Aug 31, 2017 | By Benedict

Researchers at the Fraunhofer Institute for Laser Technology (Fraunhofer ILT) are developing a green laser SLM 3D printing system for printing pure copper and copper alloys. The project has been dubbed “SLM in Green.”

Thanks to Return of the Jedi, we’re used to seeing red lasers pitted against green lasers, and [spoiler] we’re also used to seeing the green laser come out on top. That trend is now continuing at Germany’s Fraunhofer ILT, where researchers are ditching the infrared lasers in their SLM 3D printers in order to better accommodate the printing of copper.

SLM 3D printing is a great way to print with aluminum, steel, titanium, and other alloys, but its compatibility with copper is low. That’s because copper—pure copper, at least—deflects a lot of the light from an infrared laser, rather than getting melted by it.

“Depending on surface properties, pure copper reflects up to 90% of laser radiation in conventionally used wavelengths of 1 µm,” says Daniel Heussen, a research fellow in the Rapid Manufacturing group at Fraunhofer ILT.

What this means is that hardly any laser energy actually ends up penetrating the copper, while the reflected light can cause havoc as it bounces around. Furthermore, copper does actually start to absorb the infrared light as it transitions from solid to liquid, but it’s hard to control when and where this transition occurs. Unless, of course, a different kind of laser is used.

And that’s the thinking behind Fraunhofer ILT’s ambitious new “SLM in Green” project, which will see a team develop a green light laser beam that can melt both pure copper and copper alloys.

Copper, you see, is much keener to absorb light emitted at a 515 nm wavelength than a 1 µm wavelength, so the use of 515 nm green light means that less laser power is required, while also ensuring a more precise focus.

This means that, if the Fraunhofer ILT researchers can develop a green light laser for an SLM 3D printer, they could be printing copper much more effectively than ever before.

“We are hoping for...more homogeneous melt pool dynamics so that we can build components with high material density and achieve other positive effects, such as a higher detail resolution,” Heussen explains.

Currently, there is no green laser source available that would suit the researchers’ project, so they need to make their own. The laser, which will be developed in a dedicated laboratory (expected to be ready by the end of 2017), will have a single-mode operation and function with a maximum output of 400W in continuous-wave (CW) at 515 nm.

If the SLM in Green project is successful, the Fraunhofer ILT researchers hope they will have produced an SLM system capable of printing copper parts with complex geometries, hollow structures, and undercuts. Potential 3D printed copper parts include jewelry, heat exchangers and heat sinks, and complex electrical components.

“Inductors for inductive heat treatment in industrial production are excellent showcases for additive manufacturing,” Heussen says. “They are mostly produced in small numbers with a high level of complexity and a wide range of different variants.”

Eventually, the green laser 3D printing system would also be used to print non-ferrous and precious metals—an ability the jewelry industry would undoubtedly be keen to capitalize on.

Heussen, however, is keeping his feet on the ground: “Before we achieve that,” he says, “we still need to overcome a few hurdles in process and system development, and gain a deeper process understanding for the use of the new wavelength. This is currently the goal of the publicly funded project.”

Fraunhofer ILT will demonstrate the early progress made in SLM in Green at this November's formnext exhibition in Frankfurt.

The SLM in Green project, which is funded by the German Federation of Industrial Research Associations, will then continue until mid-2019.



Posted in 3D Printing Technology



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