Adhesion-Induced Demolding Forces of Hard Coated Microstructures Measured with a Novel Injection Molding Tool

Abstract

The demolding of plastic parts remains a challenging aspect of injection molding. Despite various experimental studies and known solutions to reduce demolding forces, there is still not a complete understanding of the effects that occur. For this reason, laboratory devices and in-process measurement injection molding tools have been developed to measure demolding forces. However, these tools are mostly used to measure either frictional forces or demolding forces for a specific part geometry. Tools that can be used to measure the adhesion components are still the exception. In this study, a novel injection molding tool based on the principle of measuring adhesion-induced tensile forces is presented. With this tool, the measurement of the demolding force is separated from the actual ejection step of the molded part. The functionality of the tool was verified by molding PET specimens at different mold temperatures, mold insert conditions and geometries. It was demonstrated that once a stable thermal state of the molding tool was achieved, the demolding force could be accurately measured with a comparatively low force variance. A built-in camera was found to be an efficient tool for monitoring the contact surface between the specimen and the mold insert. By comparing the adhesion forces of PET molded on polished uncoated, diamond-like carbon and chromium nitride (CrN) coated mold inserts, it was found that a CrN coating reduced the demolding force by 98.5% and could therefore be an efficient solution to significantly improve demolding by reducing adhesive bond strength under tensile loading.

Enhancing structural replication of microfluidic chips: Parameter optimization and mold insert modification

“…The results indicated that the chromium‐based nitrides exhibited the lowest surface energy and the film compositions played a decisive role in the adhesion work of non‐polar PP and PS. Schoenherr et al 26 designed a novel mold for measuring adhesion forces, enabling a more accurate measurement of demolding forces. Griffiths et al 27 investigated the effects of melt temperature, mold temperature, and packing pressure on the demolding force of COC by using a condition monitoring mold and found that temperature had the greatest effect on the demolding work.…”