Comparative study of surface quality on flat and curved UHMWPE surfaces using robotic milling

In the context of robotic machining for advanced thermoplastics, surface geometry plays a critical role in determining surface quality.This study investigates the effect of surface geometry on the surface quality of ultrahigh molecular weight polyethylene (UHMWPE) during robotic milling. Flat and curved geometries were machined using a 6-axis KUKA KR 120 R2700-2 F at spindle speeds of 6500 and 9500 RPM. Surface roughness parameters (Ra, Rq, Rz) were evaluated through a Mitutoyo SJ-410 stylus profilometer to assess the resulting surface quality. The results show that increasing spindle speed improved surface finish across both geometries. Curved surfaces consistently achieved lower roughness values compared to flat surfaces, with Ra improved by 27.5% (from 1.669 µm to 1.209 µm) and Rz by 33.1% (from 8.778 µm to 5.877 µm) on curved geometries. Conversely, flat surfaces experienced higher roughness but Ra still showed improvement by 29% (from 2.331 µm to 1.656 µm) and Rz by 36.2% (from 11.765 µm to 7.509 µm) with increased spindle speed. Despite fluctuations, all roughness values remained acceptable for industrial use, particularly in sliding components, structural spacers, and food-grade parts. The findings emphasize the importance of considering surface geometry in tool path planning and thermal compensation strategies for high-precision robotic milling of UHMWPE.