The industrial application of foam injection molding is often limited due to restricted surface qualities, limited light-weight potential as well insufficient knowledge of processing and mechanical properties. Especially the resulting structure is the key factor for mechanical properties and cannot be controlled in a wide range using conventional / low-pressure processing technologies. Here, the formation of integral structure, i.e. the density distribution and cellular characteristics like skin layer thickness and cell size define the properties. All these limitations can be counteracted by high-pressure foam injection molding with volume - expandable molds (core-back). This special process variant may decouple filling and foaming phase and allow an active control of foam characteristics, especially nucleation rate. Thus, homogeneous and flow-path independent structures can be achieved and the mechanical properties can be influenced. High-pressure foam injection molding with volume-expandable and local volume-expandable molds provide a tremendous potential for industrial applications and lightweight constructions and can offer light-weight potential also for geometrical complex parts. However, there is only insufficient knowledge about the parameters and its effects on structure formation. Thus, the potential is often unknown and seems to be more complex for applications. The knowledge of processing and the influence of boundary conditions on the cellular structure and geometrical restrictions is essential for applications and part design.
The presentation works out and clarifies the differences of high-pressure foam injection molding with volume – expandable molds to the conventional / low-pressure process route and contributes to make the structure formation within the mold during procedure more transparent and comprehensible. Mechanism of cell formation (diffusion, nucleation, cell growth, stabilization) are assigned to the process steps and process parameters to active control mechanism are illustrated.