| Summary: | 博士 === 長庚大學 === 機械工程研究所 === 95 === Water-assisted injection molding technology has been used to manufacture plastic tubes in recent years, due to its light weight, relatively lower resin cost per part and faster cycle time. This research investigates the filling phenomena of the water assisted injection moulding process by using a flow visualisation technique and deveop a novel high flow rate water pin for water assisted injection molding of plastic parts.
Experiments were carried out on an 80-tonne injection molding machine equipped with a laboratory-developed water injection unit. The material used was semi-crystalline polypropylene. A flow visualisation mould was specially designed and made for this study. A high-speed video camera was used to record the mould filling phenomena of rectangular cavities with three-channel geometry and layouts: a flat plate, a plate with two zones of different depths and a plate with symmetric ribs. The interaction between the assisting waterand the polymer melt during moulding was observed, and insight into the water penetration behaviour was summarised.
The ring type and orifice type have the disadvantage of low flow rate and high pressure drop, while for the latter one the timing of piercing pin into the cavity is a challenge and the cost of mold is high. The pin, which consists of a sintered porous surface outlet, has been tested against parts with two different geometries: a plate with a channel across the center and a float-shaped tube part. The experimental results suggest that the proposed water injection pin can mold parts of large size with a more uniform residual wall thickness distribution.
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