Additive Manufacturing Sound Makes 3D-Printed Metal Components More Stable

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Universität des Saarlandes Institut für Wirtschafts- informatik

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A team at Saarland University (Germany) aims to make 3D printing more precise. Doctoral student Oliver Maurer has now succeeded in significantly improving the quality of small metal components printed in the powder bed—using sound. This could enable industry to produce components with significantly higher load capacities. The researchers are looking for collaboration partners.

Shaking vigorously makes concrete more stable and load-bearing. The intense back-and-forth motion reduces voids between grains and pebbles, compacting everything. Similarly, the particles of metal powder in a 3D printer can move closer together. When the laser melts the compacted powder, the component that forms layer by layer from the molten metal becomes more stable, with the metal crystals forming in a finer mesh in the melt—provided all the critical parameters in the printing process are properly aligned. This has been demonstrated by the now-doctorate manufacturing engineer Oliver Maurer in his doctoral thesis under Professor Dirk Bähre, Chair of Manufacturing Technology at Saarland University. For the shaking, he used sound—after all, high precision is essential in 3D printing. "Sound can be controlled and measured very precisely," explains Oliver Maurer, highlighting why he prefers sound over a mechanical shaking device.

The melting process is more controlled with this new method. Specifically, the sound raises or lowers the powder surface within defined limits out of the laser focus. Additionally, the sound influences how the melt solidifies. Due to the densification, the supporting effect of the powder bed on the component is also higher, meaning the component stays in place, and the melt does not flow into gaps.

Oliver Maurer

3D-Printed Products Become More Durable

For this purpose, the manufacturing engineer installed a speaker in a standard metal 3D printer, specifically under the substrate plate where the metal powder is placed. The sound waves create vibrations and vertical shaking movements on the plate. Through the abrupt, intense shaking, the powder is deliberately compacted before the laser melts it. "This reduces pores, the microstructure of the metal layers becomes more homogeneous, the surface smoother, and the components are even geometrically more precise," says the researcher. This also means: 3D-printed products are far more durable due to their higher quality, they become more robust, their assembly is easier and faster, fewer defective parts are produced, and less post-processing is required.

"The melting process proceeds more controlled with this new method. Specifically, the sound raises or lowers the powder surface within defined limits out of the laser focus. Additionally, the sound influences how the melt solidifies. Due to the compaction, the supporting effect of the powder bed on the component is also higher, so the component remains in place, and the melt does not flow into gaps," explains Oliver Maurer. He further notes that the residual stress of the component is likely reduced as well, although this still needs further investigation.

After the laser melts the metal particles, metal crystals grow until they are fully solidified. "If the new component remains in constant vibration during this process, shorter rather than longer metal crystallites form in all directions. We can specifically control this process with sound," explains Oliver Maurer. This makes the printed component significantly more stable in its structure. This is because the crystallites do not simply grow long next to each other, which can lead to dreaded voids or bubbles in the melt, leaving holes in the components where there shouldn’t be any. A component weakened by such pores withstands stress less effectively. "Through the sound vibrations, the crystallites encounter neighboring crystallites more quickly, allowing us to achieve a better ratio of length to width of the crystallites, which are more densely interconnected. The metal structure is thus refined, becoming stronger and more stable," says Oliver Maurer.

Complicatedly Shaped Special Components With Many Corners And Edges are No Problem

With the new method, smaller components can be printed significantly finer, more accurately, and thus with higher quality. "Roughly up to a size that fits in one hand," adds Oliver Maurer. Prime examples would be intricately shaped specialized components with many corners and edges for aerospace, automotive industries, and even medical technology, such as prosthetics. Such metal components from 3D printers often fail to meet the high-quality standards today.

That sound can lead to better results in manufacturing processes was already known in laser cladding, the so-called laser deposition welding. To make workpieces more stable, metal structures are built on a base body by welding wire or powder.

Oliver Maurer

Anyone who thinks it's enough to just shake the 3D printer or simply expose the plate to sound is gravely mistaken: the process must be precisely calibrated on a case-by-case basis – and this is an extremely tricky task. "The individual process parameters differ significantly with and without sound," says Oliver Maurer, who specializes in this. Through countless experiments over several years, Professor Bähre's team gained experience in fine-tuning these processes. After all, the sound application must be perfectly aligned with all parameters of 3D printing, starting from laser power and speed to the thickness of the powder layer and the characterization of the metal type; otherwise, the component will not be perfect.

Three to Five Watts of Sound Power are Sufficient

"That sound can lead to better results in manufacturing processes was already known in laser cladding, the so-called laser deposition welding. To make workpieces more stable, metal structures are built up on a base material by welding wire or powder," says Oliver Maurer, who has now shown that sound can also lead to better results in powder-bed-based 3D printing. While laser cladding uses a sound power of 1000 watts, the much finer powder-bed-based 3D printing with Oliver Maurer's method requires just three to five watts of sound power. The Saarbrücken manufacturing engineer researched this method in his doctoral thesis using an aluminum alloy. "But the method can also be applied to other alloys. However, it is always crucial to tailor the entire process, especially the frequency of the sound application, to the specific requirements," says Maurer.

The manufacturing engineers are seeking interested companies to further develop their process for various applications.

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