U.S. patent application number 10/502592 was filed with the patent office on 2005-10-06 for process for producing a high density by high velocity compacting.
Invention is credited to Jiangho, Li, Olsson, Kent.
Application Number | 20050220658 10/502592 |
Document ID | / |
Family ID | 27607313 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050220658 |
Kind Code |
A1 |
Olsson, Kent ; et
al. |
October 6, 2005 |
Process for producing a high density by high velocity
compacting
Abstract
A method of producing a body from a particulate or solid
material comprises filling a precompacting mould with the material,
optionally vibrating the mould, pre-compacting the material and
compressing it by at least one stroke with high kinetic energy in
order to cause coalescence or high density of the material.
Inventors: |
Olsson, Kent; (Stockholm,
SE) ; Jiangho, Li; (Huddinge, SE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Family ID: |
27607313 |
Appl. No.: |
10/502592 |
Filed: |
May 13, 2005 |
PCT Filed: |
January 27, 2003 |
PCT NO: |
PCT/SE03/00128 |
Current U.S.
Class: |
419/66 |
Current CPC
Class: |
B21J 7/28 20130101; B22F
3/087 20130101; B22F 2999/00 20130101; B22F 2999/00 20130101; B21J
7/34 20130101; B21J 7/22 20130101; B22F 3/105 20130101; B21J 7/02
20130101; B22F 3/14 20130101; B29C 2043/3618 20130101; B30B 11/027
20130101; B22F 2003/033 20130101 |
Class at
Publication: |
419/066 |
International
Class: |
B22F 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2002 |
SE |
0200230-1 |
Claims
1. A method of producing a body from particulate material by
coalescence or compaction to higher density, characterised in that
the method comprises the steps of a) filling a pre-compacting mould
with the material in the form of powder, pellets, grains or the
like, b) vibrating the mould, c) pre-compacting the material at
least once with a pre-compacting means and d) compressing the
material in a compression mould by at least one stroke, where a
striking unit emits enough kinetic energy to form the body when
striking the material inserted in the compression mould with a
striking means, causing coalescence or higher density of the
material.
2. A method according to claim 1, characterised in that the
pre-compacting mould and the compressing mould are the same
mould.
3. A method according to claim 1, characterised in that the
pre-compacting c) is performed while vibrating the mould.
4. A method according to claim 1, characterised in that d) the
material is compressed from two opposite sides simultaneously using
two striking units.
5. A method of producing a body from solid material by coalescence
or compaction to higher density, characterised in that the method
comprises the steps of a) inserting the solid material in a mould,
c) possibly pre-compacting the material at least once with a
pre-compacting means and d) compressing the material in the mould
by at least one stroke, from two sides simultaneously, using two
striking units emitting enough kinetic energy to form the body when
striking the material, causing coalescence or higher density of the
material.
6. A method according to claim 1, characterised in that the
material is compressed from two opposite sides and at least one
further side simultaneously using at least three striking
units.
7. A method according to claim 2, characterised in that the
pre-compacting means is continuously applied against the material
with the same or a higher pressure during the compression d)
thereof with the striking unit or units.
8. A method according to claim 1, characterised in that the energy
of the compression d) is retained within the compressed material by
e) maintaining or reapplying the striking means to press against
the compressed material after the stroke or strokes.
9. A method according to claim 1, characterised in that the
temperature of the material in the mould is increased or decreased
during one or more steps.
10. A method according to claim 9, characterised in that the
material in the mould is heated before and/or during the
pre-compaction c.
11. A method according to claim 9, characterised in that the
material in the mould is heated before and/or during the
compression d).
12. A method according to claim 10, characterised in that the
material in the mould is heated by the use of electrical
current.
13. A method according to claim 12, characterised in that the
electrical current flow is syncronized with the pre-compaction c)
and/or the compression stroke or strokes d).
14. A method according to claim 1, characterised in that the
material in the mould is subjected to a sub-atmospheric pressure
before the pre-compaction c).
15. A method according to claim 1, characterised in that the
material in the mould or moulds is maintained under another gas
than air.
16. A method according to claim 15, characterised in that the gas
is an inert gas.
17. A method according to claim 15, characterised in that the gas
is a reactive gas.
18. A method according to claim 1, characterised in that the
vibration b) is maintained during compressing d) and/or during
energy retention e).
19. A body produced by the method according to claim 1.
20. A method according to claim 5, characterised in that the
material is compressed from two opposite sides and at least one
further side simultaneously using at least three striking units.
Description
[0001] The invention concerns a method of producing a body by
coalescence or compaction to higher density.
STATE OF THE ART
[0002] In WO-A1-9700751, an impact machine and a method of cutting
rods with the machine is described. The document also describes a
method of deforming a metal body. The method utilises the machine
described in the document and is characterised in that preferably
metallic material either in solid form or in the form of powder
such as grains, pellets and the like, is fixed preferably at the
end of a mould, holder or the like and that the material is
subjected to adiabatic coalescence by a striking unit such as an
impact ram, the motion of the ram being effected by a liquid. The
machine is thoroughly described in the WO document.
[0003] In WO-A1-9700751, shaping of components, such as spheres, is
described. A metal powder is supplied to a tool divided in two
parts, and the powder is supplied through a connecting tube. The
metal powder has preferably been gas-atomized. A rod passing
through the connecting tube is subjected to impact from the
percussion machine in order to influence the material enclosed in
the spherical mould. However, it is not shown in any embodiment
specifying parameters for how a body is produced according to this
method.
[0004] The compacting according to this document is performed in
several steps, e.g. three. These steps are performed very quickly
and the three strokes are performed as described below.
[0005] Stroke 1: an extremely light stroke, which forces out most
of the air from the powder and orients the powder particles to
ensure that there are no great irregularities.
[0006] Stroke 2: a stroke with very high energy density and high
impact velocity, for local adiabatic coalescence of the powder
particles so that they are compressed against each other to
extremely high density. The local temperature increase of each
particle is dependent on the degree of deformation during the
stroke.
[0007] Stroke 3: a stroke with medium-high energy and with high
contact energy for final shaping of the substantially compact
material body. The compacted body can thereafter be sintered.
[0008] In SE 9803956-3 a method and a device for deformation of a
material body are described. This is substantially a development of
the invention described in WO-A1-9700751. In the method according
to SE 9803956-3, the striking unit is brought to the material by
such a velocity that at least one rebounding motion of the striking
unit is generated, the rebounding being counteracted whereby at
least one further stroke of the striking unit is generated.
[0009] The strokes according to the method described in
WO-A1-9700751, give a locally very high temperature increase in the
material, which can lead to phase changes in the material during
the heating or cooling. When using according to SE 9803956-3 a
counteracting of the rebounding motion generating at least one
further stroke, this stroke contributes to the wave going back and
forth and being generated by the kinetic energy of the first
stroke, continuing during a longer period. This leads to further
deformation of the material and with a lower impulse than would
have been necessary without the counteracting.
[0010] It has now been found that the machine according to these
documents does not work so well. For example, the time intervals
between the strokes, which they mention, are not possible to
attain. Further, the documents do not comprise any embodiments
showing that a body can be formed. Also, the rebounding strokes
have proved to result in cracking of the material.
OBJECT OF THE INVENTION
[0011] The object of the present invention is to achieve a low cost
process for efficient production of products from a particulate
material or a solid material by coalescence or compaction to a
higher density. These products may be both medical devices such as
medical implants or bone cement in orthopaedic surgery,
instruments, such as surgical knives, or diagnostic equipment, or
non medical devices such as ball bearings, cutting tools, sinks,
baths, displays, glazing (especially aircraft), lenses and light
covers. Another object is to achieve a product of the described
type.
[0012] The object to achieve a higher density is based on the fact
that high density is a condition for high mechanical
properties.
[0013] The process should not be limited to using the above
described machine.
SHORT DESCRIPTION OF THE INVENTION
[0014] It has surprisingly been found that it is possible to
compress different materials according to the new methods defined
in claims 1 and 5. The material is for example in the form of
powder, pellets, grains and the like and is filled in a mould,
pre-compacted and compressed by at least one stroke. The machine to
use in the method may be the one described in WO-A1-9700751 and SE
9803956-3 with a vibration device added to achieve vibration of the
tool or mould. The material may also be in solid form and be
inserted into a mould and subjected to at least one stroke, from
two or more sides simultaneously, using two or more striking units
emitting enough kinetic energy to form the body when striking the
material, causing coalescence or higher density of the material. In
this case the machine used comprises at least two opposite striking
units.
[0015] The method according to the invention may utilise hydraulics
in the percussion machine, which may be constructed on the same
principle as the machine utilised in WO-A1-9700751 and SE
9803956-3. When using pure hydraulic means in the machine, the
striking unit or units can be given such movement as to, upon
impact with the material to be compressed, emit sufficient energy
at sufficient speed for coalescence to be achieved. This
coalescence may be adiabatic. A stroke is carried out quickly and
for some materials the wave in the material decay in between 5 and
15 milliseconds. The use of hydraulic may also give a better
sequence control and lower running costs compared to the use of
compressed air.
[0016] However, the invention is not limited to using a hydraulic
machine. It may also be possible to use a spring-actuated or
electrically actuated percussion machine or a machine using
compressed air. Neither is it necessary to always achieve
coalescence. In some instances it is sufficient to perform
compaction to a higher density.
[0017] The optimal machine has a large press for pre-compacting and
post-compacting and at least one small striking unit that can
strike with variable speed. Machines according to such a
construction are therefore probably more interesting to use.
Different machines could also be used, one for the pre-compacting
and post-compacting and one for the compression.
SHORT DESCRIPTION OF THE DRAWINGS
[0018] On the enclosed drawings
[0019] FIGS. 1a and 1b show schematic cross sectional views of two
embodiments of a machine for deformation of a material in the form
of a powder, pellets, grains and the like,
[0020] FIGS. 2-5 show flow diagrams illustrating the process
according to the invention and
[0021] FIGS. 6- are diagrams showing results obtained in
comparative tests described in the following examples.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The invention concerns a method of producing a body from
particulate material. The method comprises the steps of
[0023] a) filling a pre-compacting mould with the material in the
form of powder, pellets, grains or the like,
[0024] b) vibrating the mould,
[0025] c) pre-compacting the material at least once with a
pre-compacting means and
[0026] d) compressing the material in a compression mould by at
least one stroke, where a striking unit emits enough kinetic energy
to form the body when striking the material inserted in the
compression mould with a striking means, causing coalescence or
higher density of the material.
[0027] By the use of vibration the particles in the pre-compacting
mould will move closer together, forcing out air or gas from
between the particles and they will orient themselves so as to more
easily be compacted. Thereby, already before the pre-compaction
starts, a higher density is achieved. The pre-compaction will
therefore not start from a loosely packed powder, but from a more
densely packed powder. Therefor, fewer pre-compaction strokes may
be necessary. Should the vibration continue during the
pre-compacting step, a higher density will be achieved using the
same pre-compaction pressure.
[0028] The higher density achieved during pre-compaction will
facilitate the compression step.
[0029] A further advantage is obtained if the material is
compressed from two or more sides simultaneously using two or more
striking units.
[0030] The pre-compacting mould may be the same as the compression
mould, which means that the material does not have to be moved
between the steps c) and d). It is also possible to use different
moulds and move the material between the steps c) and d) from the
pre-compacting mould to the compression mould. This could only be
done if a body is formed of the particulate material in the
pre-compacting step.
[0031] The invention also concerns a method comprising the steps
of
[0032] a) inserting the solid material in a mould,
[0033] b) possibly pre-compacting the material at least once with a
pre-compacting means and
[0034] d) compressing the material in the mould by at least one
stroke, from two or more sides simultaneously, using two or more
striking units emitting enough kinetic energy to form the body when
striking the material, causing coalescence or higher density of the
material.
[0035] It is preferable that the pre-compacting means is
continuously applied against the material, with the same or a
higher pressure, during the compression d) thereof by the striking
unit or units.
[0036] By using a machine which can strike the material in the
mould from two opposite directions and also compact from these
directions the particles in the powder will be better oriented, a
better contact between the particles will be achieved and a more
efficient welding of the particles results. The body obtained is
more homogenous than a body produced at the same energy and
pressure applied from only one direction. Advantages arise from the
double-sided treatment both during pre-compaction and during
compression.
[0037] The preferred method of producing a body from particulate
material according to the invention could be described in the
following way.
[0038] 1) Powder is pressed to a green body with vibration, the
body is compressed by impact to a (semi)solid body and thereafter
an energy retention may be achieved in the body by a
post-compacting. The process, which could be described as Dynamic
Forging Impact Energy Retention (DFIER) involves three mains
steps.
[0039] a) Pressuring
[0040] The pressing step is very much like cold and hot pressing.
The intention is to get a green body from powder. It has proved
most beneficial to perform two compactions of the powder. One
compaction alone gives about 2-3% lower density than two
consecutive compactions of the powder. This step is the preparation
of the powder by evacuation of the air and orientation of the
powder particles in a beneficial way. The density values of the
green body is more or less the same as for normal cold and hot
pressuring.
[0041] b) Impact
[0042] The impact step is the actual high-speed step, where a
string unit strikes the powder with a defined area. A material wave
starts off in the powder and interparticular melting takes place
between the powder particles. Velocity of the striking unit seems
to have an important role only during a very short time initially.
The mass of the powder and the properties of the material decides
the extent of the interparticular melting taking place.
[0043] c) Energy retention
[0044] The energy retention step aims at keeping the delivered
energy inside the solid body produced. It is physically a
compaction with at least the same pressure as the pre-compaction of
the powder. The result is an increase of the density of the
produced body by about 1-2%. It is performed by for instance
letting the striking unit stay in place on the solid body after the
impact and press with at least the same pressure as at
pre-compaction, or release after the impact step. The idea is that
more transformations of the powder will take place in the produced
body.
[0045] FIG. 1a shows a machine that compacts and compresses a
material from both an upper and a lower side. FIG. 1b shows a
corresponding machine that only can compact and strike from one
side. The reference numbers for similar parts are the same in both
FIG. 1a and FIG. 1b.
[0046] The machine shown in FIG. 1a comprises an upper and a lower
striking device 1a and 1b. Each striking device has an impact ram
2a,b containing weights 10 and arranged inside an impact ram
housing 11a,b. The mass of the impact rams can be changed by
adjusting the number of impact ram weights 10 inside the impact ram
2a,b. Between the striking devices 1 a,b there is a central part
including support rods 7 connecting upper and lower static press
tables 12a, b through which upper and lower static pre-compaction
press rams 5a,b pass. On the figure two side support rods 7 are
shown. The machine comprises two further front and back rods 7 (not
shown on the figure). To the pre-compaction rams 5a,b an upper and
a lower punch 9a,b are connected. To the support rods a moulding
die table 13 is connected holding a mould 8 arranged between the
upper and lower punches 9a,b. A vibration device 6 is connected to
the moulding die table 13. There is also a hopper 3 from which
particles are fed into the mould 8.
[0047] The machine in FIG. 1b comprises the same parts as the
machine in FIG. 1a with the following exceptions. It does not
comprise any lower impact device 1b, nor the lower static
pre-compaction press ram 5b or the lower static press table 12b.
The lower punch 9b is connected to a rig fundament 4.
[0048] The process steps are schematically illustrated on FIGS.
2-5. FIGS. 2 and 3 show the process without energy retention (with
non-DFIER machines) and FIGS. 3 and 5 with energy retention (with
DFIER machines). FIGS. 2 and 4 show uni-cycle processes and FIGS. 3
and 5 multi-cycle processes where several strokes are used.
[0049] The upper part of FIGS. 2-5 shows a time base and above this
the different steps performed. The lower part of the figures
comprises a diagram showing the change of some parameters during
the process. The pressure parameter is the atmospheric pressure in
the mould.
[0050] In the process shown in FIGS. 2 and 3 particulate material
is first filled in the mould. A sub-atmospheric pressure is
achieved and the material is compressed with a ram during the
pre-compaction step. The ram is removed during the delay and
thereafter the pre-compacted material is dynamically forged by
being struck one or several times with an impact ram. The material
is in this case resistance heated during the strokes, the applied
electrical current being synchronized with the triggering of the
impacts. The vacuum is released and the component obtained is
pressed out, optionally after being compressed further with the
pre-compaction ram.
[0051] In the process shown in FIGS. 4 and 5 a sub-atmospheric
pressure is achieved and the material is compressed with a ram
during the pre-compaction step. The ram is maintained pressing
together the particles during the following steps. Vibration of the
particulate material is used during pre-compaction. As in the
process of FIGS. 2 and 3 the material is heated with an electric
current during shocking. The pressure from the pre-compaction ram
is maintained after shocking for energy retention, the vacuum is
released and the component obtained pressed out.
[0052] In the above embodiments the pre-compaction mould is the
same as the compression mould. Further, the material from which a
body is formed is in particulate form. However, it is also possible
to use a solid material. In this case it may not be necessary to
use pre-compaction. Depending on the density of the solid material
a pre-compaction step may be of advantage. After the possible
pre-compaction the solid material is shocked by two opposite impact
rams simultaneously. The same steps as when forming a particulate
material may be used.
[0053] Both when starting with a particulate material and a solid
material the forming may be performed by using two opposite impact
rams. It is also possible to use more than two impact rams such as
when a deformation sidewise should be obtained.
[0054] The pre-compaction step may comprise one or more
compactions. As the particulate material is vibrated, only one
compaction may be necessary. However, several compactions may still
give a somewhat higher density.
[0055] By using the preferred features of the invention it may be
possible to achieve material properties of the same level as those
achieved by forging of by using HIP or HIP+forging.
[0056] The features which may be modified within the definition of
the process of the invention are for instance:
[0057] 1) the direction of striking, may be in one two or more
directions,
[0058] 2) the vibration, may be during the pre-compaction step
and/or the compression step and/or the energy retention stage,
[0059] 3) the number of pre-compactions,
[0060] 4) interval between pre-compaction stokes,
[0061] 5) temperature during pre-compaction
[0062] 6) pre-compaction pressure
[0063] 7) the same parameters may be modified for the impact
step,
[0064] 8) impact stroke pressure and energy, may be the same or be
different for different strokes,
[0065] 9) post-compaction in one or more steps may be used or
not,
[0066] 10) atmospheric pressure in the mould, may be decreased or
not,
[0067] 11) use of other gases than air, for instance inert gas or a
reactive gas,
[0068] 12) the temperature of the mould and material, may be
increased and in some instances decreased or may be ambient
temperature,
[0069] 13) the material to be formed may be particulate, such as
powder, pellets or grains, or solid,
[0070] 14) electrical current may be used or not,
[0071] 15) the vibration may be modified as to amplitude, frequency
or direction, may be vertical and/or horisontal,
[0072] 16) the pre-compaction mould and compression mould may be
the same or different,
[0073] 17) the number of steps may be modified, some steps may be
repeated several times after repeating an earlier step, more
material may be filled in the mould after pre-compaction or
compression and thereafter pre-compaction and/or compression may be
repeated,
[0074] 18) the relation between the mass of the impact ram or rams,
the mass of the punch or punches and the mass of the material to be
formed may be modified,
[0075] 19) energy retention may be used or not.
[0076] The mass m of the striking unit is preferably essentially
larger than the mass of the material. By that, the need of a high
impact velocity of the striking unit can be somewhat reduced. When
the striking unit hits the material 1, this may cause a local
coalescence and thereby a consequent deformation of the material.
In any case an increase in density is obtained. Waves or vibrations
are generated in the material in the direction of the impact
direction and these waves or vibrations have high kinetic energy
and will activate slip planes in the material and also cause
relative displacement of the grains of the powder. It is possible
that the coalescence may be an adiabatic coalescence. The local
increase in temperature develops spot welding (inter-particular
melting) in the material increasing the density.
[0077] The pre-compaction is a very important step. This is done in
order to drive out air and orient the particles in the material.
The pre-compaction step is much slower than the compression step,
and therefore it is easier to drive out the air. This is further
facilitated by the use of vibration before or during the
pre-compaction. The compression step, which is done very quickly,
does not have the same possibility to drive out air. Therefore, the
air remaining after the pre-compaction may be enclosed in the
produced body, which is a disadvantage. The pre-compaction is
performed at a minimum pressure enough to obtain a maximum degree
of packing of the particles which results in a maximum contact area
between the particles. This is material dependent and depends on
the softness and melting point of the material.
[0078] The pre-compacting step in the Examples was performed by
compacting with an axial load of about 117680 N. This is done was
the pre-compacting mould or the final mould. In all Examples where
nothing else is stated the mould used was a cylindrical mould, part
of the tool and having a circular cross section with a diameter of
30 mm. The area of this cross section is about 7 cm.sup.2. This
means that a pressure of about 1.7.times.10.sup.8 N/m.sup.2 was
used. The material may be pre-compacted with a pressure of at least
about 0.25.times.10.sup.8 N/m.sup.2, and preferably with a pressure
of at least about 0.6.times.10.sup.8 N/m.sup.2. The necessary or
preferred pre-compaction pressure to be used is material dependent
and for some materials it could be enough to compact at a pressure
of about 2000 N/m.sup.2. Other possible values are
1.0.times.10.sup.8 N/m.sup.2, 1.5.times.10.sup.8 N/m.sup.2. It may
be possible to use lower pressures if vacuum or heated material is
used. The height of the cylindrical mould is 60 mm.
[0079] The compression strokes may emit a total energy
corresponding to at least 100 Nm in the described cylindrical tool,
in air and at room temperature. Other total energy levels may be at
least 300, 600, 1000, 1500, 2000, 2500, 3000 and 3500 Nm. Energy
levels of at least 10 000, 20 000 Nm may also be used. There is a
new machine, which has the capacity to strike with 60 000 Nm in one
stroke. Of course such high values may also be used. And if several
such strikes are used, the total amount of energy may reach several
100 000 Nm. The energy levels depend on the material used, and in
which application the body produced will be used. Different energy
levels for one material will give different relative densities of
the material body. The higher energy level, the more dense material
will be obtained Different material will need different energy
levels to get the same density. This depends on for example the
hardness of the material and the melting point of the material.
[0080] The energy level needs to be amended and adapted to the form
and construction of the mould. If for example, the mould is
spherical, another energy level will be needed. A person skilled in
the art will be able to test what energy level is needed with a
special mould. The energy level depends on what the body will be
used for, i.e. which relative density is desired, the geometry of
the mould and the properties of the material. The striking unit
must emit enough kinetic energy to form a body when striking the
material inserted in the compression mould. With a higher velocity
of the stroke, more vibrations, increased friction between
particles, increased local heat, and increased interparticular
melting of the material will be achieved. The bigger the stroke
area is, the more vibrations are achieved. There is a limit where
more energy will be delivered to the tool than to the material.
Therefore, there is also an optimum for the height of the
material.
[0081] The more a material is compressed by the coalescence
technique, the smoother the surface obtained. The porosity of the
material and the surface is also affected by the method. If a
porous surface or body is desired, the material should not be
compressed as much as if a less porous surface or body is
desired.
[0082] What has been described above about the energy
transformation and wave generation also refer to a solid body. In
the present invention a solid body is a body where the target
density for specific applications has been achieved.
[0083] The striking unit preferably has a velocity of at least 0.1
m/s or at least 1.5 m/s during the stroke in order to give the
impact the required energy level. Much lower velocities may be used
than according to the technique in the prior art. The velocity
depends on the weight of the striking unit and what energy is
desired. The total energy level in the compression step is at least
about 100 to 4000 Nm. But much higher energy levels may be used. By
total energy is meant the energy level for all strokes added
together. The striking unit makes at least one stroke or a number
of consecutive strokes. The interval between the strokes according
to the Examples was 0.4 and 0.8 seconds. For example at least two
strikes may be used.
[0084] The method also comprises pre-compacting the material at
least twice. It has been shown in the Examples that this could be
advantageous in order to get a high relative density compared to
strokes used with the same total energy and only one
pre-compacting. Two compactions give about 1-5% higher density than
one pre-compaction depending on the material used. The increase may
be even higher for some materials. When pre-compacting twice, the
compacting steps are performed with a small interval between, such
as about 5 seconds. About the same pressure may be used in the
second pre-compacting.
[0085] Further, the method may also comprise a step of compacting
the material at least once after the compression step. This has
also been shown to give very good results. The post-compacting
should be carried out at at least the same pressure as the
pre-compacting pressure, i.e. 2000 N/m.sup.2. Other possible values
are 1.0.times.10.sup.8 N/m.sup.2. Higher post-compacting pressures
may also be desired, such as a pressure which is twice the pressure
of the pre-compacting pressure. The pre-compacting value has to be
tested out for every material. A post-compacting effects the sample
differently than a pre-compacting. The transmitted energy, which
increases the local temperature between the powder particles from
the stroke, is conserved for a longer time and can effect the
sample to consolidate for a longer period after the stroke. The
energy is kept inside the solid body produced. Probably the
"lifetime" for the material wave in the sample is increased and can
affect the sample for a longer period and more particles can melt
together. The result is an increase of the density of the produced
body by about 14% and is also material dependent
[0086] When using pre-compacting and/or after compacting, it could
be possible to use lighter strokes and higher pre- and/or after
compacting, which would lead to saving of the tools, since lower
energy levels could be used. This depends on the intended use and
what material is used. It could also be a way to get a higher
relative density.
[0087] To get improved relative density it is also possible to
pre-process the material before the process. The powder could be
pre-heated to e.g. .about.50-300.degree. C. or higher depending on
what material type to pre-heat. The powder could be pre-heated to a
temperature which is close to the melting temperature of the
material. Suitable ways of pre-heating may be used, such as normal
heating of the powder in an oven. In order to get a more dense
material during the pre-compacting step vacuum or inert gas could
be used. This would have the effect that air is not enclosed in the
material to the same extent during the process.
[0088] Before processing the polymer could be homogenously mixed
with additives.
[0089] The body may according to another embodiment of the
invention be heated and/or sintered any time after compression or
post-compacting.
[0090] Common post-processing steps are following:
[0091] Further, the body produced may be a green body and the
method may also comprise a further step of sintering the green
body. The green body of the invention gives a coherent integral
body even without use of any additives. Thus, the green body may be
stored and handled and also worked, for instance polished or cut.
It may also be possible to use the green body as a finished
product, without any intervening sintering. This is the case when
the body is a bone implant or replacement where the implant is to
be resorbed in the bone.
[0092] It has been shown earlier that better results have been
obtained with particles having irregular particle morphology. The
particle size distribution should probably be wide. Small particles
could fill up the empty space between big particles.
[0093] The particulate material may comprise a lubricant and/or a
sintering aid. A lubricant may be useful to mix with the material.
Sometimes the material needs a lubricant in the mould, in order to
easily remove the body. In certain cases this could be a choice if
a lubricant is used in the material, since this also makes it
easier to remove the body from the mould.
[0094] A lubricant cools, takes up space and lubricates the
material particles. This is both negative and positive.
[0095] Interior lubrication is good, because the particles will
then slip in place more easily and thereby compact the body to a
higher degree. It is good for pure compaction. Interior lubrication
decreases the friction between the particles, thereby emitting less
energy, and the result is less inter-particular melting. It is not
good for compression to achieve a high density, and the lubricant
must be removed for example with sintering.
[0096] Exterior lubrication increases the amount of energy
delivered to the material and thereby indirectly diminishes the
load on the tool. The result is more vibrations in the material,
increased energy and a greater degree of inter-particular melting.
Less material sticks to the mould and the body is easier to
extrude. It is good for both compaction and compression.
[0097] An example of a lubricant is Acrawax C, but other
conventional lubricants may be used. If the material will be used
in a medical body, the lubricant need to be medically acceptable,
or it should be removed in some way during the process.
[0098] Polishing and cleaning of the tool may be avoided if the
tool is lubricated and if the powder is preheated.
[0099] In some cases it may be necessary to use a lubricant in the
mould in order to remove the body easily. It is also possible to
use a coating in the mould. The coating may be made of for example
TiNAl or Balinit Hardlube. If the tool has an optimal coating no
material will stick to the tool parts and consume part of the
delivered energy, which increase the energy delivered to the
powder. No time-consuming lubricating would be necessary in cases
where it is difficult to remove the formed body.
[0100] For example, one to about six strokes may be used. The
energy level could be the same for all strokes, the energy could be
increasing or decreasing. Stroke series may start with at least two
strokes with the same level and the last stroke has the double
energy. The opposite could also be used.
[0101] The highest density is obtained by delivering a total energy
with one sole stroke. If the same total energy instead is delivered
with several strokes, a lower relative density is obtained, but the
tool is saved. Multi-strokes can therefore be used for applications
where a maximum relative density is not necessary. However, the use
of several strokes may give as high density as one sole stroke,
provided the time interval between the strokes is extremely
short.
[0102] Through a series of quick impacts a material body is
supplied continually with kinetic energy which contributes to keep
the back and forth going wave alive. This supports generation of
further deformation of the material at the same time as a new
impact generates a further plastic, permanent deformation of the
material.
[0103] According to another embodiment of the invention, the
impulse, with which the striking unit hits the material body,
decreases for each stroke in a series of strokes. Preferably the
difference is large between the first and second stroke. It will
also be easier to achieve a second stroke with smaller impulse than
the first impulse during such a short period (preferably
approximately 1 ms), for example by an effective reduction of the
rebounding blow. It is however possible to apply a larger impulse
than the first or preceding stroke, if required.
[0104] When the material inserted in the mould is exposed to the
coalescence, a hard, smooth and dense surface is achieved on the
body formed. This is an important feature of the body. A hard
surface gives the body excellent mechanical properties such as high
abrasion resistance and scratch resistance. The smooth and dense
surface makes the material resistant to for example corrosion. The
less pores, the larger strength is obtained in the product. This
refers to both open pores and the total amount of pores. In
conventional methods, a goal is to reduce the amount of open pores,
since open pores are not possible to get reduced by sintering.
[0105] It is important to admix powder mixtures until they are as
homogeneous as possible in order to obtain a body having optimum
properties.
[0106] A coating may also be manufactured according to the method
of the invention. When manufacturing a coated element, the element
is placed in the mould and may be fixed therein in a conventional
way. The coating material is inserted in the mould around the
element to be coated, by for example gas-atomizing, and thereafter
the coating is formed by coalescence. The element to be coated may
be any material formed according to this application, or it may be
any conventionally formed element Such a coating may be very
advantageously, since the coating can give the element specific
properties.
[0107] A coating may also be applied on a body produced in
accordance with the invention in a conventional way, such as by dip
coating and spray coating.
[0108] It is also possible to first compress a material in a first
mould by at least one stroke. Thereafter the material may be moved
to another, larger mould and a further polymer material be inserted
in the mould, which material is thereafter compressed on top of or
on the sides of the first compressed material, by at least one
stroke. Many different combinations are possible, in the choice of
the energy of the strokes and in the choice of materials.
[0109] The invention also concerns the product obtained by the
methods described above.
[0110] By the use of the present process it is possible to produce
large bodies in one piece. In presently used processes involving
casting it is often necessary to produce the intended body in
several pieces to be joined together before use. The pieces may for
example be joined using screws or adhesives or a combination
thereof.
[0111] A further advantage is that the method of the invention may
be used on powder carrying a charge repelling the particles without
treating the powder to neutralize the charge. The process may be
performed independent of the electrical charges or surface tensions
of the powder particles. However, this does not exclude a possible
use of a further powder or additive carrying an opposite charge. By
the use of the present method it is possible to control the surface
tension of the body produced. In some instances a low surface
tension may be desired, such as for a wearing surface requiring a
liquid film, in other instances a high surface tension is
desired.
[0112] Here follow some Examples to illustrate the invention.
[0113] The Examples will present and illustrate how different
parameters can be varied to increase the relative density of metal,
ceramic and polymer samples processed with the present process.
Stainless steel is the material tested in all studies except in the
powder height-, theoretical density-, powder hardness- and melting
temperature studies. See table 1 for technical data of the
stainless steel used.
[0114] The sample dimensions are the same for all studies except in
the collision area study where two sample dimensions are used.
1TABLE 1 Technical data of stainless steel. Properties Stainless
steel 316L 1. Particle size (micron) <150 2. Particle
distribution (micron) 0.60 wt % > 150 42.70% < 45 3. Particle
morphology Irregular 4. Powder production Water atomised 5. Crystal
structure FCC 6. Theoretical density (g/cm.sup.3) 7.90 7. Apparent
density (g/cm.sup.3) 2.64 8. Melt temperature (.degree. C.) 1427 9.
Sintering temperature (.degree. C.) 1315 10. Hardness (HV)
160-190
[0115] The samples produced are in the form of a disc with a
diameter of .about.30.0 mm and a height between 5-10 mm. The height
depends on the obtained relative density. If a relative density of
100% should be obtained the thickness is 5.00 mm.
[0116] In the moulding die (art of the tool) a hole with a diameter
of 30.00 mm is drilled. The height is 60 mm. Two stamps are used
(also parts of the tool). The lower stamp is placed in the lower
part of the moulding die. Powder is filled in the cavity that is
created between the moulding die and the lower stamp. Thereafter
the impact stamp is placed in the upper part of the moulding die
and strokes can be performed.
EXAMPLES
[0117] 1. Powder Height Study
[0118] Metal, ceramic and polymer powders were tested in a powder
height study. The powder used were stainless steel, hydroxyapatite
and UHMWPE. See table 2 for properties for the powders tested.
2TABLE 2 Technical data for the powders tested in the powder height
study. Properties Stainless steel 316L Hydroxyapatite UHMWPE 1.
Particle size <150 <1 <150 (micron) 2. Particle 0.60 wt %
> 150 <1 -- distribution (micron) 42.70 wt % < 45 3.
Particle Irregular Irregular Irregular morphology 4. Powder Water
atomised Wet chemistry -- production precipitation 5. Crystal
structure FCC Apatite 50% amorphous 6. Theoretical 7.90 3.15
g/cm.sup.3 0.94 density (g/cm.sup.3) 7. Apparent density 2.64 0.6
50 (g/cm.sup.3) 8. Melt temperature 1427 1600 125 (.degree. C.) 9.
Sintering 1315 900 -- temperature (.degree. C.) 10. Hardness
160-190 HV 450 HV R50-70 (Rockwell)
[0119] Metal
[0120] FIGS. 6 and 7 show relative density as a function of impact
energy per mass and total impact energy, respectively, for samples
processed with different powder masses. All samples were tested in
the same cylindrical mould but with different powder heights and
thus different masses. The reference mass was 28 g.
3TABLE 3 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel Collision
area Constant Reference mass 28 g
[0121] Result
[0122] The results show that to reach the same density, less energy
per mass is required for a body with a greater powder height and
thus a higher mass compared to a body with a smaller powder height
Approximately the same total energy is required to obtain the same
density, irrespective of the powder mass or height.
[0123] Ceramic
[0124] FIGS. 8 and 9 show relative density as a function of impact
energy per mass and total impact energy, respectively, for ceramic
samples processed with different powder masses. All samples were
tested in the same cylindrical mould but with different powder
heights. The reference mass was 11.1 g.
4TABLE 4 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Meterial Hydroxyapatite Collision
area Constant Reference mass 11.1 g
[0125] Result
[0126] FIG. 8 shows that the three curves follow each other, which
means that a certain density is obtained no matter of the specimen
shape with respect to impact energy per weight. This is also shown
in FIG. 9 where density is plotted as a function of total impact
energy. The curve is shifted to the left in the diagram for a lower
sample mass. It could also be noted that higher density for the
11.1. g sample never reached the plateau density as indicated for
the 2.8 and 5.5 g samples. The results show that the sample mass
and powder height in the mould influences the density with respect
to total impact energy, i.e. a larger sample mass needs more energy
in order to obtain a certain density. The results also show that
there is a linear relation between mass and density with respect to
impact energy per mass up till at least 271 Nm/g, see FIG. 8.
[0127] Polymer
[0128] FIGS. 10 and 11 show relative density as a function of
impact energy per mass and total impact energy, respectively, for
polymer samples processed with different powder masses. All samples
were tested in the same cylindrical mould but with different powder
heights. The reference mass was 4.2 g.
5TABLE 5 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material UHMWPE Collision area
Constant Reference mass 4.2 g
[0129] Result
[0130] The curves of smaller masses are shifted to the right or to
higher energy in the density energy graph. Also shift towards lower
densities could be observed for smaller sample masses.
[0131] FIG. 10 shows that a higher density is obtained when the
powder height is increased for a given impact energy per mass.
Hence, the maximum density is reached at a lower impact energy per
mass for a heavier sample. Studying the individual density-energy
graph, it could be divided into three phases. Phase 1 could be
characterised as the compacting phase, phase 2 would be
characterised as the plateau phase and phase 3 characterised as the
reaction phase. In the compaction phase, the density-energy curve
follows a logarithmic relation with an initial high compaction
rate. The sloop decreases as the energy is increased and eventually
the curve reaches the plateau phase. The plateau phase is
characterised with an almost constant inclination and constant
density. At a certain energy level the density starts to increase
again. This part of the curve is non linear with an initial
positive and increasing derivative. The curve derivative is
eventually decreasing and the curve is approaching the 100%
relative density asymptotically. Phase 1 and phase 2 could also be
seen in the metal counterparts. The samples of phases 1 and 2 are
characterised by opaque and brittle properties. Entering phase 3,
the samples gradually change in properties. A new material phase
occurs, first at the outer edges and at the top and bottom end
surfaces. This material phase is characterised as a harder,
transparent and with a plastic and fat surface feeling. For the
smaller mass samples the reaction does not occur gradually but
rather direct. The process in phase 3 was also somewhat dramatic
and could be described as a small explosion. Directly after the
impact stroke, white smoke was observed coming from the sample, and
material had extruded out between the stamps and the moulding die.
Further, the pressure occurring at the reaction phase proved to be
very high when during one test the moulding die was cracked open. A
larger weight sample was found to densify faster at lower energy
per mass levels and the reaction shift of material phase is
occurring gradually rather than direct as for the small samples.
The limited test series of the 12.6 g was due to the limited powder
pillar height of the tool. The insertion distance was less than the
recommended distance of the 30 mm (diameter of stamp). The test was
therefore stopped at the impact energy of 2100 Nm to eliminate a
tool failure. The two large dips in density for the 8.4 g sample
depend on the sample not holding together and coming out as a
powder.
[0132] Conclusions
[0133] For ceramic powders processed according to the invention the
same density was obtained independent of the powder height or mass
with the same impact energy per mass. On the contrary, for metal
and polymer powders processed according to the invention, the same
density was obtained independent of the powder height or mass with
the same total impact energy.
[0134] 2. Collision Area
[0135] FIGS. 12 and 13 show relative density as a function of
impact energy and total impact energy, respectively, for samples
with different collision surface areas.
6TABLE 6 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel Mass (M)
M2/M1 = 25 Collision surface S2/S1 = 8 area (S)
[0136] Result
[0137] The curves show a linear relation between collision surface
area, shock energy and pressure. Samples with different diameters
will reach the same density if they are processed with same impact
energy per mass.
[0138] 3. Shrinking
[0139] FIG. 14 shows relative density as a function of shrinking in
volume % for samples processed according to the invention in
comparison with samples processed with conventional powder
metallurgy (PM). All samples were sintered after the shocking and
pressing step, respectively. FIG. 15 shows the comparison between
achieved density after sintering for a sample processed
conventionally and a sample processed according to the invention
(DFIER), respectively.
7TABLE 7 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel Material
adds Internal lubricant (1.0 wt % Acrawax) Post-processing
Sintering
[0140] Result
[0141] The samples processed with Method X reaches a higher density
compared to conventional PM processed samples. When samples are
sintered after the compacting step, the material shrink because of
internal porosity in the material. Shrinking of the material can
have negative effects on the structure and the mechanical
properties of the final product.
[0142] The curves in FIG. 14 show that the shrinking volume
decreases with increased relative density for all samples. The
samples processed with DFIER shrinks more compared with the samples
processed conventionally. The reason is probably that the samples
processed with DFIER has a better orientation of particles, and
that the energy transmitted during the shock phase is stored in the
grain boundaries and will be set free during sintering. The free
energy will increase the driving force to collapse the porosity and
solidify the material during sintering. Samples pressed
conventionally have less driving force during sintering compared
with samples processed with DFIER.
[0143] The samples processed with DFIER have high green density
before sintering, which means that the material shrinks less and
better mechanical properties are therefore achieved, compared to a
sample compacted by using conventional pressing. Samples with a low
green density require a sophisticated and expensive sintering
process to remove all porosity in the material. The high green
density of samples processed with DFIER make it possible to use a
cheaper and simpler sintering process to reach full density.
[0144] 4. Velocity Study
[0145] FIG. 16 shows relative density as a function of impact
energy for samples shocked with different impact velocities of the
impact ram. The impact velocities for the impact ram and punch,
respectively, are showed in FIGS. 17, 18 and 19. FIG. 20 shows
obtained impact velocity of the punch for different impact ram
masses for the maximum used shock energy, 3000 Nm, for all velocity
studies.
8TABLE 8 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel Impact
velocity of impact ram (m/s) V7 < V6 < . . . < V1 Impact
velocity of punch VP7 > VP6 > . . . > VP1 (m/s) Equation
of momentum M.sub.impact ram * V = M.sub.punch * VP
[0146] Result
[0147] The curves in FIG. 16 show that with a low impact velocity
of the impact ram the highest density for a specific shock energy
is reached quickest.
[0148] The differences between the maximum densities for the seven
series performed are up to 10 percent. The results indicate that a
higher density is obtained when the impact ram mass is increased or
equivalent a decreased impact velocity for a given energy level per
mass. The effect is decreased as the energy is increased. The
relative density at pre-compacting is to a great extent dependent
on the static pressure.
[0149] The mass of the impact ram decides the impact velocity of
the punch which is the velocity that accelerates the powder. A high
impact ram mass will accelerate a light punch to higher velocities
compared with a impact ram with a lower mass. FIGS. 18 and 19 show
that the highest impact velocity is achieved for the punch
accelerated by the greatest and slowest impact ram.
[0150] The diagrams show that if the mass of the impact ram
increases to infinity the impact velocity of the ram will reach 0
m/s, which means that there is a limit to how great impact ram can
be used to obtain a high punch velocity.
[0151] The relation between the mass of the impact ram and the
punch to reach the highest density was in this study 1:3846.
[0152] The material properties of the processed powder and the
configuration of the tool as well as the material used in the tool
have to be considered to find the optimal mass relation between the
impact ram and punch.
[0153] 5. Multiple Shock Study 1
[0154] FIG. 21 shows relative density as a function of the number
of shocks for samples processed with a total shock energy of 3000
Nm and 4000 Nm, respectively.
9TABLE 9 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel Total
shock energy Constant for each study
[0155] Result
[0156] The curves in the diagram show that the highest density is
reached for samples processed with one single shock, compared with
the samples processed with the same total energy performed in a
multiple shock series.
[0157] We can notice a tendency that the distance between the
curves increases with increased number of stokes.
[0158] 6. Multiple Shock-Study 2
[0159] FIG. 22 shows the relative density as a function of number
of shocks. Four studies were performed. In each study the samples
were processed with one single shock or multiple shocks with a
constant energy per shock.
10TABLE 10 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel Energy per
shock Constant for each study
[0160] Result
[0161] The curve for the samples processed with the highest energy
per shock increases fastest to a high density compared with the
samples processed with lower energies per shock. The curves show
that high densities are reached for shock energies over 50 Nm per
shock, which means that there is a lower limit for the energy per
shock when the total energy is divided into multiple shocks.
[0162] 7. Heating Study
[0163] FIG. 23 shows relative density as a function of impact
energy per mass for samples processed in increased temperature.
11TABLE 11 Conditions Pressure Atmosphere Temperature Increased
temperature Energy retention No Material Stainless steel Heating
temperature 150.degree. C.
[0164] Result
[0165] The samples processed in a temperature above room
temperature reaches nearly 100% of density. The curve increases
faster to a higher density compared with the curve showing the
density result for the samples processed in room temperature.
[0166] Heating of the powder before and during the DFIER process
increases the initial energy state of the powder. The powder
compacting starts therefore from a higher temperature level and the
result is a higher final density. This means that less energy is
required to reach a high enough temperature in the material to
achieve spot welding between the powder particles during the shock
phase.
[0167] A heating to 150.degree. C. of stainless steel powder
results in a relative density improvement of .about.2%.
[0168] The material properties of the processed powder have to be
considered to find optimal parameter values for the heating
[0169] Electric current can be used to heat the powder during
DFIER.
[0170] 8. Vacuum Study
[0171] FIG. 24 shows relative density as a function of impact
energy per mass for samples processed in vacuum.
12TABLE 12 Conditions Pressure Vacuum Temperature Room temperature
Energy retention No Material Stainless steel Vacuum -100 Pa
[0172] Result
[0173] The curve for the samples processed in vacuum increases
faster and the samples reach a higher density than the samples
processed in atmospheric pressure.
[0174] When the pressure is decreased between the powder particles
the reactivity is increased in the material and spot welding is
achieved at a lower process energy, compared with a powder
processed in atmospheric pressure.
[0175] Samples compacted to high densities in air have pores filled
with air. If these samples are sintered after DFIER, the heat
during sintering will expand the air in the closed pores expanding
the material. If the pores have a lower pressure i.e. vacuum or
near vacuum, they will not expand instead they will collapse during
sintering and 100% density can be achieved.
[0176] The material properties of the processed powder have to be
considered to find optimal parameter values for processing in
vacuum.
[0177] 9. Impact Direction
[0178] FIG. 25 shows relative density as a function of impact
energy per mass for samples processed in one or two impact
directions.
13TABLE 13 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel
[0179] Result
[0180] The samples processed by impacting in two directions
increases faster in density and reaches a higher density compared
with samples processed in one impact direction for the same energy.
The reason is that the powder processed from two directions obtains
a better orientation of the powder particles during DFIER compared
with the powder processed from one direction. A good orientation of
the powder particles facilitates the solidification process.
[0181] The material properties of the processed powder have to be
considered to find optimal parameter values for processing powders
with two impact directions.
[0182] 10. Time Interval Study
[0183] FIG. 26 shows relative density as a function of time
interval between two consecutive shocks. All samples were shocked
two times with different time delays between the shocks.
14TABLE 14 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Stainless steel Shock
energy per 800 Nm Stroke Number of shocks 2
[0184] Result
[0185] The curve shows that the time delay between two shocks
should be very short to effect the material properly.
[0186] The optimal time delay between two shocks depends on the
mechanical properties of the material processed. Important material
properties to consider are thermal conductivity and acoustic
velocity.
[0187] 11. Energy Retention Study 1
[0188] FIG. 27 shows relative density as a function of impact
energy per mass for shocked samples in comparison with samples
shocked and post-compacted by energy retention.
15TABLE 15 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention Yes Material Stainless steel
[0189] Result
[0190] The curve showing the result for shocked and post-compacted
samples increases faster and reaches a higher density compared with
the curve for only shocked samples.
[0191] The result of using an energy retention step is that the
energy transmitted during the shock phase is retained in the
material, and can effect the sample and increase the metallic
bonding and spot welding among the powder particles. It is
therefore possible to increase the relative density to near 100% by
using the post-compacting step.
[0192] The material properties of the processed powder have to be
considered to find optimal parameter values for the energy
retention.
[0193] 12. Energy Retention Study 2
[0194] FIG. 28 shows relative density as a function of impact
energy per mass for samples processed with different time delays
between the shock and the start of the energy retention.
16TABLE 16 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention Yes Material Stainless steel
[0195] Result
[0196] The curve for samples processed with a directly start of the
energy retention after the shock step increases fastest and reaches
the highest relative density. The curves show that the time between
the shock process and the energy retention should be less then 1 s
to obtain maximum effect. 1 second is not an optimum because the
optimal time varies between different material types. The energy
retention has less effect if the time delay between shock and
energy retention increases.
[0197] The time duration of the local increase in temperature
between the powder particles after the shock phase is very short.
The condition for achieving an effect of the energy retention is
that the sample still is in an elevated energy state, which is not
the case if the sample already has cooled down to room temperature.
The material properties of the processed powder have to be
considered to find optimal parameter values for the energy
retention.
[0198] 13. Energy Retention Study 3
[0199] FIG. 29 shows relative density as a function of energy
retention time for shocked and post-compacted samples. The curve
shows the effect of the duration of the energy retention.
17TABLE 17 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention Yes Material Stainless steel
[0200] Result
[0201] The curve shows that the effect of energy retention
decreases after a few seconds.
[0202] The optimal time for energy retention is depending on the
properties of the processed material in combination with the sample
size. A greater mass will retain the heat for a longer period and
it is therefore possible to increase the energy retention time and
still obtain an effect
[0203] 14. Pre-Compacting Study 1
[0204] FIG. 30 shows relative density as a function of
pre-compacting pressure.
18TABLE 18 Conditions Pressure Atmosphere Temperature Room
temperature Material Stainless steel
[0205] Result
[0206] The curve shows that an increase in pre-compacting pressure
increases the density of the pre-compacted sample.
[0207] The pre-compacting pressure on the sample before the shock
phase is an important parameter to consider, because the green
density of the sample will influence the final material properties
achieved after a complete DFIER process.
[0208] 15. Pre-Compacting Study 2
[0209] FIG. 31 shows relative density as a function of pre-compact
pressure. The curves show the effect of pre-compacting in different
surrounding pressures.
19TABLE 19 Conditions Pressure 1. Atmosphere: (P = 1) 2. Vacuum: (P
= 0) Temperature Room temperature Material Stainless steel
[0210] Result
[0211] The curve for samples pre-compacted in vacuum reaches the
highest density.
[0212] The energy necessary to overcome the atmospheric pressure
and removing the air out of the powder at pre-compaction at normal
pressure can instead directly affect the powder at pre-compaction
in vacuum.
[0213] 16. Pre-Compacting Study 3
[0214] FIG. 32 shows relative density as a function of impact
energy per mass. The samples have been pre-compacted differently by
varying the time duration of the pre-compaction phase.
20TABLE 20 Conditions Pressure Atmosphere Temperature Room
temperature Material Stainless steel
[0215] Result
[0216] The curves show that a higher density is reached if the
samples are pre-compacted longer than 1 s.
[0217] The material properties of the processed powder have to be
considered to find optimal parameter values for the pre-compacting
step.
[0218] Property Studies
[0219] Three property studies were performed: Theoretical density
study, powder hardness study and melting temperature study. Powder
properties for the powders are described in tables 21 and 22.
21TABLE 21 Powder properties for the metals used in the property
studies. Properties Ti--6Al--4V Titanium Co--28Cr--6Mo Al-alloy
Ni-alloy 1. Particle size <150 <150 <150 <150 <150
(micron) 2. Particle -- 2 wt % > 150 0.1 wt % > 250 6.57 wt %
> 125 distribution balance < 150 3 wt % > 200 50.80 wt %
> 106 (micron) 5 wt % > 160 24.25 wt % > 100 5-20 wt %
> 100 24.25 wt % > 100 20-35 wt % > 63 12.26 wt % > 90
10-25 wt % > 45 6.12 wt % < 90 35 50 wt % < 45 3. Particle
Irregular Irregular Irregular Irregular Irregular morphology 4.
Powder -- Hydrated Water Water Water production atomised atomised
atomised 5. Crystal Al stabilises HCP 85% alpha FCC FCC structure
HCP V phase 15% stabilises BCC carbides 6. Theoretical 4.42 4.5 8.5
2.66 8.38 density (g/cm.sup.3) 7. Apparent 1.77 1.80 3.4 1.22 2.59
density (g/cm.sup.3) 8. Melt 1600-1650 1660 1350-1450 658 1645
temperature (.degree. C.) 9. Sintering 1260 1000 1200 600 1315
temperature (.degree. C.) 10. Hardness -- 60 460-830 50-100 80-200
(HV) Stainless steel Low wrought Properties 316L steel Martensitic
steel Tool steel 1. Particle size <150 <150 <150 <150
(micron) 2. Particle 0.60 wt % > 150 3.2 wt % > 150 1.06 wt %
> 150 0.4 wt % 150-180 distribution 42.70% < 45 79.5 wt %
< 150 4.32 wt % > 125 24.48 wt % 106-150 (micron) 12.03 wt %
> 106 26.68 wt % 75-106 23.59 wt % > 75 28.67 wt % 45-75
19.26 wt % > 53 19.77 wt % < 45 9.04 wt % > 45 30.70 wt %
< 45 3. Particle Irregular Irregular Irregular Irregular
morphology 4. Powder Water atomised Water atomised Water atomised
Water atomised production 5. Crystal FCC BCC < 900.degree. C.
FCC BCC < 910.degree. C. structure FCC > 900.degree. C. FCC
> 910.degree. C. 6. Theoretical 7.90 7.75 7.73 7.75 density
(g/cm.sup.3) 7. Apparent 2.64 2.87 3.37 2.55 density (g/cm.sup.3)
8. Melt 1427 1540 1427 1350-1450 temperature (.degree. C.) 9.
Sintering 1315 1230 1230 1315 temperature (.degree. C.) 10.
Hardness 160-190 130-280 180-330 207-241 (HV)
[0220]
22TABLE 22 Powder properties for the ceramics used in the property
studies. Properties Silicone nitride Hydroxyapatite Alumina
Zirconia 1. Particle size <0.5 <1 <0.5 0.4 (micron) 2.
Particle <0.5 <1 0.3-0.5 <0.6 distribution (micron) 3.
Particle Irregular irregular irregular irregular morphology 4.
Powder Freeze-dry Wet chemistry Grinding Spray-dry production
granulation precipitation Freeze-dry granulation granulation 5.
Crystal 98% alfa Apatite alfa tetragonal structure 2% beta
(hexagonal) 6. Theoretical 3.18 (batch 1, 2) 3.15 g/cm.sup.3 3.98
(batch 1) density (g/cm.sup.3) 3.27 (batch 3) 3.79 (batch 2) 3.12
(batch 4) 3.98 (batch 3) 3.79 (batch 4) 6.07 7. Apparent 0.38 0.6
0.5-0.8 -- density (g/cm.sup.3) 8. Melt 1800 1600 2050 2500-2600
temperature (.degree. C.) 9. Sintering 1820 900 1600-1650 1500
temperature(.degree. C.) 10. Hardness 1570 450 1770 1250-1350
(HV)
[0221] 17. Theoretical Density Study
[0222] FIG. 33 shows maximum obtained relative density as a
function of theoretical density for different metal powders.
23TABLE 23 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Metal powder (see table
3)
[0223] Result
[0224] The diagram shows a tendency that a metal powder with a high
theoretical density is more difficult to process with DFIER to a
high density, compared with a metal powder with a low theoretical
density. In table 1 the materials used in the study are listed
together with theoretical densities and obtained relative density
for each material.
[0225] It is clear that many parameters are involved to decide if a
material is easy to process with DFIER to high densities. Other
important powder properties are powder type, alloying elements,
powder hardness, melting temperature, particle size and particle
morphology.
[0226] 18. Powder Hardness Study
[0227] FIG. 34 shows maximum obtained relative density as a
function of powder hardness for different ceramic and metal
powders, respectively.
24TABLE 24 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No Material Metal powders (see table
3) Ceramic powders (see table 4)
[0228] Result
[0229] The diagram shows that it is more difficult to process a
hard metal powder to a high density compared with a soft powder
using DFIER. The plotted test values for metal powder has a smaller
inclination compared with the values for ceramic materials. The
diverging value (400 HV, 70.6%) for the ceramic material is because
it is a water based ceramic. This explains the low powder
hardness.
[0230] A hard metal or ceramic powder can be processed in vacuum
and increased surrounding temperature to reach higher
densities.
[0231] 19. Melting Temperature Study
[0232] FIG. 35 shows maximum obtained relative density as a
function of melting temperature for different metal and ceramic
powders, respectively.
25TABLE 25 Conditions Pressure Atmosphere Temperature Room
temperature Energy retention No
[0233] Result
[0234] The metal curve shows that there is no clear relation
between the melting temperature for a metal and how easy it is to
process with DFIER to high densities. Table 26 shows two steels
with the same melting temperature but different powder hardness,
which explains that only one material property cannot decide if the
material is easy to process to high densities with DFIER.
26TABLE 26 Material type Powder hardness (HV) Melting temperature
(.degree. C.) Stainless steel 160-190 1427 Martensitic steel
180-330 1427
[0235] Ceramic powders have higher melting temperature and are also
more difficult to process to high densities compared with metal
powders, which is showen in FIG. 35.
[0236] 20. Vibratory Compacting Study
[0237] FIG. 36 shows relative density as a function of applied
pressure for samples processed with conventional static pressing
compared with samples processed with vibratory compacting (VC) in
combination with other processes.
27TABLE 27 Conditions Pressure Atmosphere Temperature Room
temperature Material Stainless steel Vibrating velocity 233
oscillations/s Shock energy 300-3000 Nm
[0238] Result
[0239] The curves show that relative density of powders vibrated
under controlled conditions during a static pressure or/and in
combination with shock energy reach much higher densities compared
with samples processed with only static pressure.
[0240] Samples compacted with vibratory compacting, shocked from
two directions and with double axial static pressure reaches the
highest density for the lowest total pressure.
* * * * *