Process for manufacturing metal parts by free forging and drop forging in a press

The process for manufacturing parts of revolution which are made from a high-density metal with great regularity of reproducibility, especially as regards the homogeneity of the matter. It consists in carrying out the following steps: forging in three dimensions by successive upsetting and drawing-out operations carried out in three perpendicular directions; closed-die forging; and recrystallisation heat treatment. Application to the manufacture of hollow-charged coatings made of tantalum.

DESCRIPTION 
1. Field of the Invention 
The invention relates to the working and forming of metal parts, the 
constituent material of which has a high density, such as tungsten, 
molybdenum, rhenium, uranium, tantalum and their alloys. It relates in 
particular to parts having a hollow shape of revolution, such as hollow 
charges or core-generating charges. 
2. Prior Art and Problem Encountered 
The search for improving the performance characteristics of hollow charges 
and of charges producing a jet of matter at very high speeds forces 
manufacturers to use heavier metals, that is to say metals of very high 
density. Attempts are thus made to manufacture hollow-charge coatings 
consisting of very heavy metals. Now, the reproducibility in the 
manufacture of core-generating charges depends on numerous technological 
parameters related to the design of the charge system, but especially on 
the reproducibility of the metallurgical structure used for constituting 
the coating of the charge. In particular, high-density coatings, such as 
tantalum, cannot be mass-manufactured to a consistent quality regarding 
performance characteristics, especially when the quality of the 
metallurgical structure has not been made consistent. 
The object of the invention is to overcome this drawback by providing a 
process for forging and recrystallising heavy metals, such as tantalum, 
which obliterates the structural history of the starting material and 
which makes it possible to obtain parts which are isotropic and have a 
fully reproducible and fine-grained structure. 
Moreover, a process is known, from European Patent Application 0,389,367, 
for obtaining parts made from copper having a very fine structure, 
starting from a continuous-cast billet. This process comprises the 
following principal phases: 
kneading the billet by upsetting and drawing-out cycles; 
sectioning the billet into blanks each intended to form a finished part; 
die-forming the blanks at room temperature; and 
recrystallization heat treatment in order to obtain a grain size below 40 
.mu.m. 
The first kneading phase comprises in particular a first upsetting of the 
billet, a first drawing out, a second upsetting and then a second drawing 
out. These four operations are carried out at a temperature of between 
400.degree. and 480.degree. C. 
Now, the drawings of this patent application show that these various 
upsetting and drawing-out phases are always performed along the same 
initial axis of the billet, that is to say the upsetting operations and 
drawing-out operations are performed along the same axis of the billet. 
This process only works the constituent matter of the billet in two 
dimensions. The operation in the third direction is only undertaken during 
the drop forging of the part. 
SUMMARY OF THE INVENTION 
The main subject of the invention is a process for manufacturing metal 
parts by free forging and drop forging in a press, starting from billets, 
each of which is associated with an orthogonal mark having three 
dimensions X, Y, Z, the process comprising the following steps: 
first upsetting along the first axis X; 
first drawing out; 
second upsetting; 
second drawing out; 
die forging; and 
recrystallization heat treatment. 
According to the invention, the first drawing out is performed along the 
second axis Y, the second upsetting is performed along the second axis Y 
and the second drawing out is performed along the third axis Z. 
The process according to the invention is particularly intended to be 
applied to high-density materials; it is thus performed at room 
temperature. 
Quench cooling operations may be effected after certain steps or between 
certain operations of certain steps. 
Preferably, the first upsetting along the first axis X is performed in the 
press and comprises: 
a single upsetting operation with a forging ratio T of less than 2.3; and 
a quench. 
The first drawing out along the second axis Y is preferably performed in 
the press by: 
a squaring by pressure on the faces perpendicular to the first and third 
axes X and Z; 
a first drawing out by pressure on the edges parallel to the axis Y in 
order to obtain an octagonal profile; 
a quench; 
a drawing out by pressure on the center in order to cause the center of the 
blank to neck; 
a quench; 
a second drawing out by action on the faces parallel to the axis Y in order 
to obtain an octagonal profile; 
a drawing out by pressure on the edges of the octagon in order to round off 
the part, that is to say to obtain a virtually cylindrical external 
surface; and 
a quench. 
The second upsetting along the axis Y is preferably performed in the press 
by means of the following steps: 
forging the end faces in order to provide a bearing surface on each of 
them; 
upsetting, in one or more operations, with a forging ratio of less than 
2.3, each operation followed by a quench. 
The second drawing out along the axis Z is preferably performed in the 
press by means of the following operations; 
squaring by action on the faces perpendicular to the first and second axes 
X and Y; 
quenching; 
drawing out by pressure on the center in order to cause the center of the 
blank to neck; 
squaring by action on the faces X and Y; 
drawing out by pressure on the center in order to cause the center of the 
blank to neck; 
drawing out by pressure on the faces perpendicular to the first and second 
axes in order to obtain an octagonal profile; 
drawing out by pressure on the edges of the octagon in order to round off; 
and 
a quench. 
Before carrying out the die forging of thin parts, the following are 
preferably carried out; 
a cutting-up of the billet in order to obtain discs; 
a facing, by turning, of the plane end faces of the discs. 
The forging is preferably performed by means of the following steps: 
closed-die forging in a press; 
sizing with a drop hammer; and 
quenching. 
In cases where the material is tantalum, the recrystallization heat 
treatment is performed at a temperature in the neighborhood of 970.degree. 
C. for approximately 1 h and is carried out under vacuum.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
The process according to the invention can in particular be produced with 
various materials and billets of different dimensions, but in particular 
with tantalum billets of 70 mm in diameter and 140 mm in height. 
Such a billet is shown in FIG. 1. An orthogonal mark having three axes X, Y 
and Z is associated with this billet and will remain associated with it 
throughout the description of the process. This will make it possible to 
better define the various directions in which the various deformations are 
applied to the billet. This mark must be displayed on the billet in order 
to facilitate the execution of the process. 
FIRST STEP: first upsetting along the first axis X. 
The first step of the process consists in carrying out a first upsetting 
along the first axis X, placed vertically in FIG. 1. Depending on the size 
and the material, this upsetting is carried out in one or more operations 
in a press. The forging ratio T, that is to say the ratio of the initial 
dimension along the relevant axis and the final dimension, is of the order 
of 2. For parts made of tantalum, it may go up to 2.3. Above this value, 
buckling problems occur. 
The operation is performed at room temperature in the case of tantalum. A 
quench may optionally be carried out after each successive operation. In 
fact, since the deformation of the shape of the billet is relatively 
great, corresponding internal heating occurs within the material bulk. 
In the case of a tantalum billet of 140 mm in height and 70 mm in diameter, 
this first operation may be carried out in a single deformation in a 
1,200-tonne press at a rate of 5 mm/s. At the end of the deformation, the 
billet is preferably quenched, its surface temperature being able to fall 
below 100.degree. C. 
SECOND STEP: first drawing out along the second axis Y. 
Referring to FIGS. 2A to 2F, the second step of the process consists of a 
first drawing out. According to the invention, this drawing out is carried 
out along the second axis Y. In order to do this, the billet 2 is placed 
on edge, so that the first axis X is horizontal, the second axis Y is 
horizontal and faces the forgeman, the third axis Z being vertical. The 
various operations of this step are preferably also carried out in a 
press. 
In the context of working tantalum billets, of the dimension described 
previously, the various operations may be the following. 
a--First of all, squaring is carried out in order to obtain a billet of 70 
mm sides. In order to carry out this operation, the billet may be rotated 
several times through 90.degree. about the second axis Y in order to be 
able to carry out this squaring alternately along the first and third axes 
X and Z, as FIGS. 2A and 2B show. A quench may be carried out at the end 
of this squaring operation in order to cool down the billet 3. 
b--With reference to FIG. 2C, the billet 4 is drawn out, still in the 
direction of the second axis Y, but so that its cross section 
perpendicular to the second axis Y is orthogonal. The octagon thus 
obtained may have a side equal to approximately 70 mm. This shape is 
obtained by acting on the edges which are perpendicular to the first and 
third axes X and Z and are obtained after the previous squaring. Of 
course, this octagonal drawing-out operation may be finished off with a 
quench. 
c--Given the length of the billet 4 thus obtained, with reference to FIG. 
2B, there is the need to cause the middle of this billet to neck. This 
operation consists in carrying out drawing out by pressure on the center 
of the billet 5. In fact, these previous drawing-out operations do not 
always force back the matter uniformly along the second axis Y. In 
particular, in the middle of the billet 5, this mass tends to be a little 
greater. The necking therefore makes it possible to even out the 
distribution of matter along the drawing-out axis, in this case the second 
axis Y. 
d--With reference to FIG. 2E, the drawing out along the second axis Y is 
continued by the thinning of the octagon thus obtained in order to obtain 
an octagonal bar 6, the side of which is in the neighborhood of 65 mm. The 
press is again used to act on these various phases of the octagon which 
are parallel to the second axis Y. 
e--This drawing out along the second axis Y may be finished off rounding 
off the billet 6 in order to obtain a cylindrical bar 7, as FIG. 2F shows. 
Of course, this drawing out along the axis Y may be finished off with a 
quench. 
It should be pointed out that, in the case of tantalum billets, it is 
advantageous to proceed at room temperature. 
During this drawing out, the forging ratio is approximately equal to 2. It 
may be slightly greater (2.3) and much less, of course. 
THIRD STEP: second upsetting along the second axis Y. 
Referring to FIG. 3, the process according to the invention consists in 
upsetting, along the second axis Y, the cylindrical bar 7 thus obtained by 
a drawing out along this same axis Y. The bearing faces 7A of the 
cylindrical bar 7 are very often not plane. In fact, the various previous 
operations tend to deform these two bearing faces 7A. In this case, the 
ends 7A may be taken up in the press by the forgeman in order to reform 
the bearing surfaces. Next, this bar 7 is placed on edge and is upset in 
the press to a ratio of 2, that is to say the bar 7 is reduced to half its 
length, while its diameter increases in order to give a cylindrical billet 
8. 
Given the very elongate shape of the bar 7, this upsetting may be carried 
out only after the verticality of the second axis Y is checked. 
This third step is preferably finished off with a water quench. 
FOURTH STEP: drawing-out along the third axis Z. 
As FIGS. 4A to 4G illustrate, this fourth step consists in drawing out the 
billet 8 in the direction in which it has not yet been worked, namely the 
third axis Z. The various operations of this step, in the case of tantalum 
billets mentioned up to now in the present embodiment, may be the 
following. 
a--With reference to FIGS. 4A and 4B, the first operation consists in 
squaring the cylindrical billet 8. The latter is therefore placed with its 
second axis Y horizontal and its first axis X vertical. The billet 8 is 
therefore upset in order to assume the shape of a flattened 
parallelepipedal billet 9. 
As FIG. 4B shows, the billet 9 thus obtained is rotated about its third 
axis Z in order to place the first axis X horizontal and the second axis Y 
vertical. A billet 10 is thus obtained of square cross section, the side 
of which is approximately equal to 70 mm. 
This first squaring operation may be finished off with a quench. 
b--As FIG. 4C shows, a necking operation is provided in the middle of the 
square billet 10 thus obtained. Partial upsetting of the matter in the 
middle of the billet is therefore carried out for the reasons already 
mentioned previously. In the center of the bar, the cross section of the 
square may thus have a side equal to approximately 60 mm. 
c--With reference to FIG. 4D, the square cross section of the billet 10 is 
evened out by squaring obtained by a drawing out along the third axis Z. A 
regular parallelepiped 11 of square cross section is thus obtained by 
acting along the first and second axes X and Y in a manner similar to the 
other squaring operations. 
d--In order to improve the distribution of matter, especially in the middle 
of this billet 11, the longitudinal edges 11A of this billet 11 are caused 
to neck. In order to do this, the billet 11 is successively positioned on 
its four longitudinal edges 11A which undergo plating, one after the 
other. Each diagonal may thus be reduced to a value of 65 mm. 
e--With reference to FIG. 4F, the drawing out along the third axis Z 
continues by actions on the four edges 11A of the billet 11 in order to 
obtain an octagonal bar of sides equal to approximately 65 mm. 
During this fourth drawing-out step along the third axis Z, the forging 
ratio may be in the neighborhood of 2.3. 
Of course, this drawing-out cycle may be finished off with a quench. 
During these operations, phenomena such as forging pinches may appear. They 
are then systematically removed by chipping. The same applies to the 
previous drawing-out operation. 
As FIG. 4G shows, this drawing out may possibly be finished off by rounding 
off the octagonal billet 12 obtained previously. A cylindrical bar 13 is 
thus produced which can be used directly for the manufacture of parts of 
revolution. 
This cylindrical shape may also be obtained by machining the octagonal 
billet 12 of FIG. 4F on a lathe. During this turning, a 5-mm radius may be 
made on the edges of the two plane faces of the cylindrical billet 13. 
FIFTH STEP: drop forging. 
Depending on the shape of the parts to be manufactured, the billet 13 
obtained after the fourth drawing-out step along the third axis Z, may be 
cut up into a large number of cylindrical parts. As FIG. 5 shows, for the 
manufacture of hollow-charge coatings of tantalum, it is advantageous to 
cut the billet up into a large number of discs 14. Moreover, it is 
possible, in order to facilitate this operation, to true up the faces of 
the billet 13 in a parallel lathe. 
The first operation of the drop-forging step consists in deforming the 
billet by means of a press. In order to manufacture hollow charges made of 
tantalum, on the base of the billets already described, a 2,000-tonne 
press may be used with a rate of drop of the ram of 5 mm/s. The die tool 
used is preferably closed and non-deformable. The die 17 and the ram 16 
may be lubricated with tungsten bisulphide. The closed-die tool shown in 
FIG. 6A comprises a fixed die 17 and a ram 16 which, once joined together, 
after the descent of the ram, form a closed space within which the billet 
15 is deformed in order to adopt a specified intermediate shape. 
A second operation of the drop forging consists in carrying out the 
finishing of the forging by accurate sizing with a drop hammer (FIG. 6B). 
This is especially useful in the case of large-sized parts. The drop 
hammer used in the case of billets intended to constitute hollow charges 
made of tantalum has a force of approximately 9,000 kgm. 
In this operation, the part has to be quenched upon opening the die tool. 
During all these operations, the working temperature for parts made of 
tantalum which are intended for producing hollow-charge coatings is room 
temperature. This thermal arrangement is not limiting, but it constitutes 
one embodiment. 
SIXTH STEP: recrystallization heat treatment. 
This heat treatment is intended to promote the fineness of the grain size 
constituting the final coating. It turns out to be the case that, for 
parts made of tantalum, a recrystallization at 970.degree. C. for 
approximately 1 h is carried out under secondary vacuum and enables a 
structure of the material to be obtained which is very homogeneous and 
very fine (G&lt;30). In addition, such a structure makes it possible to have 
homogeneity from the center through to the edges of the part obtained 
while still retaining a very significant deformation structure. This 
example of recrystallization heat treatment is particularly well suited to 
the manufacture of coatings made of tantalum for hollow charges. This 
example is therefore in no way limiting. In order to facilitate all these 
working and forging operations, it is very useful to display the three 
axes X, Y and Z on each of the faces of the initial billet. Thus, the 
various forge operators who have to work this part will easily be able to 
position it along the specified axis along which they have to draw out or 
upset the part. 
The various operations of the various steps described in this description 
are given by way of example, the principal concept of the invention being 
to upset and draw out the part along the three initial perpendicular 
directions defined by the orthogonal reference mark associated with the 
part, as explained at the beginning of the description.