U.S. patent application number 11/037730 was filed with the patent office on 2006-07-20 for method and system for enhancing the quality of deposited metal.
Invention is credited to Clifford C. Bampton, Scott W. Fowser, Thomas J. Van Daam.
Application Number | 20060157219 11/037730 |
Document ID | / |
Family ID | 36682677 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060157219 |
Kind Code |
A1 |
Bampton; Clifford C. ; et
al. |
July 20, 2006 |
Method and system for enhancing the quality of deposited metal
Abstract
Systems and methods are disclosed to effectively fracture
dendrite arms and/or reduce grain size in a solidifying metal melt
pool. Ultrasonic energy is applied to the solidifying metal in the
liquid metal pool directly or via a substrate on which the metal is
provided. In another embodiment, ultrasonic energy is applied over
a range of frequencies and/or tuned to the resonant frequency of
solidifying dendrite arms. Advantageously, the present invention
prevents or hinders the growth of large columnar dendrites and
instead allows for the formation of a high density of randomly
oriented grains with a reduction in grain size, thereby enhancing
the quality of the deposited metal and therefore improving the
mechanical properties of the fabricated or repaired structure.
Inventors: |
Bampton; Clifford C.;
(Thousand Oaks, CA) ; Van Daam; Thomas J.; (Simi
Valley, CA) ; Fowser; Scott W.; (Chatsworth,
CA) |
Correspondence
Address: |
MACPHERSON KWOK CHEN & HEID LLP
1762 TECHNOLOGY DRIVE, SUITE 226
SAN JOSE
CA
95110
US
|
Family ID: |
36682677 |
Appl. No.: |
11/037730 |
Filed: |
January 18, 2005 |
Current U.S.
Class: |
164/501 ;
164/4.1; 164/511 |
Current CPC
Class: |
B22D 27/02 20130101 |
Class at
Publication: |
164/501 ;
164/004.1; 164/511 |
International
Class: |
B22D 27/02 20060101
B22D027/02 |
Claims
1. A system for enhancing the quality of deposited metal,
comprising: a metal deposition apparatus that provides liquid metal
on a substrate; and an ultrasonic energy source operably coupled to
the metal deposition apparatus such that ultrasonic energy is
applied to solidifying metal in the liquid metal.
2. The system of claim 1, wherein the metal deposition apparatus
provides liquid metal via laser engineered net shaping, direct
metal deposition, or electron beam melting.
3. The system of claim 1, wherein the liquid metal is selected from
the group consisting of nickel, cobalt and iron-based superalloys,
steels, copper, aluminum, titanium, niobium, molybdenum, tungsten,
rhenium, and alloys thereof.
4. The system of claim 1, wherein the ultrasonic energy source is
selected from the group consisting of a transducer, a laser, a
speaker, and a filler wire.
5. The system of claim 1, wherein the ultrasonic energy is applied
to the liquid metal directly.
6. The system of claim 1, wherein the ultrasonic energy is applied
to the solidifying metal interface via the substrate.
7. The system of claim 1, wherein the ultrasonic energy source is
applied to the substrate adjacent to a boundary of a liquid metal
pool.
8. The system of claim 1, further comprising a table movable in a
plane, the table receiving the substrate.
9. A method of enhancing the quality of deposited metal,
comprising: providing a liquid metal on a substrate; applying
ultrasonic energy to solidifying metal in the liquid metal; and
solidifying the liquid metal with reduced grain size.
10. The method of claim 9, wherein the ultrasonic energy is applied
to the solid/liquid metal interface.
11. The method of claim 9, wherein the ultrasonic energy is applied
to the liquid metal directly.
12. The method of claim 9, wherein applying ultrasonic energy to
solidifying metal fractures a dendrite.
13. The method of claim 9, wherein the ultrasonic energy is
provided by a source selected from the group consisting of a
transducer, a laser, a speaker, and a filler wire.
14. The method of claim 9, wherein the ultrasonic energy is applied
to the substrate adjacent a boundary of a liquid metal pool.
15. The method of claim 9, wherein the ultrasonic energy is applied
over a range of frequencies.
16. The method of claim 15, wherein the ultrasonic energy is swept
through a range of frequencies.
17. A method of enhancing the quality of deposited metal,
comprising: calculating a dendrite arm fracture length; calculating
a resonant frequency applicable for the dendrite arm fracture
length; providing a liquid metal on a substrate; and applying a
tuned ultrasonic energy to solidifying metal in the liquid metal to
decrease grain size as the liquid metal solidifies.
18. The method of claim 17, wherein the ultrasonic energy is
applied to the solidifying metal via the substrate.
19. The method of claim 17, wherein the ultrasonic energy is
applied to the liquid metal directly.
20. The method of claim 17, wherein the ultrasonic energy is
applied over a range of frequencies.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to metal deposition
and, more particularly, to improving the quality of deposited metal
used to fabricate or repair structures.
BACKGROUND
[0002] There are several metal deposition systems driven by
computer aided design (CAD) that build metal alloy structures by an
additive layered process on a substrate. Such systems include, but
are not limited to, Laser Engineered Net Shaping (LENS) available
from Optomec, Inc. of Albuquerque, N. Mex., Direct Metal Deposition
(DMD) available from POM Group, Inc. of Auburn Hills, Mich. and
from Aeromet Corporation of Eden Prairie, Minn., and Electron Beam
Melting (EBM) available from Arcam AB of Molndal, Sweden.
[0003] In each of these systems, liquid metal is provided on the
substrate where the liquid metal solidifies. The solidifying metal
has a tendency for development of large grain size with highly
directional columnar dendrites, which are crystals that branch into
two or more parts during growth. In many alloys, this
solidification structure is undesirable due to formation of hot
tearing cracks resulting from inadequate liquid metal percolation
down the columnar dendrite interfaces and anisotropy due to closely
aligned grain crystallography. Even in the absence of hot tearing,
the large and highly directional grains can have detrimental
effects on mechanical properties of the fabricated structure.
[0004] As a result, there is a need for metal deposition methods
and systems that eliminate or reduce the large grain size and
dendrite formation and instead develop randomly oriented, equiaxed,
small grains, thereby improving mechanical properties of the
deposited metal.
SUMMARY
[0005] Systems and methods are disclosed herein to effectively
fracture dendrite arms shortly after their nucleation and growth in
a resolidifying metal melt pool. Advantageously, the present
invention prevents or hinders the growth of large columnar
dendrites and instead allows for the formation of a high density of
randomly oriented grains by nucleation and growth on the fractured
dendrite arms which are dispersed in the liquid metal, thereby
reducing grain size, enhancing the quality of the deposited metal,
and therefore improving the mechanical properties of the fabricated
structure.
[0006] In accordance with one embodiment of the present invention,
a system for enhancing the quality of deposited metal is provided,
the system including a metal deposition apparatus that provides
liquid metal on a substrate, and an ultrasonic energy source
operably coupled to the metal deposition apparatus such that
ultrasonic energy is applied to the solidifying metal at the
interface with the liquid metal.
[0007] In accordance with another embodiment of the present
invention, a method of enhancing the quality of deposited metal is
provided, the method including providing a liquid metal on a
substrate, applying ultrasonic energy to the solidifying metal in
the liquid metal, and solidifying the liquid metal with reduced
grain size.
[0008] In accordance with another embodiment of the present
invention, another method of enhancing the quality of deposited
metal is provided, the method including calculating a dendrite arm
fracture length and calculating a resonant frequency applicable for
the dendrite arm fracture length. The method further includes
providing a liquid metal on a substrate, and applying a tuned
ultrasonic energy to the solidifying metal in the liquid metal to
decrease grain size as the liquid metal solidifies.
[0009] The scope of the invention is defined by the claims, which
are incorporated into this section by reference. A more complete
understanding of embodiments of the present invention will be
afforded to those skilled in the art, as well as a realization of
additional advantages thereof, by a consideration of the following
detailed description of one or more embodiments. Reference will be
made to the appended sheets of drawings that will first be
described briefly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows a flowchart illustrating a method of metal
deposition in accordance with an embodiment of the present
invention.
[0011] FIG. 2 shows a flowchart illustrating another method of
metal deposition in accordance with an embodiment of the present
invention.
[0012] FIG. 3 shows a block diagram of a metal deposition system in
accordance with an embodiment of the present invention.
[0013] FIG. 4 shows a block diagram of another metal deposition
system in accordance with an embodiment of the present
invention.
[0014] FIG. 5 shows a block diagram of yet another metal deposition
system in accordance with an embodiment of the present
invention.
[0015] Embodiments of the present invention and their advantages
are best understood by referring to the detailed description that
follows. It should be appreciated that like reference numerals are
used to identify like elements illustrated in one or more of the
figures.
DETAILED DESCRIPTION
[0016] FIG. 1 shows a flowchart illustrating a method for improving
metal deposition in accordance with an embodiment of the present
invention. In operation 102, liquid metal is provided on a
substrate via various deposition systems and methods, including but
not limited to, Laser Engineered Net Shaping (LENS), Direct Metal
Deposition (DMD), and Electron Beam Melting (EBM). Then in
operation 104, ultrasonic energy is applied to the metal
growing/re-solidifying in the liquid metal pool in accordance with
the present invention. In one embodiment, ultrasonic energy is
provided to a substrate on which the metal is deposited and/or
directly to the liquid metal pool. In another embodiment,
ultrasonic energy is applied over a range of frequencies and/or
tuned to the resonant frequency of solidifying dendrite arms of a
specific, desired length. In yet another embodiment, ultrasonic
energy may be swept through a range of frequencies back and forth.
In operation 106, the metal is allowed to cool and solidify on the
substrate.
[0017] FIG. 2 shows a flowchart illustrating another method of
metal deposition in accordance with an embodiment of the present
invention. In this embodiment, ultrasonic energy is tuned to the
resonant frequency of solidifying dendrite arms of a specific,
desired length, for example on the order of about [0.1]-[1.0]
microns. The resulting resonant vibration of the dendrite arms will
rapidly build in amplitude until the dendrite arms are fractured.
The fractured dendrite arms then migrate randomly in the liquid
metal pool ahead of the original solidification front. As the
liquid metal pool continues to cool, a high density of fragmented,
randomly oriented, dendrite arm segments act as new solidification
nuclei. These nuclei promote growth of randomly oriented, equiaxed,
small grains on the order of about [10]-[100] microns. Continued
application of the ultrasonic vibration prevents growth of dendrite
arms beyond the critical resonant frequency length.
[0018] Referring to FIG. 2, in operation 202, a desired dendrite
arm fracture length may be calculated based on the solidification
behavior of each alloy. In operation 204, the resonant frequency of
the specific dendrite arm length may be calculated by known
physical relationships with the solid elastic moduli at the
solidification temperature, and the effect of the viscous liquid
metal surrounding the dendrite arms. Natural frequency also depends
on geometric information other than length of dendrite arms, such
as the shape of the arms (e.g., variation in cross-section area,
existence of branches). Other factors, such as impact with
vibrating fragments of broken dendrites suspended in the liquid,
may also be involved.
[0019] In operation 206, similar to operation 102 noted above,
liquid metal is provided on a substrate via various deposition
systems and methods, including but not limited to, LENS, DMD, and
EBM. Then in operation 208, the calculated resonant frequency may
be used to apply tuned ultrasonic energy to the metal melt pool in
accordance with an embodiment of the present invention. Because
many factors are involved in determining resonant frequency to
fragment the various dendrite arms and large grain sizes, and
accordingly resonant frequency may vary, a range of frequencies
centered around the calculated resonant frequency may be utilized
to fragment large grain size and dendrite arms in accordance with
another embodiment of the present invention. In a further example,
ultrasonic energy may be swept through the range of frequencies
centered about the calculated resonant frequency for a plurality of
cycles. In operation 210, the metal is then allowed to cool and
solidify on the substrate.
[0020] FIGS. 3-5 show block diagrams of different embodiments of a
metal deposition system in accordance with the present
invention.
[0021] FIG. 3 shows a metal deposition system 300 including an
ultrasonic energy source 302 that is operably coupled to a metal
deposition apparatus 304. Metal deposition apparatus 304 may
include various deposition systems, including but not limited to
LENS, DMD, and EBM systems. Ultrasonic energy source 302 is coupled
such that ultrasonic energy from ultrasonic energy source 302 may
be applied directly to a metal melt pool or a metal substrate on
which a metal melt pool is provided. p FIG. 4 shows a metal
deposition system 400 including an ultrasonic energy source 401
that provides ultrasonic energy to a solid substrate 402 on which a
liquid metal pool is provided. Advantageously, ultrasonic energy is
efficiently transferred from the substrate to the solidifying metal
to vibrate the growing dendrites and thereby fracture the dendrite
tips. The liquid metal may be considered a hindrance to the
effectiveness of the fracturing of dendrite tips by the ultrasonic
vibrations, since the liquid metal acts as an energy absorbing
medium. However, the present invention is effective despite the
viscous, energy absorbing nature of the liquid metal because the
liquid metal pool is sufficiently small (typically about 1 mm
radius) in these metal deposition processes. In one embodiment,
ultrasonic energy may be supplied by an electromechanical
transducer 404 coupled to the solid metal substrate below the
liquid metal pool. In other embodiments, ultrasonic energy may be
supplied by a pulsed laser 406 and/or an acoustic speaker 408.
Other ultrasonic energy sources may be applicable.
[0022] With the above system for injecting ultrasonic energy
directly to the dendrite tips via the solid metal substrate, an
embodiment of the present invention includes directing a primary
energy beam (e.g., a laser, an electron beam, or plasma) to develop
a very small liquid metal pool on the substrate surface. A
secondary, pulsed laser beam is also directed on to the substrate
surface in such a way as to impinge the surface close to the edge
of the liquid metal pool. The secondary laser beam may be pulsed at
a very high frequency to inject ultrasonic vibrations into the
solid substrate. The secondary pulsed laser is ideally directed to
impinge the solid substrate surface very close to the trailing edge
of the moving liquid metal pool. Alternatively, the secondary
pulsed laser can trace a ring constantly encircling the edge of the
moving liquid metal pool. This will have the effect of injecting
high frequency ultrasonic energy into the solid metal substrate
surface with most of the energy being directed towards the metal
dendrites growing in the liquid metal pool.
[0023] Advantageously, the present invention provides for
continuous, real-time fine adjustments of: 1) position and movement
relative to the primary energy beam and liquid metal pool; 2)
ultrasonic energy level and frequency; and 3) relatively simple
system hardware modifications.
[0024] Alternative systems and methods may be used to provide and
apply ultrasonic energy. FIG. 5 shows a metal deposition system 500
including an ultrasonic energy source 501 that provides ultrasonic
energy directly to the liquid metal pool 502 in accordance with an
embodiment of the present invention. In one example, the ultrasonic
energy may be generated and injected to the liquid metal pool by a
pulsed laser 506 with a very high peak energy which is pulsed at
the desired resonant frequency or range of frequencies. This pulsed
laser may be the same laser that is used to melt the substrate and
powder pool or it may be a secondary, pulsed laser to the primary
melting energy beam. In a second example, ultrasonic energy may be
applied with an electromechanical transducer 504 that moves with
and touches the solid substrate close to the liquid metal pool. In
another example, vibration may be transmitted through a filler wire
510 feeding directly to the metal pool. In yet another example,
acoustic vibration through a speaker 508 and/or induction through
magnet stirring may be used to apply ultrasonic energy.
[0025] The present invention may be utilized in a variety of
applications, including but not limited to manufacturing high
performance parts, adding features to existing components, and
precision repairing existing high value components. Furthermore, as
noted above, the present invention may be used in conjunction with
several metal deposition systems and methods driven by computer
aided design (CAD), such as LENS, DMD, or EBM.
[0026] Numerous modifications and variations are possible in
accordance with the present invention. The liquid metal may be
comprised of a variety of metals, including but not limited to
nickel, cobalt and iron-based superalloys, steels, copper,
aluminum, titanium, niobium, tungsten, molybdenum, rhenium, and
alloys thereof. The liquid metal may be provided from powder, wire,
or foil feedstock. The various metal deposition systems may also
incorporate the necessary and applicable structures to provide the
liquid metal on the substrate, such as mirrors, lenses, carrier
gases, movable tables, and controlled-environment chambers to name
a few. Any laser power used may vary greatly as well, from a few
hundred watts to 20 kW or more, depending on the particular
material, feed-rate, and other parameters.
[0027] Embodiments described above illustrate but do not limit the
invention. It should also be understood that numerous modifications
and variations are possible in accordance with the principles of
the present invention. Accordingly, the scope of the invention is
defined only by the following claims.
* * * * *