The geometric design freedom, short lead time, and customization make additive manufacturing (AM) an attractive manufacturing approach for low-volume, high-value materials and components.  In addition to rapid fabrication of ‘fit and feel’ prototypes (rapid prototyping) and large-scale tooling and molds for traditional forming operations, additive manufacturing has been used to create medical implants and protheses, shoe soles, turbine blades and impellers, dental crowns, fuel injectors, antennas and sensors, and many other commercial and custom products.  Major manufacturing companies such as Porsche and Aetrex are utilizing AM to customize automotive seats and orthopedic footwear.   However, despite considerable progress in recent years, the limited range of materials available for various AM technologies limit more widespread applications.  Currently, the high-temperature requirements from the aerospace and automotive industries provide additional, unmet challenges for additive manufacturing solutions, particularly in the area of high-performance polymer composites.

Thermoset resins, like epoxy, generally have desirable thermal and mechanical properties, and have shown great promise as feedstocks for material extrusion AM. However, most high-temperature epoxy resins have high pre-polymer viscosities and exhibit highly exothermic cure reactions, which complicates the printing process and limits volumetric scaling.  Traditionally, fast, high-temperature processing reduces the viscosity of such resins, filling a mold before crosslinking initiation; however, this is not possible for AM.

 

This work aims to address this gap in material performance by developing a high-temperature fiber-filled feedstock using high viscosity, semi-solid epoxy resins while maintaining consideration of printing and curing behavior.  Two pre-polymers are combined in varying ratios that allow the viscosity and glass transition temperature of the cured composite to be tuned to achieve a balance between thermo-mechanical performance and printability.  A heated deposition system enables facile printing of the semi-solid feedstock, but requires a more detailed understanding the curing profile and temperature-dependent flow properties.  For the present system, heating to 70°C results in a viscosity of 5.4 Pa.s and an 18-hour pot life, allowing for rapid flow through a 0.515-mm-diameter nozzle without prematurely curing during the printing process.  A slow, multi-step curing process mitigates the high heat of reaction for this epoxy system to enable curing of intermediate-sized printed objects without slumping or runaway reaction. This formulation achieves flexural strength and modulus values of 145 MPa and 4.9 GPa, respectively.  The addition of up to 30 vol.% glass fibers are shown to increase the elastic modulus, but reduce printing behavior and increase porosity in the printed composite. Glass transition temperatures were measured to range from 240°C to 260°C for the printed composites. The fibers also improve the heat deflection temperature by 100°C to 320°C and yield a 160% increase in flexure modulus; however, a 34% reduction in strength occurs as a result of porosity.


Designing a High Temperature Epoxy Composite Ink for Material Extrusion Additive Manufacturing

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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