Process Setup for Manufacturing of a Pump Impeller by Selective Laser Melting

In the water industry a strong market demand exists for small, high pressure pump systems. However, the casting of impellers for such small pumps in the required quality is difficult or impossible because of their low wall thickness and their unfavorable ratio of impeller diameter to channel height. Selective Laser Melting (SLM), one of the primary metal additive manufacturing technologies, is well-suited to be used for such impellers as the full potential of SLM can be achieved best with such small, complex parts. In this work, we describe the SLM manufacturing of an already existing impeller design at the lower limit of castability. This is motivated by the fact that if this geometry can successfully be SLM-manufactured, there should be no major obstacle for a scale-down to smaller sizes (up to a certain limit), but this SLM-manufactured existing impeller design can be tested on an already existing pump prototype and directly compared to the cast counterpart. The effort described here therefore was to find the optimal orientation of build direction as well as to design suitable support structures. This was done in a heuristic and iterative process with concurrent manufacturing trials. The final SLM-processed prototype impeller fulfilled all geometrical requirements and will be tested in the existing prototype pump in the near future. While the full potential of SLM manufacturing is reached by fundamental part redesigns, the process setup (build orientation optimization and support structure design) for a pre-existing part geometry as performed here is of large practical importance in the service and reconditioning market in the water industry and beyond.