U.S. patent application number 14/380112 was filed with the patent office on 2015-01-29 for object production.
The applicant listed for this patent is Charles Malcolm WARD-CLOSE. Invention is credited to Charles Malcolm Ward-Close.
Application Number | 20150030494 14/380112 |
Document ID | / |
Family ID | 45991783 |
Filed Date | 2015-01-29 |
United States Patent
Application |
20150030494 |
Kind Code |
A1 |
Ward-Close; Charles
Malcolm |
January 29, 2015 |
OBJECT PRODUCTION
Abstract
Methods and apparatus for producing an object, the method
comprising: performing an Additive Manufacturing process to produce
an intermediate object from provided metal or alloy, whereby the
intermediate object comprises regions having a contaminant
concentration level above a threshold level; based upon one or more
parameters, determining a temperature and a duration; and
performing, on the intermediate object, a contaminant dispersion
process by, for a duration that is greater than or equal to the
determined duration, heating the intermediate object to a
temperature that is greater than or equal to the determined
temperature and less than the melting point of the metal or alloy,
the contaminant dispersion process being performed so as to
disperse, within the intermediate object, a contaminant from
regions of high contaminant concentration to regions of low
contaminant concentration until the intermediate object comprises
no regions having a contaminant concentration level above the
threshold level.
Inventors: |
Ward-Close; Charles Malcolm;
(Hampshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WARD-CLOSE; Charles Malcolm |
|
|
US |
|
|
Family ID: |
45991783 |
Appl. No.: |
14/380112 |
Filed: |
February 20, 2013 |
PCT Filed: |
February 20, 2013 |
PCT NO: |
PCT/GB2013/050410 |
371 Date: |
August 21, 2014 |
Current U.S.
Class: |
419/19 ; 419/38;
419/42; 419/45; 425/78; 75/228 |
Current CPC
Class: |
B22F 3/15 20130101; B22F
3/1055 20130101; B23K 20/2333 20130101; B32B 15/01 20130101; B22F
3/1039 20130101; Y02P 10/25 20151101; Y02P 10/295 20151101; B23K
20/02 20130101; B22F 2003/1056 20130101; B22F 3/02 20130101; B22F
3/1035 20130101; B23K 20/002 20130101; B22F 3/24 20130101; B23K
20/227 20130101; B33Y 70/00 20141201; B23K 2101/00 20180801; B22F
3/003 20130101; B22F 3/168 20130101; Y10T 428/12806 20150115; B23K
20/233 20130101; B22F 2003/248 20130101 |
Class at
Publication: |
419/19 ; 419/45;
419/38; 419/42; 425/78; 75/228 |
International
Class: |
B22F 3/10 20060101
B22F003/10; B22F 3/15 20060101 B22F003/15; B22F 3/00 20060101
B22F003/00; B22F 3/02 20060101 B22F003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2012 |
GB |
1203359.3 |
Jan 23, 2013 |
GB |
1301173.9 |
Claims
1. A method of producing an object, the method comprising:
providing some metal or alloy; performing, using an Additive
Manufacturing apparatus, in an environment containing an amount of
a reactive contaminant, an Additive Manufacturing process to
produce an intermediate object from the provided metal or alloy,
wherein the Additive Manufacturing processes includes heating the
provided metal or alloy thereby causing at least some of the metal
or alloy to react with the reactive contaminant in the environment
so as to produce contaminated metal or alloy, the intermediate
object comprises the contaminated metal or alloy, and the
intermediate object comprises one or more regions in which
concentration level of the contaminated metal or alloy is above a
threshold level; based upon the threshold level and a concentration
level of the contaminated metal or alloy within one or more of the
regions, determining a temperature and a duration; and sintering
the intermediate object for a duration that is greater than or
equal to the determined duration at a temperature that is greater
than or equal to the determined temperature and less than the
melting point of the metal or alloy so as to disperse the
contaminated metal or alloy from the regions to one or more further
regions within the intermediate object having a lower concentration
level of the contaminated metal or alloy until the intermediate
object comprises no regions having a concentration level of the
contaminated metal or alloy above the threshold level, thereby
producing the object.
2. A method according to claim 1, wherein the sintering is
performed such that the contaminated metal or alloy is
substantially uniformly distributed within the bulk of the
object.
3. A method according to claim 1, wherein the method further
comprises, after the sintering process, performing, on the
intermediate object, a hot isostatic pressing process.
4. (canceled)
5. A method according to claim 1, wherein the determined
temperature is between 1300.degree. C. and the melting point of the
provided metal or alloy.
6. A method according to claim 1, wherein the determined duration
is greater than or equal to one hour.
7-9. (canceled)
10. A method according to claim 1, wherein the metal or alloy is
Ti-6Al-4V.
11. A method according to claim 1 wherein, the metal or alloy is
provided in powder form and the Additive Manufacturing process is a
powder bed Additive Manufacturing process.
12. A method according to claim 1, wherein the reactive contaminant
is oxygen.
13. A method according to claim 1, wherein the intermediate object
comprises a plurality of open cavities, and the method further
comprises: performing a sealing process on the intermediate object
to seal the openings of the open cavities, thereby forming a
plurality of closed cavities; and reducing the sizes of the closed
cavities by performing a consolidation process on the intermediate
object having the closed cavities.
14. A method according to claim 1, wherein the produced object
comprises a plurality of open cavities, and the method further
comprises: performing a sealing process on the object to seal the
openings of the open cavities, thereby forming a plurality of
closed cavities; and reducing the sizes of the closed cavities by
performing a consolidation process on the object having the closed
cavities.
15. A method according to claim 13, wherein the step of reducing
the sizes of the closed cavities is performed until the closed
cavities are no longer present.
16. A method according to claim 13, wherein the step of performing
a consolidation process comprises performing a hot isostatic
pressing process.
17. A method according to claim 13, wherein the step of performing
a sealing process comprises plastically deforming the surface of
the object.
18. A method according to claim 17, wherein plastically deforming
the surface of the object comprises shot peening the surface of the
object.
19. A method according to claim 17, wherein the step of performing
a sealing process further comprises sintering the object after the
surface of the object has been plastically deformed.
20. A method according to claim 1, wherein: the method further
comprises determining a concentration level of the contaminated
metal or alloy within a region of the intermediate object; and the
determined temperature and duration are determined using the
determined contaminant concentration level.
21. A method according to claim 20, wherein the determining of a
concentration level of the contaminated metal or alloy within a
region of the intermediate object comprises determining the maximum
concentration level of the contaminated metal or alloy within the
intermediate object.
22. (canceled)
23. Apparatus for producing an object, the apparatus comprising:
Additive Manufacturing apparatus configured to, using some provided
metal or alloy, in an environment containing an amount of a
reactive contaminant, perform an Additive Manufacturing process to
produce an intermediate object from the provided metal or alloy,
wherein the Additive Manufacturing process include heating the
provided metal or alloy thereby causing at least some of the metal
or alloy to react with the reactive contaminant in the environment
so as to produce a contaminated metal or alloy, and the
intermediate object comprises one or more regions in which a
concentration level of the contaminated metal or alloy is above a
threshold level; means for, based upon the threshold level and the
concentration level of the contaminated metal or alloy within one
or more of the regions, determine a temperature and a duration; and
sintering means configured to sinter the intermediate object for a
duration that is greater than or equal to the determined duration
at a temperature that is greater than or equal to the determined
temperature and less than the melting point of the metal or alloy
so as to disperse the contaminated metal or alloy from the regions
to one or more further regions within the intermediate object
having a lower concentration level of the contaminated metal or
alloy until the intermediate object comprises no regions having a
concentration level of the contaminated metal or alloy above the
threshold level, thereby producing the object.
24. An object that has been produced using a method according to
claim 1.
25-26. (canceled)
27. A method according to claim 1, wherein the step of performing
comprises: performing, using the Additive Manufacturing apparatus,
in the environment containing an amount of the reactive
contaminant, an initial Additive Manufacturing process, the initial
Additive Manufacturing processes including heating the provided
metal or alloy, thereby causing at least some of the metal or alloy
to react with the reactive contaminant in the environment so as to
produce the contaminated metal or alloy; and performing, using the
Additive Manufacturing apparatus, a further Additive Manufacturing
process, to produce the intermediate object from metal or alloy
recycled from the initial Additive Manufacturing process, the metal
or alloy recycled from the initial Additive Manufacturing process
including the contaminated metal or alloy.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is the National Stage of International
Application No. PCT/GB2013/050410, filed 20 Feb. 2013, which claims
the benefit of and priority to GB 1203359.3, filed 24 Feb. 2012,
and GB1301173.9, filed 23 Jan. 2013, the contents of all of which
are incorporated by reference as if fully set forth herein.
FIELD OF THE INVENTION
[0002] The present invention relates to the production of
objects.
BACKGROUND
[0003] Additive Manufacturing (AM) (also known as Additive Layer
Manufacturing (ALM), 3D printing, etc.) refers to processes that
may be used to produce functional, complex objects, layer by layer,
without moulds or dies. Typically, AM processes include providing
material (e.g. metal, ceramic or plastic) in the form of a powder
or a wire, and, using a powerful heat source (such as a laser beam,
electron beam or an electric, or plasma welding arc), an amount of
that material is melted and deposited upon a base work piece.
Subsequent layers are then built up upon each preceding layer so as
to form the object.
[0004] Example AM processes include, but are not limited to, Laser
Blown Powder, Laser Powder Bed, and Wire and Arc technologies.
[0005] However, objects produced using AM processes, particularly
those made using powder material, may comprise one or more
contaminated regions, i.e. regions in which the material that forms
the object has been contaminated by a contaminant (e.g. oxygen).
Also, objects produced using AM processes, particularly those made
using powder material, may comprise micro-pores and other
imperfections at or proximate to the surface of the object. The
presence of such contaminated regions and other imperfections tend
to adversely affect the fatigue performance of an object,
especially in high-cycle fatigue situations. For example, the
imperfections may act as crack initiators.
SUMMARY OF THE INVENTION
[0006] In a first aspect, the present invention provides a method
of producing an object, the method comprising: providing some metal
or alloy; performing, using an Additive Manufacturing apparatus, an
Additive Manufacturing process to produce an intermediate object
from the provided metal or alloy, whereby the intermediate object
comprises one or more regions having a contaminant concentration
level above a threshold level; based upon one or more parameters
selected from the group of parameters consisting of: the type of
metal or alloy from which the intermediate object has been
produced, the shape and/or size of the intermediate object, a
contaminant concentration level of a region of the intermediate
object, and the threshold level, determining a temperature and a
duration; and performing, on the intermediate object, a contaminant
dispersion process by, for a duration that is greater than or equal
to the determined duration, heating the intermediate object to a
temperature that is greater than or equal to the determined
temperature and less than the melting point of the metal or alloy
from which the intermediate object has been made, the contaminant
dispersion process being performed so as to disperse a contaminant
from regions of high contaminant concentration within the
intermediate object to regions of low contaminant concentration
within the intermediate object until the intermediate object
comprises no regions having a contaminant concentration level above
the threshold level, thereby producing the object.
[0007] The contaminant dispersion process may be performed such
that the contaminant is substantially uniformly distributed within
the bulk of the object.
[0008] The contaminant dispersion process may comprise performing,
on the intermediate object, a hot isostatic pressing process at a
temperature that is greater than or equal to the threshold
temperature and for a duration that is greater than or equal to the
threshold duration.
[0009] The determined temperature may be between 1100.degree. C.
and the melting point of the provided metal or alloy.
[0010] The determined temperature may be between 1300.degree. C.
and the melting point of the provided metal or alloy.
[0011] The determined duration may be greater than or equal to one
hour.
[0012] The determined duration may be greater than or equal to two
hours.
[0013] The Additive Manufacturing (AM) process may be a process
selected from the group of AM processes consisting of: a powder bed
fusion AM process, a blown powder AM process, a sheet lamination AM
process, a laser blown powder AM process, a laser powder bed AM
process, and an AM process that implements wire and arc
technology.
[0014] The metal or alloy from which the object is made may be
selected from a group of metals or alloys consisting of: titanium
alloys, steel, nickel superalloys and aluminium alloys.
[0015] The metal or alloy may be Ti-6Al-4V.
[0016] The metal or alloy may be provided in powder form.
[0017] The Additive Manufacturing process may be a powder bed
Additive Manufacturing process.
[0018] The contaminant may comprise oxygen.
[0019] The intermediate object may comprise a plurality of open
cavities. The method may further comprise performing a sealing
process on the intermediate object to seal the openings of the open
cavities, thereby forming a plurality of closed cavities, and
reducing the sizes of the closed cavities by performing a
consolidation process on the intermediate object having the closed
cavities.
[0020] The produced object may comprise a plurality of open
cavities. The method may further comprise performing a sealing
process on the object to seal the openings of the open cavities,
thereby forming a plurality of closed cavities, and reducing the
sizes of the closed cavities by performing a consolidation process
on the object having the closed cavities.
[0021] The step of reducing the sizes of the closed cavities may be
performed at least until the closed cavities are no longer
present.
[0022] The step of performing a consolidation process may comprise
performing a hot isostatic pressing process.
[0023] The step of performing a sealing process may comprise
plastically deforming the surface of the object.
[0024] Plastically deforming the surface of the object may comprise
shot peening the surface of the object.
[0025] The step of performing a sealing process may further
comprise sintering the object after the surface of the object has
been plastically deformed.
[0026] The method may further comprise determining a contaminant
concentration level of a region of the intermediate object.
[0027] The determined temperature and duration may be based upon
the determined contaminant concentration level.
[0028] The determining of a contaminant concentration level of a
region of the intermediate object may comprise determining the
maximum contaminant concentration level within the intermediate
object.
[0029] In a further aspect, the present invention provides a method
of producing an object, the method comprising: providing an initial
object, the initial object being made of a metal or an alloy, the
initial object having been produced by performing an Additive
Manufacturing process, the initial object comprising one or more
regions having a contaminant concentration above a threshold level;
based upon one or more parameters selected from the group of
parameters consisting of: the type of metal or alloy from which the
initial object has been produced, the shape and/or size of the
initial object, a concentration level of a region of the initial
object, and the threshold level, determining a temperature and a
duration; and performing, on the initial object, a contaminant
dispersion process by, for a duration that is greater than or equal
to the determined duration, heating the initial object to a
temperature that is greater than or equal to the determined
temperature and less than the melting point of the metal or alloy
from which the initial object has been made, the contaminant
dispersion process being performed so as to disperse a contaminant
from regions of high contaminant concentration within the initial
object to regions of low contaminant concentration within the
initial object until the initial object comprises no regions having
a contaminant concentration above the threshold level, thereby
producing the object.
[0030] In a further aspect, the present invention provides an
object that has been produced using a method according to any of
the above aspects.
[0031] In a further aspect, the present invention provides
apparatus for producing an object, the apparatus comprising:
Additive Manufacturing (AM) apparatus configured to, using some
provided metal or alloy, perform an Additive Manufacturing process
to produce an intermediate object from the provided metal or alloy,
whereby the intermediate object comprises one or more regions
having a contaminant concentration level above a threshold level;
means for, based upon one or more parameters selected from the
group of parameters consisting of: the type of metal or alloy (12)
from which the intermediate object has been produced, the shape
and/or size of the intermediate object, a contaminant concentration
level of a region of the intermediate object, and the threshold
level, determine a temperature and a duration; and heating means
configured to perform, on the intermediate object, a contaminant
dispersion process by, for a duration that is greater than or equal
to the determined duration, heating the intermediate object to a
temperature that is greater than or equal to the determined
temperature and less than the melting point of the metal or alloy
from which the intermediate object has been made, the contaminant
dispersion process being performed so as to disperse a contaminant
from regions of high contaminant concentration within the
intermediate object to regions of low contaminant concentration
within the intermediate object until the intermediate object
comprises no regions having a contaminant concentration level above
the threshold level, thereby producing the object.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic illustration (not to scale) showing
example Additive Manufacturing apparatus;
[0033] FIG. 2 is a process flow chart of an embodiment of a process
of producing an object;
[0034] FIG. 3 is a schematic illustration (not to scale) showing a
stage of an Additive Manufacturing process performed by the
Additive Manufacturing apparatus; and
[0035] FIG. 4 is a schematic illustration (not to scale) of a cross
section of the object at a certain stage of the process of FIG.
2.
DETAILED DESCRIPTION
[0036] FIG. 1 is a schematic illustration (not to scale) showing
example Additive Manufacturing apparatus 2 that is to be used, in
an embodiment, to perform an Additive Manufacturing process so as
to create an object 4.
[0037] The terminology "Additive Manufacturing" is used herein to
refer to all additive processes that may be used to produce
functional, complex objects, layer by layer, without moulds or dies
e.g. by providing material (e.g. metal or plastic) in the form of a
powder or a wire, and, using a powerful heat source such as a laser
beam, electron beam or an electric, or plasma welding arc, melting
an amount of that material and depositing the melted material (e.g.
on a base plate/work piece 6), and subsequently building layers of
material upon each preceding layer.
[0038] Additive Manufacture (AM) may also be known inter alia as 3D
printing, Direct Digital Manufacturing (DDM), Digital Manufacturing
(DM), Additive Layer Manufacturing (ALM), Rapid Manufacturing (RM),
Laser Engineering Net Shaping (LENS), Direct Metal Deposition,
Direct Manufacturing, Electron Beam Melting, Laser Melting,
Freeform Fabrication, Laser Cladding, Direct Metal Laser
Sintering.
[0039] In this embodiment, the AM apparatus 2 is apparatus for
performing a powder bed AM processes. Further information on powder
bed AM apparatus and processes may be found, for example in Gibson,
I. Rosen, D. W. and Stucker, B. (2010) "Additive Manufacturing
Technologies: Rapid Prototyping Direct Digital Manufacturing" New
York, Heidelberg, Dordrecht, London: Springer, which is included
herein by reference. However, in other embodiments, a different
type of AM apparatus is used produce the object 4, e.g. by
performing a different type of AM process. Examples of other
appropriate AM processes that may be used to produce the object 4
include, but are not limited, blown powder AM processes, sheet
lamination AM processes, vat photopolymerisation AM processes,
laser blown powder AM processes, laser powder bed AM processes, and
AM processes that implement wire and arc technology.
[0040] In this embodiment, the AM apparatus 2 comprises a heat
source in the form of a laser source 8 configured to produce a high
powered laser beam 10. The laser source 8 may be any appropriate
type of laser source, e.g. a laser source that is configured to
have a continuous wave power output of 500 W.
[0041] The AM apparatus 2 further comprises a source of metallic
material (hereinafter referred to as "metallic powder 12) in the
form of a powder repository 14 (or powder bed). In this embodiment,
the metallic material is titanium alloy powder (e.g. Ti-6Al-4V).
Titanium alloy powder typically has spherical grains with a
diameter in the range 0-45 .mu.m.
[0042] In other embodiments, a different type of material (e.g. a
different type of metallic power, a plastic powder, or a ceramic
powder) may be used.
[0043] In operation, a first piston 16 (that is located at the
bottom of the first repository) is raised (in the direction
indicated by an arrow in FIG. 1 and the reference numeral 18) so as
to raise an amount of the powder 12 above a top level of the
repository 14.
[0044] In this embodiment, a roller 20 is rolled (in the direction
indicated by an arrow in FIG. 1 and the reference numeral 22) over
the upper surface of the repository 14 and across an upper surface
of a further repository 24. This is performed so that the metallic
powder 12 that was raised above the level of the repository 14 by
the raising of the first piston 16 is spread over an upper surface
of the further repository 24. Thus, a top surface of the contents
of the further repository 24 is covered by a layer of metallic
power 12. In other embodiments, a different means of spreading the
metallic powder 12 across a top surface of the contents of the
further repository 24, such as a wiper, may be used instead of or
in addition to the roller 20.
[0045] After a layer of metallic power 12 has been spread across a
top surface of the contents of the further repository 24, the laser
source 8 is controlled by a computer 26 to deliver the laser beam
10 via an optical fibre 28 to focussing optics 30 which focus the
laser beam 10 to the focal point 32 on the layer of metallic power
12 has been spread across a top surface of the contents of the
further repository 24.
[0046] The laser beam 10 produced by the laser source 8 is focused
upon the layer of metallic powder 12 has been spread across the top
surface of the contents of the further repository 24 so as to melt
a portion of the layer of metallic powder 12.
[0047] In this embodiment, a portion of the metallic powder 12 on
the top surface of the further repository 24 is fully melted, and
subsequently allowed to cool so as to form a layer of solid
material.
[0048] A second piston 34, located at the bottom of the further
repository 24 is then lowered (i.e. moved in a direction indicated
in FIG. 1 by a solid arrow and the reference numeral 36) to allow
for a further layer of metallic powder 12 to be spread by the
roller 20 (and subsequently melted and allowed to solidify) across
the top surface of the contents of the further repository 24.
[0049] Many layers of material are laid on top of one another (in
accordance with a digital design model 38 for the object 4 stored
by the computer 26) to produce the object 4.
[0050] In this embodiment, the laser source 8 and focussing optics
30 are moveable under the control of the computer 26 in an X-Y
plane that is parallel to the top surface of the contents of the
further repository 24 (i.e. a top surface of the object 4). Thus,
the laser focal point 14 may be directed to any point in a working
envelope in the X-Y plane so that layers of material of a desired
shape may be deposited.
[0051] Thus, AM apparatus 2 for performing a process of producing,
in accordance with an embodiment, the object 4 is provided.
[0052] FIG. 2 is a process flow chart of an embodiment of a process
of producing (i.e. manufacturing, building, constructing, etc.) the
object 4 using the above described example AM apparatus 2.
[0053] The object 4 that is to be produced by the method of FIG. 2
may be any appropriate type of object having any appropriate size
and shape. In this embodiment, the produced object 4 is made of
titanium or a titanium alloy. However, in other embodiments, the
produced object 4 is made of a different material to the object 2
in this embodiment.
[0054] At step s2, a three dimensional digital model 38 of the
object 4 (that is to be produced) is provided. The digital model 38
of the object 4 is a digital design model for the object 4.
[0055] In this embodiment, the digital model 38 is stored by the
computer 26. In this embodiment, the digital model 38 can be
viewed, manipulated and analysed using the computer 26 e.g. by
implementing a suitable software package or tool.
[0056] At step s4, a base plate is provided. The base plate
provides a parent structure upon which layers of material are to be
added (by the AM apparatus 2 performing the AM process) so as to
form the object 4. In this embodiment, the base plate may, for
example, be secured to the second piston 34 e.g. using any
appropriate means.
[0057] At step s6, the AM apparatus is calibrated. This calibration
process may, for example, include accurately measuring the base
plate 6 and/or providing or creating a three dimensional digital
model of the base plate 6. These data and the digital model 38 of
the object 4 may be used to generate a "tool path" that, during the
AM process, will be followed by the AM apparatus 2 so as to produce
the object 4.
[0058] At step s8, using the AM apparatus 2, an AM process is
performed to add layers of material to the base plate 6, and
thereby form the object 4. In this embodiment, the AM apparatus 2
is for performing a powder bed AM process and is described in more
detail above with reference to FIG. 1. In this embodiment, the AM
process is the powder bed AM process described in more detail above
with reference to FIG. 1. Further information on powder bed AM
apparatus and the powder bed AM process can be found, for example
in the above mentioned "Additive Manufacturing Technologies: Rapid
Prototyping Direct Digital Manufacturing", which is incorporated
herein by reference. However, in other embodiments, a different
type of AM apparatus and/or process is used produce the object
4.
[0059] In this embodiment, the AM process is performed in a
substantially inert atmosphere (e.g. a chamber that is back-filled
with an inert gas e.g. argon).
[0060] In this embodiment, the AM process comprises using a laser
beam 10 to melt metallic powder 12 at the laser focal point 14.
Typically, as this is performed, small droplets of molten material,
or powder grains that have been heated by the laser beam 10, are
ejected or sprayed (e.g. by the forces created by the heating
process) away from the focal point 14 of the laser beam 10.
[0061] FIG. 3 is a schematic illustration (not to scale) showing
small droplets of molten material (hereinafter referred to as the
"droplets" and indicated in FIG. 3 by the reference numeral 40)
being ejected, expelled or sprayed away from the focal point 14 of
the laser beam 10 during the AM process. In some embodiments,
instead of or in addition to liquid droplets 40 of molten material
being ejected, expelled or sprayed away from the focal point 14 of
the laser beam 10 during the AM process, heated solid particles of
metallic material may be ejected and may also become contaminated
by gasses or vapours present in the chamber atmosphere.
[0062] In this embodiment, the droplets 40 (and solid heated
particles) have been heated by the laser beam 10. Due to their
elevated temperature and high surface area relative to their
volume, the droplets 40 (and solid heated particles) tend to be
highly reactive. Thus, the droplets 40 (and solid heated particles)
tend to react with any contaminants that are present in the chamber
atmosphere 42 in which the AM process is being performed. For
example, the droplets 40 may absorb oxygen gas that has
contaminated the chamber atmosphere 42 and is present in the
chamber in which the AM process is being performed. Also for
example, the droplets 40 may react with any water vapour that has
contaminated the chamber atmosphere 34 and is present in the
chamber in which the AM process is being performed.
[0063] In this embodiment, a proportion of the droplets 40 (and
solid heated particles), that have reacted with the contaminant
within the chamber atmosphere 42 and that have been sprayed, or
expelled away from the laser focal point 14, land on the surface of
the object 4 being formed. Such a droplet 40 (or solid heated
particle) of contaminated material may be "welded" into the
structure of the object 4 when the laser beam 10 is focused at the
location on the surface at which that contaminated material
landed.
[0064] Also in this embodiment, a proportion of the droplets 40,
that have reacted with the contaminant within the chamber
atmosphere 42 and that have been sprayed, or expelled away from the
laser focal point 14, land in a bed of un-melted titanium powder 12
contained within the further repository 24 and surrounding the
object 4 being formed. The unused metallic powder 12 contained
within the further repository 24 is recycled (i.e., reused in the
AM process that is performed to produce the object 4, or in future
AM processes). Thus, recycled powder that has absorbed a
contaminant may be bonded, or welded, into the structure of the
object 4.
[0065] Thus, the object 4 produced using the AM process of step s8
may comprise one or more contaminated regions. In other words, the
object 4 may comprise regions in which the material of the object 4
is contaminated (by a contaminant such as oxygen).
[0066] At step s10, after the object 4 has been produced by the AM
process, the object 4 is allowed to cool and, in this embodiment,
the object 4 is removed from the further repository 24. Excess
(i.e. unused or unmelted) metallic power 12 may be removed from the
object, e.g. using an air jet, or by washing the object.
[0067] Thus, the object 4 is formed. The remaining steps of the
process of FIG. 2 describe the processing of the object 4 formed at
step s10 that is performed, in this embodiment to produce the
finished object 4.
[0068] FIG. 4 is a schematic illustration (not to scale) of a cross
section of a portion of the object 4 produced by performing steps
s2 to s10 as described above.
[0069] The surface 44 of the object 4 is relatively uneven, i.e.
rough.
[0070] In this embodiment, proximate to its surface 44, the object
4 comprises a plurality of open cavities 46 (i.e. open pores or
voids in the material body). These open cavities 46 are cavities or
hollows that are open to the atmosphere, i.e. cavities or hollows
that are connected to the surface 44 of the object 4 such that gas
can flow from outside the object 4 into the those open cavities
46.
[0071] Also, the object 4 further comprises a plurality of closed
cavities 48 (i.e. closed pores or voids in the material body).
These closed cavities 48 are hollow spaces or pits in the body of
the object 4. Furthermore, the closed cavities 48 are not open to
the atmosphere, i.e. they are not connected to the surface 44. In
other words, gas cannot flow from outside the object 8 into the
closed cavities 48 and vice versa.
[0072] Also, the object 4 further comprises a plurality of
contaminated regions 50 (i.e. regions in which material that has
previously absorbed or reacted with a contaminant, such as oxygen,
has been incorporated, i.e. bonded or welded). In some embodiments,
a contaminated regions 50 may be the result of the titanium powder
raw material being contaminated e.g. by an undesired metal such as
tungsten, copper or iron or a ceramic material such as an oxide,
nitride or carbide. The contaminated regions 50 within the object
may have a different chemical structure to the material that forms
the rest of the object matrix (i.e. to the uncontaminated titanium
object 4). Also, the contaminated regions 50 within the object 4
may have different material properties (e.g. they may be harder, or
softer, and may cause degradation of fatigue performance) than the
material that forms the rest of the object matrix (i.e. to the
uncontaminated titanium object 4).
[0073] The presence of micro-pores (i.e. the open and closed
cavities 46, 48) and the other imperfections (i.e. the contaminated
regions 50) in the object 4 tend to adversely affect the fatigue
performance of the object 4, especially in high-cycle fatigue
situations. For example, the cavities 46, 48 and contaminated
regions 50 may act as crack initiators. Also, the cavities 46, 48
and the contaminated regions 50 tend to adversely affect the
load-bearing characteristics of the object 4.
[0074] In conventional methods, after the object 4 has been formed
at step s8, the object may be further processed so as to smooth the
rough surface 44. For example, a machining or polishing process may
be performed. However, such processes tend to be inappropriate when
attempting to fully remove the open cavities 46. Furthermore, such
processes tend not to shrink, or remove, the closed cavities 48 or
the contaminated regions 50 from the object 4. Machining the
surface 44 of the object 4 to a sufficient depth may be performed
to remove surface roughness and cavities connected to the surface
44. Machining may expose internal closed cavities that were
originally isolated and machining tends to be relatively expensive
and, depending on the complexity of the shape of the object 4,
would at least partly negate the cost advantage of using a
net-shape-process to form the object 4. Polishing processes also
remove material from an object and so, if continued to a sufficient
depth, may be performed to remove surface roughness and surface
connected cavities. Polishing processes also tend to be relatively
expensive to perform. Also, processes such as Hot Isostatic
Pressing (HIPing), that may be employed to remove internal pores,
tend not to have any effect on surface connected cavities.
[0075] Deficiencies of conventional methods of producing
objects/parts may be overcome by performing steps s12 to s16 on the
object 4, as opposed to just performing a machining/polishing
process. Thus, the object formed at step s10 may be thought of as
an "intermediate object" that is to be further processed (in
accordance with steps s12 to s16) to produce a "final object".
[0076] At step s12, the object 4 produced at step s10 is
peened.
[0077] A conventional shot peening process may be used. For
example, a process in which the surface 44 of the object 4 is
impacting with shot (e.g. substantially round particles made of
metal, glass or ceramic) with sufficient force such that the object
4 is plastically deformed at its surface 44 may be implemented.
Also for example, laser, or ultra-sonic, peening may be
performed.
[0078] In embodiments in which the surface 44 of the object 4 is
impacted with shot, any appropriate shot medium may be used, e.g.
S330 (cast steel with an average diameter of 0.8 mm). Also, any
appropriate shot peening pressure may be used, e.g. 0.5 bar, 0.75
bar, 1.25 bar, 2 bar and 4 bar. Also, any appropriate Almen
intensities may be used, e.g. 0.15 mmA, 0.20 mmA, 0.30 mmA, 0.38
mmA and 0.52 mmA.
[0079] After peening, the surface 44 of the peened object is
relatively smooth (compared to the surface 44 prior to
peening).
[0080] Furthermore, the process of shot peening tends to
plastically deform the object 4 at its surface 44 such that the
openings of the open cavities 46 are either closed such that gas
cannot flow from outside the object 4 into an open cavity 46 and
vice versa (i.e. such that, in effect, an open cavity 46 becomes a
closed cavity 48), or are closed such that the opening of an open
cavity 46 to the surface 44 is very small but that gas may still
flow from outside the object 4 into an open cavity 46 and vice
versa.
[0081] In this embodiment, the plastic deformation of the surface
44 of the object 4 is performed by peening. However, in other
embodiments a different plastic deformation process is used, for
example, a process of burnishing e.g. using a roller. Such
finishing methods (e.g. tumbling, burnishing, shot peening etc.)
tend not to remove material from an object.
[0082] At step s14, the peened object 4 is sintered.
[0083] In this embodiment, a temperature at which, and duration for
which, the object is sintered is selected or determined.
[0084] The value for the sintering temperature is determined based
upon any appropriate parameters, such that, when the object is
heated to or above that temperature, contaminant is diffused within
the object 4 (from region having high contaminant concentration to
regions having low contaminant concentration) at or above a desired
rate.
[0085] The value for the sintering duration is determined based
upon any appropriate parameters, such that, when the object is
heated to or above the determined sintering temperature for that
duration, the maximum contaminant concentration level within the
object 4 is below a threshold value. In some embodiments, the
sintering duration is determined such that, when the object is
heated to or above the determined sintering temperature for that
duration, the contaminant concentration level within the object 4
is substantially uniform.
[0086] Examples of appropriate parameters that may be used to
determine the sintering temperature or duration include, but are
not limited to, the type of metal or alloy from which the object
has been produced, the shape and/or size of the object, a
contaminant concentration level of a region of the object (e.g. a
maximum contaminant concentration level within the object 4), and a
threshold contaminant concentration level below which the maximum
contaminant concentration level within the object 4 is to be
reduced.
[0087] In this embodiment, the object 4 is sintered at relatively
high temperate. For example, the sintering of the peened object may
comprise sintering at a temperature in the range 900.degree. C. to
the melting point of the object. In this embodiment, the object 4
is made of Ti-6Al-4V, the melting point of which is approximately
1600.degree. C. Preferably, the object 4 is sintered at or above a
temperature of 1100.degree. C. More preferably, the object is
sintered at or above a temperature of 1300.degree. C.
[0088] In this embodiment, the object is sintered for a relatively
long period of time, e.g. 1 hour, or 2 hours, or longer. The length
of time sintering is to be performed for may depend upon the type
of material from which the object 4 is made, or any other
appropriate parameter.
[0089] In this embodiment, the sintering process is performed for a
time period, and at a temperature, that provide the following:
[0090] the openings of the open cavities 46 (that were either
closed or almost closed by the peening process of step s10) are
diffusion bonded such that, in effect, the open cavities 46 become
closed cavities 48. In other words, the openings of the open
cavities 46 are fully sealed by sintering the object 4; [0091] the
contaminant(s) within the contaminated regions 50 of the object 4
are diffused within the object 4, e.g. throughout the bulk of the
object. Preferably, this is performed such that the contaminant is
dispersed substantially uniformly throughout the bulk of the object
4, i.e. such that no one region of the object 4 has a substantially
higher concentration of contaminant than a different region of the
object 4.
[0092] In this embodiment, the peened object 4 is sintered at a
temperature that is below the melting point of the material from
which the object 4 is made.
[0093] One advantage of plastically deforming the surface prior to
sintering is that recrystallisation and diffusion bonding during
high temperature sintering tends to be faster and more effective at
smoothing the surface and closing open cavities when compared to an
undeformed surface. This may, for example, be due to stored
dislocation energy and residual stress within the object 4.
[0094] At step s16, a hot isostatic pressing (HIP) process is
performed on the sintered object 4.
[0095] A conventional HIP process is used to reduce the porosity,
and increase the density, of the sintered object 4. In this
embodiment, the sintered object 4 is subjected to elevated
temperature and elevated isostatic gas pressure by subjecting the
sintered object 4 to heated and pressurised argon. A HIP cycle
having a duration of approximately 2 hours, a temperature of
920.degree. C., and a pressure of 102 MPa may be used.
[0096] The HIP process produces a relatively high pressure at the
surface 44 of the sintered object 4, whilst the pressures in the
closed cavities 48 (including the open cavities 46 that have been
formed into closed cavities 48 as described above) are relatively
low. This is due to the closed cavities 48 not being open to the
surface 44, i.e. being gas-tight. As a result of plastic
deformation, creep, and/or diffusion bonding caused by the elevated
temperature and pressure, the closed cavities 48 in the sintered
object 4 shrink or vanish completely.
[0097] The HIP process performed on the sintered object may cause
diffusion of the contaminants within the objects 4. However, at a
typical HIP temperature of 920.degree. C., in titanium, the
diffusion rates of most contaminants e.g. oxygen, nitrogen, carbon,
etc. tend to be relatively low and sufficient to disperse
contamination over only small distances, e.g. a few microns. In
contrast, at a typical sintering temperature of 1300.degree. C.,
the diffusion rate of contaminants tends to be several orders of
magnitude faster than it is at 920.degree. C., and therefore
diffusion distances are correspondingly much greater. The sintering
process described above may be thought of as a "contaminant
homogenisation process", i.e. a process of homogenising a
concentration of a contaminant within an object produced using an
AM process.
[0098] The hot isostatic pressing of the sintered object 4 produces
the finished object 4. Thus, a process of producing the object 4 is
provided.
[0099] In the above embodiments, the process of producing the
object comprises peening, sintering and subsequently HIPing an
object. This process of peening, sintering and subsequently HIPing
an object may be performed in accordance with any of the methods
described in patent application GB1203359.3, "Processing of Metal
or Alloy Objects", filed at the United Kingdom Intellectual
Property Office (UKIPO) on 24 Feb. 2012, and incorporated herein,
in its entirety, by reference.
[0100] An advantage provided by the above described methods is that
pores, pits, or other (e.g. minute) openings, orifices, or
interstices in the surface of the object tend to be removed. In
other words, defects and/or discontinuities at or proximate to the
surface of the object may, in effect, be repaired. These open
cavities may act as crack initiators. Thus, removal of these open
cavities from the object tends to result in improved fatigue
performance, especially in high-cycle fatigue situations. The
improved surface finish and microstructure of the object tend to
improve its fatigue performance.
[0101] The above described methods also tend to remove (or shrink)
the closed cavities (or other voids or hollows that are closed to
the surface) in the body of the object. This also tends to improve
the microstructure of the object, which tends to lead to improved
fatigue performance.
[0102] A further advantage provided by the above described methods
is that regions with relatively high concentrations of contaminants
within an object produced using an AM process tends to be removed.
Regions with relatively high levels or concentrations of a
contaminant within an object (i.e. the contaminated regions 50)
tend to have different material properties than the material that
forms the rest of the object matrix, and may act as crack
initiators or adversely affect the properties of the object. Thus,
removal of these relatively contaminated regions (i.e. by more
evenly distributing the contaminant throughout the object 4) tends
to result in improved fatigue performance and material properties
of the object 4.
[0103] Conventionally, objects produced using AM processes are not
typically treated by sintering those objects at high temperatures.
This is partly for cost reasons and partly because high temperature
sintering of such an object tends to increase the grain size within
the object, thereby reducing the strength of the object. However,
the present inventors have realised that, surprisingly, the
benefits gained by sintering the object so as to more evenly (e.g.
uniformly) distribute contaminants within the object outweigh the
disadvantages of performing the sintering process (i.e. the
increased grain size).
[0104] Objects produced using an above described process tend to be
able to withstand a greater maximum stress, and/or withstand a
greater number of fatigue load cycles to failure, when compared to
objects produced using a conventional AM process.
[0105] A further advantage provided by the above described methods
is that the surface finish of the object tends to be improved. The
object tends to be smoother and shinier than those that are
produced using conventional techniques. This increased reflectivity
is important in certain applications. For example, if the object is
for decorative purposes, the improved aesthetic appearance of the
object tends to be important. Also for example, the object tends to
be less likely to retain dirt or surface contamination, and be
easier to clean and less abrasive.
[0106] A further advantage provided by the above described
processes is that an object is produced by an AM process. This
tends to provide that the object is produced with very little
wastage. Furthermore, it tends to be relatively easy to make
relatively complex shapes that may be prohibitively expensive to
machine.
[0107] The above described processes are advantageously applicable
to objects of any size. The treatment process (e.g. a process of
shot peening, sintering, and hot isostatic pressing) is performed
after the formation of the object (i.e. after the performance of
the AM process).
[0108] A further advantage provided by the above described
processes is that the some of them may be performed on a large
number of objects simultaneously. Thus, a cost of performing any or
all of these operations (per component) may be significantly
reduced.
[0109] A further advantage provided by the above described method
is that a metallic powder that is known to contain contaminants may
be used, by performing an AM process, to create an object that has
substantially the same or better material/fatigue properties as a
different object that has been produced, using the same AM process,
from a metallic powder that contains fewer impurities or
contaminants. This is because the object created from the
relatively more contaminated powder may be treated (using the
treatment processes described herein) so as to improve the
material/fatigue properties of the object to be the same or better
than those of the object formed from the relatively less
contaminated powder. Thus, costs of producing an object having
given material/fatigue properties may be reduced.
[0110] It should be noted that certain of the process steps
depicted in the flowcharts of FIG. 2 and described above may be
omitted or such process steps may be performed in differing order
to that presented above and shown in FIG. 2. Furthermore, although
all the process steps have, for convenience and ease of
understanding, been depicted as discrete temporally-sequential
steps, nevertheless some of the process steps may in fact be
performed simultaneously or at least overlapping to some extent
temporally.
[0111] Apparatus, including the computer, may be provided by
configuring or adapting any suitable apparatus, for example one or
more computers or other processing apparatus or processors, and/or
providing additional modules. The apparatus may comprise a
computer, a network of computers, or one or more processors, for
implementing instructions and using data, including instructions
and data in the form of a computer program or plurality of computer
programs stored in or on a machine readable storage medium such as
computer memory, a computer disk, ROM, PROM etc., or any
combination of these or other storage media.
[0112] In the above embodiments, the object is formed using a
powder bed AM process. However, in other embodiments the object is
formed using a different type of AM process, for example, a blown
powder process, a sheet lamination process, a vat
photo-polymerisation process, a Laser Powder Bed process, or an ALM
process that implements Wire and Arc technologies.
[0113] In other embodiments, the treatment process performed on the
object produced using an AM process comprises peening, sintering,
and hot isostatic pressing.
[0114] However, in other embodiments, the treatment process
comprises the sintering process, and not the peening or HIPing
processes. The high temperature sintering process advantageously
tends to provide that the contaminant(s) within the contaminated
regions of the object diffuse within the object, e.g. throughout
the bulk of the object e.g. such that no one region of the object
has a substantially higher concentration of contaminant than a
different region of the object. This advantageously tends to result
in improved fatigue performance and material properties of the
object.
[0115] Also, in other embodiments, the treatment process comprises
the hot isostatic pressing process, and not the sintering or
peening processes. The hot isostatic pressing process
advantageously tends to provide that the closed cavities in the
object shrink or vanish completely. This advantageously tends to
result in improved fatigue performance and material properties of
the object. Also, if performed at a suitably high temperature (i.e.
>900.degree. C.), and for a suitably long duration, the hot
isostatic pressing process advantageously tends to provide that the
contaminant(s) within the contaminated regions of the object
diffuse within the object, e.g. throughout the bulk of the object
e.g. such that no one region of the object has a substantially
higher concentration of contaminant than a different region of the
object. This advantageously tends to result in improved fatigue
performance and material properties of the object.
[0116] In some embodiments, the peening process is omitted.
[0117] In the above embodiments, the object is formed from a
titanium alloy (e.g. an alloy comprising titanium with 6% aluminium
and 4% vanadium which is also known as Ti-6Al-4V, or 6-4, 6/4, ASTM
B348 Grade 5). However, in other embodiments, the object is formed
from a different material. For example, in other embodiments, the
object is formed from a pure (i.e. unalloyed) metal or a different
type of alloy to that used in the above embodiments, or a
ceramic.
[0118] In the above embodiments, the treatment process (i.e. a
process of peening, sintering, and hot isostatic pressing) is
performed on a single object. However, in other embodiments, a
treatment process, or part of a treatment process, may be performed
on any number of (different or the same) objects. This
advantageously tends to reduce the cost of the process per
component.
[0119] In the above embodiments, the sintering of the object is
performed at the above specified temperatures, and for the above
specified time-periods. However, in other embodiments sintering of
an object is performed at a different appropriate temperature
and/or for a different appropriate time period.
[0120] In the above embodiments, the HIP process is performed at
the above specified temperatures and pressures, and for the above
specified time-periods. However, in other embodiments a HIP process
is performed at a different appropriate temperature and/or
pressure, and/or for a different appropriate time period.
[0121] In the above embodiments, the sealing process performed on
the object to seal the openings of the open cavities (i.e. the
process of shot peening and sintering, or the process of coating
and heating) is performed once before the HIP process is performed
on the object. However, in other embodiments, before the HIP
process is performed, one or both of the sealing processes may be
performed multiple times. For example, the sealing process of
peening and sintering may be performed more than once. In such an
example, the sintering process that follows a shot peening process,
tends to soften the work hardened surface formed during shot
peening and tends to disperse any surface contamination into the
bulk of the object, making the surface of the object more amenable
to another shot peening process. Furthermore, the second, and any
subsequent, shot peening processes may be performed at a lower
intensity than the first shot peening process. This tends to result
in a better surface appearance.
* * * * *