| Summary: | 碩士 === 長庚大學 === 機械工程研究所 === 90 === Liquid-assisted injection molding (LAIM) is an attractive idea, and investigated at the beginning of the 70s. The main advantage of liquid-assisted injection molding is the better cooling effective than injection molding (IM) or gas-assisted injection molding (GAIM). It permits shorter cooling times, reduced cycle times for the products. On the other hand, it had economical process medium and low plant costs. The aim of this study was to develop equipment about liquid injection system and investigate the quality of the liquid-assisted injection molded parts of thermoplastic materials.
The first part of the research is to investigate the effect of processing parameters in LAIM. Various processing parameters were studied in terms of their influence on the length of liquid penetration in liquid- assisted injection molded parts: melt temperature, mold temperature, melt filling speed, melt filling pressure, liquid temperature, liquid pressure, liquid injection delay time, liquid packing time, and short-shot size. The second part of the research is to optimize the length of liquid penetration in liquid-assisted injection molded parts. An L18 experimental matrix design based on the Taguchi method was used in this part. Experiments were conducted with an 80-ton injection molding machine provided with a liquid injection system by lab-made. The liquid injection system consisted of a liquid tank with the temperature controller, pressure regulator, valves, a solenoid, and a controller for injection time. A spiral mold was used for all experiments. The materials used were general-purpose polystyrene (GPPS), polypropylene (PP), and glass-fiber filled (20%, 30%) PP composite. The process medium used was water.
From the experiment results, the some important processing parameters affecting the length of liquid penetration in liquid-assisted injection molded parts were found. Short-shot size, delay time, liquid temperature are the key processing parameters for PP and PP composite materials. Short-shot size, melt temperature, mold temperature are the key processing parameters for PS material. On the whole, it was found that short-shot size is the most significant factor affecting the quality of the process for LAIM.
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