Droplets Deposition Forming Based On Pulsated Orifice Ejection Method (POEM)

Metal micro-droplet deposition manufacture is a novel technology of rapid prototyping and it gets rapid development in recent years. The principle of this method is to deposit droplets one by one and to obtain bonding strength by solidification between adjacent droplets to build structure component. This technology overcomes the limitation of the traditional rapid prototyping, and the applied materials can be not only non-metallic materials but also metal materials with low melting point, even metal materials with high melting point and their alloy. Compared with traditional rapid prototyping, it has many obvious advantages, such as high machining accuracy, simple equipment, and so on. As one kind of the uniform drop-on-demand ejection method, pulsated orifice ejection method (POEM) generates continuous perturbation rooting in the reciprocating action of drive rod, which is put in motion by a piezoelectric actuator. With the help of perturbation, a certain volume of molten metal breaks the constraint from surface tension of molten metal; at the same time it is pushed out of the small orifice to form a droplet. The droplets become sphere during the falling process. In short, POEM can really achieve droplet preparation on demand, and the droplets have the perfect advantages of high sphericity and narrow size distribution, so POEM is an ideal technology to produce droplets.In this paper, POEM droplet deposition equipment is developed based on 3D deposition platform pulsated orifice ejection method. This equipment includes droplets generation system, droplets deposition system, control system, image capture system and vacuum unit. This paper also explains the component of each part in detail and shows the operation procedure and experiment parameters.The feasibility of this method is carried out by a series of deposition experiments using 63Sn-37Pb alloy. The influence of different parameters on overlapping of droplets is investigated. Plane patterns and three dimensional thin-walled or solid components are fabricated successfully. The follow conclusions can be drawn that the droplets can meet the requirements of deposition, for its controllable and uniform size and narrow distribution. Droplets remain liquid during the falling distance of 80mm, which is calculated by thermodynamics and dynamics analysis and observed by high-speed camera. The deposition position accuracy of micro droplets is precise and repeatable in vertical column deposition for its smooth surface and straight shape. With the ejection frequency of 2Hz and the velocity of platform of 600μm/s, adjacent droplets can get good metallurgical bonding with the overlapping ratio of 8.9%. The ejection of droplets can remain stable at high frequency through direct observation. It’s probable to realize droplets deposition of high frequency in the future for its stable ejection even at high frequency proved by direct observation of high speed camera. The parameters including ejection frequency, line spacing and deposition path are found to affect droplets bonding. The experiments results show that good overlapping and bonding strength are obtained with optimized parameters, such as ejection frequency of 10Hz, line spacing of 300μm, line-spread unidirection path. Based on the above research works, plane patterns and three dimensional thin-walled or solid components are obtained with good metallurgical bonding. The work provides a useful theoretical and experimental guide for metal droplets deposition manufacture.