Injection molded components with functionally graded foam structures – Procedure and essential results

In the past few years, foam injection molding has increasingly gained significance in the field of technical plastic components. This is due to the development of new processes and processing combinations and efforts to produce lightweight products. In this article, a special tool technology will be introduced, which aids the process of expanding the existing areas of applications. The technology enables the production of foam injection molded components with different foaming ratios. This is made possible by core movements in the closed injection mold after the cavity has been filled volumetrically with plastic melt containing blowing agent. In doing so, functionally graded components with locally differing properties can be produced in one processing step. The method (pull and foam method) is based on the idea of equipping thin-walled components with locally foamed thick-volume elements – i.e. to increase the stiffness, create spacers, or joining surfaces. Simultaneously this method aims to exceed the limitations of conventional foam injection molding, especially with regard to scope for design. This article describes the procedure and characteristics of the process. Results with regard to the density in the differentially foamed areas, the morphology and the mechanical properties in correlation with the essential processing parameters are given.