Acoustic control of powder dispensing in open tubes

A multiple powder metering and dispensing device has been constructed to create functionally graded materials by the solid free-forming process known as selective laser sintering. The device makes use of vertical open tubes through which the flow rate of dry powder is controlled by the characteristics of acoustic vibration in the 20–200 Hz region. Flow is initiated by high amplitude ‘attack’ waveforms and stops when vibration ceases. This simple but effective device raises many questions about the factors that cause flow arrest. The effects of tube diameter, amplitude, mechanical damping and particle size distribution are investigated. By selecting optimum parameters for a metallic powder, the overflow (discharge from the open tube after silence) was brought below 1 mg.