Blank Variation Analysis


As an input to the forming process, we strive to understand the impact of specific blank size and shape variables on the current forming output. Alternatively, this analysis tool can be used as an output measure of a blanking operation.


A 1990 Taguchi Study conducted by Phoenix, along with a major stamping manufacturer, found three primary sources of variation within the stamping process. These sources were blank size/shape, blank location and lubrication. Observation suggests these findings to be relevant today.


Blank Variation Analysis enables the user to initially measure the specific amount and type of variation, and, then, use these measurements to identify the source of the variation.

  • Measure blank variation
    • Length, width and thickness of the material
    • Shape, cutout locations, fishhooks & other processing errors
    • Camber, pitch and coil width variation
  • Identify source of variation
    • Steel mill
    • Steel processor
    • Blanker
    • Weld source

Steps – with a reference blank

1. Set up a blank table

2. Create a blank for baseline reference

     a. Pull a sample of the blank currently running. No need to   consider the desirability of this sample (How well it runs). This blank will serve as a reference blank.

     b. Collect blank specification sheet

     c. Place tick marks at measurement points on blank

     d. For 2 off blank processing, determine if ‘end out’ or ‘side out’      and document

3. Pull specimen and measure

     a. Collect one blank per lift

     b. Collect lift tag

     c. Capture blanking date

     d. Place specimin on blank table, on top of reference blank

     e. Measure variation at tick marks

          i. Measure to 1/2 mm accuracy

          ii. (+) when specimen is larger than reference

          iii. (-) when specimen is smaller than reference

4. Record measurement on standard worksheet

5. Using Excel or similar, chart readings

Steps – without a reference blank

1. Collect blank specification sheet

2. Choose appropriate measurement points – Document the data collection plan

3. Measure one blank per lift

     a. Collect lift tag, capture blanking date

     b.  Measure blank

          i. Measure to 1/2 mm accuracy

     c. For 2 off blank processing, determine if ‘end out’ or ‘side out’ and document

4. Record measurement on standard worksheet

5. Using Excel or similar, chart readings.

Examples from the field

1. A tier one automotive supplier forming Body Side Outers thought they had a problem with the coating on their steel. We found excessive cutout location variation that changed strain state at critical spots near header and B pillar.

2. An American Automotive OEM, trying to save jobs by avoiding outsourcing blanker operations, used blank analysis and process control measures to improve quality and reduce cost.

3. An American automotive OEM struggling with consistency forming fenders identified significant difference between ‘side out’ and ‘end out’ blanks. Source of variation was a blanking die designed with a hard guide rail on one coil edge and a spring loaded coil edge on the opposite side. Solution involved segregating and running production with blanks grouped based on ‘side out’ or ‘end out’.

4. An American automotive OEM struggling to eliminate forming defects on a coil fed press line making truck bed side panels, spent multiple shifts tampering with form die and form press with no positive results. When someone compared current blank to the reference blank they realized the blanker was set up wrong. Another shift was required to return the form die and press to previous settings after corrections were made to the blank die setup.
Download File: Blank Variation Analysis Contributing authors Wil FrasBill ShinskeyTimothy Smith, and Kirk Wiley

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