Core-Shell Filament Stiffness for Extrusion Feeding
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Solution Overview
Problem
Elastomeric filaments used in extrusion-based additive manufacturing face challenges such as inconsistent feeding, buckling, and printing errors due to their soft nature, leading to inaccuracies and material distortion, as they tend to stick to surfaces and stretch, causing friction and elongation issues.
Innovation Solution
A core-shell filament design is implemented, where an elastomeric core with a flexural modulus of less than 31,000 psi is surrounded by a harder, non-elastomeric thermoplastic shell with a higher flexural modulus, ensuring sufficient stiffness and miscibility, allowing for consistent feeding and mixing within the print head to maintain elastomeric properties in the printed parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an elastomeric filament is used in extrusion-based additive manufacturing, then the printed parts can have elastomeric properties, but the filament feeding becomes inconsistent and inaccurate due to the soft nature of the material
Solution Approach 1:
The filament is constructed as a composite structure with an elastomeric core surrounded by a non-elastomeric thermoplastic shell. The elastomeric core (70-95% of filament cross-section) provides the desired elastomeric properties for the printed part, while the thermoplastic shell (5-30% of filament cross-section) provides sufficient stiffness and strength to enable consistent feeding through the extrusion system without buckling or sticking, thereby resolving the contradiction between maintaining elastomeric properties and achieving reliable filament feeding.
Solution Approach 2:
Different regions of the filament are assigned different material properties: the core region is made elastomeric to provide flexibility and elasticity for the printed part, while the shell region is made non-elastomeric thermoplastic to provide mechanical strength and feeding stability. This local differentiation of material properties allows each region to perform its specific function optimally.
2Reliability
If a softer elastomeric filament is used, then the printed parts exhibit desired flexible properties, but the filament tends to stick to surfaces and stretch, causing friction and elongation issues
Solution Approach 1:
The thermoplastic shell material is specifically selected to have a coefficient of friction lower than the elastomeric core material. This creates a favorable surface interaction where the shell provides smooth, low-friction contact with handling surfaces and extrusion components, while the elastomeric core maintains its flexibility. The shell acts as a protective interface that prevents direct contact between the elastomeric material and potential sticking surfaces.
3Reliability
If a harder shell material is used to provide stiffness, then filament feeding improves, but the shell material may affect the elastomeric properties of the printed part
Solution Approach 1:
The shell thickness is precisely controlled to be between 0.001 to 0.05 inches, representing a minor portion (5-30%) of the total filament cross-section. This thin shell provides sufficient mechanical support for consistent feeding while minimizing its impact on the overall part properties. The elastomeric core, comprising the majority (70-95%) of the filament cross-section, ensures that the printed part retains the desired elastomeric properties despite the presence of the harder shell material.
Solution Approach 2:
The shell thickness parameter is optimized to balance two competing requirements: it must be thick enough to provide the necessary stiffness for reliable filament feeding through the extrusion system, but thin enough to minimize its influence on the elastomeric properties of the final printed part. This parameter optimization allows the system to achieve both stable material handling and accurate part property reproduction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The core-shell configuration enhances the accuracy and consistency of filament feeding, reduces printing errors, and maintains the desired elastomeric properties of the printed parts by providing the necessary stiffness and preventing buckling, while minimizing the impact of the shell material on the final part's properties.
Implementation Method 1
The non-elastomeric thermoplastic shell material has a flexural modulus that is at least five times greater than the flexural modulus of the elastomeric core material and provides sufficient stiffness to the filament
Implementation Method 2
a shell covering the core and having a thickness t, the shell compositionally comprising a non-elastomeric thermoplastic shell material that is substantially miscible with the elastomeric core material
Implementation Method 3
heating the fed core-shell consumable filament in the print head to form a molten material
Data Source
AI summary
A filament for use in an extrusion-based additive manufacturing system includes an elastomeric core and a harder, non-elastomeric shell. The core compositionally comprising an elastomeric core material having a flexural modulus of less than 31,000 psi and a durometer of less than 80 Shore. The shell overlays the core portion and compositionally comprises a non-elastomeric thermoplastic shell material that is substantially miscible with the elastomeric core material, wherein the core material and the shell material have the same monomer chemistry. The non-elastomeric thermoplastic shell material has a flexural modulus that is greater than the flexural modulus of the elastomeric core material by at least a factor of five, wherein the shell provides sufficient strength or stiffness to the filament such that filament can be utilized as a feedstock in the extrusion-based additive manufacturing system.