Experimental Study On Molding Mechanism Of Differential Injection Molding

With the development of science and technology, the products have become more and more accurate to satisfy the requirements of industrialization, and the technology of Micro Electro Mechanical Systems (MEMS) emerges as the times require. Micro injection molding is one of the major methods to produce MEMS products. The keys of the micro injection molding technology are high quality injection molding machine, micromold insert, precise micromold base and auxiliary system. Throughout the history of micro injection molding technology, the design of micro injection molding machine is mainly depending on the miniaturization of dimensions. According to the conceptual design, micro injection molding machine is more suitable to fabricate micro plastic products than conventional injection molding machine. The processing difficulty of precision screw and plunger is great and these parts have a limited lifespan. The existing micro injection molding machine could not realize the mass production of micro parts, and the cost of the equipment is very expensive.A novel equipment which called all-electrical differential injection molding machine for molding micro plastic products has been developed based on the melt differential principle. The differential injection molding machine includes injection molding platform and differential molding system. As the core portion of molding system, a melt differential pump is driven by a servo motor for delivering, supercharging and metering of plastic melts. In order to satisfy the requirements of different products, the injection doses are directly controlled through changing the rotating angle of servo motor. The injection molding platform is used to realize plastification of polymer pellets, and to provide plastic melts and sufficient clamping force to the differential molding system.In this subject, the differential injection molding machine is applied as a platform to carry out the experimental study on molding mechanism of differential injection molding. And some study achievements are obtained as follows:(1) Study on the outlet pressure stability of the differential molding system. The relationships between outlet pressure and inlet pressure, injection angle, starting time are discussed. Analysis results indicate that the outlet pressure increased with the increases of inlet pressure and injection angle, and unrelated to the starting time. The processing properties of differential injection molding technology are illustrated through this experiment, which could provide theoretical basis for reasonably settings of inlet pressure, injection angle and starting time.(2) Study on the metering stability of the differential molding system. The relationships between injection doses and different outlets, injection angle are discussed. Analysis results indicate that the nonuniformity of injection doses changed with the variations of injection angle. The setup range of injection angle for achieving the best molding stability of differential injection molding machine is summarized through these experiments.(3) Effects of differential injection molding parameters on the injection dose repeatability are investigated by the orthogonal experiment method. The study results indicate that rotation speed of the servo motor is the most important factor affecting the injection dose repeatability, and followed by the nozzle temperature, injection pressure and injection angle. The optimal molding conditions are determined and the setup rules of differential injection molding conditions are mastered through these experiments, which could play a better guide role in practical manufacturing.(4) After mastering the processing properties and molding rules of differential injection molding, mold cavities with micro gear and micro chip are designed to perform molding experiments, which are used to evaluate the molding performance of differential injection molding machine. Study results indicate that micro plastic products could be fabricated well with the machine, and also have better appearance quality, mechanical property and molding efficiency.(5) The Moldex3D package is employed to implement numerical simulation. The filling process of molding product is observed. Effects of filling, packing, cooling conditions on the shear stress, volume shrinkage and warpage are also discussed. The molding process of differential injection molding machine is more transparent, and the solution of defects and structure optimization of molding product is more reasonable through these numerical simulation results. Furthermore, the influencing rules of micro structures on the injection rate are mastered with this analysis method, which could play a guide role in the selection and design of micro structures for differential molding products.