Comparison of post-processing methods for additively manufactured pure copper RF cavities: Evaluation of dimensional accuracy, vacuum outgassing and effective electrical conductivity

Metal-based laser powder bed fusion enables the monolithic fabrication of radio-frequency (RF) components and offers significant potential to reduce manufacturing complexity while improving performance. However, the inherently high as-built surface roughness requires post-processing to achieve high effective electrical conductivity. To date, no systematic evaluation of post-processing methods for RF components fully manufactured by metal-based laser powder bed fusion (PBF-LB/M) has been reported. In this work, four post-processing methods are comparatively evaluated using fully PBF-LB/M-manufactured 4.3 GHz single-cell pure copper RF cavities. The investigated methods are Hirtisation (HIR), Micro-Machining (MM), Mass Finishing (MF), and Plasma Electrolytic Polishing (PEP). Dimensional accuracy, integral vacuum outgassing rates, and effective electrical conductivity are studied. In contrast to MM, MF, and PEP, HIR preserves dimensional accuracy close to the nominal post-processed geometry and maintains deviations between individual geometric features comparable to the as-built condition. After bake-out for 10 hours at 150∘C , all cavities except MM achieve integral outgassing rates below 5 × 10⁻⁶\ mbarL/sm² . The lowest value is measured for HIR at (2.28 ± 0.02)× 10⁻⁶\ mbarL/sm² . Post-processing increases effective electrical conductivity from approximately 25 MS/m to 56 MS/m for HIR, 54 MS/m for MF, 50 MS/m for PEP, and 30 MS/m for MM. The results demonstrate that among the investigated methods Hirtisation represents the most suitable option for post-processing monolithic GHz copper RF cavities manufactured by PBF-LB/M. The findings further contribute to the broader characterization of PBF-LB/M-manufactured copper and are relevant for applications requiring high geometric precision, vacuum compatibility, and electrical RF performance, including quantum technologies and ultra-high vacuum systems.