U型件的气体辅助挤出成型工艺的数值模拟与实验研究

Numerical simulation and experimental study on gas⁃assisted extrusion process of U⁃shaped parts

应用Polyflow软件将气辅挤出成型引入U型件挤出成型过程中,建立了口模-气体-熔体的三相模型,在传热情况下,对口模温度、气体温度对口模内熔体的流动速度、温度及剪切速率等进行数值计算,用origin软件进行分析,通过传统挤出和气体辅助挤出成型对U型件进行挤出成型实验,选用聚丙烯(PP)材料挤出,均能顺利挤出,在达到挤出平衡后,气辅挤出时比传统挤出时更能使试样离膜下垂现象明显减弱。PP/10%玻璃纤维在传统挤出成型时,有明显的挤出胀大现象,纤维在U型截面的侧壁与底面分布不均匀,在U型件拐角处分层分离现象严重;气辅挤出成型时,可以很好改善挤出胀大和纤维在侧壁与底面分布不均匀的现象,同时在U型件拐角处纤维分层分离的现象也能得到部分缓解。PP/20%玻璃纤维在气辅挤出成型下挤出的U型件时,U型件壁厚变薄严重,试样中纤维分布比较均匀,拐角处无明显的纤维分层分离现象,但是试样表面有明显的纤维组织,且U型件的开口变形严重。结果表明,气辅挤出成型可以部分的减弱试样挤出后的下垂现象,也可以改善口模内熔体的温度场;传统挤出成型时候,口模内的U型件内外壁温度随着口模的变化而变化,气辅挤出成型时熔体高温区域集中在U型槽截面的中心线位置附近;气辅挤出成型与传统挤出时的剪切速率场分布发生了较大变化,气辅挤出成型时的剪切速率最大值比传统挤出时小很多。

A die–gas–melt three‑phase heat transfer model was established by introducing gas‑assisted extrusion into the extrusion process of U‑shaped parts.The simulation results indicated that the melt flow velocity was uniform in the same section of the die.The melt temperature field was seldom affected by the outside environment.The melt temperature range varied with the die wall temperature during the conventional extrusion process.The U‑shaped parts were prepared through both conventional extrusion and gas‑assisted extrusion.In the conventional extrusion,the PP melt could be stretched smoothly under certain technological conditions.However,the melt was affected by gravity in the gas‑assisted extrusion molding process.After the extrusion process was balanced,the sample surface was transparent and smooth,and the droop from the die was reduced significantly.The PP composite with 10 wt%glass fiber showed significant ex‑trusion swell in the traditional extrusion process.The fibers were not homogenously distributed on the side wall and bot‑tom of the U‑shaped part.The delamination was serious at the corner of the U‑shaped part.In the gas‑assisted extrusion process,the extrusion swell and the inhomogeneous distribution of fibers on the side wall and the bottom surface were im‑proved,and the fiber delamination at the corner of the U‑shaped part were also partially alleviated.The thickness of the U‑shaped part became thinner the PP composites with 20 wt%glass fiber.The fiber distribution in the sample was more homogenous,and there was no significant fiber delamination at the corner.However,there was a remarkable fiber emer‑gence on the sample surface,with serious opening deformation on U‑shaped parts.