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MECHANICS OF METAL CUTTING
Topics to be covered ,[object Object],[object Object],[object Object],[object Object],[object Object]
Elements of Metal Cutting
Heat Generation Zones (Dependent on sharpness of tool) (Dependent on   ) (Dependent on   10% 30% 60%
Tool Terminology Side relief  angle Side cutting  edge angle (SCEA) Clearance or end  relief angle Back  Rake (BR),+ Side Rake  (SR), + End Cutting edge angle (ECEA) Nose  Radius Turning Cutting  edge Facing Cutting  edge
Cutting Geometry
 
Material Removal Rate
Cutting Models ORTHOGONAL GEOMETRY OBLIQUE GEOMETRY Tool workpiece Tool workpiece
Assumptions (Orthogonal Cutting Model) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Orthogonal Cutting
‘ Turning’ Forces For Orthogonal Model End view section 'A'-'A' Note: For the 2D Orthogonal Mechanistic  Model we will ignore the radial component F t 'A' 'A' c F
‘ Facing’ Forces For Orthogonal Model End view Note: For the 2D Orthogonal Mechanistic  Model we will ignore the Longitudinal component
'Turning' Terminology ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Standard Terms Beware , for turning: In the generalized orthogonal model depth of cut (to) is f (the feed), and width of cut (w) is d (the depth of cut)
Orthogonal Cutting Model   (Simple 2D mechanistic model) Mechanism: Chips produced by the shearing process along the shear plane  t 0  + Rake  Angle Chip Workpiece Clearance Angle Shear Angle depth of cut Chip thickness Tool Velocity V tool t c
tool Cutting Ratio (or chip thicknes ratio)    t c t o  A B Chip Workpiece
Experimental Determination of Cutting Ratio   Shear angle    may be obtained  either from photo-micrographs  or assume volume continuity  (no chip density change): i.e. Measure length of chips (easier than thickness) w t L 0 0 0 w c L c c t
Shear Plane Length  and Angle   or make an assumption, such as    adjusts to minimize  cutting force: (Merchant)  t c t o  A B Chip tool Workpiece
Velocities (2D Orthogonal  Model) Velocity Diagram (Chip relative  to workpiece) V  = Chip Velocity (Chip relative to tool) Tool Workpiece Chip V = Cutting Velocity  (Tool relative to  workpiece) Shear Velocity c     V s V V s V c
Cutting Forces ( 2D Orthogonal Cutting) Free Body Diagram Generally we know: Tool geometry & type Workpiece material and we wish to know: F  = Cutting Force F  =  Thrust Force F  =  Friction Force N  =  Normal Force F  =  Shear Force F  =  Force Normal  to Shear c t s n Tool Workpiece Chip Dynamometer R R R R F c F t  s F F n N F
Force Circle Diagram (Merchants Circle) R F t F c Tool F N      F s    F n
Results from Force Circle Diagram (Merchant's Circle)
Forces on the Cutting Tool and the workpiece ,[object Object],[object Object],[object Object],[object Object],[object Object]
Stresses  On the Shear plane: On the tool rake face:
Power ,[object Object],[object Object],[object Object]
Material Removal Rate (MRR)
Specific Cutting Energy (or Unit Power) Energy required to remove a unit volume of material (often  quoted as a function of workpiece material, tool and process:
Specific Cutting Energy Decomposition 1. Shear Energy/unit volume (Us) (required for deformation in shear zone) 2. Friction Energy/unit volume (Uf) (expended as chip slides along rake face) 3. Chip curl energy/unit volume (Uc) (expended in curling the chip) 4. Kinetic Energy/unit volume (Um) (required to accelerate chip)
Specific Cutting Energy Relationship to Shear strength of Material SHEAR ENERGY / UNIT VOLUME FRICTION ENERGY / UNIT VOLUME  APPROXIMATE TOTAL SPECIFIC CUTTING ENERGY
Relation between Pressure and Cutting velocity
Effect of Rake angle on Cutting Force
Average Unit Horsepower Values of Energy per unit volume
Typical Orthogonal Model Violations ,[object Object],[object Object],[object Object],[object Object],[object Object]

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Mechanics of metal cutting

  • 2.
  • 4. Heat Generation Zones (Dependent on sharpness of tool) (Dependent on  ) (Dependent on  10% 30% 60%
  • 5. Tool Terminology Side relief angle Side cutting edge angle (SCEA) Clearance or end relief angle Back Rake (BR),+ Side Rake (SR), + End Cutting edge angle (ECEA) Nose Radius Turning Cutting edge Facing Cutting edge
  • 7.  
  • 9. Cutting Models ORTHOGONAL GEOMETRY OBLIQUE GEOMETRY Tool workpiece Tool workpiece
  • 10.
  • 12. ‘ Turning’ Forces For Orthogonal Model End view section 'A'-'A' Note: For the 2D Orthogonal Mechanistic Model we will ignore the radial component F t 'A' 'A' c F
  • 13. ‘ Facing’ Forces For Orthogonal Model End view Note: For the 2D Orthogonal Mechanistic Model we will ignore the Longitudinal component
  • 14.
  • 15. Orthogonal Cutting Model (Simple 2D mechanistic model) Mechanism: Chips produced by the shearing process along the shear plane  t 0  + Rake Angle Chip Workpiece Clearance Angle Shear Angle depth of cut Chip thickness Tool Velocity V tool t c
  • 16. tool Cutting Ratio (or chip thicknes ratio)  t c t o  A B Chip Workpiece
  • 17. Experimental Determination of Cutting Ratio Shear angle  may be obtained either from photo-micrographs or assume volume continuity (no chip density change): i.e. Measure length of chips (easier than thickness) w t L 0 0 0 w c L c c t
  • 18. Shear Plane Length and Angle  or make an assumption, such as  adjusts to minimize cutting force: (Merchant)  t c t o  A B Chip tool Workpiece
  • 19. Velocities (2D Orthogonal Model) Velocity Diagram (Chip relative to workpiece) V = Chip Velocity (Chip relative to tool) Tool Workpiece Chip V = Cutting Velocity (Tool relative to workpiece) Shear Velocity c     V s V V s V c
  • 20. Cutting Forces ( 2D Orthogonal Cutting) Free Body Diagram Generally we know: Tool geometry & type Workpiece material and we wish to know: F = Cutting Force F = Thrust Force F = Friction Force N = Normal Force F = Shear Force F = Force Normal to Shear c t s n Tool Workpiece Chip Dynamometer R R R R F c F t  s F F n N F
  • 21. Force Circle Diagram (Merchants Circle) R F t F c Tool F N      F s    F n
  • 22. Results from Force Circle Diagram (Merchant's Circle)
  • 23.
  • 24. Stresses On the Shear plane: On the tool rake face:
  • 25.
  • 27. Specific Cutting Energy (or Unit Power) Energy required to remove a unit volume of material (often quoted as a function of workpiece material, tool and process:
  • 28. Specific Cutting Energy Decomposition 1. Shear Energy/unit volume (Us) (required for deformation in shear zone) 2. Friction Energy/unit volume (Uf) (expended as chip slides along rake face) 3. Chip curl energy/unit volume (Uc) (expended in curling the chip) 4. Kinetic Energy/unit volume (Um) (required to accelerate chip)
  • 29. Specific Cutting Energy Relationship to Shear strength of Material SHEAR ENERGY / UNIT VOLUME FRICTION ENERGY / UNIT VOLUME APPROXIMATE TOTAL SPECIFIC CUTTING ENERGY
  • 30. Relation between Pressure and Cutting velocity
  • 31. Effect of Rake angle on Cutting Force
  • 32. Average Unit Horsepower Values of Energy per unit volume
  • 33.