FEATURE: ADDITIVE MANUFACTURING
Nasa produced a combustion chamber for a rocket with a copper liner made by DED additive manufacturing
g combination with the mentioned process control techniques would add great value. For instance: the optical process control unit regulates the laser parameters, adapted to the heat dissipation. A widespread portfolio of different geometries and materials would give AI the chance to learn how to identify the optimal process parameters for every single layer.’ In addition to controlling the process,
Stoll and his colleagues modified their infrared Concept Laser Mlab Cusing R machinery, produced by GE, to achieve minimal 25µm spot diameters. ‘The best results were reached with a spot size of 35µm at volumetric energy densities between 750 and 1,500J/mm³,’ he said. ‘The mean material density of the specimens was over 99 per cent at optimal process parameters.’
Going green Another way of assessing 3D-printed copper is through electrical conductivity. The FAPS team was able to reach 57MS/m, close to the maximum conductivity possible in bulk copper at 57-58MS/m. Stoll notes that switching from infrared to green lasers would be ‘a perfect solution for this problem’, but that such lasers are typically very expensive. ‘As the trend goes to visible light applications due to better absorption in metals, even high-power blue lasers are being developed.’ Laser giant Trumpf has already combined
its green TruDisk 1020 laser with its TruPrint 1000 additive manufacturing system. The 515nm laser is a lot closer to the wavelength where copper absorbs the most light, according to Damien Buchbinder, head of product management at Trumpf Additive Manufacturing. ‘Therefore, you really get power into the powder, and then the melt,’ he said. ‘Now you can process pure copper, which opens a wide range of new applications and mechanical
14 LASER SYSTEMS EUROPE SPRING 2020
The combustion chamber using DED (A) fits inside the Inconel alloy jacket (B)
properties. And the other big benefit is that copper alloys are now possible with higher productivity and better mechanical properties than before.’ Processes are two and four times faster,
offsetting the slightly higher cost of adding the powerful green laser, he asserted. The TruPrint 1000 is the company’s smallest printer, with a build volume of around 100mm3. ‘Together with the TruDisk 1020, it has a spot size of 200µm,’ Buchbinder said. ‘With it we can achieve printed wall thicknesses down to 0.4mm.’ Buchbinder also cites electrical and thermal conductivity performance
“Industry is trying very hard to improve the productivity of additive
manufacturing”
according to the International Annealed Copper Standard (IACS). Several samples made by Trumpf reached 100 per cent scores according to this standard, the highest level possible. ‘This is a unique innovation point, which
you don’t get right now in the laser metal fusion field with infrared wavelengths. Of course it’s coming together with the high density of the material. It’s over 99.5 per cent, usually 99.8 per cent.’
In the window The consequences of printing copper alloys like copper chrome zirconium up to four times faster than infrared wavelengths go beyond productivity gains. ‘The important thing is that our process window is bigger,’ Buchbinder said. ‘Typically, if you try to build
a part but you don’t have enough energy, you have a lack of fusion, and get holes inside. If you have too much energy, you get pores, bubbles form like in cooking. Between them there’s a sweet spot. If this process window is bigger, then your process is more stable, more robust. And what we could achieve due to the green wavelengths, is a lot more of a robust process window.’ Optomec, based in New Mexico,
approaches 3D printing copper from a slightly different direction. Tom Cobbs, LENS directed energy deposition (DED) product manager, said the metal’s reflectivity can affect the lasers that are melting it. ‘Laser energy reflects directly back up
through the optics train and fibre cable, and back to the laser, which can damage it,’ he said. ‘Most infrared lasers will just shut down, requiring field personnel to come and reset or restart the laser. ‘Our infrared laser incorporates a built-
in protection system, making it virtually immune to any back reflection, so the laser can operate at full power on reflective surfaces without any difficulty. Our testing with pure copper delivered amazing results – not only did it not shut down after extended use, but it also printed beautifully. This was not previously possible for infrared lasers.’ The resulting LDH 3.X laser deposition
head can print a variety of alloys with the same light source, including highly reflective materials such as copper, with DED. ‘This allows our customers to process all metals with only one infrared laser, as opposed to needing to purchase an infrared laser for most metals and then a separate blue or green laser for reflective metals,’ Cobbs said. ‘The laser is a significant portion of the cost of a DED system, so having to purchase two different wavelength lasers in order to process two different materials is a
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