Abstract: This paper presented a valve-controlled melt differential pellet 3D printer used for direct print with a variety of plastic particles and also simulated the extrusion process of non-Newtonian fluid in the valve cavity by using a multiphase flow and a dynamic grid technique. It was found that there is a positive correlation between extrusion flow rate and downward speed of the valve needle as well as between the ratio of valve needle and valve cavity diameters. The closer the valve needle to the nozzle, the greater the diameter ratio, and the greater the fluctuation of flow rate. The optimal valve needle movement distance could be determined as 0.5~1 mm. Moreover, the extrusion flow rate was improved with an increase of the ratio of the valve and valve cavity diameters. The larger the diameter ratio, the greater the fluctuation of flow rate. The melt exhibited a back flow phenomenon, when the ratio of the valve needle movement speed and back pressure was greater than 0.5. When the process parameters were accurately controlled, the steady extrusion could be realized and the precision of molded parts could be improved.

Key words: three dimensional printing, melt differential, valve-controlled system, dynamic grid technology