Since the cut blank will be retained in the die block by friction , some means of ejecting on the ram upstroke
must be provided . A knockout assembly consists of a plate , a push rod , and a retaining collar . The plate is
a loose fit with the die opening contour , and moves upward as the blank is cut . Attached to the plate , usually
by rivets , is a heavy push rod which slides in a hole in the shank of the die set . This rod projects above the
shank , and a collar retains and limits the stroke of the assembly . Near the upper limit of the ram stroke , a
knockout bar in the press will contact the push rod and eject the blank .
It is essential that the means of retaining the knockout assembly be secure , since serious damage would otherwise occur.
In the ejection of parts , positive knockouts offer the following advantages over spring strippers where the part
shape and the die selections allow their use:
1. Automatic part disposal . The blank , ejected near the top of the ram stroke can be blown to the back of the
press , or the press may be inclined and the same result obtained .
2. Lower die cost . Knockouts are generally of lower cost than spring strippers.
3. Positive action . Knockouts do not stick as spring strippers occasionally do.
4. Lower pressure requirements . There are no heavy springs to be compressed during the ram descent.