The part and the problem
The job: a family of Ti-6Al-4V mounting brackets, 40 mm thick blanks, tolerance 0.02 mm on the bore, surface finish Ra 1.6 on the flange faces. The shop ran the legacy program with conventional trochoidal roughing, a 10 mm carbide 4-flute, and 55 minutes per part in roughing alone. Tool life averaged 90 minutes before flank wear forced a change.
Setup
- Machine: 40-taper VMC, 12000 RPM, 30 kW spindle, through-spindle coolant at 70 bar
- Fixture: vacuum-assisted vise with edge clamps, part supported on risers to clear the pocket floor
- CAD/CAM: dynamic milling paths, 5 degree engagement angle on roughing
Strategy changes
1. Dynamic roughing with a high-helix variable-pitch cutter
Switched from a 4-flute standard tool to a 6 mm 4-flute variable-pitch high-helix rougher with TiAlN coating and a 0.8 mm corner radius. The variable pitch breaks chatter harmonics that plague titanium.
| Parameter | Old (conventional) | New (dynamic) |
|---|---|---|
| Spindle speed | 1800 RPM | 4200 RPM |
| Feed rate | 450 mm/min | 1650 mm/min |
| Axial depth | 6 mm | 28 mm (0.7 x blank thickness) |
| Radial engagement | 4 mm | 0.6 mm |
| Roughing time | 55 min | 34 min |
The trick in titanium is shallow radial engagement with deep axial depth: the cutting edge stays in the material for a longer arc, heat spreads over more of the flute, and the thin chip carries heat away instead of into the tool.
2. High-pressure coolant directly at the cut
Repositioned the coolant nozzles from generic flood to two 6 mm targeted jets at 70 bar aimed at the cut tangential point. Thermal checking on the workpiece stopped entirely, and tool life rose from 90 to 260 minutes.
3. Finishing pass with a dedicated tool
Finishing moved to a dedicated 10 mm 4-flute 45-degree helix finishing end mill with a 0.4 mm radius, never used for roughing. Parameters: 2800 RPM, 850 mm/min, 0.5 mm radial, achieving Ra 1.2 on the flange faces against the Ra 1.6 requirement.
Results after 40 parts
| Metric | Before | After | Change |
|---|---|---|---|
| Total cycle time | 97 min | 60 min | -38 percent |
| Roughing tool life | 90 min | 260 min | +189 percent |
| Tools consumed per part | 0.31 | 0.12 | -61 percent |
| Bore tolerance scrap | 2 parts in 40 | 0 | Eliminated |
Lessons that transfer to other titanium jobs
- Variable-pitch geometry matters more than coating in titanium: chatter, not wear, kills most titanium tools
- Radial-light, axial-deep beats radial-heavy, axial-shallow in every test we ran
- Keep a virgin finishing tool: mixing roughing and finishing on one tool doubles the finishing tolerance problems
- Targeted high-pressure coolant outperforms generic flood by a wide margin on any titanium cut deeper than 2 mm
Summary
A 38 percent cycle-time reduction on Ti-6Al-4V came from strategy, not exotic tooling: variable-pitch rougher, dynamic paths, aimed 70 bar coolant, and a dedicated finisher. Total new-tool investment paid back within the first nine parts.
