Dies and Punches F
IG . 4 — M u lt ip le p u n c h a n d d ie a s s e m b ly f o r c o in in g o r
‘ ‘ w in g in g ’ ’ b e a r in g ca g e p o c k e t s t o c o n f o r m to c o n t o u r o f ta p e r e d
r o lls
BY G . A. STUMPF AND F. R. BONTE Steel & Tube Division, Timken Roller Bearing Co., Canton, O.
be held to an absolute minim um and where special toughness is required fo r the service, approxim ately 0.25 per cent o f m olybdenum is added to the specification, this steel being called "G raph-m o” . Prelim inary and final heat treatments depend upon the application fo r which the steels are to be used.
Annealing- Permits Sawing In processing graphitic steel, care m ust be exercised to control graph- itization, fo r once the graphitic pockets are established they are per
manent unless forged together. The degree o f graphitization, however, can be largely controlled by the an
nealing treatment. Consequently, material which is to be forged to shape is w orked from the “ as rolled” condition, where a high per
centage o f com bined carbon exists, in which state it can be hot worked satisfactorily if reasonable care is exercised in keeping the tem pera
ture o f the piece between 1700 and 2000 degrees Fahr. A light anneal
in g treatment m ust be applied to Graph-mo as it com es from the mill b efore it can be sawed, but this treatment is controlled carefully to avoid graphitization.
Material fo r m achining, however, should be normalized and annealed to obtain best results. Thus, billets o f Graph-sil fo r forg in g into dies are shipped in the “ as rolled” con
dition and Graph-mo billets are only
F
IG . 3— M a d e o f g r a p h it ic s te e l c o n t a in in g s ilic o n , t h is d ie is u s e d f o r b la n k in g a n d f o r m in g r o lle r b e a r in g c a g e s f r o m h o t ro lle ds tr ip
August 30, 1937
softened enough to permit cold saw ing. All stock which is to be m a
chined to shape is shipped only after normalizing and annealing, re
gardless o f whether it has been forged to shape or is still in the bar or billet form .
Graphite particles present in graphitic steel after normalizing or annealing are utilized in the final heat treating and hardening proc
esses. When steel o f this type is held at heat above the carbon change point, part o f the graphite is absorbed, but the pockets remain the same. Quenching develops a martensitic structure, the material
reacting in much the same manner as does a eutectold tool steel. This structure is clearly evident in the photom icrograph shown in Fig. 13.
Physical properties o f graphitic steels are closely related to the m icrostructure developed in the m a
terial. This in turn depends on the heat treatment, which controls the amount o f com bined carbon. A typ
ical set o f values is presented in the accom panying table.
Although the exact heat treatment depends upon the service to which a die or punch is to be subjected, sufficient experience now is avail
able to ju stify certain general rules.
These o f course are subject to m odi
fication to meet specific cases, but the follow in g outline fo r the heat treatment o f graphitic steel dies and punches is based on practical
ex-connection with the blanking punch ju st described should be treated in the same m anner except that the hole should be plugged and the punch should be im mersed in the brine ju st past the w orking surface.
Internal diam eter dies such as are used fo r shaping cages, brake drums, etc., also can be quenched in brine from 1550 degrees Fahr., transferred to oil and drawn at 300 degrees, developing a hardness o f 62-63 R ockw ell C. The larger the section, the m ore im portant it is to be sure that ample soaking time at heat is provided.
In innumerable applications fo r blanking or perforating dies and punches, requirements o f long life, sharp edges, w ear resistant faces and freedom from chipping and spalling are essential. Likewise, these dies are com m only used in mass production operations and re
quire frequent replacement, which raises the point o f machinability, fo r the unit cost o f the die, its life be
fore and after red ressin g and the ease with which it can be touched up are im portant factors in the cost o f the finished piece made from the die.
Many such dies are in use in the Tim ken bearing factory. These form erly were made from various types o f die and tool steel, but since the development o f graphitic steel they are all made o f this m a
terial.
Cracks Can Be Prevented Ordinarily Graph-sil dies and punches are quenched in water or brine, but in the case o f draw rings or blanking dies such as are shown in Fig. 9, it is advisable to quench them in oil where the outside di
am eter is less than 4 inches, as they are likely to crack if made too hard. Quenching such a ring in oil from 1600 degrees Fahr. and draw
ing it at 300 degrees fo r 4 hours per inch o f section will develop a hard
ness o f 58-60 R ockw ell C. where larger rings are concerned, the greater mass o f metal permits such units to be quenched in water from 1550 degrees Fahr., cooled in oil and then drawn at 400 degrees, fo r a hardness o f approxim ately 60 R ock well C. W henever water is used fo r quenching, care should be exercised not to keep the ring in the tank too long, transferring it to the oil bath fo r cooling ju st as soon as the proper quenching action has been secured.
Graph-sil requires som e care in quenching, but the tough nonw arp
ing Graph-mo has proved to be easy to handle fo r dies and punches. The blanking punch shown in Fig. 1, fo r example, was made from Graph- mo, quenched in circulating oil from 1475 degrees Fahr. and then drawn at 300 degrees. This treat
X T E E L perience over a considerable period
o f time and in a num ber o f plants.
As a general rule, blanking and form in g dies or punches made from Graph-sil, or w a t e r hardening graphitic steel, should be quenched in water or brine from 1550 degrees Fahr. and drawn at 300 degrees.
The blanking punch shown in Fig.
3 is a typical exam ple o f the punches made in a wide range o f sizes for blanking and form in g Tim ken bear
ing cages from hot rolled and pick- led strip steel. Punches o f this na
ture have been used on material up to %-inch thick with uniform ly good results. The unit shown was heated to 1550 degrees Fahr., held at heat fo r 1 hour per inch o f sec
tion and then quenched in brine maintained at approxim ately 80 de
grees Fahr. It was then drawn at 300 degrees, giving a file hard sur
face o f 63 Rockw ell C.
Quenching Perform ed Carefully Such a punch should be quenched to a depth just below the first un
dercut and held in the brine until it reaches a tem perature o f 300 to 400 degrees Fahr., after which it m ay be dropped in oil fo r the final cooling. The length o f time such a punch should be held in the quench
ing bath depends o f course upon the section, but any good hardener can gage his quenching time by the rate at which the piece dries when raised out o f the brine.
Experience shows that when w orking with graphitic steel the die or punch should be held at heat fo r at least 1 hour per inch o f section before quenching and that the draw
ing operation should provide at least 4 hours at heat per inch o f section.
Tim e at heat is particularly im portant in both instances and any attempt to reduce the minim um here stated gives unsatisfactory results.
Internal diameter punches used in
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IG . 5 (to p )— P e r fo r a t in g d ie u s e d f o r m a k in g s ta n d a r d ta p e r e d r o lle r b e a r in g ca g e s . F ig . 6 (cen ter)— A n o t h e r p e r fo r a t in g d ie a n d p u n c h e s e m p lo y e d in p r o d u c in g ca g e s f o r fla t -t y p e t h r u s t b e a rin g s . F ig . 7 (b o t t o m ) — S iz in g d ies s u c h as th is o p e r a t e u n d e r h ig h p ressu re, th e r e fo r e m u s t b e h a r d a n d
t o u g h
ment produced a file hard punch, the w orking face being 63-64 R ock well C. W ith this nonw arping steel it is seldom necessary to use spe
cial quenching fixtures, drop quench
ing being ordinarily all that is needed.
Sizing dies such as the one shown in Fig. 7 operate under high pres
sure and it is essential that the working surface be exceedingly hard while the body o f the die is tough.
Consequently, t h e y should be quenched on a fixture, any bolt holes being plugged with asbestos and the sides protected. F or small dies best results will be secured by concen
trating the flow o f coolant through the hole in the die. On large dies it is necessary to quench the whole die under a fountain. In either case, the w orking surface should be file hard, tests show ing that by quench
ing from 1550 degrees Fahr. into brine and drawing at 300 degrees a hardness o f 63 R ockw ell C is de
veloped. Soaking and drawing times should be based on the same sched
ule as previously listed.
Operated at High Speed P erforating units used in multiple dies at the Timken plant fo r per
forating the pockets in bearing cages are made o f Graph-mo. These punches, which are used on strip steel up to 3/16-inch thick, are given constant high speed service. The graphitic steel parts, after having been machined and ground to size and shape are heated to 1475 de
grees Fahr., held at heat fo r 1 hour per inch o f section and quenched in circulating oil. F ollow ing the quench they are drawn at 700 degrees, hold
ing them at heat fo r 4 hours per inch o f section to assure uniform ity o f structure throughout. This treat
ment develops a surface hardness o f 52-54 R ockw ell C, which, while not file hard, has been found to give the m ost satisfactory results in service. Fig. 6 shows a die used for perforating the flat cages used in thrust bearings and Fig. 5 shows another perforating die used for m aking cages fo r the standard type Timken bearings. The same treat
ment is used on internal diameter dies.
Multiple punches such as those shown in Fig. 4 are used in the T im ken bearing factory fo r coining or
“ w inging” the edges o f cage pock
ets to con form to the contour o f the rolls. As cages are made from strip steel up to 3/16-inch thick, the die wings and punches must be file hard and withstand both heavy pres
sure and shock, retaining their sharp edges and sm ooth faces dur
ing long production runs. E xperi
ence shows that fo r dies and punches subject to service o f this nature the oil hardening Graph-mo gives excellent results when quench
August 30, 1937
ed from 1475 degrees Fahr., and drawn at 300 degrees to a hardness o f 63-64 Rockw ell C. A t least 4 hours at heat should be allowed per inch o f section in drawing Graph- mo coining dies and punches.
Higher Center Pin Life The center pins used fo r operat
ing the multiple perforating or w inging (coining) punches do not need to be as hard as the punches, but must be extrem ely tough and wear resistant, as any inequality on the operating face will affect the coined surface. Many times the form er life o f center pins has been secured in the Timken plant by using Graph-mo fo r these parts.
High fatigue strength is obtained with good wear resistance by quenching pins o f this nature from 1450 degrees Fahr. in oil and draw
ing them fo r 4 hours per inch o f section at 600 degrees, giving a hard
ness o f 55-57 Rockw ell C.
Closure dies such as the one shown in Fig. 8 may be made from either Graph-sil or Graph-mo, de
pending upon service desired. When Graph-sil is used, heat treatment is the same as that given fo r sizing dies. If Graph-mo is used, the steel is quenched from 1475 degrees Fahr.
and drawn at 300 degrees fo r 4 hours per inch o f section.
Heavy-duty coining punches re
quire a high drawing temperature, fo r toughness and freedom from chipping are essential. Graph-sil has been used at the Tim ken plant fo r coining V-inch strip (S.A.E. 1015 steel) with most satisfactory re
sults. The largest punch thus fa r used fo r this purpose has an out
side diameter o f 2% inches. It was held at 1550 degrees Fahr. fo r 2 hours, quenched in brine at 80 de
grees to a depth o f 1 inches, cooled in oil and then drawn at 650 degrees fo r 8 hours, show ing a
F
IG . 8 (top) — A t y p ic a l s m a ll c l o s u re d ie . F ig . 9 (cen ter) — D ra w r in g o r b la n k in g d ie o f g r a p h it ic s te e l c o n ta in in g s ilic o n . F ig.10 (b o t to m ) — T h e g r a p h it ic s teel ca g e d r a w in g d ie a t th e r ig h t m a d e 309,000 p ie c e s ; th e f o r m e r die a t th e le ft, 10,000 p ie c e s. T h e p r o d u c t o f e a ch d ie a ls o is
s h o w n
r .fi:
ameter. The sm ooth, wear-resistant surface, free from pick-up or scor
ing, which features graphitic steel makes it particularly suitable fo r stainless steel. As graphitic steel responds quite readily to selective quenching, fixtures and plugs may be em ployed to good advantage in quenching form in g dies which are made from it.
W here the hole in the die is under 5i-inch diameter, experience shows that it should be quenched from 1500 degrees Fahr. L arger dies should be quenched from 1550 degrees, all sizes being quenched in brine at approxim ately 80 degrees and trans
ferred to oil fo r cooling. Tests show is finish machined, including thread
ing the holes, before hardening, character, the heat treatment con
sists o f quenching in circulating oil quenching water should be directed through the hole or into the pocket, the outside o f the die being protected when necessary. The hardness de
veloped depends on the drawing temperature, increasing as the draw ing tem perature is reduced.
cations and today practically every die used in cage m anufacture at the