WO2015150071A2

WO2015150071A2 - Method for producing a hollow body by cold spraying and mould core suitable for carrying out said method

Info

Publication number: WO2015150071A2
Application number: PCT/EP2015/055611
Authority: WO
Inventors: Axel Arndt; Uwe Pyritz; Ralph Reiche; Oliver Stier
Original assignee: Siemens Aktiengesellschaft
Priority date: 2014-03-31
Filing date: 2015-03-18
Publication date: 2015-10-08
Also published as: DE102014206073A1; CA2944238A1; US20170022615A1; JP2017512908A; WO2015150071A3; EP3102718A2

Abstract

The invention relates to a method for producing a hollow body (23) by cold spraying. According to the invention, a mould core (16) is used for producing the hollow body, said mould core being prepared for the production of the hollow body (23) by cold spraying in a suitable manner by means of an auxiliary layer (21). The auxiliary layer (21) consists 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 (23). The mould core, to which the invention also relates, can therefore advantageously be produced from an inexpensive material such as sand or wood, although said materials are in principle only suitable to a limited extent or not at all for depositing metals by cold spraying. The auxiliary layer (21) can advantageously be applied to the mould core (16) as a foil, or be produced on the mould core (16) by cold-spraying particularly low-melting and/or soft materials.

Description

description

A method for producing a hollow body by means of cold gas ^¬ spraying and for performing this method suitable mandrel

The invention relates to a method for producing a hollow body. In this, the hollow body is produced by coating a mold core by cold gas spraying. In other words, the layer produced on the mandrel forms the hollow body to be produced. After completion of this hollow body of the mandrel is removed from this. Moreover, the invention relates to a mold core with a surface suitable as a substrate for the cold gas spraying. The surface must be suitable for cold gas spraying in that the particles that are accelerated with the cold gas jet to the surface of the mold ^¬ core, must adhere to this.

Cold spraying is a method known per se, are preferably accelerated at the foreseen for the coating particles by means of a convergent-divergent nozzle onto Überschallge ^¬ speed, so that they stick to the surface to be coated due to their impressed kinetic energy. Here, the kinetic energy of the particles is used, which leads to a plastic deformation of the same, wherein the coating particles are melted on impact only on their surface. Therefore, this method is referred to as cold gas spraying in comparison with other thermal spraying methods, because it is carried out at comparatively low temperatures at which the coating particles remain substantially fixed. Preferably, for cold gas spraying, which is also called kinetic spraying, using a cold gas ^¬ injection system, the gas heating means to overheat an ER- comprises a gas. To the gas heater a stagnation chamber is connected, which is connected on the output side with the convergent-divergent nozzle, preferably a Laval nozzle. Convergent-divergent nozzles have a merging section and a widening section, which are connected by a nozzle neck. The convergent-divergent nozzle produces the output side a powder jet in the form of a gas stream with particles therein at high speed, preferably supersonic speed ^¬.

A method for producing a hollow body of the type specified is known from DE 10 2010 060 362 AI. The cold gas spraying can thus be used to produce a tube on a cylindrical die. In this case, the cold gas ^{jet is} inclined against the surface of the cylinder so far that the particles primarily adhere to the pipe being produced. The cylindrical mandrel can therefore be removed after production of the tube from this. This is possible because of the typical geometry of tubes that are free from undercuts inside, so that the cylindrical shaped body can slide along the inner walls of the tube. However, more complicated geometries of hollow bodies can not be produced in this way.

The object of the invention is therefore to provide a method for producing a hollow body by means of cold gas spraying, with which hollow bodies of complex geometry can be manufactured. In addition, it is an object of the invention to provide a shaped body which can be used in the said method.

This object is achieved according to the invention with the method specified at the outset by providing the mandrel with an auxiliary layer prior to producing the hollow body. The material of this auxiliary layer according to the invention is metallic or has at least predominantly metallic components. This means that the auxiliary layer can provide a metallic matrix in which non-metallic inclusions can be embedded. In essence, such a situation still behaves like a metal. The deposits may be, for example, particles of a dry lubricant to to facilitate removal of a nucleus. Preferably, the material of the auxiliary layer has a different composition than the material from which the hollow body is to be produced. This advantageously makes it possible to optimally adapt the material which forms the surface for coating with the material of the hollow body to the requirements of a substrate for cold gas spraying. On the one hand, this material must be sufficiently ductile, so that the particles from the cold gas ^¬ beam adhere to the surface of the mandrel. In addition, this material must be sufficiently temperature resistant, taking into account, under certain circumstances, that the gas which is used for the formation of the cold gas jet, is preheated. In this case, approximately the temperatures which the carrier gas has in the stagnation chamber upstream of the cold gas injection nozzle can be achieved in the impingement flow forming in front of the mold core. Another feature that the surface of the mandrel aufwei ^¬ sen need is a resistance to the erosive effect of impacting particles. This surface is mechanically unstable, it provides the impinging particles of the cold gas ^¬ beam namely no sufficient resistance so that it which would not lead to a destruction of the mold core to a mechanical attachment of the particles on the surface and in a row.

If these properties are met by the metallic auxiliary layer, the material of the mandrel can advantageously be chosen far ^¬ de regardless of the requirements of the cold gas spraying. As a result of this, the method according to the invention also makes available materials for shaped cores whose mechanical stability would normally not be sufficient for an application of cold gas spraying. However, it is precisely these materials in a cost on the other hand easy to remove from the finished shaped body produced in the United ^¬ and application. According to one embodiment of the invention can be used for the mandrel sand, wood, metal or plastic. Sand cores have the advantage that they can be produced cost-effectively as lost cores are and can be easily removed from the cavity of the cavity structure by dissolving the bond between the individual grains of sand. Wood forms a cost-effective material that can be easily processed, especially in very small series, to produce cores of the required geometry. Metal is particularly suitable for the production of cores that are to be used several times. Their wear is advantageously low. In addition, these can be made with egg ^¬ ner high dimensional accuracy. The surface DIE ser metal cores is then passed through the auxiliary sheet before Ver ^¬ wear protected. Also plastic cores have the advantage ei ^¬ ner simple production and a cost-effective material, which can be cast for example. A mold core, which can be made in particular of the materials mentioned, is then provided according to the invention with an auxiliary layer of a metallic material, which is involved in the formation of the starting layer on the material of the mold core or forms them alone, wherein the starting layer, the surface for a subsequent cold gas injection ^¬ the cavity structure provides.

As a hollow body according to the invention, in the broadest sense, all structures are to be understood which have a concave inner surface and a convex outer surface. The concave

Inner surface can be so far supported by a molding during manufacture, while it is accessible from the convex side for the cold gas jet. To that extent a schüsseiförmiges component would be, for example, also to be understood as a hollow body according to the invention, the bowl-shaped recess would represent the cavity with a entspre ^¬ accordingly wide opening. Classical hollow body would be, for example, housing, which may have as compared to the ge ^¬ cavity formed small opening. Of course, the hollow bodies do not necessarily have exclusively convex outer walls. There may also be concave portions on the outside. According to an advantageous embodiment of the invention it is provided that the auxiliary layer consists of a metal foil, in particular ^¬ sondere an aluminum foil, is formed. 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 gas injection ^¬ . In this case, aluminum represents a very cost-effective variant, whereby this material is on the one hand ductile enough so that the sprayed particles adhere. On the other hand, this metal is mechanically stable enough to protect the molded body from erosive erosion by the cold gas jet. On wooden moldings, for example, an aluminum foil with a thickness of 0.1 mm is sufficient to allow the deposition of metallic materials. For example, it has also been possible to deposit a hollow body made of a titanium alloy thereon.

Depending on the hardness and the sensitivity of the material of the mold core, the thickness of the auxiliary layer must be selected. For example, if sand cores are used, due to the need for a higher protection, the layer thicknesses of the

Auxiliary position larger. At lower thicknesses of the auxiliary layer, it should be noted that this is plastically deformed due to the impact of the particles of the cold gas jet. However, the plastic deformation must not lead to a complete destruction of the auxiliary position, since the rest of the mold core would then no longer be protected. If the auxiliary sheet designed as a metal foil ^¬, this can advantageously be adhesively bonded to the mold core. As a result, on the one hand slipping of the film during coating, in particular at angles between the cold gas jet and the surface of unequal

Avoid 90 °. In addition, the bonding facilitates Applikati ^¬ on the film on the mold core, especially in complex overall ometrieen of the mandrel. According to a further embodiment of the invention, it is provided that the at least one auxiliary layer is produced as a starting layer by cold gas spraying of a metallic material on the shaped body. Here, a metallic chosen sches material, which is classified as unproblematic in terms of film formation on the molding in comparison to the material which is provided for the hollow body. In other words, the metallic material, which can be formed in particular by a very ductile metal, keeps on the molding without destroying it. If the starting layer is applied with a sufficient thickness to the shaped body, this then provides a sufficient resistance during the deposition of the material of the hollow body. The thickness of the seed layer thickness details given from ^¬ leadership as a foil apply accordingly.

The production of the starting layer by means of cold gas spraying also has the advantage that the starting layer can be constructed in several auxiliary layers. In this way, it is possible to deposit me ^¬ tallische materials sequentially, which is used in the sequence of producing the auxiliary layers with increasingly harder and / or higher melting metallic materials. This means that the auxiliary layer, which is produced directly on the mandrel, can be selected according to the fact that the mandrel is subjected to as little mechanical stress as possible. This is the case in particular with very low-melting and / or very ductile materials. In particular zinc, tin and lead are used here. The following layers can then be made of other metals, preferably zinc, aluminum, copper, silver and gold can be used. With the precious metals it is to be noted that these are very expensive in the purchase. However, these can take on special tasks in the hollow body, such as a corrosion protection or antimikro- bielle or catalytic effect, which justifies the cost of its A ^¬ set if necessary. Instead of the abovementioned metals, of course, it is also possible to use metal alloys which have these metals as alloy components and have comparable mechanical properties.

In the selection of metals for the auxiliary layer that forms to be ^¬ layer surface of the mold core, is to Beach- whether thermal stability is required or mechanical stability. The thermal stability is in the foreground in the selection when the temperature of the cold ^¬ gas jet is increased by preheating the carrier gas.

At the same time in this case, the processed particles are warmer and therefore exert less mechanical stress on the surface of the mandrel. The mechanical stability ^¬ formality is more in the foreground when the particles in the cold gas jet ^¬ are even slightly ductile and therefore result in a higher mechanical load on the mold core.

For the deposition of the auxiliary layer or auxiliary layers as a starting layer by the cold gas spraying, in particular the so-called low pressure gas dynamic spray (LPGDS) has been granted ^¬ . In this process, the particles are fed into the divergent part of the convergent-divergent nozzle and the carrier gas is brought to a pressure which is comparatively low for cold gas spraying. Here are lower

Particle velocities, as if the particles are fed as usual in the stagnation chamber upstream of the nozzle and accelerated from a higher pressure level of the carrier gas. So that when the mechanical LPGDS ^¬ traumatic stress of the mandrel upon impact of the particles is less on its surface. Since the material of the mandrel is oh ^¬ neh sensitive to the cold gas jet, the particles still adhere to the mandrel, without destroying this sustainable.

According to a particular embodiment of the invention, it is provided that the at least one auxiliary layer is removed from the hollow body after removal of the mold core. The demolding of the mold core can be carried out according to conventional methods of the prior art. For example, a sand core or other lost cores may be melted out or destroyed by ultrasound. Made of plastic or wood or metal can be produced cores that can be made mehrtei ^¬ lig, so that they can be removed in their individual parts from the finished hollow body. Subsequently, the auxiliary position remains in the cavity formed by the hollow body, since they are firmly connected to the latter due to the mechanical deformations by the impinging particles of the hollow body material.

If the material of the auxiliary ^layer does not interfere with the function of the manufactured hollow body, this can remain as a lining of the hollow space in the interior of the hollow body. As already indicated, the material of the auxiliary layer in the hollow body can even take on additional functions such as corrosion protection or an antimicrobial effect. However, if the material of the hollow ^¬ body is to form the inner wall of the cavity, the auxiliary layer must then be removed. This removal can be achieved mechanically, for example by sandblasting. An alternative is to remove the material by a selective etching process, wherein the etchant does not or only slightly attacks the material of the hollow body.

Further details of the invention are described below with reference to the drawing. Identical or corresponding drawing elements are each provided with the same Bezugszei ^¬ chen and are only explained several times as far as differences arise between the individual figures. Show it :

Figure 1 shows an embodiment of the invention

Method, which is carried out in a cold gas spraying, as a schematic drawing, Figure 2 and 3 embodiments of the invention

Molded core in section and

Figure 4 shows the detail IV as shown in Figure 3. FIG. 1 schematically shows a cold spray system which is accommodated in a process chamber 11. The cold ^¬ injection system is reduced to its essential components and thus represents only a schematic diagram. The cold gas Spraying plant has a convergent-divergent spray nozzle 12 which is connected to a unit 13 with a stagnation ^chamber not shown in detail. By means of an industrial robot 15, a mold core 16 is held such that it can be coated by a generated by means of the spray nozzle 12 cold gas jet. This coating process takes place in several stages. Particles of a tin solder are introduced into the divergent part 19 of the spray nozzle 12 via a first reservoir 18 and accelerated in the cold gas jet 17. These form an unspecified Darge in Figure 1 ^¬ presented first auxiliary sheet on the mandrel 16 (see also ^¬ Fi gures 3 and 4). Subsequently, copper particles are introduced into the stagnation chamber (not shown) in front of the spray nozzle 12 from a second reservoir and also accelerated via the cold gas jet 17 to the molded body 16 coated with the first auxiliary layer. A second auxiliary layer is formed, these two auxiliary layers forming a starting layer 21 (compare FIGS. 3 and 4). Finally, 22 titanium particles are taken from a third storage container and also mixed with the cold gas jet 17 via the stagnation chamber. Here, several layers of titanium can be applied to the starting layer, whereby a wall of desired thickness of a hollow body to be produced is ^{ausgebil ¬} det, wherein the cavity enclosed by the hollow body is defined by the mandrel 16.

In Figure 2, a hollow body 23 is shown as it might be prepared with egg ^¬ ner cold spray system of FIG. 1 For this hollow body, a composite mold core 16 was used which has a plurality of mold elements 24 made of wood. In the form of elements joining aids 25 are integrated, which define the position of the individual mold elements 24 to each other and facilitate assembly in this way. At the same time, these joining aids are designed such that the mold core can be removed from the cavity of the hollow body 23 without destroying the individual mold elements 24. The mold core 16 was pasted with a metal foil 26 before coating with the material of the hollow body 23, wherein the adhesive layer is not shown as such in FIG. The coating with the formation of the hollow body 23 is then carried out with cold gas spraying. The state after fertigge ^¬ imputed coating is shown in FIG. 2 After completion of the coating, the mold elements 24 can be removed in the manner already described from the cavity of the hollow body 23, wherein the adhesive bond between mold core 16 and metal foil 26 is formed weaker than the resulting by the cold gas injection connection between the hollow body 23 and the metal foil 26th Therefore, the metal foil 26 remains in the cavity while the adhesive bond is released. This can be removed in a manner not shown, for example, by a selective etching process from the cavity, if necessary.

FIG. 3 shows a molded core of bonded sand. This is coated with the starting layer 21 produced according to Figure 1, wherein in a subsequent step of

Hollow body 23 was made of titanium. In Figure 3, not shown is the ability to destroy the sand mold core at ^¬ play by means of ultrasound, so that it is lost and can be entnom- men from the cavity of the hollow body 23rd The starting layer 21 remains in the cavity, as has already been described with reference to FIG. Here, too, be ^¬ is the ability to subsequently remove those mechanically or chemically. FIG. 4 shows the detail IV according to FIG. 3 enlarged. It is clear that the core sand to ^¬ next is coated with a base layer 27, which is in accordance with Fi gur ^¬ 1 made of a tin solder. Alternative materials would be a white metal (tin-containing alloy) or zinc. The base layer is followed by a cover layer 28 which consists of copper and provides a surface 29 for coating with the material of the hollow body (here titanium). As an alternative to copper, the top layer can also be made of zinc or aluminum or Alloys containing at least one of these metals. Between the base length 27 and the cover layer 28, further auxiliary layers can be produced in order, for example, to make the transition to different property profiles of the auxiliary layers (ductility, hardness and / or temperature resistance) more fluid.

Claims

claims

1. A method for producing a hollow body, in which

- The hollow body (23) by coating a mold core (16) is produced by cold gas spraying and

- The mold core (16) after completion of the hollow body (23) is removed from this,

d a d u r c h e c e n c i n e s that

having the mandrel (16) prior to the production of the hollow body (23) with an auxiliary layer (26, 27, 28) is provided, wherein the Materi ^¬ al of the auxiliary sheet is metallic or at least predominantly metal parts, and the auxiliary layer (26, 27, 28) is removed from the hollow body (23) after removal of the mold core (16).

2. The method according to claim 1,

d a d u r c h e c e n c i n e s that

the material of the auxiliary layer differs in its composition from the material of the hollow body.

3. The method according to claim 1 or 2,

d a d u r c h e c e n c i n e s that

the auxiliary layer is formed from a metal foil (26), in particular an aluminum foil.

4. The method according to claim 3,

d a d u r c h e c e n c i n e s that

the metal foil (26) is glued to the mold core (16).

5. The method according to claim 1 or 2,

d a d u r c h e c e n c i n e s that

the at least one auxiliary layer is produced as a starting layer (21) by cold gas spraying, in particular by low-pressure gas dynamic spray, of a metallic material on the shaped body (16).

6. The method according to claim 5,

characterized in that metallic materials with a ductile material erhal ^¬ th, 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.

7. The method according to claim 6,

d a d u r c h e c e n c i n e s that

the starting layer (21) is carried out in several layers, the auxiliary layers (26, 27, 28) being produced with increasingly harder and / or higher-melting metallic materials as a result of the production.

8. The method according to claim 7,

d a d u r c h e c e n c i n e s that

the starting layer (21) with two layers

a base layer (27) made of one of the metals or metal alloys based on the metals zinc, tin and lead, lying on the mold core,

- And with a subsequent cover layer (28) made of one of the metals or metal alloy based on the metals

Zinc, aluminum, copper, silver and gold

will be produced.

9. Method according to one of the preceding claims, characterized in that

the mold core (16) made of wood, plastic, metal or gebound ^¬ ner sand is produced.

10. mold core (16) with a suitable substrate for the cold gas injection surface (29),

d a d u r c h e c e n c i n e s that

the surface (29) is formed by at least one auxiliary layer (26, 27, 28) of a metallic material which forms a starting layer on the material of the mold core (16).

11. mold core according to claim 10,

characterized in that this made of bonded sand, wood, metal or plastic be ^¬ stands.