Abstract
The economical production of lightweight structures with tailor-made properties and load-adapted geometry is limited using conventional technologies. Additive manufacturing processes offer a high potential to meet these requirements, where the established solutions are based primarily on thermoplastics matrix systems. From a process-technological point of view, thermoplastics enable simplified processing, but only a limited range of applications for high-performance components. These limitations are due to their comparatively low heat resistance, low melting temperatures and limited adhesion to embedded reinforcing fibers. In contrast, thermosets show high potential for realization of high- performance lightweight structures with adaptable properties. The present work employs a UV-curing thermoset resin for the impregnation of a continuous filament strand for 3D printing. The main challenge is to reconcile the crosslinking reaction of the thermoset and the process velocity during impregnation and cure. The liquid polymer must provide low initial viscosity to impregnate the filaments and a sufficiently high cure rate and dimensional stability after discharge from the print head to ensure sufficient bonding strength to the substrate. To demonstrate feasibility, a prototypic print head with UV-LED activation was designed and implemented. With a robot-guided printing platform, the 3D-deposition of continuous fiber-reinforcements without additional supporting structures can be realized. To derive initial process parameters, reaction and thermos-mechanical properties are determined by rheometer measurements. Impregnation and cure behavior of the glass fiber reinforced resin is investigated. The presented results provide a reliable process window and a straightforward process monitoring method for further enhancement of the conceived 3D printing process.
Highlights
Sustainable and efficient use of existing resources and the increasing demand for high-quality customizable products represent major future challenges for manufacturing industry
In order to enable flexible realization of lightweight structures with high thermo-mechanical properties, the use of thermoset matrix materials is a promising approach for additive manufacturing
Conventional processing of thermoset matrix materials suffers from long curing times ranging from some minutes to hours, which is unsuitable for 3D printing
Summary
Sustainable and efficient use of existing resources and the increasing demand for high-quality customizable products represent major future challenges for manufacturing industry. In order to enable flexible realization of lightweight structures with high thermo-mechanical properties, the use of thermoset matrix materials is a promising approach for additive manufacturing. Conventional processing of thermoset matrix materials suffers from long curing times ranging from some minutes to hours, which is unsuitable for 3D printing To circumvent this problem, radiation curable resins can be used instead of thermally activated formulations. The scope of this research is to present a methodical approach for a 3D printing process that combines a UV curing resin and continuous fiber reinforcement. For this purpose, the cure behavior of a UV activated epoxy resin is analyzed in order to define a process window for impregnation, curing and placement.
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