Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
7~73
In the conventional manufacture of steel castings con-
siderable hand work must be done on the rough casting before it
is considered a "finished" product. It is conventlonal to sever
the gates of ~he sprues and risers, wherever they are located,
as well as any partin~ line fins, by use of a cutting torch or,
if the projections are of narrow section, by a chipping hammer.
In some cases the projections are knocked off with a sledge.
Vsing such procedures, a considerable amount of finish grinding
is required to produce a smooth and flush surface. Since war-
page may occur in a casting as it cools, the cold casting mayhave to be "straightened" to bend it back into the desired shape.
Such a straightening operation is difficult and time consuming,
and imprecise at best, because of the "spring back" of the cold
metal. Cold straightening may also induce undesirable stresses
in the casting. It is, moreover, a difficult matter to form
holes of proper size and location in a cold casting.
Also it is found that "cold finishing" operations,
particularly such gross operations as sledging, can seriously
affect the integrity of the piece by reason of breakage and
formation of cracks.
As a result, where the shape and dimensions of a piece
are critical, and where a high degree of reliability and
integrity are required, it has been necessary to resort to
forging the piece from a billet in a pair of forging dies and
then machining the piece to si~e or to fabricate the desired
final piece by welding or otherwise joining together two or
i more pieces which may be castings, forgings or pieces cut to
~`~ size. It is well known that forging followed by machining
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exceeds the c08t of an equivalent unmachined casting, partly
because of the high cost and relatively short life of the
forging dies. For pieces of intricate design forging is
generally impractical and often impoæsible. Fabrications, on
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the other hand, are time consuming and expensive to make.
This invention relates to a method of making a finished
steel casting having lateral surfaces as well as upwardly and
downwardly facing surfaces, which comprises: forming a pattern
in which gates extend laterally away from the lateral surfaces
and ]ie in the region of the mold parting line and in which the
upwardly and downwardly presented surfaces are free of extraneous
protuberances in the form of gates or the like, preparing a mold
using the pattern, pouring molten steel therein, permitting the
casting thus formed to cool to produce a nonhomogeneous as-cast
grain structure, reheating the casting to a plas~.ic state above
the upper critical temperature and holding it there a sufficient
length of time for homogenization so that the as-cast grain
structure is converted into a homogeneous austenitic structure,
then, while the casting is still in a plastic state and near the
holding temperature, placing the casting in a set of dies having
cooperating shearing edges located at the lateral surfaces, and
then bringing the dies together for shearing off ~he gates as
well as any parting line fins which may have been formed in the
casting step flush with the lateral surfaces, and finally permit-
. ting the casting to cool at a controlled rate.
! It is, accordingly, an object of the present invention
to provlde
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a method of making a steel casting in which the resultant casting is highly
aceurate in shape and dimension as well as structurally sound and reliable,
while avoiding the high labor cost and other disadvantages normally associated
with cold finishing.
It is another object of the present invention to provide a method
of making a casting which produces a part which is equal, or superior, to a
part produced by forging and which may be manufactured at a lower cost
; than the latter and which may be produced on a high volume basis.
It is a related objeet to provide a method of making finished
eastings which are inherently difficult or uneconomieal to make using con-
ventional easting or forging techniques~ Examples of such castings include
those having a demensioned internal cavity or those lacking in draft so as
to require speeial coring. Although a pieee having a eavity or laek of
draft may be produeed by ~orging, it is often neeessary to resort to extreme
pressure to seeure flow of the metal under the forging dies resulting in
exeessive die wear.
It is a further ob`jeet to provide an improved method of produeing
a easting in whieh gates and parting line fins are trimmed and in which the
part is given an aeeurate form and dimension while it is in a hot plastie
state at a uniform temperature whieh is in the region of the eritieal tem-
perature.
It is a more speeifie objeet of the invention to provide a method
for produeing a steel easting in whieh the easting is allowed to eool to a
temperature at or below solidifieation and is then reheated to a holding
temperature above the upper eritieal temperature for "homogenization",
that iSg eonversion of the structure from the nonhomogeneous l'as east" to
the austenitie form and in whieh the easting is subjeeted, while still in the
region of the homogenizing temperature, to the aetion of a set of dies hav-
ing eooperating shearing edges for shearing off gate and riser eonneetions,
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as well as any parting line fins ~ormed i~ ~he casting step, while subjecting
the upwardly and downwardly facing surfaces of the casting to a precise
forming operation.
It is a still further object o~ the invention, in one of its as-
pects, to provide a method and apparatus for trimming of unwanted lateral
projections from a workpiece when in a hot plastic state and in which the
trimming dies have associated upper and lower die surfaces for engaging and
plastically forming to shape and dimension only the most significant ones
of the presented upper and lower surfaces of a complex workpiece, a work-
piece which it might be considered impractical to make as a forging~
It is a related object to provide a procedure for making a casting
~ which employs a set of dies for acting upon the casting in the plastic state
: incident to holding it at a temperature for homogenizing purposes which is
lower than normal forging temperatures and thereby results in substantially
less wear and tear upon ~he dies than is encountered in conventional -forging
operations with resulting increase in the life of the dies and a sharp low-
ering o~ the per unit cost.
Other objects and advantages of the invention will become apparent
upon reading the attached detailed description and upon reference to the
drawings in which:
Figure 1 is a top view showing a cluster of four castings utilized
in the present invention;
Figure 2 is a fragmentary vertical section looking along the line
2-2 in ~lgure 1;
Figure 3 is a fragmentary vertical section looking along the line
3-3 in Figure 1;
Figure 4 is a fragmentary vertical section looking along the line
4-4 in Figure 1 and taken through the central sp.rue;
Figure 5 is a time-temperature plot showing reheating and holding
i'3~
above the critical temperature for the purpose o~ bringing about homogeni-
zation and showing the region of the finishing step;
Figure 6 is a phase diagram for carbon steel corresponding to
Figure 5;
Figure 7 is a vertical section taken through a set of finishing
dies utilized in the present invention taken along line 7-7 in Figure 8;
Figure 7a, which appears on the second sheet of drawings, is a
schematic diagram showing the press arrangement;
Figure 8 is a vertical fragmentary section taken along line 8-8
in Figure 7;
Figure 9 is a section corresponding to Figure 8 with the dies
closed;
Figure 10 is a horizontal fragmentary section taken along line
10-10 in Figure 9;
Figure 11 is a perspective view of a .finished workpiece;
Figure 12 is a table listing e~emplary method steps;
Figure 13 is a vertical section corresponding to Figure 8 with the
dies modified for punching;
Figure 1~ is a section corresponding to Figure 13 with the dies
closed;
Figure 15 is a vertical section corresponding to Figure 8 with the
dies modified for coining to size;
Figure 16 is a section corresponding to Figure 15 with the dies
closed;
Figures 17~ 18 and 19 are top, front and side views showing a
transitional casting utili3ed in the present invention;
Figure 20 is a cross sectional diagram showing the transitional
casting interposed between a pair of dies and with a sizing mandrel in
position;
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Figure 21 shows the dies in closed position accompanied by defor-
mation of the casting to final shape; and
~ igures 22, 23 and 24 are top, front and side views of the finished
casting, Figure 22 appearing on the second to last sheet o~ drawings;
While the invention has been described in connection with certain
preferred embodiments, it will be understood that we do not intend to be
limited to the particular embodiments shown but intend, on the contrary,
to cover the various, alternative and equivalent forms of the invention in-
cluded within the spirit and scope of the appended claims.
; 10 Turning now to the drawings and particularly to Figures 1 - ~,
there is shown a composite, or "cluster", sand casting 10 which includes
four individual castings 11~ 12, 13 and 14, cast in the same mold. In the
casting step molten metal is poured through a sprue 15 with the metal dividing
and ~lowing through horizontal runners 16, 17 (Figure 4)~ In the design
of the composite casting six risers are utilized as indicated at 21 - 26,
the risers being eonnected to the castings by gates 21a - 26a and 22b, 25b,
respectively.
The term "gate" will be used in this description as meaning both
the channel connecting the sprues, runners or risers to the workpiece through
whieh molten metal ~lows and the solid metal formation whieh ~orms in this
ehannel upon solidification of the molten metal.
Figures t - 4 of the drawings serve a double purpose. They illust-
rate a typieal easting eluster utilized in practicing the present invention
but they also lllustrate the pattern which is utilized in making the mold
in which the casting is produced. Since the finished workpieee, illustrated
in Figure 11, is o~ hollow construetion, it is necessary to use a eentral
core in each of the patterns. The core elements are indicated at 27. The
~ .
flask which is used in making the casting has not been illustrated, nor is
thFre any~need ta do so sinee sueh flask is entirely eonventional. It will,
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however, be understood that the mold, of which the lower portion M has been
shown, has a parting line which has been indicated at PL in Figures 2, 3
and 4.
In accordance with the present invention, each of the individual
castings 11 - 14 has lateral surfaces, which lateral surfaces have been in-
dicated by letter subscripts, for example, the casting or workpiece 11 has
lateral surfaces lla - 1ld. In addition, the castings have upwardly an~
downwardly facing surfaces, these being indicated by corresponding numerals
with subscripts e - 1 (see Figures 2 and 3).
In carrying out the present in-vention, the gates are so located as
to extend laterally away from the lateral surfaces of each casting, and,
moreover, gates are positioned to lie in the region of the mold parting line
PL. Forming a pattern in which the gates extend laterally away from the
lateral surfaces of the casting and lie in the region of the mold parting
line, and in which the upwardly and downwardly presented surfaces are free
of extraneous protuberances in the form of gates or the like, while known
per se~. constitutes the first element, or step, of our improved method of
making castings, which element or step has been designated as A in Figure 12.
Following preparation of the pattern, the pattern i9 used for
making a mold, usi.ng ordinary molding techni~ues, and into which molten steel
`~ is poured through a central sprue (see 15 in Figure 4) in accordance with
method steps ~ and C . The molten metal flows into all portions of the mold
cavity including the risers 21 - 26. The risers serve the conventional :
purpose of feeding molten metal, through the respective gates, to the ~rork-
~ piece cavities in order to replenish the metal in such cavities and thus
compensate for the contraction ~ the ~1 which occurs as the molten metal
. begins to cool.
When it is poured the molten metal may, for example, be on the order
of 3000 F. As shown in Figure 5, the metal is allowed to cool, step D, and
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the temperature drops on the descending curve, as indicated at 30, to a
temperature at which point the metal has solidified to form a casting. At
any time after the casting has cooled sufficiently to solidify, it is re-
moved from the mold using conventional techniques, for example, by "shaking
out". Sand particles adhering to the casting may be removed by shot blasting
or the like.
The cooled casting in the as-cast condition will be found to have
a random, non-uniform grain structure characterized by one or more of the
following: a dendritic macroscopic structure, a Widmanstatten microscopic
structure, and a network-type, cellular or globular microscopic structure.
This nonhomogeneous grain structure is responsible for the poor mechanical
properties of the casting (e.g. brittleness, internal stresses, poor impact
properties, etc.) in the as-cast condition. Accordingly, it has become
customary to effect a refinement or homogeni7ation of the grain structure
and hence improve the mechanical properties, by heat-treating the casting.
Heat-treating processes involve a heating cycle during which the
casting is heated to a holding temperature above the critical or transforma-
tion temperature at which the casting is maintained for a holding period
during which refinement of the grain structure is effected by conversion o~
the characteristic as-cast structures mentioned above into homogeneous
austenite. Heating and holding are followed by controlled cooling during
which the austenite is transformed into a uniform structure consisting of
one or more of several transformation products which are desired from the
standpoint of strength, hardness, or machineability. The characteristics
of the product formed on cooling are dependent on the cooling rate~ Heat-
treatment processes are generally classi~ied according to the manner in which
and the rate at which a casting is cooled. If the casting is allowed to cool
in still air at a moderate rate the process is called "normalizing". A slow
rate o~ contralled cooling such as in a furnace or the like is referred to
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as ~annealing", an~ a rapid cooling by quenching in air, oil, water, or brine
is called "hardening" or "quenching". It should also be understood that
two or more of these he~t-treating techniques may be per~ormed sequentially
: and that the present invention includes the use of sequential heat-treating.
The metallurgy of steel castings has given rise to a highly tech-
nical vocabulary for communicating fine distinctions in crystalline struc-
ture. However, for purposes of this disclosure it is not necessary to ex-
plore the metallurgy in much detail or to enumerate all the crystalline
structures encountered in dif~erent steel alloys at different temperatures,
but it is sufficient to understand that given a particular steel alloy and
given the desired mechanical properties of the casting one can, through the
science of metallurg~, determine values for the heating rate, the holding
*emperature, the holding period~ and the cooling rate; all of which affect
the crystalline structure and hence determine the mechanical properties of
the casting. Therefore, in the following discussion, in order to simpli~y
: the description of the present invention, it will be assumed that the casting
consists of carbon steel having a typical carbon content of 0O3% as shown
in the phase diagram of Figure 6. However, phase diagrams similar to that
of Figure 6 exist for all alloy steels so that the present invention is
not limited to carbon steel but includes all steel alloys.
In carrying out step E of the present invention, the casting is
reheated at the desired rate along a reheat line 32 (Figure 5) traversing
the "upper critical" temperature TC at point 33, defined as the lower boundary
of the austenite region (see Figure 6), and proceeding to an elevated holding
temperature 34 which may, for example, be 100 F. above the upper critical
temperature. The piece is held at such temperature for a sufficient length
of time to convert the nonhomogeneous, as-cast structure to a uni~orm austeni-
tic structure (austenite) throughout the piece, the holding time depending
upon the si e of the piece and which may, for example~ be one hour per inch
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of thickness of the heaviest sec~ion. As shown in the phase diagram~ Figure
6, the effect o~ holding the temperature above the upper critical level
is to transform the as-cast structure into austenitic form as shown, -for
example, at point 35, assuming a carbon content of 0.3%.
In accordance with the present invention, instead of simply allowing
the piece to cool slowly in the furnace, cool in still air, or quench in
liquid, the casting, while still in a plastic state, and near the ho]ding
temperature, is placed between a set of dies having cooperating shearing
edges located at the lateral surfaces for shearing off the gates, all of
which extend laterally, as well as any parting line fins which may have been
formed in the casting step. In the preferred practice of the invention, the
casting is, at about the same time, acted upon by die surfaces which are
distinct from ~he dies used for trimming, having the desired shape of the
casting and which correspond to selected ones of the upper and lower sur-
faces of the casting for formingly engaging these surfaces so as to insure
that these surfaces are in precise position. Although it is preferred, in
practicing the invention~ to trim and form the casting as part of the same
press stroke, these operations ma~ be performed by successive press strokes
and in more than one die set in rather quick succession so as to make simul-
taneous use of the same heat. These two operations, trimming and forming,
have been set out in exemplary method steps F and G.
In accordance with one of the further features of the invention,
two or more casting, where cast in a cluster, are operated upon simultaneous-
ly by corresponding sets of shearing and forming dies. This is illustrated
in Figures 7 - 9 where press 40 is indicated (press details not shown) having
die assemblies 41, 42 which act respectively upon castings 11, 12 (Figure
7). Turning to Figure 8 which shows die assembly 41 immediately prior to
its initial engagement of casting 11, it can be seen that the die assembly
41 is interposed between a vertically reciprocating head 43 and a bolster
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44. As shown schematically in Figure 7a, the head 43 is reciprocated by
a ram ~5 acting through spacers 46. Interposed between the ram and the
head are cylinders ~7 of the hydraulic or pneumatic type having piston rods
~8 e~tending there--rom and through respective bores ~9 in the head. The
piston rods are biased to an extended position and each cylinder has a relief
valve RV and a check valve A for a reason which will apear below.
-~ To facilitate understanding what happens to the castings 11, 127
the risers 21, 22~ and 23 forming part of the "as-cast" assembly are shown
in Figure 7 together with their respective gates 21a, 22a, 22b and 23a, which
are severed as a result of the operation of the dies.
Focusing attention upon ~he die assembly 41, the assembly is made
up of an upper die 51 and a lower die 52. The upper die has a generally
rectangular mounting pla~e 53 bolted to the head 43. Bolted to plate 53 are
shearing blades 54, 55, 56, 57 (Figures 7 - 8) having shearing edges 58,
59, 60, 61, respectively, which are formed and dimensioned to correspond to
lateral surfaces ~la, 11b, 11c, 11d respec~ively of the casting. The movable
body portion 62 having die recess 63, and presenting surfaces which engage
corresponding upwardly facing surfaces 11e, 11f, 11i, 11j of the workpiece,
is slideably mounted between blades 56, 57 so as to permit vertical motion of
the body relative to the shearing blades. The extremes of this vertical
motion are shown in Figures 8 and 9.
For cooperating with the upper die, the lower die includes a body
portion which consists of blocks 77, 78 secured to mounting plate 81 which
is in turn bolted to bolster 44. These blocks are mounted so as to form
a recess 6S for receiving the workpiece as well as to present upwardly
facing sur~aces ~or supporting the workpiece at its downwardly facing surfaces
~ .
11k, 111. Vertical surfaces 79, 80 serve as shearing surfaces for cooperating
with the shearing edges 60, 61 of the upper die. Also included in the
lower die are sidewalls 67, 68 bolted to blocks 77, 78 and having shearing
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surfaces 71, 72 which cooperate with the shearing edges 58, 59 of the upper
die These sidewalls also support surfaces 11g and 11h.
While the die assembly 41 has been re-ferred to in detail it will be
understood that the companion die assembly ~2 is similarly const~lcted.
In the drawing (Figure 7) similar elements have been indicated by correspond-
ing reference nu~erals with the addition of subscript a.
In carrying out the present invention, castings 11, 12 ~ith their
associated risers 21, 22 and 23 intact, are seated in the respective lower
dies 52, 52a, with the die assemblies being in the retracted or "open"
condition (Figures 7 - 8). During operation of the dies, castings 13, 1~ may
be permitted to hang in an outboard condition, cantilevered on the runners
16, 17 (Figure 4) or, if desired, the runner may be severed by any desired
means prior to placing the piece in the press. Preferably gates, risers
and runners are located so as to aid in handling the casting and in accurate-
ly positioning the casting in the die. It is one of the features of the
present invention that the castings 11, 12 are placed in the dies while
still at or near the holding temperature at which point the casting is in
a plastic state, has a homogeneous refined grain structure, and is of essen-
tially uniform temperature throughout. The fact that the casting is of
essentially uniform temperature is significant in respect to die design
because the absence of temperature gradients in the casting means that the
casting, although of enlarged size due to expansion of the steel, will have
experienced the same percentage expansion at all points. Therefore, the
desired deimension between lateral surfaces such as lla and 11b3 for example,
is achieved by spacing shearing edges 58, 59 an incremental distance apart
equal to the desired final demension between 11~ and 11b increased by the
percentage expansion of the particular steel at the holding temperature,
which may be on the order of 1%. Hence, when the casting is ~inally cooled
to ambient and experiences the attendant contraction, the lateral surfaces
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11a and 11b will be accurately spaced the desired distance apart. Similarly,
all surfaces and shearing edges of the die assembly ~re located "oversize"
(about 1%) to take into account the uniform contraction of the casting which
takes place as it is cooled from the holding temperature.
The desired operating range of ~Ifinishing~ temperature is indicated
at F in Figure 5 where it will be noted that the temperature ranges down-
wardly from the holding temperature TH through the cri~ical temperature
TC to a point which may be somewhat below the critical temperature. Although
it is preferable to "finisht' the casting while it is at a temperature as
close to the holding temperature as possible~ in a practical case the lower
limit of the finishing temperature may be a temperature which lies within
the range of 100 to 200 below the critical temperature TC. In any event
the casting, or castings, ~hen placed in the press will be in a glowing red
plastic state, a state in which the metal may be sheared and bodily formed
to desired shape using a relatively light shearing-forming force, a force
which is only a fraction of ~he force which would be required if these fin-
ishing steps were carried out with the casting in its cold state.
Focusing attention on Figures 8 and 9~ the engagement of the casting
11 by the die assembly 41 will be explained. As the press completes its
2~ downward stroke but before the casting is engaged by the upper die, the
parts occupy the position shown in Figure 8. In accordance with a preferred
method o~ the present invention in which the casting is first formingly
en~agcd and at the same time held firmly in place by the dies before shearing,
the movable die body 62 of the upper die is held in its lowermost position -
relative to the shearing blades by extended piston rod 48. As the stroke
continues the lower surface 64 of the body portion butts against surfaces
1li, 11j. me force of this initial engagement may be varied by adjusting
the escape of fluid from the cylinder 47 through relief valve RV to offer the
desired retarding force to piston rod 48
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~'7~73
~fter the casting has been engaged by body portion 62 the con-
tinued downward motion of the head 43 will cause piston rod 48 to retreat
into cylinder 47 thereby allowing ~ownward motion o~ the upper shearing
blades relative to the lower. As the shearing blades 5~, 55 and 54a, 55a
(Figure 7) are lowered, the gates 21a, 22a, 22b, 23a are engaged by shearing
edges 58, 59, 58a, 59a so that, as the thrust is completed, the risers 21-
23 may fall clear into a suitable receptacle. Similarly, in referring to
Figures 8 - 9, it is apparent that as the shearing blades 56, 57 are lowered,
any parting line fins formed at surfaces 11c, 11d are engaged by shearing
tO edges 60, 61 and hence are trimmed from the workpiece. In addition, as
the head 43 nears the bottom of its downward stroke and after shearing is
complete, the lower surface of head 43 butts against the upper surface of
; movable die body 62 transmitting a final, peak forming force to the workpiece.
Operating on the casting in this "sequential" manner with only
one stroke of the press accomplishes both the removal of extraneous metal
from the casting and straightening of horizontal surfaces. Also, since
the casting is held firmly in place by piston rod ~8 acting through movable
die body 62 during shearing, high accuracy is insured in the location of
; the lateral surfaces.
After the downward stroke is complete the ram is retracted causing
the shearing edges to move up and away from the newly sheared edges~ How-
ever, until the shearing edges are clear of the casting the movable die
body 62, by reaSon of the pressure which continues to be applied to it by
piston rod~48, insures that the casting remains seated in the lower die 52.
After the shearing blades are clear of the casting the movable die body 62
H is retracted and the casting, which is still at or near the holding temper-
ature, is released and may be removed from the lower die by any convenient
means.Cooling at the desired rate completes the heat treatment.
While, for the purpose of simple illustration, no provision has
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been included in Figures 7 - 10 ~or forming in the way of piercing or coin-
ing the casting, it will be understood that such piercing and coining may
be brought about by suitable piercing elements on the cooperating dies and
suitable coining surfaces included within the inner surfaces 63, 64, 65 of
the die sections.
For example, the die assembly, modified so as to perform piercing
is shown in Figures 13, 14 in which modified die assembly ~lm is shown
having a piercing element 90 for forming a hole in the surface 11i of the
casting 11. The elements of the die assembly which have not been modified
for the piercing operation are identified by the same numbers used in Figures
7 - 10 (see for example 43, 56, 81) whereas the elements which have been
modified are identified in Figures 12, 13 by the same number used in Figures
7 - 10 with the addition of the letter m.
For present purposes the term piercing has been used in a generic
sense to include both use of ~a) a piercing, or drifting tool, which is
round-nosed and forces its way through an existing hole and (b) a punch
which is sharp edged and which removes metal in creating or enlarging a
hole. The latter has been illustrated.
; Turning to Figure 13 which sho~s the die assembly 41m just prior
-to initial engagement of casting 11, the modifications made in the die as-
sembly in order to accomplish piercing will be explained. The ram 43 has
; piercing element 90 extending from its lower surface and through bore 91
in movable die body 62 m. Block 77m in lower die 52m has a cavity 94 having
a bore 92 of a diameter equal to the size of the hole to be punched and
a larger bore 93 through which the punched metal can pass through and be
removed through opening 9S.
It is pre~erred to form an undersized hole in the casting during
the casting operation by including a suitable core element in the mold since
less resistance will then be encountered by the piercing element and such
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a hole is indicated at 96 in Figure 13. However, it should be understood
that this is a preferred technique and that punching can be accomplished with
or without forming an undersized hole.
In accordance with the preferred method of the present invention
the casting 11 is first engaged and held firmly in position by movable die
body 62m. As the press stroke continues piston rod 48 retracts allowing
downward motion of piercing element 90 relative to movable die body 62m.
Piercing element 90 will then engage surface 11i at undersized hole 96 and,
as the stroke continues, the piercing element will shear away all metal within
the region defined by dotted lines 97 in Figure 13.
The configuration at the completion of the downward stroke is
shown in Figure 14 in which piercing element 90 extends slightly into bore
92 to insure that the metal removed by the piercing element will fall through
to the bottom of cavity 94. Retraction of the dies is identical to th~ se-
quence described above except that piercing element 90 is retracted along with
shearing blade 56 while movable die body 62m through extending piston rod
48 insures that the casting remains firmly seated in lower die 52m.
Similarly, and iIl accordance with a ~urther aspect of the present
invention, coining to size is performed on the cas~ing while it is still
at or near the holding temperature. Let it be assumed simply by way of
example, that the distance between lateral surfaces 11c, 11d (Figure 8~
is not critical and that the critical dimension is the thickness of the
~wings~ having surfaces l1i, llj, 11k, 11l. In order to achieve this desired
wing thickness the die assembly ~1 of Figure 8 is modified as shown in
Figures 15, 16 in which modified die assembly 41n is illustrated. The upper
die 51n consists of movable die body 62n, slideably mounted between blocks
56n, 57n and having stop blocks 100, 101 mounted at the lower surface of
movable die body and spaced so as to allow for clearance between vertical
surfaces 11c, 11d and the stop blocks. Lower die 52n is identical to lower
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die 52 (Figure 8) except that blocks 77n, 78n are longer and extend beyond
lateral surfaces 11c, 11d so as to present surface against which stop blocks
100, 101 will abut.
Coining is accomplished at the end of the downward stroke by the
final peak force transmitted to movable die body 62n as the lower surface
of head ~3 butts against the upper surface of the movable die body. When
this coining force is transmitted to the wings: which are of a thickness
slightly larger than thickness T of stop blocks 100, 1013 there will be a
slight displacement of metal into the spaces S until the s~op blocks bottom
against blocks 77n, 78n, respectively. At this time, and immediately after
retraction of the die assembly, the wings will be of thickness T. However,
as discussed above, the casting will experience some contraction on sub-
sequent cooling and therefore the thickness T of the stop blocks is slightly
larger, on the order of 1% or so, than the desired final thickness.
; Although for purposes of simple illustration the stop blocks 100,
` 101 are shown having a relatively limited area for bottoming against the
lower die, it will be understood that in a practical case the stop blocks
would be designed with an area somewhat larger than the area o~ the part
to be coined to size. However, it should also be understood that o~ten only
selected portions need be coined to si7e. For example, movable die body
62n could be equipped with a localized disc-shaped coining element extending
slightly below its lower surface to form a small land area for surrounding
a bolt hole in the castlng.
It is particularly noteworthy that, because of the plastic state
of the metal in the region of the critical temperature, the casting freely
adopts the shape of the dies without any tendency toward spring-back, so that
a highly accurate form and dimension for the casting is established -- eveh
though the casting may, at the time of placing the dies, be in a warped
or misshapen condition. No subsequent "straightening" is therefore required,
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a major problem when a casting is "cold finished"A
Although, for simple illustration, the casting lt is shown having
planar "wings" which are formingly engaged by the dies so as to insure that
they lie true with respect to a horizontal plane, it would be obvious to one
skilled in the art that the upper and lower die assemblies could be modified
so as to present corresponding curved surfaces to the casting if it is desired
to shape or bend selected sur~aces of the casting. For example, if it is
desired that the "wing" defined by surfaces 1~k, 11~ define a curved surface
then the mold would be designed so as to form a casting having l~wingsll curved
to the approximate final desired curvature. It is apparen~ that ~he die
assembly (Figures 8 - ~) may readily be modified so as to present, to each
'lwingll of the casting 11, curved forming surfaces opposed to one another,
for example, surfaces 6~ in *he upper die assembly and the upper supporting
surfaces of blocks 77, 78. Hence, after completion of the press stroke, and
subsequent cooling of the casting, no cold "bending" or "straightening" of
the~'wings~ to the desired curvature, with the attendant spring-back problem,
would be required.
Indeed, it is seen that the operation of the dies incident to
heat treatment, and following the holding period, is effective to accomplish
automatically all of the steps which formerly required hand opera~ions.
That is, the risers and gates, or sprues, are cleanly severed from the castings
along accurate dimension lines in the single stroke of the press, together
with other irregularities such as any fins which may have been formed along
the parting line during the molding step. The shearing cut is sufficiently
smooth so that the chipping and grinding usually thought necessary to finish
the castlng may be completely dispensed with.
While it is preferred to accomplish the plastic "forming" using
dies which are in the same set as those employed for ~rimming purposes, it
will be apparent to one skilled in the art that the two or more operations
73
may be accomplished in quick succession, that is, using a first set of dies
for shearing only, with immediate transfer of the workpiece while still in
a hot and plastic state, to a second or further set of dies for forming,
including coining~ piercing and the like. Thus the term "simultaneously"
as used herein referring to the trimming and shaping steps has to do with the
fact that these ~wo operations are performed sufficien~ly close ~ogether so
as to make use of the same heat and same plastic state, and the term is not
necessarily limited to a single set of dies.
Regarding the method steps of the present invention, and method
step A in particular, it will be understood that the terms "lateral"~ "up-
wardly" and "do~wardly~ are used in a relative sense and that the casting
; cluster depicted in Figures 1 - 4 could also be cast using a pattern which
is orientated at 90 so that the parting line is in a vertical plane. In
~his case the requirements of method step A would be satisfied since a 90
rotation of the pattern would result in the configuration shown in Figures
1 - 4. In addition, although the above description of mold preparation in-
cludes reference to a conventional flask, it will be understood that the
method of the present invention is suitable for castings produced using the
"flaskless'7 mold procedure. Briefly, the flaskless procedure involves forr77ing
a series of mold cavities in a horizontal column of sc~nd having a high green
strength, advancing the column past a metal pouring station where molten
metal is poured into each mold in turn, and removing the sand mold after
solidification has occurredO The nature of the flaskless procedure requires
a vertically orientated parting line plane and gates which lie in the region
of this plane. However, changing reference position by rotating the mold
90 results in a configuration which satisfies method step A. Therefore,
. .,
the method o~ the present invention is particularly suitable for practice
~in conjunctlon with a flaskless casting operation.
It will also be apparent to one skilled in the art that the present
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procedure, invol-ving the making o-f a steel casting, the cooling and sub-
sequent heating of the casting to a holding temperature, with trimming while
in the plastic state, brings about a major economy in the making of parts.
Compared to forging procedures, a prlmary difference is that the part which
is acted upon by the dies is already ill substantially its final shape. After
the risers and gates are trimmed off all the dies are required to do is
to refine, and make more accurate, the shape which is already present, with
the result that the dies are not called upon to forcibly work a billet of
metal into the final form of the finished product. This makes it possible,
employing the present invention, for a single set of dies to be used to trans-
form the part to final shape and dimension using working forces which are
so low as to enable the trimming and shaping steps to be accomplished with
substantially reduced wear and tear on the dies, quiclcly, and using lighter
press equipment with only a limited total stroke. The net result is that
a piece is produced using the present procedures which has substantially all
of the advantages normally associated with a forging, including accurate
shape and dimension, plus reliable and consistent characteristics, but at
a per-unit cost, taking into account amortized die expense and maintenance,
which is substantially lower than the cost of the forging.
~ further reason that the die costs may be substantially reduced
i9 that the dies may be greatly simplified. Thus, in the case of forging
dies, the dies must have surfaces corresponding to each and every surface
on the finished product. The present dies, by contrast, may leave certain
portions of the workpiece unsupported, that is, unengaged, during the form-
ing step, concentrating upon those surfaces which are dimensionally signifi-
cant. For example, the upper surface 85 o-f the cylindrical portion of the
workpiece 11 is not engaged by the body portion 62 of the upper die assembly
` (see Figure 9).
After the dies shown in Figure 7 have completed a single cycle,
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the castings are independent of one another and freed of all extraneous metal
and are of accurate shape and dimension. I~hen the dies are open, thefinished
castings are discharged, using any desired conventional means. Conveniently,
the castings will be allowed to cool in still air, thus completing the
"normalizing" of the metal in the castings. Alternatively, the castings
may be annealed by cooling more slowly. Conceivably also, and without de-
parting from the invention, the castings taken from the dies may be quenched,
with or without subsequent tempering as these terms are defined in the art.
In any event, the requirement of the final step H (Figure 12) is satisfied.
lo It is one of the distinguishing characteristics of the present
invention that the "finishingl' of the casting including trimming and shaping
is done incident to reheating of the casting for homogenizing, e.g., normali-
zing purposes. Stated in other words, the invention does not make use of
the original casting heat. The reason for this is that we prefer to finish,
that is, trim and form, only after the casting has been allowed to cool and
is subsequently reheated to a holding temperature, above the upl~er critical
temperature, for a time period long enough to convert the grain to the de-
sired granular, i.e., austenitic, structure9 at a time when all of the internal
stresses have had opportunity to become equalized, and at a time when sub-
~tantially all portions of the casting are at the same temperature and de-
gree of plasticity. This is to be contrasted with any procedure utilizing
onl~ the original heat of the casting since the casting tends to cool uneven-
ly in the mold so that different portions of the casting would be at a dif-
ferent temperature than other portions with different physical characteristics
and ill-defined crystallography, and accompanied by a substantial sacrifice
in the result.
In the above discussion the procedure for finishing a casting has
involved the making of a pattern which,,but for the addition of gates and
risers~ substantially conforms to the finished workpiece, with the casting
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resulting ~rom the pattern then being placed in a set of dies for trimming,
coining and the like. The invention is not limited thereto and can be
utili7ed to produce a workpiece which includes an at least partially enclosed
cavity and the making O r which would normally require use of a core. In this
aspect of the invention the original pattern9 with its gates and risers,
is not made in the shape of the desired finished workpiece. Instead, the
pattern is made in the shape of a transitional casting with walls having ade-
quate draft to avoid use of a core. The transitional casting thus formed
is then reheated to a plastic state above the upper critical temperature and
held there a sufficient length of time for homogenization. Then, while the
transitional casting is s~ill in a plastic state and near the holding tem-
perature, the casting is placed in a set of dies for the purpose of shearing
off the gates and risers, the set of dies including opposed forming surfaces
corresponding to the desired upwardly and downwardly facing surfaces of the
f1nished workpiece. The opposed die surfaces are brought together to act
upon the transitional casting so that the walls thereof are deformed inwardly
to form an at least partly enclosed cavity. The dies are withdrawn and t~e
casting is permitted to cool at a controlled rate.
By way of example, a piece having a partially enclosed cavity is
set forth in transitional form in Figures 17 - 19 and in final form in
Figures 22 - 24~ To avoid duplication in the drawings, the illustrations in
Figures 17 - 19 may be taken as illustrative, not only of the transitional
casting, but of the pattern which is used to produce it.
The workpiece, indicated at 120 in its transitional form is of
- channel shape having side walls 121, 122, which are provided with adequate
draft for casting purposes, and which define between them a channel-shaped,
open-topped cavity 123. The walls 121, 122 are tapered in the vertical
dimension as shown in Figure 18 and the tip of the piece is "spade" shaped
as indicated at 124. Secured to the opposite, or thicker, end is a gate 125
:
73~
having a riser 126.
Using a pattern of the shape illustrated in Figures 17 - 19, a
mold is prepared and the casting is molded in the regular way. Since the
cavity 123, although bounded by upstanding walls, is open above the parting
line PL, no core is required and the casting may be made in the regular way.
When the casting thus formed is cooled a nonhomogeneous dendritic grain
structure is produced, as previously described. The transitional casting
is then reheated to a plastic state above the upper critical temperature and
held there until homogenization occurs. While the casting is still in a
plastic state and near the holding temperature, it is placed in a set of
dies which have a shearing edge 128 (Figure 18) for trimming off the gate
and riser, and at which time shearing surfaces are also applied to trim off
any parting line fins as discussed in connection with the previous embodi-
ment. Also, referring to Figure 20, while the transitional casting is in
the plastic state, it is placed between forming dies 130 (only partially
shown) including a lower die 131 and an upper die 132. The upper die has a
forming surface 133 which differs from the shape of the transitional casting
but which corresponds to the shape of the desired finished casting. Inter-
posed between the dies 131, 132 is a mandrel 13S having a ledge 136. When
the dies are brought together, as shown in Figure 21, the projection 133 on
the upper die forming engages the wall 122 of the transitional casting,
causing the plastic material of which the wall is composed to be displaced
laterally and to flow into the space defined by the upper surface 133 and
the lower ledge surface 136. The upper edges of the walls of the transitional
casting are deformed mutually inwardly so that the cavity 123, instead of
being open-topped becomes partially enclosed. The result is to produce the
workpiece illustrated in Figures 22 - 2~ which differs from the shape of
the pattern which is used to produce it and which is distinguished by a
partially enclosed cavity of a type normally requiring use of a core. In
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short, the present invention may be employed for economical production of
a cast workpiece which cannot be cast in the usual way and which would,
because of the partial enclosure, require resort to a core. Moreover, the
resulting workpiece is, by reason of its cast nature, and by use of the
extremely simple forming dies shown in ~igures 20, 21, susceptible of manu-
facture more cheaply than a forging, and with considerably reduced die ex-
pense.
After the dies have completed their stroke, the dies are opened,
the mandrel is longitudinally withdrawn, and the casting is removed and
allowed to cool at a controlled rate.
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