Abstract
In compression molding using glass-fiber-mat-reinforced thermoplastic (GMT) sheets, a slightly longer compression waiting time from sheet placement on a lower mold to the start of sheet compression by an upper mold can cause incomplete filling due to a decrease in the sheet temperature. However, precise measurement techniques for compression waiting time have not been sufficiently established. A monitoring system was produced that includes pressure—temperature sensors mounted in a compression mold that can simultaneously measure the pressure and temperature of one local surface. Two types of distance sensors were also used to measure upper mold motion widely and precisely. Determination of compression waiting time was attempted by measuring the moment when the lower mold temperature slightly increases in response to contact with the melted GMT sheet and the moment when the melt pressure increases in response to compression by an upper mold. The results showed that compression waiting time could be precisely calculated using the profile data obtained. Moreover, it was also possible to observe the melt pressure overshoot that occurs depending on sheet stacking patterns and mold cavity shape, although in some cases, the overshoot was not observed. In conclusion, this study has demonstrated that the system is effective in monitoring the compression molding process widely and precisely.
Highlights
In the automotive industry, lighter materials such as glass-fiber-reinforced plastics and carbon-fiber-reinforced plastics have been applied to vehicle parts for improvement of fuel efficiency
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Lighter materials such as glass-fiber-reinforced plastics and carbon-fiber-reinforced plastics have been applied to vehicle parts for improvement of fuel efficiency
Vehicle parts made from fiber-reinforced plastics (FRP) with excellent specific strength, specific rigidity, and good moldability are being constantly developed, e.g., [1,2,3,4,5,6,7,8,9,10]
Summary
Lighter materials such as glass-fiber-reinforced plastics and carbon-fiber-reinforced plastics have been applied to vehicle parts for improvement of fuel efficiency. In the case of the mass production of parts reinforced with discontinuous long fibers more than 10 mm long, a compression molding method using sheet-shaped fiber-reinforced thermoplastics is generally applied. GMT sheets are manufactured through a process of impregnating fibers with resin without screw mixing, so that longer fibers than the LFT remain, and most fiber bundles are not separated. This molding method for GMT parts does not require special equipment, and a general purpose heating machine and a general purpose compression molding machine are the minimum pieces of equipment needed. Sheet-shaped LFT sheets are used in a molding
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