Development Of Apparatus For Preparing Mono-sized Spherical Metal Micro Particles With High Melting Point

With the development of the high precision manufacture,as raw material,the properties of micro particles are required increasingly.Mono-sized micro particle has been found wide spread application prospect in the fields of additive manufacturing,electronic packaging,new energy,etc,due to its high sphericity,identical size and narrow size distribution.Pulsated Orifice Ejection Method(POEM)used for preparing mono-sized droplets and particles,is one of the drop-on-demand methods.With a certain gas pressure difference between crucible and chamber kept,a certain amount of melt in the crucible is ejected from the orifice and becomes a droplet by the elastic deformation of a diaphragm driven by a piezoelectric actuator.The diaphragm is replaced by a rod based on the mechanism of local pulsated disturbance proposed first in this paper.Contrast to pulsated disturbance acted on whole melt by the diaphragm,only the melt near the orifice is disturbed by the reciprocating movement of a rod.When the disturbance exceeds the stress due to surface tension of the melt around the orifice,a certain tiny quantity of melt is ejected from the orifice.The droplets becomes spherical and solidified due to the action of surface tension during the falling process.The particles prepared by this method are with the characteristic of the very narrow size distribution,the same thermal history and microstructure.Additionally,the method shows clear advantage in the preparation of particles with small size.At the same time,the range of materials which are suitable to this method is expanded due to the high temperature performance of ceramic rod.The piezoelectric actuator driving system played an important role in this apparatus,which was used to generate pulse signal and transmit vibration of rod.The property and vibration stability of the piezoelectric actuator driving system were measured and analyzed by the laser displacement test system.The results showed that the piezoelectric actuator driving system had good step response capability with the rod being unloaded.The stability of vibration was effected by the waveform of the pulse signal and rod shape.The stability became worse with the increase of the decrease of the tup time.The applied voltage,the time of thold and the vibration frequency had no effect on the stability of vibration.As for the rod with the same material,the stability of vibration was increased with the decrease of the weight of rod and the distance between gravity center of rod and piezoelectric actuator.Based on the local pulsated disturbance proposed firstly in this paper,the apparatus was established.Mono-sized spherical metal micro particles with high melting point had been successfully prepared.Under the condition of the stable pulsated disturbance supplied by the piezoelectric actuator driving system,effect of the process parameters on the particles prepared by this method were evaluated.The conclusions are drawn in the following.Mono-sized micro particles with high sphericity and good surface quality,such as copper,aluminum and silver,had been successfully prepared.Within the range of experiment,the diameter of the particles increased with the increase of the pressure difference between the crucible and the chamber,the applied voltage and the reduction of tup time.Time of thold and ejection frequency showed no obvious effect on the size of mono-sized particles.The ejection of droplet was most stable when the distance between rod bottom and orifice was fixed to 0.40 mm.