Correct surface treatment of small circular tools (carbide milling cutters, inserts, carbide drills, etc.) can increase the life of the tools (carbide milling cutters, inserts, carbide drills, etc.), reduce the processing cycle time and improve the quality of the processed surface. However, the correct selection of carbide milling cutters or drill bit coatings according to processing needs may be a confusing and laborious task.

Each coating has both advantages and disadvantages in the cutting process. If an improper coating is selected, the life of the milling cutter or drill bit may be lower than that of the uncoated milling cutter or drill bit, and sometimes it may even lead to more questions.

RZHX tools (DMTOL )will briefly introduce some common attributes of tool coatings.

Hardness

The high surface hardness brought by the coating is one of the best ways to increase the life of the milling cutter. Generally speaking, the higher the hardness of the material or surface, the longer the life of the milling cutter.

Titanium carbide (TiCN) coatings have higher hardness than titanium nitride (TiN) coatings. Due to the increased carbon content, the hardness of the TiCN coating is increased by 33%, and the hardness range is about Hv3000～4000 (depending on the manufacturer).

Abrasion Resistance

Abrasion resistance refers to the ability of a coating to resist wear. Although the hardness of some workpiece materials may not be too high, the added elements and processes used in the production process may cause the cutting edge of the milling cutter to crack or blunt.

Surface Lubricity

High friction coefficient will increase cutting heat, resulting in shortened coating life and even failure. Reducing the friction coefficient can extend the life of the milling cutter. A fine, smooth or regular-textured coating surface helps reduce cutting heat, because a smooth surface can quickly slide chips away from the rake face and reduce heat generation. Compared with uncoated milling cutters, coated milling cutters with better surface lubricity can be processed at a higher cutting speed, thereby further avoiding high temperature welding with the workpiece material.

Oxidation Temperature

The oxidation temperature is the temperature at which the coating begins to decompose. The higher the oxidation temperature, the more advantageous it is for cutting under high temperature conditions. Although the normal temperature hardness of TiAlN coating may be lower than that of TiCN coating, it has been proved that it is much more effective than TiCN in high temperature processing. Compared with high-speed steel milling cutters, the cutting speed of cemented carbide milling cutters is usually higher, which makes TiAlN the preferred coating for cemented carbide milling cutters. Carbide drill bits and end mills usually use this TiAlN coating .

Anti-adhesion

The anti-adhesion of the coating can prevent or reduce the chemical reaction between the milling cutter or drill bit and the processed material, and avoid the deposition of workpiece material on the milling cutter or drill bit.

When processing non-ferrous metals (such as aluminum, brass, etc.), a built-up edge (BUE) is often generated on the milling cutter or drill bit, which causes the milling cutter to chip or the workpiece size is out of tolerance. Once the processed material begins to adhere to the milling cutter, the adhesion will continue to expand.

When machining aluminum workpieces with forming taps, the aluminum adhering to the taps will increase after each hole is processed, and eventually the diameter of the taps will become too large, causing the workpiece size to be out of tolerance. Coatings with good anti-blocking properties can play a good role even in processing situations where the coolant performance is poor or the concentration is insufficient.