Lichtenfels, Germany - Unconventional solutions were called for in the ALPHA project, Europe's strategic contribution to the future of manned space travel -- as in, not likely to be created using the methods of the past. The task was to manufacture a model of a reusable space transport system for aerodynamic tests. The decision was made to opt for a hollow body model made from titanium using the LaserCUSING process.
For wind tunnel vibration testing, the model needs to be particularly light so that mass forces remain small and rigid, and that elastic deformations remain small. It needs to be thin-walled so that there is enough space for the measurement technology, and consist of a few individual parts to reduce weight.
The right answers were promised by tool-less laser melting with metals, known as LaserCUSING. Using just powder, almost created from nothing, this produces sophisticated geometries which were previously unthinkable.
LaserCUSING -- made up from the letter C in Concept Laser (www.concept-laser.de), the company that builds the machine, and the word fusing (complete melting) -- generates layer-by-layer buildup in an "island principle" where islands are worked in succession. The patented process producing a reduced stress component that allows solid and large parts to be generated with low distortion.
For flow tests on the ALPHA, a scaled titanium model using the LaserCUSING technology was undertaken. The completely closed laser fusing machine for processing titanium eliminated any contamination from air.
Before a component is allowed to "fly" in the wind tunnel, it needs to satisfy all quality requirements up to 300%. For this reason, the M2 cusing machine at Germany's Aerospace Center (DLR) in Cologne-Porz-Wahnheide is utilized as a material development platform and workstation in one. For the ALPHA model, a porosity of 0.02% and a surface roughness of Ra 7-8 were obtained after the process.
The DLR is focusing strategically on the LaserCUSING process because of the high speed at which parts are built up. As a rule, a component only produces 5% of expenditure, but the test assembly accounts for around 95% of the costs -- thus it is necessary to fabricate high-quality components generatively and modify them very quickly. The high speed of the part build-up reduces the costs enormously and also has a positive effect on the development advantage. One plus point is that the LaserCUSING process offers a high degree of freedom of geometry.
The requirements are increasing, both in terms of construction space sizes and with the hybrid parts. Hybrid parts can, for example, be combined with copper and steel parts. The copper is used here for the targeted dissipation of heat. To improve the surface quality, various methods are currently being tested.
Systemhaus Technik West of the DLR in Cologne-Porz is the service provider on prototype construction. The partners for the project are DLR and EADS Space Transportation Bremen.