Preparation process of a multi-layer honeycomb core and microporous plate combined sound-absorbing structure

Abstract

The present invention provides a preparation process for a multi-layer honeycomb core and microporous plate combined sound-absorbing structure; ensure that the sound-absorbing structure has sufficient strength, is applicable under a wide temperature range (-163℃~50℃), can withstand high and low temperature impacts, has good fatigue resistance, has a service life of more than 50 years, and has the characteristic of unobstructed airflow, meeting the sound-absorbing performance requirements. The present invention applies solder resist on the microporous plate, alternately assembles the multi-layer honeycomb core + multi-layer microporous plate embryos and fixes them with a mold, and then brazes them once; effectively prevents the formation of coarse-grained brittle welded joints between the honeycomb core and the panel caused by multiple brazing, and the brazing of brittle joints reduces the service life of the product. The present invention provides an effective multi-layer microporous plate anti-blocking solder arrangement method, which effectively reduces the negative impact of blocking holes on the performance of the sound-absorbing structure during welding.

Description

Technical Field

[0001] The present invention relates to the technical field of noise reduction equipment preparation, and in particular to a preparation process of a sound-absorbing structure composed of a honeycomb core and microporous plates. Background Art

[0002] Wind tunnels are crucial facilities for aerodynamic research and aircraft development, and their structural safety and suitability are crucial for conducting experiments within them. Currently, noise reduction devices in wind tunnels are mostly composite structures composed of sound-absorbing cotton and microporous panels. While simple to manufacture, these structures suffer from limited service life and the need for frequent material replacement. Low-temperature wind tunnels, crucial equipment for aerodynamic research, place even higher demands on the low-temperature resistance and durability of noise reduction equipment. Due to their harsh operating conditions, the high flatness requirements inherent in the product itself, and the high joint strength requirements for the various components of the noise reduction structure, there is currently no mature and suitable process for manufacturing such structures.

[0003] Ultra-low-temperature anechoic structures are still in the research phase. A search revealed that existing metal honeycomb components are primarily used in vibration damping, energy absorption, and heat exchange applications, such as "CN110978707A Lightweight, Broadband, Multi-Band, Strongly Absorbent Double-Layer Structure Absorbing Plate and Its Preparation Method," "CN108372393A A High-Strength Energy-Absorbing Honeycomb Composite Structure and Its Preparation Method," and "CN113733687A A Method for Making a High-Strength Honeycomb Composite Panel." None of these reports incorporate a double-layer metal honeycomb combined with multiple layers of microporous panels into an anechoic structure designed for use in anechoic devices capable of withstanding ultra-low temperatures (-163°C) and high wind speeds (28 m / s). While CN110978707A utilizes a double-layer honeycomb core and faceplate structure, the core and faceplates are bonded together using a bonding method. This bonding method has limited strength, environmental concerns, and aging issues with the adhesive, making it unsuitable for extended operation in ultra-low temperatures and high-speed airflows. Furthermore, it cannot meet the 50-year service life requirements of a wind tunnel. Although CN108372393A and CN113733687A use brazing technology, they are single-layer honeycomb core + panel structures, and the panels have no open-pore structures; this will easily lead to clogging of the honeycomb core and dimensional deformation caused by inconsistent thermal expansion and contraction. The preparation method of its multi-layer energy-absorbing structure in CN108372393A is to first prepare a single-layer honeycomb panel sample, and then assemble the single-layer honeycomb panel samples and braze them. The multiple brazing methods used will cause the grains at the interface of the weld joint to become larger and form a brittle structure, thereby reducing the structural strength of the brazed joint. CN111816151A is a double-layer honeycomb-microperforated structure with adjustable back cavity height and its design method. It involves a design method for a double-layer honeycomb microporous plate structure with adjustable back cavity height. This adjustable back cavity structure must first form small cavities separately, and then combine the adjustable structural cavities as a whole. Its manufacturing cycle, cost and difficulty are questionable.

[0004] Existing honeycomb brazing technologies are mostly based on aluminum alloy brazing (brazing temperatures do not exceed 700°C). For example, "CN103009013A Method for preparing metal honeycomb core materials and honeycomb sandwich panels" only mentions a 450°C brazing forming solution, and does not mention a process for brazing a double-layer honeycomb core and a three-layer micro-perforated panel at a high temperature exceeding 1000°C. "CN112775512A A stainless steel honeycomb heat exchanger and its vacuum brazing method" although using a high-temperature vacuum brazing method, it only welds single-layer cylindrical steel pipes, and there are no panels to connect. It does not consider the reduction in noise reduction performance of the silencer due to panel blocking. In high-temperature brazing (over 1000°C), materials will expand when heated, especially large-sized thin plate structures, where deformation is particularly obvious. How to control the thin plate structure to maintain good flatness after high temperature by designing an effective mold is also a major problem. Existing high-temperature vacuum brazing of stainless steel does not involve the brazing of plates larger than 500*400mm. 2 A process mold method is developed to weld thin panels (0.5-1.0mm) to multi-layer honeycomb cores (honeycomb core cumulative height ≥200mm) without significant panel deformation. The difficulty of this welding technology lies in the thermal expansion of large thin panels at high temperatures. Due to the large size of the panels, it is impossible to maintain a consistent temperature throughout the welding area with the honeycomb core. As a result, uneven heating of the panel causes step deformation, resulting in poor flatness of the welded product. Summary of the Invention

[0005] In response to the above-mentioned technical problems, the present invention provides a preparation process for a sound-absorbing structure composed of a multi-layer honeycomb core and a microporous plate; the purpose of the present invention is to provide a manufacturing process method for a new noise reduction structure (double-layer stainless steel honeycomb core + three-layer stainless steel micro-perforated plate) to ensure that the structure has sufficient strength, is applicable in a wide temperature range (-163℃~50℃), can withstand high and low temperature impacts, has good fatigue resistance, a service life of >50 years, and has the characteristics of unobstructed airflow, meeting the sound-absorbing performance requirements.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation process for a multi-layer honeycomb core and microporous plate combined sound-absorbing structure comprises the following steps:

[0008] Step 1: Design and process the honeycomb core, microporous plate and enclosure according to the required size; clean the honeycomb core, microporous plate and enclosure;

[0009] Step 2: Weld and fix the panels into a hollow frame at the bottom and top;

[0010] Step 3: Weld a microporous plate as a bottom plate to the bottom of the frame to form a trough structure. In the trough structure, the honeycomb core and the microporous plate are assembled into an inner core structure in an alternating manner of a layer of honeycomb core and a layer of microporous plate. Solder is arranged between the honeycomb core and the microporous plate. After the inner core structure is installed, another microporous plate is welded as a top plate to the top of the frame to obtain a sound-absorbing structure.

[0011] Step 4: Place the noise reduction structure assembled in step 3 into the mold and press and fix it;

[0012] Step 5: Place the compressed and fixed silencer structure into a vacuum furnace for vacuum brazing. After the welding is completed, remove it from the mold to obtain a silencer structure composed of a multi-layer honeycomb core and a microporous plate.

[0013] Further preferably, the solder in the above step 3 is nickel-based paste solder and / or foil-like Ni-based solder sheet.

[0014] Further preferably, the lower part of each layer of the honeycomb core is coated with nickel-based paste brazing filler metal, and the upper part is provided with a foil-like Ni-based welding sheet.

[0015] To further prevent clogging of the microporous plate, the present invention employs a method of applying a nickel-based solder paste to the lower portion of the honeycomb core and placing a Ni-based solder foil on the upper portion. During the high-temperature soldering process, both the nickel-based solder paste and the Ni-based solder foil melt. However, because the Ni-based solder foil is placed on top of the honeycomb core, gravity allows the melted solder to flow down the honeycomb tube walls without accumulating in the micropores of the microporous plate and causing clogging. After being applied to the lower portion of the honeycomb core and then contacting the microporous plate, the nickel-based solder paste avoids the micropores, so even if it melts, it will not cause extensive clogging of the micropores.

[0016] If solder paste is also used on the upper portion of the honeycomb core, additional solder paste must be added to ensure post-weld strength. Otherwise, the solder will drain due to gravity during welding, preventing sufficient weld strength. Furthermore, the lost solder paste may flow down the honeycomb tube wall and onto the next layer of microporous plates, causing blockage. If solder sheets are also used on the lower portion of the honeycomb core, the melted solder sheets will clog the micropores of the microporous plates located below the core.

[0017] Preferably, the nickel-based solder paste is BNi2, and the nickel-based solder paste is applied to a depth of 1 to 5 mm on the honeycomb core; the nickel-based solder foil is 40 to 60 μm thick. To avoid clogging the micropores, the application amounts of nickel-based solder paste and nickel-based solder foil are further optimized so that after melting the nickel-based solder foil, excess solder is deposited on the inner wall of the honeycomb core and does not flow onto the underlying microporous plate.

[0018] Further preferably, the micro-perforated plates welded to the bottom and top of the frame are coated with solder resist on the side away from the inner core structure, so that the holes of the micro-perforated plates are filled with solder resist. The solder resist can prevent the micro-perforated plates on the outermost surface of the muffler structure from clogging the holes and can also prevent the muffler structure from sticking to the mold.

[0019] Further preferably, the mold in the above step 4 includes an inner mold and an outer mold; the inner mold is a graphite mold, and the outer mold is a stainless steel mold.

[0020] At high temperatures, if there is no mold, the microporous plate on the surface of the product will deform to form wavy lines, which will make it impossible to effectively weld the microporous plate and the honeycomb core (the deformation of the honeycomb core and the microporous plate are inconsistent). Graphite molds have good stability at high temperatures and can meet the small dimensional deformation requirements at high temperatures of 1000°C, which is negligible compared to metals. If there is only a graphite mold and no stainless steel mold and bolts for fastening the outer layer, the microperforated plate cannot be completely compressed at high temperatures, resulting in ineffective welding. If an integral stainless steel mold is used for the outer layer, the plate surface of the stainless steel mold is too thick and heavy, which is not conducive to the stress release of the honeycomb core and the microporous plate, resulting in deformation of the final product; if the plate surface of the stainless steel mold is too thin and light, the stainless steel itself will soften during the high-temperature welding process, making it impossible to achieve compaction, which will also cause deformation of the final product.

[0021] Further preferably, the above-mentioned graphite mold includes an upper graphite plate and a lower graphite plate that can cover the top plate and the bottom plate respectively; the centers of the upper graphite plate and the lower graphite plate are aligned with the center of the silencer structure, with a tolerance of ≤5mm; after the upper graphite plate and the lower graphite plate are aligned, the outer edges of the plate bodies extend beyond the outer edge of the silencer structure by 20 to 50mm; the thickness of the upper graphite plate and the lower graphite plate is 50 to 80mm.

[0022] By optimizing the combined structure of the graphite mold and the muffler structure, we can effectively avoid uneven force and product deformation during high-temperature welding due to misalignment between the muffler and mold structures. Too thick graphite can cause product collapse, while too thin graphite can easily break; therefore, a moderate graphite sheet thickness is optimized.

[0023] Further preferably, the outer mold is a stainless steel clamp capable of providing clamping force for the inner mold, and the clamping torque of the stainless steel clamp is 30 to 50 N.M.

[0024] More preferably, the stainless steel clamp comprises multiple sets of clamping plates, the thickness of the clamping plates is 20-40 mm, and the size of the clamping plates is (600-550)*(180-200) mm. 2After the clamping plates are fixed to the graphite mold, the gap between each set of clamping plates is 50 to 100 mm. The main reason why a solid stainless steel mold cannot be used is that the mold is too heavy, and the discontinuous stainless steel mold has better rigidity and is more stable at high temperatures.

[0025] Further preferably, the temperature control process of the above-mentioned vacuum brazing is to heat up from room temperature to 730-780°C at a heating rate of 2-3°C / min, and then keep it warm for 60-100 minutes; then heat up to 880-920°C at the same heating rate, and then keep it warm for 40-80 minutes; heat up to 1020-1080°C at the same heating rate again, and then keep it warm for 30-60 minutes; finally cool it with the furnace. If the heating rate is too slow, the production rhythm will be slowed down and the cost will be greatly increased; if the heating rate is too fast, the material will expand too quickly and the deformation will be difficult to control, resulting in product cracking or excessive flatness. Using a multi-stage heating and insulation mode for welding can effectively release the internal stress accumulation of the product during the welding process.

[0026] Further preferably, the micro-perforated plates welded to the bottom and top of the frame are fixed to the frame by argon arc spot welding, with the welding points spaced 100 to 200 mm apart. By spot welding and maintaining appropriate spacing between the welding points, deformation of the micro-perforated plates during high-temperature welding can be avoided.

[0027] More preferably, the solder resist in step 3 is TIJO solder resist, and the amount of solder resist applied is 80-150 g / m2. TIJO solder resist can effectively prevent clogging of the micro-hole plate.

[0028] Compared with the prior art, the specific advantages of the present invention mainly include:

[0029] (1) The present invention provides a multi-layer honeycomb core + multi-layer microporous panel one-step brazing forming solution, which effectively prevents the formation of coarse-grained brittle weld joints between the honeycomb core and the panel caused by multiple brazing processes. The brazing of brittle joints reduces the service life of the product. The present invention provides a multi-layer microporous panel anti-blocking solder arrangement method, which effectively reduces the negative impact of blockage on the performance of the sound-absorbing structure during welding.

[0030] (2) This solution provides a reasonable solder arrangement method for a double-layer honeycomb core + three-layer microporous plate, so that the three-layer microporous panel and the double-layer honeycomb core can be firmly welded, while avoiding clogging of the microporous plate to affect the sound insulation effect. This solder arrangement method can be further expanded to a multi-layer honeycomb core + multi-layer microporous plate; the present invention adopts the method of applying nickel-based paste solder on the lower part of the honeycomb core and arranging foil-shaped Ni-based welding sheets on the upper part. During the high-temperature welding process, the nickel-based paste solder and the foil-shaped Ni-based welding sheet will both melt, but because the foil-shaped Ni-based welding sheet is arranged on the upper part of the honeycomb core, with the help of gravity, the molten welding sheet can flow down the honeycomb tube wall and will not gather at the micropores of the microporous plate. After the nickel-based paste solder is applied to the lower part of the honeycomb core and then contacts the microporous plate, it can avoid the micropores, so even if it melts, it will not cause large-scale clogging of the micropores.

[0031] (3) The present invention provides a mold combination suitable for vacuum brazing at high temperatures, which prevents deformation of the product surface during high-temperature welding and effectively ensures the welding rate of the product. The present invention adopts a mold combination suitable for vacuum brazing at high temperatures (>1000°C). This type of mold applies a certain pre-tightening force to make the various components of the product bear stress at high temperatures, while eliminating the problem of uneven product surface caused by the high-temperature deformation of the mold itself. This type of mold solves the problem of difficult-to-control deformation of the external dimensions of the welding body at extremely high temperatures, and also solves the problem that large-sized and extremely thin panels are easily deformed due to uneven heating at high temperatures and are difficult to effectively connect with the honeycomb core.

[0032] (4) The one-time brazing forming solution provided by the present invention makes the connection strength of the components of the sound-absorbing structure of the honeycomb core and the layer of microporous plate high, and the high and low impact fatigue resistance is excellent, and the sound-absorbing effect is outstanding; and the microporous plate is a whole plate, which has the characteristics of unobstructed air flow, meets the sound-absorbing performance requirements, and effectively realizes the sound-absorbing requirements of the low-temperature wind tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of solder arrangement in Example 1 of the present invention;

[0034] Figure 2 Schematic diagram of the assembly of the brazing mold in Example 1 of the present invention;

[0035] Figure 3 A stereoscopic diagram of the assembly of the brazing die in Example 1 of the present invention;

[0036] Figure 4 A top view of a microporous plate after molding and then sectioning of product sample 1 in Example 1 of the present invention;

[0037] Figure 5 The overall structure diagram of the low temperature resistance test results of the product sample in Example 1 of the present invention;

[0038] Figure 6 A longitudinal cross-sectional view of the product sample 2 after the low temperature resistance test results in Example 2 of the present invention;

[0039] Figure 7 Picture of micropores of the product sample after brazing in Comparative Example 1 of the present invention;

[0040] Figure 8 Photograph of the product sample before brazing in Comparative Example 2 of the present invention;

[0041] Figure 9 Photograph of the product sample after brazing in Comparative Example 2 of the present invention;

[0042] Figure 10 Photograph of the product sample after brazing in Comparative Example 3 of the present invention.

[0043] Legend:

[0044] S1, muffler structure; 1, enclosure; 2, top plate; 3, bottom plate; 4, inner core structure; 41, first honeycomb core; 42, second honeycomb core; 43, intermediate microporous plate; 44, first nickel-based solder paste; 45, second nickel-based solder paste; 46, first Ni-based foil solder; 47, second Ni-based foil solder;

[0045] S2, graphite mold; S21, upper graphite plate; S22, lower graphite plate;

[0046] S3, stainless steel clamp; S31, clamping plate; S32, bolt; S33, screw. DETAILED DESCRIPTION

[0047] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed form in conjunction with the accompanying drawings and preferred embodiments below, but the scope of protection of the present invention is not limited to the following specific embodiments. In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed form in conjunction with the accompanying drawings and preferred embodiments below, but the scope of protection of the present invention is not limited to the following specific embodiments. It should be particularly noted that in the description of the present invention, it should be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0048] Example 1:

[0049] A preparation process for a multi-layer honeycomb core and microporous plate combined sound-absorbing structure.

[0050] like Figure 1 As shown, the sound-absorbing structure S1 of the combination of multi-layer honeycomb core and microporous plate includes a surrounding plate 1, a top plate 2, a bottom plate 3 and an inner core structure 4; the inner core structure includes a first honeycomb core 41, a second honeycomb core 42 and an intermediate microporous plate 43; the top plate 2 and the bottom plate 3 are both microporous plates; solder is arranged between the honeycomb core and the microporous plate, wherein a first foil-like Ni-based welding sheet 46 is arranged between the top plate 2 and the first honeycomb core 41, a first nickel-based paste solder 44 is arranged between the first honeycomb core 41 and the intermediate microporous plate 43, a second foil-like Ni-based welding sheet 47 is arranged between the intermediate microporous plate 43 and the second honeycomb core 42, and a second nickel-based paste solder 45 is arranged between the second honeycomb core 42 and the bottom plate 3.

[0051] The specifications of the sound-absorbing structure sample 1 prepared in this embodiment are: length×width×height: 805mm×507mm×235mm.

[0052] The specific preparation process includes the following steps:

[0053] Step 1: First, process the honeycomb core, microporous plate, enclosure and other components according to the design; clean the honeycomb core, microporous plate and enclosure.

[0054] Step 2: Use a laser spot welder to weld and fix each panel into a hollow frame at the bottom and top.

[0055] Step 3: Apply TIJO solder resist on the upper surface of the top plate 2 and the lower surface of the bottom plate 3 at a coating amount of 100g / ㎡, ensuring that there is solder resist in the microholes of the top plate 2 and the bottom plate 3, and air dry for 1 hour until the solder resist solidifies.

[0056] Step 4: Using nickel-based solder paste as solder, apply a first nickel-based solder paste 44 of BNi2 on one side of the first honeycomb core 41, and apply a second nickel-based solder paste 45 of BNi2 on one side of the second honeycomb core 42; the solder is 3 mm high on the honeycomb core.

[0057] Step 5: Assemble the components into a sound-absorbing structure S1, and arrange them as follows: Figure 1 As shown:

[0058] a. Fix the bottom plate 3 to the frame formed in step 2 by argon arc spot welding, with the welding point spacing being 100mm;

[0059] b. Place the second honeycomb core 42 in the molding frame, note that the side with the second nickel-based solder paste 45 faces the solder resist-free side of the base plate 3, and arrange a second Ni-based foil-like solder sheet 47 with a thickness of 60 μm on the side without the second nickel-based solder paste 45 of the second honeycomb core 42;

[0060] c. Place the intermediate microporous plate 43 on top of the second foil-like Ni-based solder sheet 47, and place the first honeycomb core 41 on the intermediate microporous plate 43, with the side having the first nickel-based solder paste 44 facing the solder resist-free side of the intermediate microporous plate 43;

[0061] d. A first foil-like Ni-based solder sheet 46 having a thickness of 60um is arranged on one side of the first honeycomb core 41 without the first nickel-based solder paste 44;

[0062] e. The top plate 2 is covered on the first foil-like Ni-based welding sheet 46 and fixed by argon arc spot welding so that the top plate 2 is welded to the frame, requiring a welding point spacing of 100mm;

[0063] Step 6: Mold assembly, mold assembly diagram as shown Figure 2 and Figure 3 shown.

[0064] Assemble the silencer structure S1 with the inner graphite mold S2. The graphite mold S2 includes an upper graphite plate S21 and a lower graphite plate S22 that can cover the top plate 2 and the bottom plate 3 respectively. The centers of the upper graphite plate S21 and the lower graphite plate S22 are aligned with the center of the silencer structure S1 with a tolerance of ≤5mm. This prevents deformation of the microporous plate surface due to uneven weight distribution and heating of the silencer structure. After the upper graphite plate S21 and the lower graphite plate S22 are aligned, the outer edges of the plate bodies extend 20mm beyond the outer edge of the silencer structure. The thickness of the upper graphite plate S21 and the lower graphite plate S22 is 50mm.

[0065] The aforementioned silencer structure S1 and the inner graphite mold S2 are assembled with the outer mold; the outer mold is a stainless steel clamp S3 that provides clamping force for the inner mold, with a clamping torque of 50 N.M. The stainless steel clamp includes multiple sets of clamping plates S31 and bolts S32 and screws S33 assembled with the clamping plates. The bolts S32 are pre-tightened to provide a clamping force of 50 N.M for the stainless steel clamp. The clamping plates S31 are 30 mm thick and have dimensions of 560 x 200 mm. 2 After the graphite mold is clamped and fixed by the clamping plate S31, the gap between each group of clamping plates S31 is 100mm; the screw is a screw of M12 to M20.

[0066] Step 7: Place the assembled molded silencer structure into a vacuum furnace for vacuum brazing. The brazing temperature process parameters are: 120 minutes from room temperature to 300°C, then 120 minutes from 300°C to 600°C, then heating at the same rate to 750°C and holding for 80 minutes, then heating to 900°C and holding for 1 hour, and finally heating to 1050°C and holding for 45 minutes. Cool in the furnace, and after welding, remove from the mold to obtain a multi-layer honeycomb core and microporous plate combined silencer structure.

[0067] Example 2:

[0068] The structural arrangement and preparation process of the noise reduction structure in this embodiment are the same as those in embodiment 1, except for the product specifications. The noise reduction structure sample 2 prepared in this embodiment has the following specifications: length × width × height: 411 mm × 215 mm × 200 mm.

[0069] The noise reduction structures obtained in Example 1 and Example 2 were tested for product performance. Figure 4 The figure shows a view of the middle microporous plate 43 of sample 1 after forming and then cutting, and the picture shows that the micropores on the middle microporous plate 43 are less clogged. Figure 5 The figure shows the overall structure of sample 1 after the low temperature test. The figure shows that the structure of sample 1 is intact. Figure 6 The figure shows a longitudinal section of sample 2 after the low temperature test, which shows that the structure of sample 2 is intact. Table 1 below shows the specific results of the low temperature resistance test samples.

[0070] Table 1: Low temperature resistance test results

[0071]

[0072] Comparative Example 1

[0073] This comparative example is compared with Example 1, except that the soldering arrangement mode adopts the method of adding solder sheets at both the upper and lower ends of the honeycomb core, and other conditions are the same as Example 1. The obtained product was observed and tested. Figure 7 As shown, the results show that most of the middle hole plate is blocked and the silencer structure fails.

[0074] Comparative Example 2

[0075] Compared with Example 1, this comparative example uses a pure steel plate mold, and other conditions are the same as Example 1. The obtained product was observed and tested. Figure 8 and Figure 9 As shown, Figure 8 This is the surface condition of the product before brazing. Figure 9 This is the surface condition of the product after brazing. The comparison shows that the microporous plate becomes wavy and has obvious deformation after brazing.

[0076] Comparative Example 3

[0077] Compared with Example 1, the heating rate used in this comparative example is 5°C / min, the cooling rate is also 5°C / min, and other conditions are the same as those in Example 1. The obtained product was observed and tested. Figure 10 As shown in the figure, it can be seen that the product has been deformed and cannot be restored after the temperature returns to normal.

[0078] The above is only a preferred embodiment of the present invention. For other preparation methods using similar double-layer honeycomb core silencer structures, single-layer or multi-layer honeycomb cores combined with multi-layer micro-perforations, as long as they do not deviate from the content of the technical solution of the present invention, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A preparation process for a multi-layer honeycomb core and microporous plate combined sound-absorbing structure, characterized in that: The following steps are involved: Step 1: Design and process the honeycomb core, microporous plate and enclosure according to the required size; clean the honeycomb core, microporous plate and enclosure; Step 2: Weld and fix the panels into a hollow frame at the bottom and top; Step 3: Weld a microporous plate as a bottom plate to the bottom of the enclosure to form a trough structure. Within the trough structure, the honeycomb core and the microporous plate are assembled into an inner core structure in an alternating pattern of one honeycomb core layer and one microporous plate layer. Solder is placed between the honeycomb core and the microporous plate. After the inner core structure is installed, another microporous plate is welded as a top plate to the top of the enclosure to form a sound-absorbing structure. The solder applied to the bottom of each layer of the honeycomb core is a nickel-based paste solder, and the solder applied to the top is a foil-like Ni-based solder sheet. Step 4: The silencer structure assembled in step 3 is placed into a mold for compaction and fixation; the mold includes an inner mold and an outer mold; the inner mold is a graphite mold, and the outer mold is a stainless steel fixture capable of providing clamping force for the inner mold; the graphite mold includes an upper graphite plate and a lower graphite plate capable of covering the top plate and the bottom plate respectively; the centers of the upper graphite plate and the lower graphite plate are aligned with the center of the silencer structure with a tolerance of ≤5mm; after the upper graphite plate and the lower graphite plate are aligned, the outer edges of the plate bodies extend 20 to 50mm beyond the outer edge of the silencer structure; the stainless steel fixture includes multiple sets of clamping plates for clamping and fixing the graphite mold; Step 5: Place the compressed and fixed silencer structure into a vacuum furnace for vacuum brazing. After the welding is completed, remove it from the mold to obtain a silencer structure composed of a multi-layer honeycomb core and a microporous plate. The temperature control process of the vacuum brazing is as follows: heating from room temperature to 730-780°C at a heating rate of 2-3°C / min, then keeping the temperature for 60-100 minutes; then heating to 880-920°C at the same heating rate, then keeping the temperature for 40-80 minutes; heating again to 1020-1080°C at the same heating rate, then keeping the temperature for 30-60 minutes; and finally cooling with the furnace.

2. The preparation process according to claim 1, characterized in that The nickel-based paste solder is BNi2, and the height of the nickel-based paste solder applied on the honeycomb core is 1-5 mm; the thickness of the foil-like Ni-based welding sheet is 40-60 μm.

3. The preparation process according to claim 1, characterized in that The micro-porous plate welded to the bottom and top of the surrounding frame is coated with solder resist on a side away from the inner core structure so that the holes of the micro-porous plate are filled with solder resist.

4. The preparation process according to claim 1, characterized in that The thickness of the upper graphite plate and the lower graphite plate is 50 to 80 mm.

5. The preparation process according to claim 4, characterized in that The clamping torque of the stainless steel clamp is 30 to 50 N.M.

6. The preparation process according to claim 5, characterized in that: The thickness of the clamping plate is 20-40 mm, and the size of the clamping plate is (600-550)*(180-200) mm. 2 After the clamping plates clamp and fix the graphite mold, the gap between each group of clamping plates is 50 to 100 mm.

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