There are several characteristics that a satisfactory tool material must possess.
The most important of these are discussed below:
1. Hot Hardness:
It is the ability of the cutting tool to withstand high temperature without losing its cutting edge. This item becomes increasingly important as the speed of the cutting operation is increased and the high temperature strength of the metal cut becomes greater.
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The red hardness of the tool materials can be increased by adding chromium, molybdenum, tungsten and vanadium, all of which form hard carbides. High hardness usually gives the tool good wear resistance, but may be associated with low toughness and poor mechanical-shock resistance.
2. Wear Resistance:
It is the ability to resist wear. During the process of machining, tool is affected by abrasive action of work piece. If the wear resistance of the tool is not enough, there are possibilities of the failure of cutting edge which may result in poor finish on the work.
The welding and strain hardening characteristics of the tool relative to those of metal cut must be such that excessive wear does not occur in the operating range of speed. Lack of chemical affinity between the tool and work material also improves wear resistance.
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3. Toughness:
This property poses limitation on the hardness of the tool, because with high hardness tool becomes brittle and weak in tension. This is particularly important in connection with interrupted cuts.
4. Mechanical and thermal shock resistance.
5. Ability to maintain the above properties at the temperatures occurring during cutting.
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6. Low Friction:
In order to have low tool wear and better surface finish, the coefficient of friction between the chip and tool should be as low as possible in the operating range of speed and feed. Thermal conductivity should be high for quick removal of heat from chip tool interface.
7. Favourable Cost:
The increased cost of a new material and its fabrication into an improved tool must not be more than offset by the savings involved in increased production, decreased cost of labour and overhead and increased tool life.
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8. Should be easy to regrind and easily weld-able to tool. Readily obtainable and easy to manufacture.