Page 31 - MetalForming December 2009

was—a stack of parts neatly crushed into a multilayered sandwich so well jammed into the upper portion of the die that they were, upon casual obser- vation, invisible to the operator.
Just how many dies undergoing sim- ilar situations need to detonate and self-destruct before it becomes obvi- ous that there is no difference between a double (or triple, quadruple, etc.) set of hits on a stack of nonejected parts within a single-stroke tool or a pro- gressive die. Clearly a part-out sensor within the single-stroke tooling would have prevented the operator from cycling the press without first removing the previous part.
This example can be extended to single-stroke assembly operations
where, in large order environments, the company would have previously per- formed tapping, staking, nut insertion and the like within progressive dies but now, due to smaller volume orders, has these value-added operations conduct- ed in a single-stroke environment. Just what guarantees do you have that the tap performed its tapping process cor- rectly and did not break on its way down or out of the lower die? Are you sure that the nut was delivered into its proper position prior to it being staked into the part? Is it a full or a partial nut? Does the nut have the proper threads? What’s to prevent a bad nut and/or one that is out of position from being insert- ed in the first place? The same for studs. Was that a full-length stud that was just
snapped into position? How do you know? In these and many other value- added instances, the answer is “no,” unless there are electronic sensors patrolling the single-stroke processes.
Mistake-proofing should not be based solely on the quantities of parts being stamped and assembled, but rather as a preventive measure to ensure that no bad parts are being stamped or assembled in the first place. Surely today’s low-volume orders, with their just-in-time, near zero inventories, are even less tolerant of die crashes and badly made parts. There is no difference between progressive or single-stroke tooling when it comes to mistake-proof- ing as they are both prone to the same process errors. MF
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