(129c) Weld Formation in Material Extrusion Additive Manufacturing

Additive manufacturing (AM) has become an important and disruptive production method. In traditional manufacturing customized tooling requires a large initial investment and localized production, which is offset by large volumes. In AM no tooling investment is needed and per unit productions costs are flat, which is advantageous for small-volume or individualized production. This is especially important in the medical industry where many devices are custom designed for the individual, the aerospace industry where volumes are low, and for manufacturing at point-of-demand, i.e., space station or military deployment. Although interest in AM seems recent, development has been ongoing for several decades. AM is now at a point where research and development can focus on understanding and improving the process at a fundamental level.

In polymer extrusion 3D printing, a material extrusion AM method, thermoplastic filament is extruded though a rastering nozzle on the previous layer. The resulting strength of the 3D produced part is limited by the strength of the weld between each layer. While numerous factors can affect the weld strength, the temperature of the extrudate and the previous layer dictate the amount of interdiffusion and thus the weld strength. Temperature measurements were performed using forward looking infrared imaging. Interdiffusion estimates were calculated from temperature profiles, normalized using horizontal shift factors from offline rheological measurements of the neat polymer. Weld strength was measured directly by mode III fracture using a simplified geometry limiting the measurement to a single weld. Since the processing conditions are known aprioi this approach provides the data needed to estimate the final build strength at time of design. The resulting agreement between interdiffusion estimates and weld strength for a range of printing conditions and thermoplastics are discussed.