Design Of Double-lumen Microtube Extrusion Die And Study Of Gas-assisted Extrusion Molding Process Parameter

With the rapid development of medicine,medical catheters were gradually miniaturized and complicated,which puts forward higher requirements for extrusion molding technology.The deformation was more complex and the extrusion molding was more difficult.the gas-assisted extrusion molding technology can significantly reduce the defects such as extrusion deformation and extrusion expansion of microtube extrusion by changing the sliding state of the melt wall,and reducing the difficulty of mold design,but it was limited to single-lumen microtube,bar and profile,and there was little research on multi-lumen microtube gas-assisted extrusion.In this paper,a gas assisted extrusion method was proposed to extrude the double-lumen microtube by injecting gas into the mandrel and forming an air cushion layer between the inner wall of the die and the melt through a slit.The extrusion deformation law and the optimal process parameter were studied for the purpose of obtaining the expected double-lumen microtubule（diameter of outer contour was 2mm,diameter of inner contour was 0.5mm）.The main research work and achievements were as follows.（1）In order to ensure the flow balance of polymer melt,the gas-assisted extruder head was designed based on the die design theory.The orthogonal experiment was numerically simulated by Ployflow software,and the main channel structure parameters of the optimal extrusion die which can achieve a better balance of melt flow were determined,so as to reduce the defects such as extrusion deformation and swelling caused by imbalance of melt flow.（2）The deformation law and mechanism of double-lumen microtubules during simulated gas-assisted extrusion molding were analyzed.The effect of different process parameters（inlet flow,gas injection pressure,traction speed）on the ovality of the inner and outer contours of the gas-assisted extrusion double-lumen microtubule were numerically simulated,and the extrusion deformation law of this gas-assisted method was found by analysis:Under any set of process parameters,the ovality of the inner contour was larger,and the shape was similar to an ellipse.The extrusion deformation mechanism was further analyzed from the X-direction velocity field and shear rate field of the melt.The results showed that after the melt left the die,there was a large X-direction velocity and shear rate on the inner wall,which caused the inner wall to expand inward.（3）Based on the extrusion deformation law of double-lumen microtube,the improvement measures were determined,and the influence of process parameters on extrusion cross-section size was studied.The compensating mandrel structure was designed to be oval,and its feasibility was verified by simulation.It was found that the ovality of the inner contour has been greatly improved,from more than 20%to less than 6%.The influence of different process parameters（inlet flow rate,gas injection pressure,traction speed）on the section size of the gas-assisted extrusion double-lumen microtubule was further simulated and analyzed.（4）The extrusion process was studied,the optimal process parameters was determined and the best extrusion products was obtained.The effects of different process parameters（gas injection pressure,inlet flow rate,traction speed）on the ovality and diameter of the inner and outer contours of the gas-assisted extrusion double-lumen microtubule were studied through single-factor experiments.The influence law was basically consistent with the simulation,verified the numerical simulation results,which provided a reference for the selection of the level of the orthogonal experiment.The optimal process parameters of the gas-assisted extrusion double-lumen microtubule were further determined through the orthogonal experiment:P=250Pa,Q=200.08mm³/s,v_p=62mm/s,the corresponding relative errors are:Y₁=4.923%,Y₂=4.693%,δ₁=2.5%,δ₂=0.2%.The double-lumen microtubule with shape error and size error below 5%was successfully prepared.Finally,it is determined that this gas-assisted method can prepare a better double-lumen microtubule...