Mold Design And Molding Process Research Of TPU Co-Extruded Microtubes

In recent years,with the rapid development of clinical medicine and prevalence of minimally invasive operation,some stricter requirements have been put forward for the precision,geometry complexity and multi-functionality of medical microtubule.At present,most of the medical co-extrusion microtubules in our country rely on importations,and there are considerable gaps between the production technologies in our country and the ones in the developed countries,as we are lack of basic research and theoretical direction.In the production process of co-extrusion microtubule,the structural design of extrusion head flow passage and molding process of microtubule product have always been the difficult points in the extrusion molding technology.Domestic researchers have made some achievements about the researches on the structural design of extrusion head flow passage of co-extrusion microtubule,but the correlational researches are mainly focused on the design of mold structure,and the influence of rheological property of polymer materials on the co-extrusion process are rarely taken into account,especially on the materials with the viscosity largely influenced by the environment such as TPU(thermal receiver unit).Therefore,studying the changes of melt flow in the co-extrusion process based on the rheological behaviors of TPU materials to discuss the design methods of co-extrusion microtubule mold,is of important guiding significance for the mold design and process optimization in the actual productive process.Firstly,the rheological test is made for two different types of TPU,as data fitting is carried respectively through different mathematical models according to the results of rheological test.It can be found from the results of comparative fitting that the Birdcarreau model and TPU in purely viscous models has the highest degree of rheological data fitting,especially in the low shearing rate.In addition,the viscosity(η)and storage modulus(G’)in the viscoelastic model fitting results share larger deviation with the experimental data.It can be found from the comprehensive comparison that the numerical simulation made through Bird-carreau model is much more closer to the actual process of extrusion.Then,using the obtained constitutive model and the fitting parameters of the two TPU materials,numerical simulation was carried out by the Polyflow finite element analysis software,and the influence of different runner structure parameters on the uniformity of the melt flow velocity during the co-extrusion process was studied.The range and level trend analysis of each scheme and each structural parameter in the orthogonal experiment was carried out to establish the optimal flow channel structural parameters,and to complete the optimal design of the co-extrusion die.Finally,through the combination of numerical simulation calculation and extrusion molding experiment,the three process parameters of gas injection pressure,traction speed and inlet flow rate ratio during the co-extruded micro-tube processing were explored to influence the cross-sectional shape and size of the co-extruded microtube.The law of influence of precision.The results show that with the increase of steam injection pressure,the ovality of the inner and outer contours decreases,but the inner contour is more affected.The increase of the traction speed will lead to a significant decrease in the inner and outer diameters of the co-extruded microtubes,and the ovality of the inner and outer contours decreases with the increase of the traction speed,and the change trends of the two are basically the same.The study of the flow rate ratio found that the increase of the flow rate on the high-viscosity side would cause the coextruded microtubes to shift to the high-viscosity side more obviously after leaving the die.In the study of the interaction of various process parameters,it was found that the ovality of the co-extruded microtubes was the lowest when the gas injection pressure was 15000 Pa,the traction speed was 6m/min and the flow rate ratio was 5:1.Comparing the actual co-extrusion experimental results with the numerical simulation results of the Polyflow finite element analysis software,it is found that the co-extrusion flow simulated by the appropriate constitutive model is not much different from the actual processing results,indicating that the Bird-carreau constitutive model can be used.To a certain extent,the flow changes of the TPU polymer melt during the extrusion process are well predicted,which proves that the numerical simulation calculation has important guiding significance for the mold design and process optimization in the actual production process.The development and preparation of TPU microtubules provide valuable ideas.