Page 66 - MetalForming October 2010

Tooling Technology
Assembly Automation
time,” he says, “particularly in dies where space is at a premium and no other option is suitable. Also, the fact that you can pierce and install in one hit it can make self-piercing nuts a preferred choice, particularly in transfer dies. In those cases, the stamper must ensure it has included sufficient in-die sensoring to check for slug removal after each hit. And, even with a sound sensor setup, it’s still risky—I’ve never seen an applica- tion with in-die installation of self- piercing nuts where the stamper did not ship at least some parts with a slug, unless they’re inspecting and sorting 100 percent of the parts.”
The riveting-style nut, on the other hand, is growing in use for in-die automation, Lanni says, particularly in applications involving advanced high- strength steels (AHSS) and when work- ing with very thin sheet. These nuts feature a collar that protrudes com- pletely though the material and extends out the opposite side. The collar then
gets folded back over on top of the nut in the press to create a joint strong enough to satisfy the design require- ments of AHSS stampings.
Other trends identified by Lanni include development of new styles of fastener feeders that generate less noise and are less likely to jam; and develop- ment of system components that fit together with quick-connect fittings to allow stampers to quickly move the equipment among setups. Also, systems can be designed to feed not only nuts and studs, but special fasteners such as positioning pins, spacers and ball pins.
Other Concerns (Hurdles) that Block Productivity
Working with the die designer on implementing an in-die fastening solu- tion, Lanni strongly suggests that the stamper also bring the supplier of the feeder and head and fastener into the process from project inception. This will help ensure that the heads and fas-
tener-delivery mechanism do not impede the functionality of the die.
“We urge designers to set fasteners near the end of the die,” Lanni says. “This way if something does go wrong during production, it only affects the back end of the die. A common mistake I see is that the die punches the hole for the fastener too early in the process, and then subsequent forming opera- tions make it nearly impossible to repeatedly track hole alignment and maintain hole geometry.”
Another common mistake noted by Lanni: locating the fastener heads right next to where the die lubricant is being applied. “I’ve seen setups where the heads become filled with lubricant,” he says. “This is the type of error that occurs when there’s a lack of commu- nication between parties.”
Yet another concern Lanni express- es relates to operator training. “Often, we’ll perform training at PPAP, and then the stamper won’t run the die for another 6 to 8 months. By that time the operators have forgotten everything that we taught them. If they forget to follow the proper sequence of opera- tions, it can take a lot longer to set up the system and, at worst case, the heads can crash.
“In particular,” continues Lanni, “a common error we see is a stamper installing a head that already contains a nut left over from a previous run. In this case, when the die is set and the press begins to stroke, the nut may already have been set on the lower die before the strip gets there. Then, when the strip arrives and the ram comes down and makes a hit, you’ve already set a nut. Then a second nut could be fed to the same spot. Result: a double-hit and a blowout.” The moral to the story: Don’t thread the sheet until the heads have been inspected and installed.
Lastly, Lanni suggests that in-die fas- tening installations employ guided strip- pers, and that the die shop design the pilots in the web, to optimally control the part throughout the process. “This will help ensure a robust, repeatable process,” he says. MF
64 METALFORMING / OCTOBER 2010
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