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INTERNATIONAL Mechanical Engineering and Technology (IJMET), ISSN 0976 –
  International Journal of JOURNAL OF MECHANICAL ENGINEERING
  6340(Print), ISSN 0976 –AND TECHNOLOGYSep- Dec (2012) © IAEME
                          6359(Online) Volume 3, Issue 3, (IJMET)


ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)                                                    IJMET
Volume 3, Issue 3, September - December (2012), pp. 531-544
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2012): 3.8071 (Calculated by GISI)
                                                                        ©IAEME
www.jifactor.com


       INVESTIGATION OF POST PROCESSING TECHNIQUES TO
      REDUCE THE SURFACE ROUGHNESS OF FUSED DEPOSITION
                       MODELED PARTS
      Addanki Sambasiva Rao1*, Medha A Dharap2, J V L Venkatesh3, Deepesh Ojha4
         1
            Assistant Professor, Department of Mechanical Engineering, Veermata Jijabai
                 Technological Institute, Mumbai, India. Email: asrao@vjti.org.in
       2
         Professor, Department of Mechanical Engineering, Veermata Jijabai Technological
                       Institute, Mumbai, India. Email: madharap@vjti.org.in
         3
           Associate Professor, Production Engineering Department, SGGSIE&T, Nanded,
                      Maharashtra, India. Email: meghavenkatesh@gmail.com
      4
        PG Student, Department of Mechanical Engineering, Veermata Jijabai Technological
                     Institute, Mumbai, India. Email: deepeshojha@gmail.com

  ABSTRACT
           Fused Deposition Modeling is most popular rapid prototyping process because of its
  faster, economical and clean technology, however it suffers from low surface finish quality.
  To improve its surface finish quality, various attempts had been made by several researchers
  by controlling various process parameters. The main objective of this research is to apply
  chemical treatment processes through Design of Experiments using different chemicals with
  variant conditions like different levels of concentration, time of exposure, temperatures and
  initial roughness, interaction effects of the process parameters have also been analyzed.
  ANOVA technique is used to find out the significant factors affecting the surface finish.
  Results show satisfactory improvement in surface finish of FDM parts (ABS) with simple
  inexpensive and harmless chemical treatment processes.

  Keywords : Acrylonitrile Butadiene Styrene (ABS), ANOVA, Chemical Treatment, Design
  of Experiments, Fused Deposition Modeling, Post-Processing, Surface Roughness.

  I. INTRODUCTION
          Rapid prototyping (RP) technologies provide the ability to fabricate initial prototypes
  from various model materials. Stratasys’s Fused Deposition Modeling (FDM) is a typical RP
  process that can fabricate prototypes out of ABS plastic [1]. FDM rapid prototyping process
  is quite popular in industry for various reasons such as: different raw materials (thermo
  plastics) can be used as long as the appropriate hot head is available; FDM parts are very
  strong and hence can work as functional parts; it does not employ lasers, hence is less

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

expensive and there are no safety related issues; It does not use liquid/powder raw materials
and hence is a clean process; It can be kept in an office environment as a 3D printer; very
easy to remove the support material; this is probably the easiest of all RP processes; this is
the cheapest technology; etc.
         Parts produced by FDM are, however, less accurate than those produced by other
rapid prototyping processes such as Stereo lithography Apparatus (SLA), Solid Ground
Curing (SGC). Besides, FDM process is very slow as every point of the volume is addressed
by a mechanical device. The key issue with FDM process is surface roughness because of its
staircase effect (the angle between the vertical axis and surface tangents) [2]. The poor
surface finish affects the functioning of RP parts, depending on the geometry of the enclosing
surface, the building strategy, layer thickness and orientation of the part; this drawback may
outweigh the advantages of RP parts [3].
         In literature, several researchers have proposed various methods to reduce the surface
roughness of the FDM parts of ABS material. One of the prominent methods is to control the
process parameters like layer thickness, build orientation, raster width, raster angle, air gap
etc.. In this method process parameters were optimized using statistical techniques like design
of experiments and gray relational analysis have been integrated for obtaining the optimum
process parameter values [3]. The process parameters influence the responses in a highly non-
linear manner; therefore, prediction of overall dimensional accuracy is made based on
artificial neural network (ANN) [4]. Several algorithms were also developed to obtain
optimum part deposition orientation for fused deposition modeling process for enhancing part
surface finish and reducing build time [5, 6].
         Another method is adaptive slicing scheme in which slices of different thicknesses in
different zones are produced while building the part [7-10]. Daekeon Ahn et al investigated
the relation between surface roughness and overlap interval [11], they also analyzed and
discussed the effects of surface angle and filament section shape to the surface roughness.
Debapriya Chakraborty et al introduced a new kind of deposition method called Curved layer
FDM or CLFDM which offers solution to the issues of surface roughness and strength for
thin curved shell-type parts, this process proposes an entirely new building paradigm for
FDM, the filaments would be deposited along curved (essentially non horizontal) paths
instead of planar (horizontal) paths [12]. A mathematical technique has been developed by
W. Rattanawong et al to determine best part orientation based on minimum volume error
(VE) in the part due to staircase effect [13]. Noshir A. Langrana et al have developed a
method to fabricate the highest quality of multi-material parts. In this method, a virtual
simulation system and experimental real time video microscopy have been developed. In this
virtual simulation, one can check or test a variety of the layered manufacturing process
parameters, and make the best selection of tool path and other parameters to obtain high
quality parts [14]
    One more method for improving surface finish is chemical treatment method which has
been proposed by L.M. Galantucci et al [2]. In this chemical treatment method
,‘Dimethylketone (Acetone)’ with 90% concentrated solution and 10% water was used and
parts were immersed in diluted solution for 5 minutes and also suggested that further studies
need to be conducted on freeform products, also using other dimethylketone solvents such as
ethylene and using designed experiments to optimize the process in terms of the solution
concentration and process time. To the best of the author’s knowledge, no investigations of
chemical treatment method have been reported since the work of L.M. Galantucci et al. and
hence the present study has been undertaken by the authors to investigate the optimum
conditions for obtaining best surface finish from the chemical treatment process.

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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II. PROBLEM DEFINITION
        L.M. Galantucci et al [2] had proposed a method of chemical treatment of ABS
(Acrylonitrile Butadiene Styrene) parts which yields a significant improvement of the surface
finish of the treated specimens. The chemical treatment method is economical, fast and easy
to use. However chemical treatment method has not been analyzed considering different
types of chemicals, different concentration levels of chemicals, effect of elevated
temperatures, different initial roughness of the parts, time of exposure along with the
underlying interaction effects for obtaining optimum surface finish. This paper reports design
of experiments for analyzing chemical post processing treatment method to identify main
controlling factors, side effects of the process parameter settings and disturbances to the
process for ABS plastics.

III.METHODOLOGY

    In this paper we will be optimizing the chemical treatment process using Design of
Experiments (DOE). The factors affecting the chemical treatment process were identified by
performing numerous trials, based on these trials concentration, temperature, time of
exposure and initial roughness were identified as possible main factors. These are analyzed
using Design of Experiments (DOE). DOE is done for two different chemicals i.e.
Dimethylketone (Acetone) and Methylethylketone (MEK), test specimen selected are shown
in Fig.1(a) to Fig.1(e)... The optimization method is based on Design of Experiments (DOE)
and Analysis of Variance (ANOVA). It identifies significant parameters affecting the surface
finish, to which more attention must be paid in order to attain best possible results.

3.1 Statistical Design Of Experiments
     Statistical DOE refers to the process of planning the experiment so that appropriate data
that can be analyzed by statistical methods will be collected, resulting in valid and objective
conclusions [15,16]. A statistical tool is always preferred for drawing the meaningful
conclusion from a experimental design data. There are two aspects to any experimental
problem; the design of the experiment and the statistical analysis of the data. When many
factors control the performance of any system then it is essential to find out significant
factors which need special attention either to control or optimize the system performance.
Taguchi’s concept of Orthogonal Array (OA) as a part of Statistical DOE is used in such
situations to plan the set of experiments and ANOVA technique is used to find out the
significant factors.
     These techniques have been used in the current study to investigate significant factors
affecting the surface roughness of FDM parts (ABS P400) out of concentration of solution C,
temperature of the chemical bath Tp, initial roughness of parts Ri and Time for which the
parts are treated Tm. The first step in constructing an orthogonal array to fit a specific case
study is to count the total degrees of freedom that tell the minimum number of experiments
that must be performed to study all the chosen control factors. The number of degrees of
freedom associated with a factor is equal to one less than the number of levels for that factor.
In this experiment we decided to analyze surface finish for four different concentrations of
chemicals. For Acetone concentration levels of 90%, 85%, 80%, 70% were taken and time of
bath of 5 min and 10 min were found to be suitable on the other hand for Methyl ethyl ketone
concentration of 20%, 25%, 30%, 35% were taken, also 3 min and 6 min were found to be
suitable exposure time. These chemicals have higher diffusion rate at elevated temperatures
so two different temperatures i.e. 25°C and 55°C were chosen.
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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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                             Table 1 Factors and their levels for experiment
                                                                        Levels
          Sr. No.                Control Factors                  1      2            3    4
             1      C (% of concentration)       Chemical 1 70               80       85   90
                                                 Chemical 2 20               25       30   35
             2      Tp (◦C)                                 25-30            50-70    -    -
             3      Ri (Initial Roughness, µm)              0.254            0.3302   -    -
             4      Tm(Time of exposure in Min.) Chemical 1 5                10       -    -
                                                 Chemical 2 3                6
     Initial roughness of the parts was taken as roughness corresponding to 0.2540 layer thickness and
0.3302 layer thickness. Time of exposure was also identified as factor affecting the results of chemical
treatment process. Therefore degrees of freedom (DOF) of factors are (C(3), Tm(1), Ri(1), Tm(1).
Degrees of freedom of their interactions are (C&Tp (3), C&Tm(3), Tm&Tp(1). Considering all the
factors and their interactions there are 13 degrees of freedom. Hence this experiment is carried out
using L16, orthogonal array for 4 factors one at 4 level and 3 at 2 levels to design the experiments for
finding out the surface roughness of given parts under the simultaneous variation of 4 different
parameters at different levels as shown in Table 1.




Figure1(a) Test Specimen with 0.2540 mm                    Figure1(b) Test specimen with 0.3302
mm layer thickness                                         layer thickness of Sample1/A1




      Figure 1(c) Sample 2/A2          Figure 1(d) Sample 3              Figure 1(e) Sample 4

 In total, L16 has 15 degrees of freedom. The remaining (15-13) two degrees of freedom are used for
error. The design of experiments based on the L16 array for the present case is shown in Table 2.
Inability to distinguish effect of factors and interactions is called confounding [16]. As it is expected
that factors C, Tm, Tp to interact, no factors are assigned to columns 5, 6 and 7. This is done to avoid
confounding. The results of surface roughness value of various FDM samples with combinations of
parameters for chemical 1 are shown in Table 2. Similar results for chemical 2 is shown in Table 3

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

           Table 2 Orthogonal Array L16 with results of trials for chemical 1


C(1) Tp(2) Ri(3) Tm(4) CxTp(5) CxTm(6) TpxTm(7)              A11     A12    A13      A2


 1     1       1      1                                      1.182   5.99   1.934   1.63


 1     1       2      2                                      0.676   5.25   2.237   5.73


 1     2       1      2                                      0.302 3.139 1.288      1.12


 1     2       2      1                                      0.242 4.968 2.674      3.95


 2     1       2      1                                      0.263 4.187 0.837      4.53


 2     1       1      2                                      0.988 4.935 0.942      1.78


 2     2       2      2                                      0.147   0.64   0.54    4.08


 2     2       1      1                                      0.196 0.274 0.171      1.28


 3     1       2      1                                      0.141   0.67   0.622   0.22


 3     1       1      2                                      0.115 0.156 0.134 0.295


 3     2       2      2                                      0.102 0.165    0.22     1.9


 3     2       1      1                                      0.15    0.424 0.407 0.151


 4     1       1      1                                      0.281 0.855    0.12    0.264


 4     1       2      2                                      0.277 0.583 0.132 0.382


 4     2       1      2                                      0.371 0.463 0.142 0.367


 4     2       2      1                                      0.101 0.141 0.171 0.496


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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
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        Trials were carried out according to the various combinations of parameters displayed
in the Orthogonal Array and the results for surfaces roughness values were recorded. Three
readings were taken on sample1, A11 correspondence to the top surface, A12 correspondence
to the reading along the build direction, A13 correspondence to the reading perpendicular to
the build direction. These were then analyzed to obtain the optimum condition using
MINITAB software. The Data Means plot for main effects and interaction plots for Chemical
1 is shown in Fig.2.The S-N ratio plot for main effects and interaction plots for Chemical 1 is
shown in Fig 3. The experimental data was solved using both Data Means and S-N Ratio. The
condition was S-N Ratio taken was Smaller is Better hence we will be accepting the higher
value as preferred value from the graph where as in means graph lower value will be taken as
preferred value. Results from both Data Means and S-N Ratio give the same optimized
condition. Data Means plot for main effects and interaction plots for Chemical 2 is shown in
Fig.4 and S-N ratio plot for main effects and interactions is shown in Fig.5.



                                    Main Effects Plot (data means) for Means                                               Interaction Plot (data means) for Means
                                         concent rat ion                      temp                                                25           55
                                                                                                3                                                                                      concentration
                     2.5
                                                                                                                                                                                                  70
                     2.0                                                                        2                                                                                                 80
                                                                                                          concentr ation                                                                          85
                     1.5                                                                                                                                                                          90
                                                                                                1
                     1.0
 Mean of Means




                     0.5                                                                                                                                                           3   temp
                                                                                                                                                                                          25
                           70            80       85                90   25             55                                                                                         2      55
                                          roughness                            t ime                                                   temp
                                                                                                                                                                                   1
                     2.5

                     2.0                                                                        3                                                                                      time
                                                                                                                                                                                          5
                     1.5
                                                                                                2                                                                                        10
                     1.0                                                                                                                                     time
                                                                                                1
                     0.5

                                0.2540                     0.3302         5             10           70     80     85      90                           5                10




Figure-2 (a)                                                                                   Figure-2 (b)

                                                    Figure 2-Main effects and Interaction Plots for data means




                                  Main Effects Plot (data means) for SN ratios                                          Interaction Plot (data means) for SN ratios
                                                                                                                                 25           55
                                         concent ration                       temp
                     10                                                                         10                                                                                     concentration
                                                                                                                                                                                                  70
                      5                                                                                                                                                                           80
                                                                                                 0
                                                                                                          concentr ation                                                                          85
                      0
                                                                                                                                                                                                  90
 Mean of SN ratios




                      -5                                                                       -10
                                                                                                                                                                              10       temp
                     -10                                                                                                                                                                  25
                           70            80         85              90   25            55                                                                                                 55
                                                                                                                                                                              0
                                                                                                                                       temp
                                          roughness                           time
                     10
                                                                                                                                                                              -10
                      5                                                                         10                                                                                     time
                                                                                                                                                                                          5
                      0
                                                                                                                                                                                         10
                                                                                                 0
                                                                                                                                                            time
                      -5

                     -10                                                                       -10

                                0.2540                     0.3302        5             10            70     80     85      90                       5               10

Signal-to-noise: Smaller is better                                                            Signal-to-noise: Smaller is better


Figure-3 (a)                                                                                 Figure-3 (b)

                                                      Figure 3-Main effects and Interaction Plots for S-N Ratio



                                                                                                536
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME

                                     Table 3 Orthogonal Array L16 with results of trials for chemical 2
 C(1)                              Tp(2)    Ri(3) Tm(4) CxTp(5) CxTm(6) TpxTm(7) M11 M12                                                                                                           M13
  1                                  1        1      1                                       2.048 0.594                                                                                           8.081
  1                                  1        2      2                                       0.106 0.215                                                                                           0.082
  1                                  2        1      2                                       0.147 0.14                                                                                            0.123
  1                                  2        2      1                                       2.277 0.526                                                                                           6.045
  2                                  1        2      1                                       1.606 1.972                                                                                           4.247
  2                                  1        1      2                                       1.312 0.42                                                                                            3.283
  2                                  2        2      2                                       1.367 0.291                                                                                           3.775
  2                                  2        1      1                                       1.129 0.217                                                                                            0.33
  3                                  1        2      1                                       0.097 0.143                                                                                           0.178
  3                                  1        1      2                                       0.308 0.253                                                                                           0.258
  3                                  2        2      2                                       0.236 0.387                                                                                            0.32
  3                                  2        1      1                                        0.16 0.244                                                                                           0.216
  4                                  1        1      1                                       0.612 1.279                                                                                            1.66
  4                                  1        2      2                                       0.136 1.832                                                                                           1.294
  4                                  2        1      2                                       0.137 0.268                                                                                           0.241
  4                                  2        2      1                                       2.048 0.594                                                                                           8.081

                                    Main Effects Plot (data means) for Means                                              Interaction Plot (data means) for Means
                                                                                                                                 25          55
                                         concentration                       temp
                     2.5                                                                  4
                                                                                                                                                                                   concentration
                                                                                                                                                                                              20
                     2.0
                                                                                                                                                                                              25
                                                                                          2                                                                                                   30
                     1.5                                                                                 concentr ation
                                                                                                                                                                                              35
                     1.0
 Mean of Means




                                                                                          0                                                                                    4
                     0.5                                                                                                                                                           temp
                                                                                                                                                                                      25
                           20            25         30             35   25          55                                                                                                55
                                                                                                                                                                               2
                                                                                                                                      temp
                                          roughness                          time
                     2.5

                     2.0                                                                  4                                                                                    0
                                                                                                                                                                                   time
                     1.5                                                                                                                                                              3
                                                                                                                                                                                      6
                     1.0                                                                  2
                                                                                                                                                           time

                     0.5
                                                                                          0
                                0.2540                    0.3302        3           6              20      25     30       35                         3               6




Figure-4 (a)                                                                Figure-4 (b)
                                                Figure 4-Main effects and Interaction Plots for Means (MEK)

                                  Main Effects Plot (data means) for SN ratios                                          Interaction Plot (data means) for SN ratios
                                         concent ration                      temp                                                25          55
                     10                                                                                                                                                            concentration
                                                                                              10                                                                                              20
                       5                                                                                                                                                                      25
                                                                                               0          concentr ation                                                                      30
                       0                                                                                                                                                                      35
 Mean of SN ratios




                                                                                          -10
                      -5
                                                                                                                                                                                   temp
                     -10                                                                                                                                                  10          25
                           20            25       30               35   25          55                                                                                                55
                                          roughness                          time                                                     temp                                0

                     10
                                                                                                                                                                          -10

                       5                                                                                                                                                           time
                                                                                              10                                                                                      3
                       0
                                                                                                                                                                                      6
                                                                                               0                                                          time
                      -5
                                                                                          -10
                     -10
                                0.2540                    0.3302        3           6               20      25     30      35                     3               6

Signal-to-noise: Smaller is better                                                       Signal-to-noise: Smaller is better


Figure-5 (a)                              Figure-5 (b)
            Figure 5-Main effects and Interaction Plots for S-N Ratio (MEK)
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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME

3.2 Analysis of variance

    The results obtained for surface roughness data from the white light interferometer (WLI)
data are analyzed by using the statistical tool ANOVA. It determines the relative effect of the
individual factors and their interactions on the surface roughness of parts. The analysis by
using ANOVA technique is done analytically. An equation for total variation may be written
as

SS               = SS   C   + SS           + SS                     + SS        + SS          +   SS          + SS            (1)
      T                             Tp                         Ri          Tm          TmxC            TpxC           TmxTp




where SST is total sum of squares, SSC, SSTp, SSRi, SSTm, are sum of squares for Concentration
C, Temperature Tp, Initial roughness Ri, Time Tm. SSTmxc, SSTpxc, , SSTmXTp are sum of
squares of Concentration-Temperature, Concentration -Time and Time-Temperature
interactions respectively and SSE is sum of square of the error. If T is the sum of all (N)
Surface roughness values, the total sum of squares is given by

              N         
                             T 2                  (2)
 SS   T    = 
                ∑  Fi 2  −
                             N
             i = 1
                        
                         

Sum of squares of Concentration(C) factor is given as


                    N Ci           2
                                              T 2
SS         C     = ∑                       −                              (3)
                    i=1 N         Ci          N


where, N is the number of levels of Concentration factor, Ci and NCi are the sum and number
of observations respectively under ith level. Similarly, sum of squares of other five factors can
also be calculated. Sum of squares of interaction of C and Tm is given by

                    n  ( CXTm )   T 2                  2


                 = ∑             −                 i
SS                                        − SS − SS                                                             (4)
                           N     
                                                                                        C              Tm

                    i =1
          CXTm
                                       N
                                
                                         ( CXTm   )i




where (C xTm)i and N(CXTm)i are the sum and number of observations (surface roughness)
respectively under ith condition of the combinations of factors C and Tm and n is the number
of possible combinations of the interacting factors C and Tm. Similarly, the sum of squares
for other two interactions can also be found out. The results obtained from ANOVA for
chemical 1 and chemical 2 are given in Table 4 and Table 5 respectively.



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

                         Table-4 ANOVA table for Chemical 1

     Source                          DF         Seq SS          Percent contribution


     Concentration                   3          955.65                 65.90

     Temp                            1          42.45                   2.93

     Initial roughness               1          105.92                  7.30

     Time                            1          18.84                   1.30

     Concentration*Temp              3          161.79                 11.16

     Concentration*Time              3          68.9                    4.75

     Temp*Time                       1          81.09                   5.59

     Residual Error                  2          15.55                   1.07

     Total                           15         1450.2                 100.00


                         Table-5 ANOVA table for Chemical 2

    Source                                DF           Seq SS        Percent
                                                                     contribution

    Concentration                         3            770.72             37.78

    Temp                                  1            288.32             14.13

    Initial roughness                     1            12.13               0.59

    Time                                  1            11.69               0.57

    Concentration*Temp                    3            644.31             31.59

    Concentration*Time                    3            286.54             14.05

    Temp*Time                             1            10.95               0.54

    Residual Error                        2            15.23               0.75

    Total                                 15           2039.9             100.00


                                          539
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME
                                                         Sep

IV. RESULTS

        All the test sample from group 1 to 16 having average minimum and maximum
roughness 5.56 micron and 6.67 micron respectively had experienced reduced roughness
value after the chemical treatment. The minimum average roughness observed is equal to
                          treatment
0.175 micron and maximum average roughness equal to 3.47 micron for Chemical 1 and
average minimum 0.134 micron and maximum 3.58 micron for chemical 2. Fig.6 shows
                                       maximum
effect of chemical treatment on average roughness value for chemical 1 and chemical 2.
    The roughness values are analyzed on the basis on DOE and ANOVA for both the
chemicals. Following are the detailed explanation of results:-

4.1 CHEMICAL 1

       From the ANOVA table (Table 4) we find that for chemical 1 the most important
factor is concentration contributing 65.9%, concentration-temperature interaction is the
                                                  concentration temperature
second most important factor contributing 11.16% followed by initial roughness 7.3% time of
exposure is the least significant factor. Fig.2 and Fig.3 also display the similar results.



                                                                            7
                                                                            6
                                                                            5
                                                                            4
                                                                            3
                                                                            2
                                                                            1
                                                                            0
                                                                    15 16
                                                           12 13 14
                                           7   8   9 10 11
     Ra(initial)




                                   5   6
   Ra(acetone)




                               4
    Ra(MEK)




                   1   2   3
                                                                                Ra(initial)

                                                                                Ra(acetone)

                                                                                Ra(MEK)



     Figure 6 Effect of chemical treatment on average roughness value of Group1
                                                                         Group1-16

It is observed from Fig.2(a) and Fig.3(a) that the optimum condition is C4-Tp2- Ri1-Tm1 i.e.
                          (a)     F
level 4 for concentration (90%) , level 2 for temperature (55°C) , level 1 for initial roughness
                                                          (55°C)
(corresponding to layer thickness 0.2540 mm) and level 1 for exposure time (5 min. is the
                                                                                     min.)
optimum condition without taking interaction into account. Since it is clear from the results
                 tion                                                    clear
from ANOVA that concentration temperature interaction is the second most important factor
                      concentration-temperature
contributing 11.16% so when considering interactions CxTp and Tp xTm we can conclude
                                                                          Tm
from Fig.2(b) and Fig.3(b) that the optimum condition is C3-Tp2- Ri1-Tm1.



                                                      540
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME

4.2 CHEMICAL 2

    From Table 5 we find that for chemical 2, concentration, concentration- temperature
interaction, temperature and concentration-time interaction are the most significant factor
contributing 37.78%, 31.59%, 14.13% and 14.05% respectively.
From Fig4.(a) and Fig.5(a) we find that the optimum condition for chemical 2 is C3-Tp2-
Ri1-Tm1 i.e. 30% concentration, 55 °C temperature of bath, initial roughness corresponding
to 0.2540 mm layer thickness and 3 minutes exposure time. It is obvious from ANOVA
analysis that concentration - temperature interaction is the most dominant factor after
concentration factor in this chemical treatment process contributing 31.59% followed by
concentration-time interaction. Considering both C xTm and CxTp interactions we find from
Fig.4 (b) and Fig.5 (b) that the optimum condition is C3-Tp2-Ri1-Tm2.
       Samples were treated at both the conditions without interaction and with interaction
for both the chemicals 1 & chemical 2. Table 6 shows the tabulated results and roughness
values at optimum levels. It is clear from Table 6 that optimum condition with interaction
gives better results for both chemical 1 and chemical 2. Condition 1 refers to the optimum
condition without taking account for interaction while condition 2 refers to optimum
condition when taking account for interactions.

    Table 6 Results for optimum condition and roughness values at optimum levels.

Factors                          Acetone                         Methyl Ethyl Ketone
                    Condition 1(      Condition      Condition 1           Condition 2
                    C4-Tp2- Ri1-      2(C3-Tp2- Ri1- (C3-Tp2-Ri1-          (C3-Tp2-Ri1-
                    Tm1)              Tm1)           Tm1)                  Tm2)
C(% of              90                 85             30                    30
concentration)
Tp(◦C)              55                 25                55                 55
Ri (Initial         0.254              0.254             0.254              0.254
Roughness, µm)
Tm (Time of         5                  10                3                  6
exposure in
Min.)
Average             0.367              0.175             0.314              0.143
roughness value,
Ra ( µm)

Further a comparison is made between results obtained with chemical 1 and chemical 2 on
four different samples which were manufactured on Stratasys’s ‘Dimension SST 1200’ FDM
machine. Sample 1 is a cube as shown in Fig.1(a) & Fig.1(b), sample 2 is shown in Fig.1(c),
sample 3 is shown in Fig.1(d) and sample 4 is shown in Fig.1(e).The results with
comparisons for chemical 1 and chemical 2 is shown in Table 7. Fig.7 shows the original
part where as Fig.8 and Fig.9 show the parts treated with Chemical 1 and Chemical 2
respectively at their optimum conditions.




                                            541
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME

                    Table 7 Comparison between Chemical 1 and Chemical 2

                   Chemical 1( Acetone)                Chemical 2 ( Methylethylketone)
Sampl
es       Roughn     Aestheti    Curi    %            Roughn     Aestheti   Curi    %
         ess at     c           ng      change       ess at     c          ng      change
         optimu     appeara     Time    in           optimu     appeara    Time    in
         m cond.    nce         hrs     dimensi      m cond.    nce        hrs     dimensi
         µm                             ons          µm                            ons
Sampl     0.175     Very        1       Less         0.143      Glossy     2       Less
e1                  smooth              than                                       than 1%
                                        0.5%
Sampl    1.13       Very        1       Less         0.98       Glossy     2       Less
e2                  smooth              than                                       than 1%
                                        0.5%
Sampl    0.847      Very        1       Less         0.495      Glossy     2       Less
e3                  smooth              than                                       than 1%
                                        0.5%
Sampl    3.3        Very        1.5     Less         2.12       Glossy     3       Less
e4                  smooth              than                                       than 1%
                                        0.5%




    Figure 7(original)         Figure 8(Chemical1)           Figure 9(Chemical2)


The original part as shown in Fig.7 is made of ABS material in white & blue color, but the
chemically treated parts as shown in Fig.8 and Fig.9 are made of ABS material in white
color.
The size of the specimen was measured before and after the chemical treatment process in
order to account for the variation in dimensions due to chemical treatment process. Base
lengths were taken as l1 and l2 , height of the specimen was taken as H. Readings were taken
by ACCURATE SPECTRA co-ordinate measuring machine. The results show less than 1%
deviation. Detailed results are shown in Table 8.

                                            542
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME

         Table 8 Average change in dimension after chemical treatment process.

                                     Length L1         Length L2       Height H (mm)
                                     (mm)              (mm)
Chemical 1        Average            -0.42             -0.51           -0.43
                  Variance           0.01              0.01            0.01
Chemical 2        Average            -0.64             -0.68           -0.51
                  Variance           0.01              0.01            0.01
The cost of the chemical treatment process is compared with the commercially available
systems and the same is listed in the Table 9. It is observed from the Table 9 that the
proposed system is economical to use and has very small setup cost as compared to the
commercial system available in the market.

 Table 9 Cost comparison of proposed chemical treatment process with other available
                                   commercial system.
Sr.                   Capital Cost, Depreciation, Raw        Power           Labour
No                    INR(Approx.) INR             Material  Consumption Cost
                                                   cost per  cost per        per
                                                   part*,    hour, INR       hour,
                                                   INR                       INR
    1. Acetone
                         10000       2.78 per day       32          6           50
       process
    2. MEK
                         10000       2.78 per day       21          6           50
       process
    3. Commercial
                        35, 00000    959 per day        42         15           50
       system
* for part size 50x50x25 mm

V.CONCLUSION

         In this paper the surface roughness of FDM prototype parts is addressed, the parameters that
have significant effect on the surface roughness (Ra) value in the chemical treatment process have
been identified. The chemical treatment process is optimized in terms of solution concentration, time
of exposure, initial roughness and temperature of the chemical bath using Design of Experiments and
ANOVA. Two different chemical were taken, i.e. Dimethyl ketone (Acetone) and Methyl ethyl ketone
(MEK), in case of Acetone it was observed that the solution concentration, concentration-temperature
interaction and the initial roughness are the most significant factors. For Methyl ethyl ketone chemical
treatment process, it was observed that the concentration, concentration - temperature interaction and
concentration-time interaction are the most important factors, surprisingly for MEK the initial
roughness and time of exposure have negligible effect on the process. The process was applied for
simple parts to complex free form parts. The optimum levels for the parameters for chemical
treatment process are found out which shows drastic improvement in surface finish. The appearance
of the finished parts is comparable to plastic moulded parts, the parts have glossy finish and the
maximum curing time is about 2 to 4 hours. The process is very much economical compared to other
commercial systems available in the market. Further studies can be carried out to commercialize this
process to make it available in the market at an affordable price.


                                                  543
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME

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                                           544

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Investigation of post processing techniques to reduce the surface roughness of fused deposition modeled parts

  • 1. INTERNATIONAL Mechanical Engineering and Technology (IJMET), ISSN 0976 – International Journal of JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 –AND TECHNOLOGYSep- Dec (2012) © IAEME 6359(Online) Volume 3, Issue 3, (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) IJMET Volume 3, Issue 3, September - December (2012), pp. 531-544 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2012): 3.8071 (Calculated by GISI) ©IAEME www.jifactor.com INVESTIGATION OF POST PROCESSING TECHNIQUES TO REDUCE THE SURFACE ROUGHNESS OF FUSED DEPOSITION MODELED PARTS Addanki Sambasiva Rao1*, Medha A Dharap2, J V L Venkatesh3, Deepesh Ojha4 1 Assistant Professor, Department of Mechanical Engineering, Veermata Jijabai Technological Institute, Mumbai, India. Email: asrao@vjti.org.in 2 Professor, Department of Mechanical Engineering, Veermata Jijabai Technological Institute, Mumbai, India. Email: madharap@vjti.org.in 3 Associate Professor, Production Engineering Department, SGGSIE&T, Nanded, Maharashtra, India. Email: meghavenkatesh@gmail.com 4 PG Student, Department of Mechanical Engineering, Veermata Jijabai Technological Institute, Mumbai, India. Email: deepeshojha@gmail.com ABSTRACT Fused Deposition Modeling is most popular rapid prototyping process because of its faster, economical and clean technology, however it suffers from low surface finish quality. To improve its surface finish quality, various attempts had been made by several researchers by controlling various process parameters. The main objective of this research is to apply chemical treatment processes through Design of Experiments using different chemicals with variant conditions like different levels of concentration, time of exposure, temperatures and initial roughness, interaction effects of the process parameters have also been analyzed. ANOVA technique is used to find out the significant factors affecting the surface finish. Results show satisfactory improvement in surface finish of FDM parts (ABS) with simple inexpensive and harmless chemical treatment processes. Keywords : Acrylonitrile Butadiene Styrene (ABS), ANOVA, Chemical Treatment, Design of Experiments, Fused Deposition Modeling, Post-Processing, Surface Roughness. I. INTRODUCTION Rapid prototyping (RP) technologies provide the ability to fabricate initial prototypes from various model materials. Stratasys’s Fused Deposition Modeling (FDM) is a typical RP process that can fabricate prototypes out of ABS plastic [1]. FDM rapid prototyping process is quite popular in industry for various reasons such as: different raw materials (thermo plastics) can be used as long as the appropriate hot head is available; FDM parts are very strong and hence can work as functional parts; it does not employ lasers, hence is less 531
  • 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME expensive and there are no safety related issues; It does not use liquid/powder raw materials and hence is a clean process; It can be kept in an office environment as a 3D printer; very easy to remove the support material; this is probably the easiest of all RP processes; this is the cheapest technology; etc. Parts produced by FDM are, however, less accurate than those produced by other rapid prototyping processes such as Stereo lithography Apparatus (SLA), Solid Ground Curing (SGC). Besides, FDM process is very slow as every point of the volume is addressed by a mechanical device. The key issue with FDM process is surface roughness because of its staircase effect (the angle between the vertical axis and surface tangents) [2]. The poor surface finish affects the functioning of RP parts, depending on the geometry of the enclosing surface, the building strategy, layer thickness and orientation of the part; this drawback may outweigh the advantages of RP parts [3]. In literature, several researchers have proposed various methods to reduce the surface roughness of the FDM parts of ABS material. One of the prominent methods is to control the process parameters like layer thickness, build orientation, raster width, raster angle, air gap etc.. In this method process parameters were optimized using statistical techniques like design of experiments and gray relational analysis have been integrated for obtaining the optimum process parameter values [3]. The process parameters influence the responses in a highly non- linear manner; therefore, prediction of overall dimensional accuracy is made based on artificial neural network (ANN) [4]. Several algorithms were also developed to obtain optimum part deposition orientation for fused deposition modeling process for enhancing part surface finish and reducing build time [5, 6]. Another method is adaptive slicing scheme in which slices of different thicknesses in different zones are produced while building the part [7-10]. Daekeon Ahn et al investigated the relation between surface roughness and overlap interval [11], they also analyzed and discussed the effects of surface angle and filament section shape to the surface roughness. Debapriya Chakraborty et al introduced a new kind of deposition method called Curved layer FDM or CLFDM which offers solution to the issues of surface roughness and strength for thin curved shell-type parts, this process proposes an entirely new building paradigm for FDM, the filaments would be deposited along curved (essentially non horizontal) paths instead of planar (horizontal) paths [12]. A mathematical technique has been developed by W. Rattanawong et al to determine best part orientation based on minimum volume error (VE) in the part due to staircase effect [13]. Noshir A. Langrana et al have developed a method to fabricate the highest quality of multi-material parts. In this method, a virtual simulation system and experimental real time video microscopy have been developed. In this virtual simulation, one can check or test a variety of the layered manufacturing process parameters, and make the best selection of tool path and other parameters to obtain high quality parts [14] One more method for improving surface finish is chemical treatment method which has been proposed by L.M. Galantucci et al [2]. In this chemical treatment method ,‘Dimethylketone (Acetone)’ with 90% concentrated solution and 10% water was used and parts were immersed in diluted solution for 5 minutes and also suggested that further studies need to be conducted on freeform products, also using other dimethylketone solvents such as ethylene and using designed experiments to optimize the process in terms of the solution concentration and process time. To the best of the author’s knowledge, no investigations of chemical treatment method have been reported since the work of L.M. Galantucci et al. and hence the present study has been undertaken by the authors to investigate the optimum conditions for obtaining best surface finish from the chemical treatment process. 532
  • 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME II. PROBLEM DEFINITION L.M. Galantucci et al [2] had proposed a method of chemical treatment of ABS (Acrylonitrile Butadiene Styrene) parts which yields a significant improvement of the surface finish of the treated specimens. The chemical treatment method is economical, fast and easy to use. However chemical treatment method has not been analyzed considering different types of chemicals, different concentration levels of chemicals, effect of elevated temperatures, different initial roughness of the parts, time of exposure along with the underlying interaction effects for obtaining optimum surface finish. This paper reports design of experiments for analyzing chemical post processing treatment method to identify main controlling factors, side effects of the process parameter settings and disturbances to the process for ABS plastics. III.METHODOLOGY In this paper we will be optimizing the chemical treatment process using Design of Experiments (DOE). The factors affecting the chemical treatment process were identified by performing numerous trials, based on these trials concentration, temperature, time of exposure and initial roughness were identified as possible main factors. These are analyzed using Design of Experiments (DOE). DOE is done for two different chemicals i.e. Dimethylketone (Acetone) and Methylethylketone (MEK), test specimen selected are shown in Fig.1(a) to Fig.1(e)... The optimization method is based on Design of Experiments (DOE) and Analysis of Variance (ANOVA). It identifies significant parameters affecting the surface finish, to which more attention must be paid in order to attain best possible results. 3.1 Statistical Design Of Experiments Statistical DOE refers to the process of planning the experiment so that appropriate data that can be analyzed by statistical methods will be collected, resulting in valid and objective conclusions [15,16]. A statistical tool is always preferred for drawing the meaningful conclusion from a experimental design data. There are two aspects to any experimental problem; the design of the experiment and the statistical analysis of the data. When many factors control the performance of any system then it is essential to find out significant factors which need special attention either to control or optimize the system performance. Taguchi’s concept of Orthogonal Array (OA) as a part of Statistical DOE is used in such situations to plan the set of experiments and ANOVA technique is used to find out the significant factors. These techniques have been used in the current study to investigate significant factors affecting the surface roughness of FDM parts (ABS P400) out of concentration of solution C, temperature of the chemical bath Tp, initial roughness of parts Ri and Time for which the parts are treated Tm. The first step in constructing an orthogonal array to fit a specific case study is to count the total degrees of freedom that tell the minimum number of experiments that must be performed to study all the chosen control factors. The number of degrees of freedom associated with a factor is equal to one less than the number of levels for that factor. In this experiment we decided to analyze surface finish for four different concentrations of chemicals. For Acetone concentration levels of 90%, 85%, 80%, 70% were taken and time of bath of 5 min and 10 min were found to be suitable on the other hand for Methyl ethyl ketone concentration of 20%, 25%, 30%, 35% were taken, also 3 min and 6 min were found to be suitable exposure time. These chemicals have higher diffusion rate at elevated temperatures so two different temperatures i.e. 25°C and 55°C were chosen. 533
  • 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table 1 Factors and their levels for experiment Levels Sr. No. Control Factors 1 2 3 4 1 C (% of concentration) Chemical 1 70 80 85 90 Chemical 2 20 25 30 35 2 Tp (◦C) 25-30 50-70 - - 3 Ri (Initial Roughness, µm) 0.254 0.3302 - - 4 Tm(Time of exposure in Min.) Chemical 1 5 10 - - Chemical 2 3 6 Initial roughness of the parts was taken as roughness corresponding to 0.2540 layer thickness and 0.3302 layer thickness. Time of exposure was also identified as factor affecting the results of chemical treatment process. Therefore degrees of freedom (DOF) of factors are (C(3), Tm(1), Ri(1), Tm(1). Degrees of freedom of their interactions are (C&Tp (3), C&Tm(3), Tm&Tp(1). Considering all the factors and their interactions there are 13 degrees of freedom. Hence this experiment is carried out using L16, orthogonal array for 4 factors one at 4 level and 3 at 2 levels to design the experiments for finding out the surface roughness of given parts under the simultaneous variation of 4 different parameters at different levels as shown in Table 1. Figure1(a) Test Specimen with 0.2540 mm Figure1(b) Test specimen with 0.3302 mm layer thickness layer thickness of Sample1/A1 Figure 1(c) Sample 2/A2 Figure 1(d) Sample 3 Figure 1(e) Sample 4 In total, L16 has 15 degrees of freedom. The remaining (15-13) two degrees of freedom are used for error. The design of experiments based on the L16 array for the present case is shown in Table 2. Inability to distinguish effect of factors and interactions is called confounding [16]. As it is expected that factors C, Tm, Tp to interact, no factors are assigned to columns 5, 6 and 7. This is done to avoid confounding. The results of surface roughness value of various FDM samples with combinations of parameters for chemical 1 are shown in Table 2. Similar results for chemical 2 is shown in Table 3 534
  • 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table 2 Orthogonal Array L16 with results of trials for chemical 1 C(1) Tp(2) Ri(3) Tm(4) CxTp(5) CxTm(6) TpxTm(7) A11 A12 A13 A2 1 1 1 1 1.182 5.99 1.934 1.63 1 1 2 2 0.676 5.25 2.237 5.73 1 2 1 2 0.302 3.139 1.288 1.12 1 2 2 1 0.242 4.968 2.674 3.95 2 1 2 1 0.263 4.187 0.837 4.53 2 1 1 2 0.988 4.935 0.942 1.78 2 2 2 2 0.147 0.64 0.54 4.08 2 2 1 1 0.196 0.274 0.171 1.28 3 1 2 1 0.141 0.67 0.622 0.22 3 1 1 2 0.115 0.156 0.134 0.295 3 2 2 2 0.102 0.165 0.22 1.9 3 2 1 1 0.15 0.424 0.407 0.151 4 1 1 1 0.281 0.855 0.12 0.264 4 1 2 2 0.277 0.583 0.132 0.382 4 2 1 2 0.371 0.463 0.142 0.367 4 2 2 1 0.101 0.141 0.171 0.496 535
  • 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Trials were carried out according to the various combinations of parameters displayed in the Orthogonal Array and the results for surfaces roughness values were recorded. Three readings were taken on sample1, A11 correspondence to the top surface, A12 correspondence to the reading along the build direction, A13 correspondence to the reading perpendicular to the build direction. These were then analyzed to obtain the optimum condition using MINITAB software. The Data Means plot for main effects and interaction plots for Chemical 1 is shown in Fig.2.The S-N ratio plot for main effects and interaction plots for Chemical 1 is shown in Fig 3. The experimental data was solved using both Data Means and S-N Ratio. The condition was S-N Ratio taken was Smaller is Better hence we will be accepting the higher value as preferred value from the graph where as in means graph lower value will be taken as preferred value. Results from both Data Means and S-N Ratio give the same optimized condition. Data Means plot for main effects and interaction plots for Chemical 2 is shown in Fig.4 and S-N ratio plot for main effects and interactions is shown in Fig.5. Main Effects Plot (data means) for Means Interaction Plot (data means) for Means concent rat ion temp 25 55 3 concentration 2.5 70 2.0 2 80 concentr ation 85 1.5 90 1 1.0 Mean of Means 0.5 3 temp 25 70 80 85 90 25 55 2 55 roughness t ime temp 1 2.5 2.0 3 time 5 1.5 2 10 1.0 time 1 0.5 0.2540 0.3302 5 10 70 80 85 90 5 10 Figure-2 (a) Figure-2 (b) Figure 2-Main effects and Interaction Plots for data means Main Effects Plot (data means) for SN ratios Interaction Plot (data means) for SN ratios 25 55 concent ration temp 10 10 concentration 70 5 80 0 concentr ation 85 0 90 Mean of SN ratios -5 -10 10 temp -10 25 70 80 85 90 25 55 55 0 temp roughness time 10 -10 5 10 time 5 0 10 0 time -5 -10 -10 0.2540 0.3302 5 10 70 80 85 90 5 10 Signal-to-noise: Smaller is better Signal-to-noise: Smaller is better Figure-3 (a) Figure-3 (b) Figure 3-Main effects and Interaction Plots for S-N Ratio 536
  • 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table 3 Orthogonal Array L16 with results of trials for chemical 2 C(1) Tp(2) Ri(3) Tm(4) CxTp(5) CxTm(6) TpxTm(7) M11 M12 M13 1 1 1 1 2.048 0.594 8.081 1 1 2 2 0.106 0.215 0.082 1 2 1 2 0.147 0.14 0.123 1 2 2 1 2.277 0.526 6.045 2 1 2 1 1.606 1.972 4.247 2 1 1 2 1.312 0.42 3.283 2 2 2 2 1.367 0.291 3.775 2 2 1 1 1.129 0.217 0.33 3 1 2 1 0.097 0.143 0.178 3 1 1 2 0.308 0.253 0.258 3 2 2 2 0.236 0.387 0.32 3 2 1 1 0.16 0.244 0.216 4 1 1 1 0.612 1.279 1.66 4 1 2 2 0.136 1.832 1.294 4 2 1 2 0.137 0.268 0.241 4 2 2 1 2.048 0.594 8.081 Main Effects Plot (data means) for Means Interaction Plot (data means) for Means 25 55 concentration temp 2.5 4 concentration 20 2.0 25 2 30 1.5 concentr ation 35 1.0 Mean of Means 0 4 0.5 temp 25 20 25 30 35 25 55 55 2 temp roughness time 2.5 2.0 4 0 time 1.5 3 6 1.0 2 time 0.5 0 0.2540 0.3302 3 6 20 25 30 35 3 6 Figure-4 (a) Figure-4 (b) Figure 4-Main effects and Interaction Plots for Means (MEK) Main Effects Plot (data means) for SN ratios Interaction Plot (data means) for SN ratios concent ration temp 25 55 10 concentration 10 20 5 25 0 concentr ation 30 0 35 Mean of SN ratios -10 -5 temp -10 10 25 20 25 30 35 25 55 55 roughness time temp 0 10 -10 5 time 10 3 0 6 0 time -5 -10 -10 0.2540 0.3302 3 6 20 25 30 35 3 6 Signal-to-noise: Smaller is better Signal-to-noise: Smaller is better Figure-5 (a) Figure-5 (b) Figure 5-Main effects and Interaction Plots for S-N Ratio (MEK) 537
  • 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME 3.2 Analysis of variance The results obtained for surface roughness data from the white light interferometer (WLI) data are analyzed by using the statistical tool ANOVA. It determines the relative effect of the individual factors and their interactions on the surface roughness of parts. The analysis by using ANOVA technique is done analytically. An equation for total variation may be written as SS = SS C + SS + SS + SS + SS + SS + SS (1) T Tp Ri Tm TmxC TpxC TmxTp where SST is total sum of squares, SSC, SSTp, SSRi, SSTm, are sum of squares for Concentration C, Temperature Tp, Initial roughness Ri, Time Tm. SSTmxc, SSTpxc, , SSTmXTp are sum of squares of Concentration-Temperature, Concentration -Time and Time-Temperature interactions respectively and SSE is sum of square of the error. If T is the sum of all (N) Surface roughness values, the total sum of squares is given by  N  T 2 (2) SS T =   ∑ Fi 2  −  N i = 1    Sum of squares of Concentration(C) factor is given as  N Ci 2  T 2 SS C = ∑  − (3)  i=1 N Ci  N where, N is the number of levels of Concentration factor, Ci and NCi are the sum and number of observations respectively under ith level. Similarly, sum of squares of other five factors can also be calculated. Sum of squares of interaction of C and Tm is given by  n  ( CXTm )   T 2 2 = ∑   − i SS − SS − SS (4)  N  C Tm  i =1 CXTm N    ( CXTm )i where (C xTm)i and N(CXTm)i are the sum and number of observations (surface roughness) respectively under ith condition of the combinations of factors C and Tm and n is the number of possible combinations of the interacting factors C and Tm. Similarly, the sum of squares for other two interactions can also be found out. The results obtained from ANOVA for chemical 1 and chemical 2 are given in Table 4 and Table 5 respectively. 538
  • 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table-4 ANOVA table for Chemical 1 Source DF Seq SS Percent contribution Concentration 3 955.65 65.90 Temp 1 42.45 2.93 Initial roughness 1 105.92 7.30 Time 1 18.84 1.30 Concentration*Temp 3 161.79 11.16 Concentration*Time 3 68.9 4.75 Temp*Time 1 81.09 5.59 Residual Error 2 15.55 1.07 Total 15 1450.2 100.00 Table-5 ANOVA table for Chemical 2 Source DF Seq SS Percent contribution Concentration 3 770.72 37.78 Temp 1 288.32 14.13 Initial roughness 1 12.13 0.59 Time 1 11.69 0.57 Concentration*Temp 3 644.31 31.59 Concentration*Time 3 286.54 14.05 Temp*Time 1 10.95 0.54 Residual Error 2 15.23 0.75 Total 15 2039.9 100.00 539
  • 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Sep IV. RESULTS All the test sample from group 1 to 16 having average minimum and maximum roughness 5.56 micron and 6.67 micron respectively had experienced reduced roughness value after the chemical treatment. The minimum average roughness observed is equal to treatment 0.175 micron and maximum average roughness equal to 3.47 micron for Chemical 1 and average minimum 0.134 micron and maximum 3.58 micron for chemical 2. Fig.6 shows maximum effect of chemical treatment on average roughness value for chemical 1 and chemical 2. The roughness values are analyzed on the basis on DOE and ANOVA for both the chemicals. Following are the detailed explanation of results:- 4.1 CHEMICAL 1 From the ANOVA table (Table 4) we find that for chemical 1 the most important factor is concentration contributing 65.9%, concentration-temperature interaction is the concentration temperature second most important factor contributing 11.16% followed by initial roughness 7.3% time of exposure is the least significant factor. Fig.2 and Fig.3 also display the similar results. 7 6 5 4 3 2 1 0 15 16 12 13 14 7 8 9 10 11 Ra(initial) 5 6 Ra(acetone) 4 Ra(MEK) 1 2 3 Ra(initial) Ra(acetone) Ra(MEK) Figure 6 Effect of chemical treatment on average roughness value of Group1 Group1-16 It is observed from Fig.2(a) and Fig.3(a) that the optimum condition is C4-Tp2- Ri1-Tm1 i.e. (a) F level 4 for concentration (90%) , level 2 for temperature (55°C) , level 1 for initial roughness (55°C) (corresponding to layer thickness 0.2540 mm) and level 1 for exposure time (5 min. is the min.) optimum condition without taking interaction into account. Since it is clear from the results tion clear from ANOVA that concentration temperature interaction is the second most important factor concentration-temperature contributing 11.16% so when considering interactions CxTp and Tp xTm we can conclude Tm from Fig.2(b) and Fig.3(b) that the optimum condition is C3-Tp2- Ri1-Tm1. 540
  • 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME 4.2 CHEMICAL 2 From Table 5 we find that for chemical 2, concentration, concentration- temperature interaction, temperature and concentration-time interaction are the most significant factor contributing 37.78%, 31.59%, 14.13% and 14.05% respectively. From Fig4.(a) and Fig.5(a) we find that the optimum condition for chemical 2 is C3-Tp2- Ri1-Tm1 i.e. 30% concentration, 55 °C temperature of bath, initial roughness corresponding to 0.2540 mm layer thickness and 3 minutes exposure time. It is obvious from ANOVA analysis that concentration - temperature interaction is the most dominant factor after concentration factor in this chemical treatment process contributing 31.59% followed by concentration-time interaction. Considering both C xTm and CxTp interactions we find from Fig.4 (b) and Fig.5 (b) that the optimum condition is C3-Tp2-Ri1-Tm2. Samples were treated at both the conditions without interaction and with interaction for both the chemicals 1 & chemical 2. Table 6 shows the tabulated results and roughness values at optimum levels. It is clear from Table 6 that optimum condition with interaction gives better results for both chemical 1 and chemical 2. Condition 1 refers to the optimum condition without taking account for interaction while condition 2 refers to optimum condition when taking account for interactions. Table 6 Results for optimum condition and roughness values at optimum levels. Factors Acetone Methyl Ethyl Ketone Condition 1( Condition Condition 1 Condition 2 C4-Tp2- Ri1- 2(C3-Tp2- Ri1- (C3-Tp2-Ri1- (C3-Tp2-Ri1- Tm1) Tm1) Tm1) Tm2) C(% of 90 85 30 30 concentration) Tp(◦C) 55 25 55 55 Ri (Initial 0.254 0.254 0.254 0.254 Roughness, µm) Tm (Time of 5 10 3 6 exposure in Min.) Average 0.367 0.175 0.314 0.143 roughness value, Ra ( µm) Further a comparison is made between results obtained with chemical 1 and chemical 2 on four different samples which were manufactured on Stratasys’s ‘Dimension SST 1200’ FDM machine. Sample 1 is a cube as shown in Fig.1(a) & Fig.1(b), sample 2 is shown in Fig.1(c), sample 3 is shown in Fig.1(d) and sample 4 is shown in Fig.1(e).The results with comparisons for chemical 1 and chemical 2 is shown in Table 7. Fig.7 shows the original part where as Fig.8 and Fig.9 show the parts treated with Chemical 1 and Chemical 2 respectively at their optimum conditions. 541
  • 12. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table 7 Comparison between Chemical 1 and Chemical 2 Chemical 1( Acetone) Chemical 2 ( Methylethylketone) Sampl es Roughn Aestheti Curi % Roughn Aestheti Curi % ess at c ng change ess at c ng change optimu appeara Time in optimu appeara Time in m cond. nce hrs dimensi m cond. nce hrs dimensi µm ons µm ons Sampl 0.175 Very 1 Less 0.143 Glossy 2 Less e1 smooth than than 1% 0.5% Sampl 1.13 Very 1 Less 0.98 Glossy 2 Less e2 smooth than than 1% 0.5% Sampl 0.847 Very 1 Less 0.495 Glossy 2 Less e3 smooth than than 1% 0.5% Sampl 3.3 Very 1.5 Less 2.12 Glossy 3 Less e4 smooth than than 1% 0.5% Figure 7(original) Figure 8(Chemical1) Figure 9(Chemical2) The original part as shown in Fig.7 is made of ABS material in white & blue color, but the chemically treated parts as shown in Fig.8 and Fig.9 are made of ABS material in white color. The size of the specimen was measured before and after the chemical treatment process in order to account for the variation in dimensions due to chemical treatment process. Base lengths were taken as l1 and l2 , height of the specimen was taken as H. Readings were taken by ACCURATE SPECTRA co-ordinate measuring machine. The results show less than 1% deviation. Detailed results are shown in Table 8. 542
  • 13. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table 8 Average change in dimension after chemical treatment process. Length L1 Length L2 Height H (mm) (mm) (mm) Chemical 1 Average -0.42 -0.51 -0.43 Variance 0.01 0.01 0.01 Chemical 2 Average -0.64 -0.68 -0.51 Variance 0.01 0.01 0.01 The cost of the chemical treatment process is compared with the commercially available systems and the same is listed in the Table 9. It is observed from the Table 9 that the proposed system is economical to use and has very small setup cost as compared to the commercial system available in the market. Table 9 Cost comparison of proposed chemical treatment process with other available commercial system. Sr. Capital Cost, Depreciation, Raw Power Labour No INR(Approx.) INR Material Consumption Cost cost per cost per per part*, hour, INR hour, INR INR 1. Acetone 10000 2.78 per day 32 6 50 process 2. MEK 10000 2.78 per day 21 6 50 process 3. Commercial 35, 00000 959 per day 42 15 50 system * for part size 50x50x25 mm V.CONCLUSION In this paper the surface roughness of FDM prototype parts is addressed, the parameters that have significant effect on the surface roughness (Ra) value in the chemical treatment process have been identified. The chemical treatment process is optimized in terms of solution concentration, time of exposure, initial roughness and temperature of the chemical bath using Design of Experiments and ANOVA. Two different chemical were taken, i.e. Dimethyl ketone (Acetone) and Methyl ethyl ketone (MEK), in case of Acetone it was observed that the solution concentration, concentration-temperature interaction and the initial roughness are the most significant factors. For Methyl ethyl ketone chemical treatment process, it was observed that the concentration, concentration - temperature interaction and concentration-time interaction are the most important factors, surprisingly for MEK the initial roughness and time of exposure have negligible effect on the process. The process was applied for simple parts to complex free form parts. The optimum levels for the parameters for chemical treatment process are found out which shows drastic improvement in surface finish. The appearance of the finished parts is comparable to plastic moulded parts, the parts have glossy finish and the maximum curing time is about 2 to 4 hours. The process is very much economical compared to other commercial systems available in the market. Further studies can be carried out to commercialize this process to make it available in the market at an affordable price. 543
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