Feb 8, 2016 | By Alec
For the 3D printing revolution to become an indisputable success, we will obviously need 3D printing techniques that are far superior – instead of comparable – than existing manufacturing procedures. In that respect, fantastic work is being done by researchers from the University of Warwick in the UK. Though they have previously been successful at 3D printing sensors, they have now developed a whole new microstereolithography (MSL) 3D printing technique that can be used to create piezoceramic objects. Just millimeters in size, these objects form the basis of a wide range of electronic devices, from sensors to scanners. Most importantly, their technique doesn’t suffer from the limitations that affect existing piezoceramic production techniques.
This innovation is part of the team’s ongoing research into 3D printing of functional materials for sensors and electronic systems, which already resulted in the development of a low cost 3D printable conductive plastic composite back in 2012. One of their latest research projects focused instead on a very particular material class: Piezoceramics. “Piezoceramics are a special class of ceramic materials that when compressed can create an electrical response or conversely, can respond to an electrical stimulation by changing shape,” they explain. These very useful materials can already be found all around us, from the sensors in airbag systems to fuel injectors in engines and the sound generating and receiving elements in medical imaging scanners. They also have various other naval and medical applications.
The only problem is that the shape and geometry of piezoelectric ceramics directly influence their functionality, and the traditional manufacturing process doesn’t provide a lot of options in that respect. This severely limits their functionality – a more intricate structure can obtain more data from ultrasound scanners, for instance. “Conventional manufacturing of such 1–3 piezocomposites is achieved by the ‘dice and fill’ technique: cutting channels into ceramic blocks and then back-filling the channels with a suitable polymer,” the team explains. “However, the resulting regular array of ceramic elements allows standing waves to develop in the plane of the transducer. These resonances couple to the resonant frequency in the transducer thickness direction and degrade performance.”
They have therefore explored more advanced production options for piezoelectric ceramics, and as they explain in their paper Additively-manufactured piezoelectric devices, they ended up at 3D printing. The paper was authored by David I. Woodward, Christopher P. Purssell, Duncan R. Billson, David A. Hutchins, and Simon J. Leigh. “The use of 3D printing technology allows the production of ceramics with complex shapes that would be difficult to produce using many of the conventional approaches to machining of ceramics,” they reveal. “These intricately shaped ceramic components could eventually find application in high-tech scanners for medical imaging and inspection of aerospace components after manufacture.”
Essentially, they have come up with a 3D printing technique that enables production of a custom resin material that is especially suitable for piezoelectric ceramics. First this required the development of a resin containing a material called 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (or PMNT), which features one of the highest known piezoelectric coefficients, d33. A custom microstereolithography technique was then used to made remarkably small 3D printed objects. “The technique uses stereolithography to solidify a light-sensitive polymer and ceramic mixture in a layer-by-layer fashion to build-up an object. The object is then placed in an oven to remove the polymer and leave a solid ceramic object. The final functional ceramic is just as dense as a conventional sintered ceramic and exhibits nearly identical piezoelectric functionality,” they explain.
The 3D printing section is actually remarkable similar to known SLA 3D printing techniques, featuring a photocurable resin that sits in a tray that moves down while being cured by a light source – in this case a simple bundle of three LEDs delivering red, green and blue light centered on wavelengths 628, 519 and 462 nm, respectively. “It combines low capital and operating cost with simplicity, high resolution and the potential to be applied to a wide variety of materials,” they explain.
However, there’s no arguing with the results. After sintering, the ceramic devices feature an in-plane resolution of _20mm and an out-of-plane resolution of <1 mm, “without suffering a significant reduction in the piezoelectric properties when compared to conventionally produced ceramics of the same composition,” they say. “The ability to fabricate devices in complex geometries and with different material properties means that conventional limits of manufacturing are not present.” What’s more, these shapes are produced in record times, and do not require additional tooling or manufacturing processes. The technique is also capable of producing any shape necessary, while the structures can be adapted to conform to curved surfaces too.
In short, it adds a truly new dimension to piezoelectric ceramics without increasing costs – the Warwick team even sees it as an addition to the standard arsenal of production tools for material scientists and engineers. Dr Simon Leigh, one of the team members, revealed that they will now work to realize this future. “The next step in this work is to generate a library of materials and scale-up the process for making much larger ceramic components,” he said.
Posted in 3D Printing Technology
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