Tool Materials and Tool Wear

Jagadeesha TAssistant Professor

National Institute of TechnologyCalicut

TYPES OF TOOL MATERIALS

Stels

Carbides

Cermets

Ceramics

Superhard materials

TYPES OF TOOLS

Cutting toolsMachinigMillingShapingGrinding …..

Forming toolsForgingExtrusionWire drawing ….

APPLICATION OF CUTTING TOOL MATERIALS

WHY SURFACE ENGINEERING OF TOOLS

1.To protect tools from damage2.To give good surface finish3.To prolong life4.Better wear resistance

SURFACE DAMAGE OF TOOLS

1. Crater wear

2. Flank wear

3. Built up edge

4. Depth of cut notching

5. Nose wear

TOOL STEELS ~ 70 NUMBERS

High speed steels• Tungsten base•Molybdenum baseHot work steels•Chromium base•Tungsten base•Molybdenum baseCold work steels•Air hardening•High carbon high chromium•Oil hardeningShock resisting steelsLow alloy special purpose steelsMold steelsWater hardening steels

SURFACE TREATMENT OF TOOL STEELS

CarburisingNitridingBoridingToyota diffusion process – coatings of VC, NbC, Cr7C3

Steam oxidationElectroplating - Cd, Ni, CrCVDPVDIon implantationLaser treatment

LIFE IMPROVEMENT DUE TO STEAM OXIDATION

a) Machining tool

b) FORMING TOOL

LIFE IMPROVEMENT DUE TO PVD – CUTTING TOOLS

LIFE IMPROVEMENT DUE TO ION IMPLANTATION – FORMING TOOLS

CARBIDE TOOLS – 1.TYPES

WC – TiCWC- TiC – TaCWC – TiC – (TaNb)CWC – Co

2. PROPERTIES

CERMETS1. TYPES

TiC – Ni ~ Year 1930

TiC – Ni, Mo ~ Year 1960

Ti (CN) – Ni-Mo ~ Year 1970

(Ti, Mo) (C,N) ~ Later

Additions of Mo2C, TaC, NbC, ZrC,

HfC, WC, VC, Cr3C2, Al

2. PROPERTIES

CERAMICS1. TYPES

AluminaSilicon NitrideAlumina – Silicon Carbide whisker compositeSialon ~ Year 1980

2. PROPERTIES

SUPER HARD MATERIALS

TYPES & USES

Cubic Boron Nitride (CBN) – For cutting steels harder than 50 Rc

Polychristalline diamond (PCD) – for cutting non-ferrous alloys and composites and non-metals

CVD COATING ON CEMENTED CARBIDES

(a) TiC Coating

(b) TIC / TiCN /TiN Coating

TiC/Al2O3 Coating

TiC/Al2O3 / TiN Coating

Alternating layers of Al2O3 and TiN Coating

MULTILAYER CVD COATING ON COBALT SUBSTRATE

TiC/TiCN/TiN Coating

TiC/Al2O3/TiN Coating

MEDIUM TEMPERATURE CVD

Developed in 1980 and done at 700 – 900° C

TiN / Al2O3 Coating

PVD COATINGS ON CEMENTED CARBIDESDeveloped in 1980 and done at 500° C

TiN Coating

TiCN Coating

TiAlN Coating

COMBINATION OF CVD AND PVDOuter PVD layer – TiN, inner CVD layers TiN – TiCN on Co Substrate

PROPERTIES OF SURFACE COATINGS

Chemical stability

Hot hardness

Microstructure

Adhesion

Coating thickness

PROPERTIES OF CVD COATINGS

Free energy of formation against temperature

Hardness against temperature

CERMETS

CVD is not useful for cermets due to high temperatures involved (1000 °C). Intermetallic compounds of Nickel and Titanium are formed which are hard and brittle.PVD is useful

CERAMIC TOOLS

Out of total tool materials consumed in North America and Europe only 10% are ceramics. In Japan it is 35%.Silocon Nitride tools are usually coated with Alumina

FUTURE DEVELOPMENTS

CVD is well developed and the technology is well understood and usedMultilayer coatings are very usefulPVD is a tremendous improvementsIn PVD compressive residual stresses and fine grain formation occursPVD will definitely supersede CVD as it is ecofriendly. No gaseous effluents are producedPVD of metastable componds and superlattice coatings are to be expected in futurePVD can’t give crystalline Alumina coatings.

(a) CVD nd PVD

(b) Super hard materials

oDiamond coatings are expected to be available in futureoCBN coatings will definitely score over diamond coatingsoBut synthesis of CBN coatings will be a aojor challenge due to the issues of film stability, residual stress, coating thickness, adhesion and upscaling to industrial dimensions.oThe major advantage of CBN coatings over PCD coatings is that they can be used in high volume ferrous machining and cutting applications

REFERENCES

1.Yu . Geller, Tool Steels, Mir Publishers, Moscow, 1978, pp 556-595

2.ASM Handbook, Surface engineering, ASM International, Materials Park, Ohio, USA, 2002.