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Information-Laden Dies Require Your Attention

By: Peter Ulintz

Friday, June 1, 2018
 

Stamping dies can communicate important information to the press technician, die setter and toolroom personnel, so long as everyone 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 programmed pitch length?
  • Are stretch flanges splitting due to a mismatched cut?
  • Are extrusions splitting due to misaligned 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 investigate a potential problem or take immediate action. For example:

  • Do pressure pads or stripper plates make slapping sounds when contacting 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 binding 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 lubrication and begin running the press again.

If good-quality parts cannot be reproduced without simple adjustments, usually to compensate for temperature 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 parallelism with each stroke; an inconsistent feed system that forces the pilots to correct strip location in both directions; 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 distribute evenly across the press slide, causing the slide to tip and move laterally in the direction of the greatest force. If this movement occurs with the punches engaged with other die components, excessive wear or damage 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 shoulder bolts release easily and whether removal of the strippers is accomplished without any difficulty.
  • Assess if any punch-to-die interference 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

 

Related Enterprise Zones: Tool & Die


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