Classification of Tool Materials

CLASSIFICATION OF TOOL MATERIALS
 High carbon steel
 High speed steel
 Cast alloy
 Cemented carbides
 Ceramics
 Diamond
 Cubic boron nitride

HIGH CARBON STEEL
Steel → alloy of iron& carbon
Low carbon steel→0.05 to 0.15%c
Medium carbon steel→0.30 to 0.7%c
High carbon steel:
This tool is a plain carbon steel which has 0.7 to
1.5 % carbon content

High carbon steel(contd..)
 It does not contain any other alloying elements.
 This tool possesses good cold hardness but its
hardness is low at high temperature.
 This tool is preferred at low cutting speed.
 However if this tool is operated at high
temperature , the heat draws out its temper and
tool fails quickly.
 The cutting tools such as hand drills, taps, dies,
reamers, hacksaw blades are still made of high
carbon steel.

HIGH SPEED STEEL
 This tool could machine steel at higher cutting
speed . (when high temperature is generated at
cutting edge without loosing its hardness)
 The steel that had tungsten-18%, chromium-4%,
and vanadium 1% popularly known as 18:4:1 HSS.

This steel is widely used in the industries and is
considered as a standard for the HSS. With the
development of HSS, cutting speed increased from
10m/min to 30m/min on mild steel machining.
TYPE OF HSS APPLICATION
18:4:1 Most common& industrial
type
14:4:1 For greater abrasiveness
14:4:1:5(Co) For higher red hardness due
to cobalt

Super high speed steel was marketed but could
not be made commercial due to the difficulties in
forging, rolling and heat treating. Its composition is
20%W, 2%Va,4%C and 12%Co.
Grindability, machinability & wear resistance
properties of HSS are related to vanadium content.
2%Va steel is more difficult to grind than 1%Va.

This tool material is difficult to replace and is
currently used in the manufacture of tool for the
following.
1.High volume, low cutting speed operations.
2.Form tools, drills, cut off tools, end mills,
reamers, taps and hubs.
3.High positive rake tool.

CAST ALLOYS
 Cast alloy is the combination of tungsten,
chromium and cobalt.
 The tool was made by melting the elements
together and then casting into moulds, hence its name
as cast alloys.
 Its performance was far superior to that of HSS.
 Nowadays, these alloys are available in the market
under different names- Rexalloy, Chromalloy, Tantung
etc.
TANTUNG: Its one of the widely known cast alloys. It
contains chromium, tungsten, columbium & carbon in
cobalt matrix. These elements are combined in the
proper proportions and cast in chilled moulds to obtain
Tantung.

1.It retains its cutting hardness at red hot
temperature up to 800͘0C .
2.It has high transverse rupture strength, low co-
efficient of friction and excellent resistance to
corrosion, abrasion and erosion.
3.It readily absorbs shocks & impact.
4.As a cutting tool material, it can be operated
at speeds 50% to 100% higher than that of HSS,
because it can retain its hardness beyond the point
where HSS burns – up.
5.Somewhat if more , it will not loose its
hardness after cooling from red hot condition.

6.Cast alloy is at its best when working at
relatively high speeds with heavy loads that generates
considerable heat. It bridges up the gap between
maximum speeds possible with HSS & minimum
speeds practical with carbide tool materials.
7.Cast alloy and steel have very nearly the same
coefficient of thermal expansions, as a result both the
material can be brazed & welded together. A few
typical compositions are
(1) W-12.17%, Cr-30.35%, Co-45.55%, C-2%
(2) W-17%, Cr-33.35%, Co-45%, Fe-3%

CEMENTED CARBIDES
Cemented carbides are the products of carbides
of Tungsten and Tantalum with some % of cobalt. This
product is obtained by a special technique called as
“Powder Metallurgy”.
WC→ 94%W and 6%C
It was free from porosity & possessed hardness
only next to diamond.

Properties of tungsten carbides
• The material is extremely hard and more
brittle.
• It can withstand a very high temperature of
1200 c and retains its hardness.
• Its very good in compression but fragile like a
raw egg.
• It provides higher tool life.
• It provides much better surface finish.

Types of tungsten carbide
• Plain tungsten carbide(single carbide)
• Steel grade tungsten carbide
Plain tungsten carbide:
This grade of carbide contains two constituents
namely tungsten carbide and cobalt where the cobalt
act as a binder.
The factors controlling the characteristics of this
grade are “grain size of tungsten carbide” and
“percentage of cobalt”.

• Upper & lower limits of grain size are 8 micron and
1 micron respectively.
• The maximum & minimum percentage of cobalt
are 25% and 3% respectively.
• Hardness ↓, when grain size and cobalt percentage
↑, toughness ↑ grain size & cobalt percentage.
• For maximum tool life , lowest binder content and
fine grain size is recommended

APPLICATION OF TANTALUM CARBIDE
• 1. As a cutting tool material
• 2. As a die material.
• 3. As a layer on corrosion resistant alloys
Tungsten carbide + Titanium carbide + Tantalum
carbide = Triple carbide

FACTORS INFLUENCING GENERAL
SELECTION OF CARBIDE TOOLS
 When rigidity of m/c tool & w/p together high.
 When adequate m/c tool power is required.
 W/p configuration & machining operation
permit higher speeds.
 High production rate desired.

STANDARDISATION OF CEMENTED
CARBIDES
A large number of carbides manufactures all
over the world produce a variety of carbides materials
and products. Selection of a grade of carbide material
& then finding its equivalent is made easier by
establishing a system of standards by ISO. It is not
only based upon the chemical constituents but also
based on the machining characteristics of the w/p.

ISO system for carbide grade classification
P
Long chipping
material.
Eg. steel
M
K
Materials b/t P&K.
Eg. stainless steel,
steel castings and
high temp. alloy
Short chipping
material.
Eg. Cast iron
WEAR RESISTANCE
↑
↓
TOUGHNESS
01
05
10
20
30
40
50

CERAMIC TOOL MATERIAL
1.Aluminium oxide
2.Silicon carbide
3.Boron carbide
4.Titanium carbide
Among all the above tool materials, best machining
results have been obtained with sintered alumina.
Alumina→Al2O3(90%)
Remaining 10% shared by Cr2O3,MgO and NiO.

CHARACTERISTICS OF CERAMIC TOOL
MATERIAL
1.Poor thermal conductivity
2.Being an oxide, it is stable upto melting point of
18000c
3.Its corrosion resistance property is outstanding .It
remains unaffected even with the strongest acids &
chemicals.
4.It is non magnetic & non conductive to electricity.

5. It possesses high compressive strength
(33,000 to 35,000 Kgf/mm2)
6. It possesses relatively superior hardness
values both at low & high temperatures.
7. The material cannot be wetted by molten
metal, therefore the problem of built up edge is
never encountered.

ADVANTAGES OF CERAMIC TOOLS
1.Higher cutting speed
2.Longer tool life
3.Reduced/No built up edges
4.Superior surface finish
5.Coolant is not needed
6.Lower co-efficient of friction
7.Greater machining flexibility

APPLICATION
Machining of cast iron with ceramics is more
effective than with the carbide tools.
It can economically machine metals such as heat
treated steels with RC65 hardness, stellites ,
tungsten, molybdenum, etc.,
Ceramics is not recommended for aluminium &
titanium alloys which shows greater affinity for
oxygen.

DIAMOND TOOL
Natural diamond
Synthetic diamond

 Natural diamonds are obtained from mines and
they are scarce. They fracture when subjected to
impact loads during machining.
 Synthetic (artificial) diamonds are used for
industrial applications as these are produced with
different and controlled mechanical properties.

CHARECTERISTICS OF DIAMOND
Diamond is the hardest known natural material.
Due to its high compressive & bending strength and
large value of modulus of elasticity, its deformation
is least during machining operation.
It also possesses high melting point and heat
conductivity properties.

PREPARATION OF SYNTHETIC
DIAMONDS
The diamond is prepared by sintering a mixture
of graphite & nickel under the conditions of ultra high
pressure & temperature. It is known as
polycrystalline diamond (PCD).
The desired properties are created by selecting
the appropriate temperature & pressure while
carrying out the sintering operation. Thus artificially
produced diamonds are superior to natural diamonds
and are cheaper too.

APPLICATION
PCD is used for machining abrasive
materials such as pre-sintered tungsten carbide,
ceramics, fibreglass, high silicon aluminium
alloys with silicon content upto 24%, rubber,
graphite ,non ferrous alloys & composite
materials produced from plastics, epoxy and
graphite.

Properties of PCD depend primarily on
degree of bonding & crystal size
 Degree of bonding has major influence on
resistance to abrasion wear.
 Diamond particle’s size affect the sharpness of
the cutting edge & the surface of the w/p.
 Diamond tools are used with positive rake
geometry in order to reduce the cutting forces on
the cutting edge.
 In some special cases, tools with negative rake
angle are also employed. Such materials are difficult
to machine & exotic materials.

 Diamond tools offers highest tool life.
 It provides mirror like surface finish.
 Diamond is a costly material and its
application is restricted to special cases when
other tool materials fails to cut.
 It is used for truing & dressing of grinding
wheels.

CUBIC BORON NITRIDE (CBN)
 The main application of CBN is to
machine the steel and nickel-based
alloys
 Next to diamond, cubic boron nitride (CBN) is the hardest
material presently available.

Cubic Boron Nitride
 It provides shock resistance, high wear
resistance and cutting-edge strength
 At elevated temperatures, it is chemically
inert to iron and nickel
 Its resistance to oxidation is high and suitable
for cutting hardened ferrous, stainless steel
and high-temperature alloys

Cubic Boron Nitride Tools
 Resist chipping and cracking
 Provide uniform hardness
 Abrasion resistance in all directions
 Can operate at higher cutting speeds, and take deeper
cuts

TYPES OF CBN TOOLS
Tipped inserts
 Available in most carbide insert shapes
 Usually most economical
 Only one cutting edge (can be reground)
Full-faced inserts
 Layer of CBN bonded to cemented-carbide
 Available as triangles, squares and rounds
Brazed-shank tools
 Made by machining pocket in proper-style of
tool shank and brazing CBN blank in place

ADVANTAGES OF CBN
High Material-Removal Rates
 Cutting speeds (120 to 800 m/min) and feed rates (0.12 to 0.25
mm) result in removal rates three time carbide tools with less
tool wear.
Cutting Hard, Tough Materials
 Capable of machining all ferrous materials with Rockwell C
hardness of 45 and above
 Also used to machine cobalt-base and nickel-base high
temperature alloys (Rockwell c 35)

APPLICATIONS OF CBN
Applications include,
 Grinding of hardened steel, Lead Screw, bores, splines,
threads.
 Parts of ball and roller bearing and hardened cast-iron slide
ways of machine tools.
 Machining chilled cast- iron, high-strength and heat-resistant
alloys.

Classification of Tool Materials

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