U.S. patent application number 16/065879 was filed with the patent office on 2019-01-10 for method for producing wall parts of a housing for pressure vessels.
The applicant listed for this patent is HYDAC TECHNOLOGY GMBH. Invention is credited to Herbert BALTES, Peter KLOFT.
Application Number | 20190009335 16/065879 |
Document ID | / |
Family ID | 56292656 |
Filed Date | 2019-01-10 |
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United States Patent
Application |
20190009335 |
Kind Code |
A1 |
KLOFT; Peter ; et
al. |
January 10, 2019 |
METHOD FOR PRODUCING WALL PARTS OF A HOUSING FOR PRESSURE
VESSELS
Abstract
The invention relates to a method for producing wall parts (24)
of a housing for pressure vessels by means of a 3-D printing
method, wherein material is applied layer-by-layer in order to form
each wall part (24). Said method is characterized in that, in case
of wall part geometries (28) that lead to distortions (44) that
impede the application of material, the layer thickness in the
application of material must be selected in such a way that the
particular distortion (44) is avoided and that the formation of
wall part geometries (28) that are critical in this respect is
performed without support parts.
Inventors: |
KLOFT; Peter;
(Ransbach-Baumbach, DE) ; BALTES; Herbert;
(Losheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HYDAC TECHNOLOGY GMBH |
Sulzbach/Saar |
|
DE |
|
|
Family ID: |
56292656 |
Appl. No.: |
16/065879 |
Filed: |
June 18, 2016 |
PCT Filed: |
June 18, 2016 |
PCT NO: |
PCT/EP2016/001042 |
371 Date: |
June 25, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F15B 2201/605 20130101;
B22F 2003/1057 20130101; F15B 2201/4056 20130101; Y02P 10/25
20151101; B23K 15/0086 20130101; B22F 3/1055 20130101; F17C 1/16
20130101; F15B 2201/405 20130101; B33Y 10/00 20141201; F15B 1/106
20130101; F17C 2203/066 20130101; F17C 2209/00 20130101; F17C 1/00
20130101; F17C 1/14 20130101; F17C 2203/0636 20130101; F17C
2209/2109 20130101; B22F 5/10 20130101; B33Y 80/00 20141201; F17C
2270/0554 20130101 |
International
Class: |
B22F 3/105 20060101
B22F003/105; B33Y 10/00 20060101 B33Y010/00; B33Y 80/00 20060101
B33Y080/00; F17C 1/00 20060101 F17C001/00; B23K 15/00 20060101
B23K015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 31, 2015 |
DE |
10 2015 017 026.0 |
Claims
1. A method for producing wall parts (24) of a housing (10) for
pressure vessels by means of a 3D printing method, wherein material
is applied layer-by-layer to form each wall part (24),
characterized in that in the case of wall part geometries (28),
which result in warping (44) which prevents the material
application, the layer thickness for the material application is
selected sufficiently large that the respective warping (44) is
prevented and that the formation of to this extent critical wall
part geometries (28) is realized free of support parts (40).
2. The method according to claim 1, characterized in that the
critical wall part geometry (28) during construction of the housing
(10) is formed from a layer (32) projecting in a pointed or
thin-walled manner in the direction of an inner wall (30) of same,
the layer thickness of which along the material application plane
(38) is selected larger than the previous layers in the
construction of the housing (10) with non-critical wall part
geometry.
3. The method according to claim 1, characterized in that the
respective pointed or thin-walled projecting layer (32) of the
critical wall part geometry (28) with its layer (32) in the region
of the projection encloses an overhang angle (a) relative to the
material application plane (38) of less than 30.degree., preferably
of less than 15.degree., particularly preferably of less than
5.degree..
4. The method according to claim 1, characterized in that the
respective warping (44) to be avoided in critical wall part
geometries (28) is formed by hardened material parts, which project
in the direction of the continuous, layer-by-layer material
build-up on the application side (46) and which constitute a
collision hazard for a material application tool (22), which is
used for the respective 3D printing method.
5. The method according to claim 1, characterized in that the wall
parts (24) on the inner side (30) of the finished housing (10) form
a spheroid, preferably in the form of a sphere.
6. The method according to claim 1, characterized in that it is
applied in the top third, preferably in the top sixth, in
particular before closure of the spheroid.
7. The method according to claim 1, characterized in that with the
contacting of the adjacent wall parts (24) with completion of the
spheroid on the inner wall side (30) of the housing (10) the layer
application takes place with a layer thickness as is selected at
the start of the material removal process with formation of the
wall parts (24).
8. The method according to claim 1, characterized in that but for
the region of at least one potential media connection point (14)
and/or at least one potentially present reinforcement part (18),
which is preferably arranged in the equatorial region (20) of the
spheroid on the outer wall of the housing (10), the material
thickness of the housing (10) is uniformly realized by means of the
material application.
9. The method according to claim 1, characterized in that as a 3D
printing method selective laser sintering, or electron beam melting
is used, and in that the metal powder used for this is selected
from the materials steel, stainless steel, aluminum, titanium,
nickel, etc. and mixtures thereof.
10. A pressure housing, in particular envisaged for a pressure
vessel in the form of a Helmholtz resonator, an air chamber or a
hydraulic accumulator, produced with a method according to claim 1,
characterized in that in a region above the equator (20), in
particular in a top polar cap region (34) of a spheroid formed from
the inner wall (30) of the housing (10), preferably in a spherical
shape, the material roughness of the inner wall (30) before any
remachining is greater than in the region below the equator (20),
in particular in the direction of a bottom polar cap region (42),
which is passed through by a media connection point (14).
11. The pressure housing according to claim 10, characterized in
that it is formed from one piece.
Description
[0001] The invention relates to a method for producing wall parts
of a housing for pressure vessels by means of a 3D printing method,
wherein material is applied layer-by-layer to form each wall
part.
[0002] Pressure vessels are commonly understood to be essentially
closed vessels, the internal pressure of which is higher than the
ambient pressure. Pressure vessels commonly include storage vessels
for gases and compressed air vessels and silos with compressed air
application as well as pressure storage vessels such as hydraulic
accumulators, membrane extension vessels, air chambers, Helmholtz
resonators, etc. According to the European legislation on free
movement of goods, there is considered to be a difference between
simple pressure vessels according to directive 2009/105/EC and
so-called pressure devices according to the pressure devices
directive 97/23/EC.
[0003] Hydraulic accumulators, which are also referred to as hydro
accumulators in technical parlance, essentially serve to store
pressure energy. In the case of the weight- and spring-loaded,
mechanical hydraulic accumulators, this occurs by means of a change
of potential energy, whereas the gas-loaded accumulators change the
internal energy of a working gas. Depending on the design of their
separating element with which different fluids can be separated
from one another inside the accumulator housing, there is
differentiation between membrane accumulators, piston accumulators,
bladder accumulators and bellows accumulators. The operation of
these accumulators is essentially based on utilizing the
compressibility of a gas for fluid accumulation. Nitrogen is
commonly used as the energy medium. If the hydraulic accumulator
has no separating element, it is usually an air chamber
construction which is known per se. In recent times such pressure
accumulators and their housings have also been used as Helmholtz
resonators in order to dampen or to smooth pulsing fluid vibrations
which occur in particular in hydraulic circuits and which can have
a damaging effect on hydraulic circuit-connected components, such
as for example valve assemblies, hydraulic working cylinders,
pressure monitoring devices and control devices, etc. In this way
any sounds which may occur even during operation of the hydraulic
circuit and which are disruptive are acoustically dampened.
[0004] The above-mentioned pressure vessels including the Helmholtz
resonators and any separating elements thereof can be produced in a
number of ways. In addition to a machining formation for the
respective accumulator housing, it may also be obtained by means of
casting. Pressure vessels which are produced using the so-called
composite construction are also used in order to thus obtain at the
same time as low material input costs a low construction weight
together with high structural strength for the accumulator. Thus
document DE 10 2014 008 649 A1 discloses a method for producing
such a pressure vessel, preferably in the form of a bladder
accumulator, in which firstly a supporting structure, in particular
in the form of a liner, is provided, to which a fiber material is
applied to form a base structure which, in turn introduced into a
heatable molding device, permits the introduction of a matrix
between the molding device and the base structure, which at least
partially penetrates the fiber material and, appropriately hardened
after removal of the accumulator housing, produces a bladder
accumulator.
[0005] This in principle very advantageous method, which leads to
accumulator housings with high compressive strength with a
particularly low construction weight, is disadvantageous to the
extent that for each accumulator type a separate molding device has
to be created, which thus increases the production costs
considerably. The hardening of the matrix in the heatable form also
requires production time, in addition to the energy costs for the
mold heating, in spite of the relatively short reaction times of a
reactive resin system for the matrix. In addition, the manual cost
for the handling of the molding device should not be
underestimated.
[0006] The priority-establishing document DE 10 2015 017 026 by the
same property right proprietor already proposed as an alternative
production method for pressure vessels to the above-described
production method the production of pressure vessels and
potentially the parts thereof at least partially by means of a 3D
printing method, so that machining work or a molding device such as
a molding tool to be heated can be entirely dispensed with. Instead
the accumulator housing of a pressure vessel together with its wall
parts or components of such pressure vessels, such as separating
elements, can be produced in a molding tool-free manner, which also
helps to significantly reduce the manual costs during production.
The technical term pressure vessel is to be understood in a broad
sense here and includes for example liner constructions, which are
subsequently reinforced preferably with fiber fabrics (composites)
or solutions which can be used as Helmholtz resonators.
[0007] By means of the afore-mentioned 3D printing method almost
all forms of pressure vessels and pressure accumulators can be
realized, and in fact in a free forming manner so that a number of
design options can be realized, with an accumulator housing thus
being able to be relatively freely adapted in a direct manner even
to specific installation conditions in situ, so that it is not
always necessary to resort to symmetrical accumulator housings of
pressure vessels.
[0008] In practical implementation of the method for producing wall
parts of a housing for pressure vessels by means of a 3D printing
method, wherein material is applied layer-by-layer to form each
wall part, it has however been found that in particular in the case
of wall part geometries which seem complicated, with which in
particular the so-called overhang angle relative to the respective
material application plane by means of the 3D printer becomes too
steep, material warping occurs which prevents the material
application of the printer.
[0009] In a known manner a 3D printer cannot print "in air", so
that it is common for support part materials to be used in the case
of self-supporting, projecting or forwards hanging elements, in
particular with a large overhang angle, which the 3D printer
preferably applies at the same time with a separate application
nozzle during the pressure operation for the creation of the actual
workpiece, here in the form of the housing for pressure vessels.
However there are also soluble support materials, which as a
separate component can help to support the 3D printing structure to
be created and which in the dissolved state can be removed again
from the structure. It surely goes without saying at this point
that said application and the removal of support material in the
context of the 3D printing method is associated with a
corresponding time and cost outlay, which negatively affects the
production time in the 3D printing method. The dissolved support
parts can also constitute an environmental problem when disposed
of.
[0010] However, if such support parts or support structures are
dispensed with in the case of sufficiently large overhang angles,
in particular in the case of the use of plastic materials as
printing material it may be the case that it drips downwards in the
direction of the overhang and destroys the desired print structure.
This likewise applies in the event that warping occurs on the top
side of the material application, for example bubble formation or
burr formation. In the case of a metal material application, in the
region of the free end of the respective last applied layer in the
direction of the overhang, solid, projecting, annular warping may
occur due to material stress during hardening, which in the
hardened state then creates a collision hazard for the application
nozzle of the 3D printer to be moved, which in the subsequent layer
application comes into direct contact with the warping of the wall
part geometry. In addition to the destruction of the wall part
geometry, the destruction of the application nozzle of the 3D
printer must also be expected.
[0011] On this basis, the invention addresses the problem of
providing an improved 3D printing method, with which in a
cost-efficient manner and with reduced time outlay even the
production of complex wall part geometries for pressure vessels of
any type whatsoever is possible, which in the manner outlined above
tends to results in warping due to the material usage. This problem
is solved by a method having the features of Claim 1 in its
entirety.
[0012] Because, according to the characterizing part of claim 1,
with wall part geometries of the housing which lead to warping
which prevents the material application, the layer thickness for
the material application is selected large enough that the
respective warping is avoided and that the formation of to this
extent critical wall part geometries is realized free of support
parts, in a surprising manner it is possible for the average person
skilled in the art of 3D printing methods, by means of targeted
layer-by-layer material application which is to be hardened, with
respect to the layer thickness, to design the 3D printing method in
terms of the operational sequence such that the warping during
hardening of the material which prevents the 3D material
application by means of the application nozzle cannot take place at
all. In a particularly advantageous manner this occurs in a
support-free manner, so that the support parts must not be produced
in a costly manner nor must they then also be removed. In
particular in the case of wall parts to be created, which include
cavities such as spheroids, a complete or residue-free removal of
the support part material cannot always be guaranteed, so that the
production method according to the invention has particular
application here.
[0013] Because in order to avoid the warping the layer thickness in
the material application is selected suitably large, and is for
example twice or five times the previous thin-layered application,
the material behavior in the thickened layer is homogenized and has
minimal stress or is stress-free and the occurrence of the
respective material stress which generates warping, in particular
during the cooling process or hardening process, is avoided in a
support part-free manner.
[0014] Depending on the complex wall part geometries to be created
it can be envisaged that, in addition to an initially thin layer
application in the critical warping zone in multiple layer
arrangement one on top of the other the thick layer application is
selected, which in turn in the transition towards wall part
geometries which must not be critically created is again reduced,
which assists with the compact and pressure-resistant construction
of the pressure vessel housing as a whole which is to be
constructed.
[0015] Additional advantageous embodiments of the method according
to the invention and the pressure vessels which can be produced
according to this method are the subject of the other dependent
claims.
[0016] The method according to the invention will be explained in
greater detail below with reference to the production of a pressure
vessel, in particular in the form of a Helmholtz vessel. The
drawings show in schematic and not to scale depictions:
[0017] FIGS. 1 and 2 once in a sectional depiction and once in a
top view an exemplary embodiment of a pressure vessel in the form
of an air chamber or Helmholt resonator;
[0018] FIGS. 3 to 5 in an enlarged depiction, a cutout circle
identified in FIG. 1 by an X, with FIGS. 3 and 4 presenting method
solutions according to the prior art and FIG. 5 relating to the
method solution according to the invention.
[0019] As 3D printing methods for producing pressure vessels and
the parts thereof, sinter- and powder printing methods,
stereolithography and printing with liquid components are in
principle suitable. All of the above-mentioned 3D printing methods
are also frequently used in so-called rapid prototyping.
[0020] When objects such as accumulator housings are to be
constructed exclusively from metal, the so-called electron beam
melting has proven to be suitable as a 3D printing method. In
electron beam melting metal powder is melted in layers and machined
as a housing wall. Likewise suitable is selective laser melting, in
which a metal powder is melted locally only. The use of selective
laser sintering is equally possible, in which a metal powder is
heated with a laser for a short time such that it melts, and it
then solidifies again with formation of the metal accumulator
housing. All of the above-mentioned 3D printing methods belong to
the category of sintering- and powder printing methods.
[0021] When the pressure vessel is to be printed using plastic
materials, printing with liquid plastic materials is an option. In
particular multi jet modeling has proven to be successful, which in
terms of its essential construction is very like conventional
inkjet printing. In this 3D printing method liquid plastic material
is applied from a nozzle, which can preferably move in several
directions, and as soon as the material emerges from the nozzle in
a forming manner it is appropriately hardened under an energy
source, for example in the form of UV light.
[0022] With the multi-jet modeling plastic materials in droplet
form with dimensions of a few picoliters are discharged, with the
spraying of the droplets preferably occurring in a
computer-controlled manner with a high clock frequency of for
example 2 kHz. Liquefied acrylates have proven to be particularly
suitable plastic materials, the viscosity of which can be adjusted
as desired by the addition of a reactive thinner. The hardenability
with UV radiation is preferably promoted by the addition of a
photoinitiator. In one example of a housing material the plastic
material contains as an acrylate material 90% Epecryl 4835, a
prepolymer produced by the company UCB, 8% HDDA (company UCB) as
reactive thinner for viscosity adjustment and 2% Darocur 1173,
produced by the company Ciba-Geigy, as a photoinitiator.
[0023] In another example, as housing material acrylate materials
90% Epecryl 4835 and 4% Epecryl 230 by the company UCB are
envisaged. As reactive thinner 4% HDDA by the company UCB and as
photoinitiator 2% Darocur 1173 by the company Ciba-Geigy are
contained in the material for the material removal or
application.
[0024] With the above plastic materials described in detail or
other suitable plastic materials accumulator housings 10 can be
constructed in the 3D printing method, as presented by way of an
example for a pressure vessel 12 in the form of an air chamber or a
Helmholtz resonator for pulsation dampening of fluids including
gases according to the depictions in FIGS. 1 and 2. A fluid
connection point 14 is integrally mounted on the accumulator
housing 10 at the bottom 1 end with a special connection geometry
for the purpose of connection of the pressure vessel 12 in a
conventional manner to a fluid supply circuit, in particular a gas
supply circuit. The accumulator housing 10 on the inside
essentially forms a spherical cross section, into which the fluid
connection point 14 enters in a media-conducting manner via a
central channel 16. The accumulator housing 10 has an essentially
constant wall diameter; but it is provided in the center with a
corresponding annular reinforcement 18 in the equatorial region
20.
[0025] Such pressure vessels 12 can also be printed by means of a
metal powder and are then entirely pressure resistant up to 350 bar
in this embodiment, with regular operating or working temperatures
of 40.degree. C. to 150.degree. C. The pressure vessel presented
here is preferably constructed from a metal material, namely
titanium Ti5Al64V. In addition to the terms already mentioned, such
pressure vessels are also referred to in technical parlance as
silencers.
[0026] Viewed in the viewing direction of FIGS. 1 and 2 the metal
3D printing material construction begins from the bottom end, in
other words, beginning at the free end of the fluid connection
point 14. With only one 3D printing production device with one or
more application nozzles 22 (cf. FIGS. 3 to 5) such a pressure
vessel 12 can be produced in all sizes, even with changed internal
cross section forms, for example as an oval or polygonal spheroid,
and various connection points (not depicted).
[0027] As disclosed in document DE 10 2015 017 026, with such 3D
printing methods other types of accumulators can also be produced,
which have corresponding separating elements in the accumulator,
such as membranes, bladders, pistons, etc., which can preferably be
printed together with the accumulator housing in one work process
(not depicted).
[0028] The following text will now describe in detail with
reference to FIGS. 3 to 5, how an accumulator housing construction
according to FIGS. 1 and 2 is obtained with a 3D printing method.
Because the pressure vessel 12 depicted in FIGS. 1 and 2 does not
always serve only to "store" fluids or other media, in the context
of the application the terms accumulator housing 10 and housing 10
are used synonymously.
[0029] In order to produce each wall part 24 for the housing 10 a
uniform material application takes place in layers 26 by means of
the material application nozzle 22 of the 3D printing device which
is otherwise not depicted in detail. The applied material is a
titanium material, which is particularly suitable for 3D printing.
For the layer-by-layer material removal, the nozzle 22 moves in the
depicted horizontal double arrow direction. The respective nozzle
22 can however also be moved in any other planes, and in particular
it is moved for the layer-by-layer material build-up by one layer
thickness in the axial direction continuously vertically upwards,
until the housing 10 is completely produced.
[0030] The material application shown in FIG. 3 contains a
so-called critical wall part geometry 28, which is obtained in
construction of the housing 10 from a layer 32 projecting in a
pointed manner or a thin-walled manner in the direction of an inner
wall 30 of same. Such critical wall part geometries 28 are in
particular produced when, as depicted in circle X in FIG. 1, the
accumulator 10 is completed in the direction of the top polar cap
region 34. The respective layer 32 projecting in a pointed manner
or a thin-walled manner of the critical wall part geometry 28 forms
with its layer 36 in the region of the projection 36 a notional
overhang angle a relative to the material application plane 38 of
approximately 8.degree.. If in accordance with the depiction of
FIG. 3 the layer-by-layer construction of the projection 36 and
thus the critical wall part geometry 28 of the inner wall 30 is now
in a conventional manner supported by a support part body 40, a
homogeneous layer construction is produced, including for the
topmost layer 32, by means of the application nozzle 22.
[0031] A comparison of FIG. 3 with FIG. 1 clearly shows that such
support part bodies 40, which are simultaneously generated by means
of their own application nozzle (not depicted) during the actual 3D
printing method by the production machine, cannot be easily removed
due to the narrowness of the channel 16 from the spherical interior
as a spheroid of the accumulator 10. Even in the case of chemical
dissolving of the support part body 40 residue remains on the inner
wall 30 of the housing 10, which has a damaging impact on
subsequent use, in particular in the context of a use as a
Helmholtz resonator. The residue also reduces the useable volume of
the pressure accumulator or housing 10. The removal of comparable
support parts or support part bodies (not depicted) at the external
circumference of the housing 10, in other words at the outer wall
in the bottom polar cap region 42 of the housing 10, is not
critical by comparison, because they can be easily removed from the
outer wall. Irrespective thereof, the mounting of such support
parts or support part bodies is however of course associated with
production costs, which would preferably be dispensed with.
[0032] If the support part body 40 is simply omitted according to
the depiction of FIG. 4, due to material stress, in particular
during cooling, an upwards projecting material warping 44 often
appears on the inner wall side of the housing 10, in particular
when a metal material application takes place, and as soon as this
warping 44 to be avoided, formed from the projection 36, is
hardened, it forms projecting on the application side 46 of the
nozzle 22 a collision hazard for this material application tool 22,
which in the case of the collision can lead to its destruction and
to the destruction of the sought wall part geometry 28.
[0033] It is now surprising for the average person skilled in the
art of production of housings and accumulator housings using 3D
printing methods, that he can avoid such projecting warping 44 on
the application side 46 of the material application if he, in
accordance with the schematic depiction of FIG. 5, enlarges the
last applied layer in terms of the layer thickness such that the
warping 44 no longer occurs, which is associated with the largely
stress-free material cooling behavior of the metal application
material. Preferably, the material application in the region of the
critical wall part geometry 28 is selected larger by the factor 1.5
to 5 compared with a conventional layer thickness, with the
enlarged layer thickness being selected depending on the critical
wall part geometry 28 to be formed such that the warping 44
commonly in the form of a closed protrusion ring does not occur
during printing. This makes it possible to also produce critical
wall part geometries on the outer side of the accumulator 10, as
increasingly occur in the bottom polar cap region 42, from the
outer wall side in a warping-free and support part-free manner.
[0034] It has been demonstrated that with a thus produced
accumulator or pressure housing 10 in particular in the top polar
cap region 34 with the critical wall part geometries 28 due to the
enlarged layer thickness a certain amount of material roughness
occurs on the inner wall 30 of the housing 10. If one leaves the
material roughness on said inner wall side of the accumulator 10,
this proves to be advantageous for obtaining an improved vibration
damping, because the projecting material parts of the material
roughness help to prevent sound reflection and divert it into the
wall structure of the housing 10.
[0035] The housing 10 produced using 3D printing can also be formed
as a liner, which can be wrapped in a fiber fabric (not depicted)
for the purpose of completion and reinforcement. As a separating
element, for example in the form of a metal bellows membrane, it
can also be produced using the 3D printing method together with the
production of the accumulator housing 10.
* * * * *