aligned (parallel) with the pressure die
as the tube is being drawn and bent.
How a wiper die lowers the compressive forces during bending
The wiper die keeps the tube aligned with the pressure die, thus preventing the tube from realizing any additional compressive stresses during the bending process.
ues to apply a force on the tube while
the bending process is under way.
Throughout the bending cycle, the
wiper die is critical to supporting the
intrados, or inside bend, of the tube.
Right before the tube experiences a
bending torque, the wiper die goes to
work, preventing the tube from separating from the pressure die. Figure 1
depicts a tube separating from the pressure die without the aid of a wiper die.
This can be most obvious when bending
a soft material such as 3003 aluminum
or copper. The condition usually arises
when the centerline bending radius
approaches the tube’s OD (1D bend).
If the tube heels away significantly
from the pressure die before or during
the bending motion, the tube may
undergo an additional compressive
stress component in the area surrounding the bend tangent. Thus, one goal of
a wiper die is to ensure the tube stays
If you have a grip section in a bend die
opposing the pressure die, and you have
the wiper die on the other side of bend
tangent also opposing the pressure die,
then the pressure die is supported on
both sides (see Figure 2).
A wiper die imparts force on the
tube before and during the bending
motion; this force counteracts the compressive forces within the tube induced
by the bending process.
George Winton, P.E., is the founder
and president of Winton Machine
Co., 470 Satellite Blvd., Suite F,
Suwanee, GA 30024, 888-321-1499,