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UHMWPE hip liner as a molded biomedical part can
be affected by different conditions during the injection molding process. It is
well known that controlling the process and optimization its parameters are challenging
for manufacturers. The lack of knowledge about the material and process conditions
leads to mold the part with some
critical defects such as shrinkage and warpage. Non-uniform packing pressures
in the mold cavities, non-uniform molding temperatures or cooling rates,
non-uniform wall thicknesses, the
molecular structure of materials (amorphous, crystalline) and fillers are some
of the possible warpage reasons 12. The
shrinkage of molded part is influenced by cooling system, volumetric shrinkage,
flow-induced residual stresses, flow-induced crystallization and orientation.
The type of polymer and its structure can also affect the shrinkage, however,
most of those factors are arisen from process conditions, such as injection
time, packing time, melt temperature, mold surface temperature and packing
pressure. The computer aided engineering (CAE) programs such as Autodesk
Moldflow have been widely used in injection molding industry for designing and
optimizing 13. There
are not many types of research for injection molding
simulation of the medical and biomedical parts.
Recently, injection molding of poly lactic acid (PLA) based antibacterial
nanocomposite bone screws were simulated and optimized through minimizing the warpage
and volumetric shrinkage  of the bone
screws 14. The influence
of process factors such as injection time, packing time, mold temperature,
coolant temperature, melt temperature and packing pressure were examined by
using Autodesk Moldflow. The optimized material and process conditions were
proposed as the best candidates for the injection molding of bone screws on the
basis of the injection molding simulations, structural analysis as well as design
of experiments (DoE). 

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