Processing Parameters And The Microscopic Mechanical Properties In Micro-injection Moulding Products

The flow behaviour of micro-injection moulding products were influenced by wall slip effects, viscous dissipation, surface tension in the micro-cavity compared with the conventional injection molding. And the micro injection molding process induced the complex multi-layered structure in the internal of the micro-injection products as well as virous mechanical performance of the micro products. Many researchs were focused on the relationship between microstructure and macroscopic mechanics, while hardly no research on the micro-mechanical properties of the micro-injection products. Thus, the main work of this thesis is the research of multi-level internal microscopic morphology, as well as the relationship between micro-mechanical properties and microstructure. The works are shown as follows:1. The effect of mold temperature on the hardness, modulus, crystallinity, morphology, grain size, orientation,the crystal grain density of micro gear products were investigated by PLM, nanoindentation,WAXD and other testing methods. The result show that, with the mold temperature increases, the thickness of the core layer increased, the thickness of the skin layer and shear layer decreased, β crystal content decreased, the degree of crystallinity increased; The modulus of shear layer and the hardness of core is increased as the mold temperature increases; and the wall slip effects appeared at the mold temperature of 50℃.2. With the increasing of flow rate, the thickness of core layer and the shear layer decreased, the thickness of the core layer increased, and the distribution area of β crystals becames wider; higher flow rate result in lower degree of orientation; the hardness and modulus of shear layer near the gate location reach the maximum at the flow rate of 28mm/s, the hardness and modulus of the core layer decreases with increasing flow rate.3. Different processing parameters were performed to investigated its effect on the microscopic morphology structure and micromechanical properties. With the content of β nucleating agent increased, the distribution of β crystals’inlarged at core, the thickness of the core layer becomes smaller, the thickness of the shear layer becomes large; the crystallinity raised when the β nucleating agent was added to the micro gear, and reaches maximum when the content of β nucleating agent at 0.7wt%, with increasing β nucleating agent, hardness and modulus of the shear layer increases slowly. With the increase of the a nucleating agent, the crystallinity of the micro gears researches maximum when the content of nucleating agent at 0.5wt%, the melting point as well as the hardness and modulus of the core layer increased with improve of the a nucleating agent content, and reaches maximum at the content of 0.5wt%. The secondary processing increased the crystallinity and the hardness and modulus of the core layer, while the degree of orientation and grain size of the core as well as the hardness and modulus at the shear layer reduced.