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,74 Forging - S tamping - Heat Treating
Five Arm Stripper Piece
It is not often that one comes across a forging as
illustrated in Fig. 1, and in connection with the manufacture
of such a component the lay mind would conjure
up a vision of the malleable casting process.
Upon noticing the span of the arms—14 in. diameter
circle—the reader may be surprised to know that the
specified weight of the whole of the stripper piece
must be under five pounds. The weight of a finished
forging is usually a guide to the estimator as to the
price to be charged, because it is principally by experience
of work done on the basis of a fixed amount
per pound of metal used, taking into account also the
simplicity- or complexity of the forging operation, that
the price can be correctly estimated. Some forgings
come under and others over the average, and the component
now under review certainly comes in the category
of being well above the average. Four arms
Fig. I
Section on Line EE
Looking From Direction of Arrow
Section at Aft
Fig5
Showing the method of forging a five arm stripper piece.
would have presented a much simpler problem, and
the method of forging was not decided upon until
several others had been tried.
Fig. 4 gives an idea of the lightness of the arms,
and the enlarged section at AA gives the shape. It
will also be noticed that the ends of the arms are at
right angles to the arms, which greatly increases the
cost of forging.
Two pairs of dies are used. The first pair, Fig. 2,
form the center of the forging only. The material
specified is a good grade of iron, and this was a big
factor in determining the method of forging.
October. i9l5
Pieces B and C, Fig. 3, (both of circular material)
are bent to shape as shown, heated to a welding temperature
and lightly welded together, after which
they are returned to the fire. Piece D, Fig. 5, formed
from the bar, is heated at the same time as B and C,
after which all the pieces are placed in dies as illustrated
in Fig. 2, and welded with several sharp blows
under a steam hammer, which makes a good sound
job and very little flash.
The section of arm in die, Fig. 2, is of the same
diameter as the material used, so that the center boss
only is worked upon in this operation. Each arm is
cut cold under the shear to a length gauge from the
center, thus ensuring uniformity.
The final forging dies are shown in Fig. 1. No tag
way is necessary^ as the forging is laid in the dies
direct. For heating, an enclosed type oil-fired furnace
with sliding doors is used. When hot the end of each
arm has to be flattened and set on one side with the
same blow, this operation being necessary because
the ends do not form at all well when forged in any
other way. The stripper is then placed in dies and
given a printing blow, returned to the furnace and
brought to a good heat, finished off with three or
four good blows, the flash being quickly removed and
the forging set in dies. Special care has to be taken
in handling the component after it has been printed
in the dies because the slightest touch on the furnacesides
would Nickel move in an High-Speed arm, and this Tool would Steel* have to be
put An back attempt again is in usually its place made or the to forging avoid the scrapped. introduction
of nickel into high-speed tool steels, although
cobalt, which is chemically very similar to nickel, is
generally considered a useful addition to such steels.
This is just the reverse of the situation found in alloysteels
for automotive use, for example, in which
nickel plays a useful role, while cobalt is not used.
Some high-speed tool steels contain small amounts
of nickel coming from the melting stock used. It is
increasingly difficult to secure melting stock free from
nickel, because of the use of scrap in blast furnaces
and in steel-making processes. With the prevalence
of alley steel in present-day industrial uses, any lot of
scrap is almost certain to contain some nickel steel.
The performance in taking roughing cuts of highspeed
tool steels made up in the laboratory, to which
relatively large amounts of nickel were intentionally
added was studied at the bureau. Three and a half
per cent nickel in the low tungsten or high tungsten
types of high-speed steel was found to have no injurious
effect upon the life of the tool. With the normal
carbon content, however, the machining qualities of
the annealed steel were adversely affected, the steels
being almost impossible to machine. Tools formed
by grinding gave good performance.
By i educing the carbon content from 0.7 to 0.5
per cent the steel which contained 3.5 per cent of
nickel could be machined and showed normal performance
m toughing cuts. These experiments indicate
that small amounts of nickel in a high-speed tool steel
the carbon content of which is properly regulated
should exert no deleterious effect.
This work was a part of the study of the effect of
nickel, cobalt, tantalum, and molybedenum in highePeed
•From Technical t0Dl steel, News which Bulletin, will Bureau soon of be Standards.
published in full.