Effect of characteristic scale on the extrudate swelling behavior of polypropylene melt in a micro‐extrusion process

Abstract

The swelling behavior in micro‐extrusion has a significant effect on the dimensional and shape accuracy of microproducts. In this study, the effect of characteristic scale, defined as the gap of die land in an annular micro‐extrusion die, on the extrudate swelling behavior of viscoelastic melt is analyzed through numerical simulations and micro‐extrusion experiments. The results show that the swelling behavior displays an obvious dependence on the characteristic scale. An increase in the characteristic scale reduces the swell ratio and retards the process to reach the equilibrium state. In contrast, a decrease in the characteristic scale results in a larger magnitude of change in velocity field and faster relaxation development of stress field. The location of the maximum velocity layer for the laminar flow gradually deviates from the geometric center of channel toward the wall of mandrel with the increase in the characteristic scale. Moreover, an increase in the flow rate results in a larger swell ratio for a constant characteristic scale. The elastic effect plays a more dominant role than the viscous effect in determining the viscoelastic swell behavior. It is imperative to consider the complicated swelling behavior and remarkable viscoelastic effect simultaneously in micro‐extrusion process.

Comparing pellet‐ and filament‐based additive manufacturing with conventional processing for ABS and PLA parts

“…The gauge length was set at 50 mm. Consistent with previous studies 2,40,41 substantial differences were observed in the extrudate diameters for the different techniques and operating conditions, due to swelling differences 42 . Furthermore, previous research 2 revealed that at the same (set) processing temperature extrudates with larger diameters require additional time to cool down.…”

A Combined Experimental and Modeling Study for Pellet-Fed Extrusion-Based Additive Manufacturing to Evaluate the Impact of the Melting Efficiency

“…The effect of this variation in the PLA crystallinity during the sample preparation was neglected, as previous studies observed a marginal impact of the degree of crystallinity on the thermal conductivity [61]. Moreover, previous studies on the melting mechanisms in SSEs observed that small variations in the thermal conductivity have a neglectable impact on the solid bed profile (SBP) [21,38].…”

“…This is performed according to geometric and process parameters that can have a strong influence on the properties of the final parts [13][14][15][16]. In recent years, however, a growing number of AM applications introduced the use of single-screw extruders (SSEs) fed with polymer pellets [17][18][19][20][21]. The global term for such AM modifications is extrusion-based AM (EAM), complementary with conventional large-scale extrusion [22][23][24][25][26].…”

Modeling of extrusion through a Garvey die: Cost and performance

“…These models are more complex, with more parameters to be determined than the traditional power‐law model. Liu et al [ 9 ] studied a micro‐extrusion of polypropylene (PP) process by means of experiments and simulations. Their model was reduced by using symmetry in order to save on computational costs (reinforcing the need for computational capabilities at an affordable cost).…”