The advantage of additive manufacturing lies in the production of lightweight, seamless, multifunctional components. This process is proving itself in the aerospace and medical industries, where its use has skyrocketed. Until now, however, it has not been widely used in the field of particle accelerators, where unique specifications have to be met. For ultra-high vacuum, cryogenics and radiofrequency cavities, in particular, CERN produces and characterises components that need to meet very specific requirements and may require the use of rare materials like niobium.
The additive manufacturing technique adopted by CERN is selective laser melting: metallic powder is melted successively, layer by layer, using a laser beam. The laser’s trajectory is set using a three-dimensional model. The layers of powder are deposited and melted over and over, up to thousands of times, until the object takes shape.
For four years now, the Mechanical and Materials Engineering group in the Engineering department (EN-MME) has been using a metal-additive manufacturing machine (also known as a 3D printer) to produce geometrically complex parts.
This process makes it possible to conceptualise and design parts that until now would have been difficult, if not impossible, to manufacture. Selective laser melting results in robust parts of complex shapes, which include features such as cooling channels (as illustrated below in a radiofrequency spiral load for CLIC). The process requires relatively little raw material while preserving good mechanical properties. This is shown in the case of beam wire scanners, which have to be light but rigid.
Although this technology has been tried and tested with common materials, such as aluminium and titanium alloys and stainless steel, additive manufacturing involving rare materials such as niobium, a superconducting element that is used throughout the radiofrequency cavities of CERN’s accelerators, is relatively uncharted territory. A development programme has been under way for several years and has produced promising results with some of the first components, like the HOM couplers below. Nevertheless, there are still challenges to overcome, related in particular to the purity of the materials, the roughness of the surfaces and the high dimensional precision that these parts require.
In addition to the metal-additive manufacturing machine, CERN also has a plastic 3D printer, which is used by the Magnets, Superconductors and Cryogenics group (TE-MSC) to produce parts from plastic resin (mainly epoxy) using stereolithography, a technique that involves using a laser to harden the liquid resin. The applications of this technique include making radiation-resistant parts and high-voltage electrical insulation for the detectors, as well as many moulds and prototypes.
Additive manufacturing is set to continue making inroads into the world of accelerators. By expanding the range of possibilities offered by conventional technologies, this new tool is likely to help resolve many technical challenges posed by future projects, such as the Future Circular Collider (FCC).