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.