Research teams and companies around the globe are investigating ways to improve additive manufacturing at all points in the process chain—from materials and process parameters, to the printing hardware and beyond. A recent development out of the RMIT University’s School of Engineering could lead to improvements in powder-based metal 3D printing, dramatically increasing print consistency.
The RMIT research team has discovered that ultrasound technology can be used to create stronger, denser metal parts by essentially shaking powder particles into a tighter formation during the printing process.
The breakthrough, recently published in the journal Nature Communications, demonstrates how high frequency sound waves can be leveraged to change the inner micro-structure of 3D printed alloys, resulting in better strength and consistency.
“If you look at the microscopic structure of 3D printed alloys, they’re often made up of large and elongated crystals,” said Carmelo Todaro, the lead author of the study and a PhD candidate at RMIT’s School of Engineering. “This can make them less acceptable for engineering applications due to their lower mechanical performance and increased tendency to crack during printing.
“But the microscopic structure of the alloys we applied ultrasound to during printing looked markedly different: the alloy crystals were very fine and fully equiaxed, meaning they had formed equally in all directions throughout the entire printed metal part.”
In tests, the research team found that titanium parts 3D printing using the ultrasound waves had a 12% improvement in tensile strength and yield stress compared to the same parts made using conventional additive manufacturing.
The study consisted of testing the effects of sound vibrations on two commonly used metal AM powders, a titanium alloy (Ti-6Al-4V), and a nickel-based super alloy (Inconel 625). Working with these powders, the research team discovered that the ultrasound technology could also be used to change the microscopic structures of specific parts of a single component. This phenomenon, called functional grading, was achieved by simply turning the sound wave generator off and on during the printing process.
“Although we used a titanium alloy and a nickel-based superalloy, we expect that the method can be applicable to other commercial metals, such as stainless steels, aluminium alloys and cobalt alloys,” said RMIT Distinguished Professor Ma Qian, the co-author and project supervisor. “We anticipate this technique can be scaled up to enable 3D printing of most industrially relevant metal alloys for higher performance structural parts or structurally graded alloys.”
Going forward, the research team hopes its innovative breakthrough will inspire other research groups and companies to explore the potential of developing specialized ultrasound machines for metal 3D printing.