Optimization of rapid prototyping parameters for production of flexible ABS object

7/30/2019 Optimization of rapid prototyping parameters for production of flexible ABS object

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Journal of Materials Processing Technology 169 (2005) 5461

Optimization of rapid prototyping parametersfor production of flexible ABS object

B.H. Lee, J. Abdullah, Z.A. Khan

School of Mechanical Engineering, Universiti Sains Malaysia Engineering Campus, 14300 Seri Ampangan, Nibong Tebal, Penang, Malaysia

Received 12 March 2004; received in revised form 14 December 2004; accepted 9 February 2005

Abstract

In this study, the Taguchi method, a powerful tool to design optimization for quality, is used to find the optimal process parameters for fuseddeposition modeling (FDM) rapid prototyping machine that was used to produce acrylonitrile butadiene styrene (ABS) compliant prototype.

An orthogonal array, main effect, the signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) are employed to investigate the process

parameters in order to achieve optimum elastic performance of a compliant ABS prototype so as to get maximum throwing distance from the

prototype. Through this study, not only can the optimal process parameters for FDM process be obtained, but also the main process parameters

that affect the performance of the prototype can be found. Experiments were carried out to confirm the effectiveness of this approach. From

the results, it is found that FDM parameters, i.e. layer thickness, raster angle and air gap significantly affect the elastic performance of the

compliant ABS prototype. The optimum levels of parameters at different angle of displacement are also presented.

2005 Elsevier B.V. All rights reserved.

Keywords: Rapid prototyping; Flexibe ABS; Fused deposition modeling; Taguchi method

1. Introduction

Since the introduction of the first commercial rapid proto-

typing (RP) machine widely known as Stereolithography in

1986, a wide range of RP machines have been commercial-

ized, and many more newer systems continue to be developed

in various parts of the world [1]. The future is clear as rapid

prototyping is now becoming a key technology that shortens

product development time for faster building of physical pro-

totypes, tooling and models. Rapid prototyping in general, is

more flexible and can readily accommodate changes in prod-

uct design as compared to conventional method of casting,molding or machining. Studies have been conducted to im-

prove and optimize the process, so as to obtain high quality

parts produced on a wide range of commercial RP machines

[26].

Fused deposition modeling (FDM) is one RP system that

produces prototypes from plastic materials such as ABS by

Corresponding author. Tel.: +60 4 5937788x6365; fax: +60 4 5941025.

E-mail address: [email protected] (Z.A. Khan).

laying tracks of semi-molten plastic filament onto a plat-

form in a layer wise manner from bottom to top. It is known

that process parameters such as the air gap between adjacent

tracks, raster angle, raster width and thickness of deposited

layers influence the performance of parts produced on an

FDM machine. Nevertheless, the suitable levels of parame-

ters associated with different performance criteria still need

further investigation. Some studies have been conducted to

determine the optimum parametersof FDM,and performance

criteria often used include build time, strength, toughness

and surface integrity of the prototypes, normally for injec-

tion molding and tooling applications [4,5,7]. Some work todetermine the feasibility/capability of fabricating fuseddepo-

sition modeling (FDM) parts concurrently from elastomeric

and structural members using FDM 1600 machine has been

done [8]. Optimization method for producing flexible proto-

type using FDM 1650 to achieve optimum performance of

the prototype has also been reported [9]. It is to be noted that

FDM machine has potential for direct use in certain appli-

cations such as actuator in electro-mechanical systems and

construction of plastic toys. In these areas, compliant mem-

0924-0136/$ see front matter 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.jmatprotec.2005.02.259


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B.H. Lee et al. / Journal of Materials Processing Technology 169 (2005) 5461 55

bers that exhibit elastic and flexible behavior are increasingly

being used due to reduce parts counts and therefore, lead to

ease of assembly and lower product costs [10].

It has been reported that compliant member in general,

gains its mobility and performs its functions through elastic

deformation of its structure which is a function of material

properties or geometrical design [10]. Childrens toys suchas sling shot, bow and arrow are examples where compli-

ant or flexible plastic members are widely used. Toys have

long been produced using the conventional methods of cast-

ing and molding. As design becomes more complicated and

product life cycle gets shorter due to market needs, alterna-

tive approaches such as RP, that offers more flexibility and

responsiveness to design changes, are needed.

This paper attempts to describe the optimization of FDM

process parameters for optimum performance of compliant

ABS prototypes in terms of elasticity and flexibility. A model

of a catapult that can be used in sling shot toy is taken as case

example.Elasticity andflexibility areassumed to be related to

itsability to throwa plastic ball a distance.FourFDM parame-ters i.e. air gap, raster angle, raster width and layer thickness,

each with three levels, are investigated in this study. Other

parameters such as humidity and temperature are kept con-

stant. In the following, an overview of the Taguchi method

is given first. This is followed by the description of exper-

iments using the Taguchi method to determine and analyze

the optimal FDM parameters. The optimal FDM process pa-

rameters with regard to the performance criteria, i.e. throw-

ing distance and elasticity, are considered. Results are dis-

cussedand finally thepaper concludeswith thefindings of the

study.

2. The Taguchi approach

The Taguchi method is a well-known technique that pro-

vides a systematic and efficient methodology for design op-

timization. It has been widely used for product design and

process optimization worldwide [1113]. This is due to the

advantages of the design of experiment using Taguchis tech-

nique, whichincludes simplification of experimental planand

feasibility of study of interaction between different parame-

ters. Lesser number of experiments means time and costs are

reduced. This is especially vital for rapid prototyping where

cost to produce prototypes is still high. Taguchi proposes

experimental plan in terms of orthogonal array that gives dif-

ferent combinations of parameters and their levels for each

experiment. According to this technique, the entire parameter

space is studied with minimal number of necessary experi-

ments only [14,15]. Based on the average output value at each

parameter level, main effect analysis is performed. Analysis

of variance (ANOVA) is then used to determine which pro-

cess parameter is statistically significant and the contributionof each process parameter towards the output characteristic.

With the main effect and ANOVA analyses, possible com-

bination of optimum parameters can be predicted. Finally,

a confirmation experiment is conducted to verify the opti-

mal process parameters obtained from the process parameter

design.

3. Optimization of fused deposition modeling

parameters

3.1. Selection of process parameters

TheFDM3000 rapid prototyping machine with Insight 3.1

software wasused in the study. Four parameters, each at three

levels as presented in Table 1 were taken into consideration

in the study. It can be noted that raster angle was specified as

0/90, 45/45 and 30/60 in Table 1. The 0/90 angle

means that FDM machine fabricates the alternate layers of

the catapult on the horizontal plane by changing direction at

0 and 90 angles from the coordinate of the machine. Sim-

ilarly, 45/45 and 30/60 indicate the same deposition

pattern followed by the machine. The interactions between

the parameters were not considered and other factors such

as temperature and humidity were kept constant. To selectan appropriate orthogonal array for the experiments, the total

degrees of freedom need to be determined. The degrees of

freedom are defined as the number of comparisons between

process parameters that need to be made to determine which

level is betterand specifically how much betterit is.For exam-

ple, a three-level process parameter counts for two degrees of

freedom. The total degrees of freedom are obtained by mul-

tiplying the degrees of freedom of each process parameter

to the number of parameters. Therefore, in this study, four

parameters, each with three levels count for eight degrees of

freedom. Basically, the degrees of freedom for the orthogonal

array should be greater than or at least equal to those for the

process parameters. Obviouslythe appropriate orthogonal ar-

ray in this case was the standard L9, with four columns and

Table 1

FDM parameters and their levels

Symbol FDM parameter Unit Level 1 Level 2 Level 3

A Air gap mm Solid fine Sparse Double wide

B Raster angle Degree angles 0/90 45/45 30/60

C Raster width mm 0.305 0.655 0.980

D Layer thickness mm 0.178 0.254 0.305


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56 B.H. Lee et al. / Journal of Materials Processing Technology 169 (2005) 5461

Table 2

Experimental plan using L9 orthogonal array

Experiment number Parameter/level

A B C D

1 1 1 1 1

2 1 2 2 2

3 1 3 3 34 2 1 2 3

5 2 2 3 1

6 2 3 1 2

7 3 1 3 2

8 3 2 1 3

9 3 3 2 1

nine rows. The L9 orthogonal array for this study is shown in

Table 2.

3.2. Testing of compliant ABS product

Theisometric andtop views of theselected catapult designare shown in Fig. 1a and b, respectively. Nine samples were

produced on an FDM3000 machine using ABS (acrylonitrile

butadiene styrene) material according to the parameters and

their levels as indicated in Table 2. For testing, the catapult

was fixed on a specially designed fixture. The isometric and

side views of the experimental setup are illustrated in Fig. 2a

and b, respectively. The fixture was placed on a laboratory

bench. The catapult was bent and held in place using a stop-

per placed at locator holes for 10, 15 and 20 angle of

displacement from the initial position of the catapult. A 5 g

ball was loaded onto the catapult. When the stopper was re-

leased, then the catapult got deflected and threw the ball at adistance as shown in Fig. 2b. Thin powder layer was spread

evenly on the bench so that when the ball was thrown, it left a

Fig. 1. Catapult design: (a) isometric view; (b) top view.

mark upon landing. Three throws were performed using the

catapult produced from parameters settings of experiment

number 1 (Table 2), after bending it to an angle of displace-

ment of 10. The average throwing distance was recorded.

Next, this catapult was replaced by another catapult obtained

from parameters settings of experiment number 2 and aver-

age throwing distance for the same angle of displacementwas recorded. Similarly, the average throwing distances at

the same angle of displacement of 10 was recorded for the

catapults produced from parameters setting of experiment

number 39, respectively. This procedure was repeated for

the other two angles of displacements i.e. 15 and 20, re-

spectively. During testing of thecatapults it was observed that

the catapults did not loose their elastic strength and were also

not plastically deformed. This observation was based on fact

that there was consistency in the throwing distances and the

catapults did not loose their original shape. This is to mimic

the way catapult is normally used as component in toys.

4. Results and discussion

The results were obtained by testing all the nine proto-

types for different angles of displacement i.e.10, 15 and

20. Each prototype represented each experiment of the or-

thogonal array (Table 2). The average throwing distance at

different angles of displacement is summarized in Table 3. In

the latter, the results were analyzed by employing main ef-

fects, ANOVA, and the signal-to-noise ratio (S/N) analyses.

Finally, a confirmation test was carried out to compare the

experimental results with the estimated results.

4.1. Main effects

For performing the main effect, average throwing dis-

tance from the prototypes, which were produced according

to the experimental plan of the orthogonal array (Table 2),

at each angle of displacement was calculated and the results

are shown in Table 3. Figs. 35 depict graphs for the output

characteristic (average throwing distance) of the prototypes

when they were bent at angle of displacement of 10, 15,

and 20 respectively. It can be seen from Fig. 3 that on the

Table 3Average throwing distances at various angles of displacement

Experiment number Throwing distance (cm)

10 15 20

1 96.70 160.13 250.17

2 95.53 165.50 256.00

3 100.07 164.10 253.77

4 98.23 157.20 234.13

5 107.80 185.87 304.80

6 104.63 179.97 275.53

7 99.83 171.20 275.27

8 104.37 169.90 263.37

9 125.33 213.83 325.43


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Fig. 2. Experimental setup for catapult testing: (a) isometric view; (b) side view.

basis of average throwing distance, the best combination of

parameters and their levels for the optimum performance ofcompliant ABS prototype for 10 angle of displacement is

A3B3C2D1. The parameters and their levels, i.e. A3B3C2D1once again appear to be the best combination for 15 angle

of displacement as it is evident from Fig. 4. Finally, it can be

observed from Fig. 5 that the best combination of parameters

and their levels for 20 angle of displacement is A3B3C3D1.

Fig. 3. Main effect chart at 10 angle of displacement.


4.2. Analysis of variance (ANOVA)

The purpose of the analysis of variance (ANOVA) was to

investigate which parameters significantly affected the qual-

ity characteristic. In order to perform ANOVA first, the total

sum of squared deviations, SST was calculated from the fol-

lowing formula [14]:

SST =

n

i=1

y2i C.F. (1)


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where, n is the number of experiments in the orthogonal ar-

ray, yi the throwing distance of i-th experiment and C.F. the

correction factor. C.F. was calculated as [14]:

C.F. = T2

n(2)

where, Tis the total of the throwing distances.

It should be noted that the prototypes resulting from each

experiment was used three times to throw the ball at each

angle of displacement and thus the value ofn (27) was used

in the calculation.

Thetotal sum of squared deviations,SST was decomposed

into two sources: the sum of squared deviations, SSd due to

each process parameterand thesum of squared error, SSe.The

percentage contribution, p by each of the process parameter

in the total sum of squared deviations, SST was a ratio of the

sumof squared deviations, SSd due to each process parameterto the total sum of squared deviations, SST.

Statistically, there is a tool called Ftest to see which pro-

cess parameters have significant effect on the quality char-

acteristic. For performing the F test, the mean of squared

deviations, SSm due to each process parameter needs to be

calculated. The mean of squared deviations, SSm is equal to

the sum of squared deviations, SSd divided by the number

of degrees of freedom associated with the process parame-

ters. Then, the Fvalue for each process parameter is simply

the ratio of the mean of squared deviations, SSm to the mean

of squared error, SSe. Usually, when F> 4, it means that the

change of the process parameter has significant effect on the

quality characteristic.

Tables 46 show the results of ANOVA for 10, 15 and

20 angles of displacement respectively. The F-ratios were

obtained for 99% level of confidence [14]. In addition to this,

percent contribution of each parameter was also calculated. It

can be seen from Table 4 that for 10 angle of displacement,

within the range investigated as shown in Table 1, all the four

parameters i.e. air gap, raster angle, raster width and layer

thickness were significant in terms of affecting the flexible

performance resulting in maximum throwing distance. How-

ever, the contribution order of the parameters for maximum

throwing distance was air gap, raster angle, layer thickness,

and then raster width. Therefore, based on main effect and

ANOVA analyses, the optimal parameters for achieving max-

imum throwing distance from the prototype were the air gap

at level 3, the raster angle at level 3, the raster width at level

2, and the layer thickness at level 1.

Similarly, it can be observed from Table 5 that for 15 an-

gle of displacement, all the four parameters had a significanteffect on the throwing distance. However, the contribution

order of the parameters for the desired output was raster an-

gle, layer thickness, air gap, and then raster width. Based on

the main effect and ANOVA analyses, the optimal parameters

were air gap at level 3, raster angle at level 3, raster width at

level 2, and layer thickness at level 1.

Finally, Table 6 reveals that for 20 angle of displacement

all the four parameters once again had a significant affect on

the desired output. The contribution order for the parame-

ters was layer thickness, air gap, raster angle, and then raster

width. Based on the main effect and the ANOVA analyses,

the optimal parameters were air gap at level 3, raster angle

at level 3, raster width at level 3, and then layer thickness atlevel 1.

4.3. Signal-to-noise ratio (S/N)

The signal-to-noise ratio measures the sensitivity of the

quality investigated to those uncontrollable factors (error)

in the experiment. The higher value of S/N ratio is desir-

able because greater S/N ratio will result in smaller product

variance around the target value. The quality characteristic

used in this study was the-bigger-the-better, i.e. the farther

the throwing distance, the better the catapult performance.

In order to perform S/N ratio analysis, mean square devia-tion (MSD) for the-bigger-the-better quality characteristic

and S/N ratio were calculated from the following equations

[14]:

MSD =1

n

n

i=1

1

y2i(3)

S/N = 10log10(MSD) (4)

where yi is the throwing distance for ith experiment.

The S/N ratio obtained for each angle of displacement is

presented in Tables 79, respectively. It can be seen from

these tables that for each angle of displacement, the com-bination of the parameters and their levels, A3B3C2 D1 has

consistently resulted in the maximum value of S/N ratio. This

shows that in the present case study the parameters and their

levels, A3B3C2 D1 yield optimum quality characteristic with

minimum variance around the target value for each angle of

displacement.

4.4. Confirmation test

Once the optimal combination and levels of the process

parameter at each angle of displacement had been obtained,


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Table 4

ANOVA for 10 angle of displacement

Symbol FDM parameter Degrees of freedom Sum of squares Mean square F Contribution (%)

A Air gap 2 693.21 346.61 216.63 34.52

B Raster angle 2 636.60 318.30 198.94 31.70

C Raster width 2 104.51 52.26 32.66 5.20

D Layer thickness 2 545.06 272.53 170.33 27.14

All other/error 18 28.79 1.60 1.44

Total 26 2008.17 100

Table 5



A Air gap 2 2125.85 1062.93 134.38 28.58

B Raster angle 2 2408.41 1204.21 152.24 32.38

C Raster width 2 354.95 177.48 22.44 4.77


All other/error 18 142.31 7.91 1.91

Total 26 7439.01 100

Table 6



A Air gap 2 5425.93 2712.97 227.22 27.45

B Raster angle 2 4721.39 2360.70 197.71 23.88

C Raster width 2 1013.32 506.66 42.43 5.13


All other/error 18 214.94 11.94 1.09

Total 26 19,767.68 100

the final step was to verify the estimated result against ex-

perimental value. Estimated throwing distance at optimum

condition for each angle of displacement was calculated by

adding the average performance to the contribution of each

parameter at the optimum level using the following equations

[15]:

yopt = m + (mAopt m) + (mBopt m) + (mCopt m)

+ (mDopt m) (5)

m =T

n(6)

where m is the average performance, Tthe grand total of aver-

age throwing distance for each experiment, n thetotal number

of experiments and mAopt the average throwing distance for

parameter A at its optimum level, mBopt the average throwing

distance for parameter B at its optimum level, mCopt the aver-

age throwing distance for parameter C at its optimum level,

and mDopt the average throwing distance for parameter D at

its optimum level.

It was found that for 10 and 15 angle of displacement,

the optimum parameters and their levels (A3B3C2D1) cor-

responded to experiment number 9 of the orthogonal array.

And furthermore, it can be seen from Table 10 that for 10

and 15 angles of displacement the experimental value of

the throwing distance for A3B3C2D1 is same as that of esti-

mated value and thus there was no need for any confirmation

test. However, confirmation test was required for 20 angle of

displacement only because the optimum parameters and their

levels (A3B3C3D1) did not correspond to any experiment of

the orthogonal array.

The prototype at optimal levels of the factors i.e. A3, B3,

C3 and D1 was produced on the FDM machine. The proto-

type was bent at 20 angle of displacement so as to throw

the ball. This was repeated three times and for each time,

throwing distance was measured. Subsequently, the average

throwing distance was calculated. The experimental throwing

distance was compared with the estimated throwing distance

Table 7

S/N values at 10 angle of displacement

Experiment number Average distance,

yave (cm)

MSD (105) S/N

1 96.70 10.69 39.71

2 95.53 10.96 39.60

3 100.07 9.99 40.00

4 98.23 10.37 39.84

5 107.80 8.60 40.65

6 104.63 9.13 40.39

7 99.83 10.03 39.98

8 104.37 9.18 40.37

9 125.33 6.30 41.96


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Table 8


Experiment number Average distance, yave (cm) MSD (105) S/N

1 160.13 3.90 44.09

2 165.50 3.65 44.37

3 164.10 3.71 44.30

4 157.20 4.04 43.93

5 185.87 2.89 45.386 179.97 3.09 45.10

7 171.20 3.41 44.67

8 169.90 3.48 44.60

9 213.83 2.19 46.60

Table 9


Experiment number Average distance, yave (cm) MSD (105) S/N

1 250.17 1.60 47.96

2 256.00 1.52 48.16

3 253.77 1.55 48.09

4 234.13 1.82 47.39

5 304.80 1.08 49.686 275.53 1.31 48.80

7 275.27 1.32 48.79

8 263.37 1.44 48.41

9 325.43 9.45 50.25

Table 10

Estimated result against experimental value

Angle of displacement Estimated result (mm) Experimental value for

experiment number 9

(mm)

10 125.32 125.33

15 213.83 213.83

20

331.53 Does not correspond toany experiment in the

orthogonal array

Table 11

Results of confirmation experiment

Optimal condition Difference

Estimation Experiment

Level A3, B3, C3, D1 A3, B3, C3, D1

Distance achieved (cm) 331.53 330.93 0.6

S/N value 50.39

as presented in Table 11. Itcan be seenfrom Table 11 that thedifference between experimental result and the estimated re-

sult is only 0.6 cm. This indicates that the experimental value

is very close to the estimated value. This verifies that the

experimental result is strongly correlated with the estimated

result, as the error is only 0.18%.

5. Conclusions

On the basis of the results obtained the following can be

concluded:

The optimal parameters and their levels for 10 , 15 and

20 angle of displacement are A3B3C2D1, A3B3C2D1 and

A3B3C3D1, respectively.

For 10 angle of displacement, air gap produces maxi-

mum contribution to the output performance of the product

(throwing distance).

For15

angle of displacement, raster angle and layer thick-ness demonstrate almost equal maximum contribution to

the output performance of the product (throwing distance).

For 20 angle of displacement, layer thickness gives the

highest contribution to the output performance.

The parameters and their levels, i.e. A3B3C2D1 yield the

optimum quality characteristic with minimum variance for

all angles of displacements considered in the study.

Acknowledgements

Logistic support from the School of Mechanical Engineer-

ing, Universiti Sains Malaysia is acknowledged. The mate-

rial for FDM experiment is also financially supported partly

by USM short-term grant #6035064. Technical support from

the rapid prototyping laboratory personnel, Mr. Mohd. Najib

Hussain is greatly acknowledged.

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Optimization of rapid prototyping parameters for production of flexible ABS object

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