Enhancing the sensitivity of 3D printed sensors via ironing and void reduction

Material Extrusion (MEX) Additive Manufacturing (AM) has risen as a promising technology to monolithically manufacture smart structures with embedded sensors. Despite all the benefits of MEX AM, 3D printed piezoresistive sensors still suffer from low sensitivity, making them unsuitable for the detection of low values of force, displacement and bending angle. In the present paper, a simple, effective, and inexpensive method to increase the sensitivity in 3D printed sensors is proposed, based on the leveraging of the ironing strategy, which resulted in an improvement in the sensitivity of 83% compared to traditional process parameter selection. The ironing strategy reduced intralayer porosity by 59%, as verified by X-Ray CT. Additionally, the ironing strategy involves an increased healing time, which promotes the polymer chain diffusion between layers, which translated into a greater stability of the sensor when cyclically stressed. Smart structures capable of detecting small forces (0.19 N of resolution against 1.96 N for traditional MEX scenario) and smart auxetic devices have been manufactured, demonstrating the potential of the proposed approach. The present research demonstrates the ability to reduce interlayer voids by using an intrinsic feature of the MEX process and consequently improve electrical performance of 3D printed sensors.