Establishment of a Rotary Print Head to Effect Residual Stresses and Interlayer Bonding in an FLM-Process

Philipp Bengfort,Dennis Stracke,Bernd Künne

doi:10.3390/jmmp5030082

Philipp Bengfort, Dennis Stracke + Show 1 more

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https://doi.org/10.3390/jmmp5030082

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Abstract

In fused layer modeling (FLM) manufacturing technology, there is an increased demand for semi-crystalline materials due to their favorable mechanical properties, such as high strength and toughness. The reasons for their limited use are process-related residual stresses and reduced interlayer bonding, resulting in component distortion, warping and poor strength. Addressing these problems, this paper presents the development and implementation of a rotary print head that enables local laser pre-deposition heating and forced air cooling in the 2.5-dimensional FLM process. Samples of polypropylene are fabricated to investigate the effects of the modified process on residual stresses and interlayer bonding. The investigations show that local laser pre-deposition heating can positively influence the interlayer bonding. In combination with a reduction of the extrusion temperature and additional cooling, it is possible to considerably reduce the residual stresses. The results of this research show that pre-deposition heating and forced air cooling significantly improve the processability of semi-crystalline thermoplastics in the FLM process.

Highlights

Additive manufacturing technologies based on material extrusion (MEX) represent processes known as fused-filament-fabrication (FFF), fused-deposition-modeling (FDM) or fused-layer-modeling (FLM)
The layer-by-layer structure of components typical for MEX processes causes a thermally inhomogeneous manufacturing process, which leads to a considerable anisometry due to reduced interlayer bonding, the main reason for inferior products compared to injection molded components [2]
Even though the results show positive influence on the warping behavior of polypropylene, it must be noted that the mechanical properties are to some extent negatively influenced and interlayer bonding is not significantly improved or even deteriorated [9,10,11,12,13,14,15,16]

Summary

Introduction

Additive manufacturing technologies based on material extrusion (MEX) represent processes known as fused-filament-fabrication (FFF), fused-deposition-modeling (FDM) or fused-layer-modeling (FLM) These techniques are characterized as flexible and cost-effective prototyping tools, but due to unpredictable anisotropic component strength, poor surface quality and dimensional inaccuracy are not established as manufacturing solutions compared to material jetting, binder jetting, powder bed fusion or VAT polymerization [1,2,3,4,5]. The layer-by-layer structure of components typical for MEX processes causes a thermally inhomogeneous manufacturing process, which leads to a considerable anisometry due to reduced interlayer bonding, the main reason for inferior products compared to injection molded components [2] Amorphous thermoplastic materials such as PLA, ABS or PET-G can be processed to comparatively good results. The additive manufacturing of semi-crystalline and generally high temperature polymers is more challenging due to residual stresses and poor interlayer bonding, leading to dimensional inaccuracy and high anisotropy [6]

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