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introduced into the polymer melt stream, creating a homogenous mixture of polymer
and gas. The mixture is short-shot injected through nozzles into the mould in a
volume that is less than the amount required to mould a solid part. Injection pressure
and expansion of the polymer/gas mixture fills the mould.
Foam parts have thicker wall sections with low density, exhibit excellent strength-to-
weight ratio, improved thermal and acoustic insulation properties, but suffer from
lower tensile strengths. The finished part has typically 10 – 30% less weight than an
equivalent solid part. Moulds made out of aluminium are cheaper and lighter and it
can be used to produce larger parts. Low set up cost makes Structural foam
moulding attractive alternative to injection moulding for low-volume applications. .
Applications are rigid products such as polystyrene drink cups, packaging materials,
insulation panels and fast food cartons made out of HDPE, ABS, PP, PS and LDPE.
Thin Wall Injection Moulding:
The demand for plastic packaging and plastic parts that are lighter weight and
engineered for increased strength using less plastic material, have made thin wall
moulding very popular. Typically, "thin wall” is considered as plastics parts or plastic
packaging with a wall thickness less than .8 mm (0.031 inch). The process
requirements for moulding thinner wall sections are different than those for standard
plastic injection moulding with the need for higher pressures and moulding speeds,
faster cooling times, and modifications to part ejection and gating arrangements.
High speed plastic injection moulding machines, robotic systems, special thin wall
plastic injection moulds, and proper part design and material selection are also all
critical to successful thin wall plastic injection moulding. The process provides
advantages like less material used thus saving on part cost, faster production and
increased productivity and reduce weight and wide design options. Applications
include plastic housing, medical devices, electronic housing and cell phone
components, food packaging like plastic dairy containers, yogurt cups, frozen foods,
juice, fruits and bakery packaging.
Co-Injection (Sandwich) Moulding:
In this process two different (but compatible) polymer melts are injected
sequentially into a cold mould, forming a skin/core structure. The skin material is
injected first into the mould cavity, and is immediately followed by a core material.
As the skin material flows into the cavity, the material next to the cavity walls
freezes and material flows down a center channel. Finally, a seal can be created in
the sprue area with the first component, preventing the core material from
penetrating through to the surface thus forming a sandwich part. The possibility of
using recycled material in the core can be regarded as one of the main advantages
with the process. Large volumes of recycled plastics can be reused in products

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