Ask the Stamping Expert: The continuous improvement approach to die design

 

The “10 Die Design Laws,” which appeared in the September/October 2016 issue, are most effective when used along with a continuous improvement approach. At the end of every tool build and final development cycle, the die design team should review what went well and build on those strengths, but more importantly address what did not go well, including every development issue. Remember, the goal is to design the die, build the die, and run the die—with no development. Of course, that’s not always possible, but you should work on getting closer to that goal after every new build.

Together, the 10 Die Design Laws and a continuous improvement approach form a world-class die design process. But where do you begin with continuous improvement? Following is a sample check list of items to confirm and an explanation of the issues each one addresses. Use the list at the tool concept review and again after final design to confirm nothing was missed. You also should update it at the final tool development review with suggested actions to reduce development on the next tool build.

Continuous Improvement Check List

Confirm that:

1. Die lace-up is under power using designed start point. This will help you engineer in a strip start button to prevent the creation of a half-slug on lace-up. Confirm that nothing inhibits the die strip as it progresses through the tool, and make sure you have proper leads on the guide rails and lifters.
2. Press stroke complies with quoted work center. When you quote jobs, they are loaded into specific workcells. You need to confirm the tool will fit physically into that cell.
3. Tonnage does not exceed quoted work center. The workcell’s press tonnage must support the calculated tonnage the tool requires.
4. Die runs at quoted speed continuously. The die design has to facilitate running at the quoted speeds to maintain piece-part price. Part ejection, slug removal, strip lift, stripper travel, and press stroke all affect the speed at which the tool can run.
5. Parts produced meet quality requirements. In general, if the part print stipulates a process capability index (CPK) of 1.33, this translates to about a 50 percent reduction in the tolerance you can use to meet the 1.33. You have to design the tool to meet these requirements, which might mean you have to add cutting or form qualifiers.
6. Slug retention is applied. Review every trim and address even the slightest possibility of slug pulls with specific solutions (spring pins, vacuums, bazookas, slug darts).
7. Required press bolster support is used. Review the design to eliminate concerns about insufficient support. For instance, if you are doing heavy coining or forming in an area where there is no press bolster support under the bottom die shoe because it is open for scrap, you might need to design in a support beam and thicker die shoe, add a subplate, or change out the bolster completely.
8. Setup document draft is completed before die setup. The document should include clear instructions for lace-up, press setup (including shut height, tool location, and speed), feed pitch and pilot release setup, air line pressures and locations, number and location of sensors, and sensor setup.
9. Tooling log is maintained with full development history for every press trial.
10. Tooling drawings clearly define the intent and function of all stations. Have cross-section prints of every station in the die on hand for the tooling group when you get the first strip through the tool. They should show trimming, forming, coining—all stations. Once you get the tool running at speed, you can start from the first station and measure the lead strip versus design intent. If it is good, move to the next station; if not, make adjustments until debugging is complete.
11. Check list of tasks pertaining to your process is completed before you put the tool in the press:

• All air lines fitted with hose adapters and tested for air leaks.
• Mounting clamps and screws supplied.
• Sensors mounted and tested.
• Misfeed punch and actuator checked.
• Fit, form, and function of tool and all auxiliary equipment confirmed (includes part and scrap chutes, oilers, entrance and exit material liners, camber and twist mechanisms, subplate with scrap shield, and alignment pins), and all are marked with part number.Good luck, and happy stamping!