Effect of process parameters on copper droplet ejecting by pneumatic drop-on-demand technology

Stable generation of copper droplets is a key issue in fabricating copper parts by drop-on-demand (DOD) technology. The process parameters such as supply pressure and electronic pulse width have significant effect on pressure variation and droplet formation. In the present work, a pressure acquisition system was first set up to measure the pressure variation in crucible. Then the measured pressure data were applied on a 20 axisymmetric model as inlet conditions to study the influence of process parameters on copper droplet formation. The results indicated that the peak pressure in crucible increased linearly with the increase of supply pressure. As supply pressure increased, the jet velocity and the limiting length increased to critical value and droplet could be generated. The peak width increased with the rise of electronic pulse width. By increasing the electronic pulse width, the time of pressure above threshold value increased and the jet limiting length grew to critical value for breakup. However, if supply pressure and electronic pulse width were too large, satellite droplets would be formed. Pure copper droplet generating experiments were conducted to obtain appropriate parameters. Single droplet was generated while supply pressure was between 60 kPa and 100 kPa and pulse width was between 550 mu s and 1550 mu s. Also the range of pulse width varied as the supply pressure increased for generating single droplet. The statistics of droplet diameter suggested that droplet diameter increased with the increase of supply pressure. Electronic pulse width had influence on the droplets size and the standard deviation increased with the increase of electronic pulse width. So small supply pressure and electronic pulse width should be used for generating uniform droplets. (C) 2014 Elsevier B.V. All rights reserved.