Formation and prediction of the multi-layered crystalline structures in micro-injection molded small modulus gears

Abstract

Due to the temperature difference between mold and melt, micro-injection molded products, such as small modulus gears, inevitably exhibit stratification. The presence of multi-layered crystalline structures with different mechanical properties can adversely affect the kinematic stability and service life of gears. In response to this problem, the distribution and property of multi-layered crystalline structures in micro-injection molded small modulus gears was analyzed based on experiment detection. The results indicate that higher mold temperature is advantageous to manufacture gears with more homogeneous and robust structure. Furthermore, a simulation was carried out to obtain melt thermal history. It can be found that the specific crystalline structure in gears has similar cooling curves regardless of mold temperature. This similarity can be represented by the initial cooling rate. Therefore, the initial cooling rate can be used as an indicator to predict the distribution of multi-layered crystalline structures. Besides, the additional heat dissipation of top land accelerates the cooling process of the melt at the corresponding position. Therefore, the non-core layer near top land is thicker than that near flank. Similar phenomenon is speculated to appear in the other injection molded microstructures with a similar length-width ratio.

Keywords

• Small modulus gear
• Micro-injection molding
• Mold temperature
• Crystallization
• Thermal history