Research On Medical Grade TPU Gas-assited Micro Extrusion Process

With the development of micro electronic system(MEMS)in recent years,the trend of miniaturization,precision and lightening of industrial products is becoming more and more significant.Due to its low density,high specific stiffness and excellent compatibility characteristics such as strength,biological,polymer materials gradually become the main molding material in micro industrial products,especially in medical equipment such as molding,molding process of medical microtubules is the micro extrusion of one of the important applications.But the product miniaturization has also brought a series of problems,the rheological behavior of polymer melt in the micro channel is different to the traditional polymer forming process,many factors such as wall slip condition and surface tension of the micro scale effects in micro extrusion can not be ignored.As one kind of slip extrusion technology,gas-assisted extrusion technology can effectively solve the problems of micro scale effect in the process of micro extrusion.For this reason,this paper studied the process of gas-assisted micro extrusion based on medical grade thermoplastic polyurethane:First,the rheological properties of medical grade thermoplastic polyurethane were tested,an non-isothermal power-law model constitutive equation was fitted by steadystate rheological data,and a PTT viscoelastic constitutive model constitutive equation was fitted by dynamic rheological data,these equations can precisely expressed the rheological behavior of molten state medical grade thermoplastic polyurethane during the extrusion process,which providing a mathematic model basis for numerical simulation of gas-assisted micro extrusion.As 1mm diameter circular extrudate as the research object,base on the extrusion die design theory and experience of gas-assisted die design,gas-assisted micro extrusion die structure and parameters been selected,combined with surface tension model and wall slip model,2D axisymmetric model has been setted up which be used to simulated method of gas-assisted micro extrusion process with numerical method,comparison of gas assisted extrusion and micro gas assisted injection molding the process of micro extrusion,and analyzed the molding process conditions(mold temperature,melt flow,gas pressure,gas flow diameter)effect on the flow process and forming results.Finally,the extrusion experiment was carried out by using the gas assisted micro extrusion die.The experimental results show that the the introduction of gas assit slip condition on micro extrusion process,can effectively reduce the pressure drop in the die,and there is a certain degree of improvement on the extrudate surface shows that the process of micro extrudate quality;orthogonal experiment of gas-assisted micro extrusion suitable process conditions of interval is narrow.