System and method for determining polymer filament rheological properties
Inventors
Smith, Douglas E. • Chen, Jingdong
Assignees
Publication Number
US-11441990-B2
Publication Date
2022-09-13
Expiration Date
2039-05-06
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Abstract
The present disclosure provides a low-cost and accurate rheometer system and method capable of determining melt flow rheological properties of polymers, such as from Fused Filament Fabrication (“FFF”) polymeric materials. The device can include a filament feeding system, liquefier for filament melting, force transducer for measuring filament feeding force, and a temperature control system for controlling polymer melt temperatures. An electronic control system can capture data and manage operations. The system can measure a filament velocity and filament force required to extrude the FFF filament for printing. The filament velocity and force data can be used to compute data sets of melt volumetric flow relative to pressure drop across a FFF nozzle. An inverse analysis process transforms the computed data sets through nonlinear curve fitting to determine rheological parameters, independent of the customary calculation of apparent viscosity from shear stress and strain rate, that can assist in controlling the filament deposition.
Core Innovation
The invention provides a simplified, low-cost, and accurate rheometer system and method designed to measure melt flow rheological properties of polymers, such as those used in Fused Filament Fabrication (FFF). The system integrates components including a filament feeding system that measures speed, a liquefier to melt the filament, a force transducer to measure filament feeding force, and a temperature control system for maintaining polymer melt temperatures. An electronic control system manages data acquisition and operation. This system can measure filament speed and force required to extrude the polymer for purposes such as 3D printing.
The main problem addressed is the lack of accessible, low-cost resources for direct, accurate characterization of new and existing FFF print materials. Existing laboratory rheometers are costly and generally require significant expertise, whereas prior art solutions often depend on traditional calculations of apparent viscosity from shear stress and strain rate, which may not be accurate for non-Newtonian polymer flows typical in FFF. This leads to issues in print quality and material performance because filament rheology is not characterized or controlled adequately.
Unlike prior approaches, the invention uses measurements of filament velocity and the force required to extrude the filament to compute melt volumetric flow and pressure drop across the FFF nozzle. Through an inverse analysis process using nonlinear curve fitting, these data sets are transformed to determine rheological parameters directly—such as the power-law consistency and index—without relying on customary apparent viscosity calculations derived from wall shear stress and strain rate. This facilitates more accurate and affordable determination of rheological properties for FFF materials, which can assist in controlling filament deposition for higher-quality printed components.
Claims Coverage
The patent claims comprise three principal independent inventions, each outlining a system or method for determining polymer filament rheological properties based on direct measurement of filament force and flow rate and subsequent computation of rheological model constants.
System for determining rheological properties using force, speed, and temperature measurements
The system includes: - A filament feeding system configured to feed the filament and determine its speed through the system. - A liquefier with a nozzle having at least one region of smaller cross-sectional area than the filament, for at least partial melting of the filament. - A force transducer coupled to the liquefier, providing force data to measure the force required to feed the filament through the nozzle. - A temperature sensor for measuring the temperature of the liquefier, the melted filament, or both. - The system is configured to determine values for one or more rheological model constants of a non-Newtonian fluid.
Method of determining rheological properties based on measured filament force and volumetric flow
The method entails: 1. Feeding the filament through the filament feeding system. 2. Heating the liquefier to at least partially liquefy the filament for passage through the nozzle. 3. Measuring the force needed to feed the filament through the nozzle. 4. Measuring filament speed to determine volumetric flow rate. 5. Forming multiple data sets pairing filament force with volumetric flow rate. 6. Applying the force and flow data to a fluid model with one or more rheological constants to derive a relationship formula. 7. Determining the rheological model constants by applying the data sets to the model (including via inverse analysis and nonlinear curve fitting).
System for determining rheological properties independent of apparent viscosity calculation
- A system as above, but expressly configured to determine the values of rheological model constants independent of the determination of apparent viscosity from shear stress and strain rate.
In summary, the claimed inventive features focus on a system and method that utilize direct measurement of filament force and speed, together with temperature, to compute rheological model constants for polymer filaments—particularly enabling analysis that does not rely on traditional apparent viscosity calculations.
Stated Advantages
Provides a simplified, low-cost, and accurate method and system for measuring melt flow rheological properties of polymers directly from filaments.
Allows determination of rheological parameters with high accuracy comparable to laboratory rheometers, but at a fraction of the cost.
Does not require calculation of apparent viscosity from shear stress and strain rate, thereby simplifying the process.
Enables integration into FFF processes, facilitating control of material deposition for improved quality of printed components.
Provides a new Filament Flow Index (FFI) that allows for quick characterization of filament extrusion characteristics.
Documented Applications
Measurement of melt flow rheological properties of polymers, polymer composites, fiber filled polymer composites, and other thermoplastics directly from FFF filament materials.
Integration with FFF (Fused Filament Fabrication) 3D printing processes to assist in controlling material deposition for quality components.
Generation of a Filament Flow Index (FFI) for quick assessment of extrusion characteristics in FFF filaments.
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