Mission to the Moon - the lunar quattro moon rover

400 watt diode lasers draw software-generated paths into the AlSi10MgSr alloy powder.

  

20 years and counting — the length of time the material AlSi10MgSr has been used and proven its mettle in the aluminum castings of Audi Spaceframe bodies.

A thin layer of silvery powder lies like moon dust on the printer plate. Almost silently and with surgical precision, the dazzling beams of a 400-watt diode laser draw softwaregenerated paths into the AlSi10MgSr alloy powder. Along the paths, the laser energy melts the powder and the first layer of the part solidifies. The plate lowers imperceptibly, the printer lays down a fresh 0.05-millimeter (the average thickness of a human hair) layer of AlSi10MgSr on the plate, and the laser burns the next slice out of the aluminum-silicon-magnesiumstrontium dust. In tiny micro-steps, the Audi aluminum 3D printer works its way downward. Countless times. One exposure interval is around 30 seconds. After 20 layers, the part has reached a height of one millimeter.

Layer by layer, 3D printing creates a metal part, in this case the wheel of the Audi lunar quattro.

The wheel intended to be the link between extraterrestrial ground and human technology, one of the four wheels that will drive the Berlinbased Part Time Scientists’ Audi lunar quattro rover over the inhospitable surface of the moon. Before that happens, there’s still plenty of time for all kinds of improvements. Many of them are being carried out in cooperation with Audi. For example, with the aid of 3D printing.

32 hours and 20 minutes is the time it takes for the 3D printer to produce one of the Audi lunar quattro’s four wheels.
Selective laser melting is the name applied to the technology of aluminum 3D printing.

It’s a process used by Audi when it comes to manufacturing highly complex-shaped parts displaying low weight and high stiffness. Harald Eibisch, an engineer in casting and additive manufacturing technology development at Audi: “3D printing with aluminum makes it possible to produce lightweight parts of almost any shape with a closed shell. The wheel of the Audi lunar quattro has a wall thickness of only a millimeter but displays outstanding strength thanks to its sophisticated design. The material has also been thoroughly tested in the Audi laboratories. We’ve been using alloy AlSi10MgSr in the aluminum castings of our Spaceframe bodies for decades.”

The weight reduction expertise gained in manufacturing the four rings’ production cars is now also benefiting the moon rover. The weight saving achieved by Audi in the Part Time Scientists’ Audi lunar quattro rover comes to around 1.6 kilograms for the four wheels alone. Karsten Becker, the Part Time Scientists’ head of development: “A kilogram of scientific payload in the rover is worth the equivalent of 800,000 euros. Thanks to the weight saving on the wheels, we can put additional scientific material worth 1.28 million euros on board.”

1.280.000 euros is what the additional payload space freed up by the Audi lunar quattro’s weight reduction is worth. The reduced weight makes it possible to transport additional scientific equipment to the moon.
But the Audi experts not only redesigned the wheels and made them lighter by means of aluminum 3D printing, they also improved the moon rover’s suspension, wheel drive housings, swing arms and camera head.  

Yet it was the wheels in particular where a quantum leap was made within a short space of time. First, Audi designers revamped the open spoke wheel of the Part Time Scientists’ original Asimov Rover and turned it into a closed system, making it less vulnerable to moon dust. They also increased its size by 22 percent. The greater contact area brings improved climbing capability in fine-grained moon sand dunes. Then, engineers from Audi gear development enhanced the design of the wheel, originally made up of several machined aluminum parts, and tweaked the profile of the treads for better grip. The decisive step in preventing any weight gain was the use of 3D printing technology. Audi engineer Harald Eibisch: “In 3D printing, we convert design data files into a buildable format. We just take the shape of the part’s outer shell and add a millimeter of material. This results in a complex and stable surface on the inside that even the best CAD program can’t achieve. The entire wheel has a wall thickness of only one millimeter. That way, we’ve been able to reduce the weight per wheel by 400 grams.”

The Audi lunar quattro: Audi aluminum 3D printing supplies the four wheels, the links between wheels and body and the camera head housing the high-resolution cameras.
Does this mean that, after the moon dress rehearsal, parts made by aluminum 3D printing will soon make their way into automobile production?  

Audi engineer Harald Eibisch shakes his head: “A single wheel for the Audi lunar quattro costs roughly 3,000 euros and takes a good day and a half to print. At present, aluminum 3D printing is only economical for parts up to the size of a fi st, but most of the structural parts in our vehicles are bigger than that.” However, the goal for Audi is clear: “Not in fi ve, but maybe in ten to twenty years, we will be making large-scale structural parts using the 3D printer. The technology opens up fascinating new possibilities for automotive engineers and designers: We will be able to simply print sophisticated structures, integrate functional parts into them that save weight, rapidly change the geometry of cars and so make them more individual. The added value in terms of function, weight and stiff ness will be enormous.” Or you might simply say: Vorsprung durch Technik.

 

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Toy figures, sneakers, furniture — 3D printing with plastic is long since part of our daily lives. But plastics are often unable to cope with conditions in space or on the moon: Temperatures ranging from +150 to –150°C would turn them soft or brittle and cause the plasticizers they contain to escape. Tough, low-weight solutions meeting the demands of a space mission can be achieved in 3D laser printing almost exclusively using aluminum.

 
Juri Kohn (copy), Jan van Endert (photos)

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