Page 62 - MetalForming May 2012

Tooling by Design
By Peter Ulintz
Forensic Investigation—Press-Shop CSI
Forensic engineering may be defined as the investigation of materials, products, structures or components that fail or do not function as originally intended. Vital to the field of forensic engineering is the process of investigating and
• Are the pilots positioning the strip accurately?
• Is the pitch length (the distance between the pilot holes) growing or shrinking beyond design specs?
• Is a stretch flange splitting due to a mismatched cut? • Are extrusions splitting due to a burr?
• Is the die hitting too hard or not hard enough? • Are deep-drawn fea- tures splitting due to restricted material flow
or an incorrect radius?
• Is the carrier design
appropriate?
• Is the die hitting level
in all the stations?
• Is die timing correct
when the die is fully loaded?
• Do cutting clear- ances change when the die is fully loaded?
These and many other questions can only be answered by thoroughly interrogating the die strip. The first questions your CSI activities must answer: Is the die progression cor- rect in the strip?
Setting the pilot or feed release is an important step during progressive-die setting. The pilot release must release the coil strip after feeds into the die so that the pilots can properly position the strip before the die closes on the strip. Most coil feeders use feed rollers to feed the materi- al forward in the die. The feed rollers clamp onto the strip and rotate a specific amount, usually through the use of servo motors. This causes the strip to feed one progression forward. For the pilots to correctly position the strip, the feed rollers must unclamp the strip before the pilots fully enter the strip.
One of the most misunderstood part of die setup is setting feed-release timing. The strip material can slide backward after the feed releases the material and before the pilots have entered the pilot hole. This will be evident in the die strip, as the pilot holes will appear distorted or heavily marked on one side of the hole where the pilot tried to pull the strip back into progression. To avoid this situation, make the first pilot with an undersized nose longer than the other pilots (Fig. 1).
Short feeds (or misfeeds) likely cause most of the die damage occurring in the press shop. Take care to ensure that the strip starts correctly into the die. Improper positioning
collecting data—through inspection, taking meas- urements, creating numerical models or per- forming experiments.
collecting evidence, performing
Tooling Technology
Second pilot
First pilot (long nose)
Exact pitch
Pitch +0.010 in. overfeed
Pilot hole punch
1⁄2 to 1 metal thickness
Many readers may be
familiar with the applica-
tion of forensic science in
criminal investigations
(crime-scene investiga-
tion, or CSI). Well, modern
press shops running pro-
gressive dies have their
own form of CSI: Com-
prehensive Strip Inspec-
tion. A comprehensive
inspection of a progres-
sive-die strip can tell much about what has occurred in the die during the stamping process. The strip is the equivalent of an eyewitness in a criminal investigation. Like an eyewit- ness, the strip was physically present and experienced every- thing that occurred.
When a problem with a progressive die occurs, or when it becomes damaged, it is essential that engineers thoroughly investigate and analyze the strip. Unfortunately, many deci- sions are made in the press shop based on inspection reports, a die-maintenance log, past experiences, a supervisor’s opin- ion or any number of other reasons, rather than interrogat- ing the eyewitness—the die strip. The strip can provide invaluable information with regard to the stamping process:
• Is the material feeding properly?
Peter Ulintz has worked in the metal stamping and tool and die industries since 1978. He has been employed with the Anchor Manufacturing Group in Cleveland, OH, since 1989. His background includes tool and die making, tool engineering, process engi- neering, engineering management and product devel- opment. Peter speaks regularly at PMA seminars and conferences and maintains the website, www.Tooling- byDesign.com. The site serves as a web-based source for the transfer of modern metalforming technology and the advancement of “Performance-Based Die Engineering Strategies.”
Peter Ulintz
pete.ulintz@toolingbydesign.com www.toolingbydesign.com
Fig. 1
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MetalForming/May 2012
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