Department of Manufacturing Engineering Cutting Fluids Prof. Dr. S. Engin KILIÇ Atılım University Department of Manufacturing Engineering 4/27/2017 MFGE 307 - Chapter 07

Cutting fluids-definition Liquids and gases which are used in metal cutting to improve the cutting performance in comparison to dry cutting are called Cutting Fluids 4/27/2017 MFGE 307 - Chapter 07

Advantages of using cutting fluids Increase in tool life Improvement of surface finish Reduction in cutting forces and power consumption Washing chips free from cutting region Reduction in thermal distortion of workpiece Protection of finished surface from corrosion 4/27/2017 MFGE 307 - Chapter 07

The Action of cutting fluids MFGE 307 - Chapter 07 4/27/2017

The Action of cutting fluids Cutting fluids affect cutting process through their two basic actions: 1. Lubrication (reduction in tool friction) . forms boundary lubrication and a layer of soft chemical compound with chip and workpiece at very low cutting speeds a) built-up edge formation is reduced. b) Reduction in coefficient of friction, hence increase in shear angle and reduction in cutting forces. c) Improved surface finish. d) Increase in tool life. 4/27/2017 MFGE 307 - Chapter 07

The Action of cutting fluids 2. Cooling . reduces temperature in cutting area by removing heat a) Tool wear is reduced and tool life is increased; tool material retains its hardness at reduced temperature, hence . it gains more resistance to abrasion. . diffusion wear rate is reduced . due to reduced temperature, however, shear flow stress may increase, resulting reduced tool life. b) Reduced thermal expansion and distortion of workpiece (especially in grinding) 4/27/2017 MFGE 307 - Lecture 07

The Action of cutting fluids 3. Swarf removal An important subsidiary function of a cutting fluid is to wash away swarf. . Third-body abrasion is avoided, or at least reduced. . Surface finish is improved. MFGE 307 - Chapter 07 4/27/2017

Basic types of cutting fluids Straight or neat oils: blended from two types of oils: Usually undiluted mineral oils: paraffin and other petroleum oils Often include fats (fattyoils), vegetable oils, esters together with high-pressure compounds based on chlorine, sulphur, phoshorus (high pressure oils) fatty oils: organic oils of animal or vegetable origin - Mineral oils . cheaper . more stable - Fatty oils . have good lubricating properties . promote good finishes . less stable than mineral oils and may decompose if used for long periods 4/27/2017 MFGE 307 - Chapter 07

Basic types of cutting fluids - Sulphurised oil-oils with chemically combined sulphur . prevents pressure welding of chip to tool (B.U.E.) b) Soluble oils: Cutting fluids which are mainly required to carry away heat and swarf are generally based on water Oil with emulsifiers to allow oil to disperse in water, to inhibit rusting, to a certain extent for lubricating effect 2-15% in water (e.g. 2-2.5% for grinding, 5% for turning and milling) Least expensive and widely used Synthetic fluids: Oil-free solutions formulated from alkaline inorganic and organic compounds with corrosion inhibitors 3-10% in water Provide best cooling performance Semi-synthetic fluids: Combination of synthetic and soluble oil fluids 4/27/2017 MFGE 307 - Chapter 07

Basic types of cutting fluids Straight cutting oils have wide application for two major reasons: a) Employed in automatic machines because water-base coolants may find their way into headstock, contaminate lubricating oil and cause serious deterioration of mechanism. b) Promote a superior surface finish in gear cutting, honing, threading and broaching. Paraffin is sometimes used on aluminum alloys instead of soluble oils because of its wetting property. Greases are more convenient than oils in tapping and reaming operations MFGE 307 - Chapter 07 4/27/2017

Cost of using cutting fluids Cost of applying cutting fluids: Reported to constitute 20% of total manufacturing cost whereas cutting tool cost is around 7.5% in European automotive industry Potential benefits: in reducing quantities: dry cutting, near dry cutting in extending useful life of cutting fluids: use of synthetic oils central recycling systems Quantities of different types of cutting fluids (U.S. Manufacturing industry) 4/27/2017 MFGE 307 - Chapter 07

Cost of using cutting fluids 4/27/2017 MFGE 307 - Chapter 07

General characteristics of water-miscible cutting fluids After Holmes 4/27/2017 MFGE 307 - Chapter 07

General characteristics of water-miscible cutting fluids 4/27/2017 ME 303 - Lecture 07

Effects of Cutting fluids Material cut: alloy steel shear strength = 690 MPa , effective rake 15o Type of Cutting Fluid Tool Life(min) Power (kW) Dry 12 1.36 Sulphurised oil 27 1.3 Sulphurised and chlorinated oil 33 1.35 4/27/2017 ME 303 - Lecture 07

Effects of Cutting fluids Condition Coefficient of Friction Heat from friction (kj/kg of metal removed) Heat from deformation (kj/kg of metal removed) Dry 1.0 102.3 222.7 Cutting fluid 0.9 93.9 210.4 % decrease 10 19.1 12.8 4/27/2017 MFGE 307 - Lecture 07

Guide to the Selection of Cutting Fluids 4/27/2017 MFGE 307 - Chapter 07

Cutting Fluids: Pre-conditions for Applicability It must not be toxic or offensive to the operator; it should not be a fire hazard; it must not be harmful to the lubricating system of the machine tool; it should not corrode or discolor the work material; it should give some corrosion protection to the freshly cut metal surface; it should be as cheap as possible. 4/27/2017 MFGE 307 - Chapter 07

Application of Cutting Fluids Cutting fluid should be effectively delivered to the cutting zone to perform its function Lubricating fluids must be applied in such a way to form a film on the sliding surfaces Coolants must gain access to the cutting edge: flooding cutting area with fluid continuous application of cutting fluids for intermittent cutting to avoid micro crack formation in tool material Fluid application methods: Manual Flood Jet Mist Through the tool 4/27/2017 MFGE 307 - Chapter 07

Cutting Fluid Applications Different methods of cooling in milling: (a) compressed air (jet), (b) oil mist, (c) internal cooling (jet), (d) external cooling (flood) 4/27/2017 MFGE 307 - Chapter 07

Flood Application Fluid delivered from a low-pressure nozzle directed appropriately to flood tool, workpiece and cutting zone Continuous flow to cutting zone, helps remove chips from cuting zone Its effectiveness depends on the geometry of the cutting process performed Fluid recollected, filtered and pumped back to the delivery nozzle 4/27/2017 MFGE 307 - Chapter 07

Flood Lubrication in Gear Hobbing Flood Application Flood Lubrication in Gear Hobbing

Jet Application High-pressure fluid is directed through a nozzle as high speed jet at cutting zone Very effective in removing chips from cutting zone, efficient for high speed applications including grinding Fluid recollected, filtered and pumped back to the delivery nozzle 4/27/2017 MFGE 307 - Chapter 07

High pressure coolant (HPC) supply system called Jetbreak Jet Application Coolant supply at a high pressure up to 1000 bars (i.e., 200 bars is the maximum requirement for titanium machining) shortens the tool/chip contact length and provides improved chip control. The Jetbreak system, giving a specifically directed nozzle, can be coupled with the appropriate tooling system; hence, coolant supplied through the cone of the coupling into the nozzle jet is directed towards the cutting edge to form a hydraulic wedge between the chip and the rake face of the tool insert. Most applications are on single spindle turning machines such as vertical turning centres and turn- milling centres. High pressure coolant (HPC) supply system called Jetbreak 4/27/2017 MFGE 307 - Chapter 07

High pressure coolant (HPC) supply system called Hyperson Jet Application It provides a high velocity of 122 m/s and a high pressure flow of coolant at 110 bar to the interface between the tool and chip. System consists of a pumping unit, the piping necessary to transport the fluid, and a tool-holder through which the coolant can pass and which can focus the high pressure flow of coolant on the interface. High pressure coolant (HPC) supply system called Hyperson 4/27/2017 MFGE 307 - Chapter 07

Mist Application Cutting fluid as an air-carried mist; a mixing system for oil-air pulvarization needed Usually applicable when cutting speeds are high and uncut chip thickness is relatively small (i.e. end milling) Good ventillation required due to health hazard Used in minimum quantity lubrication applications Minimized lubrication system (mist application) Small lubrication particles suplied by micro-dosage pump through the capillary tube are mixed with air and directed to the cutting tool through the machine spindle

Mist Application Various methods of inducing oil/air mix 4/27/2017 (a) from the outside into the bore (b) through the cutting tool (c) oil and air flow entry and exit simultaneously (d) from a reservoir built into the tool 4/27/2017 MFGE 307 - Chapter 07

Cutting fluid requirements for different machining operations Cutting Fluids Cutting fluid requirements for different machining operations 4/27/2017 MFGE 307 - Chapter 07