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In-mold decoration (IMD) injectionmolding has been themost promising surface decoration technique in recentyears,with the in-mold roller (IMR) injectionmolding being themost automated production process. During theIMR process, heat transfer in the cavity surface is significantly retarded because of the lowthermal conductivity offilm. As a result of the asymmetric melt and mold temperature, thermal-induced part warpage easily occurs. Tounderstand the variation in the temperature field of the core and cavity caused by the plastic film, this researchuses simulation and experiments to investigate the influence of themold's (core-and-cavity) asymmetric coolingsystem temperature on product warpage, and examines the impact of the film's heat retardation effect on thecrystallinity, tensile strength, and surface roughness of the treated products.Our results showthat the filmcausesa higher contact temperature between the hotmelt andmold during themolding process, resulting in asymmet-ric temperature in themold (core and cavity), increasing the crystallinity of the cavity and consequently increas-ing product warpage. In plastic, the warpage increase is from 0.03 mm to 0.62 mm when the film thickness is0.175 mm and the temperatures of the mold and hot melt are 50 °C and 230 °C, respectively, a great increasethan with steel (P20). With the asymmetric cooling system design, in which the cavity temperature is 50 °Cand the core temperature is 65 °C, the warpage can be reduced by 53%. For crystallinity and crystalline size,the filmheat retardation effect of the IMR process increases the crystallinity of the cavity by 16%, and the crystal-lite size by 12%, along with some increase in tensile strength. In addition, the IMR process can also increase thesmoothness of the product surface, reducing the surface roughness by 50%. 1. IntroductionAmong various plastic fabrication processes, injection molding hasthe advantages of low cost, mass production, and one-step forming forproducts with complex shapes. Hence35045
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, it has become the most widelyused technique [1] in the plastics industry. Because of the persificationof consumer products in the market, the variety of requirements fromproduct developers, and rising environmental protection awareness,conventional injectionmolding techniques no longermeet the demandsof the new era. In response, using high-performance plastic materialsand advanced injection molding processes, several techniques havebeen developed. Among them, in-mold decoration (IMD) injectionmolding is a recently-evolved process [2] which combines several ma-chining techniques and mold fabrication technology. During the IMDprocess, a pre-printed filmis placed in themold prior to injection. Injec-tion is then executed after themold is closed. Compared to conventional injection molding without the film, IMD can save post processing costs(spraying, coating, screen printing, or plating). In addition, IMD prod-ucts can have beautiful and precise surfaces with persified patternsand brilliant colors, which are durable against friction and scratches[1–4]. Because of its advantages, it has been used tomakemany currentproducts, such as cellphone shells, household appliance panels, automo-bile dashboards, cellphone keys, andmouse shells,which demand goodfeel in the hand and a precision appearance. This technique has threemajor categories: in-mold label (IML), in-mold roller (IMR), and in-mold forming (IMF) [3].During the IMR process, the pre-printed film transfers ink to theproduct surface through the roller and the feeder. As the ink and filmseparate, the next cycle of the injection molding process begins again.During the molding process, because the film is attached to the cavitywall, the heat transfer along the flow path causes different temperatureboundaries for the cavity surface (with film) and core surface (withoutfilm). The non-uniform heat transfer in the cavity induces a non-uniform temperature distribution across the gapwise direction duringthe filling and cooling stages [5–7]. As a result of the asymmetric tem-perature distribution in the cavity wall, unbalanced flow front advancement, severe warpage and stress, and other effects may impactthe part's properties, and non-uniform crystallization and orientationmay occur [3,4,8–12]. To date, most research has only explored theheat retardation effect caused by the film attached to the product.