ガラスインサート金型によるウエルドライン生成および消失過程の解析
Visual Analysis of Weld-line Generating and Vanishing Processes Using a Glass-Inserted Visual Mold
横井秀俊・村田泰彦・岡 克典・渡辺広三
Yokoi, Hidetoshi /Murata, Yasuhiko / Oka, Katsunori / Watanabe, Hiromi
The occurrence of weld-lines is one of the most undesirable phenomena in injection molding because the molded product's appearance is damaged, and its strength is reduced in the area around the welded portion. It is difficult to prevent and limit the generation of these lines, thus studies have focused on their elimination or reduction. A Glass-Inserted Mold has been developed to observe the behavior of molten plastic flow inside an injection mold. In this study the weld-line generation process has been visually analyzed using this mold. The main results obtained are summarized as follows.
(1) Weld-line disappear after the meeting angle of two fronts becomes a particular vanishing angle within the range of 120°-150°, and the range particular to the material does not depend on the molding conditions and cavity shapes.
(2) The above vanishing angle depends on the pressure near the melt front because it faces the hot skin layer against the cavity wall after the front makes contact.
(3) Weld-lines are thought to be caused when a 3-D curved surface of two flow fronts swirls back towards a flat cavity wall at their meeting point due to fountain flow, thus folding the surplus area which is generated.
In future research the vanishing angle will be introduced into numerical simulations, thus allowing a prediction for when the weld-lines disappear.
Key words: Injection molding / Visual analysis / Weld-line / Glass-Inserted Mold / Weld-line vanishing angle