2Cutting FluidsEssential in metal-cutting operations to reduce heat and frictionCenturies ago, water used on grindstones100 years ago, tallow used (did not cool)Lard oils came later but turned rancidEarly 20th century saw soap added to waterSoluble oils came in 1936Chemical cutting fluids introduced in 1944
3Economic Advantages to Using Cutting Fluids Reduction of tool costsReduce tool wear, tools last longerIncreased speed of productionReduce heat and friction so higher cutting speedsReduction of labor costsTools last longer and require less regrinding, less downtime, reducing cost per partReduction of power costsFriction reduced so less power required by machining
4Heat Generated During Machining Heat finds its way into one of three placesWorkpiece, tool and chipsAct as disposable heat sinkToo much, cutting edge will break down rapidly, reducing tool lifeToo much, work will expand
5Heat Dissipation Ideally most heat taken off in chips Indicated by change in chip color as heat causes chips to oxidizeCutting fluids assist taking away heatCan dissipate at least 50% of heat created during machining
6Characteristics of a Good Cutting Fluid Good cooling capacityGood lubricating qualitiesResistance to rancidityRelatively low viscosityStability (long life)Rust resistanceNontoxicTransparentNonflammable
7Types of Cutting Fluids Most commonly used cutting fluidsEither aqueous based solutions or cutting oilsFall into three categoriesCutting oilsEmulsifiable oilsChemical (synthetic) cutting fluids
8Cutting Oils Two classifications ActiveInactiveTerms relate to oil's chemical activity or ability to react with metal surfaceElevated temperaturesImprove cutting actionProtect surface
9Active Cutting OilsThose that will darken copper strip immersed for 3 hours at temperature of 212ºFDark or transparentBetter for heavy-duty jobsThree categoriesSulfurized mineral oilsSulfochlorinated mineral oilsSulfochlorinated fatty oil blends
10Inactive Cutting OilsOils will not darken copper strip immersed in them for 3 hours at 212ºFContained sulfur is naturalTermed inactive because sulfur so firmly attached to oil – very little releasedFour general categoriesStraight mineral oils, fatty oils, fatty and mineral oil blends, sulfurized fatty-mineral oil blend
11Emulsifiable (Water Soluble) Oils Mineral oils containing soaplike material that makes them soluble in water and causes them to adhere to workpieceEmulsifiers break oil into minute particles and keep them separated in waterSupplied in concentrated form (1-5 /100 water)Good cooling and lubricating qualitiesUsed at high cutting speeds, low cutting pressures
12Chemical Cutting Fluids Also called synthetic fluidsIntroduced about 1945Stable, preformed emulsionsContain very little oil and mix easily with waterExtreme-pressure (EP) lubricants addedReact with freshly machined metal under heat and pressure of a cut to form solid lubricantReduce heat of friction and heat caused by plastic deformation of metal
13Advantages of Synthetic Fluids Good rust controlResistance to rancidity for long periods of timeReduction of amount of heat generated during cuttingExcellent cooling qualities
14Longer durability than cutting or soluble oils Nonflammable - nonsmokingNontoxic??????Easy separation from work and chipsQuick settling of grit and fine chips so they are not recirculated in cooling systemNo clogging of machine cooling system due to detergent action of fluidCan leave a residue on parts and tools
15CautionChemical cutting fluids widely accepted and generally used on ferrous metals. They are not recommended for use on alloys of magnesium, zinc, cadmium, or lead. They can mar machine's appearance and dissolve paint on the surface.
16Functions of a Cutting Fluid Prime functionsProvide coolingProvide lubricationOther functionsProlong cutting-tool lifeProvide rust controlResist rancidity
17Functions of a Cutting Fluid: Cooling Heat has definite bearing on cutting-tool wearSmall reduction will greatly extend tool lifeTwo sources of heat during cutting actionPlastic deformation of metalOccurs immediately ahead of cutting toolAccounts for 2/3 to 3/4 of heatFriction from chip sliding along cutting-tool face
18Functions of a Cutting Fluid: Cooling Water most effective for reducing heat by will promote oxidation (rust)Decrease the temperature at the chip-tool interface by 50 degrees F, and it will increase tool life by up to 5 times.
19Functions of a Cutting Fluid: Lubrication Reduces friction between chip and tool faceShear plane becomes shorterArea where plastic deformation occurs correspondingly smallerExtreme-pressure lubricants reduce amount of heat-producing frictionEP chemicals of synthetic fluids combine chemically with sheared metal of chip to form solid compounds (allow chip to slide)
21Cutting fluid reduces friction and produces a shorter shear plane.
22Cutting-Tool LifeHeat and friction prime causes of cutting-tool breakdownReduce temperature by as little as 50ºF, life of cutting tool increases fivefoldBuilt-up edgePieces of metal weld themselves to tool faceBecomes large and flat along tool face, effective rake angle of cutting tool decreased
23Built-up Edge Built-up edge keeps breaking off and re-forming Result is poor surface finish, excessive flankwear, and cratering of tool face
24Cutting Fluid's Effect on Cutting Tool Action Lowers heat created by plastic deformation of metalFriction at chip-tool interface decreasedLess power is required for machining because of reduced frictionPrevents built-up edge from formingSurface finish of work greatly improved
25Rust Control Water best and most economical coolant Causes parts to rustRust is oxidized ironChemical cutting fluids contain rust inhibitorsPolar filmPassivating film
26Rancidity ControlRancidity caused by bacteria and other microscopic organisms, growing and eventually causing bad odors to formMost cutting fluids contain bactericides that control growth of bacteria and make fluids more resistant to rancidityRancidity ControlWhen lard oil was the only cutting fluid used, after a few days, it would start to spoil and give off an offensive odor. This rancidity is caused by bacteria and other microscopic organisms, growing and multiplying almost anywhere and eventually causing bad odors to form. Today, any cutting fluid that has an offensive smell is termed rancid.
27Application of Cutting Fluids Cutting-tool life and machining operations influenced by way cutting fluid appliedCopious stream under low pressure so work and tool well coveredInside diameter of supply nozzle ¾ width of cutting toolApplied to where chip being formed
28Refrigerated Air System Another way to cool chip-tool interfaceEffective, inexpensive and readily availableUsed where dry machining is necessaryUses compressed air that enters vortex generation chamberCooled 100ºF below incoming airAir directed to interface and blow chips away