Chapter 22 Flashcards
Characteristics of cutting tool
Maintaining strength/hardness/wear at elevated temp
Toughness
Wear resistance
Thermal shock resistance
Chemical stability
Tool material
High speed steel
Cast cobalt alloy
Carbide
Ceramics
Cubic Boron Nitride
Diamond
General characteristic of HSS
High toughness, resistance to fracture, good for interrupted cut.
Low hot hardness, limited wear resistance
Cast Cobalt Alloys
High hardness, good resistance, can maintain hardness at elevated temp.
Sensitive to impact force
Carbides
- hardness over wide range temp, high elastic modulus and thermal conductivity, low thermal expansion
Cannot use at low speed
Insert edge properties
To improve edge strength = honed, chamfered, negative land
Advantage of coated tool
Lower friction, higher resistance to crack and wear, can be used with high cutting speed, longer life.
How to apply coating material
Chemical or physical vapor deposition
General coat characteristic
High hardness at +temp
chemical stability/inert to workpiece
compatible/good bonding to substrate
Little/no porosity
Example of coating
Ti nitride or carbide. Ceramic, multiple phase, diamond, miscellaneous, nanolayer, composite
Alumina-Based ceramic
High abrasion resistance and hot hardness. More stable- less like to BUE
Best in high speed, uninterrupted cutting
Lack toughness
Cubic Boron Nitride
Brittle, may crack due to thermal shock
Performed dry
Silicon Nitride Based ceramic
Toughness, hot hardness and good thermal shock.
Not suitable for steel/chemical affinity to iron
Diamond
Low friction, high wear resistance, strong cutting edge. Best for high sf and dimension accuracy. High spd
Strong chemical affinity to carbon steel or titanium
Cutting fluids
Reduce friction/wear
Cool
Force energy consumption
Flush awy chips
Protect surface from corrosion
