bending force requirements (see
•Lubrication of the material is
often recommended. As the material
flows over the die shoulder radii during bending, lubrication helps to
reduce drag, thus reducing the
amount of bending force required. It
also helps to reduce tooling wear and
material surface damage. Lubricants
specifically designed for HSS are
• Preheating the material often is
recommended to reduce the bending
force required and to reduce cracking.
CFIGURE 1 Die shoulder radii should be hardened and very smooth to help to
reduce drag during forming.
• Always bend the material to the
largest radius possible. This will help
to reduce material fatigue and the subsequent cracking that may occur on
the outside of the bend radius.
• Grind out all surface scratches
and all other surface defects, as they
may cause cracks.
•Some HSSs require that all
bends be created in a single stroke.
These materials must not be allowed
to spring back during the stroke. It is
very important for you to verify
whether this is the case with the material you will be forming if your press
brake has automatic springback compensation. Also, the yield strength of
the material has a tremendous influence on the amount of springback
that occurs during bending. The higher the yield strength is, the greater the
amount of springback will be. Be sure
to check the yield strength of the
material with your steel supplier.
•Die shoulder radii should be
hardened and very smooth. This will
help to reduce drag during forming,
which, in turn, will help to reduce the
amount of force required to bend the
material (see Figure 1).
• Dies that use hardened rollers on
the shoulders significantly reduce
Simply put, HSS requires high-quality
tooling that can withstand the great
force generated when bending it.
For example, the tip radius on the
punch and the shoulder radii on the
dies must be hardened and remain
intact. The deeper the hardening zone
is, the better, because any breach of
the hardened area will lead to a rapid
deterioration of the working surfaces,
which will decrease accuracy and
increase tooling costs.
Wear on the die shoulder radii also
increases drag on the material as it
flows over the shoulder radii. This significantly increases the amount of
force required to bend the material.
Angles Allow Overbends. Make
sure the tooling you plan to use has an
included angle on both the punch and
the die that will provide adequate
capacity to overbend the material as
necessary to compensate for springback (see lead image). Because HSSs
often have high yield strengths, the
amount of springback that occurs
probably will be greater than the
springback that occurs when you bend
softer materials such as mild steel and
aluminum. If so, your current tooling
may not be able to compensate for it.
Heavy Tooling Affects Setup.
Setup time is one of the greatest contributors to the cost of bending thick
materials in general. This is caused, in
part, because handling the large,
heavy tooling is difficult. The punches normally have large tip radii and
often are composed of a combination
of a punch holder and a large-radius
insert. The dies normally have large
openings and weigh well in excess of
100 pounds, requiring two or more
operators and possibly a forklift to
load and unload them.
The use of short, modular tooling
segments that match properly when
installed will make tooling changes
faster and safer and, during most
setups, will eliminate the need for
additional personnel and/or forklifts.
Fewer Tool Changes. Of course,
reducing the number of tool changes
or eliminating them altogether is even
better. This is where an adjustable die
Motorized Weld Curtain
• Custom engineered frame & drive unit require
no limit switches
• Maintenance-free gearless direct drive motor
• Motor can be programmed for a variety
• Ideal for robotic welding and equipment cells
THE INDUSTRY LEADER IN FC347 at
PROTECTIVE COVERS. www.ffid.net
A & A Mfg. Co., Inc.
Fax: 262-786-3280 • Sales@Gortite.com
The FABRICATOR | An FMA Publication
March 2007 | www.thefabricator.com