Thickness of the material: Large parts with thin material may require stiffener beads to add strength to the carrier for stock feeding. Another stiffening and strip guiding method is to lance and flange the edge of the stock, which also can be used as a progression notch.
The total of the strip: Heavy parts in long dies require more force to push the strip through the die. However, the weight is usually thick material, and thick material is stiffer than thin material. As a rule of thumb, flexible carriers for materials of 0.020 in. to 0.060 in. are about 3/16 in. to 5/16 in. wide. For stock thicknesses above and below this thickness range, carrier width is a "best judgment call."
Depending on all the die factors involved, under normal conditions the carriers should be a consistent width for their full length, but especially in the area of flexing. Since nearly every stock feeder pushes material through the die rather than pull the material, the carrier must be strong enough to push the parts all the way through the die.
A detection switch actuated by a complete feed of the strip at the exit of the die can detect buckling. If action of the die during closure or opening of the press requires the carriers to flex, design the carrier with loops that are long enough to flex without breaking, but still strong enough to feed all the parts to their full progression. If two flex carriers are not strong enough to feed the strip, consider three carriers.
Try to make the radii in flex loops as large as practical. Sharp corners or small radii will concentrate stress of flexing, making it the first point to fracture during flexing of the carrier. Also avoid any steps or nicks in the edges of the carrier.
Upper Pressure Pads
Because of size or function, many progressive dies require two or more pressure pads in the upper die. Each may require a different travel distance to perform the work in the inpidual die station, such as trimming or forming or drawing.
However, the upper pressure pads often are used to push the material lifters down by pressing against the strip, which pushes the lifters down. In this situation, all of the pressure pads that push material lifters down should have the same travel distance. If the upper pressure pads travel different distances, the strip will not be pushed down evenly. This can pull adjacent parts out of the progression, making it difficult to locate the parts in their proper station position after the feed cycle.
If the part requires a flange to be formed up, the part carrier must have a flex loop to allow for vertical breathing of the part or provide a pressurized punch/pad with the same travel as the other pressure pads. The force required by the pressurized punch/pad has to be adequate to form the flanges up during the downstroke while the punch/ pad is in the extended position. This keeps the strip from breathing vertically as it is pushed down from the feed level to the normal work level.
When the strip reaches the work level, the pressurized punch/pad stops its downward motion while the upper die continues down for punching, trimming, down flanging and other operations. Springs or nitrogen cylinders can be used for pressure in these pressurized punch/ pad stations, but they must have enough preload force to form the flanges up and to collapse the lower gripper pad before the upper punch/ pad recedes

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