A novel fabrication approach for high-aspect-ratio slow wave structures combining water film-assisted laser pre-channeling and micro-milling

The Slow Wave Structure (SWS), typically fabricated from particle-reinforced composite material, such as Dispersed Oxygen-Free Copper (DOFC), is a core component of terahertz travelling wave tubes. However, machining these high-aspect-ratio, multi-period microstructures with high precision through traditional micro-milling is highly challenging due to significant tool wear when employing micro-cutters with extremely small diameters. This study proposes a novel hybrid fabrication method, termed Water film assisted Laser Pre-channel combined with Micro-Milling (WLPMM), to efficiently produce SWS structures with superior precision and reduce tool wear. In the WLPMM approach, water film assisted laser processing is first utilized to generate a preliminary U-shaped pre-channel, leveraging the enhanced material removal capabilities afforded by water film's scouring effect, optimized laser power strategies, and scanning methodologies. This initial step significantly reduces material volume, facilitating subsequent micro-milling to refine dimensional accuracy and surface quality with only one micro-cutter consumed. Consequently, this method effectively eliminates clamping errors typically introduced by frequent tool changes. Comparative analyses between WLPMM, pure micro-milling, and laser-assisted micro-milling demonstrate that WLPMM significantly outperforms alternative approaches in terms of reduced tool consumption and improved machining efficiency. Furthermore, WLPMM maintains comparable surface finish and dimensional precision, highlighting its viability and advantages for fabricating high-aspect-ratio slow wave microstructures essential in advanced aerospace and precision instrumentation applications.