Classification and Selection of Cutting Tool Materials

A cutting tool, also known as a cutter, is a hard metal tool that is used to cut and remove material from a workpiece using machining and abrasive tools via shear deformation.

A cutting tool is a wedge-shaped tool with sharp edges. During machining, a cutting tool is used to shear off extra layers of material from the workpiece to obtain the desired size, shape, as well as accuracy. It is fixed to the machine tool. To handle the heat during the cutting process, the cutting tool should be tougher than the material to be cut. Single-point turning tools, drills, milling cutters, fly cutters, shapers, etc., are commonly used cutting tools.

Cutting Tool Materials

Part of the cutting tool stays in physical contact with the workpiece during machining, resulting in high cutting temperatures and constant rubbing. The cutting tool's material must be capable of withstanding such high cutting temperatures and cutting forces. Every tool material must have particular characteristics, such as high hardness, high hot hardness, high strength, a higher melting point, and chemical inertness, even at high cutting temperatures. For smooth cutting action, the hardness of the tool material should be at least double the hardness of the workpiece.

Types Of Cutting Tool Materials

Following is the list of different types of cutting tool materials:

1. Carbon Tool Steel

Carbon steel is used for low-speed machining operations. Abrasion resistance and the ability to keep a sharp cutting edge are two advantages of high-carbon steels. Carbon tool steels have high machinability. Carbon steel starts melting at a temperature of approx. 180 – 250 degrees. As a result, it is unable to operate at high temperatures.

2. High-Speed Steel (HSS)

 high-speed steel is widely used in machining operations. HSS tools are used to make complex-shaped tools like drills, reamers, taps, dies, and gear cutters. They are robust and ideal for interrupted cutting. HSS loses its hardness at a temperature of approx. 600-650 degrees. As a result, a coolant should be applied to extend the tool's life. It can be re-sharpened and used multiple times.

3. Cemented Carbide

Cobalt serves as a binder between titanium, tungsten, and tantalum carbide, which make up a cemented carbide-cutting tool. Carbide tools are extremely tough and can sustain temperatures up to 1000 degrees.

4. Ceramic

The most popular ceramic materials are aluminum oxide and silicon nitride. They are strong in compression. Ceramics can hold up to a temperature of 1800 degrees Celsius. The friction between the tool face and the chip is very low, and the heat conductivity is low; no coolant is normally required. They create a fantastic surface finish.

5. Cubic Boron Nitride Tool (CBN)

After diamonds, cubic boron nitride is the second hardest material. They're commonly seen in hand machinery. CBN has high abrasion resistance and is used as an abrasive in grinding wheels.

6.  Diamond Tool

Diamond tools are the hardest and most valuable material known to man. They have a high melting point and thermal conductivity. Diamond tools are great for surface polish and dimensional accuracy.

Classification Of Cutting Tools

There are three types of cutting tools:

• Single-point cutting tool
• Double-point cutting tool
• Multi-point cutting tool

1. Single Point Cutting Tool

A single-point cutting tool has only one main cutting edge that can remove material in a single pass. Single-point cutting tools are used in activities like turning, shaping, and other similar activities. It consists of hard materials like high-carbon steel, high-speed steel, ceramic, and diamond. As it has only one cutting edge, there is a possibility that the material cannot be removed quickly, and there is a chance of breaking the cutting edge.

Single-point cutting tools have the advantage of being easy to design and manufacture, as well as being relatively inexpensive. On the other hand, the single cutting edge has the disadvantage of remaining in continual contact with the workpiece during milling. As a result, tool life becomes shorter, and tool wear is high.  Turning tools, boring tools, fly cutters, etc., are examples of single-point cutting tools.

2. Double Point Cutting Tool

A double-point cutting tool has two cutting blades that can both cut and shear in the same operation. A drill (a common metal cutting drill that has only two flutes) is an example of a Double-point cutting tool.

3. Multi-Point Cutting Tool

These tools have multiple main cutting edges that may remove material simultaneously in a single pass. Milling cutters, broaches, gear hobbing cutters, grinding wheels, and other tools are examples of multi-point cutting tools.

How To Select Cutting Tool Materials?

Here are the points to keep in mind while selecting cutting tool materials

• High strength and toughness
• High performance
• High wear resistance
• Cutting speed and cutting temperature (both high & low)
• Heat resistance

Additional factors to consider while selecting cutting tool materials:

• Coolant: When choosing the materials for cutting tools, coolant is crucial. Coolants aid in lowering operating temperatures. Tools that are overheated may break more quickly and harm workpieces. Coolants are able to dissipate and absorb heat while maintaining the ideal cutting temperature.
• Tool coating: When choosing cutting tool materials, tool coating is another important consideration. Cutting tools can be made stronger and more durable by applying coatings, which are thin layers of material, to their surface. Additionally, it prevents heat dissipation and serves as a barrier.  
• Tool structure: Tool structure refers to the angle, shape, and design of the cutting tool. These configurations significantly affect the durability and performance of cutting tools.

CONCLUSION

Hope this article will bring better insight into cutting tools, their classifications, and the points to remember while selecting cutting tool material.