PILOTS

PILOTS & PILOTING 

PILOTS:-
Pilots play a vital role in the operation on multiple-station dies, and many press lines troubles can be traced to their faulty design. In applying pilots the following factors should always be considered:
• They must be strong enough so repeated shock will not cause fracture.
• Slender pilots must be sufficiently guided and supported to prevent bending, which can cause faulty strip positioning.
• Provision should be made for quick and easy removal of he pilots for punch sharpening .

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Purpose of pilots:-
• The pilot positions the stock strip in relation with the die opening.
• This is termed as registering.
• The strip is normally overfed more than the pitch length.
• When the press is tripped the pilot comes down and engages the pre pierced 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.

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PILOT SIZE:
The accuracy with which the work can be registered depends upon the proper location and the diameter of pilot. 
The following will indicate the pilot diameter ;
Average work Ø of pilot= ( Ø of hole to be piloted-0.05 to0.1mm )
Close work Ø of pilot = ( Ø  of hole to be piloted-0.03to 0.05mm)
Accurate work Ø of pilot =( Ø  of hole to be piloted - 0.01to 0.2mm)
However the thick stock materials & the stock materials like aluminum and copper need often  bigger tolerances between the pilot and the pierced hole.

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PILOT LENGTH:-
Registering the strip must be complete before the cutting punches come and engage the strip. Therefore the pilot must be longer than the punches. If the pilots are too short they cannot perform there function
This creates serious consequences ranging from spoiled work to damaged pilots. Care must be taken while setting the stroke of the press so that pilots clear the stock strip without obstructing the future feeding of the strip. In any case the piloting length should be extended beyond the punch face equal to the sheet thickness. 

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PILOT OPENING IN THE DIE :-
The opening of the pilot in the die should not be too large. If  so, the stock strip may tend to draw into the opening. In case of the thin material pilot may not displace the material into registry position but may instead draw the material on one side therefore it is advisable to have the opening Ø as pilot dia + double clearance. weaker pilots are guided in the stripper.

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PILOT OPENING IN DIE SHOE:
Through hole is provided in the die shoe for the pilot so that slugs produced during miss feed are cleared. It also helps in clearing the accumulated burrs dislodged from the pierced hole. 

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PILOT NOSE PROFILE:-
The main function of the pilot nose profile are to allow smooth riding of the pilot into the stock strip. The most commonly used nose profiles are described below:

Bullet nose:-
The most common pilot nose profile is bullet nose. The bullet shape is formed by radius R which is equal to piloting diameter. For piloting in holes less than 6mm the length of radius R can be increased to reduce the lateral force during piloting. Bullet nose is strong simple to make and smooth in action.

The other three commonly used pilot nose profiles are:
1. 45º conical stub nose 
2. 30º conical stub nose 
3. 15º angular long nose

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45º CONICAL STUB NOSE PILOT:-
The profile is used when a shorter nose profile is desired. 45º cone increased the relative lateral forces hence not recommended for delicate pilots used for piloting thin soft material.

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30º CONICAL STUB NOSE PROFILE :
This is same as the above pilot except the nose angle is30º this is a compromise between the 45º stub nose pilot and the conventional bullet nose.

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15º ANGULAR NOSE:
This small angle provides good mechanical advantages they are used for small pilots and for thin materials.

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TYPES OF PILOTS:

RETRACTABLE PILOTS:
In many occasions especially during hand feeding miss feeding occurs due to over shooting of the stock strip over the stoppers. This creates the problem when a tool is having pilots in it. Pilots may break or buckle obstructing smooth function of the tool. 
Generally retractable pilots are spring loaded in such away that they will be lifted upwards when they come in contact with the un pierced area during press descends. Care should be taken while selecting spring so that springs allow more telescopic  movement of the pilot.

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REMOVABLE TYPE PILOTS:
Pilots break very often due to miss  feeding of the stock strip. Much consideration must be given for changing quickly the broken pilots ,preventing greater time loss during production. Removable type of pilots can over come this difficulty. These pilot inserted through top bolster into the punch holder and fastened with a back up screw as shown in fig :

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PILOT IN PUNCHES:

Pilot mounted in punches is called punch pilots.  Piloting size should extend beyond the punch face a distance of at least stock thickness, but minimum dimensions of 1.5 mm. When pilots are mounted in blanking punches there is a tendency of pulling the blanks by the punch. When the blanking punch retracts spring-loaded pins are provided to prevent this pulling of blanks.

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METHODS OF PILOTING :-

Direct piloting :- 
It consist of piloting in holes pierced in that area of the strip which will become the blank. All pilots decided so for have been direct pilot which are retained in the blanking punch. 

Indirect piloting:-
Indirect piloting consist of piercing hole in the scrap area of the strip and locating in these holes at subsequent operations direct piloting is the preferred method but certain blank condition require   indirect piloting, as will be explained. 

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PART CONDITION :
There are seven condition that required in indirect piloting.

Close tolerance on hole. Pilots can enlarge holes in pulling a heavy strip to position.
Holes too small. Frail pilots can break or deflect in operation.
Holes too close to edge of the blank.  Distortion can occur in blank because of enlargement of holes
Holes in weak area. Piloting in projecting tabs is impractical because they may deflect before the strip is pulled to position
Holes placed too closely. Piloting in closely placed hole does not provide an accurate relation between two holes and edge of the blank
Blank without holes. Piloting is done in the scrap area where ever the blank does not contain holes.
Projection in hole. When ever the hole in the blank contain weak projection which could be bent down by the pilot, indirect piloting should be selected.