剪切历史对微注塑制品形态结构和力学性能的影响

Influence of shear history on morphology, microstructure and mechanical properties of micro injection molded parts

以厚度1、0.5和0.2 mm的微制品为研究对象,采用等规聚丙烯(i PP)材料进行微注塑实验,通过改变注射速度研究剪切历史对制品内部形态结构和力学性能的影响,并对微制品内部形态结构和力学性能的影响关系进行分析,不同注射速度下的剪切历史采用Moldflow分析获得。结果表明:1 mm和0.5 mm微制品厚度方向均呈现皮芯结构,且皮芯交界处的过渡层出现不完善的串晶层,0.2 mm微制品呈现含有柱晶结构的皮芯分层结构。对于3种厚度的微制品,熔体整体剪切水平随着注射速度的提高而提高,1 mm和0.5 mm制品的皮层厚度随注射速度增大而减小,模量、断裂强度和断裂伸长率均随皮层厚度增大而增大,屈服应力变化不明显,0.2 mm制品的皮层厚度随着注射速度的增大而增大,且随着皮层厚度的增大,断裂强度、模量和屈服应力增大,断裂伸长率逐渐减小。

Micro injection molding experiments were conducted to investigate the influence of shear history on morphology, microstructure and mechanical properties of the micro-scale parts by changing injection speed based on the iPP parts with thickness of 0.2, 0.5 and 1 mm. Shear rate was analyzed with software Moldflow. Skin-core structure appeared in the thickness direction in both 0.5 mm and 1 mm parts, and imperfect shish-kebab structure appeared in the transition layer between skin layer and core layer of 0.5 mm and 1 mm parts, however, column crystal was shown in the transition layer of 0.2 mm parts. The whole shear level in shear history increased with increasing injection speed for all the parts with three thicknesses. The ratio of skin layer of 0.5 mm and 1 mm parts decreased with increasing injection speed, and yield stress, elongation at break, breaking strength and modulus decreased as the ratio of skin layer decreased. For 0.2 mm parts, the ratio of skin layer increased with increasing injection speed, and yield stress, breaking strength, modulus increased with increasing ratio of skin layer, while elongation at break decreased.