Edinburgh Napier University

  The development and fabrication injection of moulding tools is complex and
demands highly skilled personal. The research aim is to study the effect of surface
roughness on mould filling and the ejection of parts for amorphous and semicrystalline
polymers. This study is to simulate and analyse polymers used and
investigates the ejection force needed for different selected polymer resins for a
series of cavity and core inserts with different surface roughnesses. Mould filling
and comparison studies for polymers used also were carried out. Three common
thermoplastics polymers were used for the cylindrical part: two amorphous
thermoplastics: high impact polystyrene and an acrylonitrile butadiene styrene and a
semi-crystalline polyamide. These three thermoplastics were selected due to these
polymers are engineering materials being widely used in automotive parts, in the
casing of household products and in gears. Apart from that there are different
processing conditions for an amorphous and crystalline thermoplastic in terms of
melting temperature, injection pressure, packing pressure and cooling times which
are considered in this study. A two-cavity prototype tool for cylindrically shaped
components was fabricated with variations in wall thickness by using a series of core
inserts each with a different surface roughness. The part was constructed using CAD
software and simulated in Autodesk Moldflow Insight 2010-R2 (AMI 2010-R2) in
order to carry out the simulation works to obtain the required processing parameters
for the injection moulding process. The application of simulation software packages
for mould design and injection moulding process are vital in order to optimise the
part quality and satisfy the market needs. For amorphous thermoplastics there is no
melting point in terms of physical properties and having a high toughness due to
butadiene chain present, in this case both for high impact polystyrene and an
acrylonitrile butadiene styrene. Since polyamide has a viscosity lower than these two
amorphous thermoplastics, the processing conditions and pressure will be different
which can be identified through the melt flow rate of the resin. Polyamide also has a
higher density which is 1.14 g/cm3 compared with high impact polystyrene and an
acrylonitrile butadiene styrene which were 1.04 g/cm3 and 1.04 g/cm3 respectively.
The study concludes that polyamide resin requires a shorter cavity filling time and
less pressure compared with an acrylonitrile butadiene styrene resin. Polyamide also
requires high ejection forces due to surface texture generated as compared with high impact polystyrene and an acrylonitrile butadiene styrene. The mathematical model
results for the ejection force closely agree with the experimental data for the three
materials used.