In some cases, warpage failure occurs in the injection molding plate. This warpage can be predicted by using injection molding CAE. However, the prediction accuracy is not enough in the warpage analysis of injection molding CAE. The warpage generation mechanism changes according to the material and shape. The mechanism has not been clarified in each condition. For example, there is difference in the cooling speed of the real injection plate in each position.
In this report, we considered the influence of the difference of mold temperature on warpage, assuming the mold temperature to be an asymmetric condition. And the following conclusions were arrived at. Moreover, upon examining the influence of mold temperature difference on warpage of PP plate, the following conclusions were obtained.
1) The amount of warpage grows in an asymmetrical mold temperature condition. The amount of warpage increases in the case of high mold temperature even if the difference of temperature between fixed side and moved side is constant.
2) In the case of asymmetrical mold temperature, the distribution of crystallinity becomes asymmetrical in the thickness direction. However, the thermal expansion coefficient is isotropy and constant.
3) The key factor of warpage in asymmetrical mold temperature conditions in PP is induced by thermal effect.
4) The resin flow of asymmetrical mold temperature conditions in PP becomes a symmetrical flow. This is thought to be influenced by heat of shearing and latent heat of crystallization.
5) Even under the same mold temperature asymmetric condition, differences in material cause the influence of mold temperature on flow to differ.

View full abstract

The flow instabilities of polymer melts known as viscoelastic fluid were discussed in this report. Especially the occurrence mechanisms of two typical flow instabilities of “Shark Skin” and “Melt Fracture” were experimentally analyzed and the occurrence criteria for the flow instabilities were clarified with the viscoelastic flow simulation. As for “Shark Skin” region, the surface roughness at the die exit was observed without the pressure fluctuation and the flow pattern fluctuation at the wall vicinity in the die land. This result indicates that “Shark Skin” occurs at the die exit. As for “Melt Fracture” region, the periodical oscillation of the flow pattern and the periodical pressure fluctuation corresponding to the periodical distortion of the extrudate were recognized in the die land without the periodical oscillation of the flow pattern and the periodical pressure fluctuation in the reservoir (entry region of the die land). This result indicates that “Melt Fracture” is initiated at the die entry and occurs in the die land. Furthermore with the viscoelastic flow simulation, it was confirmed that the occurrence of “Shark Skin” depends on the wall shear stress and the occurrence of “Melt Fracture” depends on the maximum normal stress of flow direction.

View full abstract