Simulation And Optimization Of PET Bottle Stretching And Blowing Molding Process

PET has been widely applied in the beverage packaging industry,and stretching and blowing molding process of PET bottle has been paid more and more attention.Stretching and blowing molding process of PET bottle is relatively complex.The process parameters such as stretching speed,pre-blow pressure,high blow pressure,delay time,heating temperature and the structure of parison have great influence on the quality of PET bottles.At present,in actual production,many enterprises mainly use trial and error method to carry out experiments until the quality of bottle meets the production requirements,which is easy to waste time and lack of market competitiveness.Based on the POLYFLOW software,this paper studied and analyzed the bottle forming to improve the mechanical properties of the bottle.Firstly,each process parameter was analyzed separately to obtain the appropriate value range,and then the optimal combination of process parameters was obtained by orthogonal test with increasing the minimum wall thickness and improving the uniformity of the bottle body thickness as the optimization indexes.Finally,the layered temperature model was used to further optimize the heating temperature of the parison.The main content is as follows:(1)The high elastic state of PET parison after heating was mainly viscoelastic.Therefore,the KBKZ constitutive model that can fully describe the stress-strain behavior of PET materials in a high elastic state was used to numerically simulate a molded bottle that had been put into production.Compared the simulation results with the actual measurement results to verify the feasibility and accuracy of the numerical simulation using POLYFLOW software.(2)Through the numerical simulation of the molding bottle that need to be optimized,it was found that the stretching blow molding process was mainly divided into three stages:stretching,pre-blowing and stretching,and high blowing.The effects of different diameters,different shapes of stretching rods and the processing parameters such as stretching speed,pre-blowing pressure,high blowing pressure,delay time,and parison heating temperature on wall thickness distribution were analyzed.The results showed that the stretching speed and delay time had a great influence on the wall thickness distribution,while the high blowing pressure had little influence on the wall thickness distribution.(3)Based on the LS-DYNA module,the numerical simulation of the drop of the mineral water bottle showed that the stress of the inclined drop was greater than that of the vertical drop;under the same drop mode,the maximum stress simulated by the mineral water bottle with different wall thickness still occurred at the bottom of the bottle,and the stress decreased with the increase of wall thickness.It was further shown that without increasing the raw material of preform,the stretching and blowing molding process of PET bottle can be improved to make the thickness distribution of the whole bottle more reasonable,and the scrap of products can be avoided due to single point of damage.(4)Taking increasing the minimum wall thickness and improving the uniformity of the bottle as the optimization index,the process parameters such as stretching speed,delay time,pre-blowing pressure and heating temperature were optimized by the interactive orthogonal test.The best combination of process parameters was obtained by range analysis:delay time 0.06s,stretching speed 1.6m/s,pre-blowing pressure 0.7MPa,parison temperature 110?.After optimization,the minimum wall thickness was increased from 0.130mm to 0.166mm,and the mean square deviation of the bottle wall thickness was changed from 0.030 to 0.011,the thickness increased by 28%and the uniformity increased by 63%.(5)The layered temperature model was adopted to further optimize the parison heating temperature in combination with the related sub-tasks in POLYFLOW.By comparison,it was found that the minimum wall thickness increased the most when the preform was divided into six sections.The minimum wall thickness increased from 0.166mm to 0.189mm,increasing by 13%.Based on the POLYFLOW simulation software and combined with the orthogonal test,the process parameters of PET stretching and blowing molding was analyzed and optimized.After optimization,the minimum wall thickness was increased by 28%and the bottle uniformity was increased by 63%.On the basis of orthogonal test optimization,the layered temperature model was used to further optimize the parison heating temperature and to explore its distribution law.The results showed that the parison heating temperature was generally distributed from high to low from the top to the bottom.