In-mold dielectric cure monitoring techniques pioneered by the aerospace industry were applied to the manufacturing process of LITEFLEX R springs. Real-time data was collected in-situ and used to interpret the progression of cure in an epoxy/fiberglass composite. This information was used to trigger mold pressurization in an attempt to lower void content and improve part appearance.
A microdielectric sensor placed on the mold surface collected temperature and conductivity data that was converted to a cure percentage scale (cure index). The optimum pressurization point for the epoxy system was at approximately 40% conversion. Although results varied somewhat depending on spring geometry, void contents were reduced to less than 1%. Composite shear strength increased 10-15%. Surface appearance was also significantly improved.