三维粘弹性异型材气辅挤出成型过程的数值模拟研究

在挤出成型中,聚合物粘弹特性与过程参数波动的耦合作用会产生波动的离模膨胀,使得生产尺寸精确且形状复杂的聚合物异型材在工程上仍是一项技术挑战。文章提出了一种高效节能,且能消除离模膨胀,实现异型材尺寸精确自动控制的新型聚合物异型材气辅挤出成型工艺,并基于建立的描述其成型过程的三维等温粘弹性理论模型和稳态有限元数值算法,通过有限元数值模拟,系统研究了聚合物异型材气辅口模挤出成型过程的机理。通过与传统异型材挤出成型对比分析,揭示了聚合物异型材气辅口模挤出成型工艺消除离模膨胀和翘曲变形的机理。研究结果表明,异型材气辅挤出成型离模膨胀率,随进口流量的增加而不变,这为实现挤出的高速化生产的实现提供了技术前提条件。此外,随着松弛时间的增大,口模出口附近气辅段的第一法向应力差增加,从而导致离模膨胀和两侧壁向内的翘曲变形均增大。

The full three dimensional viscoelastic numerical simulation on the gas assisted extrusion molding process of polymeric profile

In extrusion,interaction between the viscoelastic nature of the polymer melt and unavoidable fluctuations of the operating conditions results in fluctuating die swell which makes the production of polymer profile with accurate size and complex shape an technology challenge.Based on the technology difficult,an new the gas-assisted extrusion molding technology with the automatic and accurate control of production dimension and high efficient saving energy which can eliminate polymer profile extrusion die swell and wrapage is put forward in this paper,And based on the formulated three dimension isothermal viscoelastic theoretical model of describing the gas assisted die extrusion process of polymeric profile and the corresponding stable numerical algorithm with fast convergent ,by means of numerical simulation and experimental research,the gas assisted die extrusion molding mechanism of polymeric profile was systematically studied.Moreover,comparing analysis with traditional polymeric profile extrusion,the eliminating mechanism of polymer profile extrusion die swell and wrapage was disclosed in the gas-assisted full slip extrusion molding process.And the research results showed that the die swell of gas assisted extrusion process does hardly not vary with inlet volumetric flow rate increasing which paves the way to implement the high-speed-production of polymeric profile.And the first normal stress difference near the exit of die increases with relaxation time increasing which result in the extrusion die swell and the warpage of side walls increasing.