Metal parts printed on 3D printers are increasingly being used in complex technology like cars and even planes. Even a small defect in the parts could cause crash with fatalities, so the manufacturers prior to installation you should carefully check the structure for integrity. Usually to check internal cavities ultrasound is used, however, in the case of printed parts with this difficulty and the details you need to freeze in the water.
The fact that 3D printers cause the molten metal layer by layer, so to check the parts for defects only after their complete manufacture. With components made from a single piece of metal, the process is much faster — cracks and other damage can be identified using ultrasound waves, which bounce off any irregularities.
Due to the layered structure, 3D printed parts have a lot of external irregularities, which prevent ultrasonic waves to detect internal defects. To avoid this, the part must be immersed in a container of material, similar to the metal density. Thus, the sound waves pass freely through the material and through the metal, perfectly recognizing the irregularities of the inside details.
According to Francesco Simonetti, Professor of aerospace engineering at the University of Cincinnati, material to facilitate scanning items can serve as regular ice. It is important that it had no cracks and air bubbles — that they were not, the researcher froze the water from the bottom up, until she was stirred by means of a special apparatus.
As expected, the density of ice was enough to hide the irregularities of the external parts and to allow the ultrasound to her inner cavity. It is assumed that the properties of the ice can be markedly improved by adding the nanoparticles to increase the weight and density.