Regarding tool life, it usually depends on different workpieces and tool materials, as well as different cutting processes. One way to quantitatively analyze the end of tool life 

is to set an acceptable maximum flank wear limit (expressed as VB or VBmax). Tool life can be expressed by the Taylor formula of expected tool life, that is, VcTn=C. A more 

commonly used form of this formula is VcTn×Dxfy=C. In the formula, Vc is the cutting speed; T is the tool life; D is the cutting depth; f is the feed rate; x and y are determined 

experimentally; n and C are constants determined based on experiments or published technical information. They represent the characteristics of the tool material, workpiece 

and feed rate.

        Continuously developing technologies for optimal tool substrates, coatings and cutting edge preparation are essential to limit tool wear and resist high cutting 

temperatures. These factors, along with the chip breakers and corner radius used on indexable inserts, determine the suitability of each tool for different workpieces and 

cutting operations. The optimal combination of all these elements can extend tool life and make cutting operations more economical and reliable.

        change matrix

        By changing the particle size of tungsten carbide in the 1-5 μm range, tool manufacturers can change the matrix properties of carbide tools. The particle size of the base 

material plays an important role in cutting performance and tool life. The smaller the particle size, the better the wear resistance of the tool. On the contrary, the larger the 

particle size, the stronger and tougher the tool. The fine-grained matrix is mainly used for inserts processing aerospace grade materials (such as titanium alloy, Inconel alloy 

and other high-temperature alloys).

        In addition, better toughness can be obtained by increasing the cobalt content of cemented carbide tool materials by 6%-12%. Therefore, the cobalt content can be 

adjusted to meet the requirements of a specific cutting process, whether that requirement is toughness or wear resistance.

The properties of the tool matrix can also be enhanced by forming a cobalt-rich layer close to the outer surface, or by selectively adding other alloying elements (such as 

titanium, tantalum, vanadium, niobium, etc.) to the carbide material. The cobalt-rich layer can significantly increase cutting edge strength, thereby improving the performance 

of roughing and interrupted cutting tools.

        When selecting a tool matrix that matches the workpiece material and processing method, five other matrix properties are also considered - fracture toughness, 

transverse fracture strength, compressive strength, hardness and thermal shock resistance. For example, if a carbide tool experiences chipping along the cutting edge, a base 

material with higher fracture toughness should be used. In the case of direct failure or damage of the cutting edge of the tool, the possible solution is to use a base material 

with higher transverse fracture strength or higher compressive strength. For machining situations with higher cutting temperatures (such as dry cutting), tool materials with 

higher hardness should usually be preferred. In machining situations where thermal cracks in the tool can be observed (most common in milling), it is recommended to use 

tool materials with better thermal shock resistance.

        Coating selection

        Coatings also help improve the cutting performance of the tool. Current coating technologies include:

        ①Titanium nitride (TiN) coating: This is a general-purpose PVD and CVD coating that can increase the hardness and oxidation temperature of the tool.

        ②Titanium carbonitride (TiCN) coating: By adding carbon element to TiN, the hardness and surface finish of the coating are improved.

        ③Titanium aluminum nitride (TiAlN) and titanium aluminum nitride (AlTiN) coatings: The composite application of aluminum oxide (Al2O3) layer and these coatings can 

improve the tool life of high-temperature cutting. Aluminum oxide coatings are particularly suitable for dry and near-dry cutting. AlTiN coatings have a higher aluminum 

content and have higher surface hardness than TiAlN coatings which have a higher titanium content. AlTiN coatings are commonly used for high-speed cutting.

        ④ Chromium Nitride (CrN) coating: This coating has good anti-adhesion properties and is the preferred solution for fighting built-up edge.

        ⑤Diamond coating: Diamond coating can significantly improve the cutting performance of tools for processing non-ferrous materials, and is very suitable for processing graphite, metal matrix composites, high-silicon aluminum alloys and other highly abrasive materials. However, diamond coating is not suitable for processing steel parts because its chemical reaction with steel will destroy the adhesion between the coating and the substrate.

        In recent years, the market share of PVD-coated tools has expanded, and its price is comparable to that of CVD-coated tools. The thickness of CVD coating is usually 5-15

μm, while the thickness of PVD coating is about 2-6μm. When applied to a tool substrate, CVD coatings create undesirable tensile stresses; PVD coatings contribute to beneficial compressive stresses on the substrate. Thicker CVD coatings often significantly reduce the strength of tool cutting edges. Therefore, CVD coatings cannot be used on tools that require very sharp cutting edges.

        Cutting edge preparation

        In many cases, the preparation of the insert cutting edge (or edge blunting) has become a watershed that determines the success or failure of the machining process. 

Passivation process parameters need to be determined according to specific processing requirements. For example, an insert used for high-speed finishing of steel requires 

different edge blunting requirements than an insert used for rough machining. Edge passivation can be applied to blades processing almost any type of carbon or alloy steel, 

but its application is somewhat limited when it comes to blades processing stainless steel and special alloy materials. The amount of passivation can be as small as 0.007mm 

or as large as 0.05mm. In order to strengthen the cutting edge in harsh machining conditions, tiny T-shaped ribs can also be formed through edge passivation.

        In general, inserts used for continuous turning operations and for milling most steels and cast irons require a significant degree of edge blunting. The amount of 

passivation depends on the carbide grade and coating type (CVD or PCD coating). For inserts for heavy interrupted cutting, it has become a prerequisite to heavily passivate 

the edge or machine a T-shaped rib. Depending on the coating type, the passivation amount can be close to 0.05mm.

        In contrast, since inserts for processing stainless steel and high-temperature alloys are prone to forming built-up edge, the cutting edge is required to remain sharp and 

can only be lightly passivated (can be as small as 0.01mm), and even smaller amounts of passivation can be customized. Similarly, blades used to process aluminum alloys 

also require sharp cutting edges.