research article optimized injection molding of unfilled and … · 2019. 7. 31. · research...

Research ArticleOptimized Injection Molding of Unfilled andGlass Filled PA6 Gears

Nik Mizamzul Mehat12 Shahrul Kamaruddin2 and Abdul Rahim Othman2

1 Department of Mould Technology Kolej Kemahiran Tinggi MARA Balik Pulau Genting 11000 Balik Pulau Penang Malaysia2 School of Mechanical Engineering Universiti Sains Malaysia Engineering Campus 14300 Nibong Tebal Penang Malaysia

Correspondence should be addressed to Nik Mizamzul Mehat nik miza78yahoocom

Received 6 June 2013 Accepted 5 November 2013 Published 10 February 2014

Academic Editors G T S Ho and T R Kurfess

Copyright copy 2014 Nik Mizamzul Mehat et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Shrinkage behavior is a crucial problem in manufacturing plastic molded gear This is because it negatively affects the dimensionalstability and accuracy of the involute profile as well as the concentricity roundness tooth spacing uniformity and size of the gear Byintegrating the Taguchi robust design Grey relational analysis and principal component analysis we investigated the dimensionalstability related to the shrinkage of tooth thickness addendum circle and dedendum circle of molded gear via the optimization ofprocessing parameters and glass fiber reinforcementThe results revealed that the optimal combination of the processing parametersof the molded gear to achieve minimum shrinkage is melt temperature of 260∘C packing pressure of 60 packing time of 5 s andcooling time of 30 s The melt temperature showed the highest comparability sequence among the four key process parametersexamined followed by packing pressure cooling time and packing time Meanwhile the presence of glass fibers induced higherdeviations of tooth thickness addendum circle and dedendum circle than those of the unfilled polyamide 6 gears

1 Introduction

The evolution of plastic gears in power and motion transmis-sion application is manifested in diverse applications in con-sumer electronic items including copiers printers scannersandwashingmachinesManufacturers of automotive compo-nents such aswindshieldwipers andpower car seats andwin-dows have also used plastic gearing to produce lightweightand cost-effective drive-train designs Compared with metal-lic gears that suffer from chemical corrosion and lubrication-related failures as well as high operation and maintenancecosts plastic gears are lighter generate less noise have lowfriction and are more economical to produce in large quanti-ties with complex shapes using the injectionmolding processIn addition the molded plastic gears do not require lubricantand additional finishing operation before being mounted inthe transmission system

Although plastic gears are popular they have certaindrawbacks Plastic gears can fail by divergent mechanismsFor example Senthilvelan and Gnanamoorthy [1] observeddifferent types of failures on the Nylon 66 spur gears includ-ing gear tooth wear cracking at the tooth surface tooth root

cracking and severe shape deformation Mao [2] studiedacetal gear failure related to fatigue Li et al [3] investigatedthe wear behavior of dissimilar plastic gears and found thathigher contact force during the operation causes the drivengear tip and the driverrsquos root to wear fast Focusing on thesame plastic gear failure mode Mao et al [4 5] in their workreported that the wear rate in acetal gear increased dramati-callywhen the load reaches a critical value for a specific geom-etry and running speed The gear surface showed a slowlywear by means of a low specific wear rate if the gear is loadedbelow the critical value

Numerous studies have been conducted to improve theplastic gear limitations by material reinforcement For exam-ple in a series of studies by Kurokawa et al [6ndash8] the effect ofthe presence of carbon fibers (CFs) as reinforcement on theperformance of the plastic gear has been investigated theirresults showed that the wear properties of the composite gearfilled with CFs differed significantly depending on the com-position of CFs at various load capability levels In the workof Senthilvelan andGnanamoorthy [9] by incorporating 20short glass and 20 carbon fiber to the Nylon 66 gear thedamping capacity of the composite gear has been decreased

Hindawi Publishing CorporationInternational Journal of Manufacturing EngineeringVolume 2014 Article ID 719462 8 pageshttpdxdoiorg1011552014719462

2 International Journal of Manufacturing Engineering

thereby influencing the noise and heat generation during ser-vice Hirogaki et al [10] used cotton fiber plain woven filledphenolics resin laminate as the gear material to study thetooth root stress resulting from bending movement underrunning conditions the results revealed that the strength ofa tooth with a filled fiber angle of 45∘ is at the lowest whenthe load is applied to the tooth tip In addition Mendi et al[11] found that reinforcing the polypropylene gear tooth withmetallic wires subsequently generating a residual compres-sion stress in the structure of the gear tooth increases thenumber of cycles of fatigue failure and enhances fatiguestrength

Despite the quality of these studies the issue related to thedimensional stability in plastic gear during the early stageof gear manufacturing has not been thoroughly describedelsewhere An investigation of the literature related to plasticgears study showed that so much attention is given on plasticgear reinforcement in order to overcome the limitations ofplastic gears usage The dimensional stability of a plastic gearis indispensable to the perfect functioning of the gear when itis running which should not be underrated of its impact onthe final quality of plastic gears produced During the injec-tion molding process the dimensions of the molded plasticgear change as the parts cool due to shrinkage The irrevers-ible changes in dimensions especially in the involute profileof the plastic gear as a result of uncontrolled shrinkage dueto complexity and inappropriate process parameters settingnegatively influence concentricity roundness tooth spacinguniformity and the size of the gear produced Consequentlythe quality of the end molded gear noise and vibration aswell as the service life of the gear are affected by damagemechanisms such as tooth fatigue creep excessive wear andplastic deformation In fact the optimum properties of theplastic material with the most innovative gear and molddesign cannot be attained making them irrelevant withoutoptimal processing parameters during gear manufacturing

Thus the main objective of the current study is to explorethe effects of optimized injection molding processing param-eters on the dimensional stability related to shrinkage behav-ior in the involute profile of a molded plastic gear A system-atic study on the optimization of processing parameters isconducted via a hybrid integration of the Taguchi parameterdesign statistical Grey relational analysis (GRA) and prin-cipal component analysis (PCA) by selecting three qualitycharacteristics namely tooth thickness and the addendumand dedendum circles A side-by-side comparison betweenthe unfilled and glass fiber-filled polyamide 6 (PA6) gearswas also carried out with regard to the dimensional stabilityrelated to shrinkage in the involute profile after the optimiza-tion process

2 Experimental Procedure

21 Materials The unfilled PA6 under the grade name ofZISAMIDE TP4210 (Zig Sheng Industrial Co) as well as 15and 30 glass fiber-filled PA6 denoted as Vitamide BR13and Vitamide BY16 respectively (Perrite) were specified inthis study for the gear materials The study used the spur

R1650

R1350

10

empty10

empty12

Figure 1 Geometry and specifications of spur gear with module =15 pressure angle = 20∘ number of teeth = 20 face width = 10mm

gear design in compliance with the American Gear Manu-facturers Association (AGMA) standards The geometry andspecifications of the gear are shown in Figure 1 The finalmold design is prepared after the gear part design has beenspecified and all requirements affecting the design of themold including number of cavities type of mold types ofejection and types of venting as well as injection moldingmachine consideration have been clarified In this case thepreliminary filling analysis has been previously conductedon the gear model before optimizing the gating system forthe gear part The diaphragm gating system is selected to beincorporated with two plate mold single gear cavity basedon the uniformity of the transient progression of the polymerflow front in the cavity as shown in the analysis

22 Gear Preparation and Fabrication The PA6 gears wereinjected using a Battenfeld TM750210 injection moldingmachine The experiment was conducted with four con-trollable three-level processing parameters namely melttemperature packing pressure packing time and coolingtime Other processing parameters such as mold tempera-ture (60∘C) injection pressure (60 bar) and stroke distance(60mm) were kept constant during the experiment In addi-tion the Taguchi method based on orthogonal arrays (OA)was used to design the experiments As discussed by Mehatand Kamaruddin [12] Taguchirsquos OA are highly fractional or-thogonal designs that can be employed to study an entireparameter space with a small number of experiments Table 1lists the design of the experiment based on the L

9(34) OA in

producing nine trials of unfilled PA6 gears with five repeti-tions

23 Shrinkage Measurement All nine trials of the unfilledPA6 gears with five repetitions of each trial were left for48 hours at room temperature before the measurement ofshrinkage (ASTMD955-89) ARaxVisionDC3000Mitutoyoprofile projector was used to inspect the accuracy of thespecific profile of the involute gear teeth following the mold-ing process The projector was used in measuring the two-dimensional (2D) addendum circle dedendum circle andtooth thickness using the coordinates of selected points alongthe gear profile The gear used in this study was designed

International Journal of Manufacturing Engineering 3

Table 1 Orthogonal array L9 (34) of the experimental runs

Trial no Processing parametersMelt temperature (∘C) Packing pressure () Packing time (s) Cooling time (s)

1 260 60 5 302 260 80 10 403 260 100 15 504 280 60 10 505 280 80 15 306 280 100 5 407 300 60 15 408 300 80 5 509 210 100 10 30

Addendum circle (20 points)

Dedendum circle (20 points)

Figure 2 Two-dimensional (2D) addendum and dedendum circlesmeasurement

with 20 teeth and therefore in the process of addendum anddedendum circle measurement 20 edge points of each toothgear were set in the profile projector (Figure 2) Five injec-tion molded gears from the same batch were measured todetermine the repeatability of the part geometry The relativechanges in dimensions due to the shrinkage of the selectedquality characteristics were calculated based on the followingequation

119878 =119863119898minus 119863

119863119898

times 100 (1)

In this equation 119878 represents the relative changes in dimen-sions due to shrinkage 119863 is the reading of a correspondingdimension measurement using a profile projector and 119863

119898is

the mold cavity dimension

3 Implementation of Hybrid Optimization

After obtaining all the shrinkage data of themolded gears thesequential steps described below were adopted to determinethe optimal combination of the injection molding pro-cess parameters based on the proposed TaguchiGRAPCAhybrid method

Step 1 Signal-to-Noise (119878119873) Analysis For constant process-ing parameters we calculated the average value of five

repeated results for relative changes in dimensions due toshrinkage in tooth thickness as well as in the addendum anddedendumcircles for the final result Subsequently the resultsof relative changes in dimensions in tooth thickness adden-dum circle and dedendum circle were transformed into the119878119873 ratio The 119878119873 ratio is a measure of performance of thedevelopment of products or processes that are insensitiveto noise factors in a controlled manner The noise factorsrefer to uncontrollable factors such as humidity and weatherwhose influence on the product or process is unknownand inevitable Depending on the objective three differentmethods of calculating the 119878119873 ratio in the Taguchi methodare commonly used namely smaller-the-better bigger-the-better and nominal-the-better quality characteristics Theconversion of the results into the 119878119873 ratio involves a seriesof calculations of the mean squared deviation (MSD)

For this study the smaller-the-better category was used tocharacterize the relative changes in the dimensions of tooththickness addendum circle and dedendum circle given asfollows

119878

119873= minus10Log( 1

119873

119899

sum

119894=1

1199102

119894119895

) (2)

where 119910119894119895is the value of the quality characteristics for the 119894th

trials and119873 is the number of repetitions The final measuredresults and the 119878119873 ratios for the three quality characteristics(ie tooth thickness addendum circle and dedendum circle)are shown in Table 2

Step 2 Grey Generation of Raw Data The 119878119873 ratios werenormalized by adopting the GRA a method to measure thecorrelation degree between factors based on their similar-ities or differences GRA is characterized by less data andmultifactor analysis For the current study the normalizationof the 119878119873 ratios involved the transfer of the originalsequence to a comparable sequence Thus the smaller-the-better characteristics of the data sequence were selected toinvestigate the shrinkage behavior in molded gear and werecalculated as follows

119909lowast

119894

(119896) =max119909(119874)

119894

(119896) minus 119909(119874)

119894

(119896)

max 119909(119874)119894

(119896) minusmin119909(119874)119894

(119896)

(3)


Table 2 Average changes in dimension and 119878119873 ratios for each trial

TrialsAverage changes in dimension 119878119873 ratio

Tooth thickness (mm) Addendum circle (mm) Dedendum circle (mm)Tooth

thickness(dB)

Addendumcircle (dB)

Dedendumcircle (dB)

1 00928 00225 00195 204439 329303 3419142 00947 00173 00150 203710 351167 3618933 00615 00159 00124 239734 359816 3810004 00397 00156 00102 273704 361456 3983275 00356 00167 00118 283401 355302 3853946 00318 00144 00102 269833 368383 3979017 00811 00162 00116 212971 357943 3869928 00652 00159 00121 235700 359580 3834149 00688 00153 00123 229145 362715 381526

Table 3 The sequences after data preprocessing (Grey generation)

Trials Tooth thickness Addendum circle Dedendum circleReference sequence 10000 10000 10000Comparability sequence1 09909 10000 100002 10000 04405 064583 05480 02192 030724 01217 01773 000005 00000 03347 022936 01703 00000 000767 08838 02672 020098 05986 02253 026449 06808 01450 02978

The values of the tooth thickness addendum circle anddedendum circle were set as the reference sequence 119909(119874)

0

(119896)119896 = 1ndash3 and the comparability sequences 119909(119874)

119894

(119896) 119894 = 1 23 9 119896 = 1ndash3 Table 3 reports the sequences after datapreprocessing

According to Table 3 the deviation sequences Δ01(119896) can

be calculated as followsΔ01(1) =1003816100381610038161003816119909lowast

0

(1) minus 119909lowast

1

(1)1003816100381610038161003816 = |10000 minus 09909| = 00091

Δ01(2) =1003816100381610038161003816119909lowast

0


1

(2)1003816100381610038161003816 = |10000 minus 10000| = 00000

Δ01(3) =1003816100381610038161003816119909lowast

0


1

(3)1003816100381610038161003816 = |10000 minus 10000| = 00000

(4)Therefore Δ

01= (00091 00000 00000)

The same calculation method was performed for 119894 = 1ndash9The results of all Δ

0119894for 119894 = 1ndash9 are listed in Table 4 Based

on the data presented in Table 6 Δmax(119896) and Δmin(119896) can becalculated as follows

Δmax = Δ 02 (1) = Δ 01 (2) = Δ01 (3) = 10000

Δmin = Δ 05 (1) = Δ 06 (2) = Δ04 (3) = 00000(5)

Step 3 Computation of Grey Relational Coefficients of Re-sponse Variables The corresponding Grey relational coeffi-cients (GRC) were calculated using (6) Given that all the

process parameters had equal weight the value of 120577 in thisstudy was defined as 05 in the following equation

120576119894(119896) =Δmin + 120577ΔmaxΔ0119894(119896) + 120577Δmax

(6)

Examples of the GRC 1205761(119896)

are as follows

1205761(1)=00000 + (05) (10000)

00091 + (05) (10000)= 09820

1205761(2)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

1205761(3)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

(7)

Thus 1205761(119896)= (09820 10000 10000) 119896 = 1ndash3 A similar pro-

cedure was applied for 119894 = 1ndash9 Table 5 lists the GRC for eachtrial of the L

9OA

Step 4 Computation of the Contribution of the RespectiveQuality Characteristics Using PCAAn engineering judgmentor subjective estimation is required to determine theweightedvalues for each quality characteristic in the process of opti-mizing a problem related tomultiple quality characteristics or


Table 4 Deviation sequences

Deviation sequences Δ01

Δ02

Δ03

Trial 1 00091 00000 00000Trial 2 00000 05595 03542Trial 3 04520 07808 06928Trial 4 08783 08227 10000Trial 5 10000 06653 07707Trial 6 08297 10000 09924Trial 7 01162 07328 07991Trial 8 04014 07747 07356Trial 9 03192 08550 07022

Table 5 Calculated GRC for nine comparability sequences

Trials Grey relational coefficient (GRC)Tooth thickness

(mm)Addendumcircle (mm)

Dedendumcircle (mm)

1 09820 10000 100002 10000 04719 058543 05252 03904 041924 03628 03780 033335 03333 04291 039356 03760 03333 033507 08114 04056 038498 05547 03922 040469 06104 03690 04159

Table 6 Eigenvalues and explained variations for principal compo-nents

Principal component Eigenvalue Explained variation ()First 2562 85398Second 0424 14139Third 0014 0463

performances Adopting the conventional method in deter-mining the values for each quality characteristic dependsmainly on experience and trial-and-error which can resultin uncertainties during the decision making process ThePCA was utilized in the current study to quantitatively revealthe relative importance of each quality characteristic in theGRA Specifically the PCA was adopted to determine thecorresponding weighted values for each quality characteristicas described below

The GRCs of all quality characteristics presented inTable 4 were used to evaluate the correlation coefficientmatrix and to determine the corresponding eigenvalues andeigenvectors as in the following equation

(119877 minus 120582119896119868119898) 119881119894119896= 0 (8)

In this equation 120582119896are the eigenvalues sum119899

119896=1

120582119896= 119899 119896 =

1 2 119899 119881119894119896= [11988611989611198861198962sdot sdot sdot sdot sdot sdot 119886

119896119899]119879 are the eigenvectors cor-

responding to the eigenvalue120582119896The corresponding eigenval-

ues and eigenvectors are listed in Tables 6 and 7

030035040045050055060065070075

Gre

y re

latio

nal g

rade

s

Injection molding process parameters

Melttemperature

Packingpressure

Packingtime time

Cooling

A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3

Figure 3 Effect of injectionmolding parameter levels on the dimen-sional stability related to shrinkage behavior in plastic gear

The squares of the respective eigenvectors were thenselected as the weighted values of the related quality charac-teristics The contributions of shrinkage behavior to tooththickness addendum circle and dedendum circle of themolded PA6 gear are reported in Table 8

The variance contribution for the first principal compo-nent characterizing the three quality characteristics is as highas 85398Therefore the coefficients of119908

11199082 and119908

3in (9)

were set as 03488 03773 and 02739 respectively

Step 5 Computation of Grey Relational Grades After deter-mining the corresponding weighted values 119908

119896for each

quality characteristic to reflect its relative importance in theGRA by using PCA the Grey relational grades (GRG) werecalculated as follows

120574119894=

119899

sum

119896=1

119908119896sdot 120576119894(119896) (9)

where 119908119896represents the normalized weighted value of factor

119896 The results are listed in Table 9

4 Discussion

41 Optimal Combination of Injection Molding ProcessingParameters andTheir Levels To determine the optimal com-bination of injection molding processing parameters for thecase of dimensional stability related to shrinkage behavior intooth thickness addendum circle and dedendum circle ofthe molded gear the average GRG for each parameter levelwas calculated by employing the main effects analysis of theTaguchi method The calculation was done by classifying theGRG corresponding to the levels of the parameters in eachcolumn of the orthogonal array and taking the average ofthose with the same level The main effects analysis wasconstructed as shown in Table 10 The results were plotted inFigure 3

Given that the GRG represents the level of correlationbetween the reference and the comparability sequences thelarger GRG indicates a stronger correlation between thosesequences Basically a higher GRG indicates better multi-ple quality characteristics Figure 3 shows that the relativechanges in dimensions resulting from shrinkage behavior in


Table 7 Eigenvectors for principal components

Quality characteristic EigenvectorFirst principal component Second principal component Third principal component

Tooth thickness 0591 minus0487 minus0643

Addendum circle 0614 minus0245 0750Dedendum circle 0523 0838 minus0154

Table 8Contribution of each individual quality characteristic to theprincipal component

Quality characteristic ContributionTooth thickness 03488Addendum circle 03773Dedendum circle 02739

Table 9 Grey relational grade after computation

Trial Grey relational grade1 099512 065943 043824 035705 038946 034577 050898 044149 04528

the tooth thickness addendumcircle and dedendumcircle ofthe unfilled PA6 molded gear are influenced significantly bythe adjustments of the processing parametersThe incrementof melt temperature initially decreased the GRG but then thevalue slightly increased at level 3 On the contrary the GRG islower when the packing pressure and packing time increasedresulting in more pronounced shrinkage behavior in tooththickness addendum circle and dedendum circle On theother hand the GRG value also decreased as the coolingtime increased The more time applied during the coolingphase the greater of shrinkage behavior in tooth thicknessaddendum circle and dedendum circle of the gear

As in this case the best combination of processing param-eters and levels could be obtained easily from the main effectanalysis by selecting the level of each parameter with thehighest GRG As shown in Figure 3 A

1 B1 C1 and D

1

provide the highest GRG for factors A B C and D respec-tively Consequently the optimal parameter setting whichstatistically results in minimum shrinkage behavior of thetooth thickness addendumcircle and dedendumcircle of thePA6 molded gear was predicted to be A

1 B1 C1 D1 that is

melt temperature of 260∘C packing pressure of 60 packingtime of 5 s and cooling time of 30 s

Once the combination of optimal process parameters wasidentified the experimental verification test was carried outon five repetitions of gear samplesThepurpose of conductingthe verification test is to assess the accuracy and to verify

the improvement of relative changes in dimension related tothose shrinkage behaviors by adopting the hybrid TaguchiGRAPCA optimization method Table 11 lists the results ofthe verification test by means of the optimal process parame-ters A

1 B1 C1 D1 for the unfilled PA6 molded gear

Using the optimal process parameter setting of melt tem-perature of 260∘C 60 of packing pressure packing time of5 s and cooling time of 30 s the final unfilled PA6 moldedgear exhibited the average of relative changes in dimensionrelated to shrinkage behavior in tooth thickness addendumcircle and dedendum circle as 928 225 and 195respectively Compared with the cavity dimensions of tooththickness addendum circle and dedendum circle theunfilled PA6 gear demonstrate the optimum average dimen-sions of 21774 329013 and 270038mm respectively Theresults are generally better than those prior to optimization

42 Significance of Process Parameters To examine the extentto which injection molding parameters significantly influ-ence the performance of molded gear analysis of variance(ANOVA) of the Taguchimethodwas performed on theGRGfor nine comparability sequences (Table 9) The computedquantities of degree of freedom (DOF) sum of squares (119878)variance (119881) and percentage contribution (119875) are presentedin Table 12

In this case the percentage contribution of each process-ing parameter was directly calculated from 119878 because of thenonvalue in the DOF for the error term The significance ofeach processing parameter on the dimensional stability canbe determined by the percentage contribution Roy [13] sug-gested an alternative by using the 10 rule which considersthe insignificant parameter when its effect is less than 10 ofthe highest parameter influence From the results of ANOVAin Table 12 the melt temperature appears to be the most deci-sive processing parameter in reducing the shrinkage behaviorin tooth thickness addendum circle and dedendum circle ofthe molded gear with the highest percentage contribution of5207 outweighing the other process variablesThe analysisalso demonstrates that packing pressure packing time andcooling time are significant because their percentages areover 10 more than the highest parameter influence (521)The packing pressure cooling time and packing time arerecorded as 1958 1795 and 1004 respectively As abroad rule in the effect of shrinkage it must be anticipatedin the design of the mold and requires expert knowledgeAccurate and specific treatment of this phenomenon is aresult of years of experience in building molds for productsparticularly gears As indicated above the final size of amolded gear can be influenced by the processing parameters


Table 10 Main effects table for Grey relational grades

Symbol Process parameters Level 1 Level 2 Level 3A Melt temperature (∘C) 06975 03640 04677B Packing pressure () 06203 04967 04122C Packing time (s) 05941 04897 04455D Cooling time (s) 06124 05047 04122

Table 11 Results of verification test

Tooth thickness Addendum circle Dedendum circleMold cavity dimension (mm) 24000 336600 275400Average dimension after optimization (mm) 21774 329013 270038Relative changes in dimension () 928 225 195

From the above it becomes obvious that with the same moldby changing molding parameters parts of different sizescan be produced [14 15] In addition the form of the gearteeth itself altered as a result of shrinkage irrespective of itshrinking away from themoldThe outcomewill be impactedon the injected gear where it will be too thin at the top and toothick at the baseTherefore the pressure angle will amplifiedresulting in the possibility of binding as well as greater wearand eventually reduce the gear performance

43 Influence of Glass Fiber Reinforcement on the DimensionalStability of PA6 Molded Gear To further understand theeffects of glass fiber reinforcement on the dimensional stabil-ity related to shrinkage behavior in tooth thickness adden-dum circle and dedendum circle gears made from 15 and30 glass fiber-filled PA6 were also produced using similaroptimal processing parameters obtained in the case of theunfilled PA6 The purpose of using the similar optimal pro-cessing parameters is to control the changeability in processsetting therefore the influence of glass fiber reinforcementon the dimensional stability of the molded gears can bedirectly investigated Table 13 shows the variation of dimen-sional stability related to shrinkage behavior in the tooththickness addendum circle and dedendum circle of glassfiber-filled PA6 produced by melt temperature of 260∘Cpacking pressure of 60 packing time of 5 s and cooling timeof 30 s

As observed in Table 13 the relative changes in dimensionrelated to shrinkage behavior in tooth thickness addendumcircle and dedendumcircle decrease greatlywith the additionof glass fiber as reinforcement At the optimal process param-eter settings of melt temperature packing pressure packingtime and cooling time the relative changes in dimension dueto shrinkage behavior for PA6 + 15 GF result in 532092 and 078 for tooth thickness addendum circleand dedendum circle respectively Compared with those ofthe unfilled PA6 the addition of 30 glass fiber as rein-forcement significantly decreases the relative changes indimension due to shrinkage behavior in tooth thicknessaddendum circle and dedendum circle to 483 058and 049 correspondingly The deviation in the involuteprofile especially in the addendum and dedendum circles

is also more than those of the unfilled gears due to thepresence of hard glass fiber in the molded surface of the gearHowever less total profile deviation is observed along the geartooth thickness due to restricted shrinkage resulting from thealignment of glass fibers The presence of fibers across thetooth section also has an effect onmaterial homogeneity thusaccelerating the deviation compared to the unfilled PA6 gearsSimilar circumstances have been reported by Senthilvelanand Gnanamoorthy [16]

5 Conclusion

In relating to plastic gear proper sizing have an effect on theoverall performance of the gear injected Ametal gear is com-monly evaluated by referring to the load data however plas-tics have different properties than metals and are receptive tochanging operating conditions A plastic gear thereforemustbe designed and produced by taking into consideration theload data environmental conditions andmaterial propertiesIn relation to the work carried out the mold gear wasdesigned with single cavity two plate mold and diaphragmgate system in order to provide the uniformity in flow patternof polymer inside the cavity of the gear part during thefilling process Several trials runs are carried out by usingMoldflow Plastic Insight 61 (MPI) software in previous workto forecast and visualize the filling pattern or the transientprogression of the polymer flow front within the feed systemand mold cavity By established diaphragm gate system andno changing in cavity size themain focus of the present studyis to investigate the effects of the optimized injectionmoldingprocessing parameters on the dimensional stability related toshrinkage behavior in the involute profile of a molded plasticgear

Through a systematic Taguchi parameter designGRAPCA hybrid method in the optimization of process param-eters the variation in the dimensional stability due to shrink-age behavior of the thickness addendum circle and deden-dum circle in PA6 molded gears has been minimized Inaddition through a series of analyses and optimizationsof the selected multiple quality characteristics we foundthat the optimal combination of processing parameters forthe molded gear to achieve minimum relative changes in


Table 12 ANOVA results for the Grey relational grade for nine comparability sequences

Column Processing parameters DOF 119878 119881 119875

A Melt temperature (∘C) 2 01748 00874 5207B Packing pressure () 2 00657 00329 1958C Packing time (s) 2 00349 00175 1040D Cooling time (s) 2 00603 00301 1795All otherserror 0 00000 00000 000Total 8 03357 10000

Table 13 The effect of GF addition on the involute profile of PA6 molded gear

Relative changes in dimension ()Tooth thickness Addendum circle Dedendum circle

Unfilled PA6 928 225 195PA6 + 15 GF 532 092 078PA6 + 30 GF 483 058 049

dimension related to shrinkage behavior are A1 B1 C1

and D1 From the results of ANOVA the melt temperature

appears to be the most decisive processing parameter inreducing the shrinkage behavior of tooth thickness adden-dum circle and dedendum circle of the molded gear with thehighest percentage contribution of 5207 which outweighsthe other process variables In the case of filled PA6 gearsthe presence of glass fibers has induced greater deviation oftooth thickness addendum circle and dedendum circle thanthe nonfilled PA6 gears

Conflict of Interests

The authors would like to declare that all financial and mate-rial support for the conducting this research and preparationof this paper is clearly termed in the Acknowledgments andthere will be no conflict of interests in relation to the financialgain subject to the publication of this paper

Acknowledgment

The authors acknowledge the Short-Term Research Grantprovided by the University Sains Malaysia Pulau Pinang forfunding the study that resulted in this paper

References

[1] S Senthilvelan and R Gnanamoorthy ldquoDamagemechanisms ininjection molded unreinforced glass and carbon reinforcednylon 66 spur gearsrdquo Applied Composite Materials vol 11 no6 pp 377ndash397 2004

[2] K Mao ldquoA new approach for polymer composite gear designrdquoWear vol 262 no 3-4 pp 432ndash441 2007

[3] W Li AWood RWeidig andKMao ldquoAn investigation on thewear behaviour of dissimilar polymer gear engagementsrdquoWearvol 271 no 9-10 pp 2176ndash2183 2011

[4] K Mao W Li C J Hooke and D Walton ldquoFriction and wearbehaviour of acetal and nylon gearsrdquoWear vol 267 no 1-4 pp639ndash645 2009

[5] KMaoW Li C JHooke andDWalton ldquoPolymer gear surfacethermal wear and its performance predictionrdquo Tribology Inter-national vol 43 no 1-2 pp 433ndash439 2010

[6] M Kurokawa Y Uchiyama and S Nagai ldquoPerformance ofplastic gear made of carbon fiber reinforced poly-ether-ether-ketonerdquo Tribology International vol 32 no 9 pp 491ndash497 1999

[7] M Kurokawa Y Uchiyama and S Nagai ldquoPerformance of plas-tic gear made of carbon fiber reinforced poly-ether-ether-ketone part 2rdquo Tribology International vol 33 no 10 pp 715ndash721 2000

[8] M Kurokawa Y Uchiyama T Iwai and S Nagai ldquoPerformanceof plastic gear made of carbon fiber reinforced polyamide 12rdquoWear vol 254 no 5-6 pp 468ndash473 2003

[9] S Senthilvelan and R Gnanamoorthy ldquoDamping characteris-tics of unreinforced glass and carbon fiber reinforced nylon 66spur gearsrdquo Polymer Testing vol 25 no 1 pp 56ndash62 2006

[10] T Hirogaki E Aoyama T Katayama S Iwasaki Y Yagura andK Sugimura ldquoDesign systems for gear elements made of cottonfiber-reinforced plasticsrdquo Composite Structures vol 66 no 1-4pp 47ndash52 2004

[11] FMendi H Can andM K Kulekci ldquoFatigue properties of pol-ypropylene involute rack gear reinforced with metallic springsrdquoMaterials and Design vol 27 no 5 pp 427ndash433 2006

[12] N M Mehat and S Kamaruddin ldquoOptimization of mechanicalproperties of recycled plastic products via optimal processingparameters using the Taguchi methodrdquo Journal of MaterialsProcessing Technology vol 211 no 12 pp 1989ndash1994 2011

[13] R K Roy Design of Experiment Using the Taguchi Approach 16Steps to Product and Process Improvement John Wiley amp SonsNew York NY USA 2001

[14] T C Chang and E Faison III ldquoShrinkage behavior and opti-mization of injection molded parts studied by the Taguchimethodrdquo Polymer Engineering and Science vol 41 no 5 pp703ndash710 2001

[15] S J Liao D Y Chang H J Chen et al ldquoOptimal process con-ditions of shrinkage and warpage of thin-wall partsrdquo PolymerEngineering and Science vol 44 no 5 pp 917ndash928 2004

[16] S Senthilvelan and R Gnanamoorthy ldquoInfluence of reinforce-ment on composite gear metrologyrdquo Mechanism and MachineTheory vol 43 no 9 pp 1198ndash1209 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



thereby influencing the noise and heat generation during ser-vice Hirogaki et al [10] used cotton fiber plain woven filledphenolics resin laminate as the gear material to study thetooth root stress resulting from bending movement underrunning conditions the results revealed that the strength ofa tooth with a filled fiber angle of 45∘ is at the lowest whenthe load is applied to the tooth tip In addition Mendi et al[11] found that reinforcing the polypropylene gear tooth withmetallic wires subsequently generating a residual compres-sion stress in the structure of the gear tooth increases thenumber of cycles of fatigue failure and enhances fatiguestrength

Despite the quality of these studies the issue related to thedimensional stability in plastic gear during the early stageof gear manufacturing has not been thoroughly describedelsewhere An investigation of the literature related to plasticgears study showed that so much attention is given on plasticgear reinforcement in order to overcome the limitations ofplastic gears usage The dimensional stability of a plastic gearis indispensable to the perfect functioning of the gear when itis running which should not be underrated of its impact onthe final quality of plastic gears produced During the injec-tion molding process the dimensions of the molded plasticgear change as the parts cool due to shrinkage The irrevers-ible changes in dimensions especially in the involute profileof the plastic gear as a result of uncontrolled shrinkage dueto complexity and inappropriate process parameters settingnegatively influence concentricity roundness tooth spacinguniformity and the size of the gear produced Consequentlythe quality of the end molded gear noise and vibration aswell as the service life of the gear are affected by damagemechanisms such as tooth fatigue creep excessive wear andplastic deformation In fact the optimum properties of theplastic material with the most innovative gear and molddesign cannot be attained making them irrelevant withoutoptimal processing parameters during gear manufacturing

Thus the main objective of the current study is to explorethe effects of optimized injection molding processing param-eters on the dimensional stability related to shrinkage behav-ior in the involute profile of a molded plastic gear A system-atic study on the optimization of processing parameters isconducted via a hybrid integration of the Taguchi parameterdesign statistical Grey relational analysis (GRA) and prin-cipal component analysis (PCA) by selecting three qualitycharacteristics namely tooth thickness and the addendumand dedendum circles A side-by-side comparison betweenthe unfilled and glass fiber-filled polyamide 6 (PA6) gearswas also carried out with regard to the dimensional stabilityrelated to shrinkage in the involute profile after the optimiza-tion process

2 Experimental Procedure

21 Materials The unfilled PA6 under the grade name ofZISAMIDE TP4210 (Zig Sheng Industrial Co) as well as 15and 30 glass fiber-filled PA6 denoted as Vitamide BR13and Vitamide BY16 respectively (Perrite) were specified inthis study for the gear materials The study used the spur

R1650

R1350

10

empty10

empty12

Figure 1 Geometry and specifications of spur gear with module =15 pressure angle = 20∘ number of teeth = 20 face width = 10mm

gear design in compliance with the American Gear Manu-facturers Association (AGMA) standards The geometry andspecifications of the gear are shown in Figure 1 The finalmold design is prepared after the gear part design has beenspecified and all requirements affecting the design of themold including number of cavities type of mold types ofejection and types of venting as well as injection moldingmachine consideration have been clarified In this case thepreliminary filling analysis has been previously conductedon the gear model before optimizing the gating system forthe gear part The diaphragm gating system is selected to beincorporated with two plate mold single gear cavity basedon the uniformity of the transient progression of the polymerflow front in the cavity as shown in the analysis

22 Gear Preparation and Fabrication The PA6 gears wereinjected using a Battenfeld TM750210 injection moldingmachine The experiment was conducted with four con-trollable three-level processing parameters namely melttemperature packing pressure packing time and coolingtime Other processing parameters such as mold tempera-ture (60∘C) injection pressure (60 bar) and stroke distance(60mm) were kept constant during the experiment In addi-tion the Taguchi method based on orthogonal arrays (OA)was used to design the experiments As discussed by Mehatand Kamaruddin [12] Taguchirsquos OA are highly fractional or-thogonal designs that can be employed to study an entireparameter space with a small number of experiments Table 1lists the design of the experiment based on the L

9(34) OA in

producing nine trials of unfilled PA6 gears with five repeti-tions

23 Shrinkage Measurement All nine trials of the unfilledPA6 gears with five repetitions of each trial were left for48 hours at room temperature before the measurement ofshrinkage (ASTMD955-89) ARaxVisionDC3000Mitutoyoprofile projector was used to inspect the accuracy of thespecific profile of the involute gear teeth following the mold-ing process The projector was used in measuring the two-dimensional (2D) addendum circle dedendum circle andtooth thickness using the coordinates of selected points alongthe gear profile The gear used in this study was designed




1 260 60 5 302 260 80 10 403 260 100 15 504 280 60 10 505 280 80 15 306 280 100 5 407 300 60 15 408 300 80 5 509 210 100 10 30





119878 =119863119898minus 119863

119863119898

times 100 (1)


119898is







119878

119873= minus10Log( 1

119873

119899

sum

119894=1

1199102

119894119895

) (2)




119909lowast

119894

(119896) =max119909(119874)

119894

(119896) minus 119909(119874)

119894

(119896)

max 119909(119874)119894

(119896) minusmin119909(119874)119894

(119896)

(3)





thickness(dB)

Addendumcircle (dB)

Dedendumcircle (dB)

1 00928 00225 00195 204439 329303 3419142 00947 00173 00150 203710 351167 3618933 00615 00159 00124 239734 359816 3810004 00397 00156 00102 273704 361456 3983275 00356 00167 00118 283401 355302 3853946 00318 00144 00102 269833 368383 3979017 00811 00162 00116 212971 357943 3869928 00652 00159 00121 235700 359580 3834149 00688 00153 00123 229145 362715 381526




0


119894




0


1

(1)1003816100381610038161003816 = |10000 minus 09909| = 00091

Δ01(2) =1003816100381610038161003816119909lowast

0


1

(2)1003816100381610038161003816 = |10000 minus 10000| = 00000

Δ01(3) =1003816100381610038161003816119909lowast

0


1

(3)1003816100381610038161003816 = |10000 minus 10000| = 00000

(4)Therefore Δ

01= (00091 00000 00000)




Δmax = Δ 02 (1) = Δ 01 (2) = Δ01 (3) = 10000

Δmin = Δ 05 (1) = Δ 06 (2) = Δ04 (3) = 00000(5)



120576119894(119896) =Δmin + 120577ΔmaxΔ0119894(119896) + 120577Δmax

(6)


are as follows

1205761(1)=00000 + (05) (10000)

00091 + (05) (10000)= 09820

1205761(2)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

1205761(3)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

(7)



9OA





Δ02

Δ03





Dedendumcircle (mm)

1 09820 10000 100002 10000 04719 058543 05252 03904 041924 03628 03780 033335 03333 04291 039356 03760 03333 033507 08114 04056 038498 05547 03922 040469 06104 03690 04159





(119877 minus 120582119896119868119898) 119881119894119896= 0 (8)


119896=1

120582119896= 119899 119896 =





030035040045050055060065070075

Gre

y re

latio

nal g

rade

s


Melttemperature

Packingpressure

Packingtime time

Cooling

A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3




11199082 and119908

3in (9)



119896for each


120574119894=

119899

sum

119896=1

119908119896sdot 120576119894(119896) (9)



4 Discussion














1 B1 C1 and D

1


1 B1 C1 D1 that is

















5 Conclusion















Acknowledgment


References



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












1 260 60 5 302 260 80 10 403 260 100 15 504 280 60 10 505 280 80 15 306 280 100 5 407 300 60 15 408 300 80 5 509 210 100 10 30





119878 =119863119898minus 119863

119863119898

times 100 (1)


119898is







119878

119873= minus10Log( 1

119873

119899

sum

119894=1

1199102

119894119895

) (2)




119909lowast

119894

(119896) =max119909(119874)

119894

(119896) minus 119909(119874)

119894

(119896)

max 119909(119874)119894

(119896) minusmin119909(119874)119894

(119896)

(3)





thickness(dB)

Addendumcircle (dB)

Dedendumcircle (dB)

1 00928 00225 00195 204439 329303 3419142 00947 00173 00150 203710 351167 3618933 00615 00159 00124 239734 359816 3810004 00397 00156 00102 273704 361456 3983275 00356 00167 00118 283401 355302 3853946 00318 00144 00102 269833 368383 3979017 00811 00162 00116 212971 357943 3869928 00652 00159 00121 235700 359580 3834149 00688 00153 00123 229145 362715 381526




0


119894




0


1

(1)1003816100381610038161003816 = |10000 minus 09909| = 00091

Δ01(2) =1003816100381610038161003816119909lowast

0


1

(2)1003816100381610038161003816 = |10000 minus 10000| = 00000

Δ01(3) =1003816100381610038161003816119909lowast

0


1

(3)1003816100381610038161003816 = |10000 minus 10000| = 00000

(4)Therefore Δ

01= (00091 00000 00000)




Δmax = Δ 02 (1) = Δ 01 (2) = Δ01 (3) = 10000

Δmin = Δ 05 (1) = Δ 06 (2) = Δ04 (3) = 00000(5)



120576119894(119896) =Δmin + 120577ΔmaxΔ0119894(119896) + 120577Δmax

(6)


are as follows

1205761(1)=00000 + (05) (10000)

00091 + (05) (10000)= 09820

1205761(2)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

1205761(3)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

(7)



9OA





Δ02

Δ03





Dedendumcircle (mm)

1 09820 10000 100002 10000 04719 058543 05252 03904 041924 03628 03780 033335 03333 04291 039356 03760 03333 033507 08114 04056 038498 05547 03922 040469 06104 03690 04159





(119877 minus 120582119896119868119898) 119881119894119896= 0 (8)


119896=1

120582119896= 119899 119896 =





030035040045050055060065070075

Gre

y re

latio

nal g

rade

s


Melttemperature

Packingpressure

Packingtime time

Cooling

A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3




11199082 and119908

3in (9)



119896for each


120574119894=

119899

sum

119896=1

119908119896sdot 120576119894(119896) (9)



4 Discussion














1 B1 C1 and D

1


1 B1 C1 D1 that is

















5 Conclusion















Acknowledgment


References



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













thickness(dB)

Addendumcircle (dB)

Dedendumcircle (dB)

1 00928 00225 00195 204439 329303 3419142 00947 00173 00150 203710 351167 3618933 00615 00159 00124 239734 359816 3810004 00397 00156 00102 273704 361456 3983275 00356 00167 00118 283401 355302 3853946 00318 00144 00102 269833 368383 3979017 00811 00162 00116 212971 357943 3869928 00652 00159 00121 235700 359580 3834149 00688 00153 00123 229145 362715 381526




0


119894




0


1

(1)1003816100381610038161003816 = |10000 minus 09909| = 00091

Δ01(2) =1003816100381610038161003816119909lowast

0


1

(2)1003816100381610038161003816 = |10000 minus 10000| = 00000

Δ01(3) =1003816100381610038161003816119909lowast

0


1

(3)1003816100381610038161003816 = |10000 minus 10000| = 00000

(4)Therefore Δ

01= (00091 00000 00000)




Δmax = Δ 02 (1) = Δ 01 (2) = Δ01 (3) = 10000

Δmin = Δ 05 (1) = Δ 06 (2) = Δ04 (3) = 00000(5)



120576119894(119896) =Δmin + 120577ΔmaxΔ0119894(119896) + 120577Δmax

(6)


are as follows

1205761(1)=00000 + (05) (10000)

00091 + (05) (10000)= 09820

1205761(2)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

1205761(3)=00000 + (05) (10000)

00000 + (05) (10000)= 10000

(7)



9OA





Δ02

Δ03





Dedendumcircle (mm)

1 09820 10000 100002 10000 04719 058543 05252 03904 041924 03628 03780 033335 03333 04291 039356 03760 03333 033507 08114 04056 038498 05547 03922 040469 06104 03690 04159





(119877 minus 120582119896119868119898) 119881119894119896= 0 (8)


119896=1

120582119896= 119899 119896 =





030035040045050055060065070075

Gre

y re

latio

nal g

rade

s


Melttemperature

Packingpressure

Packingtime time

Cooling

A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3




11199082 and119908

3in (9)



119896for each


120574119894=

119899

sum

119896=1

119908119896sdot 120576119894(119896) (9)



4 Discussion














1 B1 C1 and D

1


1 B1 C1 D1 that is

















5 Conclusion















Acknowledgment


References



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












Δ02

Δ03





Dedendumcircle (mm)

1 09820 10000 100002 10000 04719 058543 05252 03904 041924 03628 03780 033335 03333 04291 039356 03760 03333 033507 08114 04056 038498 05547 03922 040469 06104 03690 04159





(119877 minus 120582119896119868119898) 119881119894119896= 0 (8)


119896=1

120582119896= 119899 119896 =





030035040045050055060065070075

Gre

y re

latio

nal g

rade

s


Melttemperature

Packingpressure

Packingtime time

Cooling

A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3




11199082 and119908

3in (9)



119896for each


120574119894=

119899

sum

119896=1

119908119896sdot 120576119894(119896) (9)



4 Discussion














1 B1 C1 and D

1


1 B1 C1 D1 that is

















5 Conclusion















Acknowledgment


References



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation




















1 B1 C1 and D

1


1 B1 C1 D1 that is

















5 Conclusion















Acknowledgment


References



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation


















5 Conclusion















Acknowledgment


References



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation





















Acknowledgment


References



















RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









research article optimized injection molding of unfilled and … · 2019. 7. 31. · research...

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