3D technique promises accurate coloured thermoforming mouldings

A new form of thermoforming is the answer, according to Swiss University ETH.

In thermoforming, a plastic sheet is warmed to near melting point and sucked onto a mould – it is the technique used to make yoghurt pots.

“The new method is a clever combination of established thermoforming and software which allows even ambitious amateurs to produce individual pieces or small batches of objects with structurally complex and coloured surfaces quickly and cheaply,” said the university.

There are two parts to the process, both starting with the same 3D virtual model, and both using an accurate simulation of material flow during thermo-forming created by researcher Christian Schüller at ETH’s Interactive Geometry Lab.

Part one uses conventional 3D printing to make a mould of polylactic acid (PLA), from which a secondary, heat-resistant, thermo-forming plaster mould is made.

ETH Zurich 3d multi-colour car print 780In part two, the software pre-distorts the required 3D coloured surface into a 2D image, which is printed onto special transfer paper using a standard laser printer. Pressure and heat allow this image to be transferred onto the surface of a flat plastic sheet.

When the flat plastic sheet is thermo-formed over the plaster mould, the outside of the plastic sheet ends up following the contours of the original 3D virtual model, and its colours stretch into their proper un-distorted places.

“The deformation of the plastic changes the printed image. But our software accurately calculates and compensates for this deformation,” said Schüller.

The thermoforming has been tested with complex objects including a Chinese mask and various model-making components, such as a car body shell and food replicas.

Teeth in the original mask are decorated with gold paint,” said Schüller. “This detail is reproduced exactly in the copy. The surface has a high-quality look, and the colors and structure are almost identical to those of the original.”

Numerous copies can be made by using the plaster cast multiple times and, “the replica has a high quality appearance, and for many applications it’s cheaper and faster than today’s 3D color printing process,” says Schüller.

The researchers are convinced the thermoforming method can be used in industrial applications to mould prototypes before large-scale production, and that architectural firms and modelers could also benefit.

Naturally high surface gloss makes the process less suitable for reproducing wood or stone surfaces, said the university.

The work will be presented at ACM Siggraph in California in July

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