Archive — This feature reflects research and supplier interviews published in 2020. Product capabilities, development targets and figures are presented in their historical context.
Metal additive manufacturing uses a range of materials, from titanium and nickel alloys to aluminium and steel. Copper presents a particular opportunity where thermal or electrical conductivity is important, but it also brings processing challenges. This dossier examines the approaches being discussed in 2020.
This paper aims to present a detailed insight into the use of pure copper in additive manufacturing and how professionals can make the most of it. To explore this topic, we have invited a 3D printer manufacturer, Farsoon Technologies, and a material producer, Elementum 3D. Wenyu Guo, Metal Product Line Manager at Farsoon Technologies will speak on behalf of the company whereas Jacob Nuechterlein, President & CEO of Elementum 3D will share the company’s expertise in this dossier.
Researches and the latest developments from Optomec, Fraunhofer Institute for Laser Technology (ILT) and The Virtual Foundry have also been mentioned.
Pure copper, copper alloys and material properties
Among all metals that exist, copper is one of the rare ones that can be found in nature in a directly usable metallic form. It is described as a soft, malleable, and ductile material that integrates a very high thermal and electrical conductivity.
Surface colour or a reaction to lemon juice cannot establish that a component is pure copper. Material identification requires appropriate compositional evidence, such as supplier certification or chemical analysis.
Density is also different from chemical purity. A density measurement can be affected by porosity and geometry; it does not identify the composition on its own. For a manufactured part, composition, density and measured thermal or electrical performance should be considered separately.
Conventional manufacturing routes
Pure copper was used in industrial production long before additive manufacturing. Choosing a process begins with the required geometry, material properties and production volume.
Copper production from ore can include smelting and refining, depending on the feedstock and route. These operations produce material for subsequent fabrication; they should not be confused with the processes used to shape a finished component.
For copper tubes, one possible high-volume route combines vertical continuous casting, hot extrusion and subsequent drawing. The appropriate sequence depends on the product and plant.
Horizontal continuous casting can also form part of a tube-production route. Production volume alone does not determine the choice: dimensions, tolerances and downstream processing matter too.
The comparison with additive manufacturing therefore needs to include the finished component’s requirements, yield, finishing operations and overall production cost.
Using additive manufacturing for pure copper
Additive manufacturing can be attractive for complex internal channels and other geometries that are difficult to make conventionally. That design freedom must be weighed against process capability and the properties of the finished part.
When asked the main reasons why pure copper raises interest in manufacturing, Jacob Nuechterlein, President & CEO of Elementum 3D replies with a key focus on additive manufacturing:
“Heat exchangers are a primary use in additive manufacturing due to complex designs and internal channeling. Pure copper has one of the highest thermal conductivities of any metal. The extremely high conductivity of over 350 W/mK drives the applications for this material.” Laser powder-bed fusion, including processes marketed as Direct Metal Laser Sintering (DMLS), is one of the routes considered in this feature.
Other additive routes include extrusion of metal-filled filament followed by binder removal and sintering.
The original example was The Virtual Foundry’s copper Filamet™. The supplier described the filament at the time as containing around 90% metal, with a density of 4.3 g/cm³, and described the furnace-processed part as “100% metal”. Filament composition, binder removal and final sintered density are different measurements: removing the polymer does not by itself establish full density or a particular conductivity.
The original article reported shrinkage of around 15–20% during processing. Dimensional compensation must be established for the material, geometry and validated furnace cycle; it should not be treated as a universal enlargement factor.
Multi-material printing may offer additional design possibilities, but combining metals requires compatible processing and a validated interface. Neither metal-filled extrusion nor a multi-metal part can be assumed to match the conductivity of fully dense pure copper without measurement.
Laser powder-bed fusion of pure copper
Reflectivity and heat conduction are two important difficulties in laser processing of copper. Absorption of the laser energy and retention of enough heat to form a stable melt pool must both be addressed.
In laser powder-bed fusion, a laser selectively melts layers of metal powder. The process can produce complex geometries, but it does not automatically yield stronger or denser parts than casting. The result depends on the material, parameters, defects and any subsequent treatment.
Metal powder handling, recovery and finishing require suitable equipment and operating procedures. The process should not be equated with ordinary sandblasting: powder exposure, ignition risks and the machine manufacturer’s requirements need specific assessment.
Farsoon described two challenges in its work on pure copper:
“Pure copper has a high laser reflectance rate of over 90% with standard Metal Laser Sintering (MLS) systems. It is difficult for the laser to continuously and regularly melt pure copper powder, which leads to issues such as interface failure and internal holes.
Due to the nature of copper material, pure copper powder tends to oxidize in open air, this includes the formation of an oxidized layer of material that prevents further corrosion, but will hinder key properties sought after with pure copper such as electrical conductivity”, explained Wenyu Guo, Metal Product Line Manager at Farsoon Technologies.
High conductivity is a reason to consider pure copper, while reflectivity at near-infrared laser wavelengths can make it difficult to process. The reflectance figure in Farsoon’s quotation describes its stated conditions, rather than a fixed value for every powder, surface and wavelength.
In a 2017 research announcement, Fraunhofer ILT explained that reflected infrared energy can reduce energy absorption and damage system components. Absorption changes as copper moves from the solid to the liquid phase, which can destabilise melting. The institute was investigating green laser light to improve absorption.
Addressing the reflectivity issue
Farsoon reported developing build, scanning and processing parameters on its open platform to address these processing difficulties. Adjusting process parameters does not necessarily change copper’s intrinsic reflectivity.
Guo described the solution as based on a standard fibre laser, without an additional major optical-system investment for the user. This was the supplier’s assessment of its development at the time, not a general cost comparison between machines.
“Copper’s thermal stress during printing is less than of other materials. Adjusting parameters of heat treatment process such as temperature, holding time and atmosphere/vacuum conditions can affect the micro structure and give preferred properties including strength and conductivity. The composition of raw material, such as oxygen content and purity of copper, also have a big influence on the conductivity behavior.
During the laser melting process of pure copper, the machine build plate is set to a higher temperature which helps relieving the thermal residual stress. The finished pure copper part will require certain level of processing state according to the application to further releasing the stress and solidify the mechanical/electric performances. Under current development, the build copper parts can achieve a density of over 97%”, explains Farsoon’s spokesperson.
Farsoon’s density figure is a reported development result. It is not a measurement of copper purity or a guarantee of electrical performance. Heat treatment and finished-part properties require qualification for the intended application.
Optomec also described a pure-copper process using its LENS directed energy deposition (DED) systems:
‘Pure copper is a big challenge for DED systems because of its high reflectance.’ said Tom Cobbs, product manager for Optomec LENS systems. ‘The infrared wavelengths on most standard, laser-based AM systems are not readily absorbed by copper, making it difficult to establish a melt pool as the laser energy is reflected back into the source, causing all kinds of havoc.’
According to Cobbs, Optomec’s process protected the laser against reflected energy and included parameters to account for heat conduction and changes in absorption. These statements refer to the supplier’s described system configuration.
What about high thermal conductivity?
Reflectivity is only part of the problem. Even where energy is absorbed effectively, rapid heat conduction can make it difficult to maintain the required melt pool. Elementum 3D emphasised that point:
“Copper is more difficult to process due to high thermal conductivity of the fused part and high natural reflectivity of copper. Many claims suggest better productivity with green lasers, but that only addresses reflectivity and not the bigger problem of high thermal conductivity”, explains the materials producer Elementum 3D.
Nuechterlein’s assessment places thermal management alongside optical absorption when considering process development.
At publication, Elementum 3D described its copper material as printable on the laser powder-bed fusion systems of one manufacturer. It also referred to a product designed for off-the-shelf printers using red or green lasers. The original account did not identify and qualify each machine–material combination, so these statements should not be read as universal compatibility claims.
Possible applications for pure copper
Potential applications include heat exchangers with complex channels, induction components and electronic parts. Suitability depends on measured conductivity, integrity, dimensional accuracy and the service conditions of the component.
“The goal of these applications is to achieve production numbers in thousands, or building up second/advanced tier of manufacturing-supply chain”, explains Wenyu Guo.
This quotation describes a production goal discussed in 2020, not confirmation that those volumes had already been reached.
Jewellery was another possible avenue mentioned in the original feature. Complex geometry and repeatability could be useful, but an advantage over conventional production would still need to be demonstrated for the design and process.
Concluding thoughts
In 2020, the approaches described here showed different ways to address copper’s reflectivity and heat conduction. Progress towards repeatable production required more than a successful print: material properties, finishing, cost and process qualification also mattered. The supplier interviews provide a historical view of those development priorities.
This dossier was initially published in the March/April 2020 issue of 3D ADEPT Mag.
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