Cutting-tool materials .: Makina Mühendisi

Carbon steels
Their use is restricted to the cutting of soft metals and wood. Performance is poor above 250°C.
High-speed St MIS
These are used extensively, particularly for multi-point tools. They have been replaced to a large extent by
carbides for single-point tools. Their main application is and broaching. They are for form tools and complex shapes, e.g. for gearcuttingalso used for twist drills, reamers, etc.Carbides

These consist of powdered carbides of tungsten, titanium, tantalum, niobium, etc., with powdered cobalt as binder. They are produced by pressing the powder in dies and sintering at high temperature. They are then ground to the final shape. They are generally used as tips and can operate up to 1oo0"C.Laminated carbide

These consist of a hard thin layer of titanium carbide bonded to a tungsten carbide very high strength at high temperature, whilst the body has high thermal conductivity and thus efficient removal body. The surface has of heat.Diamonds

These are the hardest twice final polishing can alloys, copper, brass and zinc. They have a long life.
Characteristics
Carbide and
Po1
General information on metal cutting
Cutting speeds and
Power used and volume removed in metal cutting
Surface
finish
Different processes produce different degrees
an average height
surface is indicated is shown.
of finish on machined surfaces. These are graded from N1 withof roughness of 0.025 pm, up to N12 roughness 50pm. The manner in which a machined
Merchants
circle for tool forces
‘Merchant’s circle’ is a well-known construction for
the analysis
the cutting and feed forces, the initial and final chip
thickness and the tool rake angle are known, then the
other forces, friction and shear angles can be found.
Known:
of cutting forces for a single-point tool. If
F,
F,=feed force
=cutting force
t ,
=initial chip thickness
t ,
=final chip thickness
a
The diagram can
= tool rake anglebe drawn to give:
F,
=shear force
F,
F=friction force on tool face
= resultant force
F,,
= force normal to shear force
F,
=force normal to F
p
=coefficient of friction = F/F,
6
=friction angle = tan - p
4
Machining properties
Negative rake cutting
of thermoplastics= shear anglefeed ratesand K40ceramic tools Carbides by a number from are graded according to series (see table) and01 (hardest) to 50 (toughest), e.g.of all cutting materials with low thermal expansion and good conductivity. They areas good as carbides under compression. A good finish can be obtained with non-ferrous metals andbe eliminated. Diamonds are particularly good for cutting aluminium and magnesiumof steel tools

Cutting-tool materials

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