Single stage injection blow moulding process, without preform storage and reheat, could be run on a standard injection moulding machine, with the aim of producing short series of specific blow moulded parts. Product launch time is lengthened by preform design time, which results in a less than optimal thickness profile of the blown product. in injection blow moulding, contrary to extrusion blow moulding, the polymer is not molten before blowing. As a matter of fact, the initial step of injection moulding introduces a number of variable inputs in the blowing process, such as temperature gradients, strong molecular orientation and crystallisation onset.
Therefore, mechanical, rheometrical and thermal properties of Polypropylene were measured, with the aim to get the mechanical behaviour of the polymer in conditions close to the processing conditions.
We used tensile and oscillatory testing results, at different temperatures during melting or solidification to determine the material parameters. These parameters were fed into different constitutive equations : a viscous Cross model, a viscoelastic K-BKZ model and a elastic-plastic model. These models are temperature dependent and used in finite elements calculations with axisymmetric or three-dimension shell geometries. Calculations highlight the importance of the constitutive equation and of the initial temperature field on the solution. Comparisons between calculated and measured thickness were performed.
