Authors Andrea Bareggi (presenter) Andrew Torrance Garret O’Donnell

1. Trinity College Dublin Modelling and experimental analysis of high speed air jets used in metal cutting as a cooling technique Authors Andrea Bareggi (presenter) Andrew Torrance Garret O’Donnell Department of Mechanical and Manufacturing Engineering The University of Dublin Trinity College HPC 2008

2. Trinity College Dublin Air Jet cooling: why? • environmental friendly machining • usually cheaper than traditional coolants • traditional cooling is often ineffective for HPC • operator’s health HPC 2008

3. Trinity College Dublin A new aspect: the mechanical effect • analytical model • Dry cutting modelling (specific cutting energy, primary zone by Shaw, secondary zone by Jaeger) • Heat transfer by impinging jet (isothermal plate) • Mechanical effect (bending moment on a cantilevered beam) HPC 2008

4. Trinity College Dublin A new aspect: the mechanical effect • analytical model • finite element model • Dry machining • Heat transfer only • Heat transfer and mechanical effect • Interface and overhead nozzle positioning • 4 and 7 bar of pressure HPC 2008

5. Trinity College Dublin A new aspect: the mechanical effect • analytical model • finite element model • experimental tests HPC 2008

6. Trinity College Dublin Dry cutting modelling • expression of normal cutting pressure Kn and shear stress Kf as a function of dynamometric data • expression of specific cutting energy as a function of Kn and Kf • temperature calculated by Shaw analysis (primary zone) and by Jaeger’s friction slider model (secondary zone) HPC 2008

7. Trinity College Dublin Heat transfer by impinging jet on isothermal plate length of plate, l = 1 mm area of plate, A = 0.2 mm² temperature of plate, Tw=500 °C fluid free-stream velocity, uinf = 500 m/s fluid free-stream temperature, Tinf = 4°C fluid viscosity, μ = 1.83 e-5 kg/m s fluid density, ρ = 1.22 kg/m³ fluid specific heat, Cp = 1.005 kJ/kg K fluid conductivity, k = 0.025 W/m K Reynolds Number, Re = 37900 Prandtl Number, Pr = 0.683 Nusselt Number, Nu = 114 Heat Transfer Coefficient, h = 2850 W/m² K HPC 2008

8. Trinity College Dublin Mechanical effect – bending moment on a cantilevered beam HPC 2008

9. Trinity College Dublin Analytical model results At higher feed (t) the difference due to mechanical effect became more important HPC 2008

10. Trinity College Dublin overhead Nozzle direction interface Nozzle direction Finite element modelling • No cooling, natural convection, h=20 W/m²/K • Air jet, overhead position, h=2000 W/m²/K • Air jet, interface position, h=2000 W/m²/K • 4 and 7 bar of pressure HPC 2008

11. Trinity College Dublin FEM results • more realistic cutting temperature • analog prediction for air jet cooling made by analytical model • difference between interface and overhead positioning HPC 2008

12. Trinity College Dublin Experimental test HPC 2008

13. Trinity College Dublin Test results HPC 2008 718°C

14. Trinity College Dublin Test results HPC 2008 622°C

15. Trinity College Dublin Conclusions • valid alternative to MQL • environmental friendly and cost effective • maximum temperature in chip-tool interface reduced by 15-20% • chip removal ability • wide range of application (medical, composites…) HPC 2008

16. Trinity College Dublin Conclusions Thank you for the attention Questions? HPC 2008