Oxide ceramics are alumina-based and are generally used in roughing
and finishing applications of the cast and gray irons.
Increasingly, oxide ceramics are being used in dry machining
applications at high speeds. This is due to the advancements within
materials science, including the incorporation of whisker-based
materials.
Nitride ceramics exhibit extremely high fracture toughness and are
used for roughing and semi-roughing of cast irons under harsh
conditions, such as when there is considerable starting and
stopping that would typically increase fracturing.
CMCs contain ceramics mixed with other hard materials like cemented
and titanium carbides. They can also contain reinforcing whiskers
and other materials to increase wear resistance and toughness under
hot machining conditions. These are commonly referred to as
SiC-whisker reinforced. Alumina reinforced with SiC whiskers is the
toughest and most resistant to thermal shock of the oxide-based
ceramics due to the extremely high tensile strength of the SiC
whiskers. It offers the additional benefit of being able to be run
without coolant, thus making dry machining a common application
while also being able to offer an increase in machining rates up to
800%.
All ceramic
cutting tools have excellent wear resistance at high cutting
speeds.
There is a range of ceramic grades available for a variety of
applications.
Oxide ceramics are aluminum oxide-based (Al2O3), with added
zirconia (ZrO2) for crack inhibition. This generates a material
that is chemically very stable but lacks thermal shock
resistance.
(1) Mixed
ceramics are particles reinforced through the
addition of cubic carbides or carbonitrides (TiC, Ti(C, N)). This
improves toughness and thermal conductivity.
(2) Whisker-reinforced
ceramics use silicon carbide whiskers (Siew) to
dramatically increase the toughness and enable the use of coolant.
Whisker-reinforced ceramics are ideal for machining Ni-based
alloys.
(3) Silicon
nitride ceramics (Si3N4) represent another group of
ceramic materials. Their elongated crystals form a self-reinforced
material with high toughness. Silicon nitride grades are successful
in gray cast iron, but a lack of chemical stability limits their
use in other workpiece materials.
These benefits lead to increases in efficiency. For example, many
machinists would slow cutting speed if temperatures were to
approach maximum carbide limits. It is the opposite for ceramic
tools, which excel in higher temperature conditions.
Advantages of
silicon nitride ceramic cutting tools
Compared with carbide cutting tools, silicon nitride ceramic
cutting tools have obvious advantages, which are shown in the
following aspects.
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The HRA value of silicon nitride ceramic cutter is usually 91-93
(HRA is used to represent the hardness index of soft and hard
materials), so it has good wear resistance and can be used to
process high hard materials that are difficult to be processed by
traditional tools or cannot be processed at all, such as various
kinds of hardened steel and hardened cast iron with the processing
hardness up to HRC65 (60HRA = 20HRC).
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It can be used for rough and finish machining of high hardness
materials, as well as for high-impact machinings such as milling,
planning, and intermittent cutting.
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The cutting tools made of silicon nitride ceramics can be cut at
high speed to realize the function of milling for grinding for high
hard materials, simplify the processing technology and improve the
processing efficiency, so as to save time, electricity, number of
machine tools and plant area and other effects.
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The silicon nitride ceramic blade has less friction with metal when
cutting, which makes it difficult to stick to the blade and the
roughness of the workpiece is low.
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The tools durability is several times or even dozens of times
higher than that of traditional tools, which reduces the number of
tool changes during machining, ensures the uniformity of the
workpiece, and also ensures small taper and high accuracy.
â—
The cutting tool consumes the most abundant element silicon in the
crust as raw material, which can save a lot of strategic metal
materials such as tungsten, cobalt, and titanium.
![ceramic inserts](https://vdusr.tkcdn.com/upload/images/20220628_155402.jpg)
Applications
of silicon nitride ceramic cutting tools
Auto parts
processing
A
series of parts such as milling cylinder cover, cylinder sleeve,
and automobile brake disc are processed with composite silicon
nitride ceramic blade, which can improve the efficiency. For
example, a milling cutter can increase its speed from 92r/min to
275r/min.
Bearing
machining
The
rolling bearing adopts the technology of rough, fine, quenching,
rough grinding, and fine grinding for a long time. For example,
after hardening to 63HRC, the blank of the GCr15 precision forging
bearing will be deformed and uneven and will get stuck in the rough
grinding of the automatic grinding machine directly, and even burn
the spindle of the grinding machine in serious cases. The finishing
process of the bearing ring before quenching and the rough grinding
process after quenching are combined into the finishing process of
the ceramic cutter after quenching, which will make the workpiece
fully meet the required size and geometric accuracy, realize the
substitution of grinding by car and greatly improve the processing
efficiency.
Hard cast iron
processing
If
the composite nitride ceramic tool is used to process the cold cast
iron roll, the tool life is increased four times than that of
cemented carbide; it can be used to process superhard nickel alloy
spray welding roller bushing, which can greatly improve the cutting
efficiency and speed, save time and cost and improve economic
efficiency.
Other
fields
In
the fields of machinery, metallurgy, mining, railway locomotive,
aerospace, precision instruments, molds, etc., the technology can
be reformed by using silicon nitride ceramic cutting tools to
greatly improve production efficiency, save energy and reduce
cost.