Thin-walled Plastic Injection Molding Controlled Manufacturing

With the 3C(computer, communication and consumer electronics) products such as notebook computer and mobile telephone etc. becoming lighter, thinner, shorter and smaller, Thin wall injection molding(TWIM) becomes one hotspot of research because of reducing products weights, minifying size, economizing materials and lowing costs etc. Because the research on TWIM is still at the primary stage, and the theory system has not formed completely, moreover, it is few in domestic, this paper can reinforce domestic research in this domain, and will built the good foundation for the future research.A mould was designed in this paper, which can simultaneously mold four parts of different thickness (0.3, 0.5, 0.8, 1.0 mm). By utilizing the Moldflow MPI5.0 software Flow/3D module simulation analysis and injection molding experiment, we studied the effect of different process parameters (melt temperature, injection rate and the thickness of parts) to thin-wall injection molding characteristics.The effects of the different parameters (melt temperature, injection rate and the thickness of parts) to the distribution of shear rate in thin-wall injection molding were researched by MPI/Flow 3D software. The results show the shear rate close to the gate is much higher than at other positions, and decreases with the distance to the gate; The change of the shear rate is not evidence from 1.5 mm to the end of part at flow direction, and the shear rate is 2000～4000s^-1; the shear rate at the core layer is lowest, increases from the core layer to the sub-skin layer, and come to a maximum, and then decreases to the skin layer. However the shear rate at skin layer is higher than at core layer. The thinner the thickness of the parts, the greater the shear rate close to the gate, but the difference is not in evidence at the end.By utilizing simultane thermoanalyse (STA), the distribution rule of crystallinity along the flow direction and the thickness direction of thin-wall parts were researched. The results show the crystallinity close to the gate is higher than at other positions; the crystallinity decreases rapidly near the gate, and then gets to a nearly unconverted condition farther than 5 mm or so from the gate; The crystallinity close to the skin layer is higher than that at the core layer. The crystallinity increases from the skin to sub-skin layer and then decreases gradually to its minimum at the core layer; The melt temperature influences the crystallinity in thin-wall injection molding, which have little effect on the crystallinity at lower value, while higher melt temperature have more effect.According to the different crystallinity requirement of the performance, thin wall part's controllable fabrication can be realized by adjusting the melt temperature and injection velocity parameters so as to control the crystallinity of the forming part.