ガラスインサート金型によるショートショット時のフローフロント挙動解析
Visual Analysis of Short-shot Front Behaviors by Glass-Inserted Mold
村田泰彦・横井秀俊・宇高 靖
Murata, Yasuhiko / Yokoi, Hidetoshi / Utaka, Yasushi
The melt flow patterns inside an injection mold have been approximated by utilizing the short shot method. However, whether the shape of a short shot front corresponds to that of the flow front shape during the filling process has not been investigated. It is necessary, therefore, to understand the factors which influence the behavior of the flow front during the short shot process.
In this paper, by using the "Glass-Inserted Mold" (which one of the coauthors and his research group have developed), we observed the behavior of the flow front during the short shot process, and analyzed several phenomena occurring near the flow front. In conclusion, we obtained the following results.
The flow front of the short shot is observed to move gradually during the cooling process after the end of injection. This movement is classified into the following three patterns :
(1) Advancement caused by pressure relaxation of the resin compressed in the sprue and runner.
(2) Regression caused by molding shrinkage of the resin during the cooling process.
(3) Advancement caused by the local transformation near the flow front of some crystalline polymer.
The advancement (1) accounts for more than 60% of the total, and this advancement depends on the residual pressure inside the runner and the method of screw control. The regression (2) depends on the molding shrinkages. The advancement (3) depends on the filling time inside the mold cavity and the cavity thickness. The advancement (3) of polypropylene reaches 0.1 to 0.2 times the cavity thickness, and that of polyacetal reaches 1.0 to 1.5 times the cavity thickness.
Key words: Injection molding / Visual analysis / Glass-Inserted Mold / Short shot / Flow front