Filament manufacturing via external grooving of an HDPE pipe wall: RSM optimization and mechanical tests validation

In order to explore the possibilities of manufacturing and testing specimens from extruded HDPE pipes to retrace material inherent properties, continuous filaments are circumferentially machined by grooving. The proposed protocol imposes to keep to a strict minimum damage effects since semi-crystalline polyethylene is sensitive to deformation and heat. A Taguchi plan is adopted with inputs (cutting speed; feed rate; depth of cut). The modeled performance characteristics are roughness criteria (Rt; Ra) and temperature (T°). Using ANOVA and response surface methodology, the optimized values are 137.0 m/min, 0.4 mm/rev and 4.0 mm respectively for Vc, f and ap. At the highest desirability, the values of Rt (1.100 μm), Ra (0.223 μm) and T (36.44 °C) are satisfactory compared to turning data. Tensile tests on specimens from outer, middle and inner pipe show that (σ–ε) curves are reproducible with a pronounced drawing zone, especially for the inner pipe layers. Practically, the elasticity modulus is increased by 43% from outer to inner layers while the utmost difference in the elastic limit is ~ 5%. Concerning failure strain, the increase is 47% meaning that the material shows a great predisposition to ductility. This behavior is related to the higher crystallinity in internal pipe layers.