Injection-compression moulding

The injection-compression moulding process combines elements of both the injection moulding process and the compression moulding process. It permits a clear reduction in filling pressures and leads to less anisotropy in the properties of the moulded parts. This should be an advantage for thin-walled mouldings, mouldings decorated with textiles or films and optical, transparent mouldings.

In the case of parts decorated with textiles or film, it is the residual foam thickness that remains after moulding that is the main focus of attention. The injection-compression process not only gives higher foam layer thicknesses in absolute terms but also ensures a more homogeneous distribution of the layer thickness along the flow path.

With thin-walled mouldings, dimensional stability is of key importance as a quality criterion. This is influenced to a decisive extent by the shrinkage of the moulded part. Investigations at the IKV have shown that thin-walled mouldings with wall thicknesses of between 0.5 and 0.7 mm, display less shrinkage when produced by injection-compression moulding.

Injection-compression moulding has already gained considerable importance for the group of optical mouldings. This process is used especially in the production of optical lenses. Over and above this, it can also be employed for large-area optical mouldings, since these benefit not only from the better shrinkage compensation but also from the reduced filling pressure. Study results show that optical properties such as distortion and birefringence can be improved with the aid of injection-compression moulding.

The IKV is developing new application potential for this process in research projects and in direct cooperation with industry and is also compiling the necessary process knowledge. This know-how is then implemented in products on the basis of feasibility studies.

Gas injection technique

The gas injection technique (GIT) generates cavities through the selective injection of an inert gas in specific, still molten areas of an injectionmoulded part, thereby creating a uniform gas pressure inside the moulded part. The gas injection technique became established for the production of thick-walled and rod-shaped parts many years ago. It is used particularly with ribbed and highly integrated parts, in order to minimise warpage and sink marks.

A logical step towards saving costs is to use the gas channel as a functional cavity for media lines. GIT offers particular advantages in cases where conventional production processes, such as extrusion or thermoforming, would involve a number of production operations. Costs can be reduced by comparison with 3D blow moulding for the manufacture of branched or highly integrated media lines and through the use of multi cavity moulds. The integration of media lines in a complex component is also possible.

Media lines suitable for the gas injection technique are being defined through market analyses and through cooperation with industry, and new variants of the gas injection technique are being developed at the IKV. One example of a product-oriented development of this type is the GAFIM process (Gas-Assisted Fibre Braid Injection Moulding), which can be used to meet stringent requirements, such as a high bursting pressure at high temperatures and good low-temperature impact strength.

Additional IKV processes, such as GASIM (Gas-Assisted Sequential Injection Moulding) for rigid/flexible combinations, GACIM (Gas-Assisted/Gas Counter Injection Moulding) for high volume lines and the CorePush process for branched lines will extend the range of applications still further.

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