U.S. patent application number 15/300851 was filed with the patent office on 2017-01-26 for method for producing a hollow body by cold spraying and mould core suitable for carrying out said method.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is Siemens Aktiengesellschaft. Invention is credited to Axel Arndt, Uwe Pyritz, Ralph Reiche, Oliver Stier.
Application Number | 20170022615 15/300851 |
Document ID | / |
Family ID | 52829062 |
Filed Date | 2017-01-26 |
United States Patent
Application |
20170022615 |
Kind Code |
A1 |
Arndt; Axel ; et
al. |
January 26, 2017 |
Method For Producing A Hollow Body By Cold Spraying And Mould Core
Suitable For Carrying Out Said Method
Abstract
A method is disclosed for producing a hollow body by cold
spraying. A mold core is used for producing the hollow body, the
mold core being prepared for the production of the hollow body by
cold spraying in a suitable manner by means of an auxiliary layer.
The auxiliary layer may include or consist of a metallic material
and therefore forms a suitable surface to which the particles
processed by cold spraying remain adhered to form the hollow body.
The mold core can therefore be produced from an inexpensive
material such as sand or wood, although said materials are in
principle have limited suitability for depositing metals by cold
spraying. The auxiliary layer can be applied to the mold core as a
foil, or be produced on the mold core by cold-spraying low-melting
and/or soft materials, for example.
Inventors: |
Arndt; Axel; (Berlin,
DE) ; Pyritz; Uwe; (Berlin, DE) ; Reiche;
Ralph; (Berlin, DE) ; Stier; Oliver; (Berlin,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siemens Aktiengesellschaft |
Muenchen |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Muenchen
DE
|
Family ID: |
52829062 |
Appl. No.: |
15/300851 |
Filed: |
March 18, 2015 |
PCT Filed: |
March 18, 2015 |
PCT NO: |
PCT/EP2015/055611 |
371 Date: |
September 30, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 28/027 20130101;
C23C 28/023 20130101; C23C 28/021 20130101; C23C 28/025 20130101;
B22F 2005/103 20130101; C23C 24/04 20130101 |
International
Class: |
C23C 24/04 20060101
C23C024/04; C23C 28/02 20060101 C23C028/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2014 |
DE |
10 2014 206 073.7 |
Claims
1. A method comprising, in the following order: forming a starting
coat on a mold core, wherein the auxiliary layer is metallic or
contains predominantly metallic components, coating the mold core
using a cold spraying process to produce a hollow body, removing
the mold core from the hollow body, and removing the starting coat
from the hollow body.
2. The method of claim 1, wherein the starting coat has a different
material composition than the hollow body.
3. The method of claim 1, wherein the starting coat comprises an
aluminum foil.
4. The method of claim 3, comprising adhesively bonding the
aluminum foil onto the mold core.
5. The method of claim 1, wherein the starting coat is formed on
the mold core by low-pressure gas dynamic spraying of a metallic
material.
6. The method of claim 5, wherein the metallic material comprises
one or more of zinc, tin, lead, aluminum, copper, silver, or gold,
or an alloy of zinc, tin, lead, aluminum, copper, silver, or
gold.
7. The method of claim 6, wherein the starting coat has a
multilayer design including multiple auxiliary layers, wherein
forming the starting coat comprises forming multiple auxiliary
layers of increasingly harder and/or higher-melting metallic
materials.
8. The method of claim 7, wherein the starting coat is produced by
forming two auxiliary layers comprising: a base layer lying on the
mold core and composed of zinc, tin or lead, or a metal alloy based
on zinc, tin, or lead, and a top layer formed over the base layer
and composed of zinc, aluminum, copper, silver, or gold, or a metal
alloy based on zinc, aluminum, copper, silver, or gold.
9. The method of claim 1, wherein the mold core is produced from
wood, plastic, metal, or bonded sand.
10. A mold core, comprising: a surface suitable as a substrate for
cold spraying, wherein the surface is formed by at least one
auxiliary layer composed of a metallic material, which forms a
starting coat on the mold core.
11. The mold core of claim 10, wherein said mold core consists of
bonded sand, wood, metal, or plastic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. National Stage application of
International Application No. PCT/EP2015/055611 filed Mar. 18,
2015, which designates the United States of America, and claims
priority to DE Application No. 10 2014 206 073.7 filed Mar. 31,
2014, the contents of which are hereby incorporated by reference in
their entirety.
TECHNICAL FIELD
[0002] The invention relates to a method for producing a hollow
body. In this method, the hollow body is produced by coating a mold
core by cold spraying. In other words, the coat produced on the
mold core forms the hollow body to be produced. After the
production of this hollow body, the mold core is removed from the
latter. Moreover, the invention relates to a mold core having a
surface suitable as a substrate for cold spraying. The surface must
be suitable for cold spraying to the extent that the particles that
are accelerated to the surface of the mold core by means of the
cold gas jet must adhere to it.
BACKGROUND
[0003] Cold spraying is a method known per se, in which particles
provided for coating are accelerated, preferably to supersonic
speed, by means of a convergent-divergent nozzle to ensure that
they adhere to the surface to be coated by virtue of their kinetic
energy impressed upon them. In this process, use is made of the
kinetic energy of the particles, which leads to plastic deformation
of said particles, wherein the coating particles are fused only at
the surface thereof upon impact. This method is referred to as cold
spraying, in comparison with other thermal spraying methods,
because it is carried out at relatively low temperatures, at which
the coating particles remain substantially solid. For cold
spraying, which can also be referred to as kinetic spraying, use is
preferably made of a cold spraying system which has a gas heating
device for heating a gas. Connected to the gas heating device is a
stagnation chamber, which is connected on the outlet side to the
convergent-divergent nozzle, preferably a Laval nozzle.
Convergent-divergent nozzles have a tapering segment and a widening
segment, which are connected by a nozzle throat. On the outlet
side, the convergent-divergent nozzle produces a powder jet in the
form of a gas stream containing particles traveling at high speed,
preferably supersonic speed.
[0004] A method for producing a hollow body of the type stated at
the outset is known from DE 10 2010 060 362 A1. Accordingly, cold
spraying can be used to produce a tube on a cylindrical mold. In
this case, the cold gas jet is angled relative to the surface of
the cylinder to such an extent that the particles primarily adhere
to the tube that is in production. The cylindrical mold core can
therefore be removed from the tube after the production of the
latter. This is possible because of the typical geometry of tubes
which are free from internal undercuts, thus allowing the
cylindrical former to slide along the inner walls of the tube.
However, it is not possible to produce hollow bodies with more
complex geometries in this way.
SUMMARY
[0005] One embodiment provides a method for producing a hollow
body, in which the hollow body is produced by coating a mold core
by cold spraying, and the mold core is removed from the hollow body
after the production thereof, wherein the mold core is provided
with an auxiliary layer before the production of the hollow body,
wherein the material of the auxiliary layer is metallic or contains
at least predominantly metallic components, and the auxiliary layer
is removed from the hollow body after the removal of the mold core
from the mold.
[0006] In one embodiment, the material of the auxiliary layer
differs in composition from the material of the hollow body.
[0007] In one embodiment, the auxiliary layer is formed by a metal
foil, in particular an aluminum foil.
[0008] In one embodiment, the metal foil is bonded adhesively onto
the mold core.
[0009] In one embodiment, the at least one auxiliary layer is
produced as a starting coat on the former by cold spraying, in
particular by low-pressure gas dynamic spraying, of a metallic
material.
[0010] In one embodiment, metallic materials having a ductile
material behavior, in particular one or more of the metals or metal
alloys based on the metals zinc, tin, lead, aluminum, copper,
silver and gold, are deposited.
[0011] In one embodiment, the starting coat is of multilayer
design, wherein, in the production sequence, the auxiliary layers
are produced using increasingly harder and/or higher-melting
metallic materials.
[0012] In one embodiment, the starting coat is produced in two
layers comprising a base layer lying on the mold core and composed
of one of the metals or metal alloy based on the metals zinc, tin
and lead, and comprising a top layer following thereon and composed
of one of the metals or metal alloy based on the metals zinc,
aluminum, copper, silver and gold.
[0013] In one embodiment, the mold core is produced from wood,
plastic, metal or bonded sand.
[0014] Another embodiment provides a mold core having a surface
suitable as a substrate for cold spraying, wherein the surface is
formed by at least one auxiliary layer composed of a metallic
material, which forms a starting coat on the material of the mold
core.
[0015] In one embodiment, said core consists of bonded sand, wood,
metal or plastic.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Examples aspects and embodiments of the invention are
described below with reference to the drawings, in which:
[0017] FIG. 1 shows an illustrative embodiment of the method
according to the invention, which is performed in a cold spraying
system,
[0018] FIGS. 2 and 3 show illustrative embodiments of the mold core
in section, according to one embodiment, and
[0019] FIG. 4 shows the detail IV as illustrated in FIG. 3.
DETAILED DESCRIPTION
[0020] Embodiments of the invention provide a method for producing
a hollow body by means of cold spraying, by means of which it is
possible to produce even hollow bodies of complex geometry. Other
embodiments provide a mold core, or "former," which can be used in
such method.
[0021] In some embodiments of the method, the mold core is provided
with an auxiliary layer before the production of the hollow body.
The material of this auxiliary layer may be metallic or contains at
least predominantly metallic components. This means that the
auxiliary layer can provide a metallic matrix into which
nonmetallic inclusions can be embedded. Such a layer nevertheless
behaves substantially like a metal. The inclusions can be particles
of a dry lubricant, for example, in order to facilitate removal of
a core from the mold. The material of the auxiliary layer
preferably has a different composition from the material from which
the hollow body is to be produced. This advantageously allows
optimum adaptation of the material which forms the surface for
coating with the material of the hollow body to the requirements of
a substrate for cold spraying. On the one hand, this material must
be sufficiently ductile to ensure that the particles from the cold
gas jet adhere to the surface of the mold core. Moreover, this
material must be sufficiently temperature-stable, and, under some
circumstances, allowance must be made for preheating the gas used
to form the cold gas jet. In this process, the temperatures reached
in the impact flow that forms ahead of the mold core can be
approximately the same as those of the carrier gas in the
stagnation chamber arranged upstream of the cold spraying nozzle.
One other necessary property of the surface of the mold core is
resistance to the erosive effect of the impinging particles. If
this surface is mechanically too unstable, it does not offer
sufficient resistance to the impinging particles of the cold gas
jet, and therefore there would be no mechanical bonding of the
particles to the surface and, as a consequence, the mold core would
be destroyed.
[0022] If these properties of the metallic auxiliary layer are met,
the material of the mold core chosen can advantageously be largely
independent of the requirements of cold spraying. As a result, mold
core materials, the mechanical stability of which would not
normally be adequate for application of cold spraying, are also
available for the disclosed method. However, it is precisely these
materials which, on the one hand, are inexpensive to use and, on
the other hand, are simple to remove from the finally produced
molding. According to some embodiments, sand, wood, metal or
plastic can be used for the mold core. Sand cores have the
advantage that they can be produced at low cost as lost cores and
can also be removed easily from the cavity of the cavity structure
by dissolution of the bond between the individual sand grains. Wood
forms a low-cost material which can be processed easily, especially
in the case of very small batches, in order to produce cores of the
required geometry. Metal is suitable especially for producing cores
for multiple uses. The wear of said cores is advantageously low.
Moreover, these can be manufactured with high dimensional accuracy.
The surface of these metal cores is then protected from wear by the
auxiliary layer. Plastic cores also have the advantage of simple
production and a low-cost material, which can also be cast, for
example.
[0023] In some embodiments, a mold core which can be produced, in
particular, from the materials mentioned is then provided with an
auxiliary layer of a metallic material, wherein this layer is
involved in the formation of the starting coat on the material of
the mold core or forms said coat alone, wherein the starting coat
makes available the surface for subsequent cold spraying of the
cavity structure.
[0024] As used herein, hollow bodies should be taken in the widest
sense to mean all structures which have a concave inner surface and
a convex outer surface. The concave inner surface can thus be
supported by a former during production, while it is accessible to
the cold gas jet from the convex side. Thus, for example, a
bowl-shaped component would likewise qualify as a hollow body in
the sense according to the invention, wherein the bowl-shaped
depression would form the cavity with a correspondingly wide
opening. Conventional hollow bodies would be, for example,
housings, which can have a small opening in comparison with the
cavity formed. Of course, the hollow bodies do not necessarily have
to have exclusively convex outer walls either. There may also be
concave areas on the outside. In one embodiment, the auxiliary
layer is formed by a metal foil, in particular an aluminum foil. In
this case, the metal foil is placed on the mold core and thus forms
the metallic surface on which the hollow body can be deposited by
cold spraying. Here, aluminum represents a very low-cost variant,
wherein this material is, on the one hand, sufficiently ductile to
ensure that the sprayed particles adhere. On the other hand, this
metal is mechanically sufficiently stable to protect the former
from erosion by the cold gas jet. On formers made of wood, for
example, an aluminum foil with a thickness of 0.1 mm is sufficient
to enable metallic materials to be deposited. For example, it has
even been possible to deposit a hollow body composed of a titanium
alloy thereon.
[0025] The thickness of the auxiliary layer must be chosen
according to the hardness and sensitivity of the material of the
mold core. If sand cores are used, for example, the coating
thicknesses of the auxiliary layer are somewhat greater owing to
the need for greater protection. In the case of lesser thicknesses
of the auxiliary layer, it must be taken into account that this
layer is deformed plastically owing to the impact of the particles
of the cold gas jet. However, the plastic deformation must not lead
to complete destruction of the auxiliary layer since the remaining
mold core would then no longer be protected. If the auxiliary layer
is embodied as a metal foil, it can advantageously be bonded
adhesively onto the mold core. On the one hand, this avoids
slippage of the foil during coating, especially at angles other
than 90.degree. between the cold gas jet and the surface. Moreover,
adhesive bonding facilitates the application of the foil to the
mold core, especially in the case of complex mold core
geometries.
[0026] According to another embodiment, the at least one auxiliary
layer may be produced as a starting coat on the former by cold
spraying of a metallic material. Here, a metallic material is
chosen deliberately, something that may be regarded as
unproblematic as regards coat formation on the former in comparison
with the material which is provided for the hollow body. In other
words, the metallic material, which, in particular, can be formed
by a very ductile material, remains on the former without
destroying the latter. If the starting coat is applied in
sufficient depth to the former, it then offers sufficient
resistance during the deposition of the material of the hollow
body. The thickness information given in relation to the embodiment
as a foil applies in corresponding fashion to the thickness of the
starting coat.
[0027] The production of the starting coat by means of cold
spraying furthermore has the advantage that the starting coat can
be built up in several auxiliary layers. In this way, it is
possible to deposit metallic materials in succession, wherein, in
the production sequence for the auxiliary layers, the procedure
involves working with increasingly harder and/or higher-melting
metallic materials. This means that the auxiliary layer, which is
produced directly on the mold core, can be selected to ensure that
the mold core is subject to as little mechanical stress as
possible. This is the case especially with very low-melting and/or
very ductile materials. Zinc, tin and lead, in particular, are used
here. The following layers can then be produced from other metals,
wherein zinc, aluminum, copper, silver and gold can preferably be
used. In the case of the noble metals, it should be noted that
these are very expensive to procure. However, these can assume
special tasks in the hollow body, e.g. corrosion protection or an
antimicrobial or catalytic action, potentially justifying the cost
of their use. Instead of the abovementioned metals, it is, of
course, also possible to use metal alloys which contain these
metals as alloying components and have comparable mechanical
properties.
[0028] In the choice of metals for the auxiliary layer which forms
the mold core surface to be coated, it should be taken into account
whether the requirement is more for thermal stability or for
mechanical stability. Thermal stability is a higher priority in
selection when the temperature of the cold gas jet is increased by
preheating the carrier gas. At the same time, the processed
particles are warmer in this case and therefore impose a lower
mechanical stress on the surface of the mold core. Mechanical
stability is a higher priority when the particles in the cold gas
jet are themselves not very ductile and therefore cause higher
mechanical stress in the mold core.
[0029] "Low-pressure gas dynamic spraying" (LPGDS) has proven
particularly suitable for depositing the auxiliary layer or
auxiliary layers as a starting coat by means of cold spraying. In
this method, the particles are fed into the divergent part of the
convergent-divergent nozzle, and the carrier gas is brought to a
comparatively low pressure for cold spraying. In this case, the
particle speeds are lower than when the particles are fed into the
stagnation chamber positioned upstream of the nozzle and are
accelerated by a higher pressure level of the carrier gas, which is
the usual practice. In LPGDS, therefore, the mechanical stress on
the mold core when the particles impinge upon the surface thereof
is also lower. Since the material of the mold core is in any case
sensitive to the cold gas jet, the particles nevertheless adhere to
the mold core without permanently destroying it.
[0030] According to one embodiment, the at least one auxiliary
layer is removed from the hollow body after the removal of the mold
core from the mold. The removal of the mold core from the mold can
be performed by conventional methods from the prior art. A sand
core or other lost cores can be melted out or destroyed with the
aid of ultrasound, for example. Using plastic or wood or,
alternatively, metal, it is possible to produce assembled cores,
which can be of multipart design to enable them to be removed as
individual parts from the finished hollow body. The auxiliary layer
then remains in the cavity formed by the hollow body since, as a
result of the mechanical deformations due to the impinging
particles of the hollow body material, it is firmly connected to
these.
[0031] If the material of the auxiliary layer does not interfere
with the functioning of the hollow body produced, it can remain
within the hollow body as a lining of the cavity. As already
indicated, the material of the auxiliary layer can even assume
additional functions in the hollow body, such as corrosion
protection or an antimicrobial action. However, if the material of
the hollow body is supposed to form the inner wall of the cavity,
the auxiliary layer must subsequently be removed. This removal can
be achieved mechanically, e.g. by sandblasting. One alternative is
to remove the material by means of a selective etching method,
wherein the etchant attacks the material of the hollow body only a
little or not at all.
[0032] FIG. 1 shows schematically a cold spraying system, which is
accommodated in a process chamber 11. The cold spraying system is
reduced to its essential components and thus represents only a
schematic diagram. The cold spraying system has a
convergent-divergent spray nozzle 12, which is connected to a unit
13 having a stagnation chamber (not shown). A mold core 16 is held
by means of an industrial robot 15 in such a way that said mold
core can be coated by a cold gas jet produced by means of the spray
nozzle 12. This coating process takes place in several stages. Via
a first storage container 18, particles of a tin solder are
introduced into the divergent part 19 of the spray nozzle 12 and
are accelerated in the cold gas jet 17. These form a first
auxiliary layer (not shown specifically in FIG. 1) on the mold core
16 (cf. also FIGS. 3 and 4). Copper particles are then introduced
from a second storage container into the stagnation chamber (not
shown specifically) ahead of the spray nozzle 12 and are likewise
accelerated by means of the cold gas jet 17 to the former 16 coated
with the first auxiliary layer. A second auxiliary layer is formed,
wherein these two auxiliary layers form a starting coat 21 (cf.
FIGS. 3 and 4). Finally, titanium particles are taken from a third
storage container 22 and are likewise mixed in with the cold gas
jet 17 via the stagnation chamber. Here, several layers of titanium
can be applied to the starting coat, thereby forming a wall of a
desired thickness of a hollow body to be produced, wherein the
cavity enclosed by the hollow body is defined by the mold core
16.
[0033] FIG. 2 shows a hollow body 23 of the type that could be
produced with a cold spraying system shown in FIG. 1. For this
hollow body an assembled mold core 16 has been used, comprising a
plurality of shaped elements 24 made of wood. Integrated into the
shaped elements are joining aids 25, which define the position of
the individual shaped elements 24 relative to one another and in
this way facilitate assembly. At the same time, these joining aids
are embodied in such a way that the mold core can be removed from
the cavity of the hollow body 23 without destroying the individual
shaped elements 24. The mold core 16 was adhesively bonded to a
metal foil 26 before coating with the material of the hollow body
23, although the adhesive coat as such is not shown in FIG. 2.
Coating to form the hollow body 23 is then performed by means of
cold spraying. The state after the coating has been produced is
shown in FIG. 2. After the coating has been produced, the shaped
elements 24 can be removed from the cavity of the hollow body 23 in
the manner already described, wherein the adhesive bond between the
mold core 16 and the metal foil 26 is made weaker than the bond
between the hollow body 23 and the metal foil 26 brought about by
cold spraying. The metal foil 26 therefore remains in the cavity,
while the adhesive bond dissolves. Insofar as required, this can be
removed from the cavity in a manner not shown, by a selective
etching method, for example.
[0034] FIG. 3 shows a mold core of bonded sand. This is coated with
the starting coat 21 produced in accordance with FIG. 1, wherein
the hollow body 23 composed of titanium was produced in a
subsequent step. Not shown in FIG. 3 is the possibility of
destroying the sand mold core by means of ultrasound, for example,
thus ensuring that the core is lost and can be removed from the
cavity of the hollow body 23. The starting coat 21 remains in the
cavity, as already described with reference to FIG. 2. Here too,
there is the possibility of subsequently removing it mechanically
or chemically.
[0035] FIG. 4 shows the detail IV in FIG. 3 on an enlarged scale.
It becomes apparent that the sand core is first of all coated with
a base layer 27 which, according to FIG. 1, is composed of a tin
solder. Alternative materials would be a white metal (alloy
containing tin) or zinc. This base layer is followed by a top layer
28, which is composed of copper and makes available a surface 29
for coating with the material of the hollow body (in this case
titanium). As an alternative to copper, the top layer can also be
composed of zinc or aluminum or alloys which contain at least one
of these metals. Further auxiliary layers can be produced between
the base layer 27 and the top layer 28 in order, for example, to
make the transition to various property profiles of the auxiliary
layers (ductility, hardness and/or temperature stability)
smoother.
* * * * *