Thomas Vacca
Director of Engineering

Where Should I Set the Feed Height?

Where do you recommend setting the feed-height stock line, relative to a progressive die? Should it be the stock-lifter height in the tool or the die-chase height, after the stripper clamps the stock to the die-chase plate?

A: Many in the stamping world believe that the feed height equals the passline height when the die is open (and with the stock riding on the lifters). This calculates as the feed height at die-chase level plus the lifter height equals the passline height. If the feed height is set parallel to the die lifters, when the die closes the stock check opens to allow the pilots to register the stock. As the die closes to bottom dead center (BDC), the lifter height will push the stock down, and in doing so will pull the stock some distance through the feed. This creates side load on the pilots.

Conversely, if the feed height (or passline height) is set parallel to the die chase when the die closes, and the stock check opens at the point of stripper contact at the lifter height to allow the pilots to register the stock (a must), then as the die closes to BDC the lifter height will push the stock down. In doing so, it will push the extra strip length back through the feed. It has been said that pushing the material back through the feed to the sagging loop between the raw-stock payout and the feed is simple.

So, which is correct?  

My advice: Calculate feed height plus lifter height, in which the face of the lifters sits above the die chase.

For the strip stock to feed efficiently, it must not be obstructed in any way. This means that during feeding, the material should not have to overcome pressure from the lifters pushing the strip up, which causes the strip to bow. The stock should feed perfectly parallel on the tool lifters when the tool is open.  

As the tool closes and the pilots and stripper contact the stock, the feed enters pilot-release mode, a must for the pilots to register the stock accurately prior to stamping at BDC. The concern here is that on especially heavy stock, this places side load on the pilots as they pull the strip stock through the feed. The tool must be designed robustly enough to withstand this. 

This also is important on thin-gauge material. If the feed height is set to the die-chase height and the material gets pushed back, lubricant resistance could cause thin material to stick to the liners between the feed and the tool, or even between the feed rollers. This can accumulate over several cycles, creating waves in the material. However, if the strip is pulled into position, it always will be taut and will not cause progression errors.

With any tool design that incorporates strip-stock lifters, as the tool closes the downward movement of the stock must have somewhere to go. This is achieved with an opening between the feed-stock guide plates and the tool itself. Design this opening just big enough to allow the stock to move up and down to the lifter height and not create a kink in the stock.