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- Coating selection - TiAlN, AlTiN, AlCrN, TiCN, DLC and CVD oxide, and the CVD against PVD split
- Insert grade selection - how the ISO material groups imply a coating direction
The wear mechanism decides, not the hardness
The useful question is what the tool is dying from, because that is what the coating has to address.
| Coating | Resists | Typical use |
|---|---|---|
| TiAlN | Abrasion and heat | General steel and stainless under coolant |
| AlTiN | Heat, with a harder surface | Hard milling, dry cutting, titanium |
| AlCrN | Oxidation at high temperature | Hardened steel, nickel alloys |
| TiCN | Abrasion with high toughness | Cast iron, interrupted cuts, tapping |
| DLC | Adhesion and friction | Aluminium, copper, composites |
| CVD oxide | Crater and flank wear | Continuous turning of steel and cast iron |
Why a hard coating can make aluminium worse
Aluminium fails tools by adhesion rather than abrasion, so the answer is a low-friction surface and a sharp edge. A hard coating blunts the edge and adds a rough surface for material to key into, which makes built-up edge more likely rather than less.
The same logic runs through every material group. A coating matched to the failure mode does the work; a coating chosen for its headline hardness frequently does not.
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Frequently asked questions
What is the difference between TiAlN and AlCrN?
TiAlN resists heat and abrasion well and suits general steel and stainless. AlCrN resists oxidation at higher temperature, which suits hardened steel and nickel alloys where the edge runs hotter and would otherwise oxidise rather than wear.
Which is better, CVD or PVD?
Neither in general. CVD gives better wear resistance in continuous turning of steel and cast iron, and PVD gives a sharper edge that suits milling, threading and stainless. The operation decides.
Can a coating be too thick?
Yes, particularly on small tools. A coating increases the effective edge radius, so on a micro drill it can prevent the tool cutting cleanly. Micro tools are frequently supplied uncoated or very thinly coated for that reason.
Do I need a coating at all?
For aluminium, cast iron and some composite work, uncoated can outperform a coated tool. For steel, stainless and heat-resistant alloys a coating is what makes the tool economically viable, because uncoated carbide wears too quickly at the temperatures involved.
How do I know which material group I am in?
It follows from the workpiece: P for steel and ferritic stainless, M for austenitic and duplex stainless, K for cast iron, N for aluminium and non-ferrous, S for titanium and nickel alloys, and H for hardened steel. Tell us the designation and we will place it.