The main technical issues in developing the in-mold coating (IMC) process of polymer and composite parts include: (i) flow pattern, (ii) injection pressure, and (iii) mold deflection. The injection pressure is greatly influenced by the flow field and rheological properties of the coating material. Due to the very small length scale of the IMC flow, “apparent” wall slip occurs in the IMC flow. The high shear rates encountered in the microchannels make it necessary to include the higher shear rate plateau in the viscosity models. Including these two factors is critical in developing a predictive model of the IMC flow.
Flow models based on the slip boundary conditions have been developed to determine the viscosity of microfluidics. A customized microslit rheometer — a slit rheometer with micrometer-sized channels of 100- and 25-micrometer gaps — was built to measure the viscosity. The reduced viscosity of the coating material was found in the 25-micrometer channel gap, which indicated the apparent wall slip in the flow system. The developed rheological models were used to analyze the experimental results and determine the slip parameter known as slip length. The value of the slip length was then used in modeling the slip flow to predict the pressure.
The numerical solutions based on (i) the viscosity models: the power law and the Carreau models, and (ii) boundary conditions: no-slip, true slip, and apparent slip were compared with the experimental results. It was found that the Carreau viscosity model of the coating material improved the pressure prediction while the slip boundary condition was important to predict the pressure in the 25-micrometer channel gap. This work makes it now possible to predict the pressure for IMC of thermoplastics.
The last issue, mold deflection, was studied in IMC of RTM. Simple mathematical models of IMC of RTM were derived to determine the pressure and hydraulic force. The effect of the mold deflection due to the pressure was integrated into the model in terms of the compressibility of the mold. The effect of the compressibility of both the substrate and mold on the pressure and hydraulic force is discussed in a case study.
|School:||The Ohio State University|
|Department:||Industrial and Systems Engineering|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||In-mold coating, Microfluidics, Process modeling, Rheology, Slip flow|
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