Celine Bellehumeur

Effect of processing conditions on the bonding quality of FDM polymer filaments

Purpose – The purpose of this paper is to investigate the mechanisms controlling the bond formation among extruded polymer filaments in the fused deposition modeling (FDM) process. The bonding phenomenon is thermally driven and ultimately determines the integrity and mechanical properties of the resultant prototypes.Design/methodology/approach – The bond quality was assessed through measuring and analyzing changes in the mesostructure and the degree of healing achieved at the interfaces between the adjoining polymer filaments. Experimental measurements of the temperature profiles were carried out for specimens produced under different processing conditions, and the effects on mesostructures and mechanical properties were observed. Parallel to the experimental work, predictions of the degree of bonding achieved during the filament deposition process were made based on the thermal analysis of extruded polymer filaments.Findings – Experimental results showed that the fabrication strategy, the envelope temper...

Modeling of Bond Formation Between Polymer Filaments in the Fused Deposition Modeling Process

The bonding quality among polymer filaments in the fused deposition modeling (FDM) process determines the integrity and mechanical properties of resultant prototypes. This paper investigates the bond formation among extruded acrylonitrile butadiene styrene (ABS) filaments in the FDM process. Thermal analysis of the FDM process resulted in an estimation of the cooling profile of the extruded filaments. Sintering experiments were carried out to evaluate the dynamics of bond formation between polymer filaments. Quantitative predictions of the degree of bonding achieved during the filament deposition process were made. The model was used to estimate the effects of different manufacturing parameters in the FDM process. Results suggest that better control of the cooling conditions may have strong repercussions on the mechanical properties of the final part fabricated using the FDM process.

Composite Modeling and Analysis for Fabrication of FDM Prototypes with Locally Controlled Properties

Solid freeform fabrication (SFF) technologies have the ability to manufacture functional parts with locally controlled properties, which provides an opportunity for manufacturing a whole new class of products. To a certain extent, fused deposition modeling (FDM) has the potential to fabricate parts with locally controlled properties by changing deposition density and deposition orientation. To fully exploit this potential, this paper reports a study of the materials, the fabrication process, and the mechanical properties of FDM prototypes. Theoretical and experimental analyses of mechanical properties of FDM processes and prototypes were carried out to establish the constitutive models. A set of equations is proposed to determine the elastic constants of FDM prototypes. The models are then evaluated by experiments. An example of FDM prototype with locally controlled properties is provided to demonstrate the ideas.

Pressure Effect on Hydrodynamics of a High Pressure X-ray Transparent Polyethylene Fluidized Bed

Hydrodynamics of a polyethylene fluidized bed were studied at different operating pressures (191-2908 kPa) and constant temperature of 30°C. Minimum fluidization velocity (Umf) decreased with increasing of operating pressures. Measured Umf agree well with calculated Umf as derived from the standard deviation of pressure fluctuations using Puncochar’s Method (1985). As expected, with the increase of superficial velocity, amplitude and standard deviation of pressure fluctuation series also increase, which is indication of more vigorous bubbling behavior inside the bed. Power spectral density of pressure fluctuation series indicates similar frequency distribution of the bubbling behavior at different superficial velocities. The dominant frequency from the power spectral was found to be around 1 Hz. Bubble diameter and bubble velocity were estimated from X-ray fluoroscopy images. Bubble diameter and bubble velocity increase with increasing bed height and superficial gas velocity due to bubble coalescence and more gas flowing upwards. At the same fluidization number, the average bubble size slightly decreases with increasing pressure at all bed heights because there is less gas flowing and the bubbles coalesce less rapidly. The bubble velocity is observed to have a small decrease from 191 kPa up to 2200 kPa, and then a substantial increase due to the fact that at higher pressure, the solid circulation increases at the bed.

Dynamic Flow Behavior Measurements in Gas‐Solid Fluidized Beds Using Different Non‐Intrusive Techniques and Polyethylene Powder

Pressure fluctuations and X‐ray computed tomography (CT) measurements were utilized to characterize the flow behavior of gas‐solid fluidized beds using polyethylene particles in three Plexiglas columns with diameters of 10cm, 20cm, and 30cm. Air was used as the gas phase. Gas‐solids flow dynamic under ambient conditions was characterized from statistical analysis of pressure fluctuation data and CT images. The time‐averaged voidage distribution, bubble phase area fraction, bubble diameter and bubble number distribution varying with the bed heights were extracted from all the three columns. Bed scales had significant effect on the hydrodynamics. Scale up effects on the gas‐solids two‐phase flow behavior were discussed.