So much of being successful forming sheet metal products is related to seeing the ‘invisible’; knowing how material moves during the forming process. We’re continually on the lookout for tools that provide the average tool and die professional simple access to information they can use.
The below guideline describes one approach to measuring sheet metal displacement quickly, simply, and without need of any expensive equipment.
Sheet Metal Displacement Analysis is an output measure of multiple inputs and adjustment sights. Impact lines are used to determine volume of material movement and correlates to known strains in a formed part.
There are multiple uses of Sheet Metal Displacement Analysis, including but not limited to:
- Monitor the forming process for consistent or repetitive metal flow.
- Validate process set up by comparison to a known reference.
- Root cause problem identification which serves to narrow the number of potential causes requiring investigation.
1. Create a Sheet Metal Displacement template
i) Identify high strain or quality issue location(s).
ii) Understand current or existing strain states and deformation modes.
iii) Collect set up data that created strains.
– Shut height
– Cushion – press or die
– Press speed
– Die set up – gauge, block
– Press load tonnage
B) Collect a draw shell formed with these settings.
C) Cut draw shell into template(s).
i) Segments affecting high strain locations.
ii) Use part shape to locate template on specimen later.
iii) Measure draw-in from the edge of a template or cut a window into center of template to enable viewing of draw line.
iv) Apply a rudimentary meter to measure variation.
D) Identify appropriate template storage (plastic bins from discount store work well).
2. Template use
A) Troubleshooting a new failure
i) Pull production draw shell.
ii) Measure 1 piece sample from each lift of observed production.
iii) Measure individual piece variation against template.
iv) Record on worksheet.
v) Follow the data – interpret the variation to determine which process set up variables to investigate.
B) Process control for ongoing production
i) Compare template to draw shell after each die set.
ii) Measure individual piece variation against template.
iii) Record on worksheet.
iv) After enough history is captured:
– Plot data on run chart.
– Calculate +/- sigma control limits and mean.
– Follow standard rules for discerning process variation (noise or signal).
2. Secondary template use – designed experiment
A) Due to its low cost, low tech approach, this is an excellent support tool when conducting designed experiments.
3. End of Line Application
A) Perform measurement in final part racks if impact line is visible in the finished part. Use template developed from finished part, document on worksheet, and perform data analysis.
Examples from the field:
A tier one European automotive supplier is using this approach to monitor process set up and reaction throughout the course of each production run.
An Asian automotive OEM, experiencing steel coating ‘scraping’ in the forming operation used this tool to determine if excess material was being dragged across the draw bead, restricting metal flow over time.Contributing authors George Coates, Wil Fras, Bill Shinskey, Timothy Smith, and Kirk Wiley