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SIGNIFICANCE OF DRILLING PARAMETERS

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SIGNIFICANCE OF DRILLING PARAMETERS Powered By Docstoc
					       INTERNATIONAL JOURNAL OF MECHANICAL
 International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME
          ENGINEERING AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 3, Issue 2, May-August (2012), pp. 200-209
                                                                     IJMET
© IAEME: www.iaeme.com/ijmet.html
Journal Impact Factor (2011): 1.2083 (Calculated by GISI)
www.jifactor.com
                                                                 ©IAEME



         SIGNIFICANCE OF DRILLING PARAMETERS ON
      DELAMINATION FACTOR IN GFRP: AN IMAGE ANALYSIS
                        APPROACH
                  Piyush P. Gohil*, Vijaykumar Chaudhary, Kundan Patel
      Department of Mechanical Engineering, Faculty of Technology and Engineering,
      Charotar University of Science and Technology, Changa-388421 (Gujarat-India)
      * E-mail: piyushgohil.me@charusat.ac.in Ph. No. (+91-9879016723), (91-2697-
                              247500), Fax: (91-2697-247100)

 ABSTRACT

 Drilling is one of the machining processes most widely applied to composite materials;
 nevertheless, these materials are prone to delaminate when subjected to stress
 concentration during machining operations. The damage induced by this operation may
 reduce the component performance drastically. The present study aims to realize drilling
 of glass fibre reinforced plastics (GFRP) with reduced delamination. The effects of feed
 rates, spindle speeds and the geometrical characteristics of the drill on the resulting
 delamination factor values were compared. A plan of experiments, based on the
 orthogonal array, was established considering drilling with prefixed cutting parameters in
 hand lay-up GFRP material. The digital image of the induced damage is analyzed to find
 delamination factor.

 Keywords: GFRP, Delamination, Design of experiments, Image analysis.

 INTRODUCTION

         Fibre reinforced composites are widely recognized for their superior mechanical
 properties and advantages for applications in aerospace, defence and transportation
 sectors [1]. Machining operations in composites can be accomplished using conventional
 machinery with some adaptations. Among the usual machining processes used on
 composite materials, drilling is one of the most frequently adopted to make holes for
 screws, rivets and bolts. As composites are neither homogeneous nor isotropic, drilling
 raises specific problems that can be related with subsequent damage in the region around
 the drilled holes. The most frequent defects caused by drilling are delamination, fibre
 pull-out, interlaminar cracking or thermal degradation [2]. Among the various defects
 that are caused by drilling, delamination is recognized as the most critical. Delamination
 is defined as “the separation of the layers of material in a laminate.”

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        Several techniques have been employed to measure delamination after drilling
composites, as shop microscope [3, 6], S-Can [1, 7] and digital photography [4, 8–11].
Generally speaking, a quantitative evaluation is required in order to assess the effect of
both the principal cutting parameters and the geometry of the drill [1–11].
        Damage Models on composite delamination giving a closer look on delamination;
it should be divided into two types, according to their grounds and consequences: one is
commonly known as peel-up delamination and the other as push-down delamination.
Peel-up delamination is caused by the cutting force pushing the abraded and cut materials
to the flute surface – Figure 1. At the beginning of the contact, the cutting edge of the
drill will abrade the laminate. As the drill moves forward it tends to pull the abraded
material along the flute and the material spirals up before being effectively cut. A peeling
force pointing upwards is introduced that tends to separate the upper laminas of the uncut
portion held by the downward acting thrust force. Normally, a reduction in the feed rate
adopted can reduce this effect.




        Figure 1 Peel up Delamination.            Figure 2 Push out delamination.

        On the other hand, push-out delamination is a damage that occurs in interlaminar
regions, so it depends not only on fibre nature but also on resin type and respective
properties. This damage is a consequence of the compressive thrust force that the drill tip
always exerts on the uncut laminate plies of the work piece. At some point, the loading
exceeds the interlaminar bond strength and delamination occurs, before the laminate is
totally penetrated by the drill – figure 2.
       All these defects are unwanted and lead to rejection or rework of the composite
part involved. Both options are very costly and time consuming. These damages are
especially difficult to detect by visual inspection and reduce severely the load carrying
capacity of the laminate part, in particularly under compression loading [12], as already
mentioned.
       Delamination factor is defined by ratio of maximum diameter (of damaged area
around hole) to actual hole area as shown in figure 3. The present work investigates the
influence of the cutting parameters and tool geometry on delamination factor.




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6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME




              Figure 3 Schematic layout of the damage area and hole area.

MATERIALS AND METHODS
       Specimens of 5 mm thickness were prepared using the hand lay-up process as
shown in figure 4. The reinforcement was in the form of uni-directional E-glass fiber and
the matrix was polyester. The fiber volume fraction of 0.56 was achieved for prepared
specimen.




                          Figure 4 Prepared GFRP specimen.

DESIGN OF EXPERIMENTS
        Based on the literature [1-11] it was decided to study the effect of point angle,
feed rate, speed and diameter. This design models have been prepared by choosing three
levels.
        Taguchi design was used for experimentation by applying L27 orthogonal array,
taking three levels for each factor as depicted in Table 1.




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                                 Table 1 Input parameters

            CONTROL         UNIT       LEVEL 1        LEVEL 2       LEVEL 3
             FACTOR

               Feed        mm/rev.         0.1           0.2            0.3

               Speed         Rpm           600           900           1200

            Point angle     Degree           90          104            118

             Diameter        Mm              2              3            4


       The standard HSS twist drills of 2 mm, 3 mm and 4 mm diameter with different
point angles were used in the present investigation. Drilling tests were carried on vertical
machining centre (maximum rpm, 12000, figure 5).




                              Figure 5 Experimental set up.

DAMAGE AREA DETERMINATION
       Different techniques are used to analyse and calculate the damage area of drilled
composites [1-11]. For example, Gao and Kim [13] presented a comparative study on
destructive and non-destructive evaluation techniques for characterizing the impact
damage in carbon-fibre-reinforced composites. They concluded that visual inspection has
a considerable drawback associated to the difficulty in accurately obtaining the profile
and depth of the damage. In present work, the digital image of the damage area is used to
characterize its extension at the drill entrance and exit.
       The image of damage which is shown in figure 6 was taken using a shop
microscope Mitutoyo QS – L 2010 ZB. The images were captured by improving contrast
to have clear separation of delamination. The damaged area was measured by image
analysis using MATLAB as per following steps:
       1. Read the image.
       2. Convert RGB to gray scale image.
       3. Convert greyscale image to binary image.
       4. Remove noise using “imfill” instruction.
       5. Calculate the hole area using “regionprops” instruction.

Figure 7 shows the image area calculation.

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                            Figure 6 Damage at hole periphery.




                             Figure 7 Image area calculation.

RESULTS AND DISCUSSION

        A L27 orthogonal array with, total of 27 experimental runs were carried out.
Table 2 shows the results of delamination factor, for various experimental runs of
drilling.

                              Table 2 Experimental Results.

      Sr. No.     Feed         Speed         Point     Diameter     Delamination
                (mm/rev.)      (rpm)        Angle       (mm)           Factor
                                           (degree)
         1         0.1           600           90          3           1.4551
         2         0.2           900          104          4           1.2330
         3         0.3          1200          118          2           1.1826
         4         0.1           600           90          4           1.0099
         5         0.2           900          104          2           1.6155
         6         0.3          1200          118          3           1.4270


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

         7         0.1          600           90           2           1.2112
         8         0.2          900          104           3           1.4837
         9         0.3         1200          118           4           1.6645
        10         0.1          900          118           3           1.3288
        11         0.2         1200           90           4           1.2637
        12         0.3          600          104           2           2.0942
        13         0.1          900          118           4           1.6224
        14         0.2         1200           90           2           1.8779
        15         0.3          600          104           3           1.6185
        16         0.1          900          118           2           1.5369
        17         0.2         1200           90           3           1.2748
        18         0.3          600          104           4           1.1422
        19         0.1         1200          104           3             2439
                                                                       1.2439
        20         0.2          600          118           4           1.5161
        21         0.3          900           90           2           1.3480
        22         0.1         1200          104           4           1.3956
        23         0.2          600          118           2           1.3330
        24         0.3          900           90           3           1.2443
        25         0.1         1200          104           2           1.0914
        26         0.2          600          118           3           1.4182
        27         0.3          900           90           4           2.1696


                                              delamination factor with different speed and
       Figure 8(a) – 8(c) shows the effect of delamin
point angle at various drill diameters. It is observed that with increase in speed the
delamination factor decreases and with higher point angle it increases.




                                          8(a)




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




                                            8(b)




                                            8(c)
             Figure 8 Effect of speed and point angle on delamination factor.
                                                a                           .

        Figure 9(a) – 9(c) shows the effect of delamination factor with different feed rate
and point angle at various drill diameters. It is observed that with increase in the feed rate
the delamination factor increases and is maximum for the 4 mm drill diameter.




                                                9(a)




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




                                               9(b)




                                               9(c)

           Figure 9 Effect of feed rate and point angle on delamination factor.
                                                                        factor

        The main effect of feed rate, spindle speed, point angle and drill diameter on
                                                 whi
delamination factor is represented in figures 10 which, indicates that the increase in feed
rate increases the delamination factor, whereas the increase in speed decreases the
delamination factor. It is observed that the 90o point angle gives minimum delamination
factor.




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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


                                 Main Effects Plot for delamination factor
                                                   Data Means

                                       feed                            speed
                   1.55
                   1.50
                   1.45
                   1.40
                   1.35
            Mean




                           0.1         0.2          0.3         600     900      1200
                                    point angle                       diameter
                   1.55
                   1.50
                   1.45
                   1.40
                   1.35

                           90          104         118          2        3        4




                      Figure 10 Main effect plots for delamination factor.

CONCLUSION

    Based on the experimental results obtained and concerning the damage induced after
drilling GFRP using drills with different geometries, the following conclusions are
extracted:

   •   Within the cutting range tested, delamination factor decreases as the spindle speed
       is elevated.
   •   At high spindle speed with higher drill diameter the delamination factor increases.
   •   With increase in the feed rate the delamination factor increases.
   •   The delamination factor is lower for the 90o drill point angle and increases with
       increase in point angle.


ACKNOWLEDGEMENTS

The authors gratefully acknowledge the use of machine vision lab facility developed
under AICTE – MODROB scheme (F. No. 8024/RIFD/MOD-51/2010-11).


REFERENCES

  [1] H. Hocheng, C. C. Tsao. “Effects of special drill bits on drilling-induced
  delamination of composite materials”. International Journal of Machine Tools &
  Manufacture, 2006, 1403–1416.


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6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME

  [2] C.W. Wern, M. Ramulu and A. Shukla. “Investigation of stresses in the orthogonal
  cutting of fibre-reinforced plastics - experimental mechanics”, 1994, 33-41.
  [3] J. P. Davim, P. Reis. “Drilling carbon fiber reinforced plastics (CFRP)
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  [4] H. Hocheng, C. C. Tsao. “The path towards delamination – free drilling of
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  [5] U. A. Khashaba. “Delamination in drilling GFR-thermoset composites”.
  Composite Structure, 2004, 313–327.
  [6] J. P. Davim, P. Reis. “Study of delamination in drilling carbon fiber reinforced
  plastics (CFRP) using design experiments”. Composite Structure, 2003, 481–487.
  [7] S. Arul, L. Vijayaraghavan, SK. Malhotrab, R. Krishnamurthy. “The effect of
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  [10] E. Aoyama, H. Nobe, T. Hirogaki. “Drilled hole damage of small diameter in
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