Application of Thermography for the Optimization of the Blow Molding Process

Abstract

3D blow molding is a technique by which the parison is extruded, generally from an accumulator head, and manipulated to fit the contours of a horizontal or tilted mold cavity in order to produce complex 3D shapes such as ventilation ducts, resonator tanks, connecting pipes, intake manifolds, steering shaft sleeves, etc. Thermography is a nondestructive, noncontact characterization technique that provides qualitative wall thickness distribution in real time. It can be a useful tool in the optimization of the blow molding process. Transient thermal imaging techniques allow the identification of thin and thick wall areas in a blow molded part. Thin walls can have their thickness inferred using calibration curves. The accurate measurements require minimal surface roughness and constant molding conditions. Thermal imaging, through the appearance of hot spots, can be used to detect shrinkage and poor adhesion to the mold surface. The contact resistance at the interface depends strongly on the wetting of the mold, the temperature of the parison, and the crystallinity of the plastic. The parison extrusion stage during 3D blow molding can be optimized by monitoring the surface temperature of the parison as it is being layed inside the mold. This information could be used to program the right parison thickness profile as well as the location of the interface in the case of sequential 3D blow molding.