Properties of Cutting Tools

Many types of tool materials, ranging from high carbon steel to ceramics and diamonds, are used as cutting tools in today’s metalworking industry. It is important to be aware that differences do exist among tool materials, what these differences are, and the correct application for each type of material.

Cutting tool and the Industry Advancements

 

Cutting tool users can’t afford to ignore the constant changes and advancements that are being made in the field of tool material technology. When a tool change is needed or anticipated, a performance comparison should be made before selecting the tool for the job. The optimum tool is not necessarily the least expensive or the most expensive, and it is not always the same tool that was used for the job last time. The best tool is the one that has been carefully chosen to get the job done quickly, efficiently, and economically.

A cutting tools must have the following characteristics in order to produce good quality and economical parts:

Hardness — Harness and strength of the cutting tool must be maintained at elevated temperatures, also called hot hardness.

Toughness — Toughness of cutting tools is needed so that tools don’t chip or fracture, especially during interrupted cutting operations.

Wear Resistance — Wear resistance means the attainment of acceptable tool life before tools need to be replaced.

The materials from which cutting tools are made are all characteristically hard and strong. Below are the characteristics mentione

 

Plain carbon tool steel is the oldest of the tool materials dating back hundreds of years. However, because it is quickly over tempered (softened) at relatively low cutting temperatures (300 to 500°F), it is now rarely used as cutting tool material except in files, saw blades, chisels, etc. The use of plain high carbon steel is limited to low heat applications.

The hardness of the carbide is greater than the of most other tool materials at room temperature and it has the ability to retain its hardness at elevated temperatures to a greater degree, so that greater speeds can be adequately supported. Two-thirds of all carbide tools are coated. Coated tools should be considered for most applications because of their longer life and faster machining. Coating broadens the application of a specific carbide tool.

Variety Of Cutting Tool Materials

Today cutting tools are used for variety of applications and have positioned themselves as significant equipments. Hence, it is vital to know about their characteristics and types.

Materials of the cutting tool must be equipped wit number of vital properties to prevent excessive wear, fracture failure and high temperatures in cutting.

The following characteristics are critical for cutting materials in order to pass through the heavy conditions of the cutting process and to develop high quality and affordable parts:

1) Toughness: The material should have ability to absorb energy without failing. If the cutting equipment fails soon that it is not strong enough.

2) Wear Resistance: There is a strong relation between hot hardness and wear resistance, latter depends more on hot hardness.

3) Surface Finish Of The Tool: It is also significant characteristics, which is chemical inertness of the tool material with respect to the work material.

4) Thermal Conductivity Of The Tool Material: It is affected by which maximum value of the cutting temperature at tool-chip interface.

Cutting tool materials

Carbon Steels is the oldest of the tool material. The carbon content is 0.6~1.5% with small quantities of silicon, chromium, manganese, and vanadium to refine grain size. Maximum hardness is about HRC 62. These materials possess low wear resistance and low hot hardness. The application of these materials is now limited.

High-speed steel (HSS) is another material, which was first produced in 1900s. They are alloyed with vanadium, cobalt, molybdenum, tungsten and chromium. The aforementioned are added to elevate the hot hardness and wear resistance. It can be hardened to various depths by appropriate heat treating up to cold hardness in the range of HRC 63-65. The cobalt component lends the material a hot hardness value, which is much greater than carbon steels. The high toughness and good wear resistance makes HSS suitable for all type of cutting tools with complex shapes for relatively low to medium cutting speeds. The most widely used tool material today for taps, drills, reamers, gear tools, end cutters, slitting, broaches, etc.

Cemented Carbides has also paved way in many industries. It was debuted in the 1930s. Most important tool materials today; cemented carbide is recognized because of their high hot hardness and wear resistance. The main drawback of cemented carbides is their low toughness. These materials are developed by powder metallurgy methods, sintering grains of tungsten carbide (WC) in a cobalt (Co) matrix (it provides toughness). There may be other carbides in the mixture, such as titanium carbide (TiC) and/or tantalum carbide (TaC) in addition to WC. In spite of more traditional tool materials, cemented carbides are present as inserts generated by powder metallurgy process.