Abstract
Nowadays, a challenging scenario involving additive manufacturing (AM), or 3D printing, relates to concerns on the manufacturing of electronic devices. In particular, the possibility of using fused filament fabrication (FFF) technology, which is well known for being very widespread and inexpensive, to fabricate structures with embedded sensing elements, is really appealing. Several researchers in this field have highlighted the high electrical resistance values and variability in 3D-printed strain sensors made via FFF. It is important to find a way to minimize the electrical resistance and variability among strain sensors printed under the same conditions for several reasons, such as reducing the measurement noise and better balancing four 3D-printed strain gauges connected to form a Wheatstone bridge to obtain better measurements. In this study, a design of experiment (DoE) on 3D-printed strain gauges, studying the relevance of printing and design parameters, was performed. Three different commercial conductive materials were analyzed, including a total of 105 printed samples. The output of this study is a combination of parameters which allow both the electrical resistance and variability to be minimized; in particular, it was discovered that the “welding effect” due to the layer height and printing orientation is responsible for high values of resistance and variability. After the optimization of printing and design parameters, further experiments were performed to characterize the sensitivity of each specimen to mechanical and thermal stresses, highlighting an interesting aspect. A sensible variation of the electrical resistance at room temperature was observed, even if no stress was applied to the specimen, suggesting the potential of exploiting these materials for the 3D printing of highly sensitive temperature sensors.
Highlights
Additive manufacturing (AM), known as threedimensional (3D) printing, is a new fabrication approach based on the idea of manufacturing objects layer by layer
Proof of the close link between AM and electronics has been provided by the birth of several customized 3D printers, such as the multi-process 3D printer developed by MacDonald et al [13] and the multimaterial 3D printer based on three syringes designed by Emon et al [14], which allow the manufacturing of electronic devices using non-conventional manufacturing approaches
It can be speculated that the results reported here refer to a temperature range that is, for both the examined materials, above the temperature split point between negative and positive temperature coefficient (TC)
Summary
Additive manufacturing (AM), known as threedimensional (3D) printing, is a new fabrication approach based on the idea of manufacturing objects layer by layer. An example of an additively manufactured wearable strain sensor for detecting joint motions during finger bending has been provided by Wang et al [23], who used a 3D printer machine to extrude a stretchable and conductive hydrogel Another milestone in this field is the work of Muth et al [24], in which they used AM as follows: by means of a nozzle, they deposited a conductive viscoelastic ink within an elastomeric reservoir in order to create a wearable and stretchable smart glove able to detect motions through electrical resistance changes. Strain gauges with fixed design parameters were manufactured by changing three different printing parameters in accordance with a 23 factorial plan, with three replications; from this phase, a combination of three printing parameters which ensured minimization and uniformization of the electrical resistance stood out. It was decided that the study would start with the printing parameter investigation
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