Optimal Design And Experimental Verification Of LDPE Double-Lumen Microtube Die

With the continuous development of market demand,the application of double-lumen microtubues is becoming more and more extensive.At present,the conventionally used empirical design and mold testing cannot efficiently obtain products with high precision.How to design a reasonable mold structure to obtain high-precision dual-cavity microtubes is the main problem faced by the development of domestic precision microtubes,and it is also the main problem facing the development of domestic and foreign precision microtubes.The main reason for the gap in luminal microtubules.Therefore,the research on the design of the double-cavity microtubule mold has very important theoretical and practical value.Based on a brief review of polymer extrusion swelling theory,extrusion molding die,extrusion molding numerical simulation and the basic equation of polymer flow,this paper systematically expounds two kinds of die designs based on flow balance and based on extrudate deformation pre-compensation.The related research progress of the method,and then put forward the basic idea of the work of this paper.Firstly,the design and numerical simulation of LDPE single-lumen microtube die are carried out.According to the material properties of LDPE and the characteristic size of the pipe,combined with the conventional design method of the microtube die,the structure of the LDPE single-lumen microtube die was determined.The rheological properties of LDPE materials were tested,and the characteristic parameters of the Power-law model were obtained by fitting.The extrusion flow numerical simulation of the designed structure shows that when the inlet flow rate is 3.985×107mm³/s,the pressure at the die outlet is 4.283×10⁵Pa,the velocity is 2.16m/s,and the boundary shear rate is 727s^-1,the extrusion swell ratio is 1.18.Secondly,the numerical simulation and optimization research of LDPE double-lumen microtube die is carried out.The numerical simulation of the extrusion flow of the double-lumen microtube is carried out to solve the forward numerical simulation,and it is found that the speed rearrangement degree of the die setting section is high,the deformation of the extrudate is serious,and the velocity distribution at the outlet is uneven,and the flow balance is poor;the local shear rate is high,and the flow is not balanced.It is beneficial to extrusion molding,but the surface quality of the product is bad;under the combined influence of extrusion expansion effect and gas injection deformation,the extrudate has a large degree of deformation and an irregular shape.The simulation inverse solution is carried out,and the cross-sectional shape of the double-lumen microtube setting section is optimized according to the inverse solution result,and the optimized mold structure is obtained.Analysis of the flow behavior in the melt die shows that after optimization,the degree of rearrangement of velocity in the setting section decreases,the deformation of the extrudate decreases,and the pressure drop at the die outlet decreases;the velocity gradient of the outlet section decreases,the average velocity of each sub-region is close,and the flow is balanced.substantial improvement.Finally,the exploration of the microtube extrusion molding process and the verification of the die design are carried out.The extrusion molding test of single-lumen microtubes shows that the outer diameter of single-lumen microtubes increases with the increase of extrusion speed;decreases with the increase of traction speed;and does not change significantly with the increase of die temperature.The double-lumen microtube extrusion molding experiment was carried out,and the results showed that the optimum gas injection flow rate suitable for the double-lumen microtube molding was 8mm³/s;the ovality and deviation of the outer diameter of the double-lumen microtube under different molding speeds and die temperatures were measured,and it was found that When the die temperature is 170°C,the extrusion speed is 6.0R/min,and the pulling speed is 8.2m/min,the size precision of the double-lumen microtube is the highest.The design of the double-lumen microtube die was experimentally verified,and it was proved that compared with the die obtained by the conventional design method,the cross-sectional shape of the double-lumen microtube formed by the numerical simulation inverse solution method was closer to the product design drawing and the dimensional accuracy was higher.