Why the heat stays in the tool
Cutting generates heat by deformation and friction. In steel, a large proportion leaves with the chip because the chip is hot and the material conducts heat reasonably. In titanium the thermal conductivity is low, so the heat has nowhere to go except into the tool.
In nickel alloys the mechanism is different but the outcome is similar: the material retains strength at high temperature, so the deformation zone stays narrow and the heat concentrates at the edge rather than spreading into the chip.
| Alloy | Failure mode | Tooling response |
|---|---|---|
| Titanium grade 5 | Edge softening, galling, spring-back | Sharp AlTiN edge, low speed, high coolant flow |
| Commercially pure titanium | Galling and smearing | Very sharp polished edge, generous lubrication |
| Inconel 718 | Notch wear, extreme heat | AlCrN, strong edge preparation, through-coolant |
| Waspaloy and similar | Notch wear, work hardening | AlCrN, varied depth of cut, conservative speed |
| Cobalt-chrome | Abrasion plus heat | AlCrN or AlTiN, robust edge, reduced speed |
Cutting speed is the lever, not feed
With these alloys the cutting speed has to fall, often substantially, because edge temperature rises with speed. Feed per tooth can usually be maintained or even increased, because a heavier chip carries more heat away per unit of edge contact.
That combination, lower speed and adequate feed, is the opposite of the instinct to slow everything down. Running slowly at a light feed rubs the material and work-hardens it, which is worse than either parameter alone.
Notch wear at the depth-of-cut line
In nickel alloys the tool wears fastest where it enters and leaves the cut, producing a notch that grows until the edge breaks. Varying the axial or radial depth between passes so the notch does not form at the same place is the most effective single countermeasure.
A stronger edge preparation and a coating with high oxidation resistance such as AlCrN also help, but neither substitutes for varying the depth of cut.
Coolant delivery at depth
Through-tool coolant is frequently essential rather than optional, because these operations are often deep pockets or deep holes where flood coolant never reaches the cutting zone.
High pressure is what makes through-tool delivery work: the coolant has to reach the edge with enough velocity to break the vapour barrier that forms at the high temperatures involved. A low-pressure supply through the tool is largely wasted.
Frequently asked questions
Why do titanium tools fail so quickly?
Because titanium conducts heat poorly, so the heat generated by cutting stays in the tool rather than leaving with the chip, and the edge softens and deforms. It also work-hardens and springs back. The response is lower speed, adequate feed and high-flow coolant.
Should I reduce the feed when machining Inconel?
Reduce the speed, but keep the feed adequate. A heavier chip carries heat away per unit of edge contact, so a light feed rubs the material and work-hardens it, which is worse than running at a proper feed per tooth.
How do I stop notch wear on nickel alloys?
Vary the depth of cut between passes so the notch does not form at the same point on the edge. Combine that with a strong edge preparation and an AlCrN coating, but the depth variation is the most effective single measure.
Is through-coolant tooling necessary for these alloys?
Frequently yes. These operations are often deep pockets or holes where flood coolant cannot reach the cutting zone, so through-tool delivery at high pressure is the only way to get coolant to the edge and break the vapour barrier.
Which coating for titanium and nickel alloys?
AlTiN for titanium, where a sharp edge and hot hardness matter, and AlCrN for nickel alloys, where oxidation resistance at very high temperature is the requirement. In both cases the edge preparation is as important as the coating.