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Rapid Prototyping

Reproduction of Art Objects in Rapid Prototyping Systems

Measuring Systems: ATOS

Keywords: Rapid Protoyping, STL-Data, Reproduction

The automotive industry was the driving force for the development of digitizing systems. A manually produced design model is digitized and by means of reverse engineering a CAD data set is created which is then used as master for the production process.

Today, digitizing systems are also used for various other markets and products, for example, for quality control, documentation, product development and direct reproduction.
The digitized data in STL format can directly be loaded into RP (Rapid Prototyping) and surface reconstruction systems and now more and more in CAM and inspection systems as well. Thanks to that, it is possible to produce RP models, create CAD data or drive CNC machines. In addition, deviations in the shape of products can be determined and illustrated clearly.

In the following, we explain the digitization and direct reproduction (rapid prototype model) of three art objects that were created by the Swiss artist Beatrice Charen. The ATOS system was used to digitize the objects and to process the data to an STL data set. The STL data sets were then sent to the company PROFORM AG who created precise RP copies from these data. The artist agreed to make the digitized data available for "rebuilding" these works of art.

Torso

Beatrice Charen carved out the female torso (approx. 150 mm high) from a white Indian steatite. The figure is pinned on a chromium steel wire (3 mm diameter) and is held by a dull Plexiglass pedestal (60x60x40 mm).

Fig. 1: Original torso on Plexiglass pedestal. (Animation) Fig. 2: Torso created by means of FDM, put on a chromium steel wire and on the original pedestal. (Animation)

We used the ATOS II SO system with a measuring volume of 100x80 mm to digitize the object. The torso was put on a rotary plate which already was equipped with some adhesive reference points. First, the front side was digitized with two top views and 10 scans all around the object at an angle of approx. 50 degrees with respect to the rotation axis, then, the same procedure was repeated for the rear side. ATOS calculated two individual polygon meshes from the two measuring projects that were then fitted together and saved as one data set.

Now, the torso was pinned onto the pedestal and put on the rotary plate again. A first scan recorded the bottom part of the torso with the pedestal on the rotary plate. Then, the torso was removed, the Plexiglas pedestal including the chromium steel wire was slightly sprayed and digitized.

After defining the coordinate system based on the pedestal data, the torso data were transformed into the data of the first scan of the digitized pedestal to ensure that all data were available in the same coordinate system. Now, the pedestal data were cut off and the data of the chromium steel wire were inverted, i.e. the outer surface pointed to the inside. These data were jointed with the torso data so that the RP torso would fit onto the existing chromium steel wire in the pedestal.

As the figure did not show any sharp edges and as the treatment traces were not be shown, the data could be largely reduced and thinned. Only the artist's logo "CB" needed to be visible in the resulting STL data set. The ATOS system was used, both for digitizing the figure and for editing the data to a thinned STL data set, which took less than 30 minutes for each process.

The company PROFORMA AG reproduced the torso on a scale of 1:1. They used the Insight software V3.4 of Stratasys to process the STL data of GOM, to create a minimum support structure and to calculate the individual layers and length of material. In order to reduce the amount of material and thus the reproduction time, the so-called "Sparse Mode" was selected. In this mode, the torso surface consists of a compact 1.5 mm thick skin and the internal volume of a light hatch structure. Then, the model was built on an FDM titanium system of Stratasys as follows:

Method: Fused Deposition Modeling (FDM)
Material: Polycarbonate: satin-finished
Layer thickness: 0.178 mm; Tip: T12
Reproduction time: approx. 8 hours

The reproduction method described above creates a mechanically stable and very light satin-finished copy of the figure with a slightly "ridged" surface. The first layers generate a slightly reduced surface quality and minor irregularities are visible in the part itself, originating from the on- and offset of material deposition.

Meteor Fish

Beatrice Charen carved out the meteor fish (approx. 170 mm long) from an irregularly brown veined steatite from Swaziland (South Africa). It is held by a chromium steel wire (2.5 mm diameter) free in the air. The pedestal is a dark green glazed steatite (60x50x40mm) of the Saint Gotthard mountain (Switzerland) in which the chromium steel wire is placed excentrically.

Fig. 3: Original meteor fish with support wire and pedestal (Animation) Fig. 4: Fish, created by means of stereo lithography, pinned on the chromium steel wire (Animation)

We used the ATOS II SO system with a measuring volume of 135x108 mm to digitize the fish. The chromium steel wire was slightly sprayed and the fish was put on a rotary plate which already was equipped with adhesive reference points. In three vertical overlapping scans, the reference points around the fish were captured. Now, 13 additional scans followed at an angle of approx. 50 degrees with respect to the rotation axis of the plate which captured more than half of the top side of the fish in full field. Then the fish was turned over and the other side of the object was digitized. Both projects were calculated to STL data meshes and fitted together. Then, the coordinate system was defined with the help of the chromium steel wire and the longitudinal direction of the fish. The cylinder hole for the fixture of the fish on the wire was generated from the inverted STL data of the wire shifted into the fish by translation. Afterwards, both STL data sets were jointed in order to obtain a complete STL data set.

Then, the data were thinned curvature-based such that the fine structure lines in the tail fin were maintained while reducing the data file considerably. Digitizing this figure took approx. 1 hour.
If required, the color information of the object may now be projected from the color images onto the digitized data. These color images can be recorded by means of the TRITOP photogrammetry system with suitable illumination of the object. For details on recording and representing color STL data, please refer to the application note: Colored digitized data. The resulting color STL data can be exported in an extended STL format (RGB or BGR).

After creating the support structure and layers using the Lightyear software (3D Systems), PROFORM AG reproduced the meteor fish on a scale of 1:1 using a stereolithography system SLA 250 / 50 of the company 3D Systems.

Method: Stereolithography
Material: Epoxy SOMOS DSM 9110: slightly yellowish, slightly dull transparent through the very fine ribbed surface
Layer thickness: 0.075 mm
Reproduction time: approx. 14 hours, building the figure in the shown tilted position

This method generates a half-transparent, very fine copy of the original, reproducing exactly all details in shape.

Candle Pedestal

The artist modelled the candle pedestal with jumping dolphins (approx. 250x200x200 mm) from clay. It is glazed in the area of the candle holder, the rest is left untreated and was just fired.

Fig. 5: Original candle pedestal (Animation). The right image shows a detailed view of the RP part on top of the original part. Even the smallest details and irregularities of the original were exactly reproduced in the RP part.

We used the ATOS II SO system with a measuring volume of 150x120 mm to digitize the pedestal.

PROFORM AG reproduced the candle pedestal on a scale of 1:4 using a Viper si 2 of 3D Systems. As the generation of a tailor-made support structure based on the 150 MB file is time-consuming and computation-intensive, an auxiliary model was created with an approx. 4 times smaller amount of facets. This model again was divided into 4 parts so that the numerous support elements could be edited faster. In order to reduce the massive volume (and the construction time), the central part of the original model was hollowed out with a simple polyhedron. Only an approx. 2 mm thick skin remained (in the 1:4 model) which contained all relevant details of the visible side. Then, the tailor-made support structure was combined with the hollowed out original model and the layers for the construction process were calculated.

Method: Stereolithography (high-resolution)
Material: Epoxy Accura Amethyst (RPC Ltd.), dark purple, translucent
Layer thickness: 0.05 mm
Reproduction time: approx. 30 hours in upright building position

This high-resolution method is best suitable for small components with exact details. The candle holder became a delicately worked piece of decoration.


Fig. 6: View of the digitized data. (Animation)

These examples proved that data digitized and processed with ATOS can be loaded into RP software programs without any problems and that it is possible to construct simple parts unproblematically. Detailed parts can be recorded easily and fast down to the smallest detail generating a high data density. These data sets can be thinned curvature-based, smoothed and edited in ATOS as well.

All three art objects were created by:

Beatrice Charen
Luzernerstrasse 4
CH-5040 Schöftland (Switzerland)
Phone: +41 62-721 58 73
Fax: +41 62-721 53 83
Email: speckstein-atelier@bluewin.ch


The RP parts were created by:

Proform AG
Rapid Prototyping
Dr. Paul Bernhard
Route de Chésalles 60
CH-1723 Marly 1 (Switzerland)
Phone: +41 26-436 43 83
Fax: +41 26-436 43 29
Email: proform@proform.ch


The digitized data are available for downloading from our FTP server as STL (binary) and Materialise zipped (stlzip2) data files:

STL binary Materialise zipped
Torso: torso.stl (15 MB) torso.mgx (1.3 MB)
Meteor Fish: meteor_fish.stl (55 MB) meteor_fish.mgx (4 MB)
Candle Pedestal, thinned: dolphine_red.stl (150 MB) dolphine_red.mgx (10 MB)
Candle Pedestal, dense: dolphine_dense.stl (240 MB) dolphine_dense.mgx (16 MB)

We would like to thank Beatrice Charen and PROFORM for their cooperation in this project.