Shrouded 5-Axis
Closed Impellers

Yes — closed (shrouded) impeller machining is one of HXC's core 5-axis capabilities. We machine the blade passages first (before the cover disc is closed), using tapered ball-nose tools with 5-axis simultaneous tilt to reach all internal flow surfaces. The cover disc bore and face are then machined to accept the shroud, and the assembly is inspected before any irreversible joining step.

All closed impeller toolpaths are simulated for gouge and interference in 5-axis CAM software before cutting. Key techniques: (1) tapered tools that can enter narrow channels at a working angle; (2) tilt optimisation to maximise clearance on the opposite wall; (3) staged toolpath — semi-finish scan verifies actual channel geometry before finishing. We never cut a closed impeller programme without a signed-off simulation.

Inside enclosed flow channels: Ra 0.8 µm standard with 5-axis ball-nose finishing. For high-efficiency hydraulic machines: Ra 0.4 µm with polishing passes. For sanitary (food/pharma): Ra ≤ 0.4 µm with electropolishing available. Surface finish measured using contact profilometer with extension arm or optical surface scan.

HXC uses: (1) Pre-closure CMM scan of all blade profiles and channel surfaces before the cover is added; (2) Post-assembly CMM of all external datums, bore, OD, and face runout; (3) Optical endoscope inspection of channel surface quality through inlet bore. For critical applications, CMM reports are provided for all accessible dimensions with optical images of internal surfaces.

Practical minimum: 3 mm channel width for standard tapered ball-nose tooling (R1.0 mm tip). For 2 mm channels, we use R0.5 mm micro tools with reduced feed rates — lead time increases. Below 2 mm, EDM finishing of channel surfaces may be more practical. We advise on minimum channel width during DFM review.

Yes — HXC can machine monolithic closed impellers from a single billet where the geometry allows. This is only possible if the channel opening angle is sufficient for tool entry. For very narrow channels or very high blade count, the impeller may need to be machined in two halves (blade + hub, and cover disc) then assembled. We advise the optimal approach based on your geometry during DFM.

In order of machining difficulty: Inconel 718 (work-hardens rapidly, sharp tools + low speed — add 3–5 days); Ti Grade 5 (poor thermal conductivity, controlled chip evacuation); SUS316L (work-hardening, acceptable with correct parameters); Al 7075 (easiest — standard lead time).

Prototype (new CAM programme, interference check, first article): 8–12 days. Small batch (5–15 pcs): 14–20 days. Production (20+ pcs): 18–26 days. Superalloy closed impellers: add 4–6 days.