Mike Tromm is a research associate at Thermoplastic Lightweight Construction Department in University of Kassel, Germany. He investigated the local core back operation to achieve higher expansion ratios for creating less dense part and to achieve a homogeneous foam structure in foam injection molding. Different from standard core-back operation, the cell growth and density reduction were mainly restricted to the locally expanded areas, and this operation allowed him to produce mechanically-graded components in one step. Furthermore, huge variations of wall thickness could be achieved. Nevertheless, there was a complex interaction between geometrical boundary conditions, materials, and process settings, such as SCF content, expansion ratio, delay time, core-back speed, holding pressure, and holding time. Moreover, the experimental analysis for the foam formation via microscopic analysis was restricted to only final foam structures without providing better understanding about how the formation went on during the whole process.
Moldex3D was used to provide an insight of structure formation during the process. It supported a boundary condition for local core-back operation and could depict cell size, cell density, and part density at different times in filling/packing process. The cells were first created during filling and re-dissolved by packing pressure before they finally underwent second cell formation induced by volume expansion. Moldex3D could also illustrate the relation between cell size and cell density: the bigger the cells are, the lower the cell density is. Besides, it could verify that huge part density reduction existed in the expanded area where the cell formation took place, and sensor nodes were very helpful to record pressure and cell size relations at the expanded and non-expanded areas. The simulation also accurately confirmed the effects of parameter variations, such as SCF content, from experiment: the higher SCF content is, the smaller the cell size is.
- Insight and better understanding of local core-back technology for foam injection molding
- View of how the foam formation took place during the process
- Successful qualitative verification of experiment via simulation