One of the biggest manufacturers in the world gives 3D printing a go
ULTRASOUND scanners are used for tasks as diverse as examining unborn babies and searching for cracks in the fabric of aircraft. They work by sending out pulses of high-frequency sound and then interpreting the reflections as images. To do all this, though, you need a device called a transducer.
Transducers are made from arrays of tiny piezoelectric structures that convert electrical signals into ultrasound waves by vibrating at an appropriate frequency. Their shape focuses the waves so that they penetrate the object being scanned. The waves are then reflected back from areas where there is a change in density and on their return the transducer works in reverse, producing a signal which the scanner can process into a digital image.
To make a transducer by painstakingly micro-machining a brittle block of ceramic material can take many hours of work, though. As a result, even as the size and cost of the console that controls the scanner has fallen with advances in microelectronics (some are now small enough to fit in a doctor’s pocket and cost a few hundred dollars), the cost of making the probe itself remains stubbornly high—as much as ten times that of the console.
At least, it does if you use traditional “subtractive” manufacturing techniques like cutting and drilling. However GE, a large American conglomerate, is now proposing to make ultrasound transducers by “additive” manufacturing—or three-dimensional printing, as it is also known. A new laboratory at the firm’s research centre in Niskayuna, New York, is taking a hard-headed look at the technique, which some see as a fad and others as the future, and working out which products might be made more efficiently by addition rather than subtraction.
Ultrasound transducers were an early pick both because of the complicated geometry needed to focus the sound waves and because ceramics are harder than metals to cut and drill accurately. But they are easy to print.
The GE process for making a transducer begins by spreading onto the print table a thin layer of ceramic slurry containing a light-sensitive polymer. This layer is exposed to ultraviolet light through a mask that represents the required pattern. Wherever the light falls on the polymer it causes it to solidify, binding the particles in the slurry together. The print table is then lowered by a fraction of a millimetre and the process repeated, with a different mask if required. And so on. Once finished, the solidified shape is cleaned of residual slurry and heated in a furnace to sinter the ceramic particles together.
More work will be needed to turn the process into a production-ready system. But Prabhjot Singh, who leads the project, hopes that it will be possible to use it to make not just cheaper ultrasound probes, but also more sensitive ones that can show greater detail. Although researchers have had new transducer designs in mind for years, it has been impractical to construct them subtractively. Additive manufacturing could change that.
The new laboratory will look at other forms of additive manufacturing, too. Some 3D printers spread metal powders on the print table and sinter the pattern with lasers or electron beams, rather than using masks. Others deposit thin filaments of polymer in order to build structures up. GE is interested in how the technology could be used right across the firm’s businesses, from aerospace to power generation and consumer products, according to Luana Iorio, head of manufacturing technologies at GE Global Research.
The gains include less waste and the ability to make bespoke parts more easily. But one of the most compelling advantages is freeing designers from the constraints of traditional production. Those constraints include having to design things not in their optimal shape but to be machined, often as a series of pieces. Additive manufacturing can combine parts into a single item, so less assembly is needed. That can also save weight—a particular advantage in aerospace. These new production opportunities mean manufacturers, big and small, are about to become a lot more inventive.
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