Machining Cutting Tool Materials
High Carbon Steel|
This material is one of the earliest cutting materials used in machining. It is however
now virtually superseded by other materials used in engineering because it starts to temper at about 220oC
. This softening process continues as the temperature rises. As a
result cutting using this material for tools is limited to speeds up to 0.15 m/s for
machining mild steel with lots of coolant.
This range of metals contain about 7% carbon, 4% chromium plus additions of tungsten, vanadium,
molybdenum and cobalt. These metals maintain their hardness at temperature up to about 600o, but
soften rapidly at higher temperatures. These materials are suitable for cutting mild
steel at speeds up maximum rates of 0.8 m/s to 1.8 m/s.
These cutting tools are made of various nonferous metals in a cobalt base. They can withstand
cutting temperatures of up to 760oC and are capable of cutting speeds about 60% higher than
This material usually consists of tungsten carbide or a mixture of tungsten carbide,
titanium, or tantalum carbide in powder form, sintered in a matrix of cobalt or nickel.
As this material is expensive and has low rupture strength it is normally made in the form
of tips which are brazed or clamped on a steel shank. The clamped tips are generally used as throw away inserts.
The cutting system is based on providing a thin layer of high wear-resistant titanium carbide
fused to a conventional tough grade carbide insert, thus achieving a tool combining the wear resistance
of one material with the wear resistance of another. These systems provide a longer wear
resistance and a higher cutting speed compared to conventional carbides.
Ceramics are made by powder metallurgy from aluminium oxide with additions of titanium oxide
and magnesium oxide to improve cutting properties. These have a very high hot resistance and wear
resistance and can cut at very high speed. However they are brittle and have little resistance to
to shock. Their use is therefore limited to tips used for continuous high speed cutting
on vibration-free machines.
Diamonds have limited application due to the high cost and the small size of the of the stones. They are used on very hard materials to produce a fine finish and on soft materials. especially those inclined to clog other cutting materials. They are generally used at very high cutting speed with low feed and light cuts. Due to the brittleness of the diamonds the machine has to be designed to be vibration free. The tools last for 10 (up to 400) times longer than carbide based tools.
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