A multi-component powder dispensing system for three dimensional functional gradients

New opportunities for solid freeforming (SFF) will emerge when not just the shape but the spatial arrangement of composition can be rendered from a computer file. This paper describes a method for dispensing programmed mixtures of dry powders. It provides both on/off and flow rate control in open capillaries using acoustic vibration. In a glass capillary attached to an electromagnetic transducer, the wave characteristics of the forced vibration control both flow rate and switching of powder flow. The flow rate of powder can be predicted by an explicit model on the basis of intermittent arrest and stasis of particles in the gravitational field. Forced vibration can reduce the flow rate by a factor of 0.1. Since flow stops when acoustic vibration stops, the vibrating tube is a valve that provides computer controlled powder flow metering, mixing and dispensing. The effects of acoustic frequency, amplitude, tube diameter, mechanical damping and particle size distribution have been investigated. The overflow (discharge from the open tube after vibration stops) was brought below 1mg. The dispensing device is being used to make three-dimensional functional gradients by selective laser sintering (SLS).