Page 18 - MetalForming-Jun-2018-issue

Tooling by Design
By Peter Ulintz
Information-Laden Dies Require Your Attention
Stamping dies can communicate important information to the press technician, die setter and toolroom personnel, so long as every- one is paying attention.
Progressive dies, for example, reveal process-related problems through the die strip. Analysis of the die strip can reveal the following:
• Is the coil material feeding properly?
• Are pilots positioning the strip accurately?
• Is the pitch length increasing or shrinking compared to the pro- grammed pitch length?
• Are stretch flanges splitting due to a mismatched cut?
• Are extrusions splitting due to mis- aligned punches?
• Is the die hitting too hard or not hard enough?
• Does the die hit level in all of the stations?
• Is die timing correct when the die is fully loaded? Do cutting clearances change when the die is fully loaded?
Listen Up
The sound produced by a stamping die may indicate that it’s time to inves- tigate a potential problem or take immediate action. For example:
Peter Ulintz has worked in the metal stamping and tool and die industry since 1978. His back- ground includes tool and die making, tool engi- neering, process design, engineering manage- ment and advanced product development. As an educator and technical
presenter, Peter speaks at PMA national seminars, regional roundtables, international conferences, and college and university programs. He also pro- vides onsite training and consultations to the met- alforming industry.
Peter Ulintz
Technical Director, PMA pulintz@pma.org
• Do pressure pads or stripper plates make slapping sounds when contact- ing the strip on the downstroke or make snapping sounds on the upstroke? If so, this could indicate that something has gone awry with the pressure system. Wire springs may have broken or nitrogen-gas springs may be leaking. Another possibility: The stripper plate tilts and binds due to improper setup or slugs under the stripper.
• Are there squeaking sounds when the die closes? If so, there may be a lack of lubricant on sliding surfaces, or bind- ing of the pressure pads or guidance systems due to off-center loading.
Communicating Design-Related Problems
The amount of time required to produce a good part may be one way that the die communicates design- related problems. To test this, unload all of the die stations after achieving quality approval. For progressive dies, cut the strip, leaving the remaining material in the feed equipment. Remove the die assembly completely from the press and then reinstall it. Load all of the die stations, apply lubri- cation and begin running the press again.
If good-quality parts cannot be reproduced without simple adjust- ments, usually to compensate for tem- perature changes in the tool and press, there may be a problem with the die construction or its design. After all, nothing else in the process has changed, just the die removal and reset.
Part-to-part inconsistencies may result from a sloppy press or ram slide that fails to repeat in distance and par- allelism with each stroke; an inconsis- tent feed system that forces the pilots to correct strip location in both direc-
tions; or camber in the material that shifts the strip from one side to the other within short distances.
When removed for maintenance, the die continues to communicate problems. For example, consider whether any of the punches or die sections have sheared. This occurs when the loads in a die do not dis- tribute evenly across the press slide, causing the slide to tip and move lat- erally in the direction of the greatest force. If this movement occurs with the punches engaged with other die components, excessive wear or dam- age can occur.
Other Toolroom Considerations
• Determine if any punches or any of the die sections have been shimmed, and if so, why.
• Evaluate whether pins and bushing show wear or score lines.
• Judge whether the stripper shoul- der bolts release easily and whether removal of the strippers is accom- plished without any difficulty.
• Assess if any punch-to-die inter- ference exists by bluing the punches.
• Remove all the springs and check that the stripper can bottom without interference or resistance.
• Spot-check punches and dies for proper Rockwell hardness.
• Check every lifter and shedder spring for even pressure, and ensure that the springs are long enough to prevent premature fatigue failure.
• Determine how many slugs are retained in the die bushings and die section—there should be no more than three or four.
• Inspect all wear-plate surfaces. These should be smooth, not scored. Pay particular attention to wear patterns that appear on one side only, indicating misalignment or uneven pressure from incorrectly set heel blocks. MF
16 MetalForming/June 2018
www.metalformingmagazine.com