U.S. patent application number 10/205451 was filed with the patent office on 2004-02-05 for direct manufacture of aerospace parts.
Invention is credited to Beilman, Daniel F., Bond, Gary G., DeGrange, Jeffrey E., Fink, Jeffrey, Spielman, Roger L., Taylor, Tracy L., Wannemuehler, Kevin L., Willer, Robert P..
Application Number | 20040021256 10/205451 |
Document ID | / |
Family ID | 30000117 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040021256 |
Kind Code |
A1 |
DeGrange, Jeffrey E. ; et
al. |
February 5, 2004 |
Direct manufacture of aerospace parts
Abstract
A process of fabricating aerospace parts using selective laser
sintering is provided, wherein the process generally comprises the
steps of preparing a powder nylon material, loading the powder
nylon material into a laser sintering machine, warming up the
powder nylon material according to build warm-up parameters,
building the part according to build parameters and part
parameters, and cooling down the part according to build cool-down
parameters. As a result, parts are produced that are directly used
in aerospace structures, which meet the stringent performance
requirements of aerospace applications, rather than as rapid
prototypes as with conventional selective laser sintering
processes. Additionally, specific designs for aerospace parts such
as ducts, panels, and shrouds are provided that are produced by the
selective laser sintering process.
Inventors: |
DeGrange, Jeffrey E.; (St.
Charles, MO) ; Beilman, Daniel F.; (St. Charles,
MO) ; Willer, Robert P.; (St. Louis, MO) ;
Spielman, Roger L.; (Simi Valley, CA) ; Taylor, Tracy
L.; (Simi Valley, CA) ; Wannemuehler, Kevin L.;
(St. Charles, MO) ; Fink, Jeffrey; (West Hills,
CA) ; Bond, Gary G.; (St. Louis, MO) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
30000117 |
Appl. No.: |
10/205451 |
Filed: |
July 25, 2002 |
Current U.S.
Class: |
264/497 ;
264/237 |
Current CPC
Class: |
B29K 2077/00 20130101;
B29C 41/52 20130101; B33Y 70/00 20141201; B29C 64/153 20170801;
B29L 2031/3097 20130101; B33Y 10/00 20141201; B33Y 80/00 20141201;
B29C 41/46 20130101; B29L 2031/3076 20130101 |
Class at
Publication: |
264/497 ;
264/237 |
International
Class: |
B29C 035/08; B29C
041/02; B29C 071/00 |
Claims
What is claimed is:
1. A process of fabricating at least one aerospace part, the
process comprising the steps of: (a) preparing a powder nylon
material; (b) loading the powder nylon material into a laser
sintering machine; (c) warming up the powder nylon material
according to build warm-up parameters, the build warm-up parameters
comprising a stage height, feed distances, heater set points, a
minimum layer time, and a part heater inner/outer ratio; (d)
building the part according to build parameters, the build
parameters comprising feed distances, heater set points, a minimum
layer time, and a heater inner/outer ratio; and (e) cooling down
the part according to build cool-down parameters, the build
cool-down parameters comprising a stage height, feed distances,
heater set points, a minimum layer time, and a heater inner/outer
ratio.
2. The process according to claim 1, wherein the stage height build
warm-up parameter is between approximately 0.500 in. and
approximately 0.855 in
3. The process according to claim 1, wherein the feed distances
build warm-up parameters further comprise a left feed distance and
a right feed distance build warm-up parameter.
4. The process according to claim 3, wherein the left feed distance
build warm-up parameter is approximately 0.01 in. and the right
feed distance build warm-up parameter is approximately 0.01 in.
5. The process according to claim 1, wherein the heater set points
build warm-up parameters further comprise a left feed heater set
point build warm-up parameter, a part heater set point build
warm-up parameter, and a right feed heater set point build warm-up
parameter.
6. The process according to claim 5, wherein the left feed heater
set point build warm-up parameter is between approximately
100.degree. C. and approximately 140.degree. C., the part heater
set point build warm-up parameter is between approximately a
T.sub.glaze-2.degree. C. and approximately a T.sub.glaze-4.degree.
C., and the right feed heater set point build warm-up parameter is
between approximately 100.degree. C. and approximately 140.degree.
C.
7. The process according to claim 1, wherein the minimum layer time
build warm-up parameter is approximately 30 seconds.
8. The process according to claim 1, wherein the part heater
inner/outer ratio build warm-up parameter is between approximately
0.70 and approximately 1.0.
9. The process according to claim 1, wherein the feed distances
build parameters further comprise a left feed distance build
parameter and a right feed distance build parameter.
10. The process according to claim 9, wherein the left feed
distance build parameter is approximately 0.01 in. and the right
feed distance build parameter is approximately 0.01 in.
11. The process according to claim 1, wherein the heater set points
build parameters further comprise a left feed heater set point
build parameter, a part heater set point build parameter, and a
right feed heater set point build parameter.
12. The process according to claim 11, wherein the left feed heater
set point build parameter is between approximately 100.degree. C.
and approximately 140.degree. C., the part heater set point build
parameter is between approximately a T.sub.glaze-2.degree. C. and
approximately a T.sub.glaze-6.degree. C., and the right feed heater
set point build parameter is between approximately 100.degree. C.
and approximately 140.degree. C.
13. The process according to claim 1, wherein the minimum layer
time build parameter is between approximately 20 seconds and
approximately 30 seconds.
14. The process according to claim 1, wherein the heater
inner/outer ratio build parameter is between approximately 0.70 and
approximately 1.0.
15. The process according to claim 1, wherein the stage height
build cool-down parameter is between approximately 0.015 in. and
approximately 0.200 in.
16. The process according to claim 1, wherein the feed distances
build cool-down parameters further comprise a left feed distance
and a right feed distance build cool-down parameter.
17. The process according to claim 16, wherein the left feed
distance build cool-down parameter is approximately 0.01 in. and
the right feed distance build cool-down parameter is approximately
0.01 in.
18. The process according to claim 1, wherein the heater set points
build cool-down parameters further comprise a left feed heater set
point build cool-down parameter, a part heater set point build
cool-down parameter, and a right feed heater set point build
cool-down parameter.
19. The process according to claim 18, wherein the left feed heater
set point build cool-down parameter is between approximately
100.degree. C. and approximately 140.degree. C., the part heater
set point build cool-down parameter is between approximately a
T.sub.glaze-6.degree. C. and approximately a T.sub.glaze-45.degree.
C., and the right feed heater set point build cool-down parameter
is between approximately 100.degree. C. and approximately
140.degree. C.
20. The process according to claim 1, wherein the minimum layer
time build cool-down parameter is approximately 10 seconds.
21. The process according to claim 1, wherein the part heater
inner/outer ratio build cool-down parameter is between
approximately 0.70 and approximately 1.0.
22. A process of fabricating at least one aerospace part, the
process comprising the steps of: (a) preparing a powder nylon
material; (b) loading the powder nylon material into a laser
sintering machine; (c) warming up the powder nylon material; (d)
building the part according to part parameters, the part parameters
comprising a fill beam X offset, a fill beam Y offset, a fill laser
power, and a sorted fill maximum jump; and (e) cooling down the
part.
23. The process according to claim 22, wherein the fill beam X
offset is between approximately -0.005 and approximately -0.01, the
fill beam Y offset is between approximately -0.005 and
approximately -0.01, the fill laser power is between approximately
15 and approximately 20 watts, and the sorted fill maximum jump is
between approximately 0.25 and approximately 0.5.
24. A process of fabricating at least one aerospace part, the
process comprising the steps of: (a) preparing a powder nylon
material; (b) loading the powder nylon material into a laser
sintering machine; (c) warming up the powder nylon material
according to build warm-up parameters, the build warm-up parameters
comprising a stage height, feed distances, heater set points, a
minimum layer time, and a part heater inner/outer ratio; (d)
building the part according to build parameters and part
parameters, the build parameters comprising feed distances, heater
set points, a minimum layer time, and a heater inner/outer ratio,
and the part parameters comprising a fill beam X offset, a fill
beam Y offset, a fill laser power, and a sorted fill maximum jump;
and (e) cooling down the part according to build cool-down
parameters, the build cool-down parameters comprising a stage
height, feed distances, heater set points, a minimum layer time,
and a heater inner/outer ratio.
25. The process according to claim 24, wherein the stage height
build warm-up parameter is between approximately 0.500 in. and
approximately 0.855 in
26. The process according to claim 24, wherein the feed distances
build warm-up parameters further comprise a left feed distance and
a right feed distance build warm-up parameter.
27. The process according to claim 26, wherein the left feed
distance build warm-up parameter is approximately 0.01 in. and the
right feed distance build warm-up parameter is approximately 0.01
in.
28. The process according to claim 24, wherein the heater set
points build warm-up parameters further comprise a left feed heater
set point build warm-up parameter, a part heater set point build
warm-up parameter, and a right feed heater set point build warm-up
parameter.
29. The process according to claim 28, wherein the left feed heater
set point build warm-up parameter is between approximately
100.degree. C. and approximately 140.degree. C., the part heater
set point build warm-up parameter is between approximately a
T.sub.glaze-2.degree. C. and approximately a T.sub.glaze-4.degree.
C., and the right feed heater set point build warm-up parameter is
between approximately 100.degree. C. and approximately 140.degree.
C.
30. The process according to claim 24, wherein the minimum layer
time build warm-up parameter is between approximately 20 seconds
and approximately 30 seconds.
31. The process according to claim 24, wherein the part heater
inner/outer ratio build warm-up parameter is between approximately
0.70 and approximately 1.0.
32. The process according to claim 24, wherein the feed distances
build parameters further comprise a left feed distance build
parameter and a right feed distance build parameter.
33. The process according to claim 32, wherein the left feed
distance build parameter is approximately 0.01 in. and the right
feed distance build parameter is approximately 0.01 in.
34. The process according to claim 24, wherein the heater set
points build parameters further comprise a left feed heater set
point build parameter, a part heater set point build parameter, and
a right feed heater set point build parameter.
35. The process according to claim 34, wherein the left feed heater
set point build parameter is between approximately 100.degree. C.
and approximately 140.degree. C., the part heater set point build
parameter is between approximately a T.sub.glaze-2.degree. C. and
approximately a T.sub.glaze-6.degree. C., and the right feed heater
set point build parameter is between approximately 100.degree. C.
and approximately 140.degree. C.
36. The process according to claim 24, wherein the minimum layer
time build parameter is between approximately 20 seconds and
approximately 30 seconds.
37. The process according to claim 24, wherein the heater
inner/outer ratio build parameter is between approximately 0.70 and
approximately 1.0.
38. The process according to claim 24, wherein the stage height
build cool-down parameter is between approximately 0.015 in. and
approximately 0.200 in.
39. The process according to claim 24, wherein the feed distances
build cool-down parameters further comprise a left feed distance
and a right feed distance build cool-down parameter.
40. The process according to claim 39, wherein the left feed
distance build cool-down parameter is approximately 0.01 in. and
the right feed distance build cool-down parameter is approximately
0.01 in.
41. The process according to claim 24, wherein the heater set
points build cool-down parameters further comprise a left feed
heater set point build cool-down parameter, a part heater set point
build cool-down parameter, and a right feed heater set point build
cool-down parameter.
42. The process according to claim 41, wherein the left feed heater
set point build cool-down parameter is between approximately
100.degree. C. and approximately 140.degree. C., the part heater
set point build cool-down parameter is between approximately a
T.sub.glaze-6.degree. C. and approximately a T.sub.glaze-45.degree.
C., and the right feed heater set point build cool-down parameter
is between approximately 100.degree. C. and approximately
140.degree. C.
43. The process according to claim 24, wherein the minimum layer
time build cool-down parameter is approximately 10 seconds.
44. The process according to claim 24, wherein the part heater
inner/outer ratio build cool-down parameter is between
approximately 0.70 and approximately 1.0.
45. The process according to claim 24, wherein the fill beam X
offset is between approximately -0.005 and approximately -0.01, the
fill beam Y offset is between approximately -0.005 and
approximately -0.01, the fill laser power is between approximately
15 watts and approximately 20 watts, and the sorted fill maximum
jump is between approximately 0.25 and approximately 0.5.
46. A process of fabricating at least one aerospace part, the
process comprising the steps of: (a) preparing a powder nylon
material; (b) loading the powder nylon material into a laser
sintering machine; (c) warming up the powder nylon material
according to build warm-up parameters, the build warm-up parameters
comprising a stage height between approximately 0.500 and
approximately 0.855 in., a left feed distance of approximately 0.01
in., a right feed distance of approximately 0.01 in., a left feed
heater set point between approximately 100.degree. C. and
approximately 140.degree. C., a part heater set point between
approximately T.sub.glaze-6.degree. C. and approximately
T.sub.glaze-45.degree. C., a right feed heater set point between
approximately 100.degree. C. and approximately 140.degree. C., a
minimum layer time of approximately 30 seconds, and a part heater
inner/outer ratio between approximately 0.70 and approximately 1.0;
(d) building the part according to build parameters and part
parameters, the build parameters comprising a left feed distance of
approximately 0.01 in., a right feed distance of approximately 0.01
in., a left feed heater set point between approximately 100.degree.
C. and approximately 140.degree. C., a part heater set point
between approximately T.sub.glaze-2.degree. C. and approximately
T.sub.glaze-6.degree. C., a right feed heater set point between
approximately 100.degree. C. and approximately 140.degree. C., a
minimum layer time between approximately 20 seconds and
approximately 30 seconds, and a heater inner/outer ratio between
approximately 0.70 and approximately 1.0, and the part parameters
comprising a fill beam X offset between approximately -0.005 in.
and approximately -0.01 in., a fill beam Y offset between
approximately -0.005 in. and approximately -0.01 in., a fill laser
power between approximately 15 watts and approximately 20 watts,
and a sorted fill maximum jump between approximately 0.25 and
approximately 0.5; and (e) cooling down the part according to build
cool-down parameters, the build cool-down parameters comprising a
stage height between approximately 0.015 in. and 0.200 in., a left
feed distance build cool-down parameter of approximately 0.01 in.,
a right feed distance build cool-down parameter of approximately
0.01 in., a left feed heater set point build cool-down parameter
between approximately 100.degree. C. and approximately 140.degree.
C., a part heater set point build cool-down parameter between
approximately a T.sub.glaze-6.degree. C. and approximately
T.sub.glaze-45.degree. C., a right feed heater set point build
cool-down parameter between approximately 100.degree. C. and
approximately 140.degree. C., a minimum layer time build cool-down
parameter of approximately 10 seconds, and a part heater
inner/outer ratio build cool-down parameter between approximately
0.70 and approximately 1.0.
47. An aerospace part formed by a process of: (a) preparing a
powder nylon material; (b) loading the powder nylon material into a
laser sintering machine; (c) warming up the powder nylon material
according to build warm-up parameters; (d) building the part
according to build parameters and part parameters; and (e) cooling
down the part according to build cool-down parameters.
48. The aerospace part according to claim 47, wherein the aerospace
part comprises an electrical shroud.
49. The aerospace part according to claim 47, wherein the aerospace
part comprises a power distribution panel.
50. The aerospace part according to claim 47, wherein the aerospace
part comprises a duct.
51. The aerospace part according to claim 47, wherein the aerospace
part comprises a fitting.
52. The aerospace part according to claim 47, wherein the aerospace
part comprises a closure.
53. The aerospace part according to claim 47, wherein the aerospace
part comprises a conduit.
54. An aerospace part formed by a process of: (a) preparing a
powder material; (b) loading the powder material into a laser
sintering machine; (c) warming up the powder material according to
build warm-up parameters; (d) building the part according to build
parameters and part parameters; and (e) cooling down the part
according to build cool-down parameters.
55. An aerospace duct formed by a process of: (a) preparing a
powder material; (b) loading the powder material into a laser
sintering machine; (c) warming up the powder material according to
build warm-up parameters; (d) building the part according to build
parameters and part parameters; and (e) cooling down the part
according to build cool-down parameters.
56. The aerospace duct according to claim 55, wherein the duct
comprises at least one internal stiffener.
57. The aerospace duct according to claim 55, wherein the duct
comprises at least one mounting pad.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to selective laser
sintering and more particularly to production parts and processes
using selective laser sintering.
BACKGROUND OF THE INVENTION
[0002] Selective laser sintering (SLS) is well known in the art and
has traditionally been employed to produce parts known as "rapid
prototypes," which are parts that are used to demonstrate a proof
of concept or a requirement such as proper form and fit. The
selective laser sintering process generally consists of producing
parts in a layers from a laser-fusible powder that is provided one
layer at a time. The powder is fused, or sintered, by the
application of laser energy that is directed to portions of the
powder corresponding to the cross-section of the part. After
sintering the powder in each layer, a successive layer of powder is
applied and the process of sintering portions of the powder
corresponding to the cross-section of the part is repeated, with
sintered portions of successive layers fusing to sintered portions
of previous layers until the part is complete. Accordingly,
selective laser sintering is capable of producing parts having
relatively complex geometry with relatively acceptable dimensional
accuracy and using a variety of materials such as wax, plastics,
metals, and ceramics.
[0003] Generally, SLS parts are produced directly from an
engineering master definition in a CAD (computer aided design)
model(s) and thus the time required to produce a rapid prototype is
significantly shorter than with conventional methods such as sheet
metal forming, machining, molding, or other methods commonly known
in the art. Further, powder materials that are used to date for
selective laser sintering generally have relatively low mechanical
properties due to the nature of the rapid prototype application.
Accordingly, parts formed using selective laser sintering are
typically not used within a production design or as production
parts due to limited performance capabilities such as low or
inconsistent mechanical properties.
[0004] Aerospace parts have relatively stringent design
requirements compared with parts in other applications, primarily
due to operating environments having extremely high loads and
temperatures in addition to a relatively high amount of parts in a
relatively small volume. For example, aerospace parts are commonly
subjected to fluid exposure, pressure cycling, prolonged fatigue
loads, buffeting, and a wide range of temperatures in operation,
among others, and must further be as light weight as possible to
meet performance objectives. Additionally, aerospace parts such as
ECS (environmental control system) ducts typically define
relatively intricate shapes in order to route around other parts
and aircraft systems within an aircraft. Moreover, aerospace
structures must be capable of withstanding impact loads from
maintenance, handling, and in the case of military aerospace
structures, from threats such armor piercing incendiaries (API) or
high explosive incendiaries (HEI). Accordingly, aerospace parts
must be designed to accommodate a variety of operating environments
and thus have design requirements that are beyond those of
non-aerospace parts.
SUMMARY OF THE INVENTION
[0005] In one preferred form, the present invention provides a
process of fabricating aerospace parts that comprises the steps of
preparing a powder nylon material, loading the powder nylon
material into a laser sintering machine, warming up the powder
nylon material according to build warm-up parameters, building the
part according to build parameters, and cooling down the part
according to build cool-down parameters. As a result, parts are
produced that are directly used in aerospace structures, which meet
the stringent performance requirements of aerospace applications,
rather than as rapid prototypes or other designs having less
stringent performance requirements produced with conventional
selective laser sintering processes.
[0006] In another form, a process of fabricating aerospace parts is
provided that further comprises warming up a powder nylon material
according to build warm-up parameters, building the part according
to both build parameters and part parameters, and similarly cooling
down the part according to build cool-down parameters. Furthermore,
specific values for the parameters are provided in other forms of
the present invention, which result in parts being produced that
have aerospace grade and quality.
[0007] In yet other forms of the present invention, aerospace parts
are provided that are formed by a process of preparing a powder
nylon material, loading the nylon material into a laser sintering
machine, warming up the powder nylon material according to build
warm-up parameters, building the part according to build and part
parameters, and cooling down the part according to build cool-down
parameters. The aerospace parts include, by way of example,
electrical shrouds, power distribution panels, ducts (e.g.
environmental control system), fittings, closures, and conduits,
among others.
[0008] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0010] FIG. 1 is a flow diagram illustrating a selective laser
sintering process in accordance with the teachings of the present
invention;
[0011] FIG. 2 is a diagram of a part bed configuration in
accordance with the teachings of the present invention;
[0012] FIG. 3 is a series of perspective views of aerospace parts
that can be fabricated according to the process of the present
invention.
[0013] FIG. 4 is a cross-sectional view of an ECS duct fabricated
in accordance with the teachings of the present invention;
[0014] FIG. 5 is a perspective view of an ECS duct illustrating
stiffener spacing in accordance with the teachings of the present
invention;
[0015] FIG. 6 is a graph illustrating stiffener spacing as a
function of burst pressure in accordance with the teachings of the
present invention;
[0016] FIG. 7A is a partial cross-sectional view of an ECS duct
having an integral lug for mounting in accordance with the
teachings of the present invention;
[0017] FIG. 7B is a cross-sectional view of an ECS duct having an
airflow-internal mounting lug in accordance with the teachings of
the present invention; and
[0018] FIG. 8 is a cross-sectional view of a bonded aerospace joint
constructed in accordance with the teachings of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] The following description of the preferred embodiments is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses. Additionally, the selective
laser sintering process is well known by those having ordinary
skill in the art and is not described herein in detail for purposes
of clarity.
[0020] Referring to FIG. 1, a process of fabricating, or forming,
at least one aerospace part according to the present invention is
represented in a flow diagram format as indicated by reference
numeral 10. As shown, the process generally comprises the steps of
preparing a powder material 12, loading the powder material 14 into
a laser sintering machine, warming up the powder material 16,
building the part 18, and cooling down the part 20. Additionally,
the process 10 includes several build and part parameters, which
are characterized as either "hidden," "fixed," or "variable." The
hidden and fixed parameters are generally provided by the equipment
manufacturer and are also a part of the operating software for the
laser sintering machine. Preferably, a 2500 Plus Sintering Machine
from DTM Corporation, Austin, Tex., is used to fabricate parts in
accordance with the present invention. However, the variable
parameters are critical parameters that have been developed through
extensive research and testing according to the present invention
in order to produce parts that are capable of direct application in
aerospace structures and systems.
[0021] Each of the hidden, fixed, and variable parameters are
listed below in Table I, which include both build parameters and
part parameters for each phase of the process 10. Each of the
parameters is a function of the specific sintering machine being
used, which is the 2500 Plus Sintering Machine from DTM
Corporation, Austin, Tex. as previously set forth. Generally, the
phases of the process 10 are characterized as a warm-up phase (16),
a part build phase (18), and a cool-down phase (20), each of which
has separate parameters as listed below.
1TABLE 1 BUILD AND PART SINTERING PARAMETERS BUILD PARAMETER
CLASSIFICATION WARM-UP BUILD COOL-DOWN Stage Height Variable
0.500-0.855 N/A 0.015-0.200 Blower Speed Hidden 0 0 0 Fast Add
Powder Layer Hidden 0 0 0 Left Feed Distance Variable 0.01 0.01
0.01 Left Feed Heater Fixed 80 60 60 Output Limit Left Feed Heater
Set Variable 100-140 100-140 100-140 Point Left Feed Heater Wait
Fixed 1 0 0 for Temp Minimum Layer lime Variable 30 20-30 10 Part
Cylinder Heater Fixed 1 1 1 Enable Part Cylinder Heater Fixed 100
100 100 Output Limit Part Cylinder Heater Fixed 140 140 140 Set
Point Part Heater PID Output Fixed 60 50 50 Limit Part Heater Set
Point Variable T.sub.glaze-2.degree. to T.sub.glaze-
T.sub.glaze-2.degree. to T.sub.glaze-6.degree. to 4.degree. C.
T.sub.glaze-6.degree. C. 45.degree. C. 1/ Part Heater Wait for
Fixed 0 0 1 Temp Part Heater Inner/Outer Variable 0.70-1.0 0.70-1.0
0.70-1.0 Ratio Piston Heater Enable Hidden 0 0 0 Piston Heater
Output Hidden 100 100 100 Limit Piston Heater Set Point Hidden 150
150 150 Powder Layer Delay Hidden 0 0 0 Powder Layer Fixed 0.005
0.005 0.005 Thickness Right Feed Distance Variable 0.01 0.01 0.01
Right Feed Heater Fixed 80 60 60 Output Limit Right Feed Heater Set
Variable 100-140 100-140 100-140 Point Right Feed Heater Wait Fixed
1 0 0 for Temp Roller Speed Fixed 7 7 7 Rotate Scan Order Fixed 0 0
0 Vector Bloom Fixed N/A 1 N/A Elimination Maximum Gap Distance
Hidden N/A 0.1 N/A Fill Beam Offset X Variable N/A -0.005- N/A 0.01
Outline Beam Offset X Hidden N/A 0 N/A Fill Beam Offset Y Variable
N/A -0.005- N/A 0.01 Outline Beam Offset Y Hidden N/A O N/A Fill
Laser Power Variable N/A 15-20 W N/A Fill Scan Count Hidden N/A 1
N/A Fill Jump Delay Hidden N/A 1000 N/A Fill Jump Speed Hidden N/A
200 N/A PART PARAMETER Fill Laser Off Hidden N/A 1750 N/A Fill
Laser On Hidden N/A 750 N/A Fill Stroke Delay Hidden N/A 1900 N/A
Fill Scan Speed Fixed N/A 200 N/A Outline Laser Power Hidden N/A 0
N/A Outline Scan Count Hidden N/A 0 N/A Outline Jump Delay Hidden
N/A 1000 N/A Outline Jump Speed Hidden N/A 66 N/A Outline Laser Off
Hidden N/A 1400 N/A Outline Laser On Hidden N/A 985 N/A Outline
Stroke Delay Hidden N/A 1800 N/A Outline Scan Speed Hidden N/A 14
N/A Slicer Fill First Hidden N/A 1 N/A Slicer Fill Scan Spacing
Fixed N/A 0.006 N/A Sorted Fill Enabled Fixed N/A 1 N/A Sorted Fill
Max Jump Variable N/A 0.25-0.5 N/A NOTE: 1/ If a part cake must be
removed from the machine at a set temperature, there is no control
system to maintain the 45.degree. C. part bed temperature during
cool down and turn off of the machine. Therefore, in this case, the
Operator will have to change the wait-for-temperature during cool
down to .degree. C. and manually stop the build when the set-point
has been reached.
[0022] Additionally, the variable parameters that have been
developed according to the present invention are listed below in
Table II for each of the process phases for both individual parts
or parts in a nested part build (more than one part).
2 CRITICAL (VARIABLE) BUILD AND PART SINTERING PARAMETERS COOL-
BUILD PARAMETER CLASSIFICATION WARM-UP BUILD DOWN Stage Height
Variable 0.500 to 0.855 N/A 0.015-0.200 Left Feed Distance Variable
0.01 0.01 0.01 Left Feed Heater Set Variable 100-140 100-140
100-140 Point Minimum Layer lime Variable 30 20-30 10 Part Heater
Set Point Variable T.sub.glaze-2.degree. to T.sub.glaze-2.degree.
to T.sub.glaze-6.degree. to T.sub.glaze-4.degree. C.
T.sub.glaze-6.degree. C. 45.degree.+00 C. 1/ Part Heater Variable
0.70-1.0 0.70-1.0 0.70-1.0 Inner/Outer Ratio Right Feed Distance
Variable 0.01 0.01 0.01 Right Feed Heater Variable 100-140 100-140
100-140 Set Point Fill Beam Offset X Variable N/A -0.005-0.01 N/A
Fill Beam Offset Y Variable N/A -0.005-0.01 N/A Fill Laser Power
Variable N/A 15-20 Watts N/A Sorted Fill Max Jump Variable N/A
0.25-0.5 N/A NOTE: 1/ If a part cake must be removed from the
machine at a set temperature, there is no control system to
maintain the 45.degree. C. part bed temperature during cool down
and turn off of the machine. Therefore, in this case, the Operator
will have to change the wait-for-temperature dunn cool down to
0.degree. C. and manually stop the build when the set-point has
been reached.
[0023] Preferably, the powder material used to fabricate parts
according to the present invention is a Nylon 11 material that
contains no additives or fillers. Aerospace parts fabricated from
such a Nylon material are capable of operating within a temperature
range of approximately -65.degree. F. to approximately 215.degree.
F.
[0024] Process
[0025] As previously set forth, the process of fabricating at least
one aerospace part generally comprises preparing the powder
material, loading the powder material into a laser sintering
machine, warming up the powder material (warm-up phase), building
the part (build phase), and cooling down the part (cool-down
phase). Prior to preparing the powder material, thermal
characterization tests of the sintering bed are preferably
conducted to characterize temperature uniformity over the surface
of the sintering bed. One thermal characterization test is a
thermal profile test, wherein an aluminum plate with thermocouples
is placed in a sintering or part bed and feed heaters are operating
at a set-point of 100.degree. C. or greater. Preferably, the
temperatures should not vary by more than 4.degree. C. across the
part bed. A second thermal characterization test is a thermpat
test, wherein an approximate 0.050 in. thick layer of powder
material is sintered over the entire surface of the part bed. The
thermpat test thus provides an indication of any localized areas
that are warmer than surrounding areas. Accordingly, both the
thermal profile test and the thermpat test are conducted for each
sintering machine that is used to fabricate aerospace parts.
[0026] Prior to preparing the powder, the sintering machine is
preferably cleaned prior to each build. The cleaning comprises
removal and wipe-down of dirt, dust, residue, fused powder, and
other types of contamination that might adversely affect proper
operation of the sintering machine. More specifically, parts of the
sintering machine that are preferably cleaned include a powder
feed, the part bed, a laser window and housing, IR (infrared)
sensors for both the feed and part bed control, heat deflector
shields, roller and roller scraper assemblies, interior walls, and
a table top. Additionally, monthly checks of the equipment are
conducted that include checking scrapers for wear, checking
filters, verifying scale and offset values for the machine, and
checking coolant level and operation of an external chiller.
[0027] Preparing the Powder Material
[0028] The step of preparing the powder material comprises
selecting an appropriate material type and quantity and moving the
material to a weighing area, where the material is weighed and
recorded, along with a lot number, in a log book. The powder
material is then placed in a mixer and blended thoroughly for a
minimum of approximately 20 minutes. The blended material is then
sifted with an approximate 30 mesh screen and packed into a load
container until the container is filled to capacity. Next, the
container is placed on a vibration table and vibrated until no
powder settling is evident. The packed material is then weighed and
moved to the laser sintering machine for loading.
[0029] Loading the Powder Material
[0030] Prior to loading the powder material into the machine, the
feed pistons are preferably at an upper limit and a load container
is placed on top of one feed chamber. The powder is then loaded
into the feed chamber and the process is repeated for a second feed
chamber. After filling each feed chamber, the excess material not
loaded is removed and preferably weighed and recorded.
[0031] Additionally, the part bed is prepared prior to the warm-up
phase, wherein a material roller is moved to an extreme right or
left position, as necessary, to clear the part bed for the
introduction of material. The sifted and packed powder is then
added to the part bed and feed bed boundaries, as required, to
achieve a uniform distribution of material. The material roller is
then activated to move across the build and feed chambers. Further,
right and left chamber swing gates are reinstalled, a process
chamber door and latch are closed, and the part and feed chambers
are then inerted with nitrogen until a targeted oxygen level is
attained in accordance with settings of the equipment. Once the
chambers are inert, the heaters will begin to heat the powder in
the feeds and the part bed to temperatures defined by the process
parameters as previously set forth in Table 1. When the
temperatures are reached, the warm-up phase then begins.
[0032] Warm-Up Phase
[0033] Referring now to FIG. 2, a preferred layout for a part bed
22 is illustrated. According to the process of the present
invention, layers of powder are first applied by a roller to create
a warm-up stage 24, which comprises approximately 0.500 to
approximately 0.885 in. of powder. Further, temperatures are ramped
up until a warm-up height is reached and endpoint temperatures in
feeds and the part bed 22 are set to starting temperatures of the
build phase. Additionally, the hidden, fixed, and variable
parameters according to Table I as previously set forth are used
for the warm-up phase.
[0034] Build Phase
[0035] The first step in the build phase is a laser re-fire
sequence, during which glazing of the entire surface of the
sintering bed occurs and a buffer for laser re-fire 26 is created.
If glazing occurs, an additional four layers of powder,
approximately 0.020 in. total thickness, is applied over the
sintering bed to create the buffer for laser re-fire 26. Generally,
the purpose of the buffer layer is to provide a buffer to prevent
the re-fire laser from fusing to a subsequent layer of sacrificial
tensile bars 28, which are formed after the buffer layer 26. The
tensile bars, which are fabricated in accordance with ASTM D638
Type I, are tested after part fabrication to verify required
physical and mechanical properties of the aerospace parts.
[0036] The next step of the build phase is forming a pre-part layer
30 of approximately 0.100 in. The pre-part layer 30 serves as a
buffer before sintering the actual aerospace parts. Next,
fabrication of the aerospace parts is conducted within the part
build zone 32 according to the hidden, fixed, and variable
parameters in Table I, and the variable parameters as established
by the present invention according to Table II, as previously set
forth. A further description of the selective laser sintering
process is not detailed herein, as the process is well known by
those skilled in the art.
[0037] Cool-Down Phase
[0038] The cool-down phase begins with the deposition of a buffer
layer of powder over the part build, which serves as a thermal cap.
During the cool-down phase, the nitrogen purge continues to
maintain an inert atmosphere in the build chamber at no greater
than approximately 0.2% oxygen volume content. Then, the part bed
is allowed to cool to approximately 40.degree. C. to approximately
45.degree. C., after which time the sintering machine is opened and
the part cake (the fabricated part and excess powder material) is
removed.
[0039] After the part cake is removed from the machine, "breakout"
of the part from the part cake is conducted within a breakout
station (BOS). After "breakout," unsintered material is removed
from interior surfaces of the parts using clean instruments such as
a flexible metal spatula or a stiff nylon bristle brush. Excess
unsintered material is preferably removed from exterior surfaces by
wiping or brushing. After the excess material is removed from
exterior and interior surfaces, the part is preferably bead blasted
using glass beads and a nozzle pressure of approximately 65 to
approximately 75 psi (pounds per square inch). Finally, all
surfaces are blown off using filtered, dry, compressed air, and
each part is placed in a polyethylene bag with proper
identification and is sealed for further inspection, processing,
and subsequent installation into an aircraft or aerospace system.
For example, subsequent processing may include applying at least
one seal coat and a second seal coat for subsequent bonding
purposes. Additionally, seal coats are preferably applied to
interior surfaces of aerospace parts that carry pressurized air,
such as ECS (environmental control system) ducts, among others.
[0040] A working zone or build envelope used for building parts is
approximately 13.5 inches long.times.11.5 inches wide.times.17
inches high with the equipment used with the present invention.
Although parts may be fabricated beyond the dimensional constraints
of the equipment and subsequently joined using methods such as
mechanical fastening or bonding, the process according to the
present invention preferably includes fabricating tensile
specimens, according to ASTM D638 Type I, to verify consistent
mechanical properties.
[0041] In another form of the present invention, recycled material
may be used to fabricate the parts. Generally, recycled material is
defined as powder that has been used previously in one or more part
build processes. Preferably, the material may be reused up to a
level of approximately 70% with approximately 30% being unused
material. Once a part is fabricated using the recycled material,
however, any powder remaining from the part build is preferably not
reused unless further testing is conducted to demonstrate that
mechanical and physical properties are adequate. Additionally,
powder material that is reused is preferably sifted prior to use
using a 30 mesh sieve.
[0042] Aerospace Part Applications
[0043] Referring to FIG. 3, aerospace parts that have be fabricated
using a nylon powder material in the process according to the
present invention include ducts 40, electrical shrouds 42, power
distribution panels 44, fittings 46, closures 48, and conduits 50,
among others. It should be understood by those skilled in the art
that other types of powder material other than nylon may also be
employed to fabricate the aerospace parts as shown in FIG. 3, in
addition to other types of aerospace parts. Accordingly, a unique
set of variable parameters would be established for such a material
system. Therefore, the reference to a nylon powder material and
specific aerospace parts should not be construed as limiting the
scope of the present invention.
[0044] For the nylon powder material as described herein, the
present invention further comprises general design configurations
for Environmental Control System (ECS) ducts used in aerospace
vehicles. Generally, the ECS ducts provide passageways for
temperature-controlled airflow, or other ventilation as required
for systems or personnel onboard the aerospace vehicle. Generally,
the present invention enables duct configurations that are
optimized to reduce internal pressure drop and to hold system
pressures. As shown in FIG. 4, a typical ECS duct is illustrated
and indicated by reference numeral 60. The ECS duct 60 comprises at
least one stiffener 62 having a thickness 64, a wall 66 having a
thickness 68, and a plurality of stiffener fillets 70 having radii
72. However, in another form, the ECS duct 60 does not include any
stiffeners 62. Preferably, the minimum wall thickness 68 is
approximately 0.080 in., although thinner walls may be employed
based on the location of the wall 66 relative to the stiffeners 62
and susceptibility to damage. Although the wall 66 is illustrated
as having a constant thickness, the ECS duct 60 may also define
walls 66 having a non-constant thickness while remaining within the
scope of the present invention. Additionally, the minimum stiffener
fillet radii 72 is approximately 0.150 in., and the minimum
stiffener thickness 64 is approximately 0.080 in. Further, the wall
thickness 68 is a function of a stiffener spacing 74, and sample
wall thicknesses 68 for a given stiffener spacing 74 with a burst
pressure of 14.1 psi (pounds per square inch) at 165.degree. F. are
shown below in Table I.
3 Duct Wall Thickness and Stiffener Spacing Wall Thickness 68 (in.)
Stiffener Spacing 74 (in.) 0.070 1.00 0.090 1.25 0.125 1.92 0.300
3.84
[0045] For pressures other than 14.1 psi, the wall thickness 68 is
multiplied by the square root of the ratio of the pressure (p) to a
pressure of 14.1 psi as follows: Wall Thickness (64)=({square
root}{square root over (p/14.1)}).times.wall thickness in Table
I.
[0046] Referring now to FIG. 5, lengthwise spacing 76 of the
stiffeners 62 is illustrated, wherein the lengthwise spacing 76 is
a function of burst pressure. An example of lengthwise spacing 76
versus burst pressure is shown below in FIG. 6, which is based on a
wall thickness 68 of approximately 0.080 in., a stiffener thickness
64 of approximately 0.080 in., and fillet radii 72 of approximately
0.15 in. Lengthwise spacing 76 for the wall thicknesses 68,
stiffener thicknesses 64, and fillet radii 72 other that those
corresponding to FIG. 6 are determined through strength analysis
techniques commonly known in the art.
[0047] As shown in FIG. 7A, the ECS duct 60 is typically fastened
to adjacent structure through an integral mounting lug 80.
Alternately, the ECS duct 60 may comprise an airflow-internal
mounting lug 82 as shown in FIG. 7B. Accordingly, the number of
fasteners and associated installation time is reduced through the
use of the mounting lugs 80 and 82. Preferably, the
airflow-internal mounting lug 82 is symmetrical across its section
to minimize thermal effects and is further slotted. Moreover, the
mounting lug 80 and the airflow-internal mounting lug 82 are
preferably offset from the wall 66 approximately 0.060 in. as shown
to allow for duct distortion during pressurization.
[0048] Referring to FIG. 8, a bonded joint for aerospace parts
fabricated using SLS is illustrated and indicated by reference
numeral 90. The bonded joint 90 comprises an overlap 92, a bondline
offset 94, a fillet radii offset 96, and an OML gap 98. Preferably,
the overlap 92 is approximately 0.75 in., the bondline offset 94 is
approximately 0.020 in., the fillet radii offset 96 is a minimum of
approximately 0.05 in., and the OML gap 98 is a minimum of
approximately 0.10 in. in one form of the present invention.
[0049] As additional design guidelines, rivets that are installed
through the ECS duct 60 are preferably squeezed and not vibration
driven in order to reduce the likelihood of cracking. Further, the
ECS duct 60 may be restrained with a maximum of approximately 5
lbs. to dimensionally conform to an engineering master model
definition.
[0050] Further, the aerospace parts according to the present
invention may be bonded together or to an adjacent metal or rubber
part using an epoxy adhesive, a silicone adhesive/sealant, or a
rubber based contact cement. Additionally, the aerospace parts may
be coated with a seal coat to seal the aerospace part as
required.
[0051] Application of Seal Coat
[0052] Generally, three parts by volume of a base is mixed with one
part by volume of an activator to form the seal coat material,
which typically has a pot life of approximately 2.5 to 3 hours. The
seal coat material is then applied in either one or two coats to
surfaces of the aerospace part as required by an engineering
definition. Further, the seal coat material is preferably applied
by spraying, brushing, dipping, or flow coating. For internal
surfaces such as internal walls of ducts, one end of the duct is
capped off and a quantity of the seal coat material is poured into
another end, which is subsequently capped off. Then, the duct is
rotated in all directions until all surfaces are coated (as
typically indicated by a darker color change). Further, the excess
seal coat material is drained form the part for a minimum of
approximately ten (10) minutes. Seal coated parts are preferably
air dried for a minimum of approximately sixty (60) minutes and are
force dried for approximately 2 hours at approximately 140
.+-.10.degree. F.
[0053] Bonding Parts
[0054] Generally, when bonding an aerospace part according to the
present invention to another aerospace part, whether nylon, metal,
rubber, or other, the mating surfaces are solvent cleaned, sanded,
and solvent cleaned again after sanding. Then, an appropriate
adhesive is mixed and applied to the mating surfaces, which is
followed by assembling the parts immediately. The excess adhesive
is squeezed out using a wiper or spatula and the adhesive is
allowed to cure for a specific period of time and according to a
specific cure profile according to the type of adhesive. Further,
an adhesion promoting primer may also be applied prior to bonding,
such as when a nylon part is bonded to a rubber part using a
silicone adhesive/sealant.
[0055] The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the substance
of the invention are intended to be within the scope of the
invention. Such variations are not to be regarded as a departure
from the spirit and scope of the invention.
* * * * *