Coating Guide

What a coating actually changes

A tool coating is a thin ceramic layer — typically a few micrometres — deposited on the carbide substrate. Physical vapour deposition (PVD) is the usual process for solid carbide end mills because it runs at a temperature low enough to leave the substrate and the edge geometry intact. Chemical vapour deposition (CVD) produces thicker layers at higher temperature and is more common on indexable inserts.

Three effects matter:

• Surface hardness. The coating is substantially harder than the carbide beneath it, which resists the abrasive component of wear.
• Friction and adhesion. A lower coefficient of friction means the chip slides rather than welds, which is the difference between a clean surface and a built-up edge.
• Thermal behaviour. Aluminium-bearing coatings form a stable oxide layer at temperature that acts as a thermal barrier, keeping heat in the chip and out of the tool.

What a coating does not do is fix a wrong parameter. A coating extends the window; it does not move it. A tool run below the minimum chip thickness will rub and fail whatever is deposited on it.

The main coating families

These are the general characteristics of coating families as published across the industry. They are not a specification of any EUROCUTPRECISION product.

When uncoated is the right answer

Coating is not automatically an upgrade. In soft aluminium alloys the failure mode is adhesion, and a coating with any surface roughness can give the chip something to key into. A polished, uncoated carbide flute with a sharp positive geometry is frequently the better tool — and DLC, where used, is chosen for its low friction rather than its hardness.

Sharpness is the second reason. Every coating adds thickness at the edge, and there is a lower limit on how sharp a coated edge can be. Where the process depends on an extremely keen edge — thin-wall finishing, some non-ferrous work — uncoated wins on geometry.

Reading coating wear

A coating fails visibly before the tool does, which makes inspection worthwhile:

• Even, gradual flank wear with the coating intact above it — normal wear. Plan a change at a measured wear land rather than at failure.
• Coating flaking away in patches — usually thermal shock (intermittent coolant) or adhesion, not a coating defect.
• A bright, polished band on the flank — the coating has gone and carbide is rubbing; tool life from this point is short.
• Material welded to the rake face — built-up edge; the speed is generally too low for the material, or the coolant is not reaching the cut.
• A notch at the depth-of-cut line — characteristic of stainless and superalloys; vary the axial depth between passes.

Coating on EUROCUTPRECISION tools

The Z5 series is supplied AlTiN coated. That is the manufacturer’s designation, taken from the data sheet that also supplies the series’ cutting parameters, and it is published on every Z5 product page.

The substrate is still pending final manufacturer confirmation, and so are the coating’s own properties — thickness, microhardness and maximum working temperature. The data sheet names the layer and says nothing about what is underneath it or how thick it is, and neither is inferred from the other. No hardness figure or performance claim is published for any EUROCUTPRECISION coating until the manufacturer states it in writing.

If the substrate or coating specification is required for a purchasing or engineering decision, request it with your quotation request — the requirement is recorded against the enquiry and answered directly rather than estimated here.