U.S. patent application number 14/350335 was filed with the patent office on 2014-12-04 for riblet foil and method for producing same.
The applicant listed for this patent is EADS Deutschland GmbH. Invention is credited to Franz Gammel, Oliver Rohr.
Application Number | 20140356219 14/350335 |
Document ID | / |
Family ID | 47115087 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140356219 |
Kind Code |
A1 |
Gammel; Franz ; et
al. |
December 4, 2014 |
Riblet Foil and Method for Producing Same
Abstract
A method for producing a layer-type buildup of riblet foil
involves applying a metal powder is to a reference mold, which has
a female mold of a riblet structure, in such a manner that a
metallic material is formed. The layered portion applied in this
manner is then detached, thereby forming a riblet foil having a
riblet structure.
Inventors: |
Gammel; Franz; (Ottobrunn,
DE) ; Rohr; Oliver; (Ottobrunn, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EADS Deutschland GmbH |
Ottobrunn |
|
DE |
|
|
Family ID: |
47115087 |
Appl. No.: |
14/350335 |
Filed: |
October 2, 2012 |
PCT Filed: |
October 2, 2012 |
PCT NO: |
PCT/DE2012/000960 |
371 Date: |
August 19, 2014 |
Current U.S.
Class: |
419/66 |
Current CPC
Class: |
B22F 7/02 20130101; B22F
3/18 20130101; B22F 3/115 20130101; B22F 3/00 20130101 |
Class at
Publication: |
419/66 |
International
Class: |
B22F 3/00 20060101
B22F003/00; B22F 3/18 20060101 B22F003/18; B22F 3/115 20060101
B22F003/115 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2011 |
DE |
10 2011 114 832.2 |
Claims
1-9. (canceled)
10. A method for producing a metallic riblet foil by a layer-type
buildup by implementing the following steps at least once, the
method comprising the steps of: providing a reference mold having a
structure at least on one area corresponding to a female mold of at
least one riblet structure; applying at least one layered portion
made of a metal powder onto at least one area of the reference mold
in such a manner that the at least one layered portion combines
into a metal material; and detaching the at least one layered
portion from the reference mold, which forms the metal riblet foil
having a riblet structure at least on one area thereof.
11. The method of claim 10, wherein the application of the at least
one layered portion is achieved by spraying on a metal powder.
12. The method of claim 10, wherein the at least one layered
portion comprises a first layered portion of a metal powder
comprising titanium or alloys of titanium, and a second layered
portion of a metal powder comprising aluminum or alloys of
aluminum.
13. The method of claim 10, wherein a thickness of the at least one
layered portion is variable.
14. The method of claim 10, wherein the reference mold is
reusable.
15. The method of claim 10, wherein the reference mold is
configured as a roller.
16. The method of claim 15, wherein the at least one layered
portion is adjustable by controlling a rotational speed of the
roller.
17. The method of claim 10, wherein a surface of the metallic
riblet foil is at least partially refined.
Description
FIELD OF THE INVENTION
[0001] Exemplary embodiments of the present invention relate to a
riblet foil and to a method for producing same. In particular, the
riblet foil is made of metallic material and composed by way of
layering said material onto a reference mold. The riblet foil has a
riblet structure that reduces air resistance.
BACKGROUND OF THE INVENTION
[0002] Lowering fuel consumption and reducing carbon
dioxide/nitrogen oxide (CO.sub.2/NOx) emissions are important
objectives to be met, particularly by the aviation and automotive
industries. Aside from light construction modalities to achieve
weight reductions and improvements to the efficiency of the drive
systems, reducing air resistance constitutes one essential
component in achieving these goals.
[0003] Methods for producing surfaces that reduce the resistance to
air flow are known in the art. It has been known for a long time,
and, moreover, it has been proven in oil channel experiments, that,
by providing solid surfaces with suitable structures, it is
possible to reduce the drag of liquid or gaseous media flowing over
such solid surfaces. The structure or texture of the solid surface
therein can come in different forms and sizes. Bechert, D. W. et
al, Experiments on drag-reducing surfaces and their optimization
with adjustable geometry, Journal of Fluid Mechanics, Vol. 338, pp.
59-97, 1997 teach gluing a structured plastic foil onto bodies.
[0004] Relying on this information, aviation companies, such as
Airbus and Boeing, conducted experiments with plastic foils made by
3M that had corresponding structures disposed thereupon, and which
were then glued to the exterior surfaces of an aircraft. In flight
experiments with a large aircraft that had 70% of the surface
thereof covered with such glued-on plastic foil, it was possible to
document a 2% drag reduction (Szodruch J., Dziomba, B., Aircraft
Drag Reduction Technologies, 29th Aerospace Science Meeting, Reno,
Nevada, Jan. 7-10, 1991). This resulted in fuel savings of 1.5%
(Roberts J. P., Drag Reduction: An Industrial Challenge, Special
Course on Skin Friction Drag Reduction, AGARD Report 786,
1992).
[0005] However, structured plastic foils that have been used to
date lack mechanical durability and suffer from degradation of the
plastic foil as well as of the glue by which these foils are to
adhere to the aircraft. One consequence of the lack of mechanical
durability is, for example, a rounding of the tip radii in
saw-tooth-shaped structures, which can completely neutralize the
friction-lowering effect (Hage, W., Zur Widerstandsverminderung von
dreidimensionalen Ribletstrukturen und anderer Oberflachen
[Regarding Drag Reduction of Three-dimensional Riblet Structures
and other Surfaces], Dissertation Technical University of Berlin
2004). Degradation effects can even cause the plastic foils to
become detached while in operation.
[0006] An as of yet unpublished patent application by the applicant
offers a description specifying that, with the use of structured or
textured metal foils, for example on a structural component of an
aircraft or helicopter, it is possible to achieve a considerable
reduction in the resistance to air flow. To this end, the structure
of the metal foil includes riblets, which are microscopically small
grooves in the surface of the metal foil. Such textured metal foils
will be referred to below as "riblet foils." The mechanical
resistance of riblet foils is greater than that of plastic foils.
Using riblet foils on fiber-reinforced plastic structures
simultaneously provides electric conductivity for lightning
protection.
[0007] German patent document DE 10314373A1 discloses a
precision-casting method for the production of the structured metal
foils that is involved in the production of turbine vanes made of
titanium aluminums (TiAl) having textured surfaces. Applying the
structure to the metallic surfaces is also possible by laser
processing or a grinding process, known in the art based on the
description in, for example, in Oehlert et. al., Exploratory
Experiments on Machined Riblets for 2-D Compressor Blades,
Proceeding[s] of IMECE2007, 2007 ASME Internation[al] Mechanical
Engineering Congress and Exposition, Nov. 11-15, 2007, Seattle,
Wash., United States.
[0008] However, such a direct application of a structure or texture
by means of casting method or by removal-machining methods
(structure generation by a laser or micro-milling means, etc.) does
not make technical or economic sense for use on the large areas, as
are required on aircraft, helicopters or other flying devices.
[0009] On the other hand, manufacturing methods for producing the
required quantity and/or size of riblet foils are known in the art,
where metal foils are structured/textured by mechanical processing.
For example, these are mechanical (re)shaping methods, such as
rolling (including incremental methods, such as incremental
rolling) or stamping.
[0010] To create sharp-edged structures on the metallic foil, it is
necessary for the used tools, such as, for example, the rollers, to
pressed against the foil with a high pressure. Tools such as this
are usually formed of a solid full body, such as, for example, a
steel body. Moreover, such tools must be manufactured of a
corresponding material, if it is necessary, for example, to work at
elevated temperatures to modify the metallic foil by means of a
plastic deformation, and thereby creating a riblet foil.
High-strength materials, such as, for example, titanium alloys with
tensile strength values of up to 1700 MPa, can no longer be
sufficiently plasticized by the application of a deformation
pressure, whereby the riblet structure cannot be achieved at all,
or only coarsely, on the metal foil.
[0011] Therefore, exemplary embodiments of the present invention
provide a riblet foil and a method for manufacturing the same that
overcomes the disadvantages of the prior art, that is
cost-effective and involves minimal technical complexity in terms
of use.
SUMMARY OF THE INVENTION
[0012] Exemplary embodiments of the present invention are directed
to providing a simple method for producing metallic riblet foils,
wherein the mechanical and functional properties of the riblet foil
can be adapted to the requirements of the respective application by
a suitable selection from among the most varied metals and/or
metallic alloys. The riblet foil is produced by the buildup of a
layered structure onto a reference mold and then detached from the
same. The reference mold includes at least on one surface a
structure that is a female mold of the at least one riblet texture.
The female mold includes indentations of microscopic size in the
surface of the reference mold. After detaching the reference mold,
riblets remain behind as microscopically small elevations/tips on
the formed riblet foil. The riblets can be formed on the totality
of the riblet foil or in selected partial areas. The surface of the
reference mold is textured correspondingly.
[0013] In other words, the present invention provides,
independently of the required size, form or properties of the
riblet foil, a simple method that allows for producing a riblet
foil having a desired form, size as well as any desired properties
from any metallic powder. The thickness of the riblet foil itself,
as well as the size and shape of the riblets, are variably
producible using the method according to the invention.
Advantageously, the thickness of the riblet foil is less than 500
.mu.m; especially advantageously, the thickness is between 50-400
.mu.m, particularly at least 200 .mu.m. The thickness of the riblet
foil ensures that the foil easily adjusts itself to the respective
structural component to which it is applied, while having a
minimally possible weight.
[0014] The invention involves a method for producing a riblet foil,
wherein the riblet foil is composed in layers. A reference mold has
a structure/texture at least on one surface, which corresponds to a
female mold of at least one riblet structure. At least one layered
section comprised of a metallic powder is applied in such a manner
to this area that a metallic material is formed. The application of
further layered portions of metallic powder in a vertical or
horizontal direction onto the surface of the reference mold can be
repeated as often as desired. The at least one layered portion thus
obtained is detached from the reference mold, and whereby the
metallic riblet foil is formed. The same has a riblet structure at
least on one surface.
[0015] The metal or metal alloy powder comprises at least all light
metals in the main groups and sub-groups of the periodic system; in
particular, aluminum or titanium and mixtures thereof, wherein it
is also possible for reinforcing particles to be mixed in with the
metal/metal alloy powder, as well as hard metals. The hard metals
comprise at least one compound material that is part of a
reinforcement phase, such as tungsten carbide (WC), and a matrix or
binder, such as cobalt. It is understood that the metals also
comprise metallic alloys that contain at least one of the mentioned
metals, including copper, zinc, lithium, beryllium, scandium,
vanadium or yttrium, and, in particular, also steel alloys;
preferred are titanium/titanium alloys or steel alloys, in
particular aluminum/aluminum alloys.
[0016] The reference mold can be made of a wide variety of
materials. Preferred is a reference mold, or surface that has the
mentioned structure/texture, which is formed of materials having a
high durability and that demonstrate very low wear and tear, such
as, for example, steel X45NiCrMo4, that is known from use in
stamping and shaping tools and has good polishing properties.
[0017] The area of the reference form comprises a structure
corresponding to a female mold of at least one riblet structure,
which is formed by a plurality of trapezoid, semi-circular,
streamlined and/or saw-tooth-shaped riblets or a combination
thereof. The female molds of the riblets comprise a size range with
a riblet width of approximately 20 .mu.m to 130 .mu.m, preferably
30 .mu.m to 80 .mu.m, particularly 50 .mu.m to 60 .mu.m, especially
60 .mu.m. At least one female mold of a riblet has a height that is
half the distance to the next adjacent riblet thereto.
[0018] The application of the layered portion to the area of the
reference mold is achieved in layers. It is possible to apply one
or a plurality of layers in succession of the same metal powder or
of different metal powders. Advantageously, the first layered
portion that is applied can be a layer of titanium powder (or
titanium alloy powder), and the remaining layered portions are of
aluminum powder. The thus formed riblet foil has very robust,
durable riblets and a base that can be produced cheaply from
aluminum. Moreover, the person skilled in the art can provide the
aluminum, using methods that are known in the art, such as
anodizing, with a surface that is ideally suited for the gluing
action.
[0019] The properties of the textured surface, in particular good
polishing characteristics, facilitate the easy detachment of the
one or more applied layered portion(s) from the reference mold.
[0020] The metallic powder is preferably applied to the reference
mold by a spray-on method. For example, the metallic powder is
applied in layers by a cold gas spray process, a thermo-kinetic
application process (for example, Flamecon.RTM. by Leoni), a
plasma-supported application process (for example, Plasmadust.RTM.
by Reinhausen Plasma) or known thermal spray application processes,
such as a powder process, a plasma spray process or a High Velocity
Oxygen Fuel (HVOF) process. These processes allow for creation of
textured structures having .mu.m-geometries. The formed riblet
structures comprise a size range with riblet widths of
approximately 20 .mu.m to 130 .mu.m, preferably 30 .mu.m to 80
.mu.m, particularly 50 .mu.m to 60 .mu.m. The height of the riblet
comprises a range of 50-100% of the riblet width. The riblet height
can also be equal to the riblet width, or it can comprise a
combination from the indicated range of sizes. The structure of the
female mold is formed correspondingly on the reference mold.
[0021] When building up at least one layered portion by a spray-on
process, the metal powder is accelerated, with high energy, toward
the surface of the reference mold. Upon colliding with the surface,
the metallic particles become connected to one another, due to a
plastic deformation or cold welding process, thus forming a
metallic material. During the cold-welding process, a heated gas is
accelerated for this purpose, and the metallic powder is injected
into the gas jet, thereby accelerated. During plasma spray
processes, as an example for thermal spray methods, a light arc is
generated between the cathode and anode of the plasma burner,
either under a normal or inert atmosphere or in a vacuum. The gas
flowing through the plasma burner is directed through the light arc
and ionized. The metallic powder is jet-sprayed into this heated
gas, then molten/plasticized due to the high plasma temperature.
The plasma flow accelerates the metallic particles in the direction
of the area of the reference mold. After colliding with the
reference mold, the metallic particles combine into a dense,
solidly adhesive layer due to plastic deformation and/or cold
welding and/or solidifying.
[0022] Spraying on the at least one layered portion has the
advantage that a much higher precipitation rate can be achieved on
the reference mold than, as compared to, for example, galvanic
deposition processes according to the prior art. Aside from the
economic profitability in terms of production, this process also
allows, in particular, for the generation of large riblet foils
that can be applied to the wings of aircraft, such as the wings of
an A380 model that is built by Airbus Operations GmbH. Moreover, it
is possible to select almost any conceivable metallic powder,
wherein the grain sizes can vary and the size of the riblet
structure can be selected correspondingly ranging from only very
few nm to several hundred .mu.m.
[0023] The at least one layered portion can have a differing
thicknesses. The thickness of the layer can be variable; for
example, the edge regions can be thicker or thinner than the center
region of the layered portion. It is also possible to form the
totality of the layered portion as having a substantially constant
thickness.
[0024] The reference mold can be disposable or envisioned for
several uses. A reusable reference mold is cost-effective and can
be employed in the production of riblet foils of different metallic
powders, wherein the riblet structures are identical.
[0025] In a further embodiment, the reference mold is configured as
a roller. This facilitates a continuous production of the riblet
foil according to the invention.
[0026] Advantageously, the thickness of the riblet foil is
adjustable by means of the rotational speed of the roller. When the
rotational speed is low, thicknesses of, for example, 400 .mu.m are
achieved. When, on the other hand, the riblet foil is to be thin,
for example 200 .mu.m, the rotational speed of the roller is simply
increased. This way, regulating the thickness of the riblet foil is
facilitated by simple means.
[0027] The metallic riblet foil can be refined, at least in part.
This process comprises, for example, an adhesive coating that is
applied to the back side, functionalization of the surfaces by way
of a coating or modification of the surface, thereby providing the
same with fastness properties against contamination or icing.
BRIEF DESCRIPTION OF THE FIGURES
[0028] The invention will be described below in an exemplary manner
based on the embodiments that are depicted in the figures. For
better clarity, the embodiments are not drawn to scale.
[0029] FIG. 1a shows the production of a riblet foil according to a
first embodiment;
[0030] FIG. 1b shows the detached riblet foil with a trapezoid
riblet structure;
[0031] FIG. 2 depicts the production of the riblet foil according
to a second embodiment.
EMBODIMENTS OF THE INVENTION
[0032] FIG. 1a is a sketch-type depiction of a riblet foil. A
reference mold 11 includes an area 12 and a riblet structure 13.
Using a coater system 16, metallic particles 15 of a metallic
powder are accelerated to a high speed in the direction toward the
area 12. Due to the impact, the metallic particles 15 become
deformed and combine to form a metallic material. A continuous
spraying action of metallic particles 15 against the area 12
results in a layer-type buildup of a layered portion 14. When the
thickness of the layered portion 14 has reached the thickness that
is required for the application the spray-on action of metal powder
is complete.
[0033] In this embodiment, the coater system 16 is a system for
cold gas spraying. A carrier gas is compressed and accelerated by
relaxation of the same inside a nozzle to a speed that is below the
speed of sound of the carrier gas. The metallic powder is injected
into the gas jet. The carrier gas has a temperature that is below
the temperature at which the metallic particles 15 melt, such that
these particles do not, in fact, melt. The metallic particles 15
become deformed upon colliding with the area 14, wherein the thus
resulting localized heat release ensures the cohesion and adhesion
needed, and thus forming the layered portion 14, whereby a metallic
material is formed.
[0034] FIG. 1b shows the now detached riblet foil having a
trapezoid riblet structure.
[0035] The riblet foil 10 has a base 18 and a riblet structure 17
with trapezoid riblets. The reference mold 11 is reusable in the
production of a further metallic riblet foil 10.
[0036] FIG. 2 shows the production of a riblet foil using a roller
11 as reference mold. On the area 12, the roller 11 includes a
female mold of a riblet structure 13, which has been omitted in the
drawing for better clarity.
[0037] Using the coater system 16, metallic particles 15 are
accelerated to high speeds, as described previously in connection
with FIG. 1, and collide in a high kinetic energy state with the
area 12 of the roller 11. Due to the plastic deformation of the
metallic particles 15 and cold welding, the metallic particles 15
are combined into a dense layered portion 14, thereby forming a
metallic material.
[0038] The rotational speed of the roller 11 determines the
thickness of the layered portion 14. At a low rotational speed of
the roller 11, the metallic particles 15 encounter a previously
formed layer, thereby creating an overall greater thickness of the
layered portion 14. The thickness of the layered portion 14 depends
on several factors, such as, for example, the circumference of the
roller 11 and the speed of the coater system relative to the roller
11.
[0039] When the rotation of the roller 11 is continuous, and the
metallic powder is sprayed on continuously by means of the coater
system 16, a continuous layered portion 14 is produced. This
portion is taken up by the unwinding roller 19 and detached from
the roller 11 by the rotation of unwinding roller 19 against the
direction of rotation of the roller 11.
[0040] The continuous riblet foil 10 has a base 18 and a riblet
structure 17, which have been omitted from FIG. 2 for better
clarity and which are comparable to the riblet structure 17 as
illustrated in FIG. 1b.
[0041] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
LIST OF REFERENCE SIGNS
[0042] 10 Riblet foil [0043] 11 Reference mold, roller [0044] 12
Area [0045] 13 Riblet structure [0046] 14 Layered portion [0047] 15
Metallic particle [0048] 16 Coater system [0049] 17 Riblet
structure [0050] 18 Base [0051] 19 Unwinding roller
* * * * *