A Study to Optimize the Casting Process Parameters of Al-365/LM25 Alloy using Taguchi Technique

DOI : 10.17577/IJERTV4IS060502

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A Study to Optimize the Casting Process Parameters of Al-365/LM25 Alloy using Taguchi Technique

Prashanth K Mulge M.Tech Student, Production Engineering,

Department of Mechanical Engineering, PDA College of Engineering, Gulbarga-585102,

Karnataka (INDIA)

Sunil Mangshetty

Assistant Professor, PG, Production Engineering

Department Of Mechanical Engineering, Pda College Of Engineering, Gulbarga-585102

Karnataka, (India)

Abstract: – Taguchi method is a problem solving tool which can improve the performance of the product, process design and system. This method combines the experimental and analytical concepts to determine the most influential parameter on the result response for the significant improvement in the overall performance. In this research Aluminium365/LM25 alloy was prepared by sand casting using three different parameters, Pouring temperature, Pouring time, and cooling time of the casting materials. Dye penetrant test and Ultrasonic test were conducted on each sample to study the surface and internal defects respectively. A tensile and hardness tests were done for the resulted castings. The primary objective is to use Taguchi method for predicting the better parameters that give the highest tensile strength and hardness to the castings, and then preparing casting sample at these parameters and comparing them with the randomly used ones. The experimental and analytical results showed that the Taguchi method was successful in predicting the parameters that give the highest properties and the pouring temperature was the most influential parameter on the tensile strength and hardness results of castings.

Index Term: Aluminium365/LM25, NDT methods, casting defects, Taguchi method, Pareto Anova, Tensile strength, Hardness.

I.INTRODUCTION

Aluminium 365/LM25 alloy is mainly used where good mechanical properties are required in castings of a shape or dimensions requiring an alloy of excellent castability in order to achieve the desired standard of soundness. The alloy is also used where resistance to corrosion is an important consideration, particularly where high strength is also required. It has good weldability.[1]

The wide range of the application of aluminium alloys is very obvious. Their desirable characteristics of light weight, excellent resistance to corrosion in the atmosphere and water, strength and high thermal conductivity gives them an edge over other metals in the electrical, aviation, marine, aerospace, construction and automotive industries just to mention but a few. This increased usage creates the need for a deeper understanding of their mechanical behavior and the influences of processing parameters. This knowledge enables

the designer to ensure that the casting will achieve the desired properties for its intended application. [6]

There is no doubt that casting as a process involves so many parameters such as melting temperature of the charge, temperature of the mould, pouring speed, pouring temperature, composition, microstructure, size of casting, runner size, composition of the alloy and solidification time just to mention but a few. Just to mention but a few have successfully carried out studies on the varying effects of casting process parameters on the mechanical properties of casted metals and their alloys. One of the recent most important optimization processes is the Taguchi method conceived and developed by Japanese scholar Engr. Dr. Genichi Taguchi in 1950. Taguchi technique is a powerful tool for the design of high quality systems. It provides a simple efficient and systematic approach to optimize design for performance, quality and cost. [1]

The methodology is valuable when design parameters are qualitative and discrete. Taguchi parameter design can optimize the performance characteristic through the setting of design parameters and reduce the sensitivity of the system performance to source of variation. [3] The Taguchi approach enables a comprehensive understanding of the individual and combined from a minimum number of simulation trials.

  1. EXPERIMENTAL WORK

    2.1 Samples preparation

    TheAl-365/LM25 is used as a material for samples preparation LM25 alloy is mainly used where good mechanical properties are required in castings of a shape or dimensions requiring an alloy of excellent castability in order to achieve the desired standard of soundness. The alloy is also used where resistance to corrosion is an important consideration, particularly where high strength is also requiredConsequently, LM25 finds application in the food, chemical, marine, electrical and many other industries and, above all, in road transport vehicles where it is used for wheels, cylinder blocks and heads, and other engine and body castings. Table [1] shows the chemical composition of the alloy.

    Table [1] Chemical composition of LM25 alloy

    Element

    Weight (%)

    Copper

    0.2

    Zinc

    0.1

    Magnesium

    0.27

    Lead

    0.1

    Silicon

    7.2

    Tin

    0.05

    Titanium

    0.2

    Manganese

    0.3

    Nickel

    0.1

    Iron

    0.5

    Aluminium

    Balance

    An Electric furnace is used to melt the raw material, sample 1, 2 & 3 are poured at 7000C and samples 4, 5 and 6 are poured at 7500C and samples 7, 8, and 9 are poured at 8000C. A wooden pattern is used for mould preparation and the mould is prepared from sand.The melt temperature was controlled and checked with thermocouple before pouring into a mould shown in figure (1). The dimensions of theresulted castings are (200 X 25 X 15) mm.The pouring time and cooling time are followed as per the Table [2], the figure [1] shows the experimental set up.

    Fig [1] Experimental set up

    Table [2] Control factors value for Sample preparation

    Sample No

    Pouring temp.(0C)

    Pouring time (sec)

    Cooling time(min)

    1

    700

    5

    3

    2

    700

    10

    6

    3

    700

    15

    9

    4

    750

    5

    6

    5

    750

    10

    9

    6

    750

    15

    3

    7

    800

    5

    9

    8

    800

    10

    3

    9

    800

    15

    6

  2. METHODOLOGY

      1. Non Destructive Testing of samples

        1. Dye Penetrant Testing (DPT)

          All the nine samples are tested by dye penetrant testing method to detect the surface defects which are arrived during casting samples preparation. The testing procedure is shown in figure [2].

          Fig [2[ Steps involved in DPT

        2. Ultrasonic Testing (UT)

    All the nine samples are tested byultrasonic testing to detect internal defects present in theprepared samples. An Einstein II(R) ultrasonic flaw detector (UFD) is used to observe the ecoes from the samples and Transmitter- Receiver (TR) probe is used for scanning the Samples for defects. The figure [3] shows the UFD, TR probe and scanning of samples.

    Fig[3] UFD,TR probe and scanning of samples.

      1. Mechanical Testing of samples

        1. Tensile testing

          The fundamental material science testing, in which a sample is subjected to uniaxial tension until failure. The properties that are directly measured via tensile test are maximum elongation, ultimate tensile test and reduction in area. The specimens were prepared as perASTM SA370 Pat-2. The dimension of Specimen is 50 mm gauge length and 10mm thickness for the holding proposes the 25 mm 12.5 mm (width and thickness) on both end is produced. The UTM is as shown in figure[4].

          Fig(4) UTM

          Samples before testing samples after testing

        2. Hardness testing

          Hardness test provides an accurate, rapid and economical way to determine the material deformation. The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. Hardness test has been conducted on each specimen using a load of 250 N and a steel ball indenter of diameter 5 mm as indenter. The diameter of the impression made by indenter has been measured by Brinell microscope.[7]The corresponding values of hardness (BHN) were tabulated. The figure [5] shows the Hardness Tester.

          Fig [5] Hardness tester

      2. Application of Taguchi method

    In order to observe the influencing degree of process parameters in the casting preparation, three parameters namely; (1) Pouring temperature; (2) Pouring time; and (3) Cooling time, each at three levels were considered and are listed in Table [3].Maintaining these processing parameters as constants enabled us to study the effect of Pouring temperature, Pouring time and cooling time on the resulted properties. The degrees of freedom for three parameters in each of three levels were and it is calculated as follows [1] Degree Of Freedom (DOF) = number of levels -1

    For each factor, DOF equal to: For (A); DOF = 3 1 = 2

    For (B); DOF = 3 1 = 2

    For (C); DOF = 3 1 = 2

    In this research nine experiments were conducted at different parameters, and then the specimens were machined and tested by Brinel hardness and tensile test.

    Table [3]Control factors and levels

    Factors

    Control Factor

    Level 1

    Level 2

    Level 3

    A

    Pouring

    temperature (oC)

    700

    750

    800

    B

    Pouring time (Sec)

    5

    10

    15

    C

    Cooling time (min)

    3

    6

    9

    A three level L9 34 orthogonal array Shown in Table [4] with nine experimental runs was selected. The total degree of freedom is calculated from the following

    Total DOF = no. of experiments 1

    The total DOF for the experiment is = 9 1 = 8

    Table [4] L9orthogonal array

    Expt.No

    A

    B

    C

    1

    1

    1

    1

    2

    1

    2

    2

    3

    1

    3

    3

    4

    2

    1

    2

    5

    2

    2

    3

    6

    2

    3

    1

    7

    3

    1

    3

    8

    3

    2

    1

    9

    3

    3

    2

    Taguchi method stresses the importance of studying the response variation using the signal to noise (S/N) ratio, resulting in minimization of quality characteristic variation due to uncontrollable parameter. The tensile strength and hardness were considered the quality characteristic with the concept of "the larger the better". The S/N ratio used for this type response is given by

    S/NLTB= -10log[MSD] . (1)

    .(2)

    Where dB means decibel and Yi is the response value for a

    trial Condition repeated n times. Table [5] indicates the used parameters and the result values of tensile strength and

    Table [6] S/N ratio for Tensile strength and Hardness

    Expt. No

    A

    B

    C

    E

    S/N ratio

    (Tensile strength)

    S/N ratio

    (Hardness BHN)

    1

    1

    1

    1

    1

    48.627

    44.685

    2

    1

    2

    2

    2

    49.217

    45.552

    3

    1

    3

    3

    3

    49.685

    46.424

    4

    2

    1

    2

    3

    51.457

    46.278

    5

    2

    2

    3

    1

    52.297

    41.619

    6

    2

    3

    1

    2

    50.370

    43.834

    7

    3

    1

    3

    3

    53.442

    47.497

    8

    3

    2

    1

    1

    50.075

    46.789

    9

    3

    3

    2

    2

    51.953

    45.320

    Table [7] Pareto ANOVA for three level factors

    Factors

    A

    B

    C

    E

    Total

    Sum at factor level

    A1

    B1

    C1

    E1

    T

    A2

    B2

    C2

    E2

    A3

    B3

    C3

    E3

    Sum of squares of

    difference

    SA

    SB

    SC

    SE

    ST

    Degree of

    freedom

    2

    2

    2

    2

    8

    Contribution

    ratio (X 100)

    SA

    ST

    SB

    ST

    SC

    ST

    SE

    ST

    100

    T=A1+A2+A3

    2 2 2

    hardness .

    Table [5] Experimental observation

    SA= (A1-A2) + (A1-A3) + (A2-A3)

    Expt. No

    A

    B

    C

    Tensile strength N/mm2

    Hardness(BHN)

    Trial

    1

    Trial

    2

    Average

    1

    1550

    30

    5

    270

    171

    172

    171.5

    2

    1550

    40

    10

    289

    190

    189

    189.5

    3

    1550

    50

    15

    305

    p>210

    209

    209.5

    4

    1650

    30

    10

    374

    205

    207

    206

    5

    1650

    40

    15

    412

    120

    121

    120.5

    6

    1650

    50

    5

    330

    156

    155

    155.5

    7

    1750

    30

    15

    470

    237

    237

    237

    8

    1750

    40

    5

    319

    219

    218

    218.5

    9

    1750

    50

    10

    396

    185

    184

    184.5

    SB= (B1-B2)2+ (B1-B3)2+ (B2-B3)2 S = (C -C )2+ (C -C )2+ (C -C )2

    C 1 2 1 3 2 3

    Expt.no: Experiment number, A: Pouring temperature (oC) B: Pouring time (Sec) C: Cooling time (min)

    The casting samples preparation parameters, namely pouring temperature (A), pouring time(B), and cooling time(C) were assigned to the 1st , 2nd and 3rd column of L9 34 array, respectively. The 4th column was assigned as error (E), and was considered randomly. The S/N ratios were computed for tensile strength and hardness in each of the nine trial conditions and their values are given in Table [6].

    SE= (E1-E2)2+ (E1-E3)2+ (E2-E3)2 ST= SA+ SB+ SC+ SE

  3. RESULTS AND DISCUSSIONS

    1. Dye Penetrant Test observations

      When the nine samples are tested by dye penetrant test for surface defects, sample 1,2,3,6 and 9have indicated porosity as shown in figure, sample 8 has indicated porosity and cracks as shown in figure and sample4,5, and 7 are defectless as shown in figure. The possible causes and remedies for these defects are mentioned in Table [8].

      Table [8] Possible causes and remedies for casting defects

      Defect

      Possible causes

      Remedies

      Porosity

      Crack

      • Metal pouring temperature too low

      • Pouring too slowly

      • Increase metal pouring temperature

      • Pour metal as rapidly as possible without interruption.

      • Excessive temperature while pouring

      • Sufficient cooling of the casting in the mold.

    2. Ultrasonic Test observation

      When the samples are scanned ultrasonic flaw detector and TR probe sample 4,5,7 are found with backwall echoes and samples 1,2,3,6,8,9 were found with indication of presence of internal defects in the samples along with the

      backwall echoes and these defects locations are mentioned in Table [9].

      Sample 1 Defective

      Sample 2 Defective

      Sample 3 Defectless

      Sample 4 Defectless

      Sample 5 Defectless

      Sample 6 Defective

      Sample 7 Defectless

      Sample 8 Defective

      Sample 9 Defective

      Table [9]UT Observations

      Sample No

      UT Observations

      1

      At a depth of 12.6 mm a sharp echo is observed it is a defect

      2

      After first backwall echo At a depth of 18 mm a sharp echo is observed it is a defect

      3

      At a depth of 25.6 mm a sharp echo is observed it is

      a defect

      4

      Only four back wall echoes are observed at 10,20,30 & at 40mm so no defect is present

      5

      Only four back wall echoes are observed at 10,20,30

      & at 40mm so no defect is present

      6

      At a depth of 12.8 mm,25mm and 31.2mm echoes

      are observed after the back wall echoes and these are the defects

      7

      Only four back wall echoes are observed at 10,20,30

      & at 40mm so no defect is present

      8

      More echoes are observed in between first and second back wall echoes that is in between 10-

      20mm these all related to defects

      9

      More echoes are observed in after first and second back wall echoes these all related to defects

    3. Pareto ANOVA observations

      Computation scheme of Pareto ANOVA (ANalysis Of VAriance) for three level factors is shown in table [7]. In order to study the contribution ratio of the process parameters, Pareto ANOVA was performed for tensile strength and hardness. The details are given in tables [10] and [11] respectively.

      Table(10) Pareto ANOVA for Tensile strength

      Factors

      A

      B

      C

      E

      Total

      Sum at factor level

      126.41

      128.46

      128.04

      128.35

      386.35

      129.26

      128.90

      128.84

      128.64

      130.68

      128.99

      129.42

      129.34

      Sum of squares of difference

      28.372

      0.483

      3.082

      1.539

      33.476

      Degree of

      freedom

      2

      2

      2

      2

      8

      Contribution ratio

      84.75

      1.45

      9.20

      4.60

      100

      Optimum level

      (1)

      (3)

      (2)

      A3

      B3

      C3

      Optimum

      values

      8000C

      15sec

      9min

      Table (11) Pareto ANOVA for Hardness

      Factors

      A

      B

      C

      E

      Total

      Sum at factor level

      98.535

      98.837

      100.611

      99.083

      299.617

      100.134

      100.647

      99.353

      97.738

      100.948

      100.133

      99.653

      102.796

      Sum of squares of

      difference

      9.042

      5.220

      2.590

      41.179

      58.031

      Degree of

      freedom

      2

      2

      2

      2

      8

      Contributio

      n ratio

      15.59

      8.99

      4.46

      70.96

      100

      Optimum

      level

      (1)

      (2)

      (3)

      A3

      B2

      C1

      Optimum

      values

      8000C

      10Sec

      3min

    4. Effect of Pouring Temperature on Tensile Strength and Hardness

    1. Effect of Cooling Time on Tensile Strength and Hardness

      Graph: 1 Main effect plot for pouring temperature on Tensile strength

      Graph:2 Main effect plot for pouring temperature on Hardness

      5.5 Effect of Pouring Time on Tensile Strength and Hardness

      Graph: 3 Main effect plot for pouring time on Tensile stength

      Graph:4 Main effect plot for pouring time on Hardness

      Graph: 5 Main effect plot for cooling time on Tensile strength

      Graph: 6 Main effect plot for cooling time on Hardness

    2. Discussion

From table [10], it can be seen that the third level of factor (A) give the highest summation (i.e. A3, which is 8000C Pouring temperature). The highest summation for factor (B) is at the third level (i.e. B3, which is 15 seconds pouring time) and the highest summation for factor (C) is at the third level (i.e. C3, which is 9 minutes cooling time). These predicted parameters are not used in the casting sample preparation which indicated in table [2].

We conducted an experiment at the predicted parameters (A=8000C, B=15 Sec and C=9 min), and tested the resulted sample by Tensile test. The resulted tensile strength was 170.64N/mm2 which is greater than the tensile strength values in table [5] .These results have proved the success of Taguchi method in the prediction of the optimum parameters for higher tensile strength.

In table [11] it can be seen that the highest summation is at A3 (8000C Pouring temperature), B2 (10 seconds Pouring time), and C1 (3 minutes Cooling time). The predicted parameter for giving the highest hardness by Taguchi method is already used in our experiments as shown in Table [2] and it gives the highest hardness. This also proves the success of Taguchi method.

In both tables [10] and [11], it was found that the Pouring temperature contributes a larger impact on Tensile strength and Hardness of the casting samples when compared to cooling time and pouring time.

VI.CONCLUSION

In this work Taguchi's off line quality control method was applied to determine the optimal process parameters which maximize the mechanical properties of Aluminium 365/LM25 prepared by Sand casting. For this purpose, concepts like orthogonal array, S/N ratio and ANOVA were employed. After determining the optimum process parameters, one confirmation experiment was conducted. From results the following conclusions were drawn.

  • The optimum level of process parameters to obtain good mechanical properties for the sand casting of Aluminium 365/LM25 are 8000C pouring temperature, 10 seconds Pouring time And 9 minutes cooling time for tensile strength and 8000C pouring temperature, 10 second pouring time and 3 minutes cooling time for hardness.

  • From the pareto analysis it was evident that the Pouring temperature is a major contributing factor for improving tensile strength and hardness.

  • Taguchi method has proved its success in predicting the optimum parameters to reach the best properties.

  • From observation it is conclude that the porosity will occur because of steep temperature gradient due to low and high pouring temperature and cracks are formed due to high pouring temperature.

ACKNOWLEDGEMENT

The authors wishes to thank research paper review committee, Department of Mechanical Engineering, HOD and Principal of PDA College of engineering, Gulbarga for their suggestions, encouragement and support in undertaking the present work

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