Powder Focusing

Powder focusing for beam induced laser 3D printing

The most flexible 3D freeform manufacturing method is laser melting of a powder jet oriented onto a moving substrate. One example of such an Additive Manufacturing technology is Laser Metal Deposition (LMD). The obtained dimensions of the structures are usually in the millimeter to several tens of millimeter range. Smaller structures are presently limited by several factors including the applied laser spot size, the precision of the mechanical tables, the powder particle diameters (> 20 µm) of flowable powders and the powder jet spot size.

The aim of the project is to find technical solutions for transporting small particle powders (< 10 µm largest diameter) at high rate to a spot smaller than 20 µm. The approach is to combine different processing techniques, in particular acoutic focusing, liquid jetting and microwave drying techniques, in a new type of powder focusing system. The system will be mounted on a deposition chamber with a laser focused to comparable spot dimensions (<25 µm diameter) in a 3-axis system guaranteeing the needed performance with respect to precision of better than 5 µm in all three dimensions.

Scope of Research Activities

Production of dispersions of powders in liquids and its de-agglomeration
Acoustic focussing of solid particles in liquids
Coupling the coaxially focused dispersion into a nozzle for electrohydrodynamic droplet formation
Controlled droplet or jet ejection
Microwave drying of the powder before reaching the laser spot or the melt pool
Integration of the new powder focusing system into a deposition chamber and laser melting device
Modelling and simulation of particle behaviour in liquids, drop formation, jetting and drying processes

Key Technical Problems to Solve

Re-agglomeration of particles in the powder dispersions
Abrasion in the jetting nozzle by the particles due to insufficient acoustic focusing
Insufficient speed or accuracy of the jetting process
Incomplete drying of particles and droplets before they enter the melt pool or laser beam

Demonstrators

Metal spring (40 µm wire diameter, 200 µm spring diameter, 2 mm height)

Leading Principal Investigator

Prof. Dr. Patrik Hoffmann
Laboratory for Advanced Materials Processing, Empa

Project Consortium

Prof. Dr. Jürg Dual, Institute of
Mechanical Systems, ETH Zürich
Prof. Dr. François Gallaire, Laboratory of
Fluid Mechanics and Instabilities, EPFL
Dr. Manuel Pouchon, Laboratory for
Nuclear Materials, PSI
Prof. Dr. Dimos Poulikakos, Laboratory of Thermodynamics in Emerging Technologies, ETH Zürich