A Study of the Wave-like Flow Mark Generation Process on an Injection Molded Polymer Strip with Laser Interference

Abstract

The generation of wave-like flow marks on an injection molded polymer strip was experimentally studied using laser interferometry with a He-Ne laser during the filling process. A microscope camera system was used to observe the interference fringe patterns through a calcium fluoride observation window of an experimental mold. A geometric analysis of the flow marks was calculated with a simple optical theory that gave the surface shape change as a function of optical path difference. The variation of local flow mark depths was obtained as a function of the distance from the melt flow front, and the time after the passage of the flow front. It was found that the polymer started to shrink when it contacted the mold wall surface, and this deformation caused a warp on the molded surface that was the origin of flow marks. It was also shown that the hill and valley shape of the flow marks grew with time. In a previous paper, one of the authors reported a model that described the wave-like flow mark generation from a thermal engineering point of view. The results obtained in this study correspond to the surface deformation that was discussed in the previous paper. Therefore the present authors believe that the flow mark generation model proposed in the previous paper is proper.