Roll Forming Line Automation, Part 3: Crop-off Dies
In the previous blog post, we covered the blade cut die design. Crop-off dies, the main alternative to blade cut dies, will be the subject of this post.
Crop-off Die (Slugless Type)
The crop-off die is the design most manufacturers tend to use. When I receive a part to quote, I always try to find a way to cut it slugless first. If I can’t find a way to cut the part slug-less, then I go to a blade-type die.
There are, of course, disadvantages to the crop-off die in certain cases. It is sometimes more difficult to coordinate pre-notching with a slugless cut-off when trying to get radii on the ends or when trying to cut through a pre-notched slot.
The basic action of a crop-off die is a scissor type action; the ingoing blade is stationary and the outgoing blade slides down to close off the die opening to cut off the part. There are many advantages to the crop-off die, and below are a few of them.
Since we just have to close up the die opening to cut, only a short stroke is necessary. We only use at most the bottom 5/8 inches of stroke, and in most cases, only the bottom 1/4 inches. Due to the short stroke, there is very little wear on a crop die compared to other die designs.
On high speed lines running continuously and producing short length parts, the scrap savings from not taking a slug out can be substantial by the end of a year.
The crop die is almost as versatile as a blade-cut die in that different sets of die inserts can be interchanged in a common holder as long as the cut angle is the same.
From the discussion above, you can readily see the reasons for using a crop-off die whenever possible. Only experience can tell you where to draw the line and stick to the conventional blade cut.