The Thickness Control Mechanism Of Extrusion Blow Molding

Extrusion blow molding technology is the third largest plastic processing methods which is junior to injection molding and extrusion molding technology. And it is widely used in food, medical, automotive, industrial transport and other fields. Due to the impact of gravity and lack of die opening control basis, extrusion blow molding parts exist lots of shortcomings,including unreasonable and uneven thickness distribution. These shortcomings lead to the waste of raw materials, the reduction of production efficiency, and the influence of the final parts. Therefore, the thickness control of extrusion blow molding parts has been the research focus of many scholars at home and abroad. Among these control ways, adjustment the extrusion die opening gap curve is a direct and effective method. The focus of this paper is through using the Polyflow software, predicting the die opening gap curve on the backward,and verifying the validity of the curve by experiments, with the goal of uniform reasonable thickness distribution on axial direction. The main research contents are as follows:(1) Research on the final parts thickness distribution optimization with the goal of mass minimal. Under the condition of the stacking force, the thickness distribution of the final part with the minimum mass is a reasonable thickness distribution. Using the Response Surface Optimization module of ANSYS Workbench, the axial thickness distribution of the final part was optimized, and the axial thickness distribution with the minimum mass was selected as the best axial thickness distribution. This best axial thickness distribution of the final part was treated as the goal thickness distribution to provide the target for subsequent reverse prediction.(2) Research on reverse Prediction of opening gap curve of the extrusion die. In the parison inflation stage, with the goal of the best part axial thickness distribution, using parison Progress module of Polyflow finite element analysis software, the parison was divided into fifteen layers, and the thickness of the parison was combined by layers. The axial thickness distribution of the part which was obtained from the layers combination was compared with the target thickness distribution. The thickness of layers were changed time after time until the axial thickness distribution of the part which was obtained from the layers combination matched with the target one. In the parison extrusion stage, with the goal of the best parison axial thickness distribution, using Polyflow finite element analysis software, the parison extrusion simulation was made by layers. During each layer simulation, the die opening width was constantly changed until the axial thickness of the layer in parison which was obtained from the die opening width matched with the target one. Then the die opening width adjustment simulation was made by layers, and the die opening width which was obtained from the die opening width adjustment simulation was collected as the extrusion die opening gap curve.(3) Experimental verification on the extrusion die opening gap curve and the orthogonal experiment optimization. The extrusion die opening gap curve resulted from simulation was verified by experiments. The axial thickness distribution of part obtained from the extrusion die opening gap curve by simulation was compared with the target one, and the orthogonal experiment was used to optimize the final extrusion die opening gap curve to improve the rationality and uniformity of the axial thickness distribution.