The sling ball measures an impressive 3.2 x 3.5 x 4 meters. It consists of eight triple knots, six quad knots and 24 connecting arms, which are highly complex intertwined to form a geometric endless loop. The design was made by the American artist Bathsheba, who uses CAD software to design her modern art works. The district administrator of Friedberg, Dr. Klaus Metzger, inaugurated the sling ball in June 2018. “This is the most beautiful roundabout in the district,” explained Metzger to the Augsburger Allgemeine Zeitung.

3D printed snare ball from voxeljet

An impressive work of art made from aluminium sand casting

The production of the sling ball was carried out in three essential production steps. First, the artist’s CAD data was prepared for 3D printing. The digital positive model was scaled to the desired size, dismantled into individual components and converted into negative molds suitable for sand casting.

Printing in the world's largest industrial 3D printing system

The next step involved 3D printing of the top and bottom boxes as well as the casting cores. For printing the system uses standard foundry sand for aluminum metal casting. voxeljet experts transfer the finished CAD data to the VX4000, the world’s largest 3D printer for sand printing. The combined building space measures 4 x 2 x 1 meters. Beside several smaller printing systems, voxeljet AG operates three of these high-performance systems at its service centre in Friedberg. The service center has a total capacity of up to 400 tons of printed material per month.

During the printing process, the recoater precisely applies a 300 µm layer of quartz sand to the building platform (job box). the high-performance print head with over 25,000 nozzles follows subsequently. Wherever the mold is to be produced, the sand is bonded with furan resin. This technology is called “Furan Direct Binding” (FDB). Then the next layer of sand is applied and the printing process begins anew. Layer by layer, a total of 114 components are formed for top and bottom boxes as well as casting cores. Printing a full job takes about 58 hours. Employees then remove the unprinted sand and clean the negative molds in preparation for metal casting. A total of eight VX4000 job boxes were required for this impressive work of art.

Art foundry casts aluminium components

Welding the cast individual parts together

The third production step was to send the molds to the Kunstgießerei Kollinger GmbH in Elchingen near Ulm. As a non-ferrous metal foundry, Kollinger is an expert in the field of large-format aluminium casting. The product portfolio of this foundry includes delicately crafted artistic sculptures, sacral objects, fittings, fountains for outdoor use and high-quality technical prototypes.

Both traditional and technically automated processes, such as 3D sand printing, are used to provide demanding customers with individual and versatile solutions. There is virtually no limit to the size of the castable objects.

After coating the printed molds with a ceramic liquid and assembling the individual parts, Kollinger cast the sling ball with aluminum in the alloy 226 (AlSi9Cu3) using gravitational casting. By inserting printed cores, the experts at Kollinger were able to save material and realize a wall thickness of only eight millimeters. After solidification, Kollinger removed the mold material from the raw casting, cleaned it and then welded the individual triple knots, quad knots and connectors to form the final complete object. In order to give the work of art its noble appearance, Kollinger beamed the surface of the sling ball with glass beads. The result was the impressive sling ball: economical in material and weighing only 965 kilograms.

With a crane on the roundabout

On site, workers mounted the sling ball with a crane over a stainless-steel tube that serves as static support. A unique demonstration of the size and complexity that can be achieved with 3D printing.

It is important that 3D-printed sand molds, in particular those of such size, are dimensionally stable and very accurate. Only then can the foundry assume that the part can be cast with the highest possible geometrical accuracy after solidification. With the VX4000 and the FDB process, we have a technology at hand that can produce casting moulds with maximum precision. All 114 components showed an ideal dimensional accuracy, so that the castings could be welded together without any further post-processing.

Alexander Kudernatsch, Vice President Servicesvoxeljet AG

Wildly interlaced: Eight three-nodes, six four-nodes and 24 connectors

The sling ball is an impressive eye-catcher. Not only because of its expansive dimensions, but also because of its unusual and playful form, which could not be produced with such precision using any other production technique. “An incredible work of art that attracts attention from afar,” confirms 3D printing expert Kudernatsch, who is glad to have chosen the right design by artist Bathsheba. Artist Bathsheba writes on her website:

3D printed snare ball from voxeljet

The geometries I want are not malleable, most manufacturing processes don't work well for me. That's why I started 3D printing.

Bathsheba,  Künstlerin

Kollinger art foundry: tradition, art and technology

Over the course of time, the Kollinger foundry has adjusted its strategic alignment as an art foundry to the latest requirements and trends. This came about as a result of recognizing that technology is playing an increasingly important role in working and living environments. On account of its ongoing development and experience, Kollinger has acquired a high level of competence and expertise in technical precision casting and now supplies well-known companies with prototypes and small series in Germany and abroad.

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