Investigations on roller-based filament drives

Abstract

The filament drive is a key part of the extrusion assembly of a Fused Filament Fabrication printer. This investigation examines the maximum feed force and the slip of different driving rollers using a filament made of polylactic-acid (PLA) on a test stand. The test stand systematically varies the main feed process parameters: feed velocity, pinch force between the rollers, and feed force. The maximum feed force has a characteristic dependency on the pinch force combined with a feed-velocity-dependency, which is influenced by the outer diameter of the driving roller. The slip was found to increase linearly with the feed force. The slip decreases with increasing pinch force and is nearly constant for pinch forces above 77 N—172 N, depending on the driving roller tooth geometry and outer diameter. A model derived from contact mechanics was used for phenomenological modeling of the slip in relation to pinch force and feed velocity. An exponential ansatz provided good modeling of the slip at a constant pinch force. The model of the slip combined with the extrusion forces in the liquefier can be used to estimate the material flow in the future, thus leading to increased precision of the parts in a magnitude of systems.