Analysis of the Surface of Parts Injected with ABS and Treated with Acetic Acid: Influence of Process Settings - Visual Computing: Scientific Visualization and Imaging Systems - page 144

8.1 Introduction
Injection molding is an important process for the bathroom fixture industry. The
deposition of metal layers on plastic by electroplating for the purpose of obtaining
chromed parts is one choice for a final decorative finish [ 1 , 2 ]. Currently, during
the optimization phase of injection process settings, industries can control residual
stress induced in the polymer during the injection process. These stresses can
cause deformation and even breakage of parts when these are under the influence
of particular environments where plastic parts are used. At low magnitudes of
residual stresses, small micro fractures and deformations may occur in layers of
materials which are very close to the surface (\50 lm) [ 3 ]. When there are major
residual stresses, significant warping, cracks, and fractures may occur in the part
[ 4 ]. In the case of Acrylonitrile Butadiene Styrene (ABS) injection molded parts
which subsequently undergo a galvanization process, the condition of residual
stresses on the surface is one of the most important factors, directly influencing the
quality of the polymer-metal bonding [ 1 , 2 ]. One of the quality problems is
insufficient bonding between the plastic part and the metal coat, as a result of
residual stresses present in the plastic part [ 5 ]. Several studies have been carried
out to measure residual stresses of injection-processed polymers, amongst which
''layer removal'' [ 6 ] and ''hole-drilling'' [ 7 ] are unable to measure stress too close
to surface [ 3 ]. One technique which is able to identify surface stress levels is
''chemical probe'' [ 8 ], where the relationship between stress and deformations or
cracks for different combinations of polymer-aggressive environment is studied in
order to compare results with reference values. Upon the application of numerical
methods to simulate the 3D flow of a viscoelastic material, residual stresses
induced in a virtual model were obtained. Chang et al. compared these stresses
calculated for the surface with a part treated with acetic acid and injected in the
same manner. This comparison showed promising results [ 9 ]. Since thermoplastics
used are not conductive, chemical deposition of a conductive layer serving as a
base for other electrodeposited layers is required. In the case of ABS, butadiene is
oxidized, resulting in several micro cavities and polar groups bonded to the rigid
part of ABS. The noble metal Palladium is bonded onto the polar groups, followed
by a small deposition and electrolytic nickel. At this stage the porosity is filled,
thus anchoring the layer deposited. The subsequent stages are: deposition of
copper, nickel, and a small layer of chromium [ 10 ]. Another study assesses the
concentration effect of conditioning baths on the morphology of surfaces to be
metallized and the use of different acids in the process of surface treatment [ 11 ].
8.2 Materials and Methods
In this study, several specimens were injected with different process settings in
order to carry out treatment with glacial acetic acid and perform surface analysis
through scanning electron microscopy (SEM). Analysis and measurement of the