3D-Printed Models Used for Bionic Precision Castings
By using topology optimization, bionics and 3D-printed models in precision casting, Sogeclair, the aerospace supplier, has succeeded in reducing the weight of its aluminum doors by 30 %.
To make aircrafts more fuel-efficient, an increasing number of manufacturers are demanding lightweight components from their suppliers. One solution: 3D printers that directly produce aluminum and titanium laser-sintered components with innovative, material-saving geometries. The disadvantage: The manufactured components are comparatively expensive and are currently only suitable for the production of small components. But what about larger components such as aircraft doors?
"This is a good opportunity to combine 3D printing with tried and tested precision casting," says Thierry Herrero, Director Sales West Europe at Voxeljet. And with 3D printers that print precision casting models with previously non-manufacturable geometries in plastic (PMMA) — without the need for expensive special tools. "This method combines the best of both worlds: the geometric freedom of 3D printing and the stability of tried and tested precision casting. Sogeclair is one of the users of 3D-printed molds. A research project of the French aerospace supplier deals with futuristic aircraft doors which, thanks to an ingenious, bionic weave of aluminum braces, require significantly less material at the same robustness and are therefore 30 % lighter.
Combining 3D Printing and Precision Casting
Designing such a structure on the computer using computer-aided design software (CAD) is no problem for the aerospace experts. However, difficulties arise during production with precision casting. "Especially in the development of prototypes, companies have to constantly change design details," explains Herrero. "However, it is time-consuming and expensive to produce a new precision casting mold for each change with special tools. The solution: the VX1000 3D printing system from Voxeljet, one of the largest industrial 3D printing systems for precision casting models with an installation space of 1,000 mm x 600 mm x 500 mm. "Design changes can be made directly on the screen."
Precise Printing of the Finest Structures
Voxeljet uses the CAD data of the aircraft door as input for the 3D printing system, which applies an acrylic plastic called polymethyl methacrylate (PMMA) in powder form to the construction area — in 150 µm thin layers. The print head then moves over the construction area and bonds the PMMA at certain points in accordance with the digital construction plan. Then a fresh layer of powder is applied. Layer by layer, the precision casting model is produced, that offers better quality than test prints with competing models. "Compared to other materials that can be processed additively, such as liquid resins in stereolithography, PMMA burns out perfectly. “The main reason for this is the negative coefficient of expansion of our powder material, which does not cause any shell breakage when the thin-walled model burns out later," says Herrero.
Once the PMMA model has been printed, it is infiltrated with hot wax to seal the surfaces. The next step is carried out in the foundry. Employees apply ceramic layers to the printed model and melt the model out in an oven. What remains is a ceramic mold, which is then filled with liquid aluminum. Once the metal has hardened, employees remove the ceramic layer and expose the finished aircraft door.
This article was first published by konstruktionspraxis
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