Improving Surface Quality and Dimensional Stability of Polymer Products With an Innovative Fiber‐Reinforced Double‐Sided In‐Mold Decoration Injection Molding Process

ABSTRACT Fiber‐reinforced polymer composites are prized for their lightweight and high‐strength properties. However, challenges in injection molding persist, particularly the formation of “floating fiber,” which degrades surface quality and limits their applications. Current methods, such as single‐sided in‐mold decoration (FR‐SS‐IMD), do not fully address issues of surface defects and dimensional instability caused by uneven temperature distribution. To overcome these issues, we propose a novel fiber‐reinforced double‐sided in‐mold decoration (FR‐DS‐IMD) process, which enhances traditional in‐mold decoration (IMD) technology. This method applies decorative films to both sides of the mold cavity, improving fiber orientation and temperature uniformity. We conducted numerical simulations and molding experiments using tensile splines to compare the effects of different decoration methods (no film, single‐sided, and double‐sided films) on surface quality, warpage, and mechanical properties. Our results demonstrate that the FR‐DS‐IMD process significantly reduces surface defects, such as floating fibers and flow marks, while improving surface gloss. Additionally, this method reduces warpage by 60.4% compared to FR‐SS‐IMD and increases tensile strength by 118%–135%. These results indicate that the FR‐DS‐IMD process not only addresses surface quality and dimensional stability issues but also enhances mechanical properties, providing a promising solution for expanding the use of fiber‐reinforced composites in high‐strength, low‐ductility applications.