OpenFOAM simulations for development of a mist flow diverter in aerosol jet printing

To design functional devices meeting the performance requirements for Aerosol Jet® (AJ) printing to deposit ink on substrate by a collimated impinging mist jet, understanding the internal mist flow behaviour is important. Herewith a computational fluid dynamics (CFD) model is presented with an OpenFOAM software package, for development of a mist flow diverter in the AJ printing equipment. The function of such a mist flow diverter is to direct a mist flow with specified flow rate to the deposition nozzle for printing the ink material onto substrate and to divert the mist flow away when the nozzle moves over a substrate location where ink deposition is unwanted. The CFD results can reveal detailed mist flow behaviour during mist flow switching for quantitative analysis of mist front travelling time through different regions. It is shown that such an internal pneumatic diverter inevitably brings noticeable on-delay and off-delay, more so for finer feature printing with lower mist flow rate due to time needed for mist droplets to travel from the mist flow switching chamber to substrate. Moreover, the on-delay and off-delay also come with gradual fade-in and fade-out effects in printed features especially when the substrate is moving at a considerable speed. Presented here is but one example of CFD analysis applied to performance examination of a commercial vacuum-boost diverter, although the established computational model has also been utilized to guide equipment design with evaluations of the effects of different geometric shapes and sizes by virtue of the convenience for CFD domain geometry and mesh adjustments.