Analysis of the screw feeding process in powder-based additive friction stir deposition

The screw-feeding process in powder-based additive friction stir deposition (AFSD) is analysed in this work, in which the effect of feeding conditions on the choking/jamming problem and the feeding rate is explored through experiment and numerical simulation using Discrete Element Method (DEM). The results show that a narrow gap between the funnel outlet and the base is prone to particle jamming, which would entirely block the funnel outlet and produce a huge force on the screw. Jamming is more easily to occur when the rotational speed is relatively larger than the translational speed, and a mathematical model of the critical rotational speed above which the particle jamming and blockage would occur is proposed. Jamming is also sensitive to the design of the funnel outlet, in which a contracting outlet would make the choking and jamming problem more serious. For the feeding conditions without jamming, the feeding rate not only depends on the rotational speed of the screw but also is significantly affected by the translational speed. The feeding rate is linear to the rotational speed only when it is larger than a critical value, and this critical rotational speed increases with translational speed. The results also clarify that a good understanding of the screw-feeding process is essential for powder-based AFSD, in which an example of successful manufacturing of a 3D part is briefly illustrated in this work.