U.S. patent number 3,926,029 [Application Number 05/465,711] was granted by the patent office on 1975-12-16 for heated die assembly.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Air. Invention is credited to David J. Abson, Ferdinand J. Gurney.
United States Patent |
3,926,029 |
Abson , et al. |
December 16, 1975 |
Heated die assembly
Abstract
A heated die assembly designed to bolt onto a conventional
hydraulic forge press. The heated die assembly is made of a
laminated, load bearing insulating stack to which is attached a
plurality of split heater blocks. The blocks contain
semi-cylindrical grooves and bolt around cartridge heaters. Bolt-on
die face plates are removably mounted on the heater blocks and are
readily interchangeable for a variety of forging operations.
Inventors: |
Abson; David J. (Medway,
OH), Gurney; Ferdinand J. (Dayton, OH) |
Assignee: |
The United States of America as
represented by the Secretary of the Air (Washington,
DC)
|
Family
ID: |
23848867 |
Appl.
No.: |
05/465,711 |
Filed: |
April 30, 1974 |
Current U.S.
Class: |
72/342.92 |
Current CPC
Class: |
B21J
13/02 (20130101); B21K 29/00 (20130101) |
Current International
Class: |
B21J
13/02 (20060101); B21K 29/00 (20060101); B21J
013/02 () |
Field of
Search: |
;72/342,470 ;76/107
;100/93P |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Larson; Lowell A.
Attorney, Agent or Firm: Rusz; Joseph E. Erlich; Jacob
N.
Claims
We claim:
1. A heated die assembly adapted to be used in conjunction with a
forge press comprising a load bearing insulated stack, at least one
heater block secured at one end thereof to said load bearing
insulated stack and a die face plate secured to the other end of
said heater block, said load bearing stack being made of alternate
layers of at least two plates, one of said plates being made of a
material having a high toughness, the other of said plates being
made of a composite construction of two materials, one of said
materials of said composite construction having high toughness and
the other of said materials of said composite construction having a
high compressive strength and low thermal conductivity and said
heater block being made of two heater elements which contain a
means for generating heat therein.
2. A heated die assembly as defined in claim 1 wherein said die
face plate is removably secured to said heater block.
3. A heated die assembly as defined in claim 1 wherein the other of
said plates has a cut-out portion therein, said high compressive
strength, low thermal conductive material being located in said
cut-out and the thickness of said high compressive strength low
thermal conductive material being greater than the thickness of the
plate which surrounds it.
4. A heated die assembly as defined in claim 3 wherein each of said
elements of said heater block contain at least one groove therein
thereby forming a hole in said heater block by the mating of
adjacent grooves.
5. A heated die assembly as defined in claim 4 wherein said die
face plate is removably secured to said heater block.
6. A load bearing insulated stack adapted to be used in a forge
press comprising at least two plates, one of said plates being made
of a material having a high toughness, the other of said plates
being made of a composite construction of two materials, one of
said materials of said composite construction having high toughness
and the other of said materials of said composite construction
having a high compressive strength and low thermal
conductivity.
7. A load bearing insulating stack as defined in claim 6 wherein
said other of said plates has a cut-out portion therein, said high
compressive strength, low thermal conductive material being located
within said cut-out portion and the thickness of said high
compressive strength, low thermal conductive material being greater
than the thickness of the plate which surrounds it.
8. A load bearing insulating stack as defined in claim 7 further
comprising a plurality of alternate layers of said plates and said
plates being removably secured to one another.
9. A load bearing insulating stack as defined in claim 8 wherein
said high compressive strength, low thermal conductive material is
ceramic.
10. A load bearing insulating stack as defined in claim 9 wherein
said high toughness material is a super alloy.
11. A heater block adapted to be used in a forge press comprising a
pair of heater elements, each of said heater elements having a
plurality of grooves therein, said heater elements being secured
together in such a manner that adjacent grooves form a plurality of
holes within said heater block and a means for generating heat
being located within said holes.
12. A heater block as defined in claim 11 wherein said interior
portion of said holes are coated with a means for improving the
thermal conductivity thereof.
13. A heater block as defined in claim 12 wherein said heater
elements are identical in construction and are removably secured to
one another.
14. A heated die assembly adapted to be used in conjunction with a
forge press comprising a load bearing insulated stack, at least one
heater block secured at one end thereof to said load bearing
insulated stack, said load bearing stack being made of alternate
layers of two types of material one of said materials having a high
compressive strength and low thermal conductivity and the other of
said materials having high toughness and said heater block
comprising a pair of heater elements, each of said heater elements
having a plurality of grooves therein, said heater elements being
secured together in such a manner that adjacent grooves form a
plurality of holes within said heater block and a means for
generating heat being located within said holes.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to "Isothermal Forging", and, more
particularly, to a heated die assembly designed to bolt onto a
hydraulic forge press.
The desire to fabricate new materials which are inherently
difficult to forge has lead to the emergence of new techniques
called "Isothermal Forging". In contrast to conventional forging
this process uses heated tooling and the forging is carried out at
slow speeds. The tooling in such a process calls for material which
has high strength at temperatures in the order of 1800.degree.F and
have a means of generating heat within the dies.
The use of heated dies for the forging of metal offers several
important advantages over the use of cold dies. The principal
benefits are that workability is improved and surface cracking is
reduced, and in some cases forging may be accomplished in one
operation so that earlier "blocker" forging operations are not
required. In addition, close tolerances can be achieved thereby
substantially reducing the extent of subsequent machining
operations. There are additional advantages in that when work-piece
chilling does not occur slower deformation is practical and lower
forging loads are required. This is a consequence of the lower
material flow stress resulting both from the uniform elevated
temperature, and in view of the high strain rate sensitivity of the
workpiece, from the slow speed deformation. The lower processing
loads may permit utilization of smaller, and thus less costly
equipment.
In the technique of heated die techniques as set forth hereinabove
the need arises for a load-bearing buffer between the heated
process equipment and the forging press. Such a buffer reduces heat
losses from the heated tooling and minimizes heat build-up in parts
of the equipment which are not intentionally heated.
Another problem has arisen in the area of generating heat within
the dies. A solution to this problem is to generate heat by means
of a conventional cartridge heater embedded within a die block. The
draw back of this solution is that the cylindrical holes which
contain the heater must be perfectly aligned and the gap between
hole and heater must be no more than a few thousandths of an inch
in order to insure good heat transfer. Conventional drilling of the
holes prove costly, while coring of undersized holes during casting
gives way to machining problems unless an electrode discharging
process is used and this process is also extremely costly.
An alternative method of heating the dies would be to use embedded
quartz heaters. This method, however, does not eliminate the
problems set forth hereinabove and in addition provides a low heat
output. Another alternative heat source is induction heating. This
method, however, is best suited to the forging of parts with
cylindrical symmetry using tooling which is also cylindrical, since
heat is generated within the workpiece and tooling. In addition,
this heating method is not very flexible and requires expensive
immobile RF equipment. Still another alternative heating source is
flame heating. However, flame heating not only provides an inherent
danger from flames but also has problems with insulation,
atmosphere control and removal of fumes.
In the severe service conditions imposed on forging dies operated
at elevated temperatures, swift deterioration of the dies occur
because of wear. In addition, problems such as interaction with
lubricants and the build-up of adhered lubricants makes simple
removal of the dies a desirable feature in order to minimize
"down-time" on heated die forging equipment. In the heated die
equipment of the past, however, the fabrication of the shaped dies
either contained embedded heaters or alternatively consisted of
massive blocks in which heat is generated by induction. In
conventional forging since impact loading of dies occurs such
massive dies were acceptable. However, their adaptation to heated
die forging equipment has given rise to heated dies which are
unnecessarily bulky.
SUMMARY OF THE INVENTION
The instant invention overcomes the problems set forth hereinabove
by providing a heated die assembly which is designed for easy
mounting onto a conventional hydraulic forge press. The die
assembly is made up of (a) split heater blocks which contain
semi-cylindrical grooves and which bolt in pairs around cartridge
heaters, thereby facilitating both fabrication of the blocks and
replacement of defective heaters; (b) bolt-on die face plates which
are readily interchangeable and which may have either flat or a
shaped work-face; and (c) laminated, load bearing insulating stacks
made of alternate layers of oxidation resistant material having
high toughness and a high compressive strength material having low
thermal conductivity.
In the present invention, the laminated back-up tooling consists of
alternate layers of (a) a sheet of nickel-base superalloy or other
suitable metal and (b) a ceramic slab contained within a further
sheet of metal. The presence of the ceramic, and of the many
interfaces, give a substantially lower thermal conductivity than
that of the metal alone. In addition the metal sheets can be
machined easily so that provision can be made for fastening all the
plates together, and for interfacing with adjacent tooling. By
reducing heat losses, the laminated back-up tooling of this
invention is likely to reduce operating costs along with a
substantial reduction in tooling fabrication cost.
Hot forging operations carried out at slow speeds also require the
use of heated tooling. The instant invention utilizes die bolsters
within which heat is generated by means of embedded cartridge
heaters. The die bolsters are made into matching halves, each
containing semi-cylindrical grooves on one face. These bolsters are
bolted together around the set of cartridge heaters. Such a design
simplifies fabrication of the bolster plates and also facilitates
removal and replacement of defective heaters. It is possible to
have two identical halves of the heater block, each with one flat
face. An extension of the bolt-together concept would then permit
each pair of die bolsters to be attached either to another set of
bolsters, to a replaceable die face plate, or to other parts of the
tooling.
With the new technology of heated-die forging several problems
arise such as the high cost of fabrication of massive, precision
cast dies and the handling of these dies when removal from the
forging press becomes necessary for replacement due to wear or for
cleaning. The present invention involves:(a) dissociation of the
dies from the back-up tooling, in which heat is generated by
embedded heaters or by induction, (b) reduction of the depth of the
die, to the minimum practical thickness, and (c) making provision
for easy die replacement using bolts or other suitable
fasteners.
It is therefore an object of this invention to provide a heated die
assembly which is designed for easy mounting onto conventional
hydraulic forge presses.
It is a further object of this invention to provide a split heater
block whereby fabrication of the heater assembly and replacement of
defective heaters are simplified.
Another object of this invention is to provide a load bearing
insulating stack (back-up tooling) which permits (a) a reduction in
the heat input required to maintain a given temperature, (b) an
increase in the temperature which can be maintained for a fixed
heat input, and (c) an increase in the maximum permissible work
piece height for a fixed heat loss through the tooling.
Still another object of this invention is to provide die face
plates which are of the minimum thickness consistent with having
sufficient strength and are easily mounted to back up tooling.
It is still a further object to provide a heated die assembly which
is economical to produce and which utilizes conventional, currently
available components that lend themselves to standard mass
producing manufacturing techniques.
For a better understanding of the present invention together with
other and further objects thereof, reference is made to the
following description taken in connection with the accompanying
drawing and its scope will be pointed out in the appended
claims.
DESCRIPTION OF THE DRAWING
FIG. 1 is a side elevational view of the heated die assembly of
this invention shown in conjunction with a hydraulic forging
press;
FIG. 2 is a pictorial view of the load bearing insulating stack of
this invention;
FIG. 3 is a plan view of the split heater block of this
invention;
FIG. 4 is a side elevational view of the split heater block of this
invention;
FIG. 5 is a plan view of the die face plate of this invention;
FIG. 6 is a side elevational view of the die face plate of this
invention;
FIG. 7 is a plan view of a modified die face plate of this
invention; and
FIG. 8 is a side elevational view of the modified die face plate
shown in FIG. 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is now made to FIG. 1 of the drawing which best shows the
completed heated die assembly 10 of this invention mounted on the
upper and lower sections of a conventional hydraulic forge press
12.
Heated die assembly 10 of the present invention is made up of a
load bearing insulated stack 14 fixedly secured at one end thereof
to a water cooled maraging steel block 16. Secured to the other end
of insulating stack 14 are split heater blocks 18 which contain
conventional cartridge heaters 20 therein. Heat is generated by a
plurality of cartridge heaters 20 each heater supplying up to 320
watts. The heaters 20 are powered by any suitable power supply such
as a conventional SCR power unit (not shown) which give a maximum
work-face temperature of approximately 1850.degree.F. Mounted on
the work surface of heater blocks 18 is a die face plate 22 which
contains therein thermocouples 24 for temperature control and
monitoring. Die face plate 22 is removable and may have either a
flat or shaped work-face. Compressed between die face plates 22 is
the work piece 26. All elements which make up this invention are
described in detail hereinbelow.
Reference is now made to FIG. 2 of the drawing which shows, in
pictorial fashion, the laminated insulating stack 14. Stack 14 is
made of alternate layers of ceramic 28 and metal sheets 36. The
ceramic material 28 preferably has a high compressive strength and
low thermal conductivity and may be made from any suitable material
such as alumina, beryilla, cermet or non-metallic silicon nitride.
Ceramic material 28 is contained within one or more openings 30 in
a sheet of metal 32, and this composite layer 34 is sandwiched
between complete metal sheets 36. The sheets of metal 32 and 36
should be oxidation resistant having high toughness such as super
alloys based on iron, nickel or cobalt. Examples of such super
alloys are Inconel 601 having the following composition: 23.0%Cr,
14.1%Fe, 1.35%Al, 0.05%C, 0.5%Mn, 0.007%S, 0.25%Si, 0.25%Cu with
the remainder a base of Ni; and Haynes alloy 188 having the
following composition: 22%Cr, 22%Ni, 14.5%W, 3.0%Fe, 0.15%C;
0.15%La with the remainder a base of Co.
In order to compensate for the difference in thermal expansion
coefficient, the room temperature thickness of the ceramic 28
should be slightly greater than that of the metal 32. Bolts 38 or
any other suitable fastener are utilized to hold the plates 34 and
36 together and further to attach the laminated stack 14 to
adjacent tooling. THe metal/ceramic interfaces provide planes of
easy shear as distortion occurs due to differential thermal
expansions or to non-axial loading. Even if the ceramic 28 should
fracture, the pieces would be contained by a surrounding sheet of
metal and the operation of the stack 14 would not be affected. A
typical heat transfer calculation with relative thickness of
ceramic to metal of 1.13 to 1.0, for a 13 layer stack will give an
effective thermal conductivity approximately 1.1 times that of
alumina and approximately 0.4 times that of Inconel 601.
Since the ceramic material 28 is used in the form of flat slabs,
expensive fabrication processes on this material are avoided.
Further cost reduction may be effected where the heated forging
dies are large or have an unusual shape, since the laminated stacks
14 of this invention may be utilized side by side thereby
minimizing the variety of back-up tooling required for forging a
number of different shapes and sizes.
Referring to FIGS. 3 and 4, which show a typical configuration of a
split heater block, it is shown that the present invention also
provides means whereby fabrication of the heater blocks 18 and
subsequent replacement of defective cartridge heaters 20 are
simplified. In addition, this invention insures accurate fitting of
cartridge heaters 20 to the holes 40. The heater blocks 18 are
fabricated in two parts 42 and 44, split at the diametral plane of
each heater. Holes 40 are cast into face 46 of each part 42 and 44,
respectively, as semi-cylindrical grooves. These grooves are
brought accurately to size by precision grinding. This method of
fabrication replaces an expensive drilling or machining operation
by a less expensive grinding process. The two halves or parts 42
and 44 of heater blocks 18 are fastened together around the heater
cartridges 20 by bolts 48 or other suitable fasteners.
Although it is not necessary that all the heaters 20 lie in the
same plane, such an arrangement simplifies the machining operation.
While the back face 50 of one of the block halves 42 or 44 may be
ground flat, the back face of the other piece might be expected to
contain the die shape. This is not necessarily the case, however,
since fabrication of two identical heater block halves, each with
one flat face, has several advantages. Although such a
configuration requires a separate die face plate, it does permit a
greater flexibility of use of the tooling, since heater blocks 18
can be stacked in more than one layer to provide additional heat
input or side by side to supply heat to a large die. Moreover, die
face plates 22 can be replaced easily as they become unserviceable,
or if different shapes are to be forged.
The typical configuration for a heater block 18 appears in FIGS. 3
and 4 and shows a heater half or part 42, for example, having one
flat face 50 and several projecting lugs 52 which contain bolt
holes 54 therein. The lugs 52 allow the heater block halves 42 and
44 to be clamped firmly around a single row of cartridge heaters 20
and also to be interfaced with other parts of the tooling. Since
the curved surfaces of holes 40 are easily accessable, they can be
ground accurately to fit the size and shape of the cartridge
heaters 20. Accurate fitting is important if good heat transfer is
to be obtained from heaters 20 to the blocks 18. Coating the curved
surfaces of holes 40 with graphite also improves heat transfer, and
can be done most effectively in the present invention. The heater
block 18 shown in FIGS. 3 and 4 of the drawing provide for an
embedded heater length of approximately 5". A typical heater block
18 of this invention has two rows of cartridge heaters 20 clamped
between four identical die bolster halves. Use of identical parts
reduces the initial casting cost and permits the maintenance of a
smaller inventory of spare parts. Advantages of the heater block 18
of this invention includes the reduction of "down-time" for removal
and replacement of either an unserviceable die face 22 or a
defective cartridge heater 20. Moreover, several heater blocks 18
can be used, stacked on top of one-another, to give a higher heat
input per unit area, or stacked side by side to supply heat over a
large area. This latter modular arrangement would give the system
wide flexibility since a small range of heater blocks 18 could
accommodate a wide variety of die shapes and sizes. Moreover, a
more precise temperature control can be achieved if different heat
input is arranged to different parts of the die faces 22. In this
way, a uniform temperature is achieved in spite of local
differences in heat loss; alternatively, a particular temperature
profile can be imposed for such purposes as microstructure
control.
Reference is now made to FIGS. 5 and 6 which best show the bolt-on
die face plate 22 of this invention. Die face plate 22 is cast in a
substantially rectangular configuration of, for example, 61/2
inches by 51/2 inches by 1/2 inch, out of a high strength super
alloy such as IN 100 having the following composition: 15%Co,
10.0%Cr, 5.5%Al, 4.7%Ti, 3.0%Mo, 1.0%V, 0.18%C, 0.014%B, 0.06%Zr
with the remainder a base of Ni. The plate 22 contains a plurality
of bolt holes 60 located within recesses 62 for bolt heads. The
front and back faces 64 and 66, respectively, are ground flat and
provisions are made for locating thermocouples 24 therein by
drilling holes 68 therein.
In addition to the die face plate 22 shown in FIGS. 5 and 6, a die
face plate 70 may be made of two or more materials as shown in
FIGS. 7 and 8. In such a case the die shape might be formed in a
material 72 which has good abrasion and wear resistance, surrounded
by a material 74 which has high toughness such as a super alloy or
coated refractory metal. The shape may be formed within a truncated
cone or pyramid of ceramic or metal powder which is then sintered.
Such a shape would have a flat base and could be held in place by
the inclined face of the hole 76 in the plate 74. An alternative
method of obtaining the die shape would be by electrodischarge
machining if the die material is an electrical conductor. As in die
face plate 22 shown in FIGS. 5 and 6, bolt holes 60', recesses 62'
and thermocouple holes 68' are provided in die plate 70.
The advantage of the bolt on die face plates 22 and 70 of this
invention are lower die fabrication cost, easier handling and
storage of thinner dies and shorter "down-time" when changing of
the dies becomes necessary. A further benefit is that thermocouples
24 can be located directly behind the die faces. In addition due to
the bolt-on concept, dies can be made of a different material from
that of the back up tooling.
The present invention sets forth a heated die assembly 10 which can
be substituted as a whole for the die blocks used in the past. In
addition the individual elements (insulating stack 14, split heater
blocks 18 and die face plate 20) which make up this invention
constitute a novel approach to the "Isothermal Forging" art.
Although this invention has been described with reference to
particular embodiments it will be understood to those skilled in
the art that this invention is also capable of a variety of
alternative embodiments within the spirit and scope of the appended
claims.
* * * * *