Surface Grinding with Minimum Quantity Lubrication

Transcription

1 Surface Grinding with Minimum Quantity Lubrication Director of Studies: Dr. M.N. Morgan (LJMU) Supervisors: Dr. A. Batako (LJMU) Prof. D.Sc. B. Kruszyński (TUL) Author: M.Sc. Łukasz Barczak Advanced 1 Manufacturing Technology Research Laboratory February 2009

2 Content Introduction Minimum Quantity Lubrication Experimental Work Conclusions Future Work Key Contributions Key Advances. 2

3 Introduction Turning (a) Grinding (b) Cutting speed m/s 5-90 m/s Rake angle +20 to to -60 Clearance angle 6 to 10 0 to 60 The grinding is a very challenging process in terms of thermal demands. This is mainly due to the negative rake angles of grains that require high normal force to perform efficient cutting resulting in 3 generation of high temperatures.

4 Introduction Fluid delivery is recognised as a critical factor due to its influence on the grinding performance. There are a wide range of fluid delivery methods but the most common is conventional flood cooling. 4 With this delivery method large amounts of fluid (oil and oil based emulsions) are used. During the process the fluid loses its properties to finally becomes a waste.

5 Introduction Laboratory equipment 5% Others 9% Cleaning 4% Electricity 3% Cooling 17% Staff 9% Tools 8% Machine tool 39% Service 11% Staff 14% Depreciation and waste disposal 54% General costs 27% 5 Manufacturing costs for crankshaft at a German car builder

6 Introduction FLUID REDUCTION Dry Machining machining without any fluid to lubricate or cool workpiece and tool. 6 Near Dry Machining machining with a very small (minimal or micro) amount of lubricant or coolant.

7 Minimum Quantity Lubrication MQL what is this? MQL consists of supply of a continuous and precise quantity of lubricant mixed with air to the cutting region. 7

8 Minimum Quantity Lubrication Advantages of MQL Coolant Usage Typical (not optimised) conventional flood machining may use 5000ml per minute. Minimum Quantity Lubrication means usage on a level of 30-50ml per hour vs ml/h

9 Residual Stress [MPa] Minimum Quantity Lubrication Residual Stresses in Cylindrical Grinding air=30 lub=40 air=40 lub=40 air=30 lub=60 air=40 lub=60 Dry Cooling 8.4l/min Heat Treat Al 2 O 3 CBN Heat Treat Comparative results of residual stress at a depth of approx. 10mm below the surface after 90 cycles using Al 2 O 3 and CBN grinding wheels (v air =m/s, v lub =ml/h, v s =30m/s, v f =1mm/min and a = 100mm) MQL produces the highest compressive residual stresses thus improves material resistance to fatigue and exerts a strong impact on the service life of components.

10 Minimum Quantity Lubrication Advantages of MQL - Environment Benefits for natural environment: Fluids biodegradability No coolants containing dioxins Reduced waste disposal Total loss system Lower power consumption Pollutants Amounts Reduced 10

11 Minimum Quantity Lubrication Advantages of MQL - Machining Further potential advantages of MQL: Lower thermal shock for workpiece and tool Improved fatigue properties Less expensive coolant supply and filtration system required Improved anticorrosion abilities Lower storage and preparation costs Ready to use fluid 11

12 Minimum Quantity Lubrication 12 Potential Disadvantages of MQL Potential Disadvantages of MQL: No flushing action - chips/debris are not removed from the workpiece, tool and work area Wheel susceptible to loading if no efficient cleaning system is employed MQL not appropriate for dressing process Potential thermal damage if tight regime is not maintained

13 Minimum Quantity Lubrication Issues Needing Addressing The following issues that have not been verified to date: Optimal MQL delivery flow rates/velocity for given regime of operation and wheel/workpiece combination (given quality criteria) Distribution of flow through the cutting zone Nature of flow prior to entry region 13

14 Experimental Work Project Aim The purpose of this research was to study the effects of MQL, compared to dry and conventional machining and therefore to acquire and evaluate the understanding of Minimum Quantity Lubrication phenomena. 14

15 Experimental Work 15 Apparatus CNC Jones & Shipman Dominator 624 Easy Steidle Lubrimat L50 MQL system Arboga Darenth high pressure coolant system National Instruments NI6250 DAQ Kistler 9257A dynamometer Adapted from T-Type, a J-Type single pole thermocouple Research purpose designed nozzle

16 Experimental Work The Workplace 16

17 Experimental Work Experimental Equipment MQL Nozzle 17

18 Experimental Work Experimental Equipment General Purpose MQL Nozzle 18

19 Experimental Work Process Characterisation The variables: v s 25 and 45 m/s v w 6.5 and 15 m/min 19 a 5 and 15 mm materials: hardened (EN31, M2) and mild steel (EN8) wheel type: aluminium oxide dressing: coarse and fine cut type: up-grinding fluid delivery state: WET, DRY, MQL.

20 Experimental Work Acquired Data The measurables: P - power, F t and F n tangential and normal force, q grinding arc temperature, a e real depth of cut (post process), R a surface roughness. 20

21 Experimental Work Taguchi Array A B C D E F G Level Parameter 1 2 AWheel speed 25m/s 45m/s B Workpiece speed 6.5m/min 15m/min C Dressing course fine D Depth of cut 5mm 15mm E Materials soft hard F A x D - - G B x D - -

22 Experimental Work Fluid Consumption - Comparison 0.1 l vs. 810 l 22

23 Ft' [N/mm 3 /s] Ft' [N/mm 3 /s] Ft' [N/mm 3 /s] Ft' [N/mm 3 /s] Experimental Work Results Specific Tangential Force TRIAL a e [mm] TRIAL a e [mm] TRIAL a e [mm] v s =25m/s, a=15mm, v w =6.5m/min, coarse dressing, EN31 v s =45m/s, a=5mm, v w =15m/min, coarse dressing, EN8 v s =45m/s, a=15mm, v w =6.5m/min, fine dressing, EN TRIAL a e [mm] v s =45m/s, a=15mm, v w =15m/min, coarse dressing, EN31 Conventional grinding Dry grinding MQL grinding

24 Ft/Fn Ft/Fn Ft/Fn Ft/Fn Experimental Work Results Friction Coefficient TRIAL TRIAL TRIAL Q w ' [mm 3 /mm/s] Q w ' [mm 3 /mm/s] Q w ' [mm 3 /mm/s] v s =25m/s, a=15mm, v w =6.5m/min, coarse dressing, EN31 v s =45m/s, a=5mm, v w =15m/min, coarse dressing, EN8 v s =45m/s, a=15mm, v w =6.5m/min, fine dressing, EN TRIAL Q w ' [mm 3 /mm/s] v s =45m/s, a=15mm, v w =15m/min, coarse dressing, EN31 Conventional grinding Dry grinding MQL grinding

25 T [C] T [C] T [C] T [C] Experimental Work Results Temperature 290 TRIAL 3 40 TRIAL TRIAL Q w ' [mm 3 /mm/s] Q w ' [mm 3 /mm/s] Q w ' [mm 3 /mm/s] v s =25m/s, a=15mm, v w =6.5m/min, coarse dressing, EN31 v s =45m/s, a=5mm, v w =15m/min, coarse dressing, EN8 v s =45m/s, a=15mm, v w =6.5m/min, fine dressing, EN8 TRIAL Conventional grinding Dry grinding MQL grinding Q w ' [mm 3 /mm/s] 25 v s =45m/s, a=15mm, v w =15m/min, coarse dressing, EN31

26 Ra [mm] Ra [mm] Ra [mm] Ra [mm] Experimental Work TRIAL 3 Results Surface Roughness Q w ' [mm 3 /mm/s] v s =25m/s, a=15mm, v w =6.5m/min, coarse dressing, EN TRIAL Q w ' [mm 3 /mm/s] v s =45m/s, a=5mm, v w =15m/min, coarse dressing, EN TRIAL Q w ' [mm 3 /mm/s] v s =45m/s, a=15mm, v w =6.5m/min, fine dressing, EN TRIAL Conventional grinding Dry grinding MQL grinding 26 Q w ' [mm 3 /mm/s] v s =45m/s, a=15mm, v w =15m/min, coarse dressing, EN31

27 Conclusions MQL can be successfully employed either as a finishing process or shallow cut grinding however it requires using a wheel with high porosity and perhaps larger grains (more work required) MQL can successfully compete with conventional cooling in some specific cases in this regime however it is not known how MQL will behave under Creep-feed or HEDG conditions 27

28 Conclusions 28 Cooler grinding wheel usage should improve further grinding with MQL and provide higher depths of cut MQL phenomena mainly seems to be due to decrease of the friction coefficient and reduced hydrodynamic film There seems to be no cooling effect with MQL due to convection or evaporation as suggested in some studies (there may be some very small amount due to the latent heat of evaporation)

29 Future Work Investigation into different types of wheels with different grades, hardness and porosity Further development of nozzle together with the system for grinding with MQL Cleaning system for the grinding wheel Using cooled agents for providing some cooling action 29

30 Key Contributions To This Field 30 This work provides an advanced understanding of MQL in surface grinding A new MQL nozzle was designed for surface grinding Applicable regime for MQL in grinding was established It was shown that MQL produces similar results to conventional grinding and under some conditions outperforms conventional practice

31 Key Contributions To This Field Grinding temperatures at contact arc were measured first time in MQL and compared against existing thermal models Results for tangential and normal force were obtained in terms of real depth of cut New limitations to MQL were defined: Dressing and high wheel speed with hard steel 31

32 Key Advances Successful application of MQL in surface grinding Advanced understanding of the process under given regime Determination of MQL applicability 32

33 Any questions??? Thank you for your attention