LIVE IN-MOLD MANIPULATION FOR ENHANCING MICROSTRUCTURE AND MECHANICAL PROPERTIES IN INJECTION MOLDING
António Cunha, Dimitre Tchalamov, Júlio Viana
University of Minho
Portugal
Keywords: Push-Pull, Scorim, orientation
The control of microstructural development in injection moulded semicrystalline polymers could be used for tailoring the mechanical properties of produced parts. A specially chosen set of processing conditions may lead to obtaining optimum levels of the degree of crystallinity and the overall molecular orientation. However conventional injection moulding offers a relatively limited possibility even if a large processing window is implemented. An expansion of the degrees of freedom is ensured by the application of live in-mould manipulation methods like Push-Pull and Shear Controlled Orientation in Injection Moulding or Scorim. Both methods rely on the same working principle - subjecting the still molten fraction of a polymer inside a mould cavity to an alternating shear field.
Scorim uses a conventional machine equipped with an additional module in which the polymer flow is split in two or four paths. An external hydraulic system operates two or four cylinders respectively, located along each of the flow paths. The shear field is created by reciprocating movements of the pistons.
In this study, polypropylene homopolymer was processed through Push-Pull, Scorim and conventional injection moulding. Design of experiment was used for exploring the processing-structure development-properties relationship. Polarized light microscopy displayed the microstructural development. Microhardness measurements were carried out for obtaining the across-the-thickness crystallinity profile. The flexural and impact properties of the produced parts were determined by three-point bending and instrumented falling weight tests respectively. The results reveal a statistically justified relationship between the imposed thermomechanical environments, the developed microstructures and the consequent mechanical properties. Conclusions on the determining parameters associated with each of the special techniques are drawn.