Design and experiments of extrusion die for polypropylene five-lumen micro tube

sPolymeric multi-lumen micro tube is formed by extrusion die with asymmetric flow channels. Due to the flow imbalance of polymer melts, it is difficult to design the extrusion die. In this paper, the extrusion die of a five-lumen micro tube was studied. The relationship between the structural parameters of asymmetric flow channels in right-angle extrusion die was built on the basis of flow balance of polymer melts. In the opposite direction of extrusion die channel, the lengths of the flow channels were calculated by the relationship, and the ends of the lengths were fitted. An objective function for the structural optimization of the flow channel in right-angle extrusion die was established through the fitting deviations. Then, the right-angle extrusion die for five-lumen micro tubes was designed according to the optimization results and manufactured by micro EDM machining technology. The uniform sections of extrusion products obtained by extrusion experiments with the designed and manufactured die verified the correctness of the asymmetric flow channels of extrusion die for five-lumen micro tubes. Finally, effects of extrusion process parameters on the shape accuracy of five-lumen micro tubes, evaluated by the ovality of profiles, were investigated experimentally with polypropylene as extrusion material. The optimal combination of process parameters including air injection velocity 6 ml/min, die temperature 202 °C, screw speed 16 r/min, vacuum degree of the water tank 0 and the pulling speed 10 m/min was concluded, which improved the sectional shape accuracy of the extruded micro tube by 33.6%. The ovality of outside profile, main lumen and secondary lumen in the tube section were optimized by 2.88%, 2.09% and 3.9%, respectively with the optimal combination of process parameters.