A Brief Discussion on Tool Material Classification

 

Under different conditions, there are various cutting methods, and in such cases, cutting tools require certain unique properties. To achieve this performance, cutting tools are made from different materials. The material chosen for a specific application depends on the material being processed, the type of machining, and the quantity and quality of the product.

Tool materials can be classified into several categories based on the material used:

 

1. Carbon Tool Steel

2. High-Speed Steel (HSS)

3. Cemented Carbide

4. Ceramic Tools

5. Cubic Boron Nitride (CBN)

6. Diamond Tools

 

 

I Carbon Tool Steel

 

Carbon tool steel is an inexpensive metal-cutting tool used for low-speed machining operations. These plain carbon steel cutting tools contain 0.6-1.5% carbon and very small amounts (less than 0.5%) of manganese and silicon. Other metals like chromium and vanadium are added to modify hardness and grain size.

 

High-carbon steel is wear-resistant and capable of maintaining a sharp cutting edge. Carbon tool steel has good machinability, but this material rapidly loses its hardness at around 250°C.

 

Therefore, it cannot be used in high-temperature applications, which might be why it is irreplaceable in some current machining operations.

 

Carbon steel tools are used for twist drills, milling tools, turning and shaping tools, and are suitable for soft materials like brass, aluminum, and magnesium.

 

Temperature Resistance: Up to 450°C

Hardness: Up to HRC65

 

 

II High-Speed Steel (HSS)

 

▲  HSS

 

High-speed steel is a type of high-carbon steel that contains a large amount of alloying elements such as tungsten, molybdenum, and chromium. These elements enhance hardenability, toughness, and wear resistance, providing a higher metal removal rate.

 

At a moderate temperature of around 650°C, it will lose its hardness.

 

Therefore, coolant should be used to extend tool life. High-speed steel can be reused multiple times through regrinding. Certain surface treatments are applied to high-speed steel to improve its performance.

 

Surface treatments used in high-speed steel:

Polishing: Reduces friction

Nitriding: Increases wear resistance

Chromium Plating: Reduces friction

Oxidation: Reduces friction

 

High-speed steel materials can be used to manufacture: drills, milling cutters, broaches, etc.

 

Cutting speed range: Vc = 30-50 meters/minute

Temperature resistance: Up to 650°C

Hardness: Up to HRC67

 

 

III Cemented Carbide

 

▲  Cemented carbide

 

Cemented carbide tools are produced using powder metallurgy techniques. They are composed of tungsten, tantalum, and titanium carbides with cobalt as a binder (when the binder is nickel or molybdenum, it is referred to as cermet).

 

Cemented carbide tools are extremely hard and can withstand very high-speed cutting operations.

 

Cemented carbide tools do not lose their hardness at temperatures up to 1000°C.

 

High-cobalt tools are used for roughing, while low-cobalt tools are used for finishing.

 

Cutting speed range: Vc = 60-200 meters/minute

Temperature resistance: Up to 1000°C

Hardness: Up to HRC90

 

 

IV Ceramic Materials

 

▲  Ceramic

 

The most common ceramic materials are alumina and silicon nitride. The ceramic material powder is compacted into the desired shape and then sintered.

 

Ceramic tools are chemically inert and corrosion-resistant, with high compressive strength. They remain stable at temperatures up to 1800°C, operate 10 times faster than HSS, have very low friction between the tool surface and the chips, and feature low thermal conductivity. Coolant is generally not required, and ceramic tools can provide a very fine surface finish.

 

Cutting speed: Vc = 300-600 meters/minute

Temperature resistance: Up to 1200°C

Hardness: Up to HRC93

 

 

V Cubic Boron Nitride (CBN)

 

▲  CBN

 

CBN is the second hardest material after diamond and is often used in manual equipment. It has very high wear resistance and is commonly used as an abrasive for grinding wheels. Sharp edges are not recommended for use.

 

Cutting speed: Vc = 600-800 meters/minute

Hardness: Greater than HRC95

 

 

VI Diamond

 

▲ Diamond

 

Diamond is the hardest known material and also the most expensive. It has excellent thermal conductivity and a high melting point. Diamond tools exhibit exceptional wear resistance, low friction coefficient, and low thermal expansion. They are ideal for machining extremely hard materials such as carbides, nitrides, and glass.

 

Diamond tools provide excellent surface finish and dimensional accuracy.

 

Today, we've briefly discussed the characteristics of different tool materials. There is no single best material, only the most suitable one.