Evaluation of Surface Replication of Injection Molded Products Using a Diffraction Method

Abstract

ABSTRACT

An evaluation method of surface replication for molded parts, which utilizes optical diffraction phenomena, is proposed. In general, the intensity of the diffracted light increases as the replication ratio becomes large, which leads to the increase in directly transmitted light. As a result, the surface in highly replicated region appears to be darker compared with the other region. An inversely proportional relationship between the 0th-order diffraction efficiency and the grating height is observed. It is shown that the replication ratio and uniformity can be easily evaluated simply by naked eye. The effect of injection speed and cavity thickness on the replication ratio and its uniformity are examined. Our experiments show that higher injection speed yields better replication ratio. However, in the case of cavity thickness of 1 mm, the higher injection speed makes the uniformity of surface replication worse. The better uniformity is achieved when the cavity thickness is 0.3 mm, which is because the inclination angle between the melt flow front and the orientation of the grating grooves are set to be small and the cavity pressure of the filling stage is high. Those conditions are strongly dependent on the ratio of gate thickness to that of the cavity.

Keywords: injection molding, diffraction, SWS, replication, optics, evaluation