CUTTING TOOL MATERIALS
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CUTTING TOOL MATERIALS & CUTTING FLUIDS. Chapter – 21. Introduction Carbon and medium alloy steels High speed steels Cast-cobalt alloys Carbides Coated tools Alumna-based ceramics. Cubic Boron Nitride Silicon Nitride based ceramics Diamond Whisker-reinforced tool materials

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Chapter – 21

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Chapter 21

CUTTING TOOL MATERIALS

& CUTTING FLUIDS

Chapter – 21


Topics

Introduction

Carbon and medium alloy steels

High speed steels

Cast-cobalt alloys

Carbides

Coated tools

Alumna-based ceramics

Cubic Boron Nitride

Silicon Nitride based ceramics

Diamond

Whisker-reinforced tool materials

Cutting-Tool Reconditioning

Cutting fluids

TOPICS :


Introduction

Introduction:

Characteristics of cutting tool :

  • Hardness (Elevated temperatures)

  • Toughness (Impact forces on tool in interrupted operations)

  • Wear resistance (tool life to be considered)

  • Chemical stability or inertness (to avoid adverse reactions)


Cutting tool materials

Cutting tool materials

  • Carbon & medium alloy steels

  • High speed steels

  • Cast-cobalt alloys

  • Carbides

  • Coated tools

  • Alumina-based ceramics

  • Cubic boron nitride

  • Silicon-nitride-base ceramics

  • Diamond

  • Whisker-reinforced materials


Carbon and medium alloy steels

Carbon and Medium alloy steels :

  • Oldest of tool materials

  • Used for drills taps,broaches ,reamers

  • Inexpensive ,easily shaped ,sharpened

  • No sufficient hardness and wear resistance

  • Limited to low cutting speed operation

    High speed steels (HSS)

  • Hardened to various depths

  • Good wear resistance

  • Relatively

  • Suitable for high positive rake angle tools


Chapter 21

Two basic types of HSS

  • Molybdenum ( M-series)

  • Tungsten ( T-series)

    M-series - Contains 10% molybdenum, chromium, vanadium, tungsten, cobalt

  • Higher, abrasion resistance

  • H.S.S. are majorly made of M-series 

    T-series - 12 % - 18 % tungsten, chromium, vanadium & cobalt

  • undergoes less distortion during heat treating


Chapter 21

  • H.S.S.available in wrought ,cast & sintered (Powder metallurgy)

  • Coated for better performance

  • Subjected to surface treatments such as case-hardening for improved hardness and wear resistance or steam treatment at elevated temperatures

  • High speed steels account for largest tonnage


Cast cobalt alloys

Cast-Cobalt alloys

  • Commonly known as stellite tools

  • Composition ranges – 38% - 53 % cobalt

    30%- 33% chromium

    10%-20%tungsten

  • Good wear resistance ( higher hardness)

  • Less tough than high-speed steels and sensitive to impact forces

  • Less suitable than high-speed steels for interrupted cutting operations

  • Continuous roughing cuts – relatively high g=feeds & speeds

  • Finishing cuts are at lower feed and depth of cut


Carbides

Carbides :

3-groups of materials

  • Alloy steels

  • High speed steels

  • Cast alloys

  • These carbides are also known as cemented or sintered carbides

  • High elastic modulus,thermal conductivity

  • Low thermal expansion

    2-groups of carbides used for machining operations

  • tungsten carbide

  • titanium carbide


Tungsten carbide

Tungsten Carbide

  • Composite material consisting of tungsten-carbide particles bonded together

  • Alternate name is cemented carbides

  • Manufactured with powder metallurgy techniques

  • Particles 1-5 Mum in size are pressed & sintered to desired shape

  • Amount of cobalt present affects properties of carbide tools

  • As cobalt content increases – strength hardness & wear resistance increases


Titanium carbide

Titanium carbide

  • Titanium carbide has higher wear resistance than tungsten carbide

  • Nickel-Molybdenum alloy as matrix – Tic suitable for machining hard materials

  • Steels & cast irons

  • Speeds higher than those for tungsten carbide


Inserts

Inserts


Inserts1

Inserts

  • Individual cutting tool with severed cutting points

  • Clamped on tool shanks with locking mechanisms

  • Inserts also brazed to the tools

  • Clamping is preferred method for securing an insert

  • Carbide Inserts available in various shapes-Square, Triangle, Diamond and round

  • Strength depends on the shape

  • Inserts honed, chamfered or produced with negative land to improve edge strength


Insert attachment

Insert Attachment

Fig : Methods of attaching inserts to toolholders : (a) Clamping and (b) Wing lockpins. (c) Examples of inserts attached to toolholders with threadless lockpins, which are secured with side screws.


Edge strength

Edge Strength

Fig : Relative edge strength and tendency for chipping and breaking of inserts with various shapes. Strength refers to the cutting edge shown by the included angles.

Fig : edge preparation of inserts to improve edge strength.


Chip breakers

Chip breakers:

Purpose :

  • Eliminating long chips

  • Controlling chip flow during machining

  • Reducing vibration & heat generated

  • Selection depends on feed and depth of cut

  • Work piece material,type of chip produced during cutting


Coated tools

Coated tools :

  • High strength and toughness but generally abrasive and chemically reactive with tool materials

    Unique Properties :

  • Lower Friction

  • High resistance to cracks and wear

  • High Cutting speeds and low time & costs

  • Longer tool life


Coating materials

Coating materials

  • Titanium nitride (TiN)

  • Titanium carbide (Tic)

  • Titanium Carbonitride (TicN)

  • Aluminum oxide (Al2O3)thickness range – 2-15 µm (80-600Mu.in)

    Techniques used :

  • Chemical –vapor deposition (CVD)

    Plasma assisted CVD

  • Physical-vapor deposition(PVD)

  • Medium –temperature chemical- vapor deposition(MTCVD)


Properties for group of materials

Properties for Group of Materials

Fig : Ranges of properties for various groups of tool materials.


Cutting tool characteristics for coating

Cutting tool Characteristics for coating :

  • High hardness

  • Chemical stability

  • Low thermal conductivity

  • Good bonding

  • Little or no Porosity

    Titanium nitride (TiN) coating :

  • Low friction coefficients

  • High hardness

  • Resistance to high temperatures

  • Good adhesion to substrate

  • High life of high speed-steel tools

    Titanium carbide (TiC) coating:

  • Titanium carbide coatings on tungsten-carbide inserts have high flank wear resistance.


Ceramics

Ceramics :

  • Low thermal conductivity ,resistance ,high temperature

  • Resistance to flank wear and crater wear

  • Ceramics are suitable materials for tools

  • Al2O3 (most commonly used)

    Multi Phase Coatings :

  • First layer –Should bond well with substrate

  • Outer layer – Resist wear and have low thermal conductivity

  • Intermediate layer – Bond well & compatible with both layers

  • Coatings of alternating multipurpose layers are also formed.


Multiphase coatings

Multiphase Coatings

Fig : Multiphase coatings on a tungsten-carbide substrate. Three alternating layers of aluminum oxide are separated by very thin layers of titanium nitride. Inserts with as many as thirteen layers of coatings have been made. Coating thick nesses are typically in the range of 2 to 10 µm.


Diamond coated tools

Diamond Coated tools :

  • Use of Polycrystalline diamond as a coating

  • Difficult to adhere diamond film to substrate

  • Thin-film diamond coated inserts now commercially available

  • Thin films deposited on substrate with PVD & CVD techniques

  • Thick films obtained by growing large sheet of pure diamond

  • Diamond coated tools particularly effective in machining non-ferrous and abrasive materials


New coating materials

New Coating materials :

  • Titanium carbo nitride (TiCN)

  • Titanium Aluminum Nitride(TiAlN)

  • Chromium Based coatings

  • Chromium carbide

  • Zirconium Nitride (ZrN)

  • Hafnium nitride (HfN)

  • Recent developments gives nano coating & composite coating

    Ion Implementation :

  • Ions placed into the surface of cutting tool

  • No change in the dimensions of tool

  • Nitrogen-ion Implanted carbide tools used for alloy steels & stainless steels

  • Xeon – ion implantation of tools as under development


Alumina based ceramics

Alumina-Based ceramics:

  • Cold-Pressed Into insert shapes under high pressure and sintered at high temperature

  • High Abrasion resistance and hot hardness

  • Chemically stable than high speed steels & carbides

  • So less tendency to adhere to metals

  • Good surface finish obtained in cutting cast iron and steels

  • Negative rake-angle preferred to avoid chipping due to poor tensile strength

    Cermets, Black or Hot- Pressed :

  • 70% aluminum oxide & 30 % titanium carbide

  • cermets(ceramics & metal)

  • Cermets contain molybdenum carbide, niobium carbide and tantalum carbide.


Cubic boron nitride cbn

Cubic boron Nitride ( CBN ) :

  • Made by bonding ( 0.5-1.0 mm ( 0.02-0.04-in)

  • Layer of poly crystalline cubic boron nitride to a carbide substrate by sintering under pressure

  • While carbide provides shock resistance CBN layer provides high resistance and cutting edge strength

  • Cubic boron nitride tools are made in small sizes without substrate

    Fig : (a) Construction of a polycrystalline cubic boron nitride or a diamond layer on a tungsten-carbide insert. (b) Inserts with polycrystalline cubic boron nitride tips (top row) and solid polycrystalline CBN inserts (bottom row).


Silicon nitride based ceramics sin

Silicon-Nitride based ceramics (SiN)

  • They consists various addition of Aluminum Oxide ythrium oxide, titanium carbide

  • SiN have toughness, hot hardened & good thermal – shock resistance

  • SiN base material is Silicon

  • High thermal & shock resistance

  • Recommended for machining cast iron and nickel based super alloys at intermediate cutting speeds


Diamond

Diamond :

  • Hardest known substance

  • Low friction, high wear resistance

  • Ability to maintain sharp cutting edge

  • Single crystal diamond of various carats used for special applications

  • Machining copper—front precision optical mirrors for ( SDI)

  • Diamond is brittle , tool shape & sharpened is important

  • Low rake angle used for string cutting edge


Polycrystalline diamond pcd tools

Polycrystalline-Diamond ( PCD ) Tools:

  • Used for wire drawing of fine wires

  • Small synthesis crystal fused by high pressure and temperature

  • Bonded to a carbide substrate 

  • Diamond tools can be used fir any speed

  • Suitable for light un-interrupted finishing cuts

  • To avoid tool fracture single crystal diamond is to be re-sharpened as it becomes dull

  • Also used as an abrasive in grinding and polishing operations


Whisker reinforced nanocrystalline tool materials

Whisker –reinforced & Nanocrystalline tool materials

New tool materials with enhanced properties :

  • High fracture toughness

  • Resistance to thermal shock

  • Cutting –edge strength

  • Hot hardness


Whiskers used as reinforcing fibers

Whiskers used as reinforcing fibers :

  • Examples: Silicon-nitride base tools reinforced with silicon-carbide( Sic)

  • Aluminum oxide based tools reinforced with silicon-carbide with ferrous metals makes Sic-reinforced tools

  • Progress in nanomaterial has lead to the development of cutting tools

  • Made of fine grained structures as (micro grain) carbides


Cutting tool reconditioning

Cutting-Tool Reconditioning

  • When tools get worned, they are reconditioned for further use

  • Reconditioning also involves recoating used tools with titanium nitride

    Cutting Fluids: (Lubricants + Coolants)

    Used in machining as well as abrasive machining processes

  • Reduces friction wear

  • Reduce forces and energy consumption

  • Cools the cutting zone

  • Wash away the chips

  • Protect Machined surfaces from environmental corrosion


Application of cutting fluids

Application of Cutting Fluids

Fig : Schematic illustration of proper methods of applying cutting fluids in various machining operations: (a)turning, (b)milling, (c)thread grinding, and (d)drilling


The end

THE END


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