Titanium, a popular material in the aerospace industry, oxidizes when it comes into contact with air at processing temperatures of 300 degrees Celsius or higher. As a result, the material properties change. The components become brittle and can crack. If, for example, a robot is to additively manufacture a titanium workpiece using a laser, a large chamber must first be built around the robot and component. This chamber is then either flooded with a low-reaction inert gas such as helium or argon or a vacuum must be created before production can begin. "This form of global process shielding may be suitable for small component sizes, but poses considerable difficulties in terms of process control and accessibility when manufacturing large components," explains Jakob Schneider, who conducts research on additive manufacturing at the Fraunhofer IWS. "In addition, the costs for such a chamber increase disproportionately with the size of the component to be protected, for example the costs for several cubic meters of helium or argon, which may also have to be pumped out and back in again due to intermediate work steps." The same applies to workpieces made of other "recalcitrant" materials, so-called refractory metals, such as tantalum, niobium or titanium-aluminum compounds.

Coaxshield protects titanium components

The IWS has therefore developed Coaxshield, an alternative protective shield that only directs the shielding gas where it is really needed: directly around the processing zone of the laser beam, which melts the metal powder and applies it to the component layer by layer. This is a nozzle head that can be mounted under standard processing optics. It encases the powder nozzle and forms a protective gas cone coaxially around the process zone. This cone thus only protects the hot processing zone, as this is the only place where titanium and ambient air can react with each other.

"This solution saves the user a lot of effort and costs," emphasizes Jakob Schneider. "It also allows very large titanium components to be additively manufactured or produced." One example: The European Space Agency (ESA) needs a satellite support structure made of titanium with a diameter of several meters for the Athena X-ray space telescope. The IWS is working with the organization to develop a process and the associated system technology for additive manufacturing. Coaxshield was developed with this in mind. This technology should be ready for the market in early 2020.

LIsec illuminates the powder stream

The LIsec measuring device developed at the Fraunhofer IWS allows for significantly simplified quality control and enables conclusions to be drawn about the degree of wear on a powder nozzle. © Fraunhofer IWS Dresden

While the calibration of tools is state of the art in conventional ablation processes such as milling, this is still a major challenge in laser powder cladding. To solve this problem and to push the limits of what is technically feasible, the LIsec measuring device was developed at the IWS. The abbreviation stands for Light Section and already reveals the principle: a measuring laser shines through the powder flow after it emerges from the nozzle. A camera is mounted at right angles to it, which records light sections through the powder and forwards them to analysis software. "This allows the three-dimensional distribution of the powder flow to be calculated with high precision," explains IWS engineer Rico Hemschik. "This significantly simplifies quality control and allows conclusions to be drawn about the degree of wear on the powder nozzle."

The abbreviation LIsec stands for Light Section and already reveals the principle: a measuring laser shines through the powder flow after it exits the nozzle. © Fraunhofer IWS Dresden

This can be used, for example, to repair damaged or worn aircraft turbine blades to a higher quality and more reliably than before. "In this respect, our measuring device can contribute to greater safety and lower maintenance costs in aviation," says the IWS engineer. The Dresden-based institute is already working on the transfer of the technology with several well-known international companies and research institutes.

Formnext: Hall 11.0, Stand D51 (joint Fraunhofer stand)