METAL CUTTING: Milling

METAL CUTTING: Milling

1. CNC Milling Machine

   • Most versatile

2. 5 axis profile milling machine

   • 3 linear and 2 angular movements

3. CONVENTIONAL MILLING

   • Cutter rotates in opposite direction to table feed
   • Backlash between teh lead screw and the nut of the machine table can be eliminated
   • Chip thickness increases gradually thus smoother cutter operation
   • Chips are forced onto the part and may result lower surface finish
   • parts are pulled up so better fixture required

4. CLIMB MILLING

   • Cutter rotates in same direction as table feed
   • Simpler fixture and more stable.
   • Backlash must be eliminated. Maximum thickness of chips are at the beginning of cut
   • Can only be used on machines equipped with a backlash eliminator or on a CNC milling machine
   • Will require less power in feeding the table
     • Better surface finish
   • Easy to hold parts
   • Higher impact force at tool tips
   • Easier chip removal
   • Higher tool life
   • Lower cutting power

5. MILLING PARAMETERS

   • Revolution speed
     • Rotating speed of the cutter
     • N - rpm
   • Cutting speed
     • Peripheral speed of the cutter at the cutting point
     • V - mm/min
   • Diameter
     • Size of the cutter outer diameter
     • D - mm
   • V = PI()*D*N
   • F = fr/N*z
   • t = (l+lc)/fr
   • MRR = w*d*fr
   • Feed per tooth
     • Distance that workpiece travels per tooth of the cutter
     • F - mm/tooth
   • Width & depth of cut
     • The thickness of the layer being removed from the workpiece
     • w & d - mm
   • Number of teeth
     • Cutters number of teeth
     • z
   • Feed rate
     • Linear speed of the workpiece
     • fr - mm/min
   • Cutting Time
     • Time that cutter engages the workpiece
     • t - min
   • Material Removal Rate
     • MRR - mm^3/min
     • Volume of material removed from workpiece per unit of time

6. To make sure that force on cutter tips increases and decreases gradually the cutter tips have to enter and exit workpiece in at an angle

   • Vast majority of cutters use carbide inserts
     • clamping or pinlocking them to the body of the milling cutter
     • replacable

7. INDEXING HEAD

   • Divides the circumference of a workpiece into equally spaced divisions
   • Gear cutting
   • rotate workpiece at predefined rates in relation to the table feed
     • produce CAMS and helical grooves
       • Helical milling
         • Linking the rotation of indexing head to the milling table movement
         • Spiral
           • path generated by a point moving at a fixed rate along a surface of a rotating cone
         • Helix
           • theoretical line generated on a cylindrical surface by a cutting tool that is fed lengthwise at a uniform rate
       • Uniform-rise CAMS can be cut on a milling machine with a vertical head

Images and files in the map