The control of microstructure development in injection molding had attracted several important studies in the recent years, being well established that the thermo-mechanical environment imposed to the polymer melt depends on the material properties, molding geometry and processing conditions. An entirely new design of an injection mold RCEM (Rotation, Compression and Expansion Mold) was developed and implemented, allowing for a wide variation of the filling and packing conditions in a flat disk geometry. One of the cavity walls (the ejection side) can rotate or move with a linear movement during the injection and holding stages. This enables several filling sequences and the variation of the cavity thickness. Two electric servomotors are use to directly drive those movements. Two temperatures and pressure sensors allow for the on-line process monitoring. Several examples of the potential uses of the RCEM are shown for the cases of amorphous and semicrystalline polymers. Results obtained with short-fiber reinforced polypropylene are also presented.