Cutting Fluids
1. Essential in metal-cutting operations to reduce heat and friction
2. Centuries ago, water used on grindstones
3. 100 years ago, tallow used (did not cool)
4. Lard oils came later but turned rancid
5. Early 20th century saw soap added to water
6. Soluble oils came in 1936
7. Chemical cutting fluids introduced in 1944
Economic Advantages to Using Cutting Fluids
1. Reduction of tool costs
- Reduce tool wear, tools last longer
2. Increased speed of production
- Reduce heat and friction so higher cutting speeds
3. Reduction of labor costs
- Tools last longer and require less regrinding, less downtime, reducing cost per part
4. Reduction of power costs
- Friction reduced so less power required by machining
Heat Generated During Machining
Heat find its way into one of three places
Workpiece, tool, chips
Heat Dissipation
1. Ideally most heat taken off in chips
2. Indicated by change in chip color as heat causes chips to oxidize
3. Cutting fluids assist taking away heat
- Can dissipate at least 50% of heat created during machining
Characteristics of a Good Cutting Fluid
1. Good cooling capacity
2. Good lubricating qualities
3. Resistance to rancidity
4. Relatively low viscosity
5. Stability (long life)
6. Rust resistance
7. Nontoxic
8. Transparent
9. Nonflammable
Types of Cutting Fluids
1. Most commonly used cutting fluids
- Either aqueous based solutions or cutting oils
2. Fall into three categories
- Cutting oils
- Emulsifiable oils
- Chemical (synthetic) cutting fluids
Oil Categories
1. Sulfurized mineral oils
- Contain .5% to .8% sulfur
- Light-colored and transparent
- Stains copper and alloys
2. Sulfochlorinated mineral oils
- 3% sulfur and 1% chlorine
- Prevent excessive built-up edges from forming
3. Sulfochlorinated fatty oil blends
- Contain more sulfur than other types
Inactive Cutting Oils
1. Oils will not darken copper strip immersed in them for 3 hours at 212ºF
2. Contained sulfur is natural
- Termed inactive because sulfur so firmly attached to oil – very little released
3. Four general categories
- Straight mineral oils, fatty oils, fatty and mineral oil blends, sulfurized fatty-mineral oil blend
Emulsifiable (Soluble) Oils
1. Mineral oils containing soaplike material that makes them soluble in water and causes them to adhere to workpiece
2. Emulsifiers break oil into minute particles and keep them separated in water
- Supplied in concentrated form (1-5 /100 water)
3. Good cooling and lubricating qualities
4. Used at high cutting speeds, low cutting pressures
Functions of a Cutting Fluid
1. Prime functions
- Provide cooling
- Provide lubrication
2. Other functions
- Prolong cutting-tool life
- Provide rust control
- Resist rancidity
Heat has definite bearing on cutting-tool wear
Small reduction will greatly extend tool life
Two sources of heat during cutting action
Plastic deformation of metal
Occurs immediately ahead of cutting tool
Accounts for 2/3 to 3/4 of heat
Friction from chip sliding along cutting-tool face
Water most effective for reducing heat (rust)
Functions of a Cutting Fluid: Lubrication
Reduces friction between chip and tool face
Shear plane becomes shorter
Area where plastic deformation occurs correspondingly smaller
Extreme-pressure lubricants reduce amount of heat-producing friction
EP chemicals of synthetic fluids combine chemically with sheared metal of chip to form solid compounds (allow chip to slide)
Cutting-Tool Life
1. Heat and friction prime causes of cutting-tool breakdown
2. Reduce temperature by as little as 50ºF, life of cutting tool increases fivefold
3. Built-up edge
- Pieces of metal weld themselves to tool face
- Becomes large and flat along tool face, effective rake angle of cutting tool decreased
Application of Cutting Fluids
1. Cutting-tool life and machining operations influenced by way cutting fluid applied
2. Copious stream under low pressure so work and tool well covered
- Inside diameter of supply nozzle ¾ width of cutting tool
- Applied to where chip being formed.
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