Cutting Tool Material/Fluid Flashcards
Cutting tool characteristics
- able to maintain hardness, strength and wear resistance at elevated temperatures
- toughness
- thermal shock resistance
- wear resistance
- chemical resistance
Tool material category
High spd steel
Cast cobalt alloy
Carbides
Ceramics
Cubic boron nitrides
Diamond
High speed steel (material)
Pros - good wear resistance, inexpensive, high toughness and fracture resistance
Best for
- high + rake angle
- interrupted cut
- machine subj to vibration and chatter
How to improve:
- coating
-surface treatment
- steam treatment at elevated temp
Cast-cobalt alloys (material)
Pros - high hardness, good wear resistance, can maintain hardness at high temp
Cons - sensitive to impact
Can be stellite tool - simple shapes use for deep continuous roughing cut at high feeds (2x HSS)
Carbides (material)
Pros - hardness over wide range if temp, high elastic modulus and thermal conductivity, low thermal expansion.
Tungsten carbide - tungsten + cobalt. Cobalt increase = strength, hardness and wear resistance decrease = toughness increase
Titanium carbide - higher wear resistance but less tough.
Inserts
Cutting tool with several cutting points, square have 8. Standardized so interchangeable
Insert properties
Shape affect strength, bigger angle = higher strenghts.
Produced with negative land
Carbides weakness and solution
Bad at light feed (concentrated force, chipping) and low cutting spd (cold welding).
Use cutting fluid
Coated tool
Pros - low friction and high resistance to cracks and wear. Allow high cutting spd. Reduce production cost and operations
Coated tool have 10x life span
Coated tools material characteristics
Insert by:
Chemical or physical vapor deposition
Characteristics:
1. High hardness at elevated temp
2. Chemical stability/inert to workpiece material
3. Good bonding to prevent flaking
4. Little or no porosity
Example of coating
Titanium nitride
Titanium carbide
Ceramic
Diamond
Multiphase
Titanium nitride (coating)
Pros - low friction, hardness, resistance to high temp, good adhesion. Low flank wear. Best at high cutting spd
Cons - bad at low spd, chip adhesion
Titanium carbide (coating)
High flank wear resistance
Ceramic coating
Pros- Chemically inert, low thermal conduct, resist high temp,resist flank and crater wear.
Cons - weak bond to substrates
Diamond coating
Best in non-ferrous and abrasive material.
Cubic Boron Nitride (material)
Brittle (no vibration)
Must be in dry conditions
Silicon nitride based ceramic (material)
Toughness, hot hardness and good thermal shock resistance. Bad for steel due to chemical affinity to iron.
Best for cast iron and nikel based superalloy
Diamond (material)
Low friction, high wear resistance, maintain sharp edge, good surface finish, high accuracy. Low rack angle at hugh spd. Best for uninterrupted finishing cut. Bad with carbon steel or titanium.
Cutting fluids
Reduce friction and wear, cool cutting zone, reduce forces and energy consumption, flush awy chips, prevent corrosion.
Type of Cutting fluids
Oils, emulsion, semisynthetic, synthetic
