By: A. Techel, F. Brückner, S. Nowotny, R. Wappler, S. Scharek, F. Kubisch, S. Bonß, E. Beyer

Fraunhofer Institute for Material and Beam Technology (IWS)

Laser additive manufacturing with diode, fibre or disc lasers offers outstanding possibilities for applications in aircraft manufacturing or maintenance. High-precision laser additive manufacturing requires precise tolerances of all the components like laser beam, machine configuration, powder delivery, media supply as well as process parameters and control. Only the right interaction of all components leads to precise structures. Fraunhofer IWS in Dresden has a wide experience in improvement of processes and system components for laser additive manufacturing of aircraft components and excellent equipment.

Fig.1: Laser additive manufacturing of turbine components

With a broad range of industrial uses in mind different coaxial powder nozzles were developed as a modular system named COAXn. IWS-nozzle distributes the powder in the form of a ring around the laser beam with a precision of just tenths of a millimetre. High laser beam quality and a special optimized powder nozzle allow building single tracks between 0.2 and 6 mm width and 0.1 and 2 mm height. For the special tip geometry of turbine blades a powder nozzle with a linear unit for the realization of variable weld seam widths during processing was built and successful tested.

Fraunhofer IWS offers also components for process safety and quality control. It is possible to observe and, if necessary, to record the complete process from above through the powder nozzle via a camera (e.g. the so called E-MAqS camera). The camera records the size and temperature of the melt pool. If the preset target value of the melt pool deviates from the actual size, this can be regulated by adjustment of the laser power or of the feed rate speed. Using a temperature based closed loop control system ensures minimal heat input into the part and zero defect welding zones.

Fig.2: IWS-COAX15 for high-precision laser additive manufacturing

The process control system and a special coaxial nozzle come into operation at a new machine at MTU that takes accurate measurements of the parts and uses laser powder cladding to repair the damaged areas and restore the components to an airworthy condition. In combination with a new system for optical geometry assessment process time for typical turbine blade repair or built up can be clearly reduced.

Newest developments of laser additive manufacturing process at IWS tend to large area generation of small structures to improve efficiency of stationary gas turbines and jet engines.