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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