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.

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, preferably of less than 15, particularly preferably of less than 5.

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

[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 C. to 150 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. 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.