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LAURENCE CLAUS HOT FORGING FASTENERS from page 154
the tool or by the press opening. This makes them good
choices for nuts, short bolts, forming a recess, and for
other short complicated shapes. Unfortunately it is not
a good choice for long parts.
FIGURE 7: EXAMPLE OF HOT FORMING ON HORIZONTAL PRESS
FIGURE 5: PARTS COOLING AFTER FORMING
Often the forming process requires at least two
strikes so that either the part is moved by the operator
from one die to another or the machine can reposition
tooling to strike the part a second time in the same
cycle. The formed part is either ejected or removed by
the operator and placed in a bin or tub to cool down
before moving to the next operation (Figure 5).
Vertical presses can usually apply greater force to the
part (Figure 6). The biggest drawback to a vertical press
is the limited length of part that can be accommodated in
FIGURE 6: EXAMPLE OF HOT FORMING ON VERTICAL PRESS
Horizontal presses make easier candidates for
automated or semi-automated feeding and especially
for long or very heavy parts. In a horizontal press the
tool is a clam shell configuration and closes around the
cylindrical blank (Figure 7). A punch comes in and strikes
the part forming the head (often a hex or carriage bolt
shape). These machines often strike the part twice, with
the second strike creating head markings.
One of the drawbacks of the clamshell die
configuration used on horizontal presses is that parts
often exhibit a die seam just under the head (Figure 8).
This represents where the die was not held perfectly
closed during the forming process. All of the pressure
exerted against the die opens it just a little bit and a
small amount of material flashes in-between. When the
condition is minimal it may just be ignored. If, however,
it is severe it could interfere with the application
clearance hole preventing the part from sitting flat.
This opens a critical joint to all sorts of vulnerabilities
and is not considered good practice. As a result, some
manufacturers machine underneath the head to clean
these discontinuities up. Since vertical press dies do not
split open, this is not a problem characteristic to them.
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