Ultrasonic vibrations to optimise mechanical properties of AM parts

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Experimental set-up for ultrasound-assisted laser-directed energy deposition. (Image: Fraunhofer IWS)

Researchers are using ultrasound in additive manufacturing to produce more robust, durable and cheaper components for aerospace, toolmaking and other industries.

The ultrasonic vibrations will produce tailored fine-grained microstructures in wire- and powder-based additively manufactured components, which will improve their mechanical properties and corrosion resistance.

The work is being done within the four-year, €4 million UltraGrain project launched earlier this year between Fraunhofer IWS, Fraunhofer IAPT, and the RMIT Centre for Additive Manufacturing in Melbourne, Australia.

During the additive process, the researchers will send fine vibrations with a precisely defined ultrasonic frequency through the component or directly into the melt pool. The vibrations will prevent the formation of undesirable microscopic columnar structures, whose one-sided alignment can result in poorer mechanical performance. In addition, the ultrasonic vibrations will cause finer, round-shaped micrograins to be formed with equiaxial alignment, which increases the mechanical and chemical load-bearing capacity of the additive components. 

“With UltraGrain we can significantly improve the properties like fatigue resistance, strength, toughness and ductility or reduce the cracking susceptibility of additively manufactured components,” confirmed project leader Dr Elena López from Fraunhofer IWS. 

Because the ultrasound can be controlled in a targeted manner, the researchers are able to, for example, specify exactly where the workpiece will be subjected to great stresses later in use. There, the developers can plan for an ultrasound-controlled grain structure, but also decide at which points they can do without it in favour of faster production – known as adaptive process strategy. This is particularly applicable to parts such as gas tanks for space probes, which have to endure the unique challenges of outer space for long periods, or to tools in car factories that have to resist high point loads in mass production.

Fraunhofer IWS will contribute both its expertise in laser cladding, as well as its expertise in equipment that feeds the desired titanium or steel alloys to the laser in wire form. Investigations with powder-based starting materials are also planned.

Fraunhofer IAPT will work on the optimal design of additive components with different grain structures. The scientists will develop both a methodology for the optimal placement of ultrasonically influenced material areas, as well as optimal path planning for the new process technology.

The RMIT Centre for Additive Manufacturing will explore the physical processes that ultrasound triggers in the material during the new process approach using advanced synchrotron measurements. The Australian researchers will also investigate potential unexpected side effects that could occur when scaling the process from laboratory production of centimetre-sized components, to industrial series production of components spanning several decimetres or even metres.

“UltraGrain will help bring additive manufacturing to a broad industrial application,” predicts Professor Christoph Leyens, Executive Director of Fraunhofer IWS. The professors at RMIT are also very optimistic about the application of ultrasound to microstructure manipulation. They are convinced that the next generation of aerospace as well as space part additive manufacturing will significantly benefit from the uptake of the ultrasound technology.

Industrial interest in the new UltraGrain process is already high at the start of the project, with some of the members of the industrial advisory board being internationally active companies from the aerospace, railroad and other industries.

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