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.