed q = vs/vft. I f , i n t h e c a s e of e x t e r n a l c y l i n d r i c a l plunge g r i n d i n g t h e speed r a t i o q is changed, w h i l e

F l f e ~ f - s_sr..th_eGrinal~-eroceev

t h e m a t e r i a l removal r a t e Q ' and t h e wheel p e r i p h e r a l speed vs a re h e l d c o n s t a n t . t h e n f r changes accord ingl y -

The e f f e c t s of t h e speed r a t i o on t h e workpiece roughness have t o be t a k e n i n t o c o n s i d e r a t i o n for

rr Q'

7

igt

-

vEr

-

* dw

7f

0

fr *

vft

(4)

The g e o m e t r i c length of engagement between workpiece and g r i n d i n g wheel is c a l l e d g e o m e t r i c a l contact length

1

4

.

Beside

this,

the

kinematic

2.

The i n f e e d per workpiece r e v o l u t i o n is g r e a t e r ILhan t h e workpiece rouyhness ( c r e e p f e e d g r i n rl ing ) The i n f e e d per

than

the

workpiece

workpiece

revolution

is

less

roughness ( " r e c i p r o c a t i n g

y r inding')

l e n g t h lk is of importance, e s p e c i a l l y i n

grinding

t h e c a s e of h i g h p e r i p h e r a l s p e e d s of t h e workpiece. T h i s g i v e s t h e l e n g t h of t h e c y c l o i d i c p a t h on t h e workpiece. The t h e o r e t i c a l geometric c o n t a c t l e n g t h is c a l c u l a t e d from / 5 , 6 / as: lg

-

(fr

deq)

1/1

tf

lg/vs

vs * Rz j=-=

.

into

-RZ

Iql

"ft * fr

(7)

lk lg (ltl/lql) (8) T h i s c a l c u a l t i o n b a s e s on i d e a l smooth b o d i e s .

takes

l e n g t h . The c h a r a c t e r i s t i c g r i n d i n g v a l u e J shows ILhe l e n y t h of g r i n d i n g wheel c i r c u m f e r e n c e , which

covered i n t h e d i r e c t i o n o€ t h e plunge motion.

(6)

with

The workpiece roughness is i n f l u e n c e d by t h e characteristlc g r i n d i n g v a l u e j and t h e c o n t a c t

has t o g r i n d a l o n g i t u d i n a l element of t h e workpiec e c i r c u m f e r e n c e , u n t i l t h e d i s t a n c e RZ h a s been

(5)

and t h e t h e o r e t i c a l k i n e m a t i c g r i n d i n g l e n g t h as:

one

two d i f f e r e n t r a n g e s : 1.

(3)

Q ' / V ~

WOrkp i_eceRo.w!!-ess

f

T h i s e q u a t i o n a p p l i e s f o r range If

c o n s i d e r a t i o n t h e a v e r a g e peak t o

v a l l e y roughness RZ of t h e workpiece, t h e n one obt a i n s t h e r e a l g e o m e t r i c a l c o n t a c t l e n g t h leg:

(

11)

r 2

("reciprocating

grinding"). I n range 1 ( c r e e p f e e d g r i n d i n g ) J = I q l , as t.he s u r f a c e of t h e workpiece h a s t o be ground over a t least once. A c o m b i n d i o n of t h e r e a l k i n e m a t i c g r i n d i n g l e n g t h

lek w i t h t h e c h a r a c t e r i s t i c g r i n d i n g v a l u e j r e sults i n t h e f o l l o w i n g e q u a t i o n Tor RZ:

I n t h e sdme way t h e

effective

kinematic

grinding

l e n g t h can be d e r i n e d :

F i y u r e 2 shows t h e behaviour of Lhe d i f f e r e n t conLact l e n g t h s as d f u n c t i o n of t h e speed r a t i o q . While 1 - lk -leg= leki n t h e area OF h i g h speed 9 r a t i o s . t h e y d i f f e r c o n s i d e r a b l y when t h e speed r a t i o q i s low. The g r e a t range which is covered by t h e c o n t a c t lengths increases i n proportion with t h e s q u a r e r o o t of t h e speed r a t i o q .

242

-

In ranye 1 w i t h RZ/fr 1 and a high speed r a t i o q , q u a t i o n ( 1 3 ) s i m p l i f i e s Lo:

ILions and t h e b e h a v i o u r of t h e g r i n d i n g wheel w i t h Lha t i m e . The k i n e m a t i c c o n d i t i o n s h a v e no more

From t h i s t h e r e r e s u l t s :

influence

on

this

value.

The development of t h e

r o u g h n e s s RZ/Rzmax as a f u n c t i o n of t h e s p e e d r a t i o shows a wide maximum i n t h e p r e v i o u s l y used r a n g e lJnUer t h e p r e m i s e t h a t t h e r e a l k l n e m a t i c l e n g t h lek is o n l y i n f l u e n c e d by R L , ( R / > 1 ) eyUdt.lon ( 1 3 ) becomes: L fr

grinding in range 2

( s h a d e d a r e a , f i g u r e 3 ) . If t h e c o n d i t i o n f r > R Z ( c r e e p t e e d ) was e x c e e d e d . t h e r o u g h n e s s d e c r e a s e d t.owards t h e b o r d e r v a l u e R zO/Rzmax. A break in t h e c u r v e o c c u r e d f o r aluminium o x i d e w h e e l s as w e l l a s for CBN-Wheels. The p o s i t i o n of t h e b r e a k is among o t h e r t h i n g s d e p e n d e n t on t h e c h o s e n s e t t i n g c o n d i -

In t h i s t h e

characteristic

grinding

value

in

J

e q u a t i o n ( 3 ) w a s i n s e r t e d i n t o e q u a t i o n (11). From c o n v e r s i o n and c o m b i n a t i o n t h e r e r e s u l t e d :

In t h e range t i o n s and t h e w h e e l s p e c i f i c a t i o n . t h e r o u g h n e s s d e c r e a s e d w i t h a d e c r e a s i n g q, fr
b o r d e r v a l u e RzO/RZmax.

The r a d i a l i n f e e d and t h e p e r i p h e r a l s p e e d of t h e workpiece have t o be considered f o r t h e border c a s e development of r o u g h n e s s for t h e s p e e d r a t i o s I q l - 0 and I q l --.

I n t h e upper p a r t of f i g u r e

3

calculated

of

development

the

theoretically

the

roughness

was p l o t t e d . A v e r y good a g r e e ment between t h e t h e o r e t i c a l and e x p e r i m e n t a l l y deRztheo/Rzmaxtheo

t e r m i n e d development of t h e r o u g h n e s s r e s u l t e d .

For a v e r y s m a l l q t h e t o o l is m u t i o n l e s s i n compa-

The r a d i a l i n f e e d p e r r i s o n t o t h e workpiece. w o r k p i e c e r e v o l u t i o n a p p r o a c h e s z e r o . The i n d i v i d u a l c u t t i n g p r o f i l e s s u p e r p o s e on a m u l t i p l e of t h e w o r k p i e c e c i r c u m f e r e n c e on n e a r l y one w o r k p i e c e diameter.

The r e s u l t i n g t r a n s v e r s e r o u g h n e s s R Z of

t h e w o r k p i e c e c o r r e s p o n d s t o t h e s p a r k o u t roughness. The l o n g i t u d i n a l r o u g h n e s s of t h e w o r k p i e c e

Gr i n d i n y F o r c e s and Energy Req_uu.g-e-m=nfs The g r i n d i n g forces a r e d e c i s i v e l y d e t e r m i n e d , among o t h e r t h i n g s . by t h e a c t i v e g r a i n c o u n t N act' which is engaged a t a n y moment. They are t h e p r o d u c t of r e a l g e o m e t r i c a l c o n t a c t a r e a Ak and t h e a c l i v e g r a i n c o u n t p e r u n i t a r e a Nacta

becomes n e a r l y z e r o on a c i r c u m f e r e n c e l i n e .

Nact

For v e r y h i g h s p e e d r a t i o s t h e w o r k p i e c e is m o t i o n l e s s r e l a t i v e t o t h e g r i n d i n g wheel.

nearly By Su-

p e r p o s i t i o n of t h e c u t t i n g p r o f i l e s af t h e g r i n d i n g w h e e l , t h e s p a r k o u t r o u g h n e s s / 7 / as a t r a n s v e r s e r o u y h n e s s is produced on a s h o r t s e c t i o n of t h e w o r k p i e c e c i r c u m f e r e n c e , i n s p i t e of t h e r a d i a l i n Coed.

The w o r k p i e c e roUghneSS on a w o r k p i e c e

cir-

c u m f e r e n c e l i n e a g a i n becomes z e r o . 0'= 3mm3/mm s

, v.

=

leg

Nact

(18)

Ak ' N a c t a

lu

'

*

Nacta

(19)

The c o m b i n a t i o n g r i n d i n g w h e e l - w o r k p i e c e ,

dressing

c o n d i t i o n s and t h e b e h a v i o u r of t h e g r i n d i n g w h e e l s w i t h t h e t i m e h a v e f u r t h e r i n f l u e n c e on t h e development of t h e g r i n d i n g f o r c e s . The normal- and t a n g e n t i a l f o r c e s shown i n f i g . 4 as a f u n c t i o n of t h e s p e e d r a t i o showed n e a r l y no A c h a n g e when q i n c r e a s e d f o r low s p e e d r a t i o s . marked i n c r e a s e was o n l y o b t a i n e d i n t h e r a n g e of

=60m/s

c r e e p f e e d g r i n d i n g . a s was a l s o found f o r

surface

g r i n d i n g / 3 , 4/ 0'

z

3mm3/mm s

,

y :60m/s,

d,, =lOOmm

/ 1-

I

a01

0.1

I

10

rodm I Infeed f.

300oW 8971 0

F i g u r e 3:

mm/s

3000 -workpiece

300

-

100

30

1000 pm 10000

3

0.3

e m

l

-

peripheral speed v,,

The i n f l u e n c e of t h e s p e e d r a t i o on workpiece roughness

the

I

L&-F;lEKl

I

0 -----id-.+-02 2 20

, on1

200

300000

-

2000

20000

I

I

2 m o

speed ratio - q

0.1

1

10

radial infeed f, 16975 0

F; lCBNl / - -

mm/s

3000

-workpiece

300

100

30

1000 pm 10000

3

0.3

peripheral speed w4,

The c o n s i d e r d t i o n of t h e b o r d e r c a s e showed t h a t i n bo1.h p o s s i b l e b o r d e r c a s e s of t h e s p e e d r d t i o t h e :=me rouyhness occurs,

which

corresponds

to

the

s p a r k o u t r o u g h n e s s . The s p a r k o u t r o u g h n e s s R L O is o n l y d e t e r m i n e d by t h e q r i n d i n q wheel s p e c i f i c a -

Figure 4:

C r i n d i n g f o r c e s d e p e n d e n t on t h e s p e e d r a t i o i n r e l a t i o n t o t h e c o n t a c t condi-

tions.

243

In t h e r a n g e examined t h e l e v e l of f o r c e a c h i e v e d by t h e CBN-grinding wheel was about 5 t i m e s h i g h e r

The p a r a m e t e r s of t h e p r o c e s s i n f l u e n c e t h e temper a t u r e s produced i n t h e c o n t a c t a r e a / 10, 11, 12/.

t h a n f o r t h e aluminium o x i d e wheel. CBN-grinding wheels have a number of c u t t i n g e d g e s , which is l o wer by a f a c t o r of 2 0 - 60 t h a n a comparable a l u -

R i s i n g t a n g e n t i a l f o r c e s r e s u l t in h i g h e r c o n t a c t a r e a t e m p e r a t u r e s and i n c r e a s e t h e danger of t h e r mal damage t o t h e s u r f a c e l a y e r

minium o x i d e wheel of t h e same g r i t s i z e / 8 / . In s p i t e of t h e g r e a t e r c h i p t h i c k n e s s caused by t h i s . g r e a t e r f o r c e s r e s u l t a c c o r d i n g t o / 8 / because of t h e c o n s i d e r a b l y h i g h e r bond h a r d n e s s . In a d d i t i o n Lhe f o r c e s a r e i n f l u e n c e d by t h e c h a r a c t e r i s t i c s of t h e workpiece m a l e r i a l . The q u a l i t a t i v e developments of t h e g e o m e t r i c cont a c t l e n g t h s 1 and 1 and t h e a c t i v e g r a i n count 9 eg per u n i t a r e a Nacta and Nact a r e shown i n f i g u r e 4 . When t h e speed r a t i o i n c r e a s e s t h e a c t i v e g r a i n count per u n i t area d e c r e a s e s w h i l e

the

In t h e

range

of

h i g h speed r a t i o s t h e number of c u t t i n g edges i n c r e a s e s more r a p i d l y t h a n t h e t o t a l f o r c e / 3 , 4 / . S m a l l e r normal f o r c e s c a u s e less d e f o r m a t i o n s of t h e system workpiece-tool-machine. The f a u l t s i n measurements and shape t h e r e f o r e d e c r e a s e i n c r e a s i n g speed r a t i o .

s u r f a c e of t h e workpiece a t a h i g h v e l o c i t y . Under comparable c o n d i t i o n s ,

especially

in

creep

f e e d g r i n d i n g . damages t o t h e s u r f a c e l a y e r a r e l o wer when using CBN-grinding wheels T h i s can be e x p l a i n e d by t h e lower g r a i n c o u n t .

geometric

c o n t a c t l e n g t h i n c r e a s e s (see f i g . 2). A s a f u n c t i o n of q t h e r e r e s u l t s a development of c u t t i n g edges a c t u a l l y engaged Nact, which is v e r y s i m i l a r t o t h e development of t h e f o r c e .

High p e r i p h e r a l s p e e d s of t h e workpiece reduce t h e danger of t h e r m a l damages i n t h e o u t e r l a y e r s of t h e workpiece. The s o u r c e of h e a t moves over t h e

with

an

The t a n g e n t i a l f o r c e is a measure f o r t h e energy required during t h e grinding process / 9 / . The

G r i n d i n g wheels wear d u r i n g g r i n d i n g i n g r a i n and A t t h e same t i m e t h e g r i n d i n g wheel topobond. graphy changes a s d f u n c c i o n of t h e t i m e . Transie n t and s t e a d y s t a g e s of t h e wear behaviour can be defined

A f t e r a c e r t a i n t i m e t h e wheel topography

remains c o n s t a n t , t h e s t e a d y s t a g e h a s been reached / 1 ? / . The wear behaviour of g r i n d i n g wheels is among o t h e r t h i n g s i n f l u e n c e d by t h e combinations of g r i n d i n g wheel dnd workpiece and t h e s e t t i n g

cut

Londitions. In t h e t r a n s i e n t s t a g e d r e s s i n g condit i o n s can have dn d d d i t i o n a l d e c i s i v e i n f l u e n c e .

One h a s t o d i f f e r e n t l a t e between t h e s p e c i f i c e n e r -

CBN- and aluminium o x i d e wheels d i f f e r i n t h e i r beh a v i o u r over t h e t i m e . With comparable g r a i n s i z e s t h e change i n topography of CBN-grinding wheels can occur a b o u t 20 times slower t h a n i n t h e c a s e of

s p e c i f i c energy ec n e c e s s a r y per

unit

volume

can be c a l c u l a t e d a c c o r d i n g t o :

gy on t h e s i d e of t h e g r l n d i n g wheel ecs , and on t h e s i d e of t h e t o o l ecw. The t o t a l e n e r g y 1s t h e

aluminium o x i d e wheels / 8 / .

sum of b o t h p a r t s .

The aluminium o x i d e wheels used i n t h e tests

While t h e p a r t ecw is n e g l i g i b -

l y s m a l l f o r low workpiece p e r i p h e r a l s p e e d s , it becomes d e c i s i v e f o r t h e t o t a l energy i n t h e c a s e of h i g h workpiece p e r i p h e r a l s p e e d s . There r e s u l t s

a bucket shaped c u r v e f o r ec a s a f u n c t i o n of t h e speed r a t i o ( f i g . 5 ) The s p e c i t i c energy ec inc r e a s e d c o n s i d e r a b l y f o r b o t h g r i n d i n g wheels i n t h e r a n g e of c r e e p f e e d g r i n d i n g While i n c r e a s e d power is r e q u i r e d f o r t h e g r i n d i n g wheel when g r i n d i n g w i t h a h i g h q , c o n s i d e r a b l y h i g h e r power is r e q u i r e d f o r d r i v i n g t h e workpiece if q i a small.

2ooiE K 6 0 KB'ke

-'

-. .

_.

CBN M252 SN l00N EVLCo

CkL5N

-1

5

still

showed i n s t a t i o n a r y behavlour f o r a g r i n d i n g t i m e of t c - 16 s . A f t e r t h i s t i m e t h e end of t o o l l i f e w a s reached f o r h i g h speed r a t i o s ( c r e e p f e e d g r i n ding).

The g r i n d i n g wheel

began

to

chatter

and

burn marks dppedred on t h e workpiece. T h i s i n d i c a t e d i n t e n s i v e b l u n t i n g processes during t h e g r i n d i n g p r o c e s s / 14/ G r i n d i n g could o n l y occur w h i l e d r e s s i n g w a s i n influence. From s t u d i e s of s u r f a c e c r e e p f e e d g r i n d i n g it is known Lhat o n l y g r i n d i n g wheels of low

h a r d n e s s and open s t r u c t u r e s h o u l d be used f o r

t h i s process.

The g r i n d i n g wheel used h e r e

had

a

h a r d n e s s t h a t was t o o h i g h f o r c r e e p f e e d g r i n d i n g . In t h e r a n g e of u s u a l and v e r y low speed r a t i o s (q<20) no e x c e s s i v e wear or i n t e n s i v e g r a i n hlunt i n g c o u l d be o b s e r v e d . After t h e grinding t i m e tc

= 2000 s t h e s t e a d y s t a was reached f o r CBN-grinding wheels. The g r i n d i n g wheel topography d i d n o t change any more dur i n g c r e e p feed g r i n d i n g .

ge

02

2

20

oar

,

3@JwO 1w7~D

Figure 5:

244

0.1

1 10 radial Infeed I,

-

mm/s

3000

300

-

2000

200 speed ratio - q

4

-

1M1 ,

30

20000 1000 vm

3

200000

The r a d i a l wear A r g was determined

10000

y r i n d i n g wheels. A r y w a s r e d u c e d , f o r example, by n e a r l y 5 0 p e r c e n t f o r dn i n c r e a s e of q - 100 t o g 12000.

0.3

workpiece peripheral speed v,,

S p e c i f i c energy of t h e q r i n d i n g p r o c e s s as a f u n c t i o n of t h e speed r a t l o .

for

the

CRN-

h e a t i n g - u p of t h e s u r f a c e l a y e r i n c r e e p f e e d g r i n d i n g w i t h CBN can l e a d Lo problems.

s.!um1 Y T e s t r e s u l t s from g r l n d l n q p r o c e s s e s , wh1r.h mainly r e f e r t o r o u g h n e s s , f o r c e s . wear and t e m p e r a t u r e development i n t h e s u r f a c e l a y e r s , a r e d e c i s i v e l y i n f l u e n c e d by t h e speed r a t i o q . For t h e f i r s t t i m e it h a s been shown h e r e , t h a t one can g r i n d w r t h d speed r a t i o of Iql C 10 In t h i s r a n g e

Ruughnesses, t h a t a r e i n t h e magnitude e q u a l t o t h o s e i n c r e e p f e e d g r i n d i n g , however w i t h o u t t h e o c c u r a n c e of e x c e s s i v e heating-up of t h e s u r f a c e l a y e r of t h e workpiece, r e s u l t from t h e new g r i n d i n g method w i t h s m a l l speed r a t i o s . tes

that

the

This

indica-

u s e of CBN-grinding wheels could be

g r i n d i n g r e s u l t s have been found which can be cons i d e r e d t o be e x t r a o r d m a r i l y advantageous. I t is t h u s I n d i c a t e d t h a t p r e v i o u s l y t h e k i n e m a t i c pro-

There e s p e c i a l l y a t t r a c t i v e for t h e new p r o c e s s . r e s u l t s a new f i e l d of u s e f o r CBN-grinding wheels.

c e s s e s of a r i n d i n q p r o c e s s e s which cannot have been o p t i m a l

When comparing d i f f e r e n t g r i n d i n g p r o c e s s e s w i t h d i f f e r e n t speed r a t i o s it must be p r e c o n d i t i o n , Lhat t h e o t h e r g r i n d i n g c o n d i t i o n s , i . e . t h e raw

occured

i n ranges

ex-

m a t e r i a l of t h e workpiece, t h e g r i n d i n g w h e e l s , t h e

I t i s . howt e r n a l c y l i n d r i c a l plunge g r i n d i n g e v e r , f a i r l y c e r t a i n t h a t they w l l l a l s o lead t o

I n i t i a l l y these new grinding r e s u l t s refer

t o

cooling conditions, but especially t h e material removal r a t e remain c o n s t a n t . The g r i n d i n g t i m e must

t h e same p o s l t i v e r e s u l t s f o r i n t e r n a l c y l i n d r i c a l plunge g r l n d i n g and f a c e g r i n d i n g o p e r a t i o n s .

a l s o be c o n s i d e r e d .

The r e s u l t s determined so f a r have shown: The roughnesses of t h e workpiece become e x c e e d i n g l y low

for s m a l l n e g a t i v e v a l u e s of t h e speed r a t i o q sim i l a r t o c r e e p f e e d g r i n d i n g . The h i g h p e r l p h e r a l s p e e d s of t h e workpiece which a p p l y f o r low speed r a t i o s q r e d u c e t h e danger of t h e r m a l damages i n Lhe s u r f a c e l a y e r s of t h e workplece. Models and measurements show t h a t t h e t h e r m a l s o u r c e moves over t h e s u r f a c e of t h e workpiece a t a h i g h e r speed and t h e t e m p e r a t u r e d e c r e a s e s i n t h e s u r f a c e l a y e r when t h e workpiece p e r i p h e r a l speed is h i g h e r . Und e r comparable g r i n d i n g c o n d i t i o n s lower f o r c e s r e s u l t e d from lower speed r a t i o s . Lower f o r c e s have t h e ddvantage t h a t d e f o r m a t i o n s d e c r e a s e w i t h them Advantages a l s o appeared f o r t h e wear, s i m i l a r as in creep feed grinding. D i s a d v a n t a g e s of c r e e p feed grinding respective t o t h e surface layer t e m p e r a t u r e s of t h e workpiece could n o t be found. In t h e f o l l o w i n g t a b l e t h e r e s u l t s have been summarized q u a l i t a t i v e l y f o r s e l e c t e d speed r a t i o s . vs

=

constant y

wor k p i e c e transverse roughness

-

Q' -1

'

-

constant

q

-100

-

high

i

low

q

1

-

e v e r , important consequences can a l r e a d y be

this HOW-

postu-

lated. F i r s t l y it must be s t a t e d t h a t t h e e x p e r i ments must be expanded t o o t h e r g r i n d i n g p r o c e s s e s . That

is e s p e c i a l l y t h e c a s e f o r i n t e r n a l c y l i n d r i -

c a l g r i n d i n g and f a c e g r i n d i n g . The experiments must a l s o be expanded t o o t h e r r a n g e s of material removal r a t e s . I t must be c l a r i f i e d where t h e l i m i t i n g m a t e r i a l removal r a t e s l i e and which c r i t e r i o n s d e t e r m i n e them. Then d i f f e r e n t workpiece mat e r i a l s have t o be examined w i t h d i f f e r e n t g r i n d i n g wheel s p e c i f i c a t i o n s f o r v i t r i f i e d g r i n d i n g wheels a s w e l l as f o r CBN-grinding wheels. A s it h a s been shown t h e c o n t a c t l e n g t h s i n c r e a s e

relatively

for

smaller as w e l l a s f o r h i g h e r speed r a t i o s . I t s h o u l d be examined how t h e c o n t a c t l e n g t h s i n f l u e n ce

wear,

forces

and t e m p e r a t u r e s , e s p e c i a l l y f o r

d i f f e r e n t workpiece m a t e r i a l s . An i m p o r t a n t f i e l d is t h a t of t o o l machine d e s i g n . With t h e new o p e r a t i o n , f o r example, t h e workpiece r o t a t i o n a l s p e e d s have t o be i n c r e a s e d c o n s i d e r a b l y i n e x t e r n a l c y l i n d r i c a l plunge g r i n d i n g . T h i s r e s u l t s i n new c o n d i t i o n s f o r t h e workpiece clamping.

-10000

low

1

I t m u s t b e p o s s i b l e t o a c c e l e r a t e t h e workpiece and

I

it down a g a i n w i t h i n t h e s h o r t e s t p o s s i b l e t i m e , so as t o keep t h e t o o l changing t i m e s low. I t seems a p p a r e n t t o u s e new workpiece d r i v i n g dev i c e s , as t h e power r e q u i r e d by t h e workpiece d r i v e i n t h e new g r i n d i n g p r o c e s s w i t h low speed r a t i o is i n t h e same magnitude as t h e main d r i v e . So f a r one c o u l d l e a v e t h e power r e q u i r e d t o d r i v e t h e workpiece unconsidered i n f i r s t a p p r o x i m a t i o n . For h i y h r o t a t i o n a l s p e e d s of t h e workpiece one must d l S 0 have a u t o m a t i c b a l a n c i n g . The c e n t e r s must be d r iven, too.

slow

g r ind i n g forces

wor kp i e c e surface layer temperature L

II 1I

I

I

I

shape d e v i a t i o n s as a r e s u l t of small t h e infeed s p i r a l

I

shape d e v i a t i o n s ds a r e s u l t of unbalance F i n d i n g wheel ear

large

lmedium

I

I

I

medium

medium high

small

I I

Because of t h e r e l a t i v e l y l a r g e c u t t i n g tances,

The f i r s t s e r i e s of experiments a c c o r d i n g t o new g r i n d i n g method g i v e r i s e t o h i g h hopes.

relatively

small

c

I

1

low

edge

dis-

l a r g e roughnesses are produced

w i t h CBN-yrinding wheels under comparable condit i o n s i n comparison Lo v i t r i f i e d g r i n d i n y w h e e l s . In c r e e p f e e d g r i n d i n g r e l a t i v e l y low roughness r e s u l t e d even w i t h CBN-grinding wheels because of t.he kinemat.ic i n f l u e n c e of h i y h speed r a l - i o s , b u t t h e

1 S a l j b , E . Grundlagen d e s S c h l e i f v o r g a n g e s . W e r k s t a t t und B e t r l e b , Heft 2 . 1952

245

O p f t z , H.. Frank, H. et dl. Untersuchungen llbcr den EinfluB deu Schleifscheibenaufbaueu und der Zerspanbedingungen auf die Ausbildung der Schneidflache der Schleicscheibe in Hinblick auf das Arbeitsergebnis. Forschungsbericht des Landes Nordrhein-Westfalen Nr. 1532

Brandin. H. Pendelschleifen und Tiefschleifen. Dissertation TU Braunschweig 1978 Werner. G. Technologische und konstruktive Voraussetzungen fur das Tiefschleifen. wt-Zeitschrift fur ind. Fertigung 69 (1979) Verkerk. J. The real contact length in cylindrical plunge grinding. Annals of the CIRP 24/1/1975

Hahn, R. S . , Lindsay, R. P. On the effects of real contact. and normal stresses in grinding. Annals of the CIRP 15/1967 Karatzoglou. K. Auswirkungen der Schleifflachenbeschaffenheit und der Einstellbedingungen auf das Schleifergebnis beim FlachEinstechschleifen. Dissertation TU Braunschweig 1974 Jacobs, U. Beitrag zum Einsatz von Schleifscheiben mit kubisch-kristallinem Bornitr id als Schneidstoff. Dissertation TU Braunschweig 1980 SaljC, E., Matsuo, T., Lindsay, R. P. Transfer of grinding research data for different operations in grinding. Annals of the CIRP 31/2/1982 10 Furukawa, S . et al. Selection of creep feed grinding conditions in view of burning. Annals of the CIRP 28/1/1979

11 Takazawa, K. Thermal aspects of the grinding operation. Industrial Diamond Review 4, 1972 12 Konig. W. et al. Untersuchung der beim Schleifproze0 entstehenden Temperaturen und ihre Auswirkungen auf das Arbeitsergebnis. Porschungsbericht des landes Nordrhein-Westfalen Nr. 2848 13 Weinert. K. Die zeitliche ISnderung des Schleifscheibenzustandes beim AuDenrund-Einstechschlei-

fen. Dissertation TU Braunschweig 1976 14 SaljC, E. et al. Problems in profile grinding - Angular plunge grinding and surface grinding. Annals of the CIRP 30/1/1981

246