When a model of a reusable space transport system was required for aerodynamic tests as part of the ALPHA project, Europe's strategic contribution to the future of manned space travel, the decision was made to opt for a hollow body model made from titanium, created using the LaserCUSING® process.
For wind tunnel vibration testing, the model had to be particularly light, so that mass forces remain small and also rigid to ensure that elastic deformation was kept to a minimum. The model needed to be thin-walled to allow enough space for the measurement technology to be used. A further consideration was to produce the model with just a few individual parts to reduce weight.
The technology selected to create this model was LaserCUSING®, the tool-less laser melting process. Using fine metal powder in conjunction with the laser, this process creates sophisticated geometries that are impossible or impractical to produce using conventional techniques.
The name - LaserCUSING® is made up from the letter C in Concept Laser (www.concept-laser.de), the company that builds the machines, and the word fusing (complete melting). The process generates components layer-by-layer, built up in an "island principle" where the individual islands are worked in succession. This patented process enables the creation of components with minimal stress and allows solid and large parts to be generated with low distortion.
The components required for this model were to be manufactured from Titanium. The Concept Laser M2 Cusing machine, located at Germany's Aerospace Center (DLR) in Cologne-Porz-Wahnheide, was ideally suited to this task as the M2 has been specifically designed to work with aluminium or titanium alloys, which unlike steel powders, react with oxygen. The M2 Cusing machine provides the nitrogen or argon based atmospheres required for the production of components in these materials. Before a component is allowed to "fly" in the wind tunnel, it needs to not only satisfy all quality requirements, but exceed them by a margin of up to 300%. For the ALPHA model, a porosity of 0.02% and a surface roughness of Ra 7-8 were obtained after the process.
The DLR (Germany’s Aerospace Centre) is focusing strategically on the LaserCUSING® process because of the high speed at which parts are built up. As a rule, a component only amounts to around 5% of expenditure, but the test assembly accounts for around 95% of the total costs -- therefore 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 development. One further 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 also with hybrid parts. Hybrid parts can, for example, be a combination of copper and steel parts. The copper is used in this instance for the targeted dissipation of heat. To improve the surface quality, various methods are currently being tested.