The use of copper by humans dates back to some of the earliest known civilizations, over ten thousand years ago. In fact, copper was one of the first metals ever used by humans. The trajectory of the metal has also been closely linked to the invention of various processing methods, from cold working, to annealing, to smelting and lost-wax casting, each of which created new applications for copper. Today, manufacturing processes are still shaping the way humans work with and use copper. One of the most recent advancements is additive manufacturing.
There are a handful of companies working at the forefront of copper (Cu) 3D printing today, seeking to create alloy powders that possess the properties characteristic of pure copper while still being printable (pure copper is notoriously challenging to 3D print). One of these companies is SLM Solutions, a German leader in metal AM technologies.
Material characteristics of CuNi2SiCr
SLM Solutions, which specializes in powder bed fusion technologies, has qualified a low-alloyed copper-alloy for additive manufacturing: CuNi2SiCr. The powder, compatible with all of SLM Solutions’ AM systems, is a thermally hardenable alloy characterized by high stiffness and a balanced combination of electrical and thermal conductivity. The alloy, which includes nickel and silicon, also boasts high corrosion and wear resistance.
Within the sphere of copper 3D printing, the question of conductivity is hard to pass over. This is because copper alloys are, in general, less conductive than pure copper, which has an IACS (International Annealed Copper Standard) value of 100%. The CuNi2SiCr alloy for 3D printing has an IACS value of up to 40% when heat treated (14% as built), which means that though it is less conductive than pure copper, it is still suitable for conductive applications.
The addition of alloying elements such as nickel has also resulted in a copper alloy that has superior strength to pure copper. As SLM Solutions says: “In general, conductivities are lowered with increased amounts of alloying elements, but other properties such as strength can be improved.”
Parts 3D printed from the copper alloy on an SLM Solutions system are characterized by a homogenous, nearly pore-free structure. This composition means that printed parts maintain mechanical values within the range of the raw material’s specification.
Notably, the properties of printed copper alloy components can be adapted by implementing a heat treatment process. For instance, the precipitation strengthening process (which includes solution annealing, quenching and artificial aging) results in parts with higher strength and electrical conductivity.
Copper alloy applications
Today, copper is a sought after material for a range of applications. For instance, its excellent conductivity makes it well suited for electrical applications, while its high thermal conductivity makes it desirable for many thermal applications. Still, copper manufacturing processes—such as bending and soldering—have limited applications for the material and the efficiency of certain applications.
The ability to 3D print a copper alloy has therefore opened up a host of new opportunities for the material. That is, by combining the unique benefits of copper—namely, high thermal and electrical conductivity—with the advantages of additive manufacturing—such as design freedom—existing applications for copper can be overhauled and optimized and new applications can be unlocked.
The low-alloy copper qualified by SLM Solutions for additive manufacturing is suitable for a range of applications, including toolmaking, conductive contacts for electrical engineering, welding nozzles and more. CuNi2SiCr’s strength, resistance and conductive properties have made the material well suited for producing parts used under mechanical, thermal and tribological stresses and which require conductivity.
The performance and characteristics of parts made from the copper alloy can also be improved by leveraging the benefits of AM, including topology optimization, design freedom and more. In other words, the ability to design and manufacture parts with complex internal geometries and topology optimization can result in components that are more lightweight, more cost effective and more efficient.
In order to qualify CuNi2SiCr for use on its selective laser melting systems, SLM Solutions undertook its extensive qualification and parameter validation process to ensure the material could be printed at the highest standard. This is performed for all released materials and a standard process at SLM Solutions.
First, the powder is certified for the SLM® process. This process consisted of analyzing the chemical composition of the material using inductively coupled plasma (ICP), detecting gases by thermal extraction and using modern laser diffractometry to determine particle size distribution. The flowability factor was considered and tested using a special measuring device, the SLM Flowmeter, which mimics the flow conditions inside an SLM 3D printer.
Once these tests were successfully completed, SLM Solutions and its team of expert parameter development engineers were able to establish ideal printing parameters for the metal powder. In testing these parameters, the main issue that stood out with the copper alloy was its sensitivity to oxygen. To address this, the company has recommended a maximum of 500 ppm of oxygen in its systems when working with the material.
The full material properties and printing parameter recommendations for CuNi2SiCr can be found here.
This article was published in collaboration with SLM Solutions.