Punch pilot, better known as the pilot punch, is used in progressive die as an alignment tool, keeping your strips lined up throughout the application. When a punch pierces a hole in one station, the die is cycled by the press and the material is moved to the subsequent station.
The pilot punch enters the hole and has the material positioned in the exact location before the press cycles the next stroke. Pilot precision punches are suitable for tool designers that require close tolerance, durable, accurate pilots in high production, as well as high strength materials. Pilot Punches are also used for extrusion applications.
However, you may need to opt for stubby pilot punches during high demand stamping applications because you will need a pilot that is both stronger and more precise than the standard length pilots. When these pilot punches are mounted on a guided stripper, shorter pilot length will lead to more rigidity, making it less susceptible to flexing and more accurate for piloting.
The idea of piloting is actually easier than you think. It is essentially an essential activity in strip layout for progressive dies. The strip must be aligned accurately in each station to allow operations to be performed properly. There are typically three kinds of piloting in progressive dies:
● Direct Pilots:
Direct piloting is when one or multiple circular holes of the part are used for piloting.
● Indirect Pilots:
Indirect pilots mean that one or multiple circular homes are produced in the scrap area and are used for piloting.
● Semi-direct Pilots:
In semi-direct pilots, multiple circular holes are produced inside the non-circular holes of the part for piloting. And in the last station, the entire holes are pilot punched into the intended shape.
During punch piloting, an ideal pilot hole should be circular and have diameter greater than that of an allowable diameter. Otherwise, it cannot be considered as a suitable pilot hole. The punch pilot can easily break or deflect during operation is the diameter is not great enough. It is also important to keep in mind that the pilot hole should stay as far away from other holes of the work piece as possible. If indirect piloting is applied on the scrap area, there will be a minimum increase in strip width.
When doing outer cutting of blanking work, the material is moved by the feed length using the side cut or a feeding device. At this moment, the product can be influenced by any fluctuations in the feed pitch. In such case, pilot is adopted for correcting the feed error right away before performing the cutting.
As mentioned previously, a pilot is essentially a round hole, and the error can be corrected when you insert a pilot punch into the hole. The hole can be used by one of the methods we illustrated in the previous section. You can use direct pilot to shape the hole without creating any wastage. The disadvantage of this method, however, is that you may potentially deform the hole. When involving softer material like copper, pure aluminum and so on, you need to take extra care for the piloting process.
Fortunately, you can avoid the problem described above by opting for the indirect pilot method wherein a special hole for the pilot is formed in the part that turns into scrap. With this method during outer cutting, you can determine the size and position of the pilot hole freely. In such case, a pilot punch will always be pushed into the hole for the pilot immediately after the hole is punched.
If possible, the pilot punch is inserted multiple times continuously, and reduces the load on each punch. Keep in mind that there is a direct association between the diameter of the pilot hole and the diameter of the pilot punch. When the diameter of the pilot punch is equal to the diameter of the pilot hole, positioning becomes the most accurate, and the material will be picked up as the pilot punch comes out of the hole.
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