Abstract
<title>Abstract</title> <p> Additively manufactured special-shaped waveguides with continuous blind cavities often exhibit rough internal surfaces, non-uniform finishing on boss surfaces, and excessive edge removal. This study regulates abrasive-medium viscosity to improve boss surface finishing while preserving edge morphology. A power-law fluid model was established to analyze viscosity effects on velocity distribution and near-wall velocity difference. Numerical simulations obtained near-wall velocity, PV value, and strain rate distributions on boss surfaces and edge regions. Single-factor abrasive flow finishing experiments were conducted at 1000–3000 Pa·s. Finishing performance was evaluated using the surface roughness reduction rate of boss surfaces, edge removal height, and machining uniformity among key boss surfaces. With increasing viscosity, the average surface roughness reduction rate of boss surfaces decreased from 83.80% to 67.76%, while the post-finishing \(\:\text{R}\) <sub>a</sub> increased from 1.838 µm to 4.222 µm. The average edge removal height decreased from 0.1537 mm to 0.0417 mm, and the roughness dispersion among the key boss surfaces also decreased. These results indicate that higher viscosity weakened boss surface material removal and local edge removal, while improving machining uniformity. Considering finishing efficiency, edge preservation, and uniformity, 2000–2500 Pa·s was selected as the preferred viscosity range. Within this range, the roughness reduction rate remained above 70%, \(\:\text{R}\) <sub>a</sub> decreased from above 10 µm to below 3.7 µm, and the average edge removal height was 0.0951 − 0.0641 mm. This study clarifies the coupled effect of medium viscosity on boss surface material removal, edge removal, and machining uniformity in continuous blind-cavity waveguides. </p>