SAMPE Journal - January/February 2023 - 38

FEATURE / TOOLING FOR INJECTION MOLDING
Simulation
A combination of flow simulation and finite
element analysis (FEA) was conducted in order to
identify potential weak spots of the mold inserts
and to determine baseline process parameters for
the injection molding process. The flow simulation
was
performed
using Moldex3D
software
Figure 4. Simplified cross-sectional depiction of the mold design including
metallic master mold, SLA-printed mold inserts and aluminum filler pieces.
(CoreTech Systems Co. Ltd., Zhubei, Taiwan).
The simulation yielded minimum values for the
injection pressure and injection temperature that
would guarantee complete filling of the cavity. Due
to the comparatively low thermal conductivity
of the mold inserts, cooling time is significantly
larger than for conventional metal tooling. In
addition to baseline process parameters, the flow
simulation also delivered estimations for shrinkage
and deformation of the ejected thermoplastic part.
Both factors were implemented into the mold
design as scaling factors. Output data from the flow
simulation was used as input for a finite element
analysis of the mold inserts using Abaqus software
(Dassault Systèmes, Vélizy-Villacoublay, France).
Through this approach, critical areas of the inserts
could be identified and adapted accordingly in the
mold design in order to reduce peak stresses during
injection.
Figure 5. Left: " Torture Part " for Injection Molding Trials; right: injected POM
part.
backside of the nozzle and ejector side inserts are
backfilled by standardized aluminum inserts. This
approach reduces wall thickness deviations within
the mold inserts and maximizes the contact area to
the metallic master mold (see Figure 4).
Stereolithography Process Optimization
Mold inserts were manufactured on a Formlabs
Form 2 SLA printer. Due to the inherent warpage
of UV-curing resins, support location plays a major
role in determining the dimensional accuracy of
SLA parts. Overhanging structures tend to display
convex warpage due to in-layer shrinkage during
curing9
. Preliminary tests showed that an evenspaced
distribution of support structures on large
planes and dense support on overhanging edges
significantly reduce warpage. Mold inserts for later
applications following the R&D effort were printed
directly and flat on the build platform. In order to
compensate the warpage of the bottom surface,
an offset of 1 mm was added to this surface. The
warped area is milled flat prior to mounting the
inserts into the mold frame.
Injection Molding Process Optimization
Baseline parameters for injection molding were
determined during flow simulation and applied
during the practical injection trials. Release agent
was applied after each injection. The mold surfaces
were cooled down to 100 °C after each injection
using pressurized air to avoid the build-up of
excessive heat.
38 | SAMPE JOURNAL | JANUARY FEBRUARY 2023
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SAMPE Journal - January/February 2023

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