Method of and appartus for producing a compression product

A method of producing components by compressing powdered material in a hollow die includes the use of a sleeve in the die to reduce the pressure required to remove the product from the die after compression, and to reduce cracking in the product after spring-back upon release of the component. An elastically deformable sleeve having a cylindrical internal surface and conical external surface is inserted into a tapered aperture in a die plate so as to reduce elastically the internal diameter of the sleeve. The component is produced by compressing powdered material in the interior of the sleeve by upper and lower punches. The upper punch is then removed and the sleeve is partially removed with the product from the die, by movement against the direction of the taper. The interior dimension of the sleeve increases elastically and the product is then removed from the sleeve by raising the lower punch.

This application claims benefit of international application 
PCT/GB94/01941, filed Sep. 7, 1994. 
The present invention relates to a method of, and apparatus for, producing 
a product by compression of material, particularly but not exclusively by 
compression of powdered metallic material. 
Many components for industrial applications are manufactured by the powder 
metallurgy route in which metal powders are formed into the desired shape 
with very little waste material and with high dimensional accuracy. 
However, the mechanical and physical properties of powder metallurgical 
materials depend significantly on the final density of the component. In 
general, mechanical strength improves dramatically as density is increased 
and, for example, in magnetic materials the permeability increases with 
increase in density. 
Many shaped components are made by pressing powder in fixed dies using, in 
its simplest form, a die with top and bottom punches. FIGS. 1a, b and c 
show a section through a die set used to produce a cylindrical object. 
Powder 11 is placed in the die 12 and the top and bottom punches 13 and 14 
compress the powder (FIG. 1a). The top punch 13 is then removed as in FIG. 
1b, and the compressed powder is ejected as a compact 15 which has 
sufficient strength to be handled, but insufficient to be used as a 
component (FIG. 1c). The compact is subsequently passed through a furnace 
at the appropriate temperature to induce diffusion between the powder 
particles. This so-called sintering process converts the pressed powder 
into a continuous material with sufficient strength for the proposed 
application of the component. 
One of the problems associated with pressing in a fixed die system relates 
to the compressibility of the powder and how the pressed compact is 
removed from the die. As the powder is pressed in the die set its density 
increases due to the increasing pressing pressure used during the pressing 
cycle. The compacted powder exerts an internal pressure Pi on the die 
walls, and the greater the axially applied pressure Pa the greater the 
internal pressure on the die walls (as shown in FIG. 1a). When the 
pressing pressure is removed there is still a residual stress in the 
compact 15 which exerts a pressure Pir on the die walls (as shown in FIG. 
1b). It is necessary to use an ejection force Pe (FIG. 1b) to overcome 
this die wall pressure and to eject the compact from the die. 
As the compact 15 is being ejected from the die 12 (as shown in FIG. 2), it 
is subjected to external shear forces Fe on its external surface due to 
the restraining effect of the die. As the axial pressing pressure Pa 
(previously applied) increases, this shear force Fe (arising during 
release) also increases, making it more difficult to eject the component. 
Hence the ejection force Pe which is required increases, and there is a 
danger of the compact damaging the die walls, and the compact itself being 
damaged by the contact with the die walls. Additionally, as the compact 15 
emerges from the die 12 it is no longer restrained by the die as in FIG. 
3, and as there are elastic stresses in the compact due to the pressing 
operation the compact is able to change its shape to relieve these elastic 
stresses. This is known as `spring-back`. This means, for example as shown 
in FIG. 3, that a powder compact 15 compressed in a die 12 of a specific 
internal diameter D, will, on ejection, have a diameter D+dc, where dc is 
the increase in diameter of the compact on ejection. This spring-back 
effect can result in the pressed compact developing cracks at right angles 
to the pressing direction, due to the difference in diameter of the part 
of the compact still in the die (with a diameter D), and the part which 
has been ejected free from the die (with a diameter D+dc). At the change 
in diameter at the top face of the die cracks can be formed. 
In order to produce high density components it is necessary to obtain as 
high a density in the pressed powder compact as possible, but as is now 
evident the higher the pressing pressure the more difficult it is to 
remove the compact from the die. The ejection forces will need to be 
higher the higher the compaction pressure, and there is a high probability 
that the die, and/or the compact will be damaged during the ejection 
stroke. There is also the problem that the spring-back effect will 
increase as the pressing pressure increases leading to damaged compacts on 
ejection. These problems normally mean that pressing pressures, and 
therefore pressed densities, are restricted when using fixed dies. 
In SU-A-1315135 (Zlobin et al) there is disclosed apparatus for producing a 
compacted article by compression of metal powder. A die is formed of three 
partible units and has a slotted elastic shell inside the die. The 
external surface of the die units is conical and is enclosed in a 
corresponding conical hole of a thrust ring. Axial movement of the thrust 
ring clamps the units of the die towards each other and compresses the 
slotted shell closing its slot. Then, metal powder is charged into the 
shell acting as an inner liner of the die, and the powder is compacted by 
a single ended pressing punch. After compaction, the thrust ring is 
pressed downwardly which opens the die, releasing the compacted article. 
One disadvantage of such an arrangement in practical use is that the powder 
to be compacted finds its way into the slot in the inner lining of the 
die. The behaviour of metallic powders during compaction is not that of a 
fluid. The region of the powder adjacent the moving punch will compact 
first, whilst powder remote from the piston will not at first be 
compressed. The pressure of compaction will mean that some opening at the 
slot will exist, and powder will be forced into this opening. Also 
generally during operation of the machine, despite cleaning, powder will 
build up in the crack of the shell, and that powder will itself be 
compacted during subsequent operations. The result is that it will not be 
possible to close completely the slot in the shell in subsequent 
operations, which means that accuracy is lost both in the dimensions of 
the compact produced, and in the provision of protrusions at the surface 
of the compact where the slot has been positioned. Other disadvantages of 
the arrangement are that the thrust ring will not apply pressure evenly to 
the inner shell. Furthermore, since the shell is slotted, the tensions in 
the shell will vary from compression where the edges of a slot abut each 
other, to tension on the outside of the shell diametrically opposite the 
slot. Such tensions will prevent compression of the slotted shell 
uniformly around the perimeter of the lining, which will again reduce 
accuracy of the compact being produced. 
In a paper entitled "NOVEL METHODS OF POWDER COMTION" by G. I. Begenkoff 
and G. B. Zlobin, at pages 289 to 292 of the report of PM90, World 
Conference on Powder Metallurgy held on 2-6 Jul., 1990 in London, there is 
disclosed apparatus for producing a compact from powder. The apparatus 
comprises a die formed of segments and having an outer conical surface, 
the segments being held together by a holder having a tapered opening 
corresponding to the taper of the die segments and in which the die 
segments are positioned. A single ended, upper pressing ram compresses 
powder in the segmented die against inwardly directed flanges of the die 
segments, and at the same time presses the die segments into the conical 
opening in The holder. During formation of the compact, the compacting 
pressure is transferred through the compact to the lower ram and die 
segment flanges, which causes the die segments to be radially compressed 
by the conical side walls of the tapered holder. When the load is removed 
from the upper ram, the die segments move apart under the lateral pressure 
exerted by the holder, sliding upwards along the inclined faces of the 
holder. The value of the taper angle of the holder is more than the angle 
of friction between the die segment and the holder. 
The disadvantages of this arrangement are similar to those in the patent 
mentioned hereinbefore, in that the separate die segments will again 
provide openings between the segments into which powder will find its way 
during compression. This is particularly acute in the example of the 
referenced paper, because the force provided to compress inwardly the die 
segments arises from the compaction force of the ram compressing the 
product material. Thus at the beginning of She compression stroke, the die 
segments will not be compressed inwardly, leaving even larger gaps for the 
powder to migrate into. Other disadvantages include the fact that it is 
not possible to vary the inward force on the die segments independently of 
the load force applied for compaction of the product. 
According to the present invention there is provided a method of producing 
a product by compression of material, comprising the steps of: providing 
in a hollow die a compressed lining which is elastically compressed so as 
to reduce the internal size of the lining relative to the internal size 
before compression, compressing product material in the lining to produce 
a compressed product, releasing the lining at least partially from the die 
to produce an increase in the internal size of the lining, and removing 
the compressed product from the lining, in which the lining is continuous 
around the interior the die. 
The provision of a continuous lining avoids the difficulty of powder 
finding its way into slots or other openings with consequent lack of 
accuracy. It is preferred that the lining is compressed by elastic 
deformation of the lining material uniformly around the perimeter of the 
lining. The required reduction in internal size of the lining can be 
obtained not by the movement of separated parts of a lining or die towards 
each other but by the uniform elastic deformation of the bulk material of 
the lining, as a result of inward pressure applied to the lining. This 
allows accuracy to be maintained, even in die shapes having a complicated 
interior surface, by arranging for uniform forces to be applied around the 
lining, to produce a smooth continuous elastic deformation of the lining 
material. This produces an internal shape of the lining which is reduced 
in size, but maintains dimensional integrity with the desired shape for 
the finally compressed product. 
It is believed that in the prior art set out above a slot in a sleeve was 
used because it was thought that a large recovery movement was required 
upon release of the sleeve and that this could only be achieved by a slot. 
It has now been found, unexpectedly, that the elastic recovery from a 
continuous lining can be made to be of the same order as the springback of 
the component being made, so that a continuous lining can be used, which 
gives rise to an industrially viable process. 
It is to be appreciated that the steps set out in accordance with the 
invention are not necessarily performed separately in the order given, and 
that the order may be varied, and indeed may overlap. For example the 
reduction in size of the lining may be produced partly or completely 
before insertion of the lining in the die, for example by compression of 
the lining in another member before insertion into the die. In other 
arrangements, the internal size of the lining may be decreased during the 
pressing operation itself. However, preferably the compression of the 
lining in the die is achieved during the step of inserting the lining into 
the die. The material to be compressed may be placed in the lining before 
or after the lining is inserted into the die, but normally the material 
will be inserted after the lining is inserted into the die. The invention 
is particularly applicable where the method includes placing the product 
material in the interior of the lining in powdered form, and compressing 
the material into a rigid product. 
Depending upon the shape and application of the lining, the changes in 
internal and/or external size of the lining may be changes in one or more 
than one dimension. Although the lining may assume a number of shapes, 
depending upon the shape of the die, the invention is particularly 
applicable where the lining is a sleeve and the method includes inserting 
the sleeve into the die along the direction of a common axis of the sleeve 
and the die. Preferably the exterior of the sleeve and the interior of the 
die are both tapered, and the method includes inserting the sleeve into 
the die in the direction in which the sleeve and die are tapered. 
The invention has particular application where the lining is compressed by 
the step of compressing the lining by elastic deformation of the lining 
material uniformly around the perimeter of the lining, and preferably is 
compressed by the step of compressing the lining before the step of 
compressing the product material to produce the compressed product. In 
some preferred forms, the method includes the step of producing an 
adjustable, selectable compression of the lining, whereby the increase in 
internal size of the lining on release of the lining from the die can be 
selected in relation to the expected increase in external size of the 
product on release from the die. However, in some production examples, the 
apparatus used will be set so as to produce a predetermined compression of 
the lining, for a particular product to be made. 
The amount of compression of the lining will be chosen according to the 
requirements of the product, but preferably the method includes 
compressing the lining to an extent such that the increase in internal 
size of the lining on release of the lining from the die is in the range + 
or -20% of the increase in external size of the product on release from 
the die, preferably the range being + or -10%. Normally the lining will be 
compressed to an extent such that the increase in internal size of the 
lining during release from the die is at least equal to the expansion of 
the product after release from the die, preferably substantially equal to 
the expansion of the product. 
Although it may be arranged that the product has a generally circular 
perimeter, and the said increase of size of the product and the lining is 
an increase in radius thereof, other shapes of die and lining may be 
provided, such as an oval, or a complex shape such as that of an engine 
connecting rod. The outer surface of the sleeve and the inner surface of 
the die may assume a number of shapes, but conveniently the outer surface 
of the sleeve and the inner surface of the die are both circular in cross 
section. 
In many arrangements the interior surface of the sleeve is circular in 
cross section. However the interior surface of the sleeve may have the 
configuration of a mould for producing an article of generally circular 
cross section but having a varying shape around its perimeter, e.g. the 
configuration of a mould for producing a gear wheel. Thus the interior 
surface of the sleeve may have a configuration such that the distance of 
the surface from the axis of the sleeve varies around the interior surface 
of the sleeve. In some arrangements the interior surface of the sleeve has 
a cross section which is constant along the direction of the axis of the 
sleeve, but in other arrangements the interior surface of the sleeve has a 
cross section which varies in the direction of the axis of the sleeve, for 
example in discontinuous steps. 
The invention finds particularly preferred application where the lining is 
a sleeve and the method includes inserting the sleeve into the die along 
the direction of a common axis of the sleeve and the die, and in which the 
interior of the die is tapered in the direction of the common axis so that 
insertion of the sleeve produces compression of the sleeve by the die. 
Preferably the exterior of the sleeve is also tapered, in the same sense 
as the taper of the interior of the die, and preferably the angle of taper 
of the sleeve is the same as the angle of taper of the die. Preferably the 
angle of taper of the die is in the range 0.5 to 10', most preferably in 
the range 1 to 5.degree., and particularly preferably about 2.degree.. 
The invention finds particular application where the hollow die is provided 
by an aperture in a die and the method includes compressing the material 
by moving upper and lower punches into the aperture in the die in the 
interior of the lining. However the invention is equally applicable with 
rotary compaction to densify powder. Rotary compaction is a known process 
having the following main steps. 
The bottom of the top punch of a rotary compaction die set has a conical 
surface and the central axis of the top punch is offset with respect to 
the central axis of the die at such an angle that when the top punch is 
lowered onto the powder, a line contact is produced between the top punch 
and the powder. This contrasts with the whole of the bottom surface of the 
top punch in a conventional die set contacting the surface of the powder. 
The line contact in rotary compaction is made to rotate about the centre 
line of the die by a suitable mechanical means. Methods to produce this 
are well known. Nominal line contact means that much higher specific 
pressures are applied to the powder, resulting in high density compacted 
material. 
In accordance with one particular feature of the invention, there is 
provided a method of calibrating the die and lining by the steps of: 
(a) pressing the sleeve into the die and measuring the change in inner 
diameter of the sleeve as a function of the change in axial position of 
the sleeve; 
(b) for any particular product material, measuring the compressibility and 
spring back as a function of the pressing pressure; 
(c) for a required pressing density during production of a compressed 
product, determining from the information of step (b) the spring back 
which would occur in a conventional die; and 
(d) determining from the data acquired in step (a) the extent of insertion 
of the sleeve that is required to give a value of decrease of inner 
diameter of the sleeve which is equal to the expected spring back 
determined in step (c), or falls within a predetermined range of deviation 
from that springback. 
There will now be set out a number of independent aspects of the invention, 
which may be utilised independently of the main features set out above. In 
one further aspect of the invention there may be provided a method of 
producing a product by compression of material, comprising the steps of: 
providing in a hollow die a compressed sleeve which is elastically 
compressed so as to reduce the internal size of the sleeve relative to the 
internal size before compression, inserting into the compressed sleeve a 
material to be compressed, compressing the material in the sleeve to 
produce a compressed product, releasing the sleeve at least partially from 
the die to produce an increase in the internal size of the sleeve, and 
removing the compressed product from the sleeve, in which the interior 
surface of the die and the exterior surface of the sleeve are both 
tapered, the method including the step of inserting the tapered sleeve 
into the tapered die and compressing the sleeve by the effect of the 
tapered surfaces, before the compression of the material in the sleeve to 
produce the product. 
In yet another aspect of the invention there may be provided a method of 
producing a product by compression of material, comprising the steps of: 
providing in a hollow die a compressed lining which is elastically 
compressed so as to reduce the internal size of the lining relative to the 
internal size before compression, compressing product material in the 
lining to produce a compressed product, releasing the lining at least 
partially from the die to produce an increase in the internal size of the 
lining, and removing the compressed product from the lining, including the 
step of compressing the lining by elastic deformation of the lining 
material uniformly around the perimeter of the lining. 
In a yet further aspect, there may be provided in accordance with the 
invention a method of producing a product by compression of material, 
comprising the steps of: providing in a hollow die a compressed lining 
which is elastically compressed so as to reduce the internal size of the 
lining relative to the internal size before compression, compressing 
product material in the lining to produce a compressed product, releasing 
the lining at least partially from the die to produce an increase in the 
internal size of the lining, and removing the compressed product from the 
lining, including the step of producing an adjustable, selectable, 
compression of the lining, whereby the increase in internal size of the 
lining on release of the lining from the die can be selected in relation 
to the expected increase in external size of the product on release from 
the die. 
Finally, in accordance with another aspect of the invention, there may be 
provided a method of producing a product by compression of material, 
comprising inserting into a hollow die a core which is elastically 
expanded; compressing product material in the die around the core; after 
the compression of the product material, reducing the size of the core; 
and removing the compressed product from the die and from the core. 
It is to be appreciated that where features of the invention have been set 
out in accordance with a method of the invention, these features may also 
be provided in accordance with an apparatus according to the invention. In 
particular there may be provided in accordance with the invention in a 
first aspect apparatus for producing a product by compression of material 
comprising: a hollow die; an elastically compressible lining for the die; 
means for compressing the lining to provide in the die a compressed lining 
of reduced internal size; means for compressing material in the interior 
of the lining when inside the die, and means for releasing the lining at 
least partially from the die to produce an increase in the internal size 
of the lining to allow removal of the compressed product from the lining, 
in which the lining is a continuous lining for the interior of the die. 
Preferably the lining has, when uncompressed, an external size greater 
than the internal size of the die, and the means for compressing the 
lining comprises means for forcing the elastically compressible lining 
into the die so as to compress the lining. 
In accordance with another aspect of the invention, there may be provided 
apparatus for producing a product by compression of material comprising: a 
hollow die; an elastically compressible lining for the die; means for 
compressing the sleeve to provide in the die a compressed sleeve of 
reduced internal size; means for compressing material in the interior of 
the sleeve when inside the die, and means for releasing the sleeve at 
least partially from the die to produce an increase in the internal size 
of the sleeve to allow removal of the compressed product from the sleeve, 
in which the interior surface of the die and the exterior surface of the 
sleeve are both tapered and the means for compressing the sleeve comprises 
means for forcing the sleeve into the die independently of the means for 
compressing the material in the interior of the sleeve. 
There is also provided in accordance with the invention a product formed by 
compression of material in accordance with the steps of the method set 
out, or by use of the apparatus set out. 
The invention can provide simple means which have been found to be 
effective in overcoming the problems set out hereinbefore enabling high 
pressing pressure to be applied whilst still being able to remove the 
pressed product from the die without damage to either the compact or the 
die set.

As has been described in the introduction to the specification, FIGS. 1a to 
1c illustrate a known apparatus for producing a product by compression, 
comprising a die 12 and upper and lower punches 13 and 14 for compressing 
powdered material 11, to produce a compact 15. FIG. 2 illustrates the 
shear forces which arise during ejection of the compact 15, and FIG. 3 
illustrates the change of diameter which occurs in the compact during 
ejection, in known methods. FIGS. 4 and 4a to 4f are diagrammatic 
representations in cross section of apparatus embodying the invention for 
producing a product by compression, and illustrate steps in the method of 
use of this apparatus. In these Figures, components corresponding to 
components shown in previous Figures are indicated by like reference 
numerals. As shown in FIG. 4, the modifications to the die set in 
accordance with this embodiment of the invention involve the introduction 
of a relatively thin, elastically deformable inner sleeve 16 to the die 12 
as shown in FIG. 4. This sleeve 16 has an external taper Te, which is 
matched by an internal taper Ti in the die bore, and has an unstressed 
inner diameter of Ds. 
One method of operation is as follows. In the first step, the inner sleeve 
16 is pressed into the die 12 as shown in FIG. 4a. During this movement a 
compressive stress is generated in the sleeve 16 and the inner diameter Ds 
of the sleeve is reduced by an amount ds which is dependant on the 
relative movements of the inner sleeve with respect to the die 12. The 
further the sleeve is pressed into the die the greater will be the value 
of ds. This movement has to be elastic in nature such that when the inner 
sleeve 16 is subsequently pushed out of the die, the inner diameter 
recovers to its former value Ds. Next, the bottom punch 14 is entered into 
the die and the powder 11 is placed in the inner sleeve 16. The top punch 
13 is then inserted into the die, as shown in FIG. 4b. The top punch and 
bottom punches 13 and 14 are pressed into the die to compact the powder 
11, as shown in FIG. 4c. At this stage the inner diameter of the sleeve 16 
is DS-ds and the diameter of the compressed compact 15 is also Ds-ds. The 
next step is that the top punch 13 is removed, as shown in FIG. 4d. The 
bottom punch 14, inner sleeve 16 and the compact 15 are then all moved 
upwards together relative to the die 12, releasing the inner sleeve 12 
from the taper of the bore, as shown in FIG. 4e. During this step the 
inner diameter of the sleeve 16 recovers to its original diameter Ds. As 
the diameter of the inner sleeve 16 is increased to this original diameter 
the compact also increases in diameter due to the `spring-back` effect, 
that is to say the relief of the elastic stresses in the compact due to 
the pressing operation. The diameter of the compact becomes Ds-ds+dc, 
where dc is the change in diameter due to the spring-back effect. Lastly, 
the compact 15 is ejected from the inner sleeve 16 by moving the bottom 
punch 14 relative to the inner sleeve 16, as shown in FIG. 4f. 
Two significant points arise. If the value of ds is arranged so that it is 
equal to, or slightly greater than, dc, then at the last step the inner 
sleeve 16 will not be in contact with the compact 15, and the ejection 
force required for the last step will be low. Also, it is to be noted that 
in the movement of the sleeve 16 and compact 15 to partially release the 
sleeve and the compact from the die 12 (the movement from FIG. 4d to FIG. 
4e), the internal diameter of the sleeve 16 resumes its previous diameter 
of Ds in a single movement which is uniform throughout the height of the 
sleeve 16. This arises because the sleeve 16 is released from the taper of 
the bore of the die 12 uniformly throughout its length. The advantage is 
that the compact 15 is allowed to expand to its final diameter in a 
uniform movement throughout the length of the compact. This avoids 
cracking due to gradual change of diameter as shown in the known 
arrangement of FIG. 3. 
In practice, for any specific pressing pressure the value of dc can be 
obtained experimentally by pressing compacts in a die of fixed size and 
measuring the diameter of the compact on ejection. The sleeve is then 
designed such that ds is greater than dc. This design be either by 
calculation from the known mechanical properties of the sleeve materials 
used, or by trial and error. The essential part of the process in the 
embodiment described is that the internal diameter of the inner sleeve has 
to decrease elastically before or during the pressing operation, and on 
removal of the sleeve from the die an elastic recovery of the internal 
diameter of the die takes place, preferably slightly greater than the 
elastic recovery of the external diameter of the compact. Although the 
geometry has been described in terms of a solid cylindrical component, the 
technique is applicable to other shapes, for example washers or hollow 
cylinders. These may have non-circular external shapes, such as various 
gear forms. It is also to be appreciated that the technique can be used 
for the re-repressing of partially sintered powder metallurgy compacts, 
and also fully sintered compacts either to increase their density or to 
press them to final, accurate, dimensions. 
There will now be described with reference to FIGS. 4 and 4a, and FIGS. 5 
to 8, a method of calibrating the die and lining shown in FIGS. 4 to 4f. 
In summary, this calibration is achieved by the steps of: 
(a) pressing the sleeve into the die and measuring the change in inner 
diameter of the sleeve as a function of the change in axial position of 
the sleeve; 
(b) for any particular product material, measuring the compressibility and 
spring back as a function of the pressing pressure; 
(c) for a required pressing density during production of a compressed 
product, determining from the information of step (b) the spring back 
which would occur in a conventional die; and 
(d) determining from the data acquired in step (a) the extent of insertion 
of the sleeve that is required to give a value of decrease of inner 
diameter of the sleeve which is equal to the expected spring back 
determined in step (c), or falls within a predetermined range of deviation 
from that springback. 
Referring to FIG. 4, the reference letter h indicates the height of the 
sleeve 16 above the top of the die 12, and L indicates the load on the 
sleeve 16 during insertion of the sleeve into the tapered bore in the die 
12. The first calibration step, step (a), consists of pressing the sleeve 
16 into the die 12 under the load L and measuring the change in the 
protruding height h and the change in the inner diameter of the sleeve ds 
which results. The inter-relationship between these measured parameters, 
is shown diagrammatically in FIG. 5. In this Figure the abscissa 
coordinate of the graph shows change in height h. The ordinate coordinate 
shows for the broken line the load L, and for the continuous line, the 
change in inner diameter ds of the lining 16. 
The second step of calibration, step (b), is the measurement for any 
particular powder, of the compressibility and springback as a function of 
pressing pressure. The springback is the difference between the inner 
diameter of the die and the outer diameter of the compact when ejected 
from the die. The relationship between density and springback is shown 
schematically in FIG. 6. In this figure the ordinate coordinate shows the 
pressing pressure acting on the powder during formation of the compact. 
The abscissa coordinate shows in respect of the broken line the density of 
the compact after termination at a given pressing pressure and after 
ejection from the die. The ordinate coordinate shows in respect of the 
continuous line the springback of the compact after ejection from the die. 
The third step of calibration, step (c), is the determination, for a 
required final pressing density do, the springback dco that would occur in 
conventional dies such as those illustrated in FIGS. 1a to 3. The 
relationship of this springback dco is shown in FIG. 7, in which the 
abscissa coordinate indicates pressing pressure during formation of the 
compact. The ordinate coordinate shows in respect of the broken line the 
density of the compact and shows in respect of the continuous line the 
springback dc. 
The fourth step, step (d), is to determine the change in height ho that is 
required to give a value of ds equal to dco, as illustrated in FIG. 8. In 
FIG. 8 the abscissa coordinate shows change in h. The ordinate coordinate 
shows, in respect of the broken line the change in inner diameter ds, and 
shows in respect of the continuous line the load L applied to force the 
sleeve into the die. Determination of the change in height ho that is 
required to give a value of ds equal to dco, effectively ensures that the 
elastic recovery of the die diameter on ejection is equal to increase in 
diameter of the compact when unconstrained. 
There will now be described with reference to FIGS. 9 and 10 an example of 
production tooling to put into effect the embodiment of the invention 
explained diagrammatically with reference to FIGS. 4 to 4f. Components 
which correspond to components in the earlier figures are indicated in 
FIGS. 9 and 10 by the same reference numerals. A die 12 has an internal 
taper along its internal face 17, and a sleeve 16 has a taper on its 
external face 18, corresponding to the taper of the die 12. The taper is 
approximately 2.degree.. In FIG. 9 a lower punch 14 is shown and in FIG. 
10 the lower punch 14 and an upper punch 13 are both shown. The finished 
product, a compact 15, is in this case in the shape of a ring, formed by 
an internal core 19, centrally placed in the bore of the die 12. The core 
19 is moveable vertically during compression to accommodate the downward 
movement of the upper punch 13, in conventional manner. In the example 
shown, the core 19 is conventional, of constant outer diameter, but other 
embodiments the core 19 may be made to expand elastically before 
compression, and to contract on release of the compact from the die, in 
accordance with the present invention. FIG. 9 shows the apparatus in an 
initial stage of the filing and compressing cycle, and FIG. 10 shows the 
apparatus in the final stage when the compact 15 has been fully 
compressed. 
The tooling consists of a die holder 20 into which is located the die 12. 
The die 12 is a multicomponent die, but is assembled so as to be a single 
continuous unit. Two low pressure seals 21 and 22 are positioned between 
the die 12 and die holder 20. A radial member 23 engages sleeve 16 at the 
top thereof, in a cooperating circumferential groove 24 in the sleeve 16. 
The radial member 23 is bolted to a piston 25 which can move vertically 
relative to the die holder 20 and a outer retaining structure 26, which is 
bolted to the die holder 20. The radial member 23 is actuated by the 
piston 24 in operation as will be explained hereinafter. The piston 25 can 
slide in the annular opening provided between the die holder 20 and the 
outer retaining structure 26. The piston 25 has a lower space 27 into 
which oil can be pressurised to move the piston 25 upwardly, and therefore 
to push out the sleeve 16 from the die 12. The lower space 27 is contained 
by high pressure seals 28, 29 and 30. An upper space 31 is provided into 
which oil may also be pressurized in a controlled cycle, to move the 
piston 25 downwardly and consequently to move the sleeve 16 into the die 
12. The upper space 31 is contained by high pressure seals 28 and 32. The 
whole assembly is held in a press bolster by the retaining structure 26. A 
subsidiary power pack (not shown) delivers high pressure oil to the upper 
and lower spaces 31 and 27 at the correct time during the press cycle. 
These times are taken from a master cam (not shown) on the press, the 
position of which is converted into press angle, between 0 and 360.degree. 
in conventional manner. By way of example, the dimensions of the sleeve 
may be as follows. 
______________________________________ 
Length: 103.60 mm 
Inner diameter: 44.66 mm 
Outer diameter at top: 
55.85 mm 
Outer diameter at bottom: 
49.68 mm 
Depth of groove 24: 
10.00 mm 
______________________________________ 
The operation of the apparatus will now be described. Starting from an 
initial position shown in FIG. 9 with the top punch 13 removed from the 
die 12, the cycle is as follows. The upper space 31 is pressurized to push 
the sleeve 16 into the die 12. The internal dimensions of the sleeve 16 
are consequently reduced, as has been explained hereinbefore. The degree 
of reduction of internal dimensions of the sleeve can be varied, by 
varying the degree of movement of the radial member 23 by the piston 25. 
Conveniently the degree of movement of the sleeve into the die can be 
determined by placing spacers between the radial member 23 and the top of 
the die 12. In the present case, pressurized oil is admitted to the upper 
space 31 until the undersurface of the radial member 23 rests on the upper 
surface of the die 12. The powder to form the compact 15 is then placed in 
the interior of the lining 16 of the die 12, in this case with a core 19 
protruding upwardly through the powder. The top punch 13 then enters the 
die and descends relative to the lower punch 14 and the sleeve 16. The 
compact 15 is thus produced by compression, as shown in FIG. 10. During 
the entry of the upper punch 13 into the die, the core 19 descends to the 
position shown in FIG. 10. During the compression, the lower punch 14 
rises relative to the sleeve 16 and the powder 15. 
In practice in the embodiment shown, the movements which have been 
described in relative terms, are not absolute. In known manner in double 
ended presses, the lower punch 14 stays stationery in an absolute position 
in the press bolster and the effect of the lower punch compressing the 
material is achieved by the entire assembly of die holder 20 and retaining 
structure 26, being lowered during the press cycle. Thus the double ended 
compression is achieved by the lower punch 14 remaining stationary the die 
12 descending through one measured distance, and the upper punch 13 
descending through twice the predetermined distance. 
After the compression is completed as shown in FIG. 10, the upper space 31 
is depressurized. The top punch 13 is withdrawn by the normal press cycle. 
The lower space 27 is pressurized to push upwardly the sleeve 16 with the 
compact 16 still inside it. During the sleeve withdrawal the internal 
dimensions of the sleeve revert to their original, larger dimensions, and 
there is no relative vertical movement between the compact 15 end the 
sleeve 16 during this expansion. The bottom punch 14 is then used to eject 
the compact from the sleeve. The lower space 27 is then finally 
depressurised. 
The materials used for the die 12, the sleeve 16 and the punches 13 and 14, 
are conventional tool steel compositions, conveniently AISI D3/D6. 
Examples are as follows. 
TABLE A 
______________________________________ 
Tooling Materials 
Composition of Tooling Materials by weight % 
Material 
C Cr Mo V Mn W Si Co Ni Fe 
______________________________________ 
AISI D2 1.55 12 0.7 1 bal 
AISI D3/D6 
2.05 12.5 0.8 1.3 0.3 bal 
AISI M2 0.9 4.1 5 1.9 6.4 bal 
AISI M3/2 
1.28 4.2 5 3.1 6.4 bal 
______________________________________ 
FIGS. 11a and 11b show respectively a plan view and a section of a sleeve 
suitable for use in the apparatus of FIGS. 9 and 10, to produce a 
gearwheel shown in FIGS. 12a and 12b. The dimensions of such a component 
and sleeve may be as follows. Outer diameter of sleeve at top 102.20 mm; 
outer diameter of sleeve at bottom 98.00 mm; length of sleeve 60.00 mm; 
taper of sleeve 2.degree.; outer diameter of gear wheel 93 mm. 
EXAMPLES 
There will now be described a series of examples of the production of 
compacts of different materials, made by a conventional method and by the 
method of the invention. Where a compact is produced by a conventional 
die, the die is a double ended pressing die such as shown in FIGS. 1a to 
3. Where a compact is made in accordance with the invention, it is made by 
a double ended pressing apparatus of the kind shown diagrammatically in 
FIGS. 4 to 4e, and, in a production example, in FIGS. 9 and 10. Where 
reference is made to the use of hand set dies, this refers to a 
hand-operated trial set of dies and punches. Where reference is made to 
production tooling, this refers to the production tooling apparatus shown 
in FIGS. 9 and 10. The materials used in the examples are as follows. 
TABLE B 
__________________________________________________________________________ 
Composition of Materials Used for Compacts 
Composition by Weight % 
Material C S P Mn Mo Ni Si Cr Cu Fe 
__________________________________________________________________________ 
NC100.24 0.02 bal 
Atomet 1001 
0.003 bal 
Atomet 4601 
0.003 
0.009 
0.012 
0.2 
0.55 
1.8 
0.003 
0.005 
0.02 
bal 
316L stainless st. 
0.016 
0.009 2.55 
12.9 
0.88 
17.9 bal 
__________________________________________________________________________ 
In each table of results in the Examples, the headings of the columns have 
the following meanings. Pressing Pressure indicates the pressure in tons 
per square inch applied to the powder to be compressed, by the double 
ended pressing. Density indicates the density of the compact in grammes 
per cc, after ejection of the compact from the press. % springback 
indicates the expansion of the compact after ejection from the die, 
defined as follows: 
##EQU1## 
The column headed "Die scoring or compact cracking" indicates by an x those 
samples where unacceptable difficulties arose from the high Dressing 
pressure used, either by scoring of the internal surface of the die due to 
sticking of the compact during ejection, and/or the presence of cracking 
in the compact after ejection, due to the partial expansion of the compact 
as it became partially ejected from the die. 
Example 1 
(NC100.24) 
Cylindrical compacts were made from NC100.24 ferrous powder using a 
conventional double ended pressing die with different amounts of 
lubrication, by zinc stearate, giving the following results. 
TABLE 1 
______________________________________ 
Conventional Pressing 
Material Compressed: NC100.24 + 0.8% zinc stearate. 
Pressing 
Density Die scoring or compact 
Pressure tsi 
g/cc % Springback 
cracking 
______________________________________ 
45.2 7.05 0.281 
50.9 7.08 0.307 
56.5 7.14 0.346 
65.7 7.16 0.316 x 
78.8 7.21 0.335 x 
______________________________________ 
Table 2: Conventional Pressing 
TABLE 2 
______________________________________ 
Conventional Pressing 
Material Compressed: NC100.24 + 0.6% zinc stearate 
Pressing 
Density Die scoring or compact 
Pressure tsi 
g/cc % Springback 
cracking 
______________________________________ 
52.5 7.13 0.252 
65.7 7.25 0.292 
78.8 7.29 0.328 x 
______________________________________ 
Table 3: Conventional Pressing 
TABLE 3 
______________________________________ 
Conventional Pressing 
Material compressed: NC100.24 + 0.4% zinc stearate 
Pressing 
Density Die scoring or compact 
Pressure tsi 
g/cc % Springback 
cracking 
______________________________________ 
28.3 6.63 0.171 
33.9 6.88 0.207 
39.6 6.99 0.244 
45.2 7.12 0.265 x 
50.9 7.18 0.289 x 
65.7 7.32 0.284 x 
78.8 7.38 0.328 x 
______________________________________ 
Table 4: Conventional Pressing 
TABLE 4 
______________________________________ 
Conventional Pressing 
Material Compressed: NC100.24 + 0.2% zinc stearate. 
Pressing 
Density Die scoring or compact 
Pressure tsi 
g/cc % Springback 
cracking 
______________________________________ 
11.3 5.49 0.102 
16.9 6.03 0.118 
22.6 6.34 0.131 
28.3 6.63 0.173 x 
33.9 6.84 0.184 x 
______________________________________ 
A series of compacts was then produced by means of an elastically 
compressible lining in a method embodying the invention. Compacts were 
produced using a hand set as shown in FIGS. 4 to 4f, and having the 
following parameters. 
TABLE C 
______________________________________ 
Handset. Hand Operated die set 
Applied Reduction in 
Sleeve Load Diameter Ds Diameter ds 
tonnes mm mm % ER 
______________________________________ 
0 32.157 0 0 
5 32.0895 0.0675 0.21 
7.5 32.074 0.078 0.243 
10 32.06 0.097 0.302 
Ejection load on sleeve 5 t. 
______________________________________ 
Applied sleeve load means the load in tons applied to the top of the sleeve 
(for example as shown in FIGS. 4 and 4a) to force the sleeve into the 
tapered die. Diameter Ds means the diameter of the interior of the sleeve 
which diminishes as the sleeve is forced into the conical die, measured in 
millimeters. Reduction in diameter, ds, means the reduction in the 
internal diameter of the sleeve produced by application of the load shown. 
% ER means the elastic recovery of the sleeve after release from the die 
measured as a % of the increase in internal diameter of the sleeve upon 
release, defined as follows: 
##EQU2## 
Cylindrical compacts were made from NC100.24 ferrous powder using a double 
ended pressing die embodying the invention, as shown in FIGS. 4 to 4f, 
with different amounts of lubrication by zinc stearate, with the following 
results. 
TABLE 5 
______________________________________ 
Pressing by an Embodiment of the Invention 
Material compressed: NC100.24. Hand Operated Die Set. 
Sleeve fully inserted. No die scoring or compact cracking found. 
Pressing 
Eject. 
Dens- 
ds Pressure 
pressure 
ity 
Lubrication 
(mm) % ER Springback % 
tsi tons g/cc 
______________________________________ 
0.8% zinc 
0.097 0.302 0.28 at 50 tsi 
48 0 7.13 
stearate 
0.8% zinc 
0.097 0.302 0.295 at 55 tsi 
56 &gt;5 t 7.24 
stearate 
0.8% zinc 
0.097 0.302 0.325 at 65 tsi 
64 &gt;5 t 7.29 
stearate 
0.8% zinc 
0.097 0.302 0.34 at 70 tsi 
72 &gt;5 t 7.31 
stearate 
0.8% zinc 
0.097 0.302 0.356 at 80 tsi 
80 &gt;5 t 7.39 
stearate 
die wall 0.097 0.302 0.120 at 40 tsi 
48 0 7.19 
lubrication 
die wall 0.097 0.302 0.120 at 40 tsi 
56 0 7.33 
lubrication 
die wall 0.097 0.302 0.120 at 40 tsi 
64 0 7.43 
lubrication 
die wall 0.097 0.302 0.120 at 40 tsi 
72 0 7.4 
lubrication 
die wall 0.097 0.302 0.259 at 80 tsi 
80 0 7.54 
lubrication 
______________________________________ 
A series of compacts was then produced using the production tooling as 
shown in FIGS. 9 and 10, and having the following parameters. 
TABLE D 
______________________________________ 
Production Tooling 
Sleeve Internal diameter 
Initial diameter (mm) 44.665 
Elastically constrained diameter (mm) 
44.504 
% Elastic recovery possible 
0.34 
______________________________________ 
Cylindrical compacts were made from NC100.24 ferrous powder using a double 
ended pressing die embodying the invention, as shown in FIGS. 9 and 10, 
with different amounts of lubrication by zinc stearate and with wall 
lubrication, with the following results. 
TABLE 6 
______________________________________ 
Pressing by an Embodiment of the Invention 
Material compressed: NC100.24. Production Tooling. 
Sleeve fully inserted. No die scoring or cracking of compacts found. 
ds Springback 
Pressing 
Density 
Lubrication 
(mm) % ER % Pressure tsi 
g/cc 
______________________________________ 
0.8% zinc stearate 
0.161 0.34 0.34 at 70 tsi 
70 7.09 
0.4% zinc stearate 
0.161 0.34 0.32 at 65 tsi 
65 7.31 
0.4% zinc stearate 
0.161 0.34 0.33 at 75 tsi 
75 7.35 
0.4% zinc stearate 
0.161 0.34 0.33 at 75 tsi 
75 7.4 
+ die wall lubric. 
die wall lubric. 
0.161 0.34 75 7.5 
______________________________________ 
The results in the tables, Table 5 and Table 6, are comparable with results 
in Tables 1, 2, 3 and 4. Note that, in Table 1, 2, and 3, as the amount of 
lubricant in the powder decreases the compacts become more and more 
difficult to eject from the conventional die without damage. The safe 
pressing pressure drops from about 55 tsi with 0.8% zinc stearate to about 
25 tsi with 0.2% zinc stearate added as lubricant. Table 5 shows that all 
compacts in the elastic die handsets were ejected without damage and with 
low ejection forces. It can also be seen in Table 5, that as the expected 
springback (% SB) of the compressed powder compact increases, (figures 
taken from data in Table 1) the ejection force only becomes positive when 
its value exceeds the elastic recovery (% ER) of the sleeve. With die wall 
lubrication in Table 5, all compacts were ejected with zero ejection force 
as the expected % springback even at 80 tsi (0.259%) was less than the 
elastic recovery of the sleeve (0.302%). 
Table 6 illustrates that the production tooling, designed to give an 
elastic recovery (0.34%), approximately equal to the springback expected 
with NC100.24 at 80 tsi using die wall lubrication (0.34%), produced sound 
compacts of high density with practically zero ejection force. 
Example 2 
(316L Stainless Steel) 
A similar series of sets of compacts was then produced using 316L stainless 
steel, by conventional means, and by embodiments of the present invention, 
with the following results. 
TABLE 7 
______________________________________ 
Conventional Pressing 
Material Compressed: 
316L Stainless steel + 1% lithium stearate 
Pressing 
Density Die scoring or compact 
Pressure tsi 
g/cc % Springback 
cracking 
______________________________________ 
39.6 6.6 0.254 
45.2 6.73 0.283 
50.9 6.83 0.294 
56.5 6.94 0.323 x 
65.7 7 0.324 x 
78.8 7.1 0.358 x 
______________________________________ 
Table 8: Conventional Pressing 
TABLE 8 
______________________________________ 
Conventional Pressing 
Material Compressed: 
316L stainless steel + 0.6% lithium stearate 
Pressing 
Density Die scoring or compact 
Pressure tsi 
g/cc % Springback 
cracking 
______________________________________ 
33.9 6.43 0.257 
39.6 6.57 0.275 
45.2 6.7 0.294 
50.9 6.83 0.312 x 
56.5 6.93 0.338 x 
65.7 7.01 0.338 x 
78.8 7.15 0.344 x 
______________________________________ 
TABLE 9 
______________________________________ 
Conventional Pressing 
Material Compressed: 
316L stainless steel + 0.4% lithium stearate 
Pressing 
Density Die scoring or compact 
Pressure tsi 
g/cc % Springback 
cracking 
______________________________________ 
16.9 5.7 0.215 
22.6 6.01 0.244 
28.3 6.24 0.257 
33.9 6.54 0.265 x 
39.6 6.58 0.275 x 
45.2 6.73 0.299 x 
50.9 6.86 0.331 x 
56.6 6.92 0.341 x 
65.7 7.07 0.312 x 
78.8 7.17 0.34 x 
______________________________________ 
TABLE 10 
______________________________________ 
Pressing by an Embodiment of the Invention 
Material compressed: 316 Stainless Steel. Hand Operated Die Set. 
Sleeve fully inserted. No die scoring of compact cracking found. 
Pressing 
Eject. 
ds Pressure 
press. 
Density 
Lubrication 
(mm) % ER Springback % 
tsi tons g/cc 
______________________________________ 
1% lithium 
0.097 0.302 0.29 at 50 tsi 
48 0 6.77 
stearate 
1% lithium 
0.097 0.302 0.31 at 55 tsi 
56 &gt;5 t 6.94 
stearate 
1% lithium 
0.097 0.302 0.33 at 65 tsi 
64 &gt;5 t 7.01 
stearate 
1% lithium 
0.097 0.302 0.34 at 70 tsi 
72 &gt;5 t 7.07 
stearate 
1% lithium 
0.097 0.302 0.328 at 80 tsi 
80 &gt;5 t 7.12 
stearate 
0.4% zinc 
0.097 0.302 0.31 at 50 tsi 
48 0 6.75 
stearate 
0.4% zinc 
0.097 0.302 0.325 at 55 tsi 
56 0 6.88 
stearate 
0.4% zinc 
0.097 0.302 0.34 at 65 tsi 
64 &gt;5 t 7.05 
stearate 
0.4% zinc 
0.097 0.302 0.345 at 70 tsi 
72 &gt;5 t 7.09 
stearate 
0.4% zinc 
0.097 0.302 0.355 at 80 tsi 
80 &gt;5 t 7.21 
stearate 
die wall 0.097 0.302 0.20 at 50 tsi 
48 0 6.61 
lubrication 
die wall 0.097 0.302 0.22 at 55 tsi 
56 0 6.83 
lubrication 
die wall 0.097 0.302 0.275 at 65 tsi 
64 0 6.94 
lubrication 
die wall 0.097 0.302 0.29 at 70 tsi 
72 &gt;5 t 7.09 
lubrication 
die wall 0.097 0.302 0.34 at 80 tsi 
80 &gt;5 t 7.23 
lubrication 
______________________________________ 
TABLE 11 
______________________________________ 
Pressing by an Embodiment of the Invention 
Material compressed: 316L Stainless Steel. Production Tooling. 
Sleeve fully inserted. No die scoring or cracking of compacts found. 
Pressing 
Density 
Lubrication 
ds (mm) % ER Springback % 
Pressure tsi 
g/cc 
______________________________________ 
1% lithium 
0.161 0.302 0.34 at 70 tsi 
70 7.09 
stearate 
______________________________________ 
The results in these tables, Table 10 and Table 11, are comparable with 
results in Tables 7, 8 and 9. Note that, in Tables 7, 8 and 9, as the 
amount of lubricant in the powder decreases the compacts become more and 
more difficult to eject from the conventional die without damage. The safe 
pressing pressure drops from about 50 tsi with 1.0% lithium stearate to 
about 30 tsi with 0.4% lithium stearate added as lubricant. Table 10 shows 
that all compacts in the elastic die handsets were ejected without damage 
and with low ejection forces. It can also be seen in Table 10, that as the 
expected springback (% SB) of the compressed powder compact increases, 
(figures taken from data in Tables 7 and 9) the ejection force only 
becomes positive when its value exceeds the elastic recovery (% ER) of the 
sleeve. Note, for example, that the ejection force only becomes measurable 
at 55 tsi using 1% lithium stearate, at 65 tsi using 0.4% lithium 
stearate, and at 70 tsi using only die wall lubrication. In both cases 
these pressures are those at which the expected springback of the 
compressed material becomes equal to or exceeds the elastic recovery of 
the sleeve. Even with die wall lubrication in Table 10, all compacts were 
ejected with zero or low ejection force, as the expected % springback at 
70 tsi (0.29%) was equal to the elastic recovery of the sleeve (0.302%). 
Table 11 illustrates that the production tooling, designed to give an 
elastic recovery (0.34%), approximately equal to the springback expected 
with 316L stainless steel at 70 tsi using die wall lubrication (0.34%), 
produced sound compacts of high density with practically zero ejection 
force. 
Example 3 
(ATOMET 1001 AND ATOMET 4601) 
Table 12 illustrates results with two further iron-based powders, Atomet 
1001, a pure iron powder, and Atomet 4601 an alloy powder with 
compositions as in Table A. In industrial practice it is usually necessary 
to add graphite to ferrous powder mixes for metallurgical reasons. 
Springback at various pressing pressures was determined as previously 
described and this data (not included here) is used to explain the results 
in Table 12. The results show that even with an addition of graphite the 
compacts were all produced without damage at zero or low ejection force. 
Only when the % springback was equal to or exceeded the elastic recovery 
(% ER) of the sleeve did the ejection force become noticeable. The high 
densities attainable, up to 7.65 g/cc without cracking could not be 
obtained with conventional tooling. 
As stated previously the results also show that when the expected 
springback of the compacted material becomes equal to, or greater than the 
elastic recovery of the sleeve the ejection force become positive, but 
still small enough to allow compacts to be removed rom the tools without 
damage. 
TABLE 12 
______________________________________ 
Pressing by an Embodiment of the Invention 
Material compressed: Various. Hand Operated Die Set. 
Sleeve fully inserted. No die scoring of compact cracking found. 
Pressing 
Eject. 
ds Pressure 
press. 
Density 
Lubrication 
(mm) % ER Springback % 
tsi t g/cc 
______________________________________ 
Atomet 1001 
0.097 0.302 48 0 7.37 
Atomet 1001 
0.097 0.302 56 0 7.48 
Atomet 1001 
0.097 0.302 64 0 7.57 
Atomet 1001 
0.097 0.302 72 0 7.63 
Atomet 1001 
0.097 0.302 0.34 at 80 tsi 
80 0 7.65 
Atomet 1001 + 
0.097 0.302 0.284 at 80 tsi 
80 &gt;5 t 7.59 
0.5% graphite 
Atomet 4601 
0.097 0.302 48 0 7.14 
Atomet 4601 
0.097 0.302 56 0 7.3 
Atomet 4601 
0.097 0.302 64 0 7.41 
Atomet 4601 
0.097 0.302 72 0 7.48 
Atomet 4601 
0.097 0.302 0.284 at 80 tsi 
80 0 7.55 
Atomet 4601 + 
0.097 0.302 0.21 at 50 tsi 
48 0 7.1 
0.5% graphite 
Atomet 4601 + 
0.097 0.302 0.23 at 55 tsi 
56 0 7.32 
0.5% graphite 
Atomet 4601 + 
0.097 0.302 0.27 at 66 tsi 
64 0 7.36 
0.5% graphite 
Atomet 4601 + 
0.097 0.302 0.315 at 75 tsi 
75 &gt;5 t 7.43 
0.5% graphite 
Atomet 4601 + 
0.097 0.302 0.318 at 80 tsi 
80 &gt;5 t 7.5 
0.5% graphite 
______________________________________ 
The embodiments described above related to sleeves that form the outside 
shape of the component. Centrally placed core rods, and off-centre core 
rods have to be dealt with in a different mechanical arrangement but still 
using the elastic recovery technique. In the case of core rods the 
external dimensions of the core rod have to be made larger before 
compaction. After compaction the original dimensions then need to be 
recovered, that is the external dimensions decrease. This makes it 
possible for the ore rod to be withdrawn from the component with zero, or 
very much reduced force. This not only prevents damage to the component, 
but also to the core rod itself. Expansion of the core rod is effected by 
having a sleeve on the outside of the core rod with a taper on the insider 
surface of the sleeve. When the sleeve is pulled over the core rod, which 
has a matching taper, or when the core rod is driven into this external 
sleeve, the external dimensions of the sleeve are increased in the same 
manner that the internal dimensions of the die sleeve decrease when the 
sleeve is pulled into the die. After compaction, the sleeve is pushed off 
the core rod, or the core rod is withdrawn from the sleeve allowing it to 
elastically recover to its original smaller external dimensions. The 
compact is then withdrawn from the die and the core rods removed with zero 
or low force.