A new technique to create exact plastic replicas of full-color, digital 3D models could offer a cheaper alternative to high-end 3D printing, say researchers.
They tested the technique with some very complex objects, including a Chinese mask and various model-making components, such as a car body shell and food replicas.
The Chinese mask in particular has many detailed features, which were reproduced perfectly in the replica—for instance, the teeth in the original are decorated with gold paint.
“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,” says Christian Schüller, a doctoral student at ETH Zurich.
How it works
The method is a combination of new software and an established industrial production technique called thermoforming, which is used to manufacture many commonly used molded parts, such as yogurt containers and inserts for food packaging. “But the industrial method is not suitable for inexpensive manufacture of small batches or even individual pieces of complex shape or color-printed models,” says Schüller.
The new method would allow professionals or hobbyists to produce individual pieces or small batches of objects with structurally complex and colored surfaces—quickly and cheaply.
The technique’s core is based on an accurate simulation of the thermoforming process Schüller developed under the supervision of Professor Olga Sorkine-Hornung. The simulation computes an image from the colored surface of a digital 3D model, which is then printed onto a plastic sheet.
Through thermoforming, this sheet is then heated and forced into a 3D shape. The key lies in computing the deformed image so that the colors and patterns align perfectly with the geometric details of the mold.
In a first step, a simple 3D printer is used to produce a negative mold of a model made of polylactic acid (PLA), a single-color plastic. This forms the basis for the temperature-resistant gypsum mold, which is required in thermoforming.
The software computes the correct texture for the 3D model, which is printed with a standard laser printer on to a special transfer paper. With the help of pressure and heat, the image is then transferred on to a plastic sheet.
The printed plastic sheet is clamped in a thermoforming machine above the gypsum mold and heated until it becomes malleable. A vacuum quickly sucks the air from between the sheet and the gypsum cast, setting the plastic tight on to the gypsum mold like a skin—creating the plastic replica.
After the thermoforming, it is possible to see whether the software has computed the printed image correctly.
“The deformation of the plastic also changes the printed image. But our software accurately calculates and compensates for this deformation,” says Schüller.
Cheaper and faster than 3D printing
Due to the plastic used, the method is less suitable for reproducing the properties of objects made from materials such as wood or stone, since the surface has a high gloss. But this may even be preferable depending on the application.
The researchers think the new method can be used in digital fabrication and industrial applications to mold prototypes before large-scale production. Architectural firms and modelers could also benefit from this method to cheaply and quickly fabricate a 3D model based on their plans and visualizations.
The technique may even be of interest to the hobby sector or schools, since the equipment needed is readily available and the gypsum cast can be used multiple times to produce numerous, high-quality copies.
“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 will present their paper at the ACM SIGGRAPH 2016.
Source: ETH Zurich
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