State of the art : additive manufacturing of copper
In this section, we give an insight to the current technologies and limitations of additive manufacturing of copper.
Powder Bed Fusion for pure copper
Pure copper is particularly interesting thanks to its excellent thermal and electrical conductivity, offering a wide range of applications in all industries. However, in traditional additive manufacturing techniques such as powder bed fusion, an infrared laser is used to melt copper powder and this laser is reflected by the particles. To solve this problem, researchers of the Fraunhofer Institute in Germany used a green laser with a wavelength of 515 nm as shown in the image below.
Layer copper powder exposed to a green laser during the SLM 3D printing process – Fraunhofer ILT
Powder Bed Fusion is the most common family of techniques for additive manufacturing of metals. It uses a focused laser beam to melt the metallic powder and build the part layer by layer. The high power density of the laser melts the metal which then solidifies while cooling. The main technology for additive manufacturing of copper is Selective Laser Melting (SLM), a Powder Bed Fusion technique.
Limitations of traditional SLM technology
Despite SLM being an excellent additive manufacturing process for many metals, there was a particular challenge when it came to 3D printing with copper. Its absorption properties cause the heat of the laser beam to be reflected instead of absorbed. This creates porosities in the metal and unmelted zones, resulting in poor mechanical properties.
A second problem issued by the Fraunhofer Institute was the cracking of the parts during cooling. The cracking is caused by high thermal gradient induced by the passage of the laser and the temperature in the building chamber. The thermal gradient creates residual stress in the part which relives in the form of propagating cracks.
Development of innovative solutions
In this section, we present the innovative solutions used to 3D print high quality copper parts.
Green laser technology
To address those problems and create high quality parts, researchers of the Fraunhofer Institute proposed two solutions now used in industrial 3D printers such as the TruPrint 1000 Green Edition of Trumpf. The image below shows the graph of absorption versus wavelength for copper, courtesy of TRUMPF.
Absorption of an electromagnetic beam by copper – Trumpf
The graph shows that the infrared beam traditionally used in SLM is poorly absorbed by copper. The copper powder remains partially or totally unmelted resulting in mediocre properties. The green laser used has a wavelength of 515 nm. At this wavelength, copper can absorb up to 40% of energy resulting in homogeneous melting in a layer and much better final parts.
Preheating plate
To overcome the cracking problem due to high thermal gradient in the part, one solution could be to reduce the gradient by preheating the building plate to a given temperature. Reducing the thermal gradient helps to relieve the thermally induced stress in the part. Trumpf TruPrint 5000 3D printing system provides preheating plates as shown in the image below.
Trumpf TruPrint 5000 preheating plate – Trumpf
The TruPrint 5000 was demonstrated at the Formnext, 3D print fair in Frankfurt in November 2018. The machine also prints with other high added value metals such as steels, titanium alloys or nickel-based alloys.
Applications of 3D printed copper parts
Copper is a soft and ductile metal. It has very high electrical and thermal conductivity (up to 400 W/(m.K)). Common applications for copper are:
- Electrical wiring (copper is a conductor of heat and electricity,
- Building material for roofing, plumbing, decorative elements and sculptures (for ex the Statue of Liberty is made from copper). The copper oxidizes and becomes a light green color.
- Constituent of various metal alloys, such as bronze (a copper-tin alloy) and brass (a copper-zinc alloy) and Sterling silver (silver-copper alloy)
- Machinery and motors
- marine applications: copper is biostatic, bacteria or other life forms will not grow on it. It was used in shipping to prevent growth on hulls.
- Sinks, faucets, doorknobs, handrails etc. Because copper is biostatic it is used (in various alloys) in appliances that are handled by many people, to avoid spreading bacteria.
However, copper is also widely used in high added value industries such as aerospace or electronics. As explained in this article on a 3D printed heat pipe printed by Beamler for Calyos, copper has several thermal applications. It can also be used as a traditional heat exchanger but featuring complex inner channels allowing higher efficiency.
Conclusion
As pointed out, copper has interesting thermal and electrical properties and together with the advantages of additive manufacturing, particularly the design freedom, 3D printed copper parts are now perfectly suitable for use in a broad range of applications. To anticipate the demand for copper in additive manufacturing, different companies are developing special copper and copper alloy powders for the 3D printing market.
Curious about the cost of printing your part with copper?
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Copper is widely used in industry thanks to its excellent thermal and electrical properties. Recent developments in additive manufacturing of copper made it available for 3D printing of high quality complex parts. This article gives an in depth view of this new technology and its application.