No‐flow temperature in injection molding simulation

Abstract

Most injection molding simulation packages use the no-flow temperature (NFT) as a means of determining whether the polymer flows or is solid. The NFT is not well defined, and a standard method for measuring it does not exist. A sensitivity analysis of the filling stage has been carried out with two different packages [VISI Flow (Vero Software Limited, Gloucestershire, UK) and Moldflow (Autodesk, Inc., San Rafael, CA)] to estimate the influence of the NFT on the main processing parameters. The NFT has a large influence on the thickness of the frozen layer, but it does not appreciably affect the filling pressure. Because the NFT affects the frozen layer, an effect on the estimation of shrinkage and warpage is expected. Software packages have also been compared, and similar simulations have been found to produce contrasting results. A simple correlation for NFT estimation, derived from the Cross-Williams-Landel-Ferry equation, is proposed for both amorphous and semicrystalline polymers.

A statistical analysis of nanocavities replication applied to injection moulding

“…The replicated height (H) for each simulation is measured as the height reached by the polymer at the center of the cavity when all the fluid inside the cavity is below its glass transition temperature, as it is shown in figure 11. It must be pointed out that some authors (Rytka [15] or Mannella [16]) consider that the polymer stops its movement not when its temperature is below the glass transition temperature but when is below its no flow temperature (NFT). The NFT does not have a standard method for measuring it and is considered a not well defined value.…”

The use of variotherm systems for microinjection molding

“…As shown in Figure , the real mold temperature is higher than the warm circuit temperature. No‐flow temperature is generally used to determine whether the polymer flows or is solid, which is estimated as T no = T g + 30°C . In our case, although the real mold temperature (∼144°C) is above the glass transition temperature of COC5013 (∼130°C) at the 130°C warm circuit, it is still lower than the no‐flow temperature and results in poor replication.…”

The influence of flow and thermal properties on injection pressure and cooling time prediction

“…In some cases, larger deviations (~20-30 %) were identified. In one study [14] it was stated that the change of NFT did not appreciably affect the injection pressure. However, in this work under present conditions it was found that the pressure values obtained by true viscosity with NFT=T g , NFT=T g +15 °C (data not shown) and NFT=T g +30 °C were overestimated on average by 7%, 12% and 18% relative to the experimental data.…”

“…This parameter is used for simplifying the flow calculation and overcoming the lack of accuracy of the viscosity model in low-temperature regions (i.e. temperature close to solidification) [14]. This material property may be measured by conducting flow experiments and recording the temperature below which the material will cease flowing.…”