Modelling and experimental analysis of high speed air jets used in metal cutting as a cooling techni

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Modelling and experimental analysis of high speed
air jets used in metal cutting as a cooling
technique
Trinity College Dublin

• Authors Andrea Bareggi (presenter)
• Andrew Torrance
• Garret ODonnell

Department of Mechanical and Manufacturing
Engineering The University of Dublin Trinity
College
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Trinity College Dublin
Air Jet cooling why?

• environmental friendly machining
• usually cheaper than traditional coolants
• traditional cooling is often ineffective for HPC
• operators health

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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)

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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

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A new aspect the mechanical effect

• analytical model
• finite element model
• experimental tests

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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 Jaegers friction slider model
  (secondary zone)

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Heat transfer by impinging jet on isothermal plate
length of plate, l 1 mm area of plate, A 0.2
mm² temperature of plate, Tw500 C fluid
free-stream velocity, uinf 500 m/s fluid
free-stream temperature, Tinf 4C fluid
viscosity, µ 1.83 e-5 kg/m s fluid density, ?
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
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Mechanical effect bending moment on a
cantilevered beam
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Analytical model results
At higher feed (t) the difference due to
mechanical effect became more important
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Finite element modelling

• No cooling, natural convection, h20 W/m²/K
• Air jet, overhead position, h2000 W/m²/K
• Air jet, interface position, h2000 W/m²/K
• 4 and 7 bar of pressure

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FEM results

• more realistic cutting temperature
• analog prediction for air jet cooling made by
  analytical model
• difference between interface and overhead
  positioning

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Experimental test
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Test results
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718C
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Test results
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622C
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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)

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Conclusions
Thank you for the attention Questions?
HPC 2008