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TYPES OF TOOL MATERIALS

TYPES OF TOOL MATERIALS

Following are main type of cutting tool materials

1. Carbon + medium alloy steel2. High speed steel (HSS)3. Cast cobalt alloys4. Carbides5. Coated tools6. Ceramics7. Cubic boron nitride8. Silicon nitride9. Diamond1) Carbon+ Medium alloy SteelsIt is the oldest of tool material. The carbon content is 0.6~1.5% with small quantities of silicon,

Chromium, manganese, and vanadium to refine grain size. Maximum hardness is about HRC 62.

This material has low wear resistance and low hot hardness. The use of these materials now is very

Limited.

2) High Speed Steel (HSS)They were invented in early 1900s.they are now very highly used alloy steel and can be

hardened to various depths. They have good wear resistance, High toughness, Good for positive

rake angle tools. The nave two basic types of HSS

Tungsten: (T Series) Molybdenum: ( M Series)

T Series

12 18 % Tungsten Chromium, vanadium etc.

M Series

10% Molybdenum Chromium, Vanadium, Tungsten, Cobalt Better abrasion resistance Less expensive Less distortion 95% of HSS used is M series.

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3) Cast Cobalt (Stellate tool)They have following composition

y 38 53% Cobalty 30 33% Chromiumy 10 20 % TungstenThey have following properties

y High hardness (58-64 HRC)y Good wear resistancey High temperature hardnessy No Toughness

o not suitable for intermittent cuttingy Good for deep boring, continuous turning ( better than HSS)4) CARBIDES

a. High temp Hardnessb. Low thermal expansionc. High modulus of elasticity

TungstenCarbide (W-C)

Used for cutting nonferrous abrasive and metal + cast iron Tungsten Carbide particles are bonded in Cobalt matrix

Coated Carbide

Made of WC Co TiC - TiN 3 4 coatings of Al2O3 Particles sized 1- 5 mm are pressed and sintered into desired shapes (% of Co may vary) W-C is also compounded, sometimes with Titanium and Tantalum to improve hot hardness and

crater wear

Titanium Carbide

Ti-C has Ni-Mb matrix Good wear resistance and poor toughness Good for machining steel Higher speed than W-C Stiffness of the machine is important Low feed, low speed and chatter can cause failure5) COATED TOOLS

The coating is 5-10 mm in thickness

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Titanium Nitride

Low friction High hardness Resistance to high temperature Improves life of HSS, carbides6) CERAMICS High temperature resistance Chemical inertness Wear resistance Al203 Fine grained , high purity Al203 cold pressed at high temperature and sintered at high

temperature (white)

70% Al20

330 % T-C

Very high temperature hardness High abrasion resistance More chemical stability Less tendency for adhesion so less BUE Good surface finish while machining steel and C I Poor toughness for intermittent cutting

7) CUBIC BORON NITRIDE Next to diamond, the hardest material 0.5-1mm polycrystalline cubic boron nitride High wear resistance But brittle Used for machining hardened steel and high temperature alloys ( Ni for instance)8) SILICON NITRIDE Used for super alloys9) DIAMOND Low friction and high wear resistance Good cutting edge Single crystal diamond are used to machine copper to a high surface finish Because they are brittle rake angle has to be low

Polycrystalline diamond tool

(Compacted) synthesized crystals Fused at high temperatures and high pressures

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TABLE:Following table shows the characteristics and limitations of different cutting materials