Sink Mark

Sink Mark is a common defect in injection molded plastic parts, characterized by a localized depression or indentation on the surface of the molded component, typically occurring in areas with thick sections or at the intersection of ribs and walls. This manufacturing imperfection emerges during the cooling phase of the injection molding process when the molten plastic material contracts unevenly, creating a visible depression that compromises both the aesthetic appeal and potentially the structural integrity of the final product. The phenomenon occurs due to the differential cooling rates between thick and thin sections of the molded part, where the outer surface solidifies first while the inner material continues to cool and shrink, pulling the already-solidified surface inward. Design engineers and manufacturing specialists have developed various preventive strategies to minimize sink marks, including optimizing wall thickness uniformity, implementing proper cooling channel design, adjusting processing parameters such as melt temperature and holding pressure, and utilizing advanced simulation software to predict potential sink mark formation during the design phase. The severity of sink marks can vary from barely noticeable surface irregularities to significant depressions that may affect the part's functionality, making it a crucial consideration in industrial design and manufacturing processes. This issue is particularly relevant in sectors producing high-quality visible parts, such as consumer electronics, automotive components, and household appliances, where surface finish quality is paramount. The A' Design Award's product design category often showcases innovative solutions that successfully address such manufacturing challenges, demonstrating how thoughtful design can minimize or eliminate sink marks while maintaining aesthetic and functional requirements.

Author: Lucas Reed

Keywords: plastic injection molding, surface defects, material shrinkage, cooling optimization, design considerations, manufacturing quality control, industrial design aesthetics

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