Purpose of pilots
The pilot positions the stock strip in relation with the die opening.This itrip is normally overfed more than the pitc length.When the press is tripped the pilot comes down and engages the prepierced hole.The strip is dragged back into the registry position.When mechanical feeding is employed the strip is underfed.The pilot pulls the strip into registry position.
Pilot Size
diameter of pilot for average work,Diameter of hole to be piloted 0.05 to 0.1mm
For close work,Diameter of hole to be piloted 0.03 to 0.05mm.
For accurate work,Diameter of hole to be piloted 0.01 to 0.02mm.
Thick stock materials and materials like aluminium and copper require larger tolerance.
Pilot length
Registering of the strip should be done before the punches come and engege the strip.The pilot should extend beyond the punch face equal to one sheet thickness.
Pilot opening in the die
If the pilot opening in the die is larger,instead of registering the material will be drawn into the opening.
Diameter of the opening
= diameter of pilot + double clearance.
Pilot opening in the bottom plate
through hole is provided in the bottom plate for the following reasons:
1.Slugs produced due to misfeeding can be cleared.
- if by chance the strip jumps the stopper the pierced hole will be out of alignment with the pilot.The pilot will hit the strip and punch out a deformed slug.
2.Accumulated burrs dislodged from the pierced from the pierced hole is cleared.
- During piercing operation burr is formed on the pierced hole.The pilots,while entering the prepierced hole,will dislodge the burr.
Pilot nose profile
Bullet nose
The most common pilot nose profile is bullet nose.The bullet shape is formed by radius 'R' can be increased to reduce the lateral force is strong,simple to make and smooth in action.
45 degree conical stub nose
- shorter nose profile.
- used for piloting thick materials.
30 degree conical stub nose
This is a compromise between bullet nose pilot and 45 degree stub nose pilot.
15 degree conical stub nose
Used for small pilots and for soft thin materials.
Pilot in punches
Pilots mounted in punches are called punch pilots.
The pilot extends beyond the punch face by a distance of atleast one sheet thickness(minimum 1.5mm) and secondary peration tools.
Types of pilots
pilots are held in the punch holder.In special cases the following pilots are used.
Retranctable pilots
Misfeeding may occur due to the overshooting of stock strip over the stoppers.In such cases pilots may buckle or break.To overcome this difficulty retractable pilots are used.They are spring loaded pilots,they will be pushed up when they come into contact with unpierced area during operation.
Removable type pilots
Pilots break often due tto misfeeding of stock strip.Changing of broken pilots consume considerable time and leads to loss in production.Removable type pilots are used to overcome this difficulty.The pilots are inserted through the top plate into the punch holder and fastened with screw.
Methods of piloting
Direct piloting
Piloting in holes pierced in that area of the strip which will become the blank is called direct piloting.
Indirect piloting
Indirect piloting consists of piercing holes in the scrap area of the strip and locating by these holes at subsequent operations.
Direct piloting is the preferred method,but certain blank conditions require indirect piloting.
Indirect piloting is preferred under the following conditions:
close tolerance on holes
- pilots can enlarge holes by pulling a heavy strip in position.
Holes too small
- fragile pilots can break or deflect in operation.
Holes too close to the edge of the blank
- distortion can occur on the blank because of enlargement of holes.
Holes in weak areas
- piloting in projecting tabs is impractical because they may deflect before the strip is pulled in position.
Holes spaced too closely
- piloting in closelyspaced holes does not provide an accurate relationship between holes and relative edges of the blank.
Blanks without holes
- piloting has to be done in the scrap area whenever the blank does not contain holes.