CUTTING TOOL MATERIALS

& CUTTING FLUIDS

Ankush SethiPresents

TOPICS :

Introduction Carbon and medium

alloy steelsHigh speed steelsCast-cobalt alloysCarbidesCoated toolsAlumna-based

ceramics

Cubic Boron NitrideSilicon Nitride based

ceramicsDiamond Whisker-reinforced

tool materials Cutting-Tool

ReconditioningCutting fluids

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

Carbon & medium alloy steels High speed steels Cast-cobalt alloysCarbidesCoated toolsAlumina-based ceramicsCubic boron nitrideSilicon-nitride-base ceramics DiamondWhisker-reinforced materials

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

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

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

Commonly known as stellite tools Composition ranges – 38% - 53 % cobalt

30%- 33% chromium10%-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 :

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

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 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

Individual cutting tool with severed cutting pointsClamped on tool shanks with locking mechanismsInserts also brazed to the tools Clamping is preferred method for securing an insertCarbide Inserts available in various shapes-Square,

Triangle, Diamond and roundStrength depends on the shape Inserts honed, chamfered or produced with negative

land to improve edge strength

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

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:

Purpose :Eliminating long chipsControlling chip flow during machiningReducing vibration & heat generatedSelection depends on feed and depth

of cutWork piece material,type of chip

produced during cutting

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

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

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

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 :

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

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 :

Use of Polycrystalline diamond as a coatingDifficult to adhere diamond film to substrateThin-film diamond coated inserts now commercially

availableThin films deposited on substrate with PVD & CVD

techniquesThick films obtained by growing large sheet of pure

diamondDiamond coated tools particularly effective in

machining non-ferrous and abrasive 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:

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 ) :

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)

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 :

Hardest known substance Low friction, high wear resistanceAbility to maintain sharp cutting edgeSingle crystal diamond of various carats used

for special applicationsMachining copper—front precision optical

mirrors for ( SDI)Diamond is brittle , tool shape & sharpened is

importantLow rake angle used for string cutting edge

Polycrystalline-Diamond ( PCD ) Tools:

Used for wire drawing of fine wiresSmall synthesis crystal fused by high pressure and

temperatureBonded to a carbide substrate Diamond tools can be used fir any speed Suitable for light un-interrupted finishing cutsTo avoid tool fracture single crystal diamond is to be

re-sharpened as it becomes dullAlso used as an abrasive in grinding and polishing

operations

Whisker –reinforced & Nanocrystalline tool materials

New tool materials with enhanced properties :

High fracture toughness Resistance to thermal shock Cutting –edge strengthHot hardness

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

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

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