Abstract
In injection molding, cooling channels are usually manufactured with a straight shape, and thus have low cooling efficiency for a curved mold. Recently, additive manufacturing (AM) was used to fabricate conformal cooling channels that could maintain a consistent distance from the curved surface of the mold. Because this conformal cooling channel was designed to obtain a uniform temperature on the mold surface, it could not efficiently cool locally heated regions (hot spots). This study developed an adaptive conformal cooling method that supports localized-yet-uniform cooling for the heated region by employing micro-cellular cooling structures instead of the typical cooling channels. An injection molding simulation was conducted to predict the locally heated region, and a mold core was designed to include a triply periodic minimal surface (TPMS) structure near the heated region. Two biomimetic TPMS structures, Schwarz-diamond and gyroid structures, were designed and fabricated using a digital light processing (DLP)-type polymer AM process. Various design parameters of the TPMS structures, the TPMS shapes and base coordinates, were investigated in terms of the conformal cooling performance. The mold core with the best TPMS design was fabricated using a powder-bed fusion (PBF)-type metal AM process, and injection molding experiments were conducted using the additively manufactured mold core. The developed mold with TPMS cooling achieved a 15 s cooling time to satisfy the dimensional tolerance, which corresponds to a 40% reduction in comparison with that of the conventional cooling (25 s).
Highlights
Injection molding is the most widely-used polymer processing technology, in which a hot polymer melt fills the mold cavity and is solidified by subsequent coolant cooling.In injection molding, the mold temperature must be kept high to improve the fluidity of the polymer melt and the relevant part quality, while it must be kept low below the softening temperature of the polymer for appropriate demolding [1]
The cooling channel should be located near the hot spot for adaptive conformal cooling
Numerical simulation was conducted to predict the hot spots of the injection molded part
Summary
Injection molding is the most widely-used polymer processing technology, in which a hot polymer melt fills the mold cavity and is solidified by subsequent coolant cooling. Various studies have used metal AM processes such as powder bed fusion (PBF) or directed energy deposition (DED) to develop injection molds containing conformal cooling channels [6,7,8,9,10,11] This conformal cooling channel with a consistent distance from the mold surface was based on the assumption that the initial temperature of the mold surface was uniform. Other disadvantages of an additively manufactured injection mold are the high manufacturing costs and low surface quality To overcome these disadvantages, several studies developed hybrid molds for conformal cooling by combining the traditional machining and AM processes [16,17]. The cooling performance of the developed TPMS mold was compared with that of typical channel-type cooling by analyzing the dimensional accuracy of the molded parts according to cooling time
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