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Driving the Development of Film-Insert Molding

(October 2013) posted on Fri Oct 25, 2013

Find out how FIM functions in a variety of high-end applications and determine whether it’s a fit for your business.

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By Neil Bolding

Furthermore, by printing the component’s decoration on the underside of the film, the hard-coated substrate used forms a tough, protective skin over the complete surface of the finished part. This makes the component considerably more resistant to scratches and abrasions than those that have been sprayed or have had designs applied to them.

Film selection
Many polymer films are available in different thicknesses and surfaces finishes and with a variety of coatings: protective, decorative, and functional. The film provides a dimensionally stable support for the decorative layer during printing drying and forming stages, an optically clear medium through which the decorative layer can be seen clearly with minimal color distortion, a protective layer between the outside world and the decoration, and an environmental barrier against moisture ingress, gas ingress, etc. The most common polymer substrates are polycarbonate, PC/PBT-blend films, PMMA, and PET.

Film thickness is a key consideration. It is a common misconception that deep-draw parts always require thick film. True, the mechanical integrity of the film will decrease as it is drawn, and a film with a higher initial thickness will be capable of drawing further than a thinner film before it loses so much strength that it cannot retain its shape. However, in a real part, it is not the absolute draw depth that is important, but the draw ratio.

The draw ratio is defined as the film thickness before forming, divided by the film thickness after forming. This ratio will vary over the surface of a form profile. The most critical point is where this ratio reaches a maximum. It is important to understand that this point of maximum draw ratio will not necessarily coincide with the deepest draw.

Another factor that’s not visible on the finished part is the amount of film material available to form the shape required. This is often limited by the amount of material between one form feature and the next, or between a form feature and the clamp of the forming tooling. In reality it is rare to find a draw ratio on a part greater than three. In other words the film rarely forms to less than one third of the original thickness. Where formable, hardcoated films are used, the coating itself will usually fail before this limit is reach in any case.


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