Flood, MQL or Dry? The Right Coolant Strategy for Every CNC Material in Malaysia

Ask most Malaysian machine shops why they use flood coolant on every job and the answer is usually the same: 'That's what we've always done.' Flood coolant is a safe default — it cools, it lubricates, it clears chips. But it is not always the right strategy, and in some applications it actively damages your tooling and your parts.

Understanding when to use flood coolant, when MQL (Minimum Quantity Lubrication) is better, and when dry machining is actually the correct answer will improve your tool life, your surface finish, and in some cases your compliance with environmental regulations.

The three coolant strategies

• Flood coolant — large volume water-soluble cutting fluid applied continuously at the cutting zone. Cools aggressively, provides lubrication, clears chips. Most common in Malaysian manufacturing. Requires coolant sump, filtration, and regular maintenance.

• MQL (Minimum Quantity Lubrication) — a very small quantity of near-dry cutting oil (typically 5–50 ml/hour) is atomised and directed precisely at the cutting edge via compressed air. Lubricates the cut without bulk cooling. Chips come off dry. Lower environmental impact, cleaner parts, no coolant disposal cost.

• Dry machining — no cutting fluid at all. Heat is carried away by the chips. Requires tools and cutting parameters specifically suited to generate chips that evacuate heat effectively. Cleanest, lowest cost, but not suitable for all materials and operations.

Steel (mild, carbon, alloy steel)

• Recommended: Flood coolant for general milling, turning, and drilling. Water-soluble fluid at 5–8% concentration.

• MQL is acceptable for finishing operations on steel where surface contamination from flood coolant is undesirable.

• Dry machining is possible for turning mild steel with coated carbide inserts (AlTiN) at moderate cutting speeds — but not recommended as a default approach.

• Tapping in steel: always use tapping fluid or neat cutting oil — flood coolant alone is insufficient for threading lubrication in steel.

Aluminium alloy

• Recommended: Flood coolant or air blast depending on operation. High-speed aluminium machining (Vc 800+ m/min) can be done with air blast — chips carry most of the heat away.

• MQL works well for aluminium — the lubrication prevents built-up edge (aluminium welding to the tool face) more effectively than flood coolant alone.

• Never use flood coolant without chip clearing — aluminium chips are large and soft. Flooded chips that re-enter the cut cause surface damage on machined faces.

• Dry machining is possible for aluminium with uncoated carbide at high cutting speeds — but built-up edge risk increases without lubrication. Monitor closely.

Stainless steel (304, 316L, duplex)

• Recommended: Flood coolant — mandatory. High pressure preferred (20–40 bar) for drilling operations.

• MQL is not recommended as the primary strategy for stainless — insufficient cooling allows work hardening to develop at the cutting edge.

• Dry machining: never. Stainless work-hardens almost immediately without cooling and lubrication — tool life collapses within seconds.

• Critical for 316L medical and marine components: never use chlorinated cutting fluids. Use synthetic or semi-synthetic coolants rated chlorine-free.

Titanium (Ti-6Al-4V and CP grades)

• Recommended: High-pressure flood coolant — minimum 70 bar through spindle. This is non-negotiable for titanium.

• Titanium's extremely low thermal conductivity means almost all cutting heat stays in the tool — not in the chip. Without high-pressure coolant directed exactly at the cutting edge, tool life is measured in minutes.

• MQL is not suitable as the primary strategy for titanium — insufficient cooling. MQL can supplement high-pressure coolant but cannot replace it.

• Dry machining: never for titanium. Fire risk in addition to tool destruction — titanium chips and dust are highly flammable.

Hardened steel (Mold & Die — H13, S136, 48 HRC+)

• Recommended: Dry machining or MQL — flood coolant is actively harmful for hard milling.

• Here is why: when flood coolant contacts a very hot cutting edge in hardened steel machining, it causes thermal shock — micro-cracking of the carbide substrate. The tool fails prematurely not from wear but from thermal fatigue cracking.

• Use dry cutting with AlTiN or AlCrN-coated end mills designed for hard milling (MOLDINO Impact Miracle series). The coating acts as a thermal barrier — heat stays in the chip and is evacuated, not absorbed by the tool.

• MQL (very light oil mist) is acceptable for hard milling — provides lubrication without the thermal shock of flood coolant.

CFRP carbon fibre composites

• Recommended: Dry machining or MQL only — flood coolant must not be used on CFRP.

• CFRP absorbs moisture — flood coolant penetrates the composite matrix, causing swelling, delamination between plies, and long-term structural degradation.

• Dry machining with diamond-coated or PCD-tipped drills and end mills is the standard approach for aerospace CFRP machining.

• MQL provides lubrication for the diamond coating without moisture risk — acceptable for high-volume CFRP drilling.

• Dust extraction is mandatory for CFRP dry machining — carbon fibre dust is hazardous to respiratory health and damages electronic equipment.

Inconel and high-temperature alloys

• Recommended: High-pressure flood coolant — minimum 70 bar through spindle for drilling and end milling.

• Inconel's low thermal conductivity and high work hardening rate make it as demanding as titanium for coolant requirements.

• For ceramic insert turning of Inconel at very high cutting speeds (Vc 500+ m/min) — dry machining only. Flood coolant on ceramic inserts at high speed causes immediate thermal shock fracture.

Engineering plastics (PEEK, Delrin, Nylon)

• Recommended: Dry machining or air blast only — flood coolant causes moisture absorption in PEEK and Nylon, changing dimensional characteristics.

• The primary goal in plastic machining is keeping cutting temperature low — use sharp, uncoated tools, high helix angles, and light feeds.

• Air blast clears chips and provides some cooling without moisture risk.

• MQL is acceptable for plastics — the small oil quantity does not cause the absorption issues of flood coolant.

Quick reference summary

• Mild and alloy steel — Flood coolant (standard). MQL for finishing.

• Aluminium — Flood or air blast. MQL effective for built-up edge prevention.

• Stainless steel — Flood coolant mandatory. High pressure for drilling.

• Titanium — High-pressure flood (70 bar+) mandatory. Never dry.

• Hardened steel (48+ HRC) — Dry or MQL only. Never flood.

• CFRP composites — Dry or MQL only. Never flood.

• Inconel — High-pressure flood for milling/drilling. Dry for ceramic turning.

• Engineering plastics — Dry or air blast. MQL acceptable.

Need help optimising your coolant strategy?

KS Precision Tools provides free process optimisation consultations for manufacturers across Malaysia. If you are experiencing premature tool failure, poor surface finish, or unexpected scrap — coolant strategy is often a contributing factor. Our technical team will review your application and recommend the right approach.

Call 03-8941 7168 or email kokyong@ks-precision.com. Based in Seri Kembangan, Selangor.