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June, 1925
Fbrging-Stamping - Heat Treating
P o w e r P r e s s e s — T h e i r U s e in I n d u s t r y
For Duplicate Production of Metal Parts in Large Quantities
There Are Few if Any General Types of Tools Which
T H E demand for reduced labor costs, production
in large quantities, economy in material and a
uniform product is responsible for the rapid
growth of the press industry and its continual expansion
into new fields. For duplicate production of
metal parts in large quantities there are few if any
general types of tools which can compare with power
presses. Their infinitely varied possibilities have
necessitated an almost equal variety in the tools developed
to perform operations, which in many cases,
have become quite complex. Necessarily this rapid
expansion of the art has only been made possible by
the efforts of a great many men in widely different
lines.
Many parts previously made from castings or
drop forgings and finished up by machining, are now
made far more economically, and also better, in power
presses. Many parts could not be produced at a reasonable
price except in power presses. Even greater
development is ahead as the engineers and designers
of articles produced in quantity, become more familiar
with the old and the new methods of press production.
The impetus given to the automotive industry by
the application of power presses is classic. Blanking
and drawing, forming or stretching methods are now
employed to produce heavy side rails and cross frame
members, cowl, body and door parts, crank-cases,
fenders, hubs, axle housings (even for the heaviest
trucks), disc wheels, radiator shells and brake drums.
Hot forming and press forging methods are being
used on step hangers, pinion blanks, trim hardware,
valve heads and miscellaneous small forged parts. Instead
of milling the faces of connections, levers and
the like, many are now using knuckle joint type of
presses to squeeze the cleaned forgings accurately
to size. Caps, lamps, tanks, bushings, covers and
many small electrical parts are also press produced and
all this work is done at rates of a thousand to fifty
thousand or more pieces per day.
The case of the automotive industry is cited to give
an idea of the variety and extent of press usage in one
industry. A similar story might be told about the
production of adding machines, typewriters, vending
machines, locks, all sorts of electrical products, metal
furniture, kitchenware, metal packages, miscellaneous
hardware, metal lath, tractors and endless variety of
manufacturing industries. Some firms have developed
one particular operation to a very high degree and
reduced the designing of the dies involved to a mere
matter of form. In so doing they frequently lose track
of other press methods and of the new processes continually
being worked out in other lines.
The different basic methods by which metals can
be press worked may be classified generally according
•Paper presented before the Providence Engineering
Society.
tStaff Engineer, E. W. Bliss Company, Brooklyn, N. Y.
Compare Favorably with Power Presses
By E. V. CRANEf
213
to whether the principal stress they create in the metal
is shearing, tensile or compressive. There are, of
course, processes in which more than one direct stress
enters, and also processes in which simple operations,
such as blank cutting and forming, are combined and
performed simultaneously in one set of tools.
Work which puts the metal in shear includes cutoff,
blank cutting, repunching and piercing or hole
punching operations, all of which are subject to about
the same general rules. For ordinary purposes, to
save unduly frequent regrinding, clearance should be
allowed between the cutting edges where they pass,
amounting to about a tenth of thickness of the stock
for brass and soft steel, and up to an eighth for hard
steel.
To reduce the shock on the tools and strain on
the press, the tools are usually sheared, that is faced
at an angle so that the cutting is not all done at once.
This shear deforms the metal somewhat and accordingly
when cutting blanks the punch should be flat
and the shear should be on the die so that the scrap
will be deformed. For the same reason, in punching
out holes the die should be flat and the shear should
be on the punch.
Below the cutting edge the die should be opened
out at an angle of about 2 deg. for a short distance and
then allowed greater clearance so that slugs or blanks
pushed through will not stick or clog. It is well on
medium size blank cutting dies to provide pilot pins
to guide the punch holder and on very delicate work
to use a special press construction in which the die
and punch are practicallyr a unit independent of the
guidance of the press slide.
Multiple punching and perforating dies are modifications
of hole punching dies, being a collection of
a number of punches arranged in a line or in several
lines as the cast may be. The punches are frequently
flat faced and shear is obtained by stopping
the punches so that some enter ahead of others. As a
punch has to penetrate the metal only about %-in. or
1/3-in. of its thickness to effect shearing, this amount
is usually sufficient for each step. In arranging a line
of punches it is well to have the longest punch, that
is the one that will enter first, in the center. There
is a certain amount of spreading action in the material
evidenced by the bulge or distortion in perforated
stock, which tends to spread and shear or break the
punches when they all enter together, or when the
outer ones enter first. To stand up properly the
punches should be as short and stubby as possible.
Cam actuated strippers which fit the punches and
which move with the slide of the press until they
reach the stock are very useful both in holding the
stock flat on light material and in guiding punches and
permitting the use of short ones.
Another class of shearing operations include the
trimming of shells, blanks and forgings. For the trim-