【正文】 ture in the final foam products. To meet this requirement, an advanced structural foam molding technology with continuous polymer/gas mixture formation was developed at the University of ,5 This technology facilitates the uniform dispersion and dissolution of gas in the polymer melt during the structural foam molding process, thereby safe guarding against the creation of large, undissolved gas pockets. In a previous work,5 we demonstrated the feasibility of using a customized small injection molding system consisting of a miniinjection unit and a foaming extruder based on this new technology. However, in addition to improved hardware technology, it is also required to develop appropriate processing strategies to control cell nucleation and growth inside the mold cavity. In this context, the current article discusses some processing strategies required to obtain a uniform cell structure with a high void fraction in an advanced structural foam molding process. We investigated the following critical parameters: blowing agent content, injection flow rate, and melt temperature. The structural foams obtained using our advanced molding technology were characterized in terms of void fraction, cell density, and cell size distribution。 threedimensional Xray topography was used to show the 3D cell morphologies of the structural foams. The pressure profile inside the mold cavity was also recorded under various BackgroundIn recent years, the advantages of foam injection molding have prompted improvements in structural foam molding technologies. Trexel Inc. developed a microcellular injection molding technology (MuCell technology) based on a reciprocatingtype injection molding ,7 A great deal of work has been carried out to further improve the quality of the microcellular foams produced using the MuCell process. Turng et al., for example, investigated the impact of changing processing conditions on the microcellular foam structures, especially in cases of coinjection molding with nanoposites Kanai et al. reported the creation of microcellular foams with a good cell structure and surface quality using copolymer polycarbonate reported the use of CaCO3 for controlling the microcellular foam morphology of polypropylene (PP). Sporrer et al. reported that a classA surface and a high void fraction could be achieved in foaming by using a breathing Recently, Bledzki et al. reviewed microcellular polymer materials and microcellular posites reinforced with mineral fillers and natural fibers. In 2000, Shimbo reported an alternative microcellular foam process that employed a preplasticatingtype injection molding A screw was used to plasticate the polymer, and a plunger was used to inject the polymer into the mold cavity as in typical structural molding. Another alternative foam injection molding process was developed at IKV, Aachen, this system, gas was injected in a specially designed injection nozzle mounted between the plasticizing unit and the shutoff nozzle of a conventional injection molding machine. Furthe rmore,to achieve better dispersion of the gas, static mixing ，elements were mounted between the gas injection nozzle and the shutoff nozzle. This technology was later mercialized by Sulzer Chemtech. In 2006, Park et al. presented an advanced structural foam molding technology based on a preplasticatingtype injection molding ,5 The conventional structural foaming technology was improved such that the injected gas would pletely dissolve into the polymer. The enhanced technology consisted of a gear pump and an additional accumulator to make the polymer/gas mixture formation step continuous regardless of the stopandflow molding operations. In other words, the newer design pletely decoupled the gas dissolution step from the injection and molding operations using a positivedisplacement pump. The details of this advanced structural foaming technology are outlined in the next section.This technology4 promotes uniform gas dispersion and plete (or substantial) dissolution in the polymer melt, despite the non steady molding process. Recognizing that stop andflow molding behavior inevitably causes inconsistent gas dosing, this design allows the flows of the polymer melt and gas to be continuous (., not to stop during the injection period Figure 1 shows a schematic of the advanced structural foam molding machine developed at the University of This machine prises a positivedisplacement pump (., a gear pump) and an additional accumulator, which is attached between the extrusion barrel and the shutoff valves. (One shutoff valve is located before the plunger, and the other is located at the nozzle.) The design pletely decouples the gas dissolution step from the injection and molding operations using the positivedisplacement gear pump and maintains steadystate gas dissolution. During the injection and molding operations, the plasticating screw rotates, and the generated polymer/gas mixture collects in the extra accumulator. After the mixture has been subjected to both injection and molding and has been collected,it moves through the plunger mechanism to be injected into the next cycle. This technology ensures that the pressure in the extrusion barrel is relatively constant and that consistent gas dosing is attained so that a uniform polymer/gas mixture is achieved regardless of the pressure fluctuations in the plunger. This technology has been patentedHomogeneous Distribution and Complete Dissolution of Blowing Agent. To maintain consistent gas dosing of the polymer and to pletely or nearpletely dissolve all of the gas in the polymer melt, the screw must rotate at a relatively constant The advantages of having the screw move ata constant rotational speed are twofold. First, consistent gas dosing is easily realized because the pressure fluctuations inside the extrusion barrel are minimized. Second, maintaining a high pressure guarantees the dissolution of the in