Lecture #33 part 2 ERDM. Issues Associated with the Use of Cutting Fluids in Machining Operations

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Karen Nicholson
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1 Lecture #33 part 2 ERDM Issues Associated with the Use of Cutting Fluids in Machining Operations

2 Modeling Process Waste Streams Inputs - Material - Machining parameters - Energy Catalysts -Fluids -Additives Process Equipment -Cutting tools -Machines tools Product Process Waste Streams -Chips -Cutting Fluids -Aerosols -Energy

3 Cutting Fluid Applications

4 Background Cutting Fluids Oil Based Chemical Straight Oils Emulsions Synthetics Semi-synthetic Additives: Chlorine, Sulfur, Phosphorus, Biocides, Odorants

5 Cutting fluids: what are they?! Straight Oil Lubricity, Oil Oil Rust Inhibitors Emulsifiers! Soluble Oil! Semi-Synthetic! Synthetic Cooling Water Other

6 Cutting Fluid Usage in the U.S. U.S. Utilization of Cutting Fluid (100,000,000 gallons annually)

7 Traditional View

8 Traditional View of Cutting Fluids Essential in metal cutting operations, especially high volume machining Primary functions: Cooling and Lubrication Secondary functions: Chip Flushing, Corrosion Inhibition, Workpiece Cleaning, & Slideway Lubrication Cutting fluids are the economical solution to reduce the effect of heat on product quality

9 Cutting Fluid Effect on Forces Air Lubricated CCl 4 Lubricated From Shaw M., 1958, The Action of Cutting Fluids at Low Speeds, Wear, pp

10 Coefficient of Friction Chemical reactions have been identified, e.g., 2 Al + 6 CCl 4 2 AlCl C 2 Cl 6 From Shaw M., 1984, Metal Cutting Principles, Oxford University Press.

11 Cooling Effect of Cutting Fluids: Temperatures & Distortion

12 Temperature History

13 Dimensional Errors Boring of aluminum cylinders Radial, tangential and axial forces cause deformation Heat produced in cutting zone causes thermal deformation of work, tool, fixtures, & machine

14 Surface Error: difference between desired & actual machined surface Bore Surface Error Error (micron) Dry in Wet Axial Position (cm)

15 Heat Transfer in Peripheral Milling Peripheral Milling (End View) Heat Transfer Model for Milling has been established

16 Predicted vs. Measured Temperature for Dry and Wet Milling (a) Dry, 500rpm, /t, 0.2 RD, 1.2 AD (b) Wet, 500rpm, /t, 0.2 RD, 1.2 AD

17 Cutting Fluid Lubrication Drilling Experiments

18 Drilling Experiments Chip clogging in the absence of fluids the fluid appears to provide lubrication within the drill flute Experiments also showed that " Fluid flow rates can be reduced by 2 orders of magnitude " Tool coatings show promise as fluid replacement

19 Tapping Experiments

20 Economic Effects of Wet Machining Machining Costs per Piece for Wet Machining 6% 0% 0% 2% 9% 1% 8% 2% 1% 1% 23% 45% Pow er Costs Machine Costs Coolant Sys. Costs Mist Collection Costs Chip Handling Sys. Costs Labor Cost for Machining Tool Costs Cost of Defective Parts Coolant Purchase Costs Disposal Costs Labor for Fluid Chg. Cost of Dow ntime Environ. & Health Costs 2% Fluid Costs: 15-20%

21 Cutting fluids: what s the problem? S. Skerlos U of M! Expensive! The Environment! Health

22 Health Effects NIOSH:-1.2 million are exposed to cutting fluids [Hands et al., 1996] Aerosols from PM10 to PM2.5 and PM1.0 (EPA) Airborne particulate from 5 mg/cu. m to 0.5 and 0.1 mg/m 3 (UAW and OSHA) Bacteria / fungi in cutting fluid produce toxins [Thorne et al., 1996] Mist collectors are sometimes ineffective [Leith, 1996]

23 Environmental Effects Spent cutting fluid disposal waste water POTW changes Chemical reactivity Spills and Leaks (e.g., from chips) Recyclability Effect on BOD level in ground water and lakes

24 Mist in Machining Vapor Condensation Vaporization Mist nozzle coolant stream Atomization generated heat tool workpiece

25 Mist Concentration vs. Time

26 Vaporization vs. Atomization Mist Produced via Cutting Mist Produced via Atomization 30 Speed = 500 sfm Feed =.006 ipr Doc =.020 in Mass Conc., mg/m Mass Conc., mg/m Speed = 500 sfm Time, sec Time, sec Speed = 1250 sfm Feed =.015 ipr Doc =.10 in Mass Conc., mg/m Mass Conc., mg/m Speed = 1250 sfm Time, sec Time, sec

27 Drop Size Distribution for Submicron Particles

28 Cutting Fluid System Modeling PLANT CUTTING FLUID SYSTEM Additives (Cau stic, O il A dd ition s,...) System Dynamics M easurem ents (ph, O il C on c.,...) Manual Fee dback

29 Large Fluid Systems Currently -- challenge to manage large fluid systems -- maintain oil conc., ph, etc. -- complex dynamic behavior. Dynamics for several large-scale systems have been characterized. Data reveals management of such systems difficult -- poor performance. Work at MTU has led to the development of optimal maintenance strategies: better control of oil conc., ph, etc. AND reduced caustic & oil additions.

30 Cutting Fluids are a Concern: Alternative Approaches Dry Machining " Acceptable in some cases - Reduced Tool Life - Drilling / tapping chip clogging loss of lube - Thermal distortion - Airborne Dust - Chip management challenges MQL (Minimum Quantity Lubrication) " Near-dry machining " Micro- or milli- lubrication

31 Economic Comparison of Wet vs. Dry Machining Important factors include Tool Life, Coolant Life, Product Quality, Environmental and Health Liabilities Unit Cost Comparison of Wet vs. Dry Machining Mass Conc.,mg/m 3 Mass Conc.,mg/m Time, sec Wet Turning (Mist) s=381 m/min f=.152 mm/rev d=.508 mm s=152 m/min f=.38 mm/rev d=2.54 mm Mass Conc.,mg/m 3 Mass Conc.,mg/m Time, sec Dry Turning (Dust) s=381 m/min f=.152 mm/rev d=.508 mm s= 152 m/min f=.38 mm/rev d=2.54 mm Total Cost ($/part) $22 $21 $20 $19 $18 $17 $16 Environ. & Health Liabilities?? $0.73 $0.60 $1.15 $1.14 $0.24 $0.05 $0.42 $0.30 $0.04 $0.04 $18.35 $18.35 $20.55 $20.89 Dry Wet Environ. & Health Liabilities?? $0.04 Environ. & Health Costs Cost of Downtime Fluid Purchase, Disposal, & Change Costs Cost of Defective Parts Tool Cost Labor Cost Fixed Equip. Cost Power Cost Mat'l Cost Time, sec Time, sec

l/min Milli-application " Flow rates on the order of

32 Definitions Flood application " Flow rates > 1 gal/min Stream/jet application " Flow rates on the order of l/min Milli-application " Flow rates on the order of ml/min Micro-application " Flow rates on the order of ml/hour

33 The Technology Pressurized Tank Throughthe-tool Positive Displacement Venturi Courtesy: UNIST & Horkos

34 TechSolve Workpiece: AISI 4340 Steel Water soluble oil Drilling: ½ inch coated HSS, 135 split point, 55 sfpm, ipr Milling: 1 inch carbide tool, 400 sfpm, ipr, 0.5 inch axial depth, 0.06 inch radial depth " Flood: 1.7 gallon / minute " MQL: gallon / minute Conclusions " in drilling, no difference in tool life, 20% lower thrust force with MQL " in milling, 30~40% longer tool life and 20~30% lower resultant force with MQL

35 NCMS & Marubeni/Horkos No. Operation Description Measurement Process Capability Index MQL wo Vacuum MQL w Vacuum Flood 1 Mill datum surface Surface profile Drill 11 mm hole Diameter Drill 11 mm hole Location Drill 13 mm hole Diameter Drill 10.5 mm hole Diameter Drill 10.5 mm hole Location Drill 6.5 mm hole Diameter Mill mounting surface Surface profile Mill width surface Face distance Average Economics: Near-dry Chip Management: Wet Switching Difficult

36 Tool Carbide parting tool with MQL channel

37 Michigan Tech Cylinder Boring Flow Rate = 15mL/min Speed = 600 RPM Feed =.015 in/rev Flow Rate = 2L/min Speed = 600 RPM Feed =.015 in/rev

38 Fluid Application Costs $ per Workpiece Machine Cost Cutting Fluid Cost Chip Handling Cost Ventilation Cost Tooling Cost Total Cost $ per Workpiece Machine Cost Cutting Fluid Cost Chip Handling Cost Ventilation Cost Tooling Cost Total Cost MQL Cost Breakdown Cost = $0.59 / unit Flood Cost Breakdown Cost = $0.65 / unit

39 Summary Cutting Fluids " For some processes they provide a benefit can the benefits be delivered by another method? " Negatives: Cost, Environment, & Health Alternatives " Dry Machining - Possible in some situations (open-faced machining operations) - Concerns: tool life, dust, lubricity, thermal distortions, chip management " MQL - A promising alternative to Traditional Fluid Applications and Dry Machining - Less environmental impact, less cost, process concerns addressed - Concerns: Chip management, air quality, lack of data (new technology)

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