Modeling of interlayer contact and contact pressure during fused filament fabrication

Timothy J Coogan,David O Kazmer

doi:10.1122/1.5093033

Abstract

An in-line rheometer and data acquisition system are used to monitor the melt pressure, melt temperature, and environmental temperatures while producing parts via fused filament fabrication (FFF). Melt pressures are observed to increase when printing parts with small layer heights, which is attributed to the confined space created between the nozzle and the previous layer (i.e., an exit pressure). These exit pressures (referred to as contact pressure) and the resulting interlayer contact areas are analyzed for 2863 layers created at 21 different processing conditions. The measured contact pressure was found to directly influence the shape of the layers and the resulting interlayer contact. An intimate contact model based on contact pressure is combined with a wetting model to accurately predict the interlayer contact of FFF parts. This pressure-driven intimate contact model for FFF shows strong agreement with the observed interlayer contact. No theoretical model has previously existed for predicting interlayer contact, so this research provides a critical component for developing a comprehensive part strength model. Both the measurements and proposed model are sufficiently simple and accurate for real-time analysis of FFF quality, so the described in-line sensors provide valuable quality insights and are recommended for future researchers, printer manufacturers, and end-users.

Highlights

Fused filament fabrication (FFF), known as fused deposition modeling (FDM®), is a form of additive manufacturing where layers of polymeric filament are oriented into a desired shape by pushing the material through a heated nozzle as is described more thoroughly in other works [1,2,3,4]
While printing FFF parts, the confined space created between the nozzle tip and the previous layer causes the pressure of the melt at the exit of the nozzle (Pcontact) to increase with increasing melt viscosity, volumetric flow rate, road width, and layer height
Small layer heights contribute most significantly to increasing the exit contact pressure, which is responsible for forcing the new layer into intimate contact with the previous layer

Summary

Introduction

Fused filament fabrication (FFF), known as fused deposition modeling (FDM®), is a form of additive manufacturing where layers of polymeric filament are oriented into a desired shape by pushing the material through a heated nozzle as is described more thoroughly in other works [1,2,3,4]. A review of parts made from acrylonitrile butadiene styrene (ABS) (a common material used in FFF) indicates that complete strength is typically not achieved along the z-axis [10], motivating our focus on interlayer strength and the physical contact between layers. The work by Sun et al showed that wetting did not significantly contribute to the interlayer contact of ABS because the rapid cooling and corresponding viscosity increase prevented interlayer contact growth. They proposed that diffusion was likely the dominant factor in determining strength [5]

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Discussion

Conclusion