METAL CUTTING: More drills

METAL CUTTING: More drills

1. DESIGN CONSIDERATIONS

   • Design should allow holes to be drilled on flat surfaces and perpendicular to the drill motion
     • Otherwise drill tends to deflect and the hole will not be located accurately
   • If holes with large diameters required, the workpiece should have a pre-existing hole, preferably made during fabrication of the part
   • TROUBLESHOOTING
     • Drill breakage
       • caused by
         • dull drill
         • drill seizing in hole because of chips blocking flutes
         • Feed to high
         • Lip relief angle too small
     • Excessive tool wear
       • Too high cutting speed
       • ineffective cutting fluid
       • rake angle too high
       • drill burned and lost strength when sharpening
     • Tapered hole
       • drill misaligned or bent
       • lips not equal
       • web not central
     • Oversize hole
       • Same as above
       • Chisel edge not central
       • side force on workpiece
     • Poor surface finish
       • Dull drill
       • ineffective coolant
       • improper alignment to the center
       • vibration
       • High feed rate
       • Low cutting speed

2. REAMING

   • to make an existing hole dimensionally more accurate
   • improves surface finish
   • manually or automotive
   • process should involve centring, drilling, reaming and grinding (if necessary)

3. TAPPING

   • produce internal threads in workpiece
   • a tap is a threaded tool with multiple cutting teeth that can be used manually or on a machine
   • designed in a tapered form to reduce the torque required for tapping

4. BORING

   • producing internal profiles in workbiece
   • on large parts requires vertical boring machines

5. PLANING OPERATION

   • producing flat surface, grooves or notches by cutting through the length of the workpiece
   • slow
   • designed for heavy parts
   • Mainly for rough cutting and low quantity

6. BROACHING OPERATION

   • involves the use of a multiple tooth cutter that oves linearly relative to the workpiece in the direction of the tool axis. The shape of the machined surface is determined by the contour of the cutting edges on the broach
   • Highly productive
   • Expensive tooling cost
   • mass production operation

7. BROACHING TOOLS

   • makes successively deeper cuts
   • total depth of material removed in one stroke is the sum of cuts by each tooth
     • as deep as 6 mm

8. BROACHING MACHINES

   • only have to move the broach in a precise linear motion at a certain speed
   • Push broaches are shorter and may divert from the straight line following irregularity of the workpiece

9. ROTARY BROACHING

   • method to produce irregular shapes without using broaching machines

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