Page 57 - MetalForming April 2014

Stampers have other options for determining if a stamping process is running in a stable mode, or is drifting away from job-one settings. They can use, for example, an ultrasonic-thick- ness (UT) gauge or circle-grid analysis to track stamping-process stability. Potential problem areas are measured at die buyoff.
The easiest and fastest procedure: Use a UT gauge to measure part thick- ness at critical locations. The change in thickness is proportional to the change in surface deformation (strain) at that location.
Stampers typically pull a die at the end of a run and move it to a storage area. With a new run scheduled, the dies return to the press and production begins. An operator or inspector checks the first stampings made to verify com- pliance with specifications. If part dimensions fall out of spec, production ceases and repair procedures begin.
As an alternative, before pulling the die at the end of a run an inspector can use a UT gauge to check the last stamp- ing made against the target values. If he detects a problem, the die moves to the repair bay before being stored. For more complex problems, the whole stamping can be circle gridded to study material flow in more detail.
As a variation of this procedure, the metalformer can evaluate a stamping made 2 hr. before the end of the run. If problems are detected that can be repaired with the die still in the press, the stamper can make the corrections immediately following the run. It then makes a number of stampings before it pulls the die to verify the repairs.
In some cases, stampings will pass inspection at the end of a run yet fail inspection at the beginning of the next run. Again, the stamper must compare UT readings taken on the approved stampings at the end of the previous run to those from the defective first stampings of the next run. Useful infor- mation about the die/press setup will quicken the correction process. The same procedure can be used to evalu- ate whether a new coil is affecting the process (last stamping/old coil com-
pared to first stamping/new coil). Many press shops display their most complex stampings on their walls to show potential customers. While many of these stampings look impressive, they also can hold large amounts of infor- mation. Circle-grid each stamping. After forming, neutralize the electrolyte, degrease, wash/dry and protect the stamping surface with Krylon spray. This will protect the surface and grid for
decades. The stamping also remains available for UT measurements so that if the shop runs the die later or has a prob- lem with a similar stamping, it can refer to the preserved stamping for correc- tive information.
Finally, when showing potential cus- tomers around the press shop, your defor- mation-control procedures on the stamp- ings can be explained, making a great
The Science of Forming
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Operations Manager Kitagawa-NorthTech
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