Sintering parameter optimisation of the SS316L Metal Injection Molding (MIM) compacts for final density using taguchi method

SINTERING PARAMETER OPTIMISATION OF THE SS316L

METAL INJECTION MOLDING (MIM) COMPACTS FOR FINAL

DENSITY USING TAGUCHI METHOD

K. R. Jamaludin1,2,

N. Muhamad

2,

M. N. Ab.

Rahman", S. Y. M. Amin", S. Ahmad

2,3,

M.H.I. Ibrahim

2,3

1.

College of Science and Technology

University of Technology Malaysia

Int. Campus Kuala Lumpur

54100 Kuala Lumpur. Malaysia

2. Precision Process Research Group

Dept. of Mechanical and Materials Engineering

Faculty of Engineering

National University of Malaysia

43600 Bangi.

Selangor Darul Ehsan. Malaysia

3. Faculty of Mechanical

&

Manufacturing Eng

.

University Tun Hussein Onn

,

86400 Batu Pahat, Johor,

Malaysia

ABSTRACT

Sintering parameters of the SS316L water atomised injection moulded compact has been optimized for its best sintered density. The L9 (3

4 ) Taguchi orthogonal array is used in the experiment while sintering temperature, sintering time, heating rate and coofing rate was selected as factors that influenced the sintered density. The sintering environment was in the vacuum and four replications were done for each trial. The analysis of variance shows that the confidentlevel for the experiment was

99.5 % (a

=0.005)and all factors are highly significant at

a

=

0

.005

to the sintered density. The study concluded that the heating rate has the highest influence to the sintered density

(41.29

%) followed by sintering temperature

(31

.60

%), sintering time

(11

.13

%

)

and cooling rate (11.10%). The optimum sintered density obtained is 98.48 % of the theoretical density and the optimum parameter has been verified that the sintered density obtained is in

a

range of confident interval.

Key words: Sintering; Stainless steel; Taguchi method; Metal injection moulding; Powder injection moulding

I. INTRODUCTION

Metal injection moulding(MIM)is a relativ ely new processing techn ology used in powd er metallurgy processing industr ies. This proces s is espe cially c ost-effec tive and benefic ial for manufacturing small and complex compo ne nts in large quant ities. Metal injection moulding is used in an increasin g range of different field s, includ ing auto motive, med ical and tel ecommunications industri es. It includes four basic steps consisting of mixin g the powders and binders, injection mould ing, debind ing and finally sintering . Both injecti on mould ing and sintering are the most important steps related to forming the green part and thefinalpart respect ively.

(DOE) methodology. The tradi tio nal expe rimenta l approach that vary one variable at a time. holding all other variables as fixed does 1101produce satisfactory

resu

l

ts

ina widerangeof

experi

m

enta

l

settings.Thusit requires a 101 of experiments attempt before the optimised

smtcrtng

para meter is obtained without havinganystatisticalconfidence level.

DOE for the injection parameter has been studied by Khairu r Rijal Jamaludm eral. (~008a, 2oo8b) and Jamaludin ct

at

.

(2008) resulting a signi ficantoptimum inject ion parameier for MIM feedstock. As a conseq ue nce to the inject ion parameter optimised by those litera tures, this parer presents a sintering paramet er optimis ation which utilises the optimised injection parameter. In addition , study by Ji et

al

(200 1) has shown the significance of sintering variab les suc h as heating rate, dwell lime , sintering temperature and sintenng atmosphere.Jiet al. l200i) foundthai the vacuumenvironment isbestforstntering SS316L and thus. this study attempts to continue the study by using a high vacuu m environme nt in the

expcnmem

.

Despite

cooling

ra

r

e

is replacing the sintering env ironment in the orthogona l array. heating rate, dwell time and sintenng temperature remains as

sin

r

ering

var iabl es for

t

he

opn r nisano n. These variables can influen ce the microstructure. pore size and shape and finaldensityof the sintered pans .

2.

EX

PERIM

ENTAL

MPIF 50 standardtensile baris used asa specimen. Awateratomiscd 316Lstainless steelpowder withO~o of 7.157 urn. pycnometer density of 7.90 g/emJ is mixed with 73 % PEG weightofpolyethylene glycol (PEG) and 15 % weight of

polyme

thy

l

methacrylate (PMMA). About 1 % weig ht ofstearic acid (SA) is usedasasurfac tan t.

Priorto the moulding.compositio nsare mixed ina sigma blade mixer for95 minut es at a temperature of 70°C. Bartcnfeld. BA 250 CDC injection mouldi ng machine was used to prepare the greens while high vacuum furnace Korea VAC-TEC. VTC 500HTS F

with vacuum pressure up to 9.5 " 10 .(,mbar was used forsintering.

3.

DESIGNOF

E

XPERI

M

ENT

There arc many simcring parameters that have someeffect on the prop ert ies of the sintered density. Therefore. a design ofexper ime nt (DO E) methods is TII.'C'r~ry for the experimental work invo lvi ng many inputs. Themostfrequentl yused methods are partialor fullfactorialdesignand the Taguch iapproach.With an appropriate DOE. one can quickl y and with fewer amounts of tria ls, found whether the va riables have an effecton the output quality. The Taguchi approach is mostly used in the industrial environment. but it can also be used for scientific rese arch. The method is

based on balan ced orthogona l arrays (Park 1996). In

Ihis paper.

4

(3~) orthogo nal array co nsis ting of 9

expe rim ent trials and 4 column is used as DOE followedby A!'JOVA todetermine the significant level and contribution of each variab les to Ihe

sin

rcrcd

density. The main variables involved in this study are as sho w n in Table I. Three levels for each variable refer to the maximum and minimum limit that infl uences

s

in

tcrcd

density.

Table

1

:

Factor

level

(variab les) intheexpe riment

Facto r Leve l

0 1 2

Smlc ring

A Temperet u ])40 J)(\() ₁₃₈₀

re (0C)

B dwell lime

so

120

(minute) ::!~O

Healing C

""

,

8 10

(OOmm) Cooling

0 raft

,

8 10

(oOmln)

4. RESULTS& DISC USSiON

The density of the smtcrcd pan was measu red by Archimedes immersion method accord ing 10 the MPIF 41. Four replications were reco rded for eac h experiment as shown in Table 2. The theoretica l den sit y sho wn in Tab le

2

is calculated from the average of the rep lication , As shown in Tab le 1, a combin atio n of AI B~ Co D. results a maximum sintered density (98.48 % of the theoret ical density) while, a

com

bin

ation

of A2

80

C2

0

1 prod uce a minimum sintered density (93.53 % of theoretical density). Although the sintering temperature is only 1360°C. slow heating rate (6 °C/minutes) and longer dwell time(140 minutes) enables tile compactto obtain a maximum sintered density. Neverthele ss, with high

simcnng temperature(IHO°C)and quick heating rate

atshorter dwelltime willminimise the sintereddens ity.

followed by heating rate (7.3 77 %), sintering temperature(5.538% ) and dwell time (5, [68 %),Thus. based on his study, a high vacuum sintering environ ment has been conside red. Beside that. the influence of coo ling rate to the sintered density is investigatedas this variable hasnot beenstud ied by Ji et al. (2001) in his DOE.This is by the fact that the coo ling rate is another sintering variable (Kang2005). Althoug h cooling rate is oneofthesinteringvariab les.

it has been demonstrating a lowest contribution percentage. Despit e the contribution is low , the high significan t level, nas shown byTable3 is still indicate the importanceof this variable.This is as import ant as dwell time wh ich.has been reported less influe ntial by Jietal. (200[) tothesinrereddensity.

Table 2:Orthogonal arrayandsinrered density

Replication (density(gfcmJ) )

Trial A B C D 2 )

,

f

%Theoretical

dcnsuv

I 0 0 0 0 7.5078 7.4329 7.4704 7.4704 7.4704 94.56

2 0 I I I 7.57lW 7.500R 7.5394 7.5394 7.5394 95.44

"

.~ 43 0I 02 2I 22 7₇._.58463972 ₇7.3929_{.5058 7}7_{.54 52},39 50 ₇7._.54523950 77.395,54520 _95.593.61₁

E _{S I I 2 0 7.5279 7.45L5 7.4897 7.4897 7.4R97 94.81}

~

"

6 I 2 0 I 7.73?7 7.82 18 7.?H03 7.7803 7.7803 98.48

e,

<

7 2 0 2 7.3880 7.3894 7.3890 7.3890 7.3890 93.53

~ I

8 2 I 0 2 7.5452 7.5410 7.543l 7.543 1 7.543 1 95.48

9 2 2 J 0 7.4760 7.5262 7.5011 7.50 1 l 7.50II 94.95

Average 7.5170 95. 15

Max 7.7803 98.48

Min 7.3890 93.53

Tab le3:Al':OVA for the sintered part at a=0.005

Sum Varianc

Degreeof Variance. Pure Sum Contribution

Variable squared. eratio. CruicalFvalue

freedom,fn

"

.

squared.S/ . P,

S

.

F

,

"

2 0.140 0.070045 0.139 114.39 _{Fooo~,~,~7-,0 .4 8 8 5} 31.60

B _{2 0.050 0,025065 0.04 9 40.94}

Fo oos. ~.27=(;.4885 11.13

C _{2 0.IX3} 0.0913 [7 0. 181 149.13 _F"oo~.

2.27=6.4885 41..29

D _{2 0.050 00.25001} 0,049 40.10 _{FO OO~.l.}

l7'6.4885 I1.10

error _{27 0.OJ7 0.000612 4,88}

Totlll _{35 0.439 100}

Based on the A""OV A, the main effect of the experiments is calculated based on the highest average valuesas shown inFigu re I. As shown by the response plotinFigure l, a combination of AI.B2, Co,and D1 is

the highest yield. i.e.• sintering temperature J360 DC. dwell time 240 minutes,heatin grate 6 "Czrmnures and cooling rate 8 "Ominutes. On the other hand , faster heating rate (20 "Czmin ures) forsirucring temperat ure at 1250 DC and dwell time of 90 minutes has been reported as the optimumsinter ingparameterbyJi et

at.

(200I).

The AKOVA shown in Table 3 signify that the effects of the variab les are all significan t at 99.5 %

significance level. lienee the expected result at

optimum performan ce is as sho wn in Table 4. The expected optimum performance is as highas 98.48 %

of theoretica ldensity while the range of the optimum performance basedon 90%confidence level is 98.22 <

~l < 91U 5 % of the theoretical density. The optimum

parameter has been pro ven in the confirmation

experimentthat is conduc ted atthecombinedsettingof

Ai. B:, . Co. and D, and the result fell within the predicted90%confidenceintervalas shownin Table4. A densityat op timum perform ance reportedby Jier at

(200I) is 7.592

g/c

rn",

which is lower than that

achievedby this study asshowninTable4.

~;

"'

•

i\

~\ ~

1

_"'

s

,

,,

i

_,

'"

9';

,

_,

_,

~B

Figure I:Responseplot of fractionaldensity agai nstsinterin g variables

Ta b le4:Optimumsintenng parameter.optimu m perfor ma nceand confir mationexperim e nt.

Optimumparameter:

A1B2CO DI

(SinreringTemperature. 1360"C;dwelltime.240 minute;Heatingrate.6"Czmmurc:Coolingrare.x"C/minute)

Optimum performance:7.780] grcrnJor98.48%theoreticaldensity

Confidentinterval:±0,02at 90%confidentlevel(0 "0.1 )

Range ofopnmurnpcrformancc:7.7592gzcnr <I.l<nW l3gzcrn'or 98,22%theoreticaldensity <!1<n .75% theoreticaldensity

Confirmation experiment

Repeat 2 J 4 Average

,

gc m _{7.8]77 7,8365 7.7296 7.7296 7.7834}

%theoretical

density 9921 99.20 97.84 97.84 98,52

5. CONCLUSIONS

Sintered density of the water ato mis ed SS3 16L MJM parts was optim ised byusingtheTaguchi method.

An L~ ort hogo nal arra y was used to vary the

experimentvar iabl es. ANO VAsho wedthatall the four

sinrering vari ables: sinteri ng temperature, dwell time, healing ra te and cooling rate, affected the sintere d

dens itysign ifica ntly.The optim umsinter ing para meter

were found to be Aj, B~, Co,and D[,correspo nding to

si

nrering

te mperature of 1360

"

c.

dwe ll time of 240

minute,hea ting rateof6"Czminutc andcooling rate of

8

"Czrmnu

tc.

Confirmation experiments indicat ed that when sintering SS 3 16 L at the optim um condition, a

high98.52%of theo re ticalde nsit y call beac hie ved .

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Fu,G.,Loll , N.II., To r, S.B.,Tay, B.Y ., Murakosm, Y. and Maeda. R., Inj ectio n mold ing, debinding and

s

mtenng

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1::1.

,

K

a

m

p

u

s

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Tct

motogiic

.

Vol.40,No,5,pp. 193-198,2006.

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powde r during siutering, Materials Science and Engineering,Vol A390,pp.171-177,2005.

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J

16L

sta inless steel, Po wderMet,1I1mgy ,Vol:46. No. 3, pp. 241-245,2003.

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Khairur Rij a lJamatudin.Norhamid i Muham ad, Mohd Nizam Ab. Ra hman. Sri Yulis M.

Arnin

and Murtadhahadi. Molding paramet er optimization for red uc ing a gree n defec ts for MetalInje ctio n Moulding greenpart. (in Malay) The Joumalof The Institution of

Enp ;u;,ers. Mal,1y s ia.Vol.69, t\o . 2,pp40-46,2008a.

Khair ur Rij alJamaludin. No rhamidi Muhamad, Moh d

Nizam Ab. Rahm an, Sri Yulis M. Am in and 'vlurtad hahadi, Analys is of Varian ce on the Metal Inj ec tion mold ing param eters using a bimodal particl e size distribution feedstock.

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ro

cec

di

og

o

ttnter nsnoost

C

o

nter

c

nce

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2008.

Jamatudin, K.R.. Muhamad. N., Amin. S,Y.M., Ab. Rahm an . M.N ., Is ma il, M.H. and Murtadhahadi, I., Injec tio n Molding Pa ramet er Optim izatio n Using

Tag uch i Met hod For Highest Green Strength For Bimodal Po wd er Mixture with SS316 L in PEG. and PMMA,AdvancesIii Po wderMetallurgy & Parncutstc

Materiel s.Yo U ,pp. 186-19 4,20Ofs.

Ji,C.H.,Lob,N.II.,Khor, K.A. and Tor, S.B,Sintenng

study of 316L Slainless steel Metal Inj ectio n Moldin g

pan s usi ng Taguch i meth od : final density,

M

stcriats

Park, S.H, Robust design and analysis for quality

engineering,

U

K

:

Chepmon

&

11

.111

,

1996,

Kang, SJ.L, Sintering densification,grain growth and microstructu re, UK:ElsevierButterw orth- Heinemann. 2005.

P

ROFILE

EngrK.R.Jamaludin

Dept of Mechanical Eng.•

Collegeof Science&

Technology,

UniversiriTeknologiMa lays ia,

T

n

t

Campus,

54\00KualaLumpur

Researc h area.Powder

Metallur

Assoc.Prof.Dr.N.Muhamad

Dept ofMechanical& Materials.

Faculty of Eng.& Architecture. NationalUniversityofMalaysia,

43600Bang i, Selangor

Research area:Powder

r...=

"--

-;

r-_

-:N"

I

-"

eta'CJ;,J",,,g.~,,-==

---1

Dr. M.N.Ab. Rahman

Dept ofMechanical& Materials,

Faculty of Eng.& Architecture,

National Univers ity of Malaysia,

43600Ban gi,Selangor

Researcharea:Total Quality