In this study, an injection molding machine with a mixing mechanism of nitrogen (N-2) and melt was designed, and the melt-fill/porous-foaming behavior is observed under the novel barrel design (plasticizing stage) of the gas/melt mixing for the porous injection molded thermoplastic. The thermoplastic employed in this study was polypropylene (PP), and the gas for forming the porous structure is N-2. In addition, a thickness of 5 mm and a width of 10 mm paper-clip shape and the mold were constructed for studying the melt-fill-length and fill-length ratio through an experiment. The experimental results showed that the use of an injection molding machine with a mixing mechanism of N-2 and melt decreased the melt-fill-length when the N-2-output pressure was increased. The reason is that when the gas output, the speed of the screw will be affected. Therefore, during the gas/melt mixing and the plasticization rate will also affect the volume of the foam and the melt. But during plasticizing setting back pressure, can improve its melt volume reduction. When passing through the mixing mechanism and the injected melt, the melt is filled into the mold cavity, and the pressure in the melt is released/porous-foaming grows. At the same time, when the output pressure increases, the amount of melt in the injection barrel will decrease, and its relative porous structure/density distribution will increase. In addition, the mixing/flow direction of the melt impacted the density distribution and dispersion of porous foaming, thus the sample weight/shrinkage of melt-fill-length test sample (Mfl-ts) was improved.
