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 145

influence of injection parameters on treated surface morphology and correlation
with surface residual stress determined through simulation were thus obtained. For
the injection of specimens, the Tairilac-AG-12AO copolymer ABS supplied by
Formosa Chemicals & Fibre Corporation was used. The ABS was dried in an oven
at 80 C for 8 h before processing. Injection equipment used was a Battenfeld
model 250 plus with a 22 mm screw, shot weight 34.5 g PS and clamping force
25t. Glacial acetic acid 99 % purity was used to identify the presence of residual
stress on the surface of the injected parts. The following experiment was carried
out: immersion in acid for 2 min [ 12 ] at room temperature followed by washing in
running water, drying with compressed air and subsequent SEM analysis at
magnifications of 50, 100, 200, and 2,000. Five specimens from each test were
obtained. After repetitive trials, only one specimen from each experiment was
analyzed through SEM. An optical microscope of 200 magnification with a digital
camera was used to determine the layer deposited.
8.3 Results and Discussion
8.3.1 Analysis of One Part from the Assembly Line
In order to carry out flow rate simulations with the software Moldflow version MPI
5.0 [ 13 ], a finite element model was developed, as shown in Fig. 8.1 . Details of the
mold, such as part dimension, mesh grade, number of elements and nodes, and
process input settings for the Moldflow program can be found in a master science
thesis by Murakami [ 2 ]. The part analyzed is an ASTM D 638, type I tensile shear
test specimen. Material used for simulation is an injected ABS counter type grade
GG-22 from BASF.
Twenty-seven simulations were carried out to determine variations of Surface
Residual Stresses.
A centrally located mesh node of the specimen was chosen to determine surface
residual stresses, as shown in the surface residual stresses curve of Fig. 8.1 . The
surface residual stresses curve starts on one side of the specimen and reaches the
opposite surface. Figure 8.1 shows the point of the curve where residual stress
tension was determined.
Figure 8.2 shows the layers deposited onto the surface of an ABS injected part.
The effects of butadiene oxidation on the surface of the part, the incorporation of
the metal Palladium, or the electrolytic nickel in this interface cannot be observed.
Optical microscopy enables the measurement of the copper layer thickness as
17 lm and nickel thickness as 12 lm. Chrome layer deposited onto nickel is lower
than 1 lm. Total thickness deposited is around 30 lm. These figures are in the
range suggested by the literature [ 10 ]. Figure 8.3 shows a photograph of the
surface of a part from the assembly line to be chromed. This part was treated with
acetic acid as described in the trial procedure. In the photograph, one can see that
some areas are bleached whereas others are not.