optimisation of shock absorber parameters using failure mode and effect analysis and taguchi method

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  • 7/30/2019 Optimisation of Shock Absorber Parameters Using Failure Mode and Effect Analysis and Taguchi Method

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    International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 2, May-August (2012), IAEME

    328

    OPTIMISATION OF SHOCK ABSORBER PARAMETERS USING

    FAILURE MODE AND EFFECT ANALYSIS AND TAGUCHI

    METHOD

    A.Mariajayaprakash

    Assistant Professor and Head, Department of Mechanical Engineering,

    Rajiv Gandhi College of Engineering and Technology,Puducherry, India;

    e-mail : [email protected]

    Dr.T. SenthilVelan

    Professor and Head , Department of Mechanical Engineering,

    Pondicherry Engineering College, Puducherry, India;e-mail: [email protected]

    K.P.Vivekananthan

    Deputy General Manager (manufacturing),TENNECO, Puducherry, Indiae-mail: [email protected]

    ABSTRACT

    The various process parameters affecting the quality characteristics of the shock absorber

    during the process were identified by using the Ishikawa diagram and FMEA. The

    identified process parameters are: Welding process parameters (squeeze, heat control,wheel speed and air pressure), tamper sealing process parameters(load, hydraulic pressure

    , air pressure and fixture height),Washing process parameters(total alkalinity,

    temperature, PH value of rinsing water and timing),Painting processparameters(flowability, coating thickness, pointage and temperature).Out of above

    mentioned four process parameters welding and tamper sealing process parameters were

    optimized by using Taguchis method in the earlier work. In this paper, the remainingprocess parameters namely washing and painting process parameters are optimized by

    using Taguchis method.

    Key words: Taguchis method, Ishikawa diagram, ANOVA, FMEA

    INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING

    AND TECHNOLOGY (IJMET)

    ISSN 0976 6340 (Print)ISSN 0976 6359 (Online)

    Volume 3, Issue 2, May-August (2012), pp. 328-345

    IAEME: www.iaeme.com/ijmet.html

    Journal Impact Factor (2011):1.2083 (Calculated by GISI)www.jifactor.com

    IJMET

    I A E M E

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    LIST OF SYMBOLS

    r Number of tests in a trial

    yi Response value of observation in the ith test

    DOE Design of experiments Degrees of freedom

    A Degrees of freedom for factor A

    kA Number of levels for factor A

    required Total degrees of freedom required

    LN Total degrees of freedom of the available orthogonal array

    N Number of trials

    ANOVA Analysis of varianceM Overall mean percentage defects

    VFactor Variance of factor

    SS Sum of squareV Expected amount of variation

    P Percent contribution

    Mean

    Level of riske Degrees of freedom for the error

    Ve Error variance

    F(, 1, e) F ratio required at the level of riskeff Effective number of replications

    n Total number of experiments

    CI Confidence interval

    T Average values of defects at different levels

    1.0 INTRODUCTION

    Shock absorber is one of the major component used in automobiles. It is used to absorb

    vibrations when the vehicle is moving. Otherwise that vibrations affect the vehicle andthe rider. The defects which are occurred during the process affect the quality of the

    shock absorber. In order to minimize the defects and improve the quality, the following

    tools are employed. First, Cause and effect diagram or Ishikawa diagram is used foridentifying the parameters that may affect the quality of the shock absorber during the

    process. Then, Failure Mode Effect Analysis tool is applied to find out the most

    significant process parameters that may affect the quality of the shock absorber. Finally,

    Taguchi method is used to optimize the process parameters. Taguchi method is anefficient and powerful tool that can reduce the experimental trails necessary to determine

    the optimal conditions. It has been widely used in many different fields (Yung-Tien Liu

    et al., 2010).

    Tsai et al. (2008) used Taguchi design experiments to identify the optimal abrasive jet

    polishing parameters when applied to the polishing of electrical discharged machinedSKD 61 mold steel specimens. This paper shows that ANOVA provides an indication of

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    the significance of the individual control factors. Mahapatra and Vedansh Chaturvedi

    (2009) proved that Taguchis experimental design is a simple and systematic way ofanalyzing a complex process with less experimental design.

    In this paper, test parameters are optimized for minimum wear by using Taguchis

    method. Ganapathy et al. (2009) optimized the operating parameters in Jatropha bio

    diesel engine by using Taguchi method.In this paper it is proved that signal to noise ratio is used to optimize the various input

    parameters of the model. This paper shows that the Taguchi approach based

    thermodynamic model has improved the performance parameters slightly. Pishbin et al.(2010) investigated the effects of processing parameters, including suspension

    concentration, pH and electric field by using Taguchis DOE approach in electrophoretic

    deposition of bio glass suspension. Mojtaba momeni et al. (2010) obtained the optimalcondition for DOS measurement based on Double- loop EPR technique in H2 SO4

    containing KSCN solution using the Taguchi method. In this paper, it is concluded that

    higher the S/N ratio, greater is the effect on the DOS measurement. Te-Sheng Li et al.(2009) explained how Taguchi method is utilized for optimizing the parameters in

    thermal flow techniques for sub-35 nm contact-hole fabrication. In this article, theoptimal thermal flow parameter settings are determined by signal to noise ratio and

    ANOVA analysis. Balamurugan Gopalsamy et al. (2009) applied Taguchi method to findoptimum process parameters for end milling while hard machining of hardened steel.

    Results obtained from Taguchi method closely match with ANOVA and it is found that

    cutting speed is most influencing parameters corresponding to quality characteristics.

    Khandoker abul Hossain et al. (2010) illustrated that the cause and effect diagram

    provides the solution to reduce the emission of co2. Andrejkovic et al. (2011) explainedthat Ishikawa diagram quickly identify the causes of quality problems. Tlale et al. (2008)

    applied the usage of cause and effect diagram in cost drivers for manufacturing process.

    Hu-chen liu et al. (2011) reported about the usage of FMEA tool and how it is appliedto identify the failure modes. Arabian-Hoseynabadi et al. (2010) explained that theFMEA tool is applied in wind turbine systems. In this paper, the reliability of the wind

    turbine system is improved by applying FMEA tool. Boldrin et al. (2009) identified and

    reduced the risks of failure in ITER NB injector using FMEA tool. .

    2.0 CAUSE AND EFFECT DIAGRAM

    Cause and effect diagram is a tool for identifying the root causes of quality problems. It is

    also called as Ishikawa diagram or Fishbone diagram ( Ilie and Ciocoiu , 2010).An

    Ishikawa diagram is constructed as shown in Fig.1. By using this diagram the various

    process parameters that affect the quality of the shock absorber are identified ( Mohansen and shan, 2005).The identified process parameters are listed below:

    1.Washing parameters

    2.Welding parameters3.Painting parameters

    4.Tamper sealing parameters

    5.Assembly parameters6.Lubrication parameter

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    7.Inspection and Checking Parameters

    8.Dimensioning parameters9.Polishing parameter

    10.Testing parameters

    DEFECTSIN

    SHOCK

    ABSORBR

    DEFECTSINSHOCK

    ABSORBR

    painting

    DIMENSIONING

    INSPECTION/CHECKING POLISHING

    Paint notadheringRustcorrosion

    Pointagetemperature

    FlowabilityCoatingthickness

    Cylinder notball sized

    Ballsizing

    Cylinder notball sized

    1.concentricity2.cylinderbendchecking

    1.Breakage2.burrs

    1.Concentricity morethan specification2.wrong jaws3.worn out jaws

    .

    Setupnot correct

    Poorsurfacefinish

    Bad stonecondition

    WASHING

    Improperfrequency ofchange

    Presence ofoil/grease

    1.wrong parameters2.improperpreparationof solvent

    Fig.1Cause and effect diagram

    3. FAILURE MODE AND EFFECT ANALYSIS

    After constructing Ishikawa diagram, it is important to perform Failure Mode Effect

    Analysis. FMEA is a powerful tool which is used to define, identify and eliminate known

    potential failures, problems, errors and so on (hu-chen liu et al, 2011).Today, FMEAtechnique has been applied in many places, such as automobiles, aerospace, military,

    electricity and mechanical industries. FMEA is conventionally carried out by a team of

    engineers. By using their knowledge and past data, Risk Priority Number(RPN) value isassigned for each failure component.(Zaifang Zhang and Xuening Chu, 2011). RPN is the

    product of the occurrence (o), severity(s), and detection (d) of a failure. The three risk

    factors are evaluated using 10 points scale. Failure modes with higher RPN values areassumed to be more important and are given higher priorities than those with lower RPN

    values (Ying ming wang et al., 2009). In this paper, washing and painting process

    parameters are having higher RPN values. Hence these two process parameters areconsidered as most significant process parameters.

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    4. TAGUCHIS METHOD

    Taguchi method is an efficient tool for acquiring optimal process parameters. In thismethod, number of experiments are reduced. In this method two important tools are used.

    i) orthogonal array and ii) Signal to noise ratio ( Cevdet Gologlu and Nazim Sakarya,

    2008).

    First, experiment parameter factors and their levels are selected. In this study, fourpainting process parameters are used as control factors and each parameter is designed to

    have three levels ( kilickap, 2010).The selected process parameters, ranges and their

    levels are shown in Table 1.

    Table 1 Process parameters with their ranges and values at three levels

    Parameter

    designationProcess parameters Range Level 1 Level 2 Level 3

    A Flowability ( sec) 15-25 15 20 25

    B Coatingthickness(microns)

    20-50 20 40 50

    C pointage 6-12 6 8 12

    D Temperature ( C) 20-50 2 35 50

    4.1. Selection of Orthogonal array

    An orthogonal array for process design is applied on the knowledge of control factors and levels.The number of experiments can be reduced by using orthogonal array.( yu - tang yen et

    al.,2010).The degrees of freedom for the orthogonal array should be greater than or at least equal

    to those for the process parameters. In this study, L9 orthogonal array having 8 degrees of

    freedom is selected ( Anawa and Olabi, 2008).This orthogonal array has four columns and nine

    experiments runs and it is shown in Table 2.

    Table 2 L9 orthogonal

    array Table 3 Experimental L9 array

    Run A B C D

    1 1 1 1 1

    2 1 2 2 2

    3 1 3 3 3

    4 2 1 2 3

    5 2 2 3 1

    6 2 3 1 27 3 1 3 2

    8 3 2 1 3

    9 3 3 2 1

    Trial

    no.A B C D

    Flow

    ability

    ( sec)

    Coating

    thickness

    (microns)

    pointageTempe-

    rature (0C)

    1 15 20 6 20

    2 15 40 8 35

    3 15 50 12 50

    4 20 20 8 505 20 40 12 20

    6 20 50 6 35

    7 25 20 12 35

    8 25 40 6 50

    9 25 50 8 20

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    4.2. Conducting the Experiment

    After selecting the orthogonal array, the factors at different levels are assigned for eachtrial. The assigned experimental array is shown in Table 3.The experiments are conducted

    using single randomization technique. Each experiment is repeated three times for the

    same set off parameters.(Ross,1988 ; Hazura Mohamed et.al.,2008).In each trial, the

    defects occurred are recorded and it is shown in Table 4. In this work, the defects thatoccur during the welding, washing, painting, and tamper sealing process are considered.

    The percentage of the defects for each repetition was calculated by using the given

    formula, and then the average of the defects were determined for each trial condition andit was shown in Table 5.

    No. of defects occurring due to Painting processPercentage of defects =

    Total no. of defects occurring in the process

    (welding, washing, painting and tamper sealing)

    Table 4 Defects and number of defects occurred during the experiments

    Defects No. of defects

    Trial

    1Trial 2 Trial 3

    paint not

    adheringrusting

    not

    drying

    not

    cleaning4 4 4

    paint not

    adhering1 2 1

    paint not

    adhering

    manual

    coating

    powder

    deposit

    over

    heating4 4 4

    powder deposit not drying 2 2 2

    rusting not cleaning 2 2 2

    paint not comingpowder

    deposit2 2 2

    paint not coming rustingover

    heating2 4 4

    paint not coming not drying 3 2 2

    21 24 23

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    Table 5 Painting defects values and signal to noise (S/N) ratios against trail numbers

    4.3. S/N Ratio

    Taguchi technique utilises the signal to noise ratio(S/N) approach to measure the qualitycharacteristic deviating from the desired value. S/N ratio is used as an objective function

    for optimizing parameters. (Gunawan Setia Prihandana et.al., 2009).Control factors are

    easily adjustable and it is set by the manufacturer. These factors are most important indetermining the quality characteristics. Noise factors are difficult, impossible, or

    expensive to control (weather, temperature, humidity etc.). The S/N ratio is the ratio of

    mean (signal) to the standard deviation (noise). There are several S/N ratios availabledepending on the type of characteristics

    ( Mahapatra et.al., 2008 ; Sanjit Moshat et al., 2010).Usually three types of S/N ratio

    analysis are applicable:

    1) smaller is better

    n

    = -10 log 1/n yi2

    i=1

    2) nominal is the bestn

    = -10 log 1/n 2/2

    i=1

    3) higher is better.

    n

    = -10 log 1/n 1/yi2

    i=1

    = S/N ratio, yi = value of quality characteristic at ith setting, = Mean,n= total number of trial runs at ith setting, = standard deviation.

    Trial

    no.% of defects in experiment

    1 2 3 average S/N ratio

    1 4.00 5.00 5.19 4.73 -13.55

    2 2.67 2.50 1.30 1.71 -7.00

    3 5.33 5.00 5.19 5.18 -14.28

    4 1.33 3.75 2.60 2.56 -8.77

    5 2.67 2.50 2.60 2.59 -8.26

    6 2.67 2.50 2.60 2.59 -8.26

    7 2.67 2.50 2.60 2.59 -8.26

    8 2.67 3.75 5.19 4.31 -12.06

    9 4.00 2.50 2.60 3.03 -9.85

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    In this study, in order to minimize the defects, smaller is better S/N ratio is chosen.Smaller is better S/N ratios are computed and the values are recorded in table 5. The

    main objective of shock absorber process is to minimize the defects by determining

    optimal level of each factor. Since log is monotone decreasing function, it implies that

    we should maximize the S/N ratio.(Fang-Jung Shiou and Chih-Cheng Hsu, 2008).Theaverage values of the painting defects and S/N ratios for each parameter at different

    levels are calculated and are recorded in Table 6.

    Table 6. Average values of painting defects and S/N ratios at different levels

    Factors Level 1 Level 2 Level 3

    Painting

    defects

    S/N

    ratios

    painting

    defects

    S/N

    ratios

    painting

    defects

    S/N

    ratios

    A 4.02 -11.61 2.58 -8.43 3.16 -10.06

    B 3.29 -10.19 2.87 -9.10 3.60 -10.80C 3.73 -11.29 2.58 -8.54 3.45 -10.27

    D 3.45 -10.55 2.45 -7.84 3.87 -11.70

    The values given in table 6 are plotted in fig 2 and fig 3 .Fig 2 and fig 3 show the average

    values of casting defects and S/N ratios for each parameter at different levels. From fig2and fig.3 it is clear that the casting defects are minimum at the parameter levels A2, B2,

    C2 and D2 and the S/N ratios are maximum at the same levels of the parameters (A2, B2,

    C2 and D2.). Since a higher S/N ratio means a better quality characteristic (minimumdefects), the optimal combination of control factor levels is therefore determined as

    A2B2C2D2.

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

    Fig 2 Average values of painting process defects for each parameters

    at different levels

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    A B C D

    1 2 3 1 2 3 1 2 3 1 2 3Fig.3Average values of S/N ratios for each parameter at different levels

    4.4. Analysis of Variance (ANOVA)

    The purpose of ANOVA is to investigate which process parameters significantly affect

    the quality characteristic. The total variation may be decomposed into manycomponents.In this paper, the total variation present in the process is decomposed to the

    following components:

    1. variation due to factor A2. variation due to factor B

    3. variation due to factor C4. variation due to factor D

    5. variation due to error

    The total variation is calculated using the values given in table 4.

    Total variation SST = SSA +SSB +SSC +SSD +SSe

    Variation due to error SSe = SST (SSA +SSB +SSC +SSD)

    Total degrees of freedom T =(A+B+C+D +e)

    e =T (A+B+C+D)

    = 26 (2+2+2+2)= 18

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    Table. 7 ANOVA for painting defects and S/N ratios

    sourcesum of

    squares

    Degrees of

    freedom variance F ratio

    Painting

    defects

    S/N

    ratio

    Painting

    defects

    S/N

    ratio

    Painting

    defects

    S/N

    ratio

    Painting

    defects

    S/N

    ratio

    A 9.44 14.97 2 2 4.72 7.49 8.90 24.87

    B 2.40 4.20 2 2 1.20 2.10 2.26 6.98

    C 6.44 11.39 2 2 3.22 5.70 6.07 18.92

    D 9.63 23.41 2 2 4.81 11.70 9.07 38.89

    error 9.56 0.60 18 2 0.53 0.30 1.00 1.00

    total 37.47 54.57 26 8 1.44 6.82

    The results of analysis of variance (ANOVA) are shown in table 7. In table 7, it is clearthat the parameters A, C and D significantly affect both mean and variation in the

    painting defects.

    5. RESULTS AND DISCUSSIONS

    5.1. Percent contribution

    Percent contribution is the function of the sum of squares of each significant item.Percent contribution to the total sum of square can be used to evaluate the importance of

    a change in the process parameter on these quality characteristics

    (Lakshminarayan and Balasubramanian, 2008; Balamurugan Gopalsamy et al.,2009). It is

    calculated using the formulae given below:

    Percent contribution (P) = (SSA/ SST) *100SSA = SSA (e) (A)

    VA = VA+ V error

    where VA is the expected amount of variation due solely to factor A given below:

    VA = SSA /A

    VA = SSA /A

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    Table 8 ANOVA for painting defects, including percent contribution

    source

    Sum

    ofsquares

    Degrees

    offreedom

    Variance F ratioExpected

    SS'

    Percent

    contribution(P)

    A 9.44 2 4.72 8.90 6.94 18.52

    B 2.40 2 1.20Pooled(2.6)

    C 6.44 2 3.22 6.07 6.44 17.19

    D 9.63 2 4.81 9.07 9.63 25.69

    error

    (pooled)9.56 18 0.53 1.00 14.46 38.60

    total 37.47 26 1.44 37.47 100.00

    Table 9 S/N ratios for painting defects, including percent contribution

    sourcesum of

    squares

    Degrees

    offreedom

    Variance F ratioExpected

    SS'

    Percent

    contribution(P)

    A 14.97 2 7.49 24.87 12.72 23.31

    B 4.20

    C 11.39 2 5.70 18.92 9.68 17.73

    D 23.41 2 11.70 38.89 19.89 36.44

    error(pooled) 0.6 2 0.30 1.00 12.29 22.52

    Total 54.57 8 6.82 54.57 100.00

    The percentage of contribution of flowability, , pointage, and temperature is shown in

    table 8.

    5.2. Estimating the meanFrom table 8, it is clear that factor B has the least effect on the quality characteristic. In

    order to prevent over estimation, factor B is not considered and the estimation of meanfor painting defects is calculated by the following equation: (Te sheng Li et al., 2009)

    =T+ (A2-T) + (C2-T) + (D2-T)

    where T is the average values of painting defects at different levels.The mean for a selected trial condition for parameters at (A2,B2,C2,D2) is 1.11.

    5.2.1. Confidence Interval around the estimated mean

    An important step in Taguchis optimization technique is to conduct confirmation

    experiments for validating the predicted values. Thus a 95% confidence interval (CI) for

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    the predicted mean of optimum quality characteristic on a confirmation test is estimated

    using the following two equations : (Horng Wen Wu and Hui Wen Gu, 2010).CI3 = [ F( , 1, e) Ve (1/eff +1/r)]1/2

    eff = N/ (1+ total DOF associated in the estimate of mean )

    where is the level of risk, Ve is the error variance, e is the degrees of freedom for the error,

    eff is the effective number of replications and r is number of test trials.

    Using the values in Table 5, the CI was calculated as follows

    eff = N/ 1+ (total DOF associated in the estimate of mean )

    = 27/ (1+2)= 9

    = 1- confidence limits ( 95%)= 0.05

    F ratio = (1, 0.05, 18)

    = 4.41 (tabulated)Confidence Interval CI3 = 1.02

    The 95% confidence interval of the predicted optimum of the shock absorber defect is:0.09

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    Table 10 Optimum parameters under economic considerations

    Parameter

    designationParameter

    Optimum

    levels

    Optimum

    value

    A Flowability (sec) 2 20B

    Coating thickness(microns)

    2 40

    C pointage 2 8

    D Temperature (oC) 2 35

    In the same manner calculations are carried out and optimum values are found for

    washing process.

    Table 11 Process parameters with their ranges and values at three levels

    Parameterdesignation

    Process parameters Range Level 1 Level 2 Level 3

    A Total Alkalinity (g/lit.) 40-80 40 70 80

    B Temperature(oC) 45-75 45 60 75

    C Rinsing water (PH) 5.5 -8.5 5.5 6.5 8.5

    D Timing (min) 0-25 5 15 25

    Table 12 Defects and number of defects occurred during the experiments

    Defects defects number

    oil presence over heatedmore time

    taken3 2 3

    oil presence over heated 1 2 1

    oil presencepowder

    deposited2 2 2

    oil presence more time taken 1 2 1

    oil presence 1 1 1

    oil presence 1 1 1

    over heated 1 1 1

    over heated more time taken 1 1 2

    over heated oil presenceMore time

    taken1 3 2

    12 15 14

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    Table 13 washing defects values and signal to noise (S/N) ratios

    against trail numbers

    Trial

    no.% of defects in experiment

    1 2 3 average S/N ratio

    1 4.00 2.50 3.90 3.47 -10.96

    2 1.33 2.50 1.30 1.71 -5.10

    3 2.67 2.50 2.60 2.59 -8.27

    4 1.33 2.50 1.30 1.71 -5.10

    5 1.33 1.25 1.30 1.29 -2.24

    6 1.33 1.25 1.30 1.29 -2.24

    7 1.33 1.25 1.30 1.29 -2.24

    8 1.33 1.25 2.60 1.73 -5.279 1.33 3.75 2.60 2.56 -8.77

    Table 14 Average values of washing process defects and S/N ratios

    at different levels

    Factors Level 1 Level 2 Level 3

    washing

    defects

    S/N

    ratios

    washing

    defectsS/N ratios

    washing

    defects

    S/N

    ratios

    A 2.59 -8.11 1.43 -3.19 1.86 -5.43

    B 2.16 -6.10 1.58 -4.20 2.15 -6.43

    C 2.16 -6.16 2.00 -6.32 1.73 -4.25

    D 2.44 -7.32 1.43 -3.19 2.00 -6.21

    Table 15 ANOVA for washing process defects and S/N ratios

    sourcesum of

    squares

    Degrees of

    freedomVariance F ratio

    washing

    defects

    S/N

    ratio

    washing

    defects

    S/N

    ratio

    washing

    defects

    S/N

    ratio

    washing

    defects

    S/N

    ratio

    A 6.14 36.25 2 2 3.07 18.13 7.51 112.84

    B 1.98 8.54 2 2 0.99 4.27 2.42 26.58

    C 0.87 7.85 2 2 0.44 3.93 1.07 24.45

    D 4.59 27.30 2 2 2.30 13.65 5.62 84.97

    error 7.36 0.32 18 2 0.41 0.16 1.00 1.00

    total 20.95 108.23 26 8 13.53

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    Table 16 ANOVA for washing process defects, including percent contribution

    sourcesum of

    squares

    Degrees

    offreedom

    Variance F ratioExpected

    SS'

    Percent

    contribution(P)

    A 6.14 2 3.07 7.51 5.32 25.40

    B 1.98 2 0.99 pooled(2.42)

    C 0.87 2 0.44 pooled(1.06)

    D 4.59 2 2.30 5.62 3.78 18.02

    error

    (pooled)7.36 18 0.41 1.00 11.85 56.58

    total 20.95 26 20.95 100.00

    Table 17 S/N ratios for washing process defects, including percent contribution

    sourcesum of

    squares

    Degreesof

    freedom

    Variance F ratioExpected

    SS'

    Percent

    contribution(P)

    A 36.25 2.00 18.13 112.84 35.93 33.20

    B 8.54 2.00 4.27 26.58 8.22 7.59

    C 7.85

    D 27.30 2.00 13.65 84.97 26.98 24.93

    error

    (pooled) 0.32 2.00 0.16 1.00 37.10 34.28

    Total 108.23 8.00 13.53 108.23 100.00

    The mean for a selected trial condition for parameters at (A2, B2, C2, D3) is 0.90.

    The 95% confidence interval of the predicted optimum of the shock absorber defect is:

    0.13< 0.90 < 1.67.

    Table 18 Optimum parameters under economic considerations

    Parameter

    designation ParameterOptimum

    levels

    Optimum

    value

    A Total Alkalinity (g/lit.) 2 70

    B Temperature(oC) 2 60

    C Rinsing water(PH) 2 7.5

    D Timing(min) 3 10

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    6. Conclusion

    In this study, Taguchi method has been employed for optimizing the process parametersof painting and washing during shock absorber manufacturing and the following

    conclusions are drawn:

    * It is proved that, the quality of shock absorber is improved by Taguchis method at the

    lowest possible cost.* Ishikawa diagram or cause and effect diagram is very effective to sort out all the

    possible causes affecting the shock absorber quality.

    * The most significant parameters affecting the quality of the shock absorber areidentified by using the FMEA tool.

    * The parameter pointage is significantly affect the painting process and parameter timing

    is significantlyaffect the washing process.

    * The optimum levels of flowability, coating thickness, pointage, and temperature in

    painting process and total alkalinity, temperature, rinsing water, and timing in washingprocess are estimated.

    * The predicted range of optimum painting defects is 0.09

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