Gas-Assisted Injection Molding is a process where an inert gas is
introduced at pressure, into the polymer melt stream at the end of
the polymer injection phase.
The gas injection displaces the molten polymer core ahead of the
gas, into the as yet unfilled sections of the mold, and compensates
for the effects of volumetric shrinkage, thus completing the
filling and packing phases of the cycle and producing a hollow
Traditionally, injection molded components have been designed with
a relatively constant wall thickness throughout the component. This
design guideline helps to avoid major flaws or defects such as sink
marks and warpage. However, apart from the simplest of parts, it is
impossible to design a component where all sections are of
identical thickness. These variations in wall thickness result in
different sections of the part packing differently, which in turn
means that there will be differentials in shrinkage throughout the
molding and that subsequently distortion and sinkage can often
occur in these situations.>
By coring out the melt center, gas injection molding enables the
packing force (which compensates for differential shrinkage) to be
transmitted directly to those areas of the molding which require
attention. This dramatically reduces differentials in shrinkage and
thus the sinkage. In addition, the internal stresses are kept to a
minimum, considerably reducing any distortion that may otherwise
have taken place.
Maximum clamp pressures are normally required during the packing
phase of a molding cycle. This is due to the force which has to be
exerted at the polymer gate in order to pack melt into the
extremities of the mold cavity in an effort to compensate for the
volumetric shrinkage of the solidifying melt. In comparison to
compact injection molding, gas injection molding typically has
considerably shorter distance over which the solidifying melt is
required to be packed because of the gas core. This means that
proportionally lower packing pressures are required to achieve the
same results and in turn, lower machine clamp forces are required.
Gas injection allows cost effective production of components with:>
- >Thick section geometry.
- >No sink marks.
- >Minimal internal stresses.
- >Reduced warpage.
- >Low clamp pressures.
Gas-assisted Fill+Pack analysis benefits
Gas-assisted Fill+Pack analysis provides you with the ability to
study polymer and gas flow behavior within a part model and examine
the influence that design modifications make on both the polymer
and gas flow paths.
Using this information, the design engineer will be able to
optimize product design and accurately position polymer and gas
injection points. Also to ensure that the product specifications
are met, utilizing the full capabilities of the gas injection
molding process. Expensive tool modifications, long lead times and
trial and error will also be kept to a minimum.
The process engineer will benefit from the program's capacity to
examine the effects that varying processing conditions will have on
the component and enable optimum processing conditions to be
established prior to mold commissioning.