METHOD FOR THE MANUFACTURE OF A CHANNELED MONOLITHIC DEVICE DEFINING A HEAT EXCHANGER

Abstract

A method for manufacturing a monolithic channeled device comprising at least one manifold in which at least one channel opens, the method being based on the diffusion bonding technique, comprising the following successive steps: (Step 1) etching a plurality of metal plates to create internal channels; (Step 2) diffusion bonding to obtain an internally channeled monolithic device; (Step 3, 3DS) machining the manifold by electrical discharge machining (EDM). Figure 4

Description

Title of the invention: METHOD FOR THE MANUFACTURE OF A CHANNELED MONOLITHIC DEVICE DEFINING A HEAT EXCHANGER Scope of application of the invention

[0001] The present invention relates to the field of manufacturing monolithic channeled devices using the diffusion bonding process. In particular, monolithic channeled devices include printed circuit heat exchangers (PCHEs) and printed circuit reactors (PCRs). Furthermore, the present invention also relates to a furnace for implementing the process. State of the art

[0002] The "diffusion bonding" technology (diffusion welding) is also referred to as diffusion welding and consists of reciprocally welding two metallic surfaces by compressing them together at high temperature and very high vacuum.

[0003] Welding between such similar or different metal surfaces takes place because of the interdiffusion of atoms of the two surfaces in reciprocal contact with the subsequent assembly for local plastic deformation.

[0004] Generally, the temperature at which such a process takes place is in the order of 80% to 90% of the melting temperature of the material being welded.

[0005] Monolithic channeled devices, hereinafter referred to as "channeled devices" for simplicity, are made by stacking pre-etched metal plates to form a semi-finished product. They are designated by the term PCHE, from the English acronym "Printed Circuit Heat Exchanger," or PCR, from the English acronym "Printed Circuit Reactor." The stack is then subjected to a simultaneous compression and heating process, resulting in the mutual welding of the plates.

[0006] This technique is generally carried out at very high vacuum, since the materials with which the semi-product is formed must be degassed.

[0007] The stacking of two or more consecutive plates previously engraved defines paths and channels for fluids.

[0008] Within the same device, different paths can be found, even parallel to each other, in the direction of the stacking.

[0009] The introduction of fluids into the paths is carried out by means of fluid inlet and outlet manifolds.

[0010] A collector is internal when it is defined by a hole in the direction of the stacking in which at least one of the paths and conduits defined by the stacking opens.

[0011] Generally, the metal plates are pre-drilled to create the aforementioned collector. However, despite the maximum possible precision in creating the openings, the stack presents an internal collector characterized by various types of asperities.

[0012] Similar problems are encountered when the channeled device must be coupled to an external collector. This is essentially due to the impossibility of obtaining perfect etching and alignment of the plates corresponding to the collector.

[0013] Figures 1 to 3 show a section of a channeled device corresponding to a collector, produced according to three different techniques.

[0014] In particular, in [Fig. 1], the plates are cut using laser technology. It can be seen from the enlargements of Figures IA and IB that, although the cuts are fairly perpendicular to the surface of the plates, the various openings exhibit a misalignment with respect to the tolerance chain for positioning the plates themselves. The surface of the collector is therefore offset.

[0015] This depends on the fact that the different plate production technologies, including laser technology, provide for positioning and cutting tolerances which are added to the stacking tolerances.

[0016] Figures 2 show a collector with enlargements of Figures 2A and 2B, in which it can be seen that the cuts are not perpendicular to the faces of the plates, as they are made using a water jet. Also in this case, the cutting tolerances are added to the stacking tolerances.

[0017] Figures 3 show a collector with enlargements of Figures 3A and 3B, in which it can be seen that each plate has a small ridge along its edge. This is due to the fact that the plates are photo-etched on both sides, and in this case, the cutting tolerances are added to the stacking tolerances.

[0018] The surface of the collector according to the known art is "rough", that is to say the opposite of "smooth".

[0019] In addition to the machining defects described above, it is necessary to take into account that the high pressures to which the stack is subjected can cause reciprocal slippage of the plates relative to each other.

[0020] If one tries to carry out a finishing machining of the collector, one risks removing a lot of material which, by forming chips, tends to clog the channels with the result of obtaining an unusable product.

[0021] Another problem that may concern these components is the so-called "edge effect", that is to say the fact that on a few millimeters of the edge of the stack, the welding is of inferior quality, determining a minor mechanical resistance, especially near the collector.

[0022] Another problem arises from the fact that when the channeled device is used as a PCHE (Polyhydrogen Containment Helicopter) for high-pressure hydrogen gas, this chemical element tends to weaken the channeled device by infiltrating, especially at discontinuity points located on the edge of the manifold corresponding to the weld line. At these discontinuity points, there is also a concentration of mechanical stress, as can be verified by finite element analysis, and this occurs in the weakest zone. Therefore, at the manifold surfaces, the probability of crack formation due to stress concentration is higher, possibly exacerbated by hydrogen diffusion within the material's crystal lattice.

[0023] If not specifically excluded in the detailed description that follows, what is described in this chapter shall be considered as forming part of the detailed description. Summary of the invention

[0024] The object of the present invention is to indicate a method of manufacturing a ducted device defining a heat exchanger according to the diffusion bonding technique (diffusion welding) in a more efficient and economical manner.

[0025] The basic idea of ​​the present invention is to produce an internal collector from plates that are not pre-drilled or have pre-drilled holes of reduced dimensions compared to the final dimensions of the collector, and then to carry out mechanical machining based on the electro-erosion procedure to achieve these final dimensions.

[0026] Similarly, in the case of an external collector, the idea is to remove the edge parts of the collector by means of an electro-erosion procedure, possibly preceded by the removal of excess material by means of a conventional cut, for example using a saw or a milling cutter.

[0027] Advantageously, it is possible to reduce or eliminate the side effect.

[0028] Another advantage is that it avoids the formation of burrs or chips which can clog the microchannels that open into the collector.

[0029] Advantageously, it is possible to obtain a right prism collector, not necessarily cylindrical.

[0030] Two electrical discharge machining (EDM) techniques are known. The first is the so-called "die-sinking technique," also known by its Anglo-Saxon name. This technique allows a volume to be eroded through a predetermined number of layers defining the channeled device. This technique can create the entire hole with smooth walls or can correct a hole previously made using other methods, obtaining smooth walls without the risk of clogging the channels.

[0031] The second electrical discharge machining (EDM) technique is wire EDM. This technique cuts metal using a wire held by a fork-shaped support. The cut is made along a predetermined path to obtain a desired shape for the collector, for example, cylindrical or parallelepiped. Obviously, to introduce the wire and make the cut, it is necessary to pre-drill the channeled device to allow the wire to be inserted and then remove the volume of material cut for all the layers defining the channeled device. This implies that following the wire EDM operation, it is necessary to plug one of the two ends of the opening.

[0032] In the case of an external or partially external collector, when the collector is intended to close an internal face of the channeled device, the fastest technique is wire electrical discharge machining (EDM). However, depending on the shape of the collector and the parts of the channeled device to be removed, both wire and die-sinking techniques are valid.

[0033] Any one of the electro-erosion techniques used makes it possible to obtain collectors with smooth walls, without discontinuity zones, eliminating areas affected by minor resistance (DB edge effect); finally, the collectors thus obtained can then be polished without damaging the openings of the microchannels, also obtaining a beveling of the sharp edges.

[0034] The dependent claims describe preferred variants of the invention, forming an integral part of this description. Brief description of the drawings

[0035] Other objects and advantages of the present invention will become clearer from the following detailed description of an exemplary embodiment thereof (and its variants) and from the accompanying drawings provided by way of pure explanatory and non-limiting example, in which:

[0036] [Fig.1] [Fig.1A] [Fig.1B] [Fig.2] [Fig.2A] [Fig.2B] [Fig.3] [Fig.3A] [Fig.3B] Figures 1 to 3 with the relative enlargements A and B show collectors made in channeled devices obtained by means of the diffusion bonding technique, in which the collectors are respectively made, according to the known technique, by means of laser cutting, water cutting and photogravure;

[0037] [Fig.4] [Fig.5] [Fig.6] Figures 4 to 6 represent flow diagrams illustrating the manufacturing process which is the subject of the present invention.

[0038]

[0039] The same numbers and the same reference letters on the figures identify the same elements or components or the same functions.

[0040] It should also be noted that the terms "first", "second", "third", "superior", "lower", and similar terms may be used here to distinguish different elements. These terms do not imply a spatial, sequential, or hierarchical order for the modified elements unless specifically stated or inferred from the text.

[0041] The elements and features illustrated in the various preferred embodiments, including the drawings, may be combined with each other without departing from the scope of protection of this application as described below. Detailed description of embodiment examples

[0042] The technique for producing the micro-channeled monolithic blocks involves engraving a plurality of stainless steel plates to obtain the microchannels.

[0043] These are then stacked and welded by diffusion welding by subjecting them to high temperature and high pressure.

[0044] According to a first variant of the present invention, the collector is made in a solid manner after the welding process by means of electro-erosion by sinking.

[0045] Figure 4 represents a first flow diagram illustrating the machining operations to be performed successively: Step 1: engraving the plates to create the internal pipes; Step 2: Welding by diffusion welding, obtaining a monolithic device internally channeled; Step 3: fabrication of a collector of the device obtained in the previous step by means of electrical discharge machining.

[0046] Electrical discharge machining (EDM) allows the perforation to be stopped at a predetermined point in the thickness of the monolithic device.

[0047] On the contrary, wire electro-erosion requires a through opening to be able to connect the wire in the relative support.

[0048] According to a second preferred embodiment of the invention shown in [Fig.5], the collector is partially made using any pre-drilling technique and is then completed by electro-erosion.

[0049] In detail, the process comprises the following successive steps: Step 1: engraving of the plates to create internal channels; Step 2: Diffusion welding resulting in an internally channeled monolithic device; Step 3P: pre-drilling of the device obtained in the previous step by means of mechanical machining, for example drilling or milling; Step 3DS: creation of a collector by means of a new machining of the pre-drilling of the previous step by means of electro-erosion by sinking or wire.

[0050] In the case where the electro-erosion operation is of the wire type, then the pre-drilling is through and the operation must be completed with: Step 5: closing one end of the collector.

[0051] Advantageously, this solution proves to be very fast, in that the electro-erosion technique is all the faster when the quantity of material to be eroded is small, so pre-drilling, which is in itself a relatively fast operation, makes it possible to accelerate the electro-erosion operation.

[0052] However, pre-drilling can also be carried out at the level of the engraving of the individual plates. Figure 6 shows a variant of the process comprising the following steps in succession: Step 1: engraving the plates to create internal channels; Step Ibis: engraving of pre-drillings in relation to a collector to be carried out in at least some of the plates from the previous step; Step 2: diffusion bonding (diffusion welding) obtaining an internally channeled monolithic device; Step 3DS: production of the collector by means of a new machining of the pre-drilling of step Ibis by means of electro-erosion by sinking or wire, and in the case in which the electro-erosion operation is of the wire type, then all the plates are subjected to the engraving of the pre-drillings and it is therefore necessary to complete the operation with: Step 5: closure of one end of the collector.

[0053] All variants may include an optional step, indicated with the number 4, which provides for the lapping / polishing of the manifold, making the fluid path as smooth as possible.

[0054] In the case of the present invention, it is understood that the collector obtained is smooth, that is to say, free from scratches and / or burrs.

[0055] Advantageously, the break-in operation carried out after the opening or finishing of the manifold does not produce metal shavings such as to clog the passages and the channels that open in the manifold. In addition, the honing process produces even a minimal rounding of the sharp edges of the etched channel margins. Since these channels are defined partly in one plate and partly in the next, this rounding, in synergy with the rest of the process, helps to limit the edge effect, also having a positive effect on the pressure drop of the fluid flowing through the conduits themselves.

[0056] From what has been described so far, it is clear that, thanks to the present invention, it is possible to obtain a channeled device comprising a manifold in which at least one internal channel opens, the manifold having a particularly smooth internal surface. The effects of these surfaces consist of a significant reduction in turbulence inside the manifold, in addition to a reduction in edge effect. There are possible embodiments from the non-limiting example described, without departing from the scope of protection of the present invention, including all embodiments equivalent to the content of the claims for those skilled in the art.

[0057] In the description given above, a person skilled in the art is able to carry out the object of the invention without introducing any further construction details.

Claims

Demands

1. A method for manufacturing a monolithic channeled device, defining a heat exchanger, comprising at least one internal or external manifold in which at least one channel opens, the method being based on the diffusion bonding technique, comprising the following successive steps: (step 1) etching a plurality of metal plates to make the internal channels; (step 2) welding a stack comprising the plurality of plates by diffusion bonding, obtaining an internally channeled monolithic device; (step 3, 3DS) making the manifold by electro-erosion.

2. The method according to claim 1, wherein said electro-erosion is carried out by means of die-sinking electro-erosion.

3. Method according to claim 1, wherein said electro-erosion is carried out by means of wire electro-erosion.

4. A method according to any one of the preceding claims, wherein, where the manifold is internal, the method further comprises a preliminary step of pre-drilling the manifold (Ibis, 3P) and wherein the step of making the manifold (step 4) comprises a further machining of the pre-drilling by means of electro-erosion.

5. A method according to claims 3 and 4, wherein said pre-drilling is carried out by means of: (Step Ibis) engraving the metal plates before the welding step, or (Step 3P) drilling or milling the internally channeled monolithic device previously obtained.

6. A method according to any one of claims 1 to 3, wherein, where the collector is external, the method includes a preliminary pre-cutting step of a portion of the channeled device intended to be associated with an external collector (Ibis, 3P) and wherein the collector fabrication step (Step 4) includes a further pre-cutting machining by means of electro-erosion.

7. A method according to any one of the preceding claims, wherein at least said engraving operation is carried out according to at least one of the following techniques: laser cutting; waterjet cutting; photogravure.

8. A method according to any one of the preceding claims, further comprising (Step 4) a procedure for polishing or lapping the resulting collector.

9. A method according to any one of claims 1 to 5, further comprising (Step 5) a step of closing one end of the internal collector when said electro-erosion step is carried out by means of wire electro-erosion.

10. A channeled device comprising at least one internal or external collector in which at least one channel opens, characterized in that the collector has a smooth and preferably polished or honed surface.

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