Multi-component injection moulding processes

A limitation to achieving the aspirations of designers has been the ability to process multiple parts or materials into a single component when moulding plastic assemblies, writes Jon Hobden

The advancement of plastics and rubber mouldings technology over the past forty years has been steady and impressive. However, a limitation to achieving the aspirations of designers, in industries such as medical, automotive and aerospace in particular, has been the ability to process multiple parts or materials into a single component, without the need to bond or join the parts in separate assembly processes.

Multi-component injection moulding is not new but the difficulties involved make it expensive and inconsistent in many cases.

Processes such as encapsulation of a first-process mould by a second, often by mould indexing, are common.

But the ability to insert-mould or two-shot mould to exacting accuracies and repeatability requirements are still the domain of specialist mould shops.

One such is British technical moulder A K Industries (AKI) of Hereford, providing design and manufacturing offerings using multi-component moulding.

A particle analyser manufactured by Malvern Instruments utilises a disposable capillary unit or cell, designed to measure as small as 6nm particles.

The cell has gold plated electrodes moulded-in to the clear, polycarbonate component, with a AKI-designed carrier loading the electrodes with very high precision.

Two moulded halves are welded ultrasonically as part of the process to partly encapsulate the terminals.

Every piece is tested before shipping.

The cell is required to be optically clear to prevent light scattering in the plastic, watertight under pressure and accurate to accept the correct amount of liquid in the measuring chamber.

A complete manufacturing cell built by AKI moulds, inserts, welds ultrasonically, inspects inline and packs after testing.

AKI is also able to manufacture complex mouldings using two different polymers in one cycle on the same machine.

Where compatible materials are specified, fusing of the two parts takes place when the second part is moulded-in to the first.

Mechanical bonding is also available for incompatible materials, where the two cannot be chemically bonded or where movement/articulation are required by the design.

The two-shot injection moulding process is the ability to produce complex mouldings from two different polymers at the same time during one machine cycle.

Separate but compatible materials or colours are very strongly fused together (chemically bonded at the molecular level) through the forming process when the second material is injected into the mould.

Alternatively, incompatible materials can be mechanically connected by two-shot moulding without fusing, in order to meet specific product design and assembly needs such as articulation or movement.

A trace detector made by AKI for 3M Health Care, that measures ATP for hygiene applications, involves a two shot process to produce a cuvette which is tapered and possesses a seal of TPE that is moulded into the component.

A sixteen-cavity tool is divided into four, each segment having a precision water cooling facility to maintain the integrity of the completed unit.

Two different polymers are also used in a muscle toning system the company makes for Dezac Group, the toning pad bonded into the back of an oval hinged surround.

With a complete concept-to-delivery service, combined with the expertise and experience to push boundaries, AKI has brought multi component moulding into the mainstream with precise and consistent results possible.