FPM related to rim speed?
•Coil material specifications (
tensile and yield strength)
•Forming/drawing speed (FPM
and n specification)
BY DENNIS CATTELL
Q: I was reading your column in the
April issue, “How can I convert SPM
to FPM?” I have done some research
on this topic, and I found a source
that stated that the maximum ram
velocity of any press is 225 feet per
Is this statement true? If true,
where does the math come from?
A formula is:
Flywheel revolutions per minute
(RPM) = strokes per minute (SPM) /
Flywheel rim speed = (Flywheel
RPM / 3. 14 / Diameter of fly-
Cast-iron flywheels have a max.
within the steel manufacturer’s material tolerances.
The lower the slide velocity the better to get good part quality, tolerance,
and accuracy while maintaining the
required volume economically.
I do not know if your formula is
correct, but it is not related to the
conversion of SPM to FPM.
Three types of material are used for
flywheels: cast iron, ductile iron, and
steel. The maximum rim speed is
important to know because above
this speed, the flywheel material
would crack (disintegrate) from centrifugal force.
The flywheel is driven by the main
Your formula is not
related to the conversion
of SPM to FPM.
rim speed of 6,600 FPM
Steel flywheels have a max. rim
speed of 12,000 FPM
Does this formula tie into the
maximum ram velocity of 225
FPM? We do some very deep-draw
materials (up to 12 inches) for the
automotive industry, and because
our presses have up to 1 meter of
stroke, there has been some discussion as to why we cannot run faster.
Some speculation has been raised as
to whether a maximum ram velocity of 225 FPM is to blame.
A: The conversion of SPM to FPM
allows you to see if the press slide
velocity of any mechanical crank- or
eccentric-shaft press at a given speed
exceeds the coil material specifications for drawing or forming of that
specific material. It’s important to stay
electric motor and stores kinetic energy. This energy is distributed through
the clutch to the press drive. For each
press stroke, the energy consumed by
the die is removed from the flywheel
(flywheel slows down). This slowdown cannot exceed 10 to 15 percent, or else the press will jam on the
bottom of the stroke after several
strokes. The electric motor must be
able to restore the energy removed
from the flywheel in the nonworking
part of the next press stroke.
The main criteria and calculations
for press selection are:
•Die space (length, width, and shut
•Die tonnage required to complete
all part stations (tons)
•Die energy consumed for each
press stroke (inch/tons)
Maximum Slide Velocity
However, to answer your question,
the maximum velocity of any press
slide is governed by the total press
mass compared to the inertia developed by the combined weight of the
upper die plus the weight of the slide.
If the inertia exceeds the press mass,
the press will walk around the floor if
it is not bolted down to a very heavy
Special high-speed presses (450 to
2,000 SPM) have a dynamic balancing system (a reciprocating weight
opposing the slide) to counter the
slide inertia force. This system is not
installed on a standard press.
The FMA does offer training courses on this subject.
As far as maximum running
speed, when it comes down to it,
after capacity is out of the way, you
can only run fast enough to form the
steel properly. At the point of impact
when the punch starts to draw the
material, the velocity must be within the coil material specifications;
otherwise it will split.
One way to increase production on
deep draws by up to 25 percent is to
use a link-drive press, or a hydraulic
press, or servo press that can be set to
slow down during the working part
of the stroke during the drawing and
accelerate on the nonworking part of
the press cycle. However, this will
Has a shop floor stamping situation
or tool and die question stumped
you? If so, send your questions to
firstname.lastname@example.org to be
answered by Thomas Vacca, director
of tooling and design engineering at
Micro Stamping Corp., or by industry veteran and press expert Dennis