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Source: Fraunhofer ILT post
AACHEN, Germany – Since 2012 Fraunhofer ILT has been intensively researching and developing Extreme High-speed Laser Material Deposition (EHLA), a process in which the laser melts the powder particles above the melt pool.
This fast and reliable process applies 25 to 250 micrometer thin layers at a speed of up to 500 meters per minute in an economical manner that conserves resources; it has already proven to be a reliable alternative to hard chromium plating.
Since then, the process has been opening up new areas of application and conquering industrial sectors. The latest highlight is the 3D EHLA system, in which the building platform is moved extremely quickly in parallel and kinematically by three linear drives with a stationary laser processing head.
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Series production, however, requires a new nozzle that can be easily exchanged so that users can work with EHLA in a safe, precise and highly reliable manner. Here is a look at the nozzles commonly used up to now: In laser material deposition (LMD), different powder nozzles are used depending on the application.
For areas that are difficult to access, the lateral powder nozzle, which directs the powder jet laterally into the laser beam, has proven its worth. In contrast, the coaxial powder nozzle, which generates a conically bundled powder-gas jet, works independently of direction. It is particularly suitable for integration into automated systems for coating and Additive Manufacturing.
Nonetheless, EHLA places special demands on the quality of powder feed nozzles: To melt particles in the laser beam, their trajectories and speeds must be precisely adjusted. Even small deviations of the powder flow lead to non-optimal results, such as insufficient layer thickness or layer defects in the applied layers.
For this reason, Fraunhofer ILT, together with the company Harald Dicker – Special Optics for Laser Technology from Aachen, has developed a coaxial nozzle called “HighNo (High Quality Powder Nozzle)” which directs a ring or cone shaped powder-gas jet onto the workpiece at a very precisely defined distance. Depending on the application, this precision leads to powder efficiencies of up to 95 percent. The nozzle tips are classically manufactured from a proven copper alloy and then machined with ultra-high precision.
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