Production of electrodeposited diamond wheels and grinding performance for hard metals and ceramics

Journal

of

Materials Processing Technology Journal of Materials Processing Technology 62 (1996) 303-308

Production of Electrodeposited Diamond Wheels and Grinding Performance for Hard Metals and Ceramics K. Sate”, T. Yokoyam$,

K. Suzukib

aScienceUniv. ofTokyo,2641 Yamazaki,Noda-Shi, 278 JAPfl b TOME1DIANOND Co., Ltd. 4-5-l Joto, Oyama-Shi, 323 JAPM

Abstract Influence of material properties and electrodepositing condition on occurence of the detriminal phenomena, ‘over plating’ and ‘nodule’, were investigated for eighteen kinds of synthetic diamond abraisive grains. Grinding performance of a electrodeposited wheel for hard metals, ceramics, and cennet were tested. Grinding tests were carried out at constant thrust pressure. Some patterns of growth of ‘over plating’ and ‘nodule’ were observed and their photographs were taken with a SEM microscope. Ratios of number of over plated abrasive grains and nodules to total numbers of electrodeposited abrasive grains were smaller than 2% under the current density of 6 A/dm’ for all kinds of tested grains. These ratios were abruptly increaed for the abrasive grains with high friability in current density of 10 A/dm’. Grinding performance for the high friability abrasive grains was good for a hard metal and a TIN cermet. On the contrary, abrasive grains with low friability were suitable for grinding of ceramics, as AlaO, and Si3N4.

Keywords: Electrodeposition,

Diamond abraisive grain, Diamond grinding wheel, Grinding performance,

1. Introduction Over plating phenomenon that a abrasive grain is covered with electrodeposited layer and a nodule that is piles of electrodeposited layer occur on electrodeposition with synthetic diamond abrasive grains. As these phenomena reduce the grinding ability, it is very important subject to restrain occurence of the phenomena in production process of a electrodeposited diamond wheel. One of the purposes of the present paper is to make clear influences of material properties of abrasive grains and wheel production process on occurence of these phenomena. In addition, grinding ability of wheels with various diamond grains is tested for several work materials, such as hard metals(K20 and P20), ceramics(AlzO, and Si,NS, and cermet(TiN). Material properties of abrasive grains that are suitable for each work are considered. 2. Materials

and experimental

apparatus

Hard metal, Ceramics

properties are shown in Table 1. Symbol BD in the Table 1 is bulk density, which indicates the mass of diamond abrasive grains stuffed in a measuring vessel of 10 mL. In the symbol F/120”, F indicates friability of a diamond, and the figure 120” is the vibrating time indicated in second. (b) Electrodeposition bath Electrodeposition was carried out in bright nickel bath which was maintained in pH 4. (c) Wheel bodys All the wheel bodies have same shape, cup type, and are made of steel(S4SC in Japan Industrial Standard). The shape and dimensions of a wheel body are shown in Fig.1. Surface area except for grinding surface was coated with enamel paint for insulation on electrodeposition. (d) Work materials Work materials are hard metal(K20 and P20), ceramics(AlaOa and SiaN4), and a cermet(TiN). Dimensions of those works are 2.5 10.7 50mm for AlaO, and 3 10 50mm for the other works.

2.1. Materials

2.2. Eperimental apparatus

(a) Abrasive grains Eighteen kinds of synthetic diamond abrasive grains made in TOME1 DIAMOND Co., Ltd. in Japan were tested. The material

(a) A electrodeposition tank The tank is made of acrylic regin and its dimension is 300 400 250mm. A nickel plate for Hull cell test was used as an anode.

0924.0136/96/$15.00 0 1996 Elsevier Science S.A. All rights reserved PI.’ 0924-0136(96)02425-9

304

K. Sato et

al.Nournal of Materials

Processing

Technology

62 (1996)

303-308

Table 1 Properties of diamond abrasive grains

Diamond abrasive grains RH-I RH-2 RH-3 RH-4 RH-5 RE-I RE-2 RE-3 RE-4 RE-5 BY-I BY-I 2 BY-2 BY-3 AT-I AY-I 2 AY-2 AY-3

Metal

contents

: wt.%

Particle ize

9

CO 0.760 0, 760 0, 240 0. I20 0.052 2s 550 0s 720 0, 340 0. 130 0, 042 0. 0037 0. 0085 0. 0320 0, 1200 0.002 0.009 0.056 0, II0

Fe 0, 160 0.070 0. 034 0.019 0.016 0. 240 0, 077 0s 037 0. 023 0, 016 0. 086 0. 200 0. 290 I. 040 0. 096 0. 200 0. 500 1, 030

Ni 0.0340 OS0240 0. 0110 0.0056 0~0040 0s 0830 0.0250 0. 0140 0s 0072 0, 0058 0. 023 0. 045 0. 100 0. 230 O! 021 0, 042 0, I20 0. 230

Mn 0, II0 0.160 0s 098 0. 066 0, 040 0, 290 0, 150 0. 096 0. 058 0, 032 0, 010 0. 013 0. 018 0, 034 0, 012 0, 016 0. 015 0, 032

Sum I. 064 I.014 0s 381 0, 211 0, II2 3, 1830 0. 9720 0. 4870 0, 2182 0, 0956 0, 1227 0. 2665 0, 4400 I, 4240 0. I31 0, 267 0. 691 II 402

140/170 u II /I l4o;lio /I u I/ lro;l70 /I II l4o;lio II II II

Bu Ik density BD II 79 Is 78 I. 81 1, 84 Is 83 1, 75 I. 74 I. 74 II 74 I1 76 I. 96 I. 98 II 99 I. 98 2s 01 2* 03 2, 02 2. 02

Friability F/l 20” 57. 3 60, 9 58. 5 56. 5 57. 8 59, 2 62. I 62. 7 62. 4 61, 7 44. 0 42. 5 31. 8 44, 7 35. 7 36. 8 37. 7 41, 1

er

Y

Platinq

surface

Fig.1. Wheel body Figure 2 shows a apparatus to rotate a cathode. A cathode, namely a wheel body, is held in liquid and is rotated with low speed for uniform sprinckle of abrasive grains and uniform electrodeposition. (b) Grinding test method Grinding tests were carried out at constant thrust pressure and at wet grinding. Tool dynamometer that consists of a octagonal

01 02 03 04 05

Wheel body

I

Motor Reduction Spur

gear box

gear

Brush

Fig.2. Apparatus for rotating cathode ring and strain gauges were used for measurement of normal and tangential grinding force.

305

K. Sato et al./Journal of Materials Processing Technology 62 (1996) 303-308 3. Experimental 3.1. Grinding

procedure

Op=(sum of over plated grain numbers and nodule numbers in restricted area(25 mm’) on a wheel)/(total abrasive grain numbers in the same restricted area(25 mm*)).

test

Peripheral speed of a wheel at tests is 1000 m/min constant and thrust pressure of grinding is 490 kPa(S kgf/cm’) constant. Grinding time, stock removal, tangential and normal grinding force are measured. 3.2. SEA4 obsenlation Electrodeposited surface was observed by SEM to clarify the state of electrodeposited abrasive grains and influence of current density on over plated grain numbers. Ratio of over plated grain numbers to total grains, Op, is defined in following expression.

(a) Grain:RH-3 Cd :6A/dm2 Fig.3. SEM micrographs

50pm

4. Experimental

4.1. SEMobservation (a) Over plating phenomenon Abrasive types RH and RE have rugged shape and BY and AY are blocky. Examples of SEM photographs of electrodeposited abrasive grains are shown in Fig.3. Figure 3(a) shows a example of rugged shape, and (b) blocky type grains. An example of a nodule photograph is shown in Fig.4. A nodule means partial piles of deposited layer. The nodule phenomenon does not occur

(b) Grain : BY-2 Cd: 6A/dm2

5Opm H

of diamond gral .ns

(a)Grain:RH-5 Cd: 2A/dm2

5O,,m ’

Fig.5 SEM micrographs

of overplated diamond grains

1

(b) Grain:RH-3 Cd:2A/dm2

results and discussion

2Opm H

Cd:lOAldmL

e

Fig.4. SEM micrograph

of nodule

(c)Grain:RH-2 Cd :10A/dm2

50pm

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K. Sate et aUJourna1

of Materials

in ordinary electrodeposition, that is in the case of no abrasive grain on electrodepositing surface. As nodules are undesirable for grinding performance, its occurence should be restrained. Photographs of over plated grains are shown in Fig.5. Three types of over plating are observed :(a) is partially covered abrasive grains, (b) is electrodeposited layer grown up from the bottom of a grain, and (c) is perfectly covered grains. The mechanism that over plating phenomenon occurs has not made clear up to the present. But it is likely that the phenomenon may be related to metal catalyst used on synthesis process of diamonds. Namely, network structure of metal impurities is created in a diamond on the synthesis process and the diamond results in having electroconductivity. Therefore, electrodeposition will be done on diamond surface, too. From the explanation above, over plating will be able to be prevented I

,

I

I

I

Processing

2

4.2.

ability

Grinding

6

8

of abrasive grains

10

1

I

Grain:

b

I

10 8-

P

(b) I

I

101

8 -

I

I A: 0: q: V:

Grain: I

RE 1

Grain AY-3 AY-2 AY-12 AY-1

6-

; a.

O4

2

2

(c)

4

6 Cd (A/dm*)

Grain:

I-

Cd(A/dm*)

GrainBY-3 BY-2 BY-12 BY-l

A: 0: 0: V’:

I

10

RH ,

I

Grain RE-1 RE-2 RE-3 RE-4 RE-5

Cd (A/dm*)

(a)

303-308

To estimate grinding ability reasonably, it is necessary to take account of the effect of normal grinding force in addition to

0: A: Cl: +: Y:

4

62 (1996)

by removing the metal network structure from grains or by coating grains with nonconductive oxides. (b) Over plating ratio Relations between over plating ratio Op and current density are shown in Fig.6. Generally speaking, the ratio Op is increased with increase of current density, and is smaller than 2% under 6 A/dm’ in current density. The magnitude of Op depends on types of abrasive grains. The growth rate of diamond grains in synthetic process is different at every grain type and its difference causes the difference in material structure.

Grain 0: RH-1 Lf: RH-2 0: RH-3 l : RH-4 V: RH-5

0

Technology

8

4

10

BY

Fig.6. Relation between current density Cd and ratio of overplated grains Op

(d)

6 Cd ( Aldm*)

Grain:

8

AY

I

K. Sato et al./Journal

tangential one. So, the following

Technology

62 (1996)

303-308

301

I” F,dL

q

Processing

variable is introduced.

L, w,

of Materials

Ft

t

dt

s L,-I

s L,-, Here, L is grinding length, L,-r grinding length at the beginning of grinding, and Lo grinding length at the end of grinding. symbols Fn and F, are normal and tangential grinding force, respectively. Quantity Wcn is cumulated work of Wn until1 n +W,. Wn is named grinding and is expresses in Wdl=W,+W2+ work and W,, the cumulative grinding work. The necessity for good grinding performance is not only that cutting ability is good, but also that grinding force is small. Stock removal is the effective factor to decide the grinding ability of abrasive grains when the grinding work is taken equal. (a) Hard metal The relations between cumulative grinding work and cumulative stock removal are shown in Fig.7 for hard metal K20 and in Fig.8 for hard metal P20. In Fig.7, grinding ability for K20 is put in RH-5, RE-5, RE-3, AY-1, BY-2, AY-2, and BY-l in order of good ability. It is found that grinding ability is correlated to friability of grains. Similar results is derived from Fig.8 for P20. (b) Ceramics The same relations as Fig.7 and Fig.8 are shown in Fig.9 for AlaO, and in Fig.10 for Si,N,. In contrast with hard metal, grinding ability of low friability grains for ceramics are superior to one of high friability grains. lOO(I-

,

I

I

Work: P20 Cd: 6 Aldm2

1

400

300

3 200 0: A 0 A

0

?

1

2

RH-3 : RH-5 : RE-3 : RE-5

q :BY-1 0 :BY-2 H :AY-1 + :AY-2

3 4 Wcn ( kgf.m)

5

6 x105

Fig.7. Relation between cumulative grinding work W, and cumulative stock removal V, for Work K20

12OJP

.,...-0 P

‘lo

Work

:A1203

100 f

aoc ) -

90 I

60C )E E 60 s 50

, -

O:RH-3 a: RH-5 0 : RE-3 A: RE-5

q :BY-1 0 : BY-i n : AY- 1 l : AY-;

0 :RH-3 q l:BY-1 fL:RH-5 O:BV-2 0 : RE-3 n :,AY- 1 A:RE-5 +:AY-2

‘or, 4 6 Wcn(kgf.m)

0

Fig.8. Relation between cumulative grinding work W, and cumulative stock removal V, for Work P20

0

,

,

,

12345 Wcn (kgf.m)

, 6: u105

Fig.9. Relation between cumulative grinding work W, and cumulative stock removal V, for Work AlaO,

308

K. Sam et al.lJmmal

of Materials

Processing

Technology

62 (1996)

Work:

303-308

TIN Cd:

A: RH-5 @: RE-3 A: RE-5.

Wcn(

6Aldm*

0 : BY-2 n : AY-1 : AY-2

kgf.m)

1

20 Wcn

Fig.10. Relation between cumulative grinding work WC” and cumulative stock removal Vc for Work Si3N4 (c) Cermet The relation between cumulative grinding work and cumulative stock removal on a cermet is shown in Fig.11. Difference of grinding ability between grain types is small for cermet in comparison with the ones for hard metal and ceramics. Stock is removed by slip deformation in metal and by brittle fracture in ceramics. So, self-sharpening of abrasive grains in grinding of metal is significant and abrasive grains with high friability are suitable for metal grinding. On the other hand, the abrasive grains that are strong for impact, in other word, lower friability abrasive grains are suitable for the grinding of ceramics. 5. Conclusions The results obtained in the present experiment in followings.

I

10

are summed up

( kgf.m

I

30 ilO 1

Fig.11. Relation between cumulative grinding work W, and cumulative stock removal Vc for Work TiN (1) Over plating ratio is smaller than 2 % under 6 A/dm’ in current density, and do not depend on the kinds of abrasive grains. In current density of 10 A/dm2, over plating of high friability abrasive is abruptly increased. Over plating is not simply proportional to the quantity of metal impurities. It seems to be necessary in estimation on suitability of abrasive grains to electrodeposition to take account of surface properties of diamond abrasive grains besides physical properties. (2) Grinding ability of abrasive grains with high friability was suitable fOT hard metals and a TIN cermet. On the contrary, abrasive grains with low friability were suitable for grinding of ceramics, such as N,Oa and Si,N4.