Development of an original overmoulding device to analyse heat transfer at polymer/polymer interface during overmoulding

Abstract

Weather seals in the automotive industry are manufactured by overmoulding vulcanizate thermoplastic elastomers (TPV) profiles. This process is assumed to be a fusion bonding in which the quality of the thermal contact is essential to develop the mechanical strength of the assembly. This paper aims to evaluate for the first time the evolution of the thermal contact between the extruded and injected TPV during the holding and cooling phases of the overmoulding process. Within this aim, an experimental instrumented mould has been designed. Heat flux and pressure sensors have been integrated into the moulding cavity. Heat flux sensors have also been integrated into the insert during injection and in the mould cavity, allowing the temperature fields to be recorded during the entire overmoulding cycle. An inverse heat conduction problem is used to determine the time evolution of the surface temperature of the insert and the injected material. Heat flux densities crossing the interfaces are also evaluated. The average calculated heat flux density at the interface ranges between 1.75 × 104 W/m2 at the end of filling to 2.5 × 103 W/m2 at the ejection. The specificity of the developed method is to obtain non-intrusive quantitative information on surface temperature and heat fluxes. These measurements are used to calculate the Thermal Contact Resistance (TCR). The calculated TCR at the interface ranges between 2 × 10−2 m2 K/W and 1 × 10−2 m2 K/W over the whole overmoulding cycle. The temperature levels obtained during overmoulding were then compared to those calculated using a unidirectional scheme using the boundary conditions determined experimentally. The simulation highlights the influence of crystallization on the TCR.