Just like pilots of a plane, they guide your material to the destination or registration
Purpose of Pilots
It is the function of pilots to position workpieces or stock strips accurately for die working. When the work is brought into the required position by the pilot, it is said to be registered. So just like its name sounds, the pilot guilds the stock strip to its location
Registry Action
When dies are equipped with pilots, all stops except for the first stop are positioned to allow overfeeding. The actual feeding distance is equal to the advanced distance plus the overfeed distance.
Registry Action
When an operator feeds a strip against the stop and the strip is now at the stop position or registered. As the pressed descends, the pilot’s bullet nose enters the previously pierced opening in the stock strip. As the press ram continues to descend, the bullet nose on the pilot will cam or push the strip opening into alignment with the pilot. Overfeeding is a very important feature of the relationship of stops to pilots. Do not try to make the stop position coincide exactly with the registry position. All secondary and final steps in piloted dies should allow the strip to be overfed a slight amount. When a stock strip is fed automatically by mechanical means, pilot action is the same in principle, with one exception, the direction in which the strip is fed is normally reversed. Instead of being overfed the stock strip is underfed. This is especially true for feeding mechanisms which incorporate unidirectional locking strips.
In summary, hand-fed strips are overfed and backed into registry position by the pilots. Mechanically fed strips are normally underfed and pulled forward into the registry position by the pilot.
Piloting Size
The term piloting size refers to the part of the pilot that is doing the gauging.
If the pilots are precisely located, accuracy of registration then depends upon the relationship of the piloting size to the size of the respective opening in the stock material. When working with very precise work, pilot fit becomes very important. The desired effect is to have the pilot to fit the opening exactly, allowing no lateral movement of the material when the pilot is inserted. Excessive piloting friction can cause undue pilot wear, which results in loss of the accuracy and possible galling. Where such a close fit is not needed, piloting size should permit a slight clearance between the pilot and the work. Having this tends to alleviate piloting friction and evens out any minor construction discrepancies; for the most part, work clearance will range from 0.001 to 0.002 per side. Large, crude work may not only need clearance, but require it. Since piloting size comes from the corresponding opening size, it is, therefore, related to the size of the punch which pierces the opening.
Pilot Length
The registry must be completed before any work begins which makes it mandatory for the pilot to be larger than the punches in the given die. This can have serious consequences ranging from spoiled work to damaged dies. Pilots that are longer than necessary will in most cases perform the function of registry. One exception to this would be a progressive die mounted in a short stroke press and requiring a relatively long feed stroke. In such instances, pilot length can become quite critical because overlong pilots may not permit an adequate feeding cycle. In many dies, the punches will not all be the same height. For such applications, keep in mind that at least one set of pilots must act to register before the longest punch contacts the work. Many dies are equipped with pressure pad strippers, which are quite commonly spring actuated.
Pilot Openings in Die Blocks
The most common type of pilot opening provided in die blocks, is the clearance opening. This method applies to pilots which are strip guided and to pilots which are unguided. To ease die making, it is usually desirable to make the opening the largest practical size, in order to allow as much discrepancy as possible in both the size and location. If the opening is too large in proportion to the stock thickness, the stock will tend to draw into the opening distorting the material in the area of the pilot. With soft material, if the die block opening is too large, the pilot may not displace the material into the registry position, but may instead draw the material on one side of the pilot opening into the clearance opening. If the opening is too large the material will tend to extrude and become jammed.
Pilot Supported in Die Block
Occasionally, a situation is encountered where it is desirable to support the pilots, but not necessarily to guide any of the punches. In such cases, it may be practical to guide the pilot in the die block where a bushing is installed in the die block. One advantage of this procedure is that, in the event of rapid wear in the opening, the bushing may be easily replaced. Bushings are considered a necessity in high production dies, if it is intended to support the pilot in the die block. To provide support, the size of the opening which receives the pilot is made a slip fit for the pilot. The opening should be made straight for a distance of at least 1/8 of an inch or more if deemed advisable. The pilot is guided in the stripper and receives additional support from the die block opening. This double support method is used where the pilot is relatively small and weak, in proportion to the stock thickness, and where relatively high lateral forces are imposed upon the pilots.
Pilot Punches
The general configuration of these punches is very similar to that of perforators. As far as die assembly is concerned, mounting methods and procedures for pilot punches are identical with those employed for perforators. Always keep in mind of course, the piloting size and piloting length relationships described earlier in this article. The text reminds us here that there is a relationship between the two.
Pilot Nose Contours
The most prevalent nose profile is the bullet nose. The bullet shape is formed by creating a radius that is equal to the pilot diameter. Radius is tangent to a piloting length, the tip is finished with a spherical radius that is equal to 1/4 of p and tangent to R.( insert image included A B C) The bullet nose pilot profile is popular because it is strong, simple to make, and smooth. A piloting action is comparatively gentle, because of smooth accelerated lateral motion which is imparted to the stock material during the piloting act.
A: 45-degree conical stub nose radius is made approximately one-quarter p and is tangent to pee at E-nose side is conical at 45 degrees and tangent to R.
B: 30° conical stub nose procedure same as for previous nose, except core angle is made 30 degrees and radius R is Turbo Droid instead of spherical. This is a compromise between the 45° stub nose and the conventional bullet nose.
C: 15-degree angular nose procedure same as for a 45° stub-nosed, except core angle is 15 degrees.
Removable Pilot Punches (inset image)
As far as fit proportions are concerned, mounting methods and procedures are generally the same as for perforators. There is assembly variation, where a thrust plate acts as a head for the pilot, in addition to backing it up. Whenever feasible, the wrenching flat should be provided on the pilots to prevent rotation when tightening the pilot mounting screws. The pilot may be a tap or a close slip fit in the punch plate.
A: Clearance hole for the pilot head is drilled through the punch plate holder. The hole is threaded from the top surface of the punch holder deep enough to receive the set screws. A spacer plug of suitable length is inserted between the pilot and the set screw.
B: The punch plate opening may provide a slip fit or tap fit for pilot diameter as required.
C: This is a compromise method using a spacer plug to provide the plug with a head, to achieve the effect where the head of the pilot is held in place by a slug. This construction eliminates the inherent hazards of the A method; however, it is an expensive method and, in most circumstances, is not as efficient.
D: This is a semi-retractable pilot; the punch plate opening should be a slip fit to the pilot. Generally, the construction is identical to method A, except that a heavy spring of a plane plug is incorporated to serve as a spacer.
Retractable Pilots
For a pilot to be considered retractable it must be fully retractable. That is, in the event of a miss-hit, the pilot telescopes into the punch holder for the distance necessary to produce the possibility of piercing the stock material. The spring must be long enough and flexible enough to permit the required telescoping travel, but at the same time, it must be strong enough to assure normal piloting action.
Pilots in Punches
A Pilot Mounted in Bending Punches
The pilot is, in this case, a standard step-headed pilot. The pilot hole in the punch should be a light drive-fit for the pilot, because this will facilitate grinding the pilot head flush with a punch base in assembly. The hole should be relieve drilled slightly larger than the depth, which leaves sufficient fitted length F to provide adequate pilot location and support.
Some exceptions include:
Exception 1: Pilot mounted in blanking punches: Fitted diameter P should be a closed slip fit or tap fit.
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Exception 2: Because this is a cutting punch, grinding life must be considered.
Peened in Pilots
The back end of the pilot shank is left soft and is peened into the countersink, forming a bevel head, which holds the pilot in assembly. Repeated peening may deteriorate the shank end. If deterioration occurs, grind the punch face to lower the punch height. This will expose the pilot shank a slightly greater distance at the,providing new stock for peening.
Threaded Pilots
The pilot has a threaded shank and is secured by a nut threaded length.
Fitted Pilots
Pilots are on occasion provided with a flat. The purpose of the pilot flats is to reduce the amount of pilot contact. This is appropriate on large pilots since the reduced contact area will permit freer piloting and stripping pilot flat can be desirable on punch pilot to help eliminate blanking pulling.
Material and Heat Treatment
Normally the piloting portion should be quite hard in order to resist wear. Heads on pilot punches should be drawn to a spring temper or softer; this also applies to shanks on step-down pilots. For a given application, it is good practice to make the pilots of the same material that is used for the punches and or perforators.
Conclusion
This article is a summary of the chapter on punches in the text that we used for the course. For more in-depth information or more detailed examples, I encourage you to look at the text. The purpose of these articles is to act as summary study aids as I am preparing for my C of Q. Thank you for taking the time to read to this point and I hope this has been helpful. Feel free to subscribe to our email to be notified of more articles as they come out.