Press Mold Special Edition: Mold Maker Column - What is the Hull Bottom Phenomenon?

In the mold shop column, we will be sharing various topics about molds from time to time! (We also publish the mold shop column on our Instagram.)

In this column, I will introduce the "boat bottom phenomenon"! When you want to punch out terminal shapes like those in the icon, processing each pitch as shown in Figure A results in a smaller area being held down during the punching process. This can lead to the stripper plate being unable to hold the product securely in the narrower areas, causing it to tilt due to the force of the punch coming down. This is known as the boat bottom phenomenon. The product that has tilted ends up resembling a boat bottom, hence the name. To avoid this, while changes in layout are necessary, one possible solution is to use a multiple pitch feed as shown in Figure B. In the case of multiple pitch feeding, a single group is punched out at once (all punches come down simultaneously), leaving no room for the product to tip over, thus preventing such issues. However, on the other hand, this will reduce the spacing between the dies, which raises concerns about the strength of the dies. It is necessary to determine specifications based on strength calculations.

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