Which coating to use, and when it matters.
PVD coatings extend tool life by reducing friction, dissipating heat, and increasing surface hardness. The right coating can double or triple tool life. The wrong one can cause built-up edge or coating delamination.
| Coating | Max Temp | Hardness | Best For | Color |
|---|---|---|---|---|
| AlTiN | 800°C | 3,300 HV | Steel, stainless, general purpose | Blue-gray |
| TiSiN | 1,100°C | 3,800 HV | Hardened steel (HRC 45-65), titanium | Copper |
| TiAlN | 700°C | 3,000 HV | Steel, cast iron, moderate applications | Violet-gray |
| TiCN | 450°C | 3,500 HV | Aluminum, non-ferrous, abrasive materials | Dark gray |
| AlCrN | 1,100°C | 3,200 HV | High-temp alloys, stainless | Dark blue |
| DLC | 350°C | 5,000 HV | Aluminum, plastics, composites | Black |
| NACO (Blue) | 700°C | 2,800 HV | Aluminum, copper, low-carbon steel | Blue |
Aluminum Titanium Nitride is the most common coating for general machining. It forms a hard aluminum oxide layer at high temperatures that acts as a thermal barrier. Works well on steel and stainless steel up to 45 HRC. Good for both roughing and finishing.
Titanium Silicon Nitride is the hardest common coating. The silicon content creates a nanocomposite structure that significantly increases hardness and temperature resistance. Use for hardened steel (HRC 45+), titanium alloys, and superalloys. Excellent for dry machining where no coolant is used.
Diamond-Like Carbon has the highest surface hardness and the lowest friction coefficient. It prevents built-up edge when machining aluminum, copper, and plastics. Not suitable for steel — the chemical reaction between carbon and iron will destroy the coating quickly.
Not always a downgrade. For aluminum, copper, and some plastics, uncoated tools with sharp edges often perform better than coated ones. They're also significantly cheaper. Keep a set of uncoated end mills for non-ferrous work.