The Numerical Simulation And Optimization Of Process Parameters In Parison Inflation Of Plastics Extruding Blow Molding

At present,the domestic industrial economic structure is constantly upgradingand changing as the world economy is constantly changing.In the process of industrial upgrading,the plastic bottle enterprises have been improved continuously production and sales striving to increase the added value of plastic bottles.Plastic bottles are used in all walks of our life,such as food containers in the food industry,large storage tanks in factories,pipe fittings,and so on.The most of plastic bottle is made of material such as polyethylene or polypropylene.When material has been heated at a high temperature,then a plastic container is formed by means of blow molding or extrusion blowing or injection molding,and so on.the plastic bottles are popular in various industries with many advantages which are formed with high-density polyethylene(HDPE)plastic bottles.However,the biggest challenge is the problem of uneven wall thickness in actual production.Most plastic bottles have notch sensitivity.Sharp corners,roots of the mouth thread,neck,and the bottom of the plastic bottle is weak position where the wall thickness is too thin to cracking of the mechanical properties of the plastic bottle.This paper takes 1L ink bottle as the research object which was representing suchstructural characteristics with the formed method and optimization method.The technological analysis of 1L ink bottle was carried out by combining with the shape and structure characteristics of 1L ink bottle and the actual production situation.The extrusion blow moulding billet blowing process of ink bottle was numerically simulated by Workbench-Polyflow software.The thickness variation law of billet blowing process was observed by CFD-Post and the wall thickness was optimized by two progressive methods,one was the response surface method,on this basis,the second one was optimized non-uniform parison.Finally,the result meets the actual production requirements of blow moulding parts.In order to solve the uneven wall thickness of blow-moulded parts,the response surface analysis method was used to optimize the extrusion blow-moulding process parameters and the Box-Behnken design method in response surface methodology was adopted.The design variables were blow molding pressure P(MPa),blow time t(s)and closing speed v(m/s).The response targets were wall thickness variance R1(mm~2)and average thickness R2(m).The response surface model was obtained by fitting the Workbench-Polyflow simulation data with analyzed equation to minimize the variance of wall thickness.The optimum combination of process parameters was obtained:factor A(blow molding pressure)was 0.1 Mpa,factor B(blow molding time)was 1 s and factor C(closing speed)was 0.1 m/s.On this basis,considering the setting of initial billet thickness,the non-uniform initial billet thickness could be optimized by stages according to the different deformation of billet during blowing process.In the process of blown billet expansion,the parts with large deformation amount correspond to the billet with large initial thickness,and the parts with small variable amount correspond to the billet with small initial thickness.Through the analysis of the numerical simulation results of ink bottle by Workbench-Polyflow software,we could clearly see the change of thickness and velocity during the blowing process of extrusion blow moulding parison,we got the position of thinner parison wall thickness.For this position,the appropriate parison wall thickness optimization algorithm was used.In this paper,the iterative global optimization method and the deformation method were adopted in turn to improve the thickness of thinner position and reduce the thickness of thicker position,so as to achieve the goal of optimizing thickness uniformity on the basis of meeting production requirements.In the first step,the iterative global optimization method was used to optimize the parison thickness,and the uniformity was improved effectively,and the optimization effect was good.Secondary optimization based on deformation was carried out for the sake of excellence.The results were as follows:the average wall thickness was 3.1E-3 m,and thevariance of wall thickness was 6.9E-4 m~2 before optimization.After optimization by response surface method,the thickness range was reduced to 1.2E-3 m to 2.3E-3 m,and the average wall thickness was about 1.5E-3 m.The result shows that the variance of optimized wall thickness was 23.2%lower than that before optimization,and the optimization effect was remarkable.Because the mean value was too large,then the non-uniform parison optimization was adopted:after the first optimization,the mean wall thickness was 1.3E-3 m,the fluctuation range of wall thickness was 0.52E-3?2.3E-3 m,and the variance was 5.6E-6 m~2.After the second optimization,the variance was reduced to 2.78E-08 m~2,the thickness range was between 0.8E-03 m and 1.3E-03 m,the average value was reduced to 1.0E-03 m,which meets the production requirements(0.8E-03 m to1.3E-03 m).The results show that the uniformity of wall thickness was effectively improved by optimizing process parameters and homogeneous initial billet thickness.The product was qualified by experimental verification and product quality testing.