U.S. patent application number 15/995829 was filed with the patent office on 2018-09-27 for method of forming green part and manufacturing method using same.
The applicant listed for this patent is PRATT & WHITNEY CANADA CORP.. Invention is credited to Marc Lorenzo CAMPOMANES, Jean FOURNIER, Guillaume POITRAS, Orlando SCALZO.
Application Number | 20180272562 15/995829 |
Document ID | / |
Family ID | 53938070 |
Filed Date | 2018-09-27 |
United States Patent
Application |
20180272562 |
Kind Code |
A1 |
CAMPOMANES; Marc Lorenzo ;
et al. |
September 27, 2018 |
METHOD OF FORMING GREEN PART AND MANUFACTURING METHOD USING
SAME
Abstract
A method of manufacturing a part, including providing a green
body made of powder injection molding material and connected to a
solid support member partially contained in the green body. The
support member is engaged with a retaining fixture of a machine
tool. While supporting the green body through the engagement
between the support member and the retaining fixture, the green
body is machined to obtain a machined green part. The machined
green part is debound and sintered. A method of forming a powder
injection molding part in a green state including machining a
molded body using a machine tool while supporting the blank with a
retaining fixture, and a machining blank having a green body and a
solid support member including one locating feature of a pair of
complementary locating features snuggly engageable with one another
are also discussed.
Inventors: |
CAMPOMANES; Marc Lorenzo;
(Longueuil, CA) ; SCALZO; Orlando; (Boucherville,
CA) ; FOURNIER; Jean; (Longueuil, CA) ;
POITRAS; Guillaume; (Longueuil, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PRATT & WHITNEY CANADA CORP. |
Longueuil |
|
CA |
|
|
Family ID: |
53938070 |
Appl. No.: |
15/995829 |
Filed: |
June 1, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14479738 |
Sep 8, 2014 |
10011044 |
|
|
15995829 |
|
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|
|
62026989 |
Jul 21, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 2235/6022 20130101;
B22F 3/225 20130101; C04B 35/56 20130101; B28B 11/12 20130101; C04B
35/6455 20130101; B22F 2998/10 20130101; B22F 7/08 20130101; B22F
2998/10 20130101; B22F 3/225 20130101; B22F 3/162 20130101; B22F
3/1021 20130101 |
International
Class: |
B28B 11/12 20060101
B28B011/12; B22F 7/08 20060101 B22F007/08; B22F 3/22 20060101
B22F003/22; C04B 35/645 20060101 C04B035/645; C04B 35/56 20060101
C04B035/56 |
Claims
1. A machining blank comprising: a green body made of powder
injection molding material, the powder injection molding material
including a solidified binder and a powder material mixed with the
binder; and a solid support member having a greater rigidity than
the green body, the support member having an inner portion embedded
within the green body and an outer portion extending out of the
green body, the outer portion including one locating feature of a
pair of complementary locating features snuggly engageable with one
another, the outer portion being adapted to be engaged with a
retaining fixture including the other locating feature of the pair
of complementary locating features.
2. The blank as defined in claim 1, wherein the support member is
made of solid metal.
3. The blank as defined in claim 1, wherein the one locating
feature is a locating pin protruding from the outer portion.
4. The blank as defined in claim 1, wherein the outer portion of
the support member surrounds a perimeter of the green body, and the
inner portion includes a plurality tabs protruding inwardly from
the second portion into the green body.
5. The blank as defined in claim 1, wherein the support member and
the green body have a common axis of axisymmetry, the support
member defining a shaft.
6. A method of forming a powder injection molding part in a green
state, the method comprising: providing a blank having a molded
body, the molded body being in the green state and made of powder
injection molding material, the powder injection molding material
including a solidified binder and a powder material mixed with the
binder material; engaging the blank with a retaining fixture of a
machine tool; and while supporting the blank with the retaining
fixture, machining the molded body using the machine tool to obtain
a machined green part in the green state.
7. The method as defined in claim 6, wherein providing the blank
includes molding the molded body by injecting a feedstock of the
powder injection molding material into a mold cavity containing an
inner portion of a solid support member to connect the inner
portion with the molded body, and removing the connected molded
body and support member from the mold cavity, and wherein engaging
the blank with the retaining fixture of a machine tool is performed
by engaging an outer portion of the support member with the
retaining fixture, the machining being performed while supporting
the blank through the engagement between the outer portion of the
support member and the retaining fixture.
8. The method as defined in claim 7, further comprising disengaging
the support member from the machined green part.
9. The method as defined in claim 8, wherein: machining the molded
body is performed to obtain the machined green part and a retaining
portion engaged to the inner portion of the support member and
connected to the machined green part; after the machining, the
machined green part remains connected to the support member only
through the retaining portion; and disengaging the support member
from the machined green part is performed by separating the
machined green part from the retaining portion.
10. The method as defined in claim 6, wherein engaging the blank
with the retaining fixture maintains the molded body in a fixed
position during the machining.
11. The method as defined in claim 6, wherein machining the molded
body includes rotating the blank with the retaining fixture.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/479,738 filed Sep. 8, 2014, which claims priority on
United States Provisional Application No. 62/026,989 filed Jul. 21,
2014, the entire contents of both of which are incorporated herein
by reference.
TECHNICAL FIELD
[0002] The application relates generally to powder injection
molding and, more particularly, to green part(s) obtained by powder
injection molding.
BACKGROUND OF THE ART
[0003] Powder injection molding such as metal injection molding may
offer a cost-savings advantage on small, complex parts that are
difficult to machine. However, the process to design the mold for a
given workpiece is often iterative, for example because of
difficulties in predicting the amount of shrinkage during the
debinding and sintering steps; as such, it may be required to
successively manufacture and test several molds before the
dimensions for the final mold can be determined. Accordingly,
design, manufacture, and test of a mold can lead to significant
lead-time initial cost.
SUMMARY
[0004] In one aspect, there is provided a method of manufacturing a
part, the method comprising: providing a green body made of powder
injection molding material, the powder injection molding material
including a solidified binder and a powder material mixed with the
binder, the green body being connected to a solid support member
partially contained in the green body; engaging the support member
with a retaining fixture of a machine tool; while supporting the
green body through the engagement between the support member and
the retaining fixture, machining the green body using the machine
tool to obtain a machined green part; and debinding and sintering
the machined green part.
[0005] In another aspect, there is provided a machining blank
comprising: a green body made of powder injection molding material,
the powder injection molding material including a solidified binder
and a powder material mixed with the binder; and a solid support
member having a greater rigidity than the green body, the support
member having an inner portion embedded within the green body and
an outer portion extending out of the green body, the outer portion
including one feature of a pair of complementary locating features
snuggly engageable with one another, the outer portion being
adapted to be engaged with a retaining fixture including the other
feature of the pair of complementary locating features.
[0006] In a further aspect, there is provided a method of forming a
powder injection molding part in a green state, the method
comprising: providing a blank having a molded body, the molded body
being in the green state and made of powder injection molding
material, the powder injection molding material including a
solidified binder and a powder material mixed with the binder
material; engaging the blank with a retaining fixture of a machine
tool; and while supporting the blank with the retaining fixture,
machining the molded body using the machine tool to obtain a
machined green part in the green state.
DESCRIPTION OF THE DRAWINGS
[0007] Reference is now made to the accompanying figures in
which:
[0008] FIG. 1 is a schematic, cross-sectional tridimensional view
of a mold including a support member in accordance with a
particular embodiment;
[0009] FIG. 2 is a schematic, exploded tridimensional view of the
mold of FIG. 1 and of a green body molded therein, with a support
member partially broken away to show an underlying portion of the
green body, in accordance with a particular embodiment;
[0010] FIG. 3a is a schematic tridimensional view of the green body
and support member of FIG. 2 retained in a machine tool;
[0011] FIG. 3b is a schematic tridimensional view of a green body
in accordance with another particular embodiment, in a support
member similar to that of FIG. 2, retained in a machine tool;
[0012] FIG. 3c is a schematic tridimensional view of the green body
and support member of FIG. 3a during machining;
[0013] FIG. 4 is a schematic, cross-sectional tridimensional view
of a mold including a support member in accordance with another
particular embodiment;
[0014] FIG. 5 is a schematic, cross-sectional tridimensional view
of the support member engaged to a green body molded in the mold of
FIG. 4;
[0015] FIG. 6a is a schematic tridimensional view of the green body
and support member of FIG. 5 retained in a machine tool; and
[0016] FIG. 6b is a schematic tridimensional view of the green body
and support member of FIG. 6a during machining.
DETAILED DESCRIPTION
[0017] The present application discusses a method of manufacturing
a part using powder injection molding, in which the green part is
machined after being molded and before the debinding and sintering
steps are performed.
[0018] As is typical in powder injection molding, a suitable
feedstock is injected into a mold cavity to obtain the green part.
Such a feedstock can include high temperature resistant powder
metal alloys (metal injection molding), such as a nickel
superalloy, or ceramic, glass, carbide powders or mixtures thereof,
mixed with an appropriate binder. Other high temperature resistant
material powders which may include one material or a mix of
materials could be used as well. The feedstock is a mixture of the
material powder and of a binder which may include one or more
binding material(s). In a particular embodiment, the binder
includes an organic material which is molten above room temperature
(20.degree. C.) but solid or substantially solid at room
temperature. The binder may include various components such as
surfactants which are known to assist the injection of the
feedstock into mold for production of the green part. In a
particular embodiment, the binder includes a mixture of binding
materials, for example including a lower melting temperature
polymer, such as a polymer having a melting temperature below
100.degree. C. (e.g. paraffin wax, polyethylene glycol,
microcrystalline wax) and a higher melting temperature polymer or
polymers, such as a polymer or polymers having a melting
temperature above 100.degree. C. (e.g. polypropylene, polyethylene,
polystyrene, polyvinyl chloride). Different combinations are also
possible. In a particular embodiment, the material powder is mixed
with the molten binder and the suspension of injection powder and
binder is injected into the mold cavity and cooled to a temperature
below that of the melting point of the binder. "Green state" or
"green" as discussed herein refers to a molded part produced by the
solidified binder that holds the injection powder together.
[0019] Since the feedstock is wax and/or polymer based, machining
the green part can be performed with cutting feeds and speeds that
are higher and cutting forces that are lower than typical feeds,
speeds and forces for the machining of solid metal (for example the
same metal as that found in powder form in the green part), and
even when compared with "soft" metals such as aluminum. In a
particular embodiment, a machine tool that is designed for
machining wax and plastics (e.g. small desktop CNC milling machine)
is used to machine the green part. In a particular embodiment, the
cutting feeds and speeds are similar to that used during the
machining of wax. In a particular embodiment, the metal powder
present in the green part provides for an increased material
conductivity when compared to the binder material alone, which may
help dissipate heat that may be generated during machining.
[0020] In a particular embodiment, the method may be used for the
rapid-prototyping of powder injection molding parts, for example to
obtain a part for tests. This may allow the final part to be
manufactured within a timeline in the order of days rather than
months, allowing for quicker manufacture of parts available for
testing. For example, shrinkage and deformations of the part until
the end of the sintering process can be observed and measured, and
a new green part with different dimensions can be produced by
machining if the desired final dimensions are not obtained.
Iterations in the green part design can thus be done by machining
rather than by mold modifications, which in a particular embodiment
significantly reduces the development time and development cost for
the part. Once the final design has been confirmed, a mold can be
ordered for mass production.
[0021] The green part may be molded with an integral solid support
member which is used to support the part during the machining
process. An example of a mold and support member in accordance with
a particular embodiment is generally and schematically shown in
FIGS. 1-2. In this embodiment, the mold 20 includes a plurality of
mold elements which together define a mold cavity 22 having a
substantially prismatic shape to define a substantially prismatic
green body 50. The mold elements include a bottom plate 24, the
support member 26 resting against the bottom plate, an intermediary
element 28 resting against and on top of the support member 26, and
a top plate 30 resting against and on top of the intermediary
element 28. The top surface 32 of the bottom plate 24 and the
bottom surface 34 of the top plate 30 both border the mold cavity
22. The intermediary element 28 and an outer portion 36 of the
support member 26 both have similar hollow rectangular shapes
defining a closed perimeter having an inner surface 38, 40
bordering the mold cavity 22. Although not shown, additional
intermediary elements can be used to vary the shape of the green
blank; for example, an intermediary element may be received within
the support member 26 to close part of the area defined within the
support member 26, such as to define a smaller green body 50a as
shown for example in FIG. 3b. Additional element(s) may also be
added above and/or below the support member 26. Alternately, the
intermediary element 28 may be omitted, for example to obtain a
thinner green body. Other configurations are also possible.
[0022] The mold elements 24, 26, 28, 30 are interconnected to
enclose the mold cavity 22. In the embodiment shown and with
reference to FIG. 2, this connection is defined by two corner pins
42 extending upwardly from opposed corners of the bottom plate 24
and received in corresponding aligned holes 44 defined through the
other mold elements 26, 28, 30. It is understood that the number
and configuration of the mold elements may vary, as long as they
create the desired shape for the mold cavity and can be
disassembled for removal of the molded part without damaging
it.
[0023] Referring back to FIG. 1, it can be seen that the support
member 26 also includes an inner portion 46 protruding from the
outer portion 36 into the mold cavity 22, in the form of a
plurality of tabs extending inwardly from the inner surface 38. The
inner portion 46 is shaped such as to be gripped and retained
within the green body 50 after the minimal shrinkage (e.g. 0.5 to
2%) that typically occurs as the binder solidifies after molding.
In the particular embodiment shown, the tabs of the inner portion
46 extend perpendicularly from the inner surface 38 to define
complementary grooves 48 in the green body 50 (FIG. 2), which
compress the tabs as the green body 50 shrinks to lock each tab
into its respective groove 48.
[0024] After molding, the green body 50 and support member 26
engaged thereto are removed from the mold cavity 22 and disengaged
from the other mold elements 24, 28, 30, as shown in FIG. 2. In the
embodiment shown, a machining blank 52 includes the green body 50
and the support member 26. The green body 50 is made of the mix of
solidified binder and powder material, and accordingly is rigid
enough to be able to maintain its shape and for some manipulation.
The support member 26 has its inner portion 46 embedded within the
green body 50 and its outer portion 36 extending out of the green
body 50 and surrounding its perimeter. The support member 26 is
made of a solid material having a greater rigidity than that of the
solidified green body 50 after molding. In a particular embodiment,
the support member 26 is made of the same material as the other
mold elements 24, 28, 30; alternately, different materials may be
used. An example of a suitable material includes, but is not
limited to, solid metal such as hardened steel.
[0025] Referring to FIG. 3a, the support member 26 is engaged with
a retaining fixture 54 of the machine tool 56, such as to retain
the blank 52 for machining of the green body 50. In a particular
embodiment, the outer portion 36 of the support member 26 includes
one feature 58 (FIG. 2) of a pair of complementary locating
features snuggly engageable with one another, with the other
feature of the pair being defined in the retaining fixture 54 of
the machining tool 56. In the embodiment shown, the feature 58 of
the outer portion 36 is a male locating feature such as a locating
pin extending from the outer portion 36 away from the green body
50, and it is snuggly engaged within a corresponding female
feature, e.g. locating hole, defined in the machine tool's
retaining fixture 54. More than one pair of locating features may
be used and/or the configurations of the locating features may
vary, but are configured to allow for the support member 26 to be
engaged to the retaining fixture 54 with a known location for the
machine tool 56. In the embodiment shown, the outer portion 36
further includes a locating hole 57 (FIG. 2) engaging a tailstock
59 (FIG. 3a) of the retaining system of the machine tool 56.
[0026] Referring to FIG. 3c, the green body 50 is then machined
using the machine tool 56 while the blank 52 is supported through
the engagement between the support member 26 and the retaining
fixture 54, until the desired shape defining the machined green
part 50' is obtained. In a particular embodiment, the retaining
fixture 54 maintains the blank 52 in a fixed position during
machining by a moving tool, e.g. a CNC milling machine. In another
embodiment, the retaining fixture 54 is movable, for example to
reposition (e.g. pivot) the blank 52 between machining steps,
and/or to move the blank 52 during machining. In a particular
embodiment, machining includes performing a first machining
operation, then disengaging the support member 26 from the
retaining fixture 54 and re-engaging them in a different relative
position and/or orientation before performing another machining
operation using the same or a different tool. The complementary
locating features on the support member 26 and retaining fixture 54
allow for the location of the green body 50 to be determined during
the machining operations.
[0027] In the embodiment shown, the green body 50 is machined to
produce the machined green part 50' having the desired shape and a
retaining portion 50'' engaged to the support member 26 and
connected to the machined green part 50'. The machined green part
50' remains connected to the support member 26 only through its
connection with the retaining portion 50'', defined here by a
plurality of tabs 51. Accordingly, the support member 26 is
disengaged from the machined green part 50' by breaking the
connection between the machined green part 50' and the retaining
portion 50'', either manually or through the machining process.
[0028] In a particular embodiment, the support member 26 is freed
from the green body, cleaned and re-used in the molding and
machining of another green part.
[0029] The machined green part 50' is then submitted to a debinding
operation to remove most or all of the binder. The green part can
be debound using various debinding solutions and/or heat treatments
known in the art, to obtain a brown part. After the debinding
operations, the brown part is sintered. The sintering operation can
be done in an inert gas environment, a reducing atmosphere (H.sub.2
for example), or a vacuum environment depending on the composition
of material to be obtained. In a particular embodiment, sintering
is followed by a heat treatment also defined by the requirements of
the material of the finished part. In some cases, it may be
followed with hot isostatic pressing (HIP). Coining may also be
performed to further refine the profile of the part. It is
understood that the parameters of the sintering operation can vary
depending on the composition of the feedstock, on the method of
debinding and on the configuration of the part.
[0030] In another particular embodiment, the support member 26
remains engaged to the machined green part 50' during
debinding.
[0031] An example of a mold and support member in accordance with
another particular embodiment is generally and schematically shown
in FIG. 4. In this embodiment, the mold 120 includes two mold
elements 124 (only one of which is shown, the other being a mirror
image thereof) which together define a mold cavity 122 having a
substantially cylindrical shape to define a substantially
cylindrical green body 150 (FIG. 5). Each mold element 124 defines
one-half of the mold cavity 122 with opposed semi-circular wall
surfaces 132, 134 interconnected by an arcuate inner wall surface
140 bordering the cavity 122. The mold elements 124 are
interconnected to enclose the mold cavity 122. It is understood
that the number and configuration of the mold elements may vary, as
long as they create the desired shape for the mold cavity and can
be disassembled for removal of the molded part without damaging
it.
[0032] The support member 126 is made of solid material having a
greater rigidity than that of the solidified green body 150 and is
in the form of a shaft, including an outer portion 136 extending
out of the mold cavity 122 and an inner portion 146 extending from
the outer portion 136 into the mold cavity 122. In this embodiment,
the mold cavity 122 and as such the green body 150 molded
therefrom, as well as the support member 126, have a common axis of
axisymmetry 160. This configuration may thus be particularly
suitable for use with a machine-tool of the turning type (e.g.
turning lathe or mill-turn machine).
[0033] The inner portion 146 of the support member 126 is shaped
such as to be gripped and retained within the green body 150 after
the shrinkage occurring during solidification. In the embodiment
shown, the inner portion 146 has an annular groove 162 defined in
its outer surface, in which the material of the green body 150
engages to form a complementary lip 164 (FIG. 5). The inner portion
146 also includes a series of protruding teeth 166 in which the
material of the green body 150 engaged to form complementary teeth
(not shown) to form an anti-rotation locking feature. Shrinkage of
the green body 150 during solidification tightens the fit between
the lip 164 and groove 162 and between the teeth 166 to engage the
support member 126 to the green body 150. The green body 150 and
support member 126 engaged thereto are removed from the mold cavity
122 and disengaged from the mold elements 124, as shown in FIG. 5,
to form the blank 152.
[0034] Referring to FIG. 6a, the support member 126 is then engaged
with a retaining fixture 154 of the machine tool 156, such as to
retain the blank 152 for machining. Complementary locating features
may be provided in the retaining fixture 154 and outer portion 136
of the support member 126, such as for example a locating pin 158
(FIG. 5) extending from the outer portion 136 for snug engagement
in a complementary locating hole (not shown) in the retaining
fixture 154.
[0035] Referring to FIG. 6b, the green body 150 is then machined
using the machine tool while the blank 152 is supported through the
engagement between the support member 126 and the retaining fixture
154, until the desired shape defining the machined green part 150'
is obtained. In the embodiment shown, the retaining fixture 154
rotates the blank about its central axis 160 while it is being
machined by a moving tool. The machining may include performing two
or more machining operations, and disengaging/re-engaging the
support member 126 from the retaining fixture 154 between the
machining operations. A face 129 of the support member 126 may be
used as reference for locating of the blank 152 between set ups
and/or additional features may be included in the support member
126 to facilitate location of the blank 152, such as for example a
flat reference surface 127.
[0036] In the embodiment shown, the machining is performed to
obtain the machined green part 150' having the desired shape for
the element to be produced, and a retaining portion 150'' engaged
to the support member 126 and connected to the machined green part
150'. The machined green part 150' remains connected to the support
member 126 only through its connection with the retaining portion
150''. Accordingly, the support member 126 is disengaged from the
machined green part 150' by breaking the connection between the
machined green part 150' and the retaining portion 150'', either
manually or through the machining process. The machined green part
150' is then debound and sintered.
[0037] In particular embodiment, the support member 126 is then
cleaned by removing the green material remaining connected thereto
(e.g. by destroying the retaining portion 150''), and re-used in
the molding and machining of another green part.
[0038] Although in the embodiments shown the molded green body 50,
150 is depicted as a block shape, i.e. having none of the features
of the desired final shape for the part which are thus all obtained
by machining, it is understood that in other embodiments the green
body may be molded having some of the features of the desired final
shape such that only part of the green body is machined, or with an
intermediate shape between the block shape and the desired final
shape, for example a rough shape approximating and larger than the
desired final shape. The method may also be used to perform
secondary machining operations on molded parts in the green state,
including the removal of gates created by the molding process,
testing new/modified features on already molded parts (as opposed
to directly molding the modified part using a new/modified mold),
and machining difficult to mold features with easier to mold
features being directly obtained in the molding step.
[0039] The method may be used to shape any type of part that may be
obtained by a metal or powder injection molding process, including,
but not limited to, gas turbine engine elements such as pieces of
fuel nozzles, combustor panels, brackets, vanes, vane segments,
vane rings, heat shields, combustion air swirlers, shroud segments,
bosses, flanges, tube fittings, adaptors, airfoils, blades, levers,
etc.
[0040] The shape of the support member 26, 126 may vary and is
selected based on the machine tool used and on the configuration of
the green body to be machined.
[0041] In some embodiments, the configuration of the green body
and/or the properties of the feedstock and/or the machining
operations to be performed allow for the green body to be
sufficiently resistant to be directly supported during the
machining operation(s), and accordingly the support member is
omitted.
[0042] It is understood that the machined green part 50', 150' may
be assembled to one or more other green part(s) (whether machined
or directly molded to shape) prior to debinding, and these parts
may be assembled in their green state, connected using any type of
suitable non-detachable connections or detachable connections, and
debound and sintered to fuse them together to form the final
element. In a particular embodiment, the parts are fused during the
debinding step. Alternately, the parts are joined after the
debinding step and prior to the sintering step.
[0043] The above description is meant to be exemplary only, and one
skilled in the art will recognize that changes may be made to the
embodiments described without departing from the scope of the
invention disclosed. Modifications other than those specifically
described above which fall within the scope of the present
invention will be apparent to those skilled in the art, in light of
a review of this disclosure, and such modifications are intended to
fall within the appended claims.
* * * * *