Integrated manufacture of polymer and conductive tracks for real-world applications

Abstract

The present study demonstrates for the first time a unique UK-designed and built Additive Manufacturing (AM) hybrid system that combines polymer based structural deposition with digital deposition of electrically conductive elements. This innovative manufacturing system is based on a multi-planar build approach to improve on many of the limitations associated with AM, such as poor surface finish, low geometric tolerance and poor robustness. Specifically, the approach involves a multi-planar Material Extrusion (ME) process in which separated build stations with up to 5 axes of motion replace traditional horizontally-sliced layer modelling. The construction of multi-material architectures also involved using multiple print systems in order to combine both ME and digital deposition of conductive material. To demonstrate multi-material 3D Printing (3DP) we used three thermoplastics to print specimens, on top of which a unique Ag nano-particulate ink was printed using a non-contact jetting process, during which drop characteristics such as shape, velocity, and volume were assessed using a bespoke drop watching system. Electrical analysis of printed conductive tracks on polymer surfaces was performed during mechanical testing (static tensile and flexural testing and dynamic fatigue testing) to assess robustness of the printed circuits. Both serpentine and straight line patterns were used in the testing of Ag particle loaded ink and they showed very similar resistance changes during mechanical exposure. Monitored resistance and stress changed as a function of strain exhibiting hysteresis with more prominent residual strain during stretching and compression cycles and 3-point bending flexural tests of PA and CoPA substrates. Bare and encapsulated tracks exhibited low electrical resistivity (1–3*10−6 Ω*m), and its change was more rapid on ABS and minor on PA and CoPA when increasing tensile and flexural strain up to 1.2% and 0.8%, respectively. Resistance of Ag tracks on ABS also increased rapidly during fatigue testing and the tracks easily fractured during repeated stretching-compression cycles at 1% and 1.2% strain. No resistance changes of Ag tracks printed on PA and CoPA were observed at lower strain amplitudes whereas at higher strain amplitudes these changes were the lowest for conductive tracks on CoPA. Thermal analyses were conducted to determine the printed material’s glass transition temperature (Tg), stability and degradation behavior to find the optimum annealing conditions post printing. The novel AM printer has the ability to fabricate fully functional objects in one build, including integrated printed circuitry and embedded electronics. It enables product designers and manufactures to produce functional saleable electronic products. This new technology also gives the opportunity for designers to improve existing products, as well as create new products with the added advantages of geometrically unconstrained 3DP.