How To Select Cutting Tool Materials?

With the rapid development of manufacturing industry, the workload of metal cutting is increasing day by day.

15% – 30% of the world’s steel production has to be cut, so the cost of metal cutting is huge.

Cutting tools play an important role in metal cutting.

With the continuous emergence of new engineering materials, the requirements for tool materials are also increasing.

When cutting, we must consider comprehensively according to the specific situation and reasonably select the tool material. We should not only give full play to the characteristics of the tool material, but also meet the requirements of cutting economically.

1. Properties of tool materials

Fig. 2-1 shows the development time and cutting speed of various tool materials.

The abscissa is the year of tool material development, and the ordinate corresponds to the cutting speed that can be achieved by a kind of material.

development of tool materials

Fig. 2-1 development of tool materials

The development process of tool materials is actually a process of continuously improving the heat resistance, wear resistance, cutting speed and surface processing quality of tool materials.

The performance of tool materials directly affects whether the cutting process can be carried out normally.

The cutting tool carries out cutting work at high temperature and also bears cutting force, impact and vibration.

Therefore, the tool material should meet the following basic requirements:

(1) High hardness:

The hardness of the tool material must be higher than that of the processed material. Generally, the normal temperature hardness of the tool material is above 62HRC.

(2) High flexural strength:

In order to withstand cutting force, impact and vibration, the tool material should have sufficient strength, that is, it should have certain edge collapse resistance and damage resistance.

(3) High heat resistance:

Heat resistance refers to the ability of tool materials to maintain hardness at high temperature.

(4) Good chemical stability:

The cutting tool material shall have oxidation resistance and diffusion resistance.

(5) Good heat conductivity:

The cutting tool material shall have good heat shock resistance and heat crack resistance.

The greater the thermal conductivity, the more heat is transferred from the tool, which is conducive to reducing the cutting temperature and improving the tool life.

(6) Low affinity:

The tool material shall be resistant to melting and solidification (sticking).

(7) Good workmanship:

In order to facilitate manufacturing, tool materials are required to have good machinability, including forging, rolling, welding, cutting and grindability, heat treatment characteristics, etc.

2. Tool material classification

There are many kinds of tool materials, including carbon tool steel, alloy tool steel, high-speed steel, cemented carbide, ceramics, diamond (natural and man-made) and cubic boron nitride.

The cutting tool materials can be divided into:

  • Tool steel
  • Sintered body
  • Natural diamond

Tool steel include:

  • Carbon tool steel
  • Alloy tool steel
  • High speed steel
  • Cast tool steel

High speed steel include:

  • General purpose high speed steel (tungsten steel, tungsten molybdenum steel)
  • High performance high speed steel (high carbon high speed steel, high vanadium high speed steel cobalt, high speed steel aluminum, high speed steel)
  • Powder treated high speed steel
  • Coated high speed steel

Sintered body include:

  • Cemented carbide
  • Cermet
  • Ceramics
  • Ultra high pressure sinter

The comparison of physical and mechanical properties of various tool materials is shown in table 2-1.

Table 2-1 physical and mechanical properties of various tool materials

Material typeHardnessDensity / (g / cm3)Flexural strength / GPAImpact toughness / (kJ / m2)Thermal conductivity / [w / (m · K)]Heat resistance / ℃
Carbon tool steel63~65HRC7.6~7.82.2 41.8200~250
high speed steel63~70HRC8.0~8.81.96~5.8898~58816.7~25.1600~700
Cemented carbide89~94HRA8.0~150.9~2.4529~5916.7~87.9800~1000
ceramics91~95HRA3.6~4.70.45~0.85~1219.2~38.21200
cubic boron nitride8000~9000HV3.44~3.490.45~0.8 19.2~38.21200
diamond10000HV3.47~3.560.21~0.48 19.2~38.21200

3. Main overview of tool material application

Various tool materials and their applications are shown in table 2-2.

Table 2-2 various tool materials and their applications

Type of tool material Application
High speed steel tool material
High speed steel tool material
High speed steel (HSS) is a kind of high alloy tool steel with more alloying elements such as W, Mo, Cr and V.High speed steel cutting tools have excellent comprehensive properties in strength, toughness and manufacturability.High speed steel still plays a major role in complex cutting tools, especially some cutting tools with complex edges, such as hole manufacturing tools, milling tools, thread cutting tools, broaches, gear cutting tools and so on.High speed steel tools are easy to grind out sharp cutting edges.At present, the high-speed steel grades commonly used in international standards are M35 and M42
Cemented carbide tool material
Cemented carbide tool material
Class k cemented carbide is mainly used for processing cast iron, non-ferrous metals and non-metallic materials.When the cobalt content is the same, the hardness and wear resistance of fine grain cemented carbide are higher than that of medium grain. It is suitable for processing some special hard cast iron, austenitic stainless steel, heat-resistant alloy, titanium alloy, hard bronze and wear-resistant insulating materials.The outstanding advantages of class P cemented carbide are high hardness, good heat resistance, higher hardness and compressive strength at high temperature than class k, and good oxidation resistance.M-type cemented carbide has the properties of K and p-type cemented carbide, with good comprehensive properties.
Cermet
Cermet
Cermet is a kind of cemented carbide with Ti (C.N) and tic as basic components and Ni Mo as binder.Features: higher thermal hardness than ordinary alloy, good wear resistance, suitable for high-speed machining, good chemical stability, significantly improved adhesion and wear resistance, suitable for viscous material processing, small friction coefficient with steel, small cutting force, light cutting, suitable for precision machining.
Coated tool material
Coated tool material
It not only maintains the good toughness and high strength of the matrix, but also has the high hardness, high wear resistance and low friction coefficient of the coating.PVD coating is recommended for wear-resistant and sharp cutting edges and processing soft and sticky materials.This application is common, including all solid carbide end mills and drills, as well as most grades of grooving, threading and milling.PVD coating is widely used in finish machining and as an important tool brand in drilling.Coated cemented carbide combines cemented carbide and coating.Together, they form a specific brand suitable for their application.Coated cemented carbide is the first choice for many cutting tools and applications.
Ceramic tool materials
Ceramic tool materials
Ceramics is one of the cutting tool materials mainly used for high-speed finishing and semi finishing.Ceramic cutting tools are suitable for cutting all kinds of cast iron (gray cast iron, nodular cast iron, malleable cast iron, chilled cast iron, high alloy wear-resistant cast iron) and steel (carbon structural steel, alloy structural steel, high strength steel, high manganese steel, quenched steel, etc.), as well as copper alloy, graphite, engineering plastics and composite materials.Ceramic cutting tools have the problems of low bending strength and poor impact toughness, which are not suitable for cutting under low speed and impact load.
Cubic boron nitride tool material
Cubic boron nitride tool material
Cubic boron nitride is suitable for finishing all kinds of hard cutting materials such as quenched steel, hard cast iron, superalloy, cemented carbide and surface spraying materials.The machining accuracy can reach it5 (the hole is IT6), and the surface roughness value can be as small as Ra = 1.25-0.20 μ m。Cubic boron nitride tool material has poor toughness and bending strength.Therefore, the cubic boron chloride turning tool is not suitable for rough machining with low speed and high impact load. At the same time, it is not suitable for cutting materials with high plasticity (such as aluminum alloy, copper alloy, nickel base alloy and steel with high plasticity), because serious shoulder tumors will be produced when cutting these metals, which will worsen the processing surface.
Diamond tool material
Diamond tool material
Polycrystalline diamond (PCD) has been synthesized by high pressure synthesis technology, which solves the problem of rare and expensive natural diamond.Diamond tools have the characteristics of high hardness, high compressive strength, good thermal conductivity and wear resistance, and can obtain high machining accuracy and machining efficiency in high-speed cutting. At present, the processing range of PCD tools has been extended from traditional metal cutting to stone processing, wood processing, metal matrix composites, glass and engineering ceramics.
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