Coolant is not always the right answer. Many production shops have switched to dry or near-dry machining for specific operations.
When Dry Wins
- Cast iron — Coolant + dust = abrasive sludge
- Hard turning (CBN) — Thermal shock cracks CBN
- Aluminum HSM — Air blast better than flood
- Some plastics — Coolant causes stress cracking (polycarbonate)
When Coolant Is Mandatory
- Stainless steel — Without coolant, work hardens immediately
- Titanium — Heat must be removed
- Inconel/superalloys — HP coolant required
- Deep hole drilling — Internal coolant for chip evacuation
- Threading taps in steel — Tapping fluid critical
Coolant Types
- Soluble oil (5-10%) — Most common, general use
- Synthetics — High-pressure applications, less misting
- Cutting oils (sulfur-active) — Hard materials and tapping
- Air blast (dry) — Cast iron, aluminum, plastic
- MQL — Tiny droplets, bridges dry and flood
- HP coolant (1000+ PSI) — Superalloys and titanium
Concentration Matters
Use refractometer weekly:
- Too dilute (less than 4%): BUE, rust, poor lubricity
- Too concentrated (more than 10%): foaming, residue, wasted money
- Right (5-8%): optimal
Maintenance
- Skim tramp oil weekly
- Filter chips daily
- Test pH monthly (8.5-9.5)
- Refresh when pH below 8 or smells bad
For specific recommendations: titanium coolant guide.
