METAL CUTTING: Chip Formation

METAL CUTTING: Chip Formation

1. Geometric definition

   • t0= depth of cut (d) = un-deformed chip thickness
   • tc= chip thickness
   • alpha = rake angle
     • angle between vertical and cutting tool
     • positive angle
       • Sharper cutting edge
         • typically better finish
       • Reduce shear plane size
       • Lower strain than negative rake
       • Lower cutting force
       • Lower power consumption
     • Negative angle
       • Stronger edge
         • longer tool life
       • Increase shear plane size
       • Tool can be turned over
         • more economical
       • Require higher cutting force
       • Typically larger cutting depth
   • phi = shear angle
     • angle between horizontal (datum at chip formation point) and primary shear zone
   • zeta = clearance angle
     • angle between tool and cut surface

2. The resultant of 2D forces on a cutting tool must be collinear to balance the forces

3. CUTTING TYPES

   • Depends on whether the stress and deformation in cutting occur in a plane (2D) or in the space (3D), we consider two principle types of cutting
     • ORTHOGONAL CUTTING
       • the cutting edge is straight and is set in a position that is perpendicular to the direction of primary motion
         • Deals with stresses and strains that act in that plane
     • OBLIQUE CUTTING
       • The cutting edge is set at an angle
         • tool cutting edge inclination = gamma
         • 3D stress and strain conditions
       • i = inclination angle
         • different i angle produces different chips

4. CUTTING POINTS

   • SINGLE-POINT CUTTING
     • cutting tool has only one major cutting edge
       • turning
       • shaping
       • boring
   • MULTI-POINT CUTTING
     • cutting tool has more than one major cutting edge
       • drilling
       • milling
       • broaching
       • reaming

5. CUTTING CONDITIONS

   • cutting velocity, V:
     • the traveling velocity of the tool relative to the work-piece
       • measured in m/s or m/min
   • depth of cut, d:
     • the axial projection of the length of the active cutting tool edge
       • measured in mm
       • in orthogonal cutting it is equal to the actual width of cut, bD
   • Feed, f:
     • the relative movement of the tool in order to process the entire surface of the workpiece
       • in orthogonal cutting it is equal to the thickness of cut hD
       • Measured in mm tr-1 in turning
       • measured in mm/min in milling and drilling

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