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Scottish Plastics and Rubber Association Scottish Plastics and Rubber Association

Advances in Injection Moulding: Seven More Solutions

Nikolaj Gadegaard (left) and Graeme Herlihy see eye to eye (almost) on advances in injection moulding

At the February SPRA technical meeting on “Advances in Injection Moulding”, sponsored by Engel UK and held at the Dakota Hotel, Eurocentral, the two speakers, Graeme Herlihy, MD of Engel UK and Dr Nikolaj Gadegaard, University of Glasgow, informed and entertained an audience of 28, drawn from moulders, toolmakers, end users and academics, on some of the latest developments in the field of plastics injection moulding.

Graeme Herlihy, MD of Engel UK, reminded the audience that he had addressed an SPRA meeting 3 years ago with a presentation entitled “7 solutions for 7 applications” and it seemed appropriate to entitle his latest presentation on current developments in application technologies as “7 more solutions for 7 more applications”

Solution 1 Blow Moulding in an Injection Moulding Machine

To produce wide necked jars, the production of performs and the subsequent blow moulding of the performs is carried out within the same mould unit, using a complex mould that moves laterally to take the performs from the moulding station to the blowing station. The advantages over traditional injection blow moulding are that there is no need to handle performs, a change of product geometry is easily achieved by changing the blow mould inserts and capital investment is greatly reduced although tooling can be expensive.

Solution 2 Joinmelt

Complex hollow components can be produced by moulding the two halves and welding them together, all within the same mould unit and mould cycle, by bringing in a hot gas welding unit between the two faces of the component followed by a press assembly for the final stage of the mould cycle. Compared to conventional friction or vibration welding as a secondary operation, Joinmelt minimises weld flash, simplifies the mating surface design, eliminates warping, copes with 3-D contact surfaces and eliminates interim storage of individual parts.

Solution 3 Variomelt

Variomelt: heater station mounted on top of mould
In conventional injection moulding based on a constant tool temperature, there is a trade-off between selecting a low mould temperature to minimise cycle times and a high mould temperature to facilitate mould filling and creating good surface quality. In Variotherm control, the mould is first heated and then cooled in each moulding cycle. An infrared heating station mounted above the mould unit allows a two cavity mould to rotate from the heating station to the moulding station, the latter being equipped with a highly effective cooling system.

Solution 4 Flomo

Flomo water distribution block and display
Amid all the developments of faster and more precise injection, better pressure control and clamping options, mould cooling is a much neglected area of injection moulding. Now there is a water distribution block which monitors and controls both coolant temperature and flow rate to optimising mould cooling. The visual display on the control panel makes it easy to control inlet/outlet temperature differentials to optimise and maintain production quality and output. The system also identifies any gradual changes in the coolant system and hence more effective maintenance.

Solution 5 Optimelt

Optimelt technique for moulding lenses
Moulding high quality optical lenses is one of the most challenging applications because of the sink marks and shrinkages affecting the optical properties. Optimelt solves the problems by creating the lens in a series of moulded layers. By moulding the core in one stage and then overmoulding thinner layers, in the same mould unit, optical and dimensional quality is greatly improved. There is a choice of geometry options and a choice of mould design (3 + 3 or 2 + 2 + 2, in rotating, sliding and indexing plates) to meet the conflicting demands of optical quality, production output and mould complexity.

Solution 6 Clearmelt

Overmoulding polyurethane layers onto simple components gives an attractive deep gloss, with good scratch resistance. This decorative effect can be enhanced by incorporating a printed foil but the real potential is in creating smart plastics by incorporating electronic circuitry for touch control. This innovation is creating novel applications in the automotive and consumer electronics markets.

Solution 7 Organomelt

To produce complex shapes with high rigidity, the Organomelt process starts with a sheet of long glass fibre impregnated with a thermoplastic. The sheet is thermoformed to give the rigid skeleton structure and then overmoulded with other functional features. Like some of the previous solutions, all operations, even the final trimming, are carried out in a single moulding cell, in cycle times of less than 60 seconds to produce the thermoplastic hybrid structure.

Report by Charlie Geddes, SPRA Hon. Secretary, February 2012

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