In the metal cutting process, the cutting part of the tool is directly responsible for the cutting work. Therefore, the material of the cutting part of the tool is generally called the tool material.
Reasonable choice of tool material is an important part of the cutting process, as it largely determines the level of cutting productivity, tool consumption and processing costs, as well as the size of machining accuracy and quality of the surface.
The development of materials for cutting tools is also promoted and influenced by the development of materials for parts.
Today, I will share with you the basics of cutting tool materials as well as methods for selecting them.
The properties that cutting tool materials must have
During the cutting process, the cutting tool is subjected to large cutting pressure, friction and impact force, resulting in high cutting temperature.
The tool works in a high temperature, high pressure and severe friction environment. Using unsuitable materials will quickly wear or break the tool.
Therefore, the tool material must meet some basic requirements.
1 . High hardness and good wear resistance
Hardness is a fundamental characteristic that tool materials must possess.
To cut chips from a workpiece, the hardness of the tool must be greater than that of the workpiece material.
The cutting edge of tools used to cut metallic materials generally has a hardness above 60HRC.
For carbon steel tool materials, the hardness should be above 62HRC at room temperature.
The hardness of high-speed steel is 63-70HRC, while the hardness of carbide tools is 89-93HRC.
Wear resistance refers to the ability of the tool material to resist wear.
In general, the higher the hardness of the tool material, the better the wear resistance.
Wear resistance depends on the hardness of the hard points (such as carbides, nitrides, etc.) in the metallographic structure of the tool material, the number of these points, their particle size and their uniformity of distribution, as well as the chemical composition, resistance, microstructure and temperature of the friction zone of the tool material.
If the quality of the material is taken into account and the temperature in the friction zone and chemical wear are not considered, the following method can be used to express the wear resistance WR of the material:
(1) When processing parts of common materials, common high-speed steel and carbide are generally used. New classes of high-performance tool materials can be selected when processing difficult-to-machine materials. CBN and PCD inserts should only be considered when processing high hardness materials or when conventional tool materials in precision processing cannot meet the processing accuracy requirements.
(2) It is difficult to fully consider the strength, composition, hardness and wear resistance of any cutting tool material. When selecting the type of tool material, the machinability and processing conditions of the workpiece material must be considered. Wear resistance is generally considered initially, and the chipping problem should be solved with reasonable geometric parameters of the tool as much as possible. Only when the tool material is very brittle and causes chipping, it is necessary to reduce the wear resistance requirements and it is necessary to choose a grade with better strength and toughness.
Under normal circumstances, when cutting at low speeds, the cutting process is not stable and chipping is easy to occur. It is advisable to choose a type of tool material with good strength and toughness. When cutting at high speed, the cutting temperature has a greater impact on the wear of tool materials. It is recommended to select durable consumer goods tool materials with good grinding properties.
