Background: The extrusion of polymer profile products with complex micro cross section is difficult due to the extrudate deformation, especially for the profile with multi hollow lumens and inner ribs.
Method of approach: In order to investigate the effect of die lip geometry on extrudate deformations, three-dimensional simulations have been undertaken for typical small profile extrusions both inside and outside the die using finite element method. The Carreau model was used to describe the shear-thinning behavior of polymer melt. The systematic definitions of the die lip geometric parameters and evaluations of the extrudate deformations were proposed.
Results: It was found that, the thickness and profile deformations happen asynchronously, and the existence of the inner rib changes the global deformation, which cannot be predicted by a deformation combination of the basic geometries. Among the investigated die lip geometric parameters, the wall thickness ratio has the most pronounced effect on both thickness and external profile deformations of the extrudates. The decrease of the hollow ratio significantly reduces the extrudate deformation extent. Even with uniform thickness, the location and shape of the inner rib also generates extrudate deformations.
Conclusions: Comprehensive understandings on the mechanism of extrudate deformations and effects of die lip geometry were obtained. Some hints for micro profile die design were provided accordingly. Numerical results showed qualitative and quantitative agreement with the experiments.
Keywords: die lip, extrudate deformation, profile extrusion, polymer, three-dimensional simulation