Copper is one of the newest materials being used in additive manufacturing applications. But it can be a challenge to work with. Renishaw recently explored how to overcome some of the various challenges of using additive technology with this material.
Key applications for copper material include heat exchangers and electrical components because of the material’s thermal and electrical properties.
Traditionally, heat exchangers have been made from thin sheets of material that are welded together. But the geometry of these devices makes them difficult to machine using traditional manufacturing technologies. Additive manufacturing, however, is known for its ability to handle complex geometry. The technology of building a part layer-by-layer, only adding material where needed, makes it attractive for manufacturing heat exchangers. In addition, the final parts are often light in weight, despite the complex geometries.
With copper material, though, one concern is high thermal conductivity. For example, consider the use of the additive process laser sintering with an infrared laser at a wavelength of 1070 nm. Copper powder is highly reflective at this wavelength. This means only a small amount of the laser energy is absorbed into the powder, usually not enough to melt the powder together. Combining the high thermal conductivity of copper and the laser energy required can mean the finished part shows instability and has poor mechanical properties.
Renishaw collaborated with nTopology to demonstrate to manufacturers that, by using the right software and system together, they can reliably additively manufacture intricate structures from copper. In demonstrations, Renishaw engineers used the Renishaw’s RenAM 500S AM system, nTopology software, and Renishaw’s build preparation software, QuantAM.
The RenAM 500S system has a single 500 Watts laser and 70-micron laser spot size. The build bed was loaded with 99.9% pure copper powder supplied by Carpenter Additive. The additive machine is optimized to work with this material. It can manufacture thin walls with a thickness of 0.35 mm and solids with a density of more than 98% prior to heat treatment in 30-micron layers.
nTopology software was used to generate Triply Periodic Minimal Surfaces (TPMS) designed for heat exchangers as they generally require maximizing the amount of surface area within a given volume.
First, a wall thickness of 0.35 mm and cell sizes of 2 mm and 5 mm were used to design these gyroid TPMS structures. Then, nTopology was used to slice the design into 30-micron layers and export the boundaries and hatches as CLI files. The CLI files were then imported into the QuantAM software to generate the build file for printing. CLI files remove the need for the traditional STL file format which has many disadvantages when used to describe complex intricate structures like these.
To design the TPMS gyroids, the process began with the Walled TPMS Block in nTopology to generate a gyroid with a wall thickness of 0.1 mm and cell sizes of 2 and 5 mm.
The Walled TPMS was then sliced using the Slice Body Block to give the sliced boundaries of the gyroid. A layer thickness of 0.03 mm is used as that is the layer thickness of the machine.
The first boundary slice stack was sliced again to give the area between the boundaries, also commonly known as hatching. Generally, when 3D printing a part in layers, the laser would scribe or infill the body of the part for that layer first and then scribe the boundary for the part. An offset of -0.05 mm was used to standoff the hatching from the boundary using the Offset Slice Stack Block.
Both the Sliced Boundary and Hatching Stacks were exported as 2 CLI files for print preparation. The CLI files were imported into QuantAM.
QuantAM adds the machine parameters and generates a file that enables the machine to print the part. Note: Using CLI files removes the need of converting to STL files which are often huge in size and difficult to generate for complex geometries.
This is an example of the progress in additive manufacturing of commercially pure copper with the Renishaw AM systems.