Updates from SIEMENS

Siemens researcher prints Christmas trees from gas turbine steel

SIEMENS – Temperatures inside gas turbines can reach 1,400 degrees Celsius or more. The hotter, the higher the energy yield. The special steel that Rehme uses for his personal project of printing Christmas trees is a nickel alloy. It starts to melt at around 1,300 degrees Celsius and can be used, for example, for the burners in gas turbines. Steels that are even more resistant are used for the hottest turbine parts. Rehme gets the print data for his trees from the website grabcad.com.

High centrifugal forces: Heat isn’t the only thing impacting the steel
To generate electricity, turbines have to turn. And turn fast. Turbine blades also have to turn, exposing them to massive centrifugal forces that place high demands on the ductability of their materials. 3D printing with metals can’t yet meet these demands. For the little steel-hard trees, however, the technology is sufficient.

Layer by layer: The fine structure has to be ground down
If you look closely, you’ll see the printed tree’s fine structure. To make the surfaces completely smooth, 3D printed materials sometimes need to be polished at the end.

More complex shapes: Traditional processes such as casting and drilling have reached their limit
With 3D printing processes, shapes can be produced that would be impossible using any other production process. Someday it may be possible to print turbine blades with delicate internal air ducts. This would improve blade cooling, which would not only permit higher temperatures in the combustion chamber but also increase efficiency.

From square to round – More freedom in product design
This short pipe section connects two parts of a gas turbine. The fluid transition from round to square is difficult to achieve using conventional production methods. But with 3D printing, it’s easy.

Shower of sparks: Lasers fuse metal powder
The laser beam hits the bed of metal powder, releasing high energy in the form of heat and melting the metal, layer by layer. The metal then cools relatively quickly into a solid shape. If hot, liquid metal were poured into a mold, it would take longer to fully solidify and cool. This is somewhat of an advantage of conventional production methods, because slow cooling increases ductility. Researchers at Siemens CT are now working on processing techniques that would also endow printed objects with extremely high ductility – a requirement if turbine blades are ever to be printed.

We’ve come a long way since Gutenberg: Olaf Rehme analyzes a CAD model for his next printed object
When book printing was in its infancy, all printers were highly respected specialists and craftsmen. The same can now be said of 3D printing experts. Although 3D printers are already available for home use, most are suitable only for producing plastic parts. Standard devices for printing metals can already generate many shapes. But when products must withstand extreme stresses, experienced material researchers like Rehme are required to perfect the raw materials and process.

Furnace cleaner: When the printer is finished, large quantities of metal powder are left behind – and must be carefully removed
Metal powder covers the floor of the printer. The laser beam moves across the bed of metal dust and generates an initial layer of the three-dimensional object. Another layer of metal powder is then spread evenly over the object’s surface. Now the laser can print a second layer. Step by step, a complex shape is created. At the end of the process, a large amount of powder is left over that can be reused for the next printing cycle.


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