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Materials Today: Proceedings 5 (2018) 19011–19018 www.materialstoday.com/proceedings

ICMPC_2018

Optimizing Surface Texture and Coating Thickness of Nickel

Coated ABS-3D Parts
M. S. Khana*, S. B. Mishrab, M Ajay Kumarc, Dipabrata Banerjeed
a
Associate Professor, Kalinga Instituute of Industrial Technology, Deemed to be University, Bhubaneswar -751024, INDIA
b
Assistant Professor, Kalinga Instituute of Industrial Technology, Deemed to be University, Bhubaneswar -751024, INDIA
c,d
Research Scholar, Kalinga Instituute of Industrial Technology, Deemed to be University, Bhubaneswar -751024, INDIA

Abstract
Fused deposition modelling (FDM) is one of the additive manufacturing technique frequently used in industry due to
its simplicity of operation and ability to fabricate parts with locally controlled properties. Material constraints is a
major demerit of FDM build parts apart from the low surface finish. Most of the FDM machines utilizes plastic
materials such as Acrylonitrile Butadiene Styrene (ABS), Poly Lactic Acid(PLA), etc. Metal FDM machines are
being used now a days but it is still in a very nascent stage. In order to build complicated functional parts and to
achieve better mechanical and electrical properties, weight and cost reduction it is necessary to manufacture ABS
parts by FDM and metallise the surface. In this study, Nickel has been considered as the coating material due to its
low cost and aesthetic look. Apart from controlling the important machining parameters such as raster angle (RA)
and air gaps (AG), coating parameters such as 'Voltage' (V) and 'Time of metal plating' (T) are also considered
under controlled environment. The result showed significant improvement in the surface finish of ABS-FDM build
parts.
© 2018 Elsevier Ltd. All rights reserved.
Selection and/or Peer-review under responsibility of Materials Processing and characterization.

Keywords: Additive Manufacturing; FDM; ABS Plastics; Surface Roughness; Raster Angle; Air Gap

1.Introduction
Plastic materials are generally metal plated to bring about properties of the metals to the polymer substrate [1-3].
Metallization on plastic imparts reflectivity, abrasion resistance, electrical conductivity, and a variety of decorative
lusters, high wear and corrosion resistances, electromagnetic shielding, weight reduction, formability enhancements.

*Corresponding author. Tel.

E-mail address: mskhanfme@kiit.ac.in

2214-7853 © 2018 Elsevier Ltd. All rights reserved.

Selection and/or Peer-review under responsibility of Materials Processing and characterization.
19012 M. S. Khan et al./ Materials Today: Proceedings 5 (2018) 19011–19018

High impact resistance and weather proofing, lower cost, flexibility in parts design, and reduced weight compared
to its metal counterparts [4-8]. Metallised plastics become useful in electronic industry, petroleum industry, defence
field, toys manufacturing industry, automotive and computer body parts, electronic housings, wheel covers, lamp
housings, ventilation, air conditioning parts, pipes and fittings, and many more things [9-11]. Generally, non-
conductors (plastics) are utilized as the raw material for fabrication in order to reduce low cost, complex design,
weight reduction and for eliminating secondary operations (no de-flashing or buffing). Among a number of polymer
plastics, Acrylonitrile-Butadiene-Styrene (ABS) is the most widely accepted plastic for metal coating or plating
industry. The reason being, it a ter-polymer thermoplastic that has an acrylonitrile-styrene matrix with butadiene
rubber uniformly distributed in it. This quality makes it unique for plating, as the butadiene can be selectively etched
out of the matrix, leaving microscopic holes that are used as bonding sites by the electroless plate. Further, ABS
polymers exhibit high toughness (even in cold conditions), adequate rigidity, good thermal stability, and high
resistance to chemical attack and environmental stress cracking. Other significant properties of ABS include
cheapness, durability, good metal adhesion to the substrate, good appearance after plating and low coefficient of
thermal expansion. The ease of moulding allows the fabrication of dimensionally stable ABS parts with superior
surface quality. No other thermoplastic material displays such a wonderful combination of technically important
properties. It has a melting temperature of 1040C, tensile strength 3200 psi and Rock well hardness R110 that
provides a better choice of material for plating as far as cost of the product as well as the production is concerned.

Fused deposition modelling (FDM) is one of the most widely used additive manufacturing technique for
fabricating prototypes and functional parts using common engineering plastics. It can handle a range of plastic
materials, low running cost, good accuracy, moderate building speed and require a cold environment. The process is
based on the extrusion of heated feedstock plastic filaments through a nozzle tip to deposit layers onto a platform to
build parts layer by layer directly from a digital model of the part. [12].
Metal plating on plastics are usually carried out in two ways such as electroless plating and electroplating.
Electroless plating evenly deposits an electrically conductive metallic layer on the insulated ABS substrate and also
prepares the surface for further adherent coating of electroplated layer. Electroplating step with the aid of current
builds additional thickness of metals like copper, nickel, or chrome just as and when required by the part or for
finishing purposes [13-18].
Realizing the immense uses of plastics both in industry and domestic applications it is important to address
some issues related to "Plating on plastics" (POP). Firstly, the plastic substrates are electrically non-conductive and
cannot be immersed in a plating solution for electroplating as with metal parts. Therefore, some methods are
required by which a conductive film could be deposited onto the plastics surface to provide the basis for subsequent
metal deposition. Secondly, in addition to being electrically conductive, the deposited metals should adhere
considerably to the plastic substrate for better mechanical and wear property. Thirdly, fabricating complex plastic
components by injection moulding involves high clamping and tooling costs. The defects such as flash, warping,
bubbles, unfilled sections, sink and ejector marks make it difficult to fabricate highly intricate and thin walled
machine parts by injection moulding. The injection moulding products suffers from internal stresses due to the
pressure build up during the moulding process which poses problem of flaking during the metal plating. In order to
overcome all these drawbacks, additive manufacturing is a better option for fabrication of plastic model. This
method eliminates many intermediate stages and defects in production. Fused Deposition Modelling (FDM) is one of
the most popular additive manufacturing process for fabricating prototypes and functional parts due to its low
running cost, good accuracy, moderate building speed and require a cold environment. The present work uses
Acrylonitrile-Butadiene-Styrene (ABS) plastic which is a better choice of material over other plastics.
Currently, studies of plating on ABS, is accomplished by employing two popular methods, viz.
electroplating following the electroless plating process and direct electroplating. Electroless plating route consists of
three major steps of surface preparation such as etching, activation, and metal deposition. Electroplating step with
the aid of current, builds additional thickness of metals like copper, nickel, or chrome just as and when required by
the part or for finishing purposes [19, 20]. However, the electroless plating method suffers from serious drawbacks
since it requires a multi-stage operation, longer deposition times, expensive catalyst, and complex and
environmentally hazardous solutions. Also it is not possible to achieve fair control over film thickness and
uniformity. This calls for alternate procedure development for surface preparation [4, 21]. The first attempt of direct
 M. S. Khan et al./ Materials Today: Proceedings 5 (2018) 19011–19018 19013

electroplating was made in a patented work published in 1972 [22]. The disadvantages of the process include
unavoidable steps of etching and neutralization in most cases, and the need of an expensive catalyst [1].
The related literature reveals that plating on plastics has been least explored related to substrate, coating materials,
mechanical and other properties. Also, it is evident from the literature that AM process is highly beneficial as far as
production of intricate products with low cost is concerned. Therefore, the present work attempts to utilize AM
technology such as FDM process for substrate and electroplating with Nickel. In this study, steps has been taken to
understand the multiple interacting phenomena involved with the process of FDM and metallization of ABS plastics.
Investigation on surface roughness, adhesiveness of coating and thickness of coating have also been carried out as
far as quality of the build part is concerned.

1. Experimental Methods

The FDM modelling process is one of the widely appreciated technology that produces prototypes basically from
acrylonitrile butadiene styrene (ABS) plastic materials by putting semi molten filaments one over another. The
heated filaments are extruded from the extrusion nozzle as defined by the machine software (Insight 10. 2) in a layer
wise manner. FDM manufacturing process is a parametric dependant process. Some process parameters have large
influence over the mechanical properties as well as on the surface texture of the build parts. While using as an end
user product, the wear adversely affects the durability of the FDM build part. Therefore, present research paper is
devoted to study the effect of some important controllable machine process parameters (Raster angle and Air gap)
on the surface roughness and surface texture of the FDM build parts. Other supplementary parameters such as part
contour number, layer thickness, part orientation, interior style, shrinkage factor, perimeter to raster gap etc. are kept
at default levels. Raster angle is the angle of raster with respect to x-axis in the raster fill pattern. The term air gap
represents the distance between two nearby rasters in a layer. The FDM build parts with the said parameters are then
used for metallization with nickel. The purpose of metallization is to make the part electrically conductive for
various applications. It is expected that the raster angle and air gap in the FDM parts will play a major role while
metal plating as far as the adhesive strength of the metal plate on the build part is concerned.
The process of electroplating on ABS plastics is similar to that on metals with the difference that the former
are made conducting by some treatments before electroplating. The preparatory operations on plastic substrates
include etching or conditioning and subsequently coated with graphite powder in order to make it conductive.
All the process parameters (machine parameters and plating parameters) along with their respective levels are
listed below in Table 1.
Table 1. Factors and their Levels

Factors (Units) Low Level (-1) Zero Level (0) High Level (1)
Raster Angle (degree) 0 45 90
Machine Parameter
Air gap (mm) 0 0.05 0.1
Voltage ( volt) 6 9 12
Plating Parameter
Time (min) 10 15 20

2.1. Fabrication of specimens

To study surface roughness and coating thickness of the plated ABS parts, specimens are manufacture using
Fortus 250 mc (Stratsys Inc.) FDM machine. The part specifications are 30×20×5 mm. The parameters set are raster
angle (0o, 45o and 90o) and Air gap (0, .05 and 0.1mm). Since the numbers of experimental runs are 21, for each
experiment three specimens are fabricated. Hence, a total of 63 numbers of Ni specimens have been fabricated. The
material used for fabrication of test specimen is acrylonitrile butadiene styrene (ABS M30).
19014 M. S. Khan et al./ Materials Today: Proceedings 5 (2018) 19011–19018

2.2. Nickel plating of ABS plastics

The coating of a non-metallic object with a metal is known as metallization. Coating is usually done to improve
certain characteristics of the substrate so that it can be used for various other applications like increasing
conductivity, corrosion resistance, for aesthetic purposes, etc. In this research, a number of coating processes have
been studied that can be used to metalize ABS plastic and the most feasible of all i.e. electroplating, has been chosen
keeping in mind the cost and complexity of the process. The substrates have been pre-treated with graphite power
(50 mesh) followed by smoothing the surface with the help of sand paper (1000 grit size dry) Then the specimen is
taken for electroplating. According to the number of experimental runs, 21(average of three specimens with same
parameter settings have been considered as one reading) specimens are plated with different values of parameters
such as voltage and time of plating to see the variation in the surface roughness of the coatings.

2.3. Plating techniques

Electroplating is a metallization process which requires electric current to coat the substrate. An electroplating kit
consists of an Eliminator (dc current source), Standard Electrolyte solution, Cathode (graphitized specimens), Anode
(Ni metal) and beaker or container to hold the solution. In electroplating, the work piece is connected to the cathode
and the coating source to the anode. Both the cathode and the anode are connected to the power source and the
circuit gets completed by dipping both in the electrolyte solution. Refer Fig. 1(a). The nickel coated ABS plastic
specimen is shown in Fig. 1(b).
b
a

Fig.1.(a) Experimental set up for Ni; (b) Ni-Plated Specimen

The following electrolytic solutions are prepared to conduct the experiments by mixing the following Nickel Plating
Electrolytic Solution in appropriate amount in one litre of distilled water
 NiSO4 (275 g/L)
 NiCl2 (55 g/L)
 H3BO3 (45 g/L)
 Brightener spectra 77 (0.3 mL/L)
 Ni additive 22 (3 mL/L), 55-60 °C
2.4. Experimental results
The surface roughness of the Nickel plated FDM Build parts are measured using the surface tester Taylor-
Hobson ,Sutronic 25. Using the metallurgical microscope, surface texture and coating thickness of the Nickel plated
FDM build parts are measured. The surface textures through metallurgical microscope (INVERTED 12V/50Watt –
EWF 10XMG/20) of some of the specimens are shown in Fig. 2 (a) & (b) respectively.
 M. S. Khan et al./ Materials Today: Proceedings 5 (2018) 19011–19018 19015

Fig. 2.(a) Surface Texture of Ni-Plating (Sample 9,11 &18)

Fig. 2. (b) Plating Thickness(Sample 7 & 21)

2. Results
Tests have been conducted on the specimens and the average value for each run is listed in Table 2. The software
Design Expert 9.0 have been used for analysis of the results.

Table 2. Experimental Details

Air gap Voltage Nickel Plated ABS

Sl.No. Raster Angle (A) Time (D)
(B) (C) Surface Roughness Plating Thickness
1 90 0.1 12 5 1.98 35.65
2 90 0.1 6 5 1.93 36.41
3 90 0 12 15 1.36 34.07
4 0 0.1 6 15 2.11 38.24
5 90 0 6 15 2.01 32.51
6 0 0 12 5 1.92 35.68
7 0 0.1 12 15 1.99 36.87
8 0 0 6 5 1.83 44.68
9 0 0.05 9 10 1.71 61.65
10 90 0.05 9 10 2.08 34.56
11 45 0 9 10 1.68 32.07
12 45 0.1 9 10 2.04 38.62
13 45 0.05 6 10 1.98 36.12
14 45 0.05 12 10 1.78 36.21
15 45 0.05 9 5 1.98 35.67
16 45 0.05 9 15 2.05 36.57
17 45 0.05 9 10 1.85 34.56
18 45 0.05 9 10 1.85 33.25
19 45 0.05 9 10 1.85 34.34
20 45 0.05 9 10 1.85 34.19
21 45 0.05 9 10 1.85 34.65
19016 M. S. Khan et al./ Materials Today: Proceedings 5 (2018) 19011–19018

The experimental data obtained using FCCCD design runs are fitted with following empirical model (Equation
1):

γ=β +∑ β x +∑ β x +∑ ∑β x x (1)

where y is the performance measure and xi and xj are ith and jth factor respectively, k is the total number of factors. In
the analysis of variance (ANOVA) table, the terms which have the P value less than 0.05 are considered as the
significance parameters with 95% confidence level.

3. Analysis of results

In the Analysis of Variance (ANOVA) table shown in Table 3, the significant terms influencing the surface
roughness of Nickel plated FDM built parts can be identified at significance level of 0.05. However, time (D) is not
a significant parameters but its interaction with other parameters exhibits significant influence. The coefficient of
determination (R2), which indicates the percentage of variation explained by the terms in the model to the total
variation in the response, is 0.9791 for coating thickness of Ni plated FDM Parts. It is to be noted from the table that
lack of fit is not significant. Residual analysis has been carried out and found that residuals are normally distributed.
The Regression Model for Surface Roughness of Ni plating involving all important parameters is shown in equation
6. The optimal parameter setting to minimize the surface roughness of Nickel Plated ABS parts is shown in Table 4.
Table 3. ANOVA Table for Surface Roughness of Nickel plated FDM Parts
Sum of Mean F p-value
Source Squares df Square Value Prob> F
Model 0.55 14 0.040 20.05 0.0927
A-A 0.068 1 0.068 34.73 0.0011
B-B 0.065 1 0.065 32.88 0.0012
C-C 0.069 1 0.069 34.96 0.0010
D-D 2.450E-003 1 2.450E-003 1.24 0.3075
AB 5.522E-003 1 5.522E-003 2.80 0.1452
AC 0.041 1 0.041 20.61 0.0039
AD 7.563E-003 1 7.563E-003 3.84 0.0978
BC 0.030 1 0.030 15.23 0.0080
BD 0.11 1 0.11 53.31 0.0003
CD 0.10 1 0.10 52.52 0.0004
A^2 4.655E-004 1 4.655E-004 0.24 0.6442

B^2 6.006E-003 1 6.006E-003 3.05 0.1315

C^2 2.074E-003 1 2.074E-003 1.05 0.3445
D^2 0.029 1 0.029 14.69 0.0086
Residual 0.012 6 1.971E-003
Lack of Fit 0.012 2 5.912E-003
Pure Error 0.000 4 0.000
Cor Total 0.56 20

Surface Roughness = 1.7996+0.0051×A-9.5599×B+0.1085×C-0.075×D+0.02611×A×B-

0.0005278×A×C+0.0003056×A×D+0.40833×B×C+ 1.025×B×D-0.00758×C×D-6.668e-006×A2-
19.40127×B2-0.00317×C2+ 0.00426×D2 (2)
 M. S. Khan et al./ Materials Today: Proceedings 5 (2018) 19011–19018 19017

Table 4. Optimum Parameter Setting for Nickel Plated ABS to Minimize the Surface Roughness
Raster Angle Air gap Voltage Time Ra
5.047 0.002 11.557 12.510 1.295

From the Response Surface Plots it can be observed that with an increase value of raster angle and air gap, the
surface roughness of the Nickel plated FDM build parts increases significantly (Figure 3. C1). From the Fig. 3 C2, it
is evident that raster angle with voltage have less effect on the surface roughness. Similarly, with an increase in
raster angle surface roughness increases and decrease in voltage surface roughness increases as shown in Fig. C3 &
C4.

Design-Expert® Software Design-Expert® Software

Factor Coding: Actual Factor Coding: Actual
R1 R1
Design points above predicted value Design points above predicted value
Design points below predicted value Design points below predicted value
2.11 2.11

1.36 2.4 1.36

2.4

X1 = A: A X1 = A: A
2.2
X2 = B: B X2 = C: C 2.2

2 Actual Factors
Actual Factors 2
B: B = 0.05
C: C = 9
D: D = 10
D: D = 10 1.8
1.8

1.6
R1

1.6

R1
1.4
1.4

1.2
1.2

0.1
12 90
80
0.08 11
70
90 10 60
0.06 80 50
70 9
40
60
0.04 50 8 30
B: B 40 C: C 7
20 A: A
0.02 30 10
20 6 0
10
0 0 A: A

C1 C2
Design-Expert® Software Design-Expert® Software
Factor Coding: Actual Factor Coding: Actual
R1 R1
Design points above predicted value
Warning! Surface truncated by selected response (Y) range Design points above predicted value
Design points below predicted value Design points below predicted value
2.11 2.11

1.36 2.4
1.36
2.4
X1 = C: C
X1 = B: B X2 = D: D
2.2
X2 = D: D 2.2

Actual Factors 2
Actual Factors 2 A: A = 45
A: A = 45 B: B = 0.05 1.8
C: C = 9
1.8
1.6
R1

1.6
R1

1.4

1.4
1.2

1.2

7
0.1 6
5
9 7
0.08
7 8
11 9
0.06 9 D: D 10
13
0.04 11 11
15 12 C: C
B: B 0.02 13 D: D
0 15

C4
C3

Fig. 3. Response Surface Plot for Surface Roughness of Nickel Plated FDM Build Parts

4. Conclusions

The current study not only explain the complex part building mechanism but also the effect of four selected
process parameters on the surface roughness and plating thickness of plated FDM build parts. It is observed that
among two FDM machine parameters, raster angle has most significant effect on the surface roughness and plating
thickness for Nickel plated FDM parts. The plating parameter i.e. voltage has more influence over the surface
roughness as well as on the plating thickness. Since the FDM part building mechanism is more complex, it is really
very tough to establish relation between process parameters with the performance measures. Therefore, attempts has
been made to develop regression equations relating the process parameters with the performance measures and
optimal parameter setting are suggested to decrease the surface roughness and to increase plating thickness of
metalized FDM build parts. Form the response surface plots, it is observed that an increase in raster angle, the
surface roughness increases, whereas an increase in air gap, surface roughness decreases significantly. For the
19018 M. S. Khan et al./ Materials Today: Proceedings 5 (2018) 19011–19018

plating thickness, an increase in raster angle, plating thickness increase, whereas time factor has less influence than
other process parameters. This research can be extended to different metal coating such as chromium for specific
applications. Further, other metallurgical as well as mechanical properties can also be investigated in future.

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