Technical Assessment of 3D-Printed Spur Gears Produced from Recycled Polylactic Acid

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Abstract
Plastic gears are primarily used in manufacturing and automotive industries due to their quiet operation, resistance to corrosion, and lightweight characteristics. Traditionally, injection molding (IM) has been the preferred method for producing gears. However, the high cost associated with IM has made additive manufacturing (AM, otherwise known as “3D printing”) an increasingly attractive alternative. This study experimentally compares the performance of three-dimensional (3D)-printed spur gears made from polylactic acid (PLA) in three forms: virgin PLA (vPLA), 100 % recycled PLA (rPLA), and a 50:50 (vPLA: post-consumer household PLA waste [PC-PLA]) blend (blended PLA). These were compared with commercially available IM-PLA and IM-nylon gears. Gears with varying tooth counts were selected to represent different load distribution conditions and were designed based on commercially available models to ensure industrial relevance. All 3D-printed gears were fabricated using optimized printing parameters (layer height, infill density, and nozzle temperature) to ensure consistent print quality and minimize variability in performance testing. Performance was evaluated using a custom-built test rig at rotational speeds of 500, 1,000, and 1,500 revolutions per minute under a torque of 1.5 Nm. Key metrics measured included sound level, operating temperature, wear loss, wear rate, and service life. The results revealed that rPLA gears exhibited the poorest performance across all metrics, whereas blended PLA gears demonstrated wear characteristics similar to vPLA gears but remained below the performance of IM counterparts. These findings highlight the potential of blended PLA as a partial substitute for vPLA in gear applications, offering a balance between sustainability and mechanical performance, while also emphasizing the superior performance of IM gears under identical operating conditions. By diverting PC-PLA from landfill into blended formulations, this study contributes to advancing circular economy practices while providing data to guide sustainable material selection and gear design strategies.

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