Some design challenges in the award-winning Gallagher T20 Terminal

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The Gallagher T20 Terminal, an intelligent card & PIN access control device, received Gold & Silver awards in the NZ Plastics Industry 2014 Design Awards.

The Gallagher T20 Terminal, an intelligent card & PIN access control device, received Gold & Silver awards in the NZ Plastics Industry 2014 Design Awards.

The Gallagher T20 Terminal, an intelligent card and PIN access control device, was awarded Gold for Tool Making, Gold for Co-Moulded Injection Moulding, and Silver in the Industrial Product categories of The New Zealand Plastics Industry 2014 Design Awards held in October 2014. NZEN editor Romy Udanga looks at some of the design features of the product.

“We’re delighted at winning three accolades,” says Gallagher Security chief technology officer Steve Bell. “The Gallagher T20 Terminal has a highly innovative design, utilising advanced over-moulding techniques to deliver a very robust, environmentally protected device, designed to complement both internal and external decor. The T20 is a product we’re extremely proud of, and for our team, this recognition is well deserved.”

The T20 front fascia incorporates a perfectly flush lens for protection of the LCD screen behind it. The lens is created by over-moulding clear polycarbonate over the top of a black or white substrate. This method gives a deep lustre, elegant lines, and incredible robustness due to all the design elements being embodied in one solid part.

Combating warp

All thermoplastics undergo a size change as they solidify in the mould. This shrinkage is often benign and when uniform it is easy to compensate for it in the tool making process. At the outset of the design stage, it was identified that in the unique case of the T20, something more advanced would be required.

The clear polycarbonate over-mould is almost entirely on one side of the substrate, and ordinarily this would cause the resultant part to warp significantly. If designed in the conventional way, the parts would have been unusable. They would have been warped into a dish shape, and unable to fit into the assembly and perform other functions.

Using Finite Element Analysis (FEA), the degree of warp was determined for a range of moulding conditions and material combinations. The FEA results were then compared with real-life parts in a simplified ‘rapid learning cycle’ experiment using prototype tooling. The theory matched the (simplified) reality, so work commenced in applying ‘reverse warp’ to the T20 parts proper. The idea being that if the parts were going to dish by a certain amount, Gallagher R&D could design them domed in the other direction by precisely the same amount, such that the resultant mouldings would end up perfectly flat.

It worked. But it is no easy thing to design an entire product as an accurately reverse warped version of its future self.

Producing the injection mould tooling was no picnic either. The tool cavities for both substrate and over-mould tools have no straight lines, no flat surfaces, and no truly circular holes. An extremely high quality surface finish was also required.

Combating substrate erosion

Conventional over-moulding usually employs a relatively soft, relatively low melting temperature over-mould compared to the substrate, so that it does not erode the underlying material during the injection phase of the cycle.

The T20 front fascia in contrast uses polycarbonate as the over-mould, which is a rigid material injected at the fairly high temperature of 300 degrees C. The substrate material is a coloured version of the exact same material, which gives inseparable bonding of the two layers as they literally melt into one another.

A little melting is good, but too much leads quickly to the phenomenon known as substrate erosion. This is where the over-mould gouges away the substrate as it flows across it, around it, and in several deliberate places on the T20 fascia, through it.

Again, Gallagher R&D were able to predict this in advance with FEA, and make the necessary geometry adjustments so that the issue was resolved before any waste was incurred.

Gallagher’s security solutions are regularly recognised for quality and innovation in awards across the world. The Gallagher T20 Terminal was released to the global security market in July 2013.

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