Modelling and experimental verification of pressure prediction in the in-mould coating (IMC) process for injection moulded parts

Abstract

In-mould coating (IMC) is carried out by injecting a liquid low viscosity thermosetting material onto the surface of the injection moulded part after it has solidified, while it is still in the mould. The coating then cures and adheres to the substrate. Due to its successful application to exterior body panels made from compression moulded sheet moulding compound, IMC is being developed as an environmentally friendly technology that would ultimately replace painting of injection moulded thermoplastic parts. In the short term, however, we believe IMC has the potential of being a substitute for primers. In a previous paper, we presented a Hele–Shaw based mathematical model to simulate the coating flow during the IMC process assuming the coating to be a power law fluid and using the traditional no-slip boundary condition. This model adequately predicted the fill patterns but did not predict pressures correctly. This deviation has been attributed to slip (or apparent slip) at the wall, as often found in flow through microchannels, due to the microscopic length scale of the flow, and the existence of a high shear rate Newtonian plateau for the coating viscosity. In this paper we present a mathematical model that includes the slip boundary condition and the Carreau viscosity model to properly describe the rheological behaviour of the coating material at high shear rates. The rheological and slip parameters of the coating material were measured using a customized micro slit rheometer. The predicted pressures are compared with experimental results obtained using our IMC pilot facility. It was found that the predicted pressures and coating thickness agree well with the measured values.

Insights into the slip flow phenomena encountered during in-mold coating (IMC) of plastic parts

“…Please note that the original equations derived by Aramphongphun had a misprint as corrected by Cortright [8] . In the denominator for true slip shear rate, the equation showed…”

“…Using their device, they measured the slip coefficient and extended the viscosity measurements to the high shear rate region. Bhagavatula and Castro [8] improved the model by using the three-parameter Carreau model to represent the coating rheology as a function of shear rate and allowing for slip at the wall. They were able to successfully predict both fill patterns and filling pressures, using the rheology and slip coefficient measured by Aramphongphun and Castro [4] .…”

Modeling and Simulations of Buongiorno’s Model for Nanofluid in a Microchannel with Electro-Osmotic Effects and an Exothermal Chemical Reaction

“…Its also been described that the slip conditions occurred at the microchannel walls for both Newtonian [ 20 , 21 ] and Non-Newtonian fluids [ 15 , 16 , 17 , 18 , 19 ]. Bhagavatula and Castro [ 22 ] derived the mathematical model for describing the rheological behavior of the coated substance for the high shear rates based on the Carreau viscosity model with the linear Navier slip boundary conditions. Babaie et al [ 23 ] investigated the thermal transport attributes of the electroosmotic pressure-driven flow of power-law fluids through a slit microchannel.…”

Decreasing the cycle time for in‐mold coating (IMC) of sheet molding compound (SMC) compression molding

“…We can thus say that there is no single optimal solution but a set of best compromises, which define the efficient or Pareto frontier (PF). A PF is a set of solutions that represent the best compromises among different PMs . A multiple criteria optimization (MCO) method was used to obtain the PF.…”