| Solving
Slug Pulling with Slug Free® Die
by
Frank Baeumler
Vice President – Marketing
Mate Precision Tooling
Usually
in this column I write about the newest items being developed.
However, when an idea proves itself to be remarkably successful,
and withstands the test of time, it deserves mention. In
this issue, I address the solution to the age-old problem
of slug pulling and a very successful Mate product, the Slug
Free® die.
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|
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Slug
Free® Die Components
 1.
Punch
2.
Stripper
3.
Material
4.
Slug Free® Die
5.
Slug
6.
Grind Life
7.
Entry – Constricting
Taper
8.
Pressure Point
9.
Exit – Relief
Taper
Hole/Slug
Geometry
A.
Rollover
B.
Burnish
C.
Fracture
D.
Burr |
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Control
of the slug generated by the punching cycle has been
an issue since the first slug was created. Various die
design
solutions have been tried. One die design solution has
proven itself in the past two decades as being reliable
in both
standard and extreme applications. Mate has pioneered the
use of the Slug Free die design and uses it as a standard
in nearly all of its product lines.
By definition, slug pulling is the condition where the
slug returns to the top of the sheet during the return portion
of the punching cycle and then comes between the punch
and the top of the sheet on the next cycle(s) causing damage
to the piece part and the tooling.
A quick word on the objective and philosophy behind the Slug
Free die. The objective is that the slug must not be allowed
to interfere with subsequent punching cycles. The best counter
to this possible event is for the slug to pass through the
die and on down into the slug shoot with each cycle so it
never has the chance to end up on the top of the work piece.
The philosophy is for the slug to be cleared from the die
with each stroke of the punch. The Mate Slug Free die is
the product that we produce that meets this objective and
philosophy.
The design of the Slug Free die is simple and effective.
Essentially, the die is made with an opening that has a “one
way door” so that the slug cannot return once it
passes through the door.
To create a one-way door, Mate uses sophisticated manufacturing
techniques and equipment to produce a double taper opening geometry on the
interior of the die
opening, It looks a bit like an hour glass. The first taper and the second
taper are in opposite directions causing a constriction point. This constriction
point
is overcome during the punching cycle with the force of the ram, but acts
like a one-way door to prevent the slug from following
the punch during the return
portion of the cycle.
The
constriction point is the key. The entry taper angle
that is actually created in manufacturing the die is
about one
half a degree.
The exit taper angle is
considerably more and does vary by tooling style. The constriction point
causes the slug to be separated from the punch as the punch returns for the
next cycle.
Once the slug is separated from the punch, it is free
to fall away from the punching area. The importance of clearing the slug
with each cycle can hardly be over
stated.
The challenge of clearing the slug with each cycle changes
with the application. For instance, if the application calls for full hits, where
the slug takes the
complete shape of the punch, the entire perimeter of the slug is in contact
with the constriction point all the way around the slug.
However, if the application calls for partial hits, a
nibbling or a slitting application for example, the slug has only part of
its perimeter in contact with
the constriction point.
In either case, the slug is separated from the punch
with the action of the one-way door because the Slug Free die constriction is
uninterrupted throughout the entire
interior of the die hole.
 |
 |
 |
 |
Material
held
securely by
stripper before
punch makes
contact. |
Punch
penetrates
the material. Slug
fractures away
from sheet. |
Pressure
point
constricts slug.
Punch stroke
bottoms out as
slug squeezes
past pressure
point. |
Punch
retracts
and slug is free
to fall down and away through
exit taper. |
|
The
progressive images shown here illustrate the sequence
of events during the punching cycle. The key to the success of the Slug
Free die is that the slug
is cleared from the die with each cycle.
The Slug Free die design details are well published,
time tested, and customer proven. Piece part quality and sheet utility
are improved when using the Slug
Free die. Damage to piece parts and to tooling as a result of slug pulling
is eliminated and user satisfaction is assured. Finn-Power punch press
owners all
over the world know this to be true.
For more information, please contact:
Mate Precision Tooling
1295 Lund Boulevard
Anoka, MN 55303
Phone: 800-328-4492
Phone: 763-421-0230
Fax: 800-541-0285
Fax: 763-421-0285
www.matept.com
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710
Remington Road 
Volume
13 Issue 1 -
July 2003