effects of cryogenic cooling by liquid nitrogen jet on forces, temperature and surface residual...

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Cryogenics 35 (1995) 515-523

0 1995 Elsevier Science Limited

Printed in Great Britain. All rights reserved

001 l-2275/95/ 10.00

Effects of cryogenic cooling by liquid

nitrogen jet on forces temperature and

surface residual stresses in grinding steels

S. Paul* and A.B. Chattopadhyay

Department of Mechanical Engineering, Indian Institute of Technology Kharagpur,

West Bengal 721 302, India

Received 20 January 1995; revised 14 February 1995

Grinding is a widely employed finishing process for different materials such as metals,

ceramics, glass, carbides, rocks, etc. to achieve good geometrical (form) and dimen-

sional accuracy with acceptable surface finish and surface integrity. However, it is

inherently characterized by high specific energy requirements, unlike other conven-

tional machining processes such as turning, milling, etc., which lead to a high grinding

zone temperature and poor surface integrity. Many methods have been investigated

to control this high grinding zone temperature, but all have their shortfalls, both tech-

nological and environmental, in exchange for controlling the grinding zone tempera-

ture. This paper briefly discusses the results obtained with regard to grinding forces,

specific energy, grinding zone temperature and surface residual stress when using

cryogenic cooling and compares them to the results from dry grinding and grinding

with soluble oil. Cryogenic cooling seems to have the edge over other coolants in

terms of controlling the temperature, residual stresses and grinding forces, and it is

also environment friendly.

Keywords: cryogenic grinding; grinding

residual stresses

Grinding is a widely used machining process mainly

applied to finish surfaces, both internal and external, in a

wide variety of materials, such as metals, ceramics, car-

bides, stones, etc. Grinding is employed to achieve good

dimensional and form accuracy of the product with accept-

able surface integrity.

However, grinding is inherently associated with high

specific energy requirements which result in a very high

grinding zone temperature. Such high grinding zone tem-

peratures, if not well controlled, would lead to thermal

damage to the ground surface in the form of plastic defor-

mations, the formation of micro- and macro-cracks (which

could be both surface and subsurface cracks), redeposition,

induction of tensile residual stresses, etc. In other words,

it would impair the surface integrity of the ground surface

significantly. Marshall and Shawl, Backer et al.* and Out-

water and Shaw3 were among the first scientists to study

grinding processes and to identify high grinding zone tem-

perature as one of the main causes of high tensile residual

*Currently Post-Doctoral Research Fellow at the Laboratory for

Flexible Production Automation, Faculty of Mechanical Engin-

eering and Marine Technology, TU Delft, Landbergstraat 3,2628

CE Delft, The Netherlands

forces; grinding temperature; surface

stress on the ground surface. Other problems such as wheel

loading, wheel wear and surface damage are also substan-

tially influenced by the high grinding zone temperature.

Many methods have been investigated to control the

grinding zone temperature. Some workers have advocated

the use of neat oils instead of cutting compounds to control

temperature - .6 Nee7 studied the applicability of additives

and solid lubricants in grinding. But it was realized that the

effectiveness of grinding fluids is restricted by the fact that

they lose their cooling properties upon film boiling and that

the film boiling temperatures of conventional fluids are low

(maximum =350C)6.8. Another problem associated with

control of temperature in grinding fluid applications is that

the fluid fails to reach the grinding zone due to the forma-

tion of a stiff boundary layer around the rotating grinding

wheel. To counteract this problem, several methods have

been investigated:

1 painting of the faces and cardboard scrapper tech-

nique,O;

2 grooves on the periphery of the whee15,1,12;

3 curved grooves on the face of the wheel;

4 randomly distributed holes parallel to the wheel axis in

the case of face grinding12;

5 on-line ultrasonic cleaning of the wheel surfacelo;

Cryogenics 1995 Volume 35, Number 8 515


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Effects of cryogenic cooling in grinding steels: S. Paul and A.B. Chattopadhyay

6 hybrid wheels;

Table 2 Experimental conditions

7 ZZ method (i.e. through-wheel coolant supply

method) 3;

8

jet infusion technique14; and

Item Description

9 cubic boron nitride CBN) wheels15 and monolayer

CBN wheels16,.

Most of the above methods use grinding fluids with or with-

out additives which need to be specially treated to make

them biologically harmless during storage and use. But dur-

ing application they do pollute the air in the machine shop.

Hence future trends could also include the replacement of

such grinding fluids with non-polluting coolants, like some

liquefied gases, e.g. liquid nitrogen.

Research in the field of grinding with a cryogenic cool-

ant, to the best of our knowledge, was initiated by Chatto-

padhyay et al. I9 In a preliminary investigation they

observed some benefits of cryogenic cooling with liquid

nitrogen with respect to the grinding forces and surface

quality. Recent publications20~2 also indicate successful

application of cryogenic cooling in other machining oper-

ations. Paul

et al.

have recently studied the effects of

cryogenic cooling by liquid nitrogen in grinding steels,

mainly on the chip formation mechanism, grinding forces

and surface quality. In another study, Paul et aLz3 compu-

tationally determined the grinding zone temperature and

residual stress field using the finite element method, which

indicated the effectiveness of cryogenic cooling in con-

trolling both the grinding zone temperature and residual

stress with respect to dry and wet grinding (i.e. with normal

soluble oil as a coolant).

Machine

Wheel

Spindle speed

Wheel speed

Table speed

lnfeed

Environment

Dresser

Dressing depth

Dressing lead

Spindle speed

Environment

(dressing)

Jung horizontal surface grinder,

2.2 kW

A60K5V

(150mmx13mmx31.75mm)

3000 rev min-

23.5 m s

8 m min

10 to 40 pm in steps of 10 pm

Dn/

Flood cooling with soluble oil

(1:20)

Liquid nitrogen jet

1 carat single point diamond

dresser

10 pm, single pass

160 pm

3000 rev mini

Dry

Table 3 Dressing conditions for force experiments

Type of

dressing Parameter

Coarse

Fine

Depth

10

Lead 160

Depth

5

Lead

80

In the present paper, the effects of cryogenic cooling by

liquid nitrogen jet have been reviewed with respect to dry

grinding and grinding with soluble oil as coolant. The

effects on grinding forces, grinding zone temperature and

residual stresses have been presented to obtain an overall

view of cryogenic cooling.

Experimental conditions

any coolant. In wet grinding, soluble oil ( 1:20) was applied

at the grinding zone using the flood cooling application

method available with the machine. For cryogenic cooling

of the grinding zone, a jet of liquid nitrogen was made to

impinge at the grinding zone from a suitable distance

(40 mm) and angle (20). The liquid nitrogen jet was pro-

duced by pressuring the Dewar to 0.35 MPa (3.5 bar) using

dried air and fitting a suitably designed nozzle in the deliv-

ery line. The liquid nitrogen delivery set-up has been shown

schematically in a previous paperz3.

For the present study five steels commonly used in industry

have been chosen; their chemical composition and bulk

hardness are given in Table 1. The experimental conditions

are given in

Table 2.

For grinding force measurements, the

dressing conditions have been changed and are listed in

Table 3.

The grinding forces, specific energies, temperatures and

residual stresses reported are those when the process has

stabilized; this point was decided to be when there was

almost no fluctuation in the mean values of the grinding

forces in the normal and tangential directions over a num-

ber of passes.

To study the effects of cryogenic cooling on the grinding

forces and specific energy, as compared to dry and wet

grinding, the grinding forces in the normal and tangential

directions were measured by a three component Kistler pie-

zoelectric dynamometer and were recorded on a thermal

pen type recorder, under different environments, infeeds

and dressing conditions. The specific energy U is obtained

by the following formula

FtVc

u=-

aV,b

The dry grinding was carried out without application of where: F, = tangential force; V, = peripheral speed of grind-

Table 1 Chemical composition of materials

Size (pm)

Material Designation

c (%) Ni 1%) Cr t%)

MO (%) v (%) w (%)

1

Mild steel MS/AISI lOZO/Rc 14

High carbon steel

HCS/AISI 1080/Rc 32

Cold die steel CDS/D2/Rc 43

Hot die steel HDS/H 1 /Rc 53

High speed steel HSSlM2lRc 64

Traces of P, S and Mn present

0.15 =

0.80 a

2.00 0.10 12.3 0.30

0.40 0.10 4.00 1.40

0.80 4.00 4.00 2.00 6.00

516

Cryogenics 1995 Volume 35, Number 8


3/9

Effects of cryogenic cool ing

in gr inding steels : S Paul and A B Chattopadh yay

ing wheel;

a =

infeed;

VW =

speed of work piece; and

b = width of cut. Temperature measurements were also car-

ried at the grinding zone for different infeeds and environ-

ments using the method cited by van Luttervelt and Zhou24.

The effect of cryogenic cooling on residual stress has

also been investigated by measuring the residual stress at

the ground surface in the direction of grinding by an X-ray

diffraction method. A two-tilt (or exposer) method25 has

been used for an iron (FeK,) target. Necessary corrections

were undertaken for the Lorenz polarization factor and

absorptionZ5

and K, doublet splitting leading to partial or

complete blending of K, doublets26. Also, the measure-

ments were repeated three times to minimize the levels of

error. For smoothing of the data, neighbourhood averaging

over three points has also been included*.

Results and discussion

Grinding forces consist of different elements which largely

depend on the wheel characteristics, the working material

characteristics, the process parameters, the chosen environ-

ment and the grinding zone temperature. In the main, there

are two groups of elements which add to the total grinding

force; one of them is productive and more or less pro-

portional to the infeed, and the other is mainly non-pro-

ductive or frictional, and may not depend on the infeed.

Figures 1-5 show the variation of grinding forces in the

0

10

I

ink3 (rni%n)

40 50

CL

0

I

1

infee2da (mi%n)

40 50

normal and tangential direction and the specific energy with

the infeed for different environments under coarse and fine

dressing conditions for all the different materials used for

the current study.

Irrespective of the working materials, environment and

infeed, the normal forces were found to be around twice

the tangential forces, unlike in other machining processes

like turning and milling. This can only be attributed to the

very large negative rake of the grits, the excessive rubbing

action and adverse chip accommodation space, often lead-

ing to wheel loading and smaller uncut chip thickness. It

can also be noted that the normal and tangential forces

increase gradually with increase in infeed, as expected. But

the specific energy is observed to decrease gradually with

increase in infeed, irrespective of the working material and

environment. This may be attributed to the interplay of two

groups of forces, i.e. the productive and non-productive

(frictional) ones. At low infeed the percentage contri-

butions of the friction between the grit tips and working

material, rubbing, primary and secondary ploughing, and

friction between loaded chip particles and the working sur-

face are more predominant; the percentage contribution of

the same group of factors at higher infeed levels is reduced

because most of them are more or less independent of

infeed; in contrast, the productive parts, i.e. the forces due

to shearing and micro-fracturing, are almost proportional to

the infeed level. Hence the specific energy decreases with

increase in infeed.

wdt

-q-2

b

I I

10 20 30 sb 5

infeed (micron)

Qoa dry

4Au.b

wet

U Iq. N2

D

0 1

infee2d (rniZ0n)

4.0

Figure Variation in grinding forces and specific energy with infeed for mild steel under different environments



4/9


QQQ W dry

finnnh wet

Qou o Lq.Nz

infeed (micron)

0,

I

0

10

r 6

infee2d0 (rni,yon)

4Q F

*

1

0-

0

10

infeZ? {rni2on)

40 30

0~ dry

&bbU

wet

QAQM Iq. N2

-,J_

10

infee2d0 (rn&l)

40 1

Figure2 Variation in grinding forces and specific energy with infeed for high carbon steel under different environments

A very interesting point to note is that both the normal

and tangential forces and hence the specific energy have

been found to be less under cryogenic cooling, throughout

the infeed range for all the materials undertaken and under

both dressing conditions, as compared to dry and wet grind-

ing. This again may be attributed to smaller chip size22,23,

a predominantly fractured mode of material remova12*~*,

reduction in wheel loading26, retention of grit sharpness due

to an inert atmosphere26 and a much lower grinding zone

temperature23.

temperature can be seen in Figure 6 for all the materials

investigated. The results shown are experimental in nature

and are the average of a few passes after the process has

stabilized.

Another very interesting point that has been observed,

is that as the work piece hardness increases the benefit of

cryogenic cooling decreases. At higher work piece hardness

and for materials which retain their hardness at higher tem-

peratures (e.g. high speed steel), even under dry and wet

grinding, fractured chips are found.

Dressing parameters should have an influence on the

grinding forces and specific energy, as they control the dis-

tribution of grits, their initial sharpness or bluntness, the

number of active cutting edges and the chip accommo-

dation spaces. As expected, coarse dressing produced lower

forces for almost all the materials and environments. It

should also be noted that the effectiveness of cryogenic

cooling increased with coarse dressing, especially for

harder materials like cold die steel, hot die steel and high

speed steel.

Figure 6 shows that there has been a substantial

reduction in the grinding zone temperature on application

of the liquid nitrogen jet for all the materials tested and

throughout the infeed range. But it seems that the effective-

ness of cryogenic cooling increases at higher infeeds. It is

also important to note that the application of soluble oil

fails to control the temperature to the desired level and its

effectiveness decreases at higher infeed. Soluble oils

remove heat from the grinding zone by flood cooling. If

the temperature exceeds the film boiling temperature of the

grinding fluid then it loses its cooling abilities because of

the formation of a film which hampers the local heat trans-

fer situation.

The liquid nitrogen jet seems to be rnore effective in the

case of ductile materials (e.g. mild steel) in controlling the

temperature. This is because of its better effectiveness in

controlling the grinding forces and specific energy for mild

steel. Such control of grinding zone temperature led to

better surface characteristics of the ground surfaces, as

observed under the scanning

electron microscope

( SEM)22,23, and less wheel loading and wheel wear26.

The variation of surface residual stress in the grinding

The effect of cryogenic cooling on the grinding zone

direction with infeed under different environments, as

518 Cryogenics 1995 Volume 35, Number 8


5/9

Effects of cryogenic cool ing in gr inding steels : S Paul and A B Chattopadhyay

0-l

10

1

infeZ: (rni%)

I

40 50 10

1

I

infez (rni~~0n)

40

t I

CH

0 10infeezda (rni%n)

40 50

a

10 infeZ? (rni~~on)

40 :

Figure 3 Variation in grinding forces and specific energy with infeed for cold die steel under different environments

determined by X-ray diffraction, can be seen in Figure 7.

For almost all the materials, the surface residual stress is

found to be tensile in nature irrespective of the environment

and infeed. The tensile residual stress is induced in grinding

for three reasons, thermal, metallurgical and mechanica15~28-30.

At a high grinding zone temperature, the upper hot layer of

the working material is plastically deformed by the cooler

sublayers, leading to tensile residual stress on cooling.

Residual stress is also generated because of austenitic-

martensitic transformation due to the high grinding zone

temperature and its gradient. Mechanical hot working by

local normal Hertizian pressure also introduces residual

stress. But previous investigators have pointed out that the

thermal source is the main one in the development of tensile

residual stress.,5,28,30 As the temperature increases at higher

infeeds, for all the materials and environments, the tensile

residual stresses have also increased with increase in infeed.

It is also noteworthy that application of soluble oil could

not control the tensile residual stress to the desired level,

as can be seen in

Figure 7.

This can only be attributed to

its failure to control the grinding zone temperature Figure

6) and forces Figures 1-5).

Application of liquid nitrogen has, as expected, con-

trolled the tensile residual stress and can substantially

reduce it though this depends on the material character-

istics. These effects could be attributed not only to effective

temperature control but also to a desirable reduction in

grinding forces. And it should be stressed that the control

of tensile residual stress has not followed the same trend

as the control of temperature. This is because of different

material characteristics, especially at higher temperatures,

of the working materials. Hence it appears that cryogenic

cooling has provided substantial benefits in the case of

those steels which are ductile and adhesive at high tempera-

tures, such as mild steel, and those steels which are hot

hard and are to some extent brittle in nature, such as hot

die steel and high speed steel.

Conclusions

Based on the experimental results presented in this paper

the following conclusions can be drawn.

1 While grinding the steel specimens under different con-

ditions, cryogenic cooling provided significant improve-

ments, as expected, though to varying degrees, with

respect to grinding forces, specific energy requirements

and surface residual stresses, mainly due to a substantial

reduction in grinding zone temperature.

2 Cryogenic cooling has substantially reduced the grind-

ing zone temperature and kept the temperature well



6/9


z:

In

fine dressing

QQD.RU dry

------ norm01

u wet

U444 Lq.Nz

3-

3

f

0

Sk-&

al

::

o- 0

10 infeZ (mi%n)

40 50

10 infe2 (mi&on) 40

3

hot die steel

u& codrse dressing

o-.

t . ,

0 10 infet? (miJc%n)

40 50 0

10

ink62 (mi%)

- so

Figure 4 Variation in grinding forces and specific energy with infeed for hot die steel under different environments

c

6 10

Cl

infee? (m&7)

40 50

10

infee2d0 (mi%n)

4-b

O

I

0

10

ink2 (nG on)

40 50

Figure 5 Variation in grinding forces and specific energy with infeed for high speed under different environments

below the critical temperature range for the steels. Such

4 Favourable chip formation and effective temperature

benefits increased with the increase in ductility of the

control enabled cryogenic grinding to reduce substan-

working material, the fracture mode of chip formation

tially the magnitudes of the grinding forces, both tan-

and infeed level.

gential and normal, and hence the specific energy

3 Flood cooling by soluble oil could not control the grind- requirement. Such a reduction in the forces seems to be

ing zone temperature appreciably and its effectiveness

more predominant when the steels are more ductile and

decreased further with an increase in infeed.

less heat resistive, when the wheel is coarse dressed and

when the infeed is sufficiently large.

520 Cryogenics 1995 Volume 35, Number 8


7/9

Effects o f cryogenic cool ing in gr inding steels : S Paul and A B Chattopadhyay

mild steel

0

0

10

20 30

40

inieed, micron

-I

high carbon steel

10 20 30 40 f

infeed, micron

I

cold die steel

Of

IO 20 30 40

infeed, micron

hot die steel

high speed steel

Oo

10 20

30

40 50

10

20 30 50

infeed,

micron

40

infeed, micron

Figure 6 Variation in grinding temperature with infeed for different materials under different environments

5 Dry grinding yielded high tensile residual stress at the

residual stress for all the materials, though to varying

ground surface of all the steels investigated and the

degrees, under all the infeed levels, a change which can

stress values increased with the increase in infeed. Wet

only be attributed to its efficient cooling action, better

grinding failed to improve the situation appreciably,

modes of chip formation, less specific energy and,

mainly due to its failure in controlling the grinding

finally, lower grinding zone temperature.

zone temperature.

7 The benefits of cryogenic cooling have been more sub-

6 Cryogenic cooling reduced the magnitude of the tensile

stantial for those steels which are either quite soft, duc-



8/9


uQRn J

dry

&.%A wet

QQ0.43 Iq. nit

F

mild steel

E

O

10 20 30 40

infeed (micron)

81 high

cut-bon steel

4:

00

IO

10

infee2da (miZ*n)

40 50

u-l

IO

10 20

infeed (rni%n)

40 E

i

hot die steel

K

O

10

infee2d0 (miZx7)

40 50

g

high speed steel

u-l

O

10

infee2d0 (rni~~on)

4-o E

Figure 7 Variation in surface residual stress of work piece for different materials under different environments

tile and sticky or to some extent hot hard and relatively

2

brittle in nature.

3

References

4

1

Marshall, E.R. and Shaw, M.C.

Forces in dry surface grinding

5

Trans ASME

1952)

74 5

1

522 Cryogenics

1995 Volume

35, Number 8

Backer, W.R., Marshall, E.R. and Shaw, M.C.

The size effects in

metal cutting Tram ASME (1952) 74 61

Outwater, J .O. and Shaw, M.C.

Surface temperature in grinding

Tram ASME 1952) 74 73

Malkin, S. and Lenz, E.

Burning limit for surface and cylindrical

grinding of steels

Ann CIRP 1978) 27

1)

233

Snoeys, R., Maris, M. and Peter, J .

Thermally induced damages in

grinding Ann CIRP 1978) 27 2) 57 1


9/9


10

11

12

13

14

15

16

17

Howea, T. Assessment of the cooling and lubricating properties of

grinding fluids

Ann

CIRP (1990) 39( 1) 313

Nee,

A.Y.C. The

effects of grinding fluid additives on diamond abras-

ive wheel efficiency Inr J MTDR (1979) 19 21

Yasui, H. and Tsukuda, S. Influence of fluid type on wet grinding

temperature Bul l JSPE

1983) 17 133

Akiyama, T., Shibata, J . and Yonetsu, S.

Behaviour of grinding

fluid in the gap of the contact area between a grinding wheel and

work piece Proc 5th ICPE Japan Society of Precision Engineering,

Tokyo, Japan (1984) 52

Aoyama, T. and Inasaki, I.

Suppression of temperature rise in creep

feed grinding

Proc 5th KPE

Japan Society of Precision Engineering,

Tokyo, Japan (1984) 46

Nakayama, K., Takagi, J . and

Abe, T. Grinding wheel with helical

grooves - an attempt to improve the grinding performance

Ann

CZRP

(1977) 26( 1) 133

Shaw, M.C. Interrupted grinding principle

Inst Eng In di a) J Prod

Eng 1985) 66 29

Graham, W. and Whitson, M.G.

Some observations of through

wheel coolant application in grinding Int J. MTDR (1978) 18 9

Eda, H., Kishi,

K., Ueno, H.

and Nomura, K.

Effective method of

using the jet infusion in grinding Bul l JSPE (1985) 19 49

Pecherer, E. and Malkin, S.

Grinding of steels with CBN Ann CIRP

(1984) 33(l) 211

Chattopadhyay, A.K., Chollet, L. and Hintermann, H.E. On per-

formance of chemically bonded single layer CBN grinding wheel

Ann

CIRP

(1990) 39(l) 309

Chattopadhyay, A.K., Chollet, L. and Hintermann, H.E.

On per-

formance of brazed bonded monolayer diamond grinding wheel

Ann

CIRP 1991)

40(l)

347

18

Inasaki, I., Tonshoof, H.K. and Howes, T.D.

Abrasive machining

19

20

21

22

23

24

25

26

21

28

29

30

in the future

Ann CIRP 1993) 42 2) 723

Chattopadhyay, A.B., Bose, A. and Chattopadhyay, A.K.

Improvements in grinding steels by cryogenic cooling

Precision

Eng

(1985) 7(2) 93

Evans, C.

Cryogenic diamond turning of stainless steel

Ann CIRP

1991)

40(l) 571

Bhattacharya, D., Allen, M.N. and Mander, SJ . Cryogenic mach-

ining of Kevlar composites

Materials

and Man@

Proc

(1993) S(6)

631

Paul, S., Bandyopadbyay, P.P. and Chattopadhyay, A.B.

Effects

of cryo-cooling in grinding steels J Mat Proc (1993) 37 791

Paul, S. and Chattopadhyay, A.B.

A Study of effects of cryo-

cooling in grinding Int J

MTM 1995) 35

1) 109

Zhou, Z.X. and van Luttervelt, C.A.

The real contact length

between grinding wheel and work piece - a new concept and a new

measuring method

Ann CIRP 1992) 41

1) 387

Cullity,

B.D. Elements of X-Ray Diffraction

2nd Edn, Addison-

Wesley, Reading, MA, USA (1978)

Paul, S. Improvements in grinding some commonly used steels by

cryogenic cooling PhD D issertati on IIT, Kharagpur, India (1994)

Ku, K.S.,

Gonzalez, R.C. and Lee, C.S.G.

Robot ics - Contr ol, Sens-

ing, Vi sion and Intell igence McGraw-Hill, New York, USA (1987)

Wakabashi, M. and Nakayama, M.

Experimental research on

elements composing residual s tresses in surface grinding

Bul l

JSPE

(1979) 13 75

El-Helieby, S.O.A. and Rowe, G.W.

A quantitative comparison

between residual stresses and fatigue properties of surface ground

bearing steel Wear (1980) 58 115

Vansevenant, E.

An improved mathematical model to predict

residual stress in surface plunge grinding Ann CIRP 1987) 36 1) 413


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