Design and fabrication of microturbine rotors for small power generation

TASC/INFM, Sincrotrone Trieste (ELETTRA), and Mechatronic GmbH have started the design of a microturbine powered with compressed gas to be used as an electrical generator in a micro/nanosatellite. The research is funded by ESA for the realization of a liquid bipropellant micro-rocket engine that uses a micro-turbine and micro-pumps in order to pressurize the propellants. The turbine rotors have been fabricated with LIGA technology and die sinking Electro Discharge Machining. LIGA is well adapted to the production of high aspect ratio microstructures with very steep and well polished side walls and it does not limit the choice of material to silicon and derivative but offers the possibility to fabricate the turbine in metallic compounds. Moreover it has been found that LIGA, when coupled with EDM, is an optimum technique to obtain enbloc rotors with small diameter and high aspect ratio blades. The first step of the process is the fabrication of an X-ray mask containing a set of turbine rotors. The mask has been used on the ELETTRA deep X-ray lithography beamline to expose millimeter thick PMMA sheets glued on metallic substrates. After development the substrate is selectively electroplated with copper. The negative tone structures are then used as microelectrodes in a following EDM process. This further step allows obtaining turbines made of every conductive material. In particular we machined rotors made of aluminium, stainless steel and magnetic alloys (FeNdB). In this communication the different steps of the fabrication process of the micro rotors will be presented, as well as the first results obtained (turbine rotors of 3.4mm and 10mm external diameter) and the preliminary tests performed to measure the output power.