A vibration curing forming method for honeycomb sandwich structure

Abstract

The present invention provides a vibration curing forming method for a honeycomb sandwich structure, belonging to the technical field of composite material connection. The vibration curing forming method includes: providing components of the honeycomb sandwich structure, encapsulation auxiliary components, a vacuum bag, and a mold, wherein the components include an upper skin, a lower skin, a honeycomb core, and two layers of adhesive films; laying the components and the encapsulation auxiliary components on the mold and encapsulating them using the vacuum bag to obtain an assembled component; providing a fixing member and a vibration device having a receiving cavity, first fixing the assembled component on the vibration table of the vibration device, then evacuating the vacuum bag, and then curing according to a preset vibration curing process to obtain the honeycomb sandwich structure. The present invention forms the honeycomb sandwich structure based on the vibration device, and by optimizing the forming process, the prepared honeycomb sandwich structure has a lower skin porosity and better mechanical properties compared with autoclave forming, thereby improving the forming quality and efficiency of the honeycomb sandwich structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material connection, and particularly relates to a vibration curing forming method for a honeycomb sandwich structure. Background Art

[0002] A honeycomb sandwich structure includes a honeycomb core, and a lower skin and an upper skin respectively disposed on both sides of the honeycomb core and connected to the honeycomb core. Among them, the honeycomb core is connected to the lower skin and the upper skin through adhesive films. The honeycomb sandwich structure has the advantages of light weight, high specific strength and specific stiffness, and is widely used in primary and secondary load-bearing parts such as high-precision satellites, the leading edge of aircraft wings, wing tips, tail fins, and control surfaces.

[0003] The forming methods for honeycomb sandwich structures provided by the prior art mainly include two forming methods: the co-adhesive method and the co-curing method. For the honeycomb sandwich structure formed by the co-adhesive method, the skin and the internal forming quality are good, but the manufacturing cycle is prolonged, the manufacturing cost is increased, and the difficulty of precise matching between the skin and the honeycomb core is great. The co-curing method is a method of curing the skin, the adhesive film and the honeycomb core at one time, and has the advantages of high forming efficiency and the ability to manufacture structures with complex profiles.

[0004] At present, the co-curing forming of honeycomb sandwich structures mainly uses autoclave forming. Based on the characteristics of autoclave process forming, the honeycomb sandwich structure needs to be cured under the combined action of pressure and temperature, and the requirements for the process system are extremely strict. If the pressure in the autoclave is too high, problems such as honeycomb slippage, shrinkage and skin wrinkles will occur in the formed structure due to the poor lateral compressive performance of the honeycomb core material itself; if the pressure in the autoclave is too low, the skin quality and bonding performance of the formed honeycomb sandwich structure will be poor, manifested as a large number of pores in the skin and the adhesive layer. As can be seen from the above, too high or too low pressure will cause the quality of a single formed part to exceed the standard, resulting in the scrapping of the whole part, high manufacturing cost, low efficiency, etc. Summary of the Invention

[0005] The purpose of the present invention is to provide a new process for one-time curing and forming of a honeycomb sandwich structure. This process is based on a vibration device for forming, and by optimizing the forming process, the prepared honeycomb sandwich structure has a lower skin porosity and better mechanical properties compared with autoclave forming, thereby improving the forming quality and efficiency of the honeycomb sandwich structure.

[0006] To achieve the above purpose, the present invention provides a vibration curing forming method for a honeycomb sandwich structure. The honeycomb sandwich structure includes a lower skin, a honeycomb core and an upper skin stacked along the height direction. The upper skin and the lower skin are both connected to the honeycomb core through adhesive films. The vibration curing forming method includes the following steps:

[0007] Step (1): Provide the components of the honeycomb sandwich structure, the encapsulation auxiliary components, the vacuum bag, and the mold for carrying the components of the honeycomb sandwich structure and the encapsulation auxiliary components. Among them, the components include an upper skin, a lower skin, a honeycomb core, and two layers of adhesive films; Step (2): Lay the components and the encapsulation auxiliary components on the mold according to a preset method, and use the vacuum bag to encapsulate the components of the honeycomb sandwich structure and the encapsulation auxiliary components to obtain an assembled component; Step (3): Provide a fixing member and a vibration device with a receiving cavity. First, place the assembled component in the receiving cavity and use the fixing member to fix the assembled component on the vibration table of the vibration device. Then, evacuate the vacuum bag and maintain the vacuum degree ≤ -0.098 MPa. Then, cure according to a preset vibration curing process to obtain the honeycomb sandwich structure. The preset vibration curing process includes first raising the temperature in the receiving cavity of the vibration device from room temperature to a first curing temperature and maintaining the temperature at the first curing temperature for a first duration. Then, raise the temperature from the first curing temperature to a second curing temperature and maintain the temperature at the second curing temperature for a second duration. When the second curing temperature holding ends, cool down to a preset temperature to complete the curing. At the same time, when the temperature in the receiving cavity of the vibration device reaches the first curing temperature, turn on the vibration function of the vibration device and apply vibration excitation in three directions, namely the X direction, the Y direction, and the Z direction, to the vibration table at a preset vibration acceleration, and the duration of the vibration excitation is the same as the first duration. Among them, the first curing temperature is 90 °C, the first duration is 30 min, and the preset vibration acceleration is 10g.

[0008] In a specific embodiment, the vibration device further includes a box body, a spring assembly for supporting the vibration table, and a vibration module. The vibration table is installed in the box body and divides the box body into the receiving cavity and the accommodating cavity. The vibration module is used to apply vibration excitation to the vibration table.

[0009] In a specific embodiment, the vibration module includes a plurality of inclined pneumatic hammers arranged in a preset arrangement, a plurality of ventilation ducts, and an air compressor. The pneumatic hammer includes a first end and a second end. The first end of the pneumatic hammer is fixedly connected to the lower surface of the vibration table. One end of each ventilation duct is connected to one of the pneumatic hammers and the other end is connected to the air compressor. The preset arrangement is that a plurality of pneumatic hammers are evenly distributed in multiple circles around the central axis of the vibration table.

[0010] In a specific embodiment, the pneumatic hammer further includes a pneumatic hammer housing having a cavity, a piston located within the cavity and capable of sliding back and forth along the length direction of the pneumatic hammer housing, a cushion block provided on the inner wall of the pneumatic hammer housing and adjacent to the first end of the pneumatic hammer, a gas connector installed on the pneumatic hammer housing and communicating with the ventilation duct, and a gas delivery pipe provided on the piston and communicating with the gas connector. The output end of the gas delivery pipe faces the second end of the pneumatic hammer. The gas compressed by the air compressor sequentially enters the cavity through the ventilation duct, the gas connector, and the gas delivery pipe, driving the piston to move from the second end of the pneumatic hammer to the first end. After the piston collides with the cushion block, under the action of the reaction force and gravity, the piston moves from the first end of the pneumatic hammer to the second end.

[0011] In a specific embodiment, based on the installation positions, a plurality of the pneumatic hammers are classified into a first pneumatic hammer, a second pneumatic hammer, and a third pneumatic hammer. The preset arrangement method is specifically as follows: a plurality of first pneumatic hammers are uniformly arranged along a large square, a plurality of second pneumatic hammers are uniformly arranged along a small square located within the large square, and a third pneumatic hammer is arranged at the center of the small square. The center points of the large square and the small square coincide. Among them, the first pneumatic hammer is a large pneumatic hammer, and the second pneumatic hammer and the third pneumatic hammer are small pneumatic hammers.

[0012] In a specific embodiment, the number of the pneumatic hammers is 13. The first ends of 8 first pneumatic hammers are located on the sides or vertices of the large square, the first ends of 4 second pneumatic hammers are located at the vertices of the small square, and the first end of the third pneumatic hammer is located at the center point of the small square.

[0013] In a specific embodiment, the angle between the central axis of the first pneumatic hammer and the side where the first end of the first pneumatic hammer is located is 45 degrees, and the angle between the central axis of the second pneumatic hammer and the side where the first end of the second pneumatic hammer is located is 45 degrees.

[0014] In a specific embodiment, the second curing temperature is 130 °C, and the second duration is 2 h.

[0015] In a specific embodiment, the encapsulation auxiliary component includes a first isolation film, a second isolation film, a pressure equalizing plate, a breathable felt, two metal stoppers, and two rubber stoppers. Laying the components of the honeycomb sandwich structure and the encapsulation auxiliary component on the mold according to a preset method specifically includes: from bottom to top, first laying the mold, the first isolation film, the lower skin, a layer of adhesive film, the honeycomb core, another layer of adhesive film, and the upper skin in sequence. Then, place the two metal stoppers at both ends of the assembled honeycomb sandwich structure and make them abut against each other. Next, place the two rubber stoppers on both sides of the assembled honeycomb sandwich structure and make them abut against each other. Finally, lay the second isolation film, the pressure equalizing plate, and the breathable felt on the upper skin in sequence.

[0016] In a specific embodiment, the vibration excitation is a random vibration excitation.

[0017] The beneficial effects of the present invention at least include:

[0018] First, the present invention provides a vibration curing forming method for a honeycomb sandwich structure. The vibration curing forming method includes: Step (1), providing components of the honeycomb sandwich structure, an encapsulation auxiliary component, a vacuum bag, and a mold for carrying the components of the honeycomb sandwich structure and the encapsulation auxiliary component. Among them, the components include an upper skin, a lower skin, a honeycomb core, and two layers of adhesive film. Step (2), laying the components and the encapsulation auxiliary component on the mold according to a preset method, and encapsulating the components of the honeycomb sandwich structure and the encapsulation auxiliary component by using the vacuum bag to obtain an assembled component. Step (3), providing a fixing member and a vibration device with a receiving cavity. First, place the assembled component in the receiving cavity and fix the assembled component on the vibration table of the vibration device by using the fixing member. Then, evacuate the vacuum bag and maintain the vacuum degree ≤ -0.098 MPa, and then cure according to a preset vibration curing process to obtain the honeycomb sandwich structure. The present invention uses a vibration device for curing and forming. When the adhesive film is in a viscous flow state, the vibration device simultaneously applies vibration excitation in the X direction, Y direction, and Z direction to replace the forming pressure of the autoclave, so that the pores and impurities in the resin can escape along the horizontal direction (X direction and Y direction) and the vertical direction (Z direction), and at the same time promote the resin flow and the combination of resin-fiber (upper skin / lower skin), thereby reducing the generation of defects such as pores at the joint between the formed composite skin and the skin-honeycomb core, and improving the out-of-plane compressive performance of the honeycomb sandwich structure obtained by forming manufacturing and the bonding mechanical properties of the skin-honeycomb core, etc.

[0019] II. Based on the preset vibration curing process (90 - 30 - 10g), using the vibration device provided by the present invention for curing and forming, the peel strength of the skin - honeycomb core of the prepared honeycomb sandwich structure reaches 78.4 N·mm / mm, and the out - of - plane compressive strength reaches 2.237 MPa, which is superior to the peel strength of 74.7 N·mm / mm and the out - of - plane compressive strength of 2.092 MPa under the condition of 0.2 MPa in the autoclave. By comparing the test results, it can be seen that the honeycomb sandwich structure formed by using the preset vibration curing process of the present invention has better mechanical properties and the forming quality has been improved.

[0020] III. A plurality of pneumatic hammers provided by the present invention are arranged according to a preset layout. Specifically, the small pneumatic hammers and the large pneumatic hammers are distributed in a circular pattern from the inside out. On the one hand, it can ensure that the assembled components placed on the vibration platen receive more uniform excitation in the X - direction, Y - direction, and Z - direction, making the resin flow more uniformly. In this way, the skin obtained by curing and forming has a low porosity, the chamfer shape formed in the skin - honeycomb core connection area is good, and the prepared honeycomb sandwich structure has better bonding performance and better out - of - plane compressive performance. On the other hand, it can make the vibration transfer rate in the horizontal direction and the vertical direction higher, avoiding the distortion of vibration transfer caused by the attenuation of vibration excitation.

[0021] IV. The preset vibration curing process provided by the present invention (the first curing temperature is 90 °C, the first duration is 30 min, and the preset vibration acceleration is 10g) is an optimized curing process. When curing and forming by this process, the lower skin and the upper skin have lower porosities and the honeycomb sandwich structure has better mechanical properties. Among them, the better mechanical properties are specifically manifested in the better bonding performance between the skin and the honeycomb core and the better out - of - plane compressive performance.

[0022] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings to make a further detailed description of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a vibration device installed with assembled components and the assembled components in a disassembled state provided by an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of the structure of components, encapsulation auxiliary components, molds, vacuum nozzles, and fixing components provided by an embodiment of the present invention;

[0025] Figure 3 Schematic diagram of the laying of assembled components provided by an embodiment of the present invention;

[0026] Figure 4 Schematic diagram of the structure of a vibration device at an angle provided by an embodiment of the present invention;

[0027] Figure 5 Schematic diagram of the structure of the vibration device provided by an embodiment of the present invention from another angle;

[0028] Figure 6 is Figure 4 Cross-sectional view of the air hammer in the vibration device shown;

[0029] Figure 7 Process parameter diagram of the vibration curing process for preparing the honeycomb sandwich structure in Example 1;

[0030] Figure 8 Process parameter diagram of the curing process for preparing the honeycomb sandwich structure in Comparative Example 1;

[0031] Figure 9 Comparison diagram of the porosity of the lower skin and the upper skin in the honeycomb sandwich structures prepared in Example 1 to Example 5 and Comparative Example 1;

[0032] Figure 10 Metallographic diagrams of the upper skin in the honeycomb sandwich structures prepared in Example 1, Example 3 and Comparative Example 1. Among them, Figure 10 in (a) is the metallographic diagram of the upper skin in the honeycomb sandwich structure prepared in Comparative Example 1, Figure 10 in (b) is the metallographic diagram of the upper skin in the honeycomb sandwich structure prepared in Example 1, Figure 10 in (c) is the metallographic diagram of the upper skin in the honeycomb sandwich structure prepared in Example 3;

[0033] Figure 11 Metallographic diagrams of the lower skin in the honeycomb sandwich structures prepared in Example 1, Example 3 and Comparative Example 1. Among them, Figure 11 in (a) is the metallographic diagram of the lower skin in the honeycomb sandwich structure prepared in Comparative Example 1, Figure 11 in (b) is the metallographic diagram of the lower skin in the honeycomb sandwich structure prepared in Example 1, Figure 11 in (c) is the metallographic diagram of the lower skin in the honeycomb sandwich structure prepared in Example 3;

[0034] Figure 12 Load-displacement curves corresponding to the peel strength tests of the honeycomb sandwich structures prepared in Example 1, Example 3 and Comparative Example 1;

[0035] Figure 13 Comparison diagram of the peel strength test results of the honeycomb sandwich structures prepared in Example 1, Example 3 and Comparative Example 1;

[0036] Figure 14 Load-displacement curves corresponding to the compressive strength tests of the honeycomb sandwich structures prepared in Example 1, Example 3 and Comparative Example 1;

[0037] Figure 15 Comparison chart of out-of-plane compressive strength test results of honeycomb sandwich structures prepared in Example 1, Example 3 and Comparative Example 1. Detailed implementation mode

[0038] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be defined and covered by the claims in various different embodiments.

[0039] Aiming at the technical problem that when the honeycomb sandwich structure is cured and formed by an autoclave, the quality of the formed parts is poor due to poor pressure control in the autoclave, the present invention uses a vibration device for curing and forming. When the adhesive film is in a viscous flow state, the vibration device simultaneously applies vibration excitation in the X direction, Y direction and Z direction to replace the forming pressure of the autoclave, so that the pores and impurities in the resin can escape along the horizontal direction (X direction and Y direction) and the vertical direction (Z direction), and at the same time promotes the resin flow and the combination of resin - fiber (upper skin / lower skin), thereby reducing the generation of defects such as pores at the joint of the formed composite skin and the skin - honeycomb core, and improving the bonding mechanical properties and out-of-plane compressive properties of the honeycomb sandwich structure obtained by forming and manufacturing.

[0040] Please refer to Figures 1 to 6 , the present invention provides a vibration curing and forming method for a honeycomb sandwich structure. The honeycomb sandwich structure includes a lower skin, a honeycomb core and an upper skin stacked along the height direction, and both the upper skin and the lower skin are connected to the honeycomb core through an adhesive film.

[0041] In the present invention, the vibration curing and forming method is a one-time curing and forming method, which includes the following steps:

[0042] Step (1), providing the components 10 of the honeycomb sandwich structure, the encapsulation auxiliary components 20, the vacuum bag 30, and the mold 40 for carrying the components 10 of the honeycomb sandwich structure and the encapsulation auxiliary components 20.

[0043] In the present invention, the components of the honeycomb sandwich structure include a lower skin 11, an upper skin 12, a honeycomb core 13 and two layers of adhesive film 14.

[0044] In the present invention, both the lower skin 11 and the upper skin 12 are formed by laminating 6 to 18 layers of pre-impregnated fiber materials, and the adjacent two layers of pre-impregnated fiber materials are laid in an orthogonal cross-laying manner.

[0045] In the present invention, the pre-impregnated fiber material is a carbon fiber reinforced resin matrix composite material, the reinforcing body is carbon fiber, and the matrix is epoxy resin.

[0046] In an optional embodiment, the honeycomb core 13 is an aramid honeycomb core formed by compounding aramid paper and phenolic resin.

[0047] In the present invention, the adhesive film 14 is a toughened epoxy resin adhesive film.

[0048] In an alternative embodiment, the encapsulation auxiliary component 20 includes a first isolation film 21, a second isolation film 22, a pressure equalizing plate 23, a breather felt 24, two metal stoppers 25 and two glue stoppers 26.

[0049] In the present invention, the vacuum bag 30 is used to encapsulate the components 10 of the honeycomb sandwich structure.

[0050] In an alternative embodiment, the mold 40 is a pre-treated mold. Wherein, the pre-treatment method of the mold includes: first cleaning the stains and grease on the mold with ethanol and kerosene cleaning agents respectively, and then placing it in a ventilated place for 2 - 3 minutes to air dry naturally until all the moisture on the mold surface volatilizes.

[0051] Step (2): Lay the component 10 and the encapsulation auxiliary component 20 on the mold 40 according to a preset method, and use the vacuum bag 30 to encapsulate the component 10 of the honeycomb sandwich structure and the encapsulation auxiliary component 20 to obtain an assembled component 200.

[0052] It can be understood that in the present invention, the assembled component 200 includes a mold, and the components and the encapsulation auxiliary component sealed with a vacuum bag.

[0053] Please refer particularly to Figure 2 and Figure 3 , laying the component 10 and the encapsulation auxiliary component 20 on the mold 40 according to a preset method specifically means: first, lay the mold 40, the first isolation film 21, the lower skin 11, one layer of adhesive film 14, the honeycomb core 13, another layer of adhesive film 14, and the upper skin 12 flat in sequence from bottom to top, then respectively set the two metal stoppers 25 at both ends of the assembled honeycomb sandwich structure and make them abut against each other, then respectively set the two glue stoppers 26 on both sides of the assembled honeycomb sandwich structure and make them abut against each other, and finally lay the second isolation film 22, the pressure equalizing plate 23 and the breather felt 24 on the upper skin 12 in sequence.

[0054] The encapsulation specifically means: using the vacuum bag 30 to encapsulate the first isolation film 21, the lower skin 11, one layer of adhesive film 14, the honeycomb core 13, another layer of adhesive film 14, the upper skin 12, the second isolation film 22, the pressure equalizing plate 23, the breather felt 24, the metal stoppers 25 and the glue stoppers 26 assembled together as a whole to facilitate subsequent vacuum pumping to form a vacuum environment.

[0055] In the present invention, the metal stopper 25 is arranged on the first isolation film 21, and is respectively arranged at both ends of the assembled honeycomb sandwich structure along the length direction of the mold 40, and is used to prevent the honeycomb sandwich structure from shifting during the curing process.

[0056] In the present invention, the height of the metal stopper 25 is the same as the height of the assembled honeycomb sandwich structure.

[0057] In the present invention, two glue stoppers 26 are arranged on the first isolation film 21 and are respectively arranged on both sides of the assembled honeycomb sandwich structure along the width direction of the mold. Their functions include: 1) Limiting the assembled honeycomb sandwich structure together with the metal stopper 25; 2) Preventing the resin inside the skin from flowing to the outside during the curing process of the honeycomb sandwich structure.

[0058] In the present invention, the height of the glue stopper 26 is 3 - 4 mm.

[0059] It can be understood that when using a vacuum bag for encapsulation, it also includes using a sealing strip for sealing.

[0060] In the present invention, a vacuum nozzle 50 is further provided. The vacuum nozzle 50 is installed on the mold 40 and is used to communicate with a vacuum pumping device.

[0061] Step (3): Provide a fixing member 60 and a vibration device 70 having a receiving cavity 70A. First, place the assembled component in the receiving cavity and use the fixing member to fix the assembled component on the vibration table 71 of the vibration device 70. Then, evacuate the vacuum bag and maintain the vacuum degree ≤ -0.098 MPa, and then cure according to a preset vibration curing process to obtain the honeycomb sandwich structure.

[0062] The preset vibration curing process includes first heating the temperature in the receiving cavity of the vibration device from room temperature to a first curing temperature and maintaining the first curing temperature for a first duration, then heating from the first curing temperature to a second curing temperature and maintaining the second curing temperature for a second duration. When the second curing temperature holding ends, cool down to a preset temperature to complete the curing. At the same time, when the temperature in the receiving cavity of the vibration device reaches the first curing temperature, turn on the vibration function of the vibration device and apply a vibration excitation to the vibration table according to a preset vibration acceleration, and the duration of the vibration excitation is the same as the first duration. Among them, the first curing temperature is 90 °C, the first duration is 30 min, and the preset vibration acceleration is 10g.

[0063] Preferably, the second curing temperature is 130 °C, the second duration is 2 h, and the preset temperature is 60 °C.

[0064] Preferably, the heating rate of the temperature in the receiving cavity 70A of the vibration device 70 from room temperature to the first curing temperature is 1 - 3 °C / min, and the heating rate from the first curing temperature to the second curing temperature is 1 - 3 °C / min.

[0065] Preferably, the vibration excitation is random vibration excitation.

[0066] In an alternative embodiment, the fixing member 60 includes a first metal bar 61 and a second metal bar 62. The first metal bar 61 and the second metal bar 62 are respectively disposed at two ends of the mold 40. The middle part of each metal bar abuts against the surface of the mold away from the vibration table, and both ends are detachably connected to the vibration table respectively.

[0067] Specifically, the first metal bar and the second metal bar are connected to the mold by bolts.

[0068] Please refer to Figure 4 and Figure 5 , in an alternative embodiment, the vibration device 70 further includes a box body 72, a spring assembly 73, a vibration module 74, and a heater.

[0069] In the present invention, the box body 72 is a square box body, specifically a box body in the shape of a cuboid.

[0070] In the present invention, the box body 72 includes a bottom wall 721, four side walls 722 extending away from the bottom wall 721 respectively from two ends and two sides of the bottom wall 721, and a top wall 723 that together with the bottom wall 721 and the plurality of side walls 722 encloses the box body 72.

[0071] In the present invention, the vibration table 71 is used to carry the assembled components and is arranged parallel to the bottom wall / top wall of the box body 72.

[0072] In the present invention, the vibration table 71 is installed in the middle of the box body 72 and divides the box body 72 into an upper receiving cavity 70A and a lower accommodating cavity 70B.

[0073] The spring assembly 73 includes four fixing seats 731 respectively fixed on the four side walls 722 of the box body 72, and four springs 732 with one end connected to the fixing seat 731 and the other end connected to the vibration table 71.

[0074] The vibration module 74 is used to apply vibration excitation to the vibration table in the X direction, Y direction and Z direction simultaneously.

[0075] In an alternative embodiment, the vibration module 74 includes a plurality of inclined pneumatic hammers 741 arranged in a preset layout, a plurality of ventilation ducts 742, and an air compressor. The pneumatic hammer 741 includes a first end and a second end. The first end of the pneumatic hammer is connected to the vibration platen 71. One end of each ventilation duct 742 communicates with one of the pneumatic hammers 741 and the other end communicates with the air compressor. The preset layout is that a plurality of pneumatic hammers 741 are evenly distributed in multiple circles around the central axis of the vibration platen 71.

[0076] In the present invention, a plurality of pneumatic hammers 741 directly act on the vibration platen 71 to generate vibration impacts. The ventilation duct 72 is used to convey compressed air in the air compressor to the pneumatic hammers 741, and the air compressor is used to provide compressed air.

[0077] In the present invention, the first end of the pneumatic hammer 741 is an inclined surface, so that the connection area between the pneumatic hammer and the vibration platen can be increased.

[0078] Please refer to Figure 6 , in an alternative embodiment, the pneumatic hammer 741 further includes a pneumatic hammer housing 7411 having a cavity, a piston 7412 located in the cavity and capable of sliding back and forth along the length direction of the pneumatic hammer housing 7411, a cushion block 7413 provided on the inner wall of the pneumatic hammer housing 7411 and near the first end of the pneumatic hammer, a gas connector 7414 installed on the pneumatic hammer housing 7411 and communicating with the ventilation duct 742, and a gas delivery pipe 7415 provided on the piston 7412 and communicating with the gas connector 7414. The output end of the gas delivery pipe 7415 faces the second end of the pneumatic hammer.

[0079] Preferably, the pneumatic hammer housing 7411 includes a housing main body having a cavity and a connecting portion provided at one end of the housing main body. The cross-section of the housing main body portion is circular. The inner diameter of the housing main body portion near the connecting portion is smaller than the inner diameter of the housing main body portion away from the connecting portion to form a stepped structure. The piston 7412 includes a first piston rod near one end of the cushion block 741 and a second piston rod connected to the first piston rod. The diameter of the first piston rod is the same as the inner diameter of the housing main body portion near the connecting portion, and the diameter of the second piston rod is the same as the inner diameter of the housing main body portion away from the connecting portion. In this way, when the second piston rod abuts against the stepped structure, it reaches the limit position.

[0080] The gas compressed by the air compressor sequentially enters the cavity through the ventilation duct 742, the gas connector 7414, and the gas delivery pipe 7415, driving the piston 7412 to move from the second end to the first end of the pneumatic hammer. After the piston 7412 collides with the cushion block 7413, under the action of the reaction force and gravity, the piston 7412 moves from the first end to the second end of the pneumatic hammer.

[0081] In the present invention, specifically, the gas input is adjusted in real time through a feedback system (acceleration sensor), and the gas flow rate and pressure are regulated through a servo valve and a proportional valve to push the piston to reciprocate, thereby stabilizing the vibration frequency and vibration acceleration.

[0082] In the present invention, under the random vibration of the preset vibration acceleration, the frequency will continuously change within a broadband range (20 - 2000 Hz). The vibration device dynamically adjusts the gas flow rate and pressure to ensure that the flow rate of the frequency components conforms to the PSD spectrum.

[0083] In a specific embodiment, multiple pneumatic hammers are classified into a first pneumatic hammer 741A, a second pneumatic hammer 741B, and a third pneumatic hammer 741C based on the installation position. The preset arrangement is specifically as follows: a plurality of first pneumatic hammers 741A are evenly arranged along a large square, a plurality of second pneumatic hammers 741B are evenly arranged along a small square located within the large square, and a third pneumatic hammer 741C is arranged at the center of the small square. The center points of the large square and the small square coincide. Among them, the first pneumatic hammer 741A is a large pneumatic hammer, and the second pneumatic hammer 741B and the third pneumatic hammer 741C are small pneumatic hammers.

[0084] In the present invention, the large pneumatic hammer and the small pneumatic hammer are defined based on the cross-sectional area of the pneumatic hammer. The cross-sectional area of the large pneumatic hammer is larger than that of the small pneumatic hammer.

[0085] In a specific embodiment, the number of pneumatic hammers is 13. The first ends of 8 first pneumatic hammers 741A are located on the sides or vertices of the large square, the first ends of 4 second pneumatic hammers 741B are located at the vertices of the small square, and the first end of the third pneumatic hammer 741C is located at the center point of the small square.

[0086] In the present invention, the small pneumatic hammers and the large pneumatic hammers are distributed in a surrounding manner from the inside to the outside. On the one hand, it can ensure that the assembled components placed on the vibration table are more evenly subjected to the excitation effects in the X direction, Y direction, and Z direction, making the resin flow more evenly. In this way, the skin obtained by curing and forming has a low porosity, the chamfer shape formed in the skin-honeycomb core connection area is good, and the prepared honeycomb sandwich structure has better bonding performance and better out-of-plane compressive performance. On the other hand, it can make the vibration transfer rate in the horizontal direction and the vertical direction higher, avoiding the distortion of vibration transfer caused by the attenuation of vibration excitation.

[0087] Preferably, the angle between the central axis of the first pneumatic hammer and the side where the first end of the first pneumatic hammer is located is 30 to 60 degrees, the angle between the central axis of the second pneumatic hammer and the side where the first end of the second pneumatic hammer is located is 30 to 60 degrees, and the angle between the central axis of the third pneumatic hammer and the plane of the vibrating platen is 30 to 60 degrees.

[0088] More preferably, the angle between the central axis of the first pneumatic hammer 741A and the side where the first end of the first pneumatic hammer 741A is located is 45 degrees, the angle between the central axis of the second pneumatic hammer 741B and the side where the first end of the second pneumatic hammer 741B is located is 45 degrees, and the angle between the central axis of the third pneumatic hammer 741C and the plane of the vibrating platen 71 is 45 degrees.

[0089] In the present invention, the first pneumatic hammer 741A, the second pneumatic hammer 741B, and the third pneumatic hammer 741C are inclined in the same direction.

[0090] In the present invention, the heater is an electric heater for heating the accommodation cavity of the vibrating device 70.

[0091] Example 1

[0092] Prepare a honeycomb sandwich structure by using the vibration curing and forming method provided by the present invention

[0093] Step 1.1: First, clean the stains and grease on the forming mold with ethanol and kerosene cleaning agents respectively. Then, place the mold in a ventilated place for 2 - 3 minutes, wait for the moisture on the mold surface to volatilize and air-dry naturally. Then, lay a first isolation film 21 on the forming side surface of the mold 40.

[0094] Step 1.2: Lay 7 layers of pre-impregnated fiber materials on the first isolation film 21 in an orthogonal cross-laying manner, and gently press with hands after each layer of pre-impregnated fiber material is laid to complete the preparation and laying of the lower skin 11.

[0095] Step 1.3: Lay a toughened epoxy resin film 14 on the lower skin 11, place the honeycomb core (Nomex honeycomb) 13 on the film, and then lay another layer of toughened epoxy resin film 14 on the honeycomb core 13.

[0096] Step 1.4: First, lay 7 layers of pre-impregnated fiber materials (T700 / TRE231 prepreg) in an orthogonal cross-laying manner, and gently press with hands after each layer of pre-impregnated fiber material is laid to complete the preparation of the upper skin 12; then place the upper skin on the film and press it.

[0097] Step 1.5: First, place the metal stoppers 25 and the rubber stoppers 26 at the edges of the outer contour of the assembled honeycomb sandwich structure for positioning. Then, sequentially lay the second isolation film 22, the pressure equalizing plate 23, and the breathable felt 24 on the assembled honeycomb sandwich structure. Finally, perform overall encapsulation with the vacuum bag 30 to obtain the assembled component. Meanwhile, place the vacuum nozzle 50 at an appropriate position on the mold 40 and open the vacuum channel.

[0098] S6: Place the entire assembled component 200 on the vibrating platen 71 of the vibrating device 70 and fix it with the first metal bar 61 and the second metal bar 62. Meanwhile, connect the vacuum pipeline to ensure full vacuum pumping treatment with a vacuum degree ≤ -0.098 MPa. Finally, perform curing according to the preset vibration curing process to obtain the honeycomb sandwich structure.

[0099] Please refer to Figure 7 , the preset vibration curing process is specifically as follows: Turn on the heater to heat the temperature of the receiving cavity from room temperature to the first curing temperature of 90°C at a heating rate of 2°C / min and keep it at 90°C for the first duration of 30 min. When the curing temperature reaches 90°C, turn on the vibration function and apply a vibration excitation to the vibrating platen of the vibrating device at the preset vibration acceleration of 10 g, and set the duration of the vibration excitation to 30 min. After the insulation at 90°C ends, then raise the temperature of the receiving cavity from 90°C to the second curing temperature of 130°C at a heating rate of 2°C / min and keep it for the second duration of 2 h. Finally, cool the cavity temperature to 60°C by air cooling (at a cooling rate of 2°C / min).

[0100] Examples 2 to 5

[0101] Examples 2 to 5 are the same as Example 1, except that the preset vibration curing processes are different. Specifically: The first curing temperature, the first duration, the second curing temperature, and the second duration of Examples 2 and 3 are the same as those of Example 1, only the preset vibration acceleration is different. The preset vibration acceleration of Example 2 is 5 g, and the preset vibration acceleration of Example 3 is 15 g. The first duration, the second curing temperature, the second duration, and the preset vibration acceleration of Example 4 are the same as those of Example 1, only the first curing temperature is different. The first curing temperature of Example 4 is 80°C. The second curing temperature, the second duration, and the preset vibration acceleration of Example 5 are the same as those of Example 1, only the first curing temperature and the first duration are different. The first curing temperature of Example 5 is 80°C, and the first duration is 50 min.

[0102] To distinguish the honeycomb sandwich structures prepared in each embodiment, the honeycomb sandwich structures of different embodiments are marked based on the first curing temperature - the first duration - the preset vibration acceleration corresponding to the vibration curing process. Among them, the honeycomb sandwich structure prepared in Embodiment 1 is denoted as 90 - 30 - 10g, that is, the first curing temperature is 90 °C, the first duration is 30 min, and the preset vibration acceleration is 10 g. Similarly, the honeycomb sandwich structure prepared in Embodiment 2 is denoted as 90 - 30 - 5g, the honeycomb sandwich structure prepared in Embodiment 3 is denoted as 90 - 30 - 15g, the honeycomb sandwich structure prepared in Embodiment 4 is denoted as 80 - 30 - 10g, and the honeycomb sandwich structure prepared in Embodiment 5 is denoted as 80 - 50 - 10g.

[0103] Comparative Example 1

[0104] Comparative Example 1 is the same as Embodiment 1, and the only difference is that the curing device is different. Comparative Example 1 uses autoclave curing and molding. Correspondingly, the curing process is also adjusted.

[0105] Please refer to Figure 8 , the specific curing process corresponding to Comparative Example 1 is as follows: Starting from room temperature, the temperature is raised at a rate of 2 °C / min to 90 °C, and then maintained at 90 °C for 30 min. After the heat preservation ends, the temperature is continued to be raised from 90 °C to 130 °C at a rate of 2 °C / min and maintained at 130 °C for 2 h. After the heat preservation ends, the temperature gradually decreases until it reaches 60 °C; The pressure application program is started at the beginning of the temperature rise, and the pressure in the tank is increased from 0 MPa to 0.2 MPa and kept until the temperature in the tank drops to 60 °C. After the pressure holding ends, the pressure in the tank is reduced from 0.2 MPa to 0 MPa; The vacuum bag pressure of 0.098 MPa is applied from the beginning of the experiment and maintained until the end of the pressure holding stage, and then reduced to 0 MPa.

[0106] The honeycomb sandwich structure prepared in Comparative Example 1 is denoted as 0.2 MPa autoclave.

[0107] Porosity test

[0108] Porosity test method: Randomly select five different areas on the surfaces of the lower skin and the upper skin of the prepared honeycomb sandwich structure, and use a marker pen to mark 10mm×10mm square grids in these five areas respectively. Then, use a grinding wheel cutting machine to cut the honeycomb sandwich structure to obtain five groups of parallel specimens with a skin surface size of 10mm×10mm. Next, use water sandpapers with 800 mesh, 1000 mesh, and 1500 mesh and metallographic sandpapers with 1000 mesh, 1200 mesh, and 1400 mesh to polish the cross-sections of the five groups of parallel specimens on a polishing machine in sequence, ensuring that there are no obvious scratches and impurities on the polished specimen cross-sections. Then, polish the specimen cross-sections with 1μm diamond polishing paste. After completing the above operations, use a hair dryer to dry the moisture on the specimen surface and seal it in a vacuum chamber. Finally, place the polished specimens under a metallographic microscope for observation and characterization, record the microtopographies of the skin cross-section and the skin-core layer bonding interface at the same time. Finally, use Image-Pro Plus software to analyze and process the metallographic images of the specimen cross-sections obtained by recording, and take the average porosity of the five groups of parallel specimens as the porosity of the honeycomb sandwich structure composite parts under the corresponding process conditions.

[0109] Use the porosity test method described above to test the porosities of the upper skin and the lower skin of the honeycomb sandwich structures prepared in Examples 1 to 5 and Comparative Example 1 respectively. The test results are shown in Figures 9 to 11 as follows.

[0110] From Figure 9 it can be seen that the porosities of the upper skin and the lower skin prepared in Example 1 (under the vibration curing condition of 90-30-10g) are the lowest, which are 0.27% and 0.39% respectively, while the porosities of the upper skin and the lower skin prepared in Comparative Example 1 (under the autoclave condition of 0.2MPa) are 0.83% and 1.24% respectively, and the porosities of the upper skin and the lower skin prepared in Example 3 (under the vibration curing condition of 90-30-15g) are 0.87% and 1.31% respectively.

[0111] Please refer to Figure 10 and Figure 11 , where Figure 10 in (a) is the metallographic image of the upper skin of the honeycomb sandwich structure prepared in Comparative Example 1, Figure 10 in (b) is the metallographic image of the upper skin of the honeycomb sandwich structure prepared in Example 1, Figure 10 in (c) is the metallographic image of the upper skin of the honeycomb sandwich structure prepared in Example 3; Figure 11 in (a) is the metallographic image of the lower skin of the honeycomb sandwich structure prepared in Comparative Example 1, Figure 11 in (b) is the metallographic image of the lower skin of the honeycomb sandwich structure prepared in Example 1, Figure 11Among them, (c) is the metallographic diagram of the lower skin in the honeycomb sandwich structure prepared in Example 3. From Figure 10 and Figure 11 in terms of the pore morphology distribution, under the condition of 0.2 MPa autoclave, depressions are generated on the skin surface, which will affect the contour accuracy of the honeycomb sandwich structure; and small round and strip-shaped pores are mainly distributed at section A of the skin. Under the vibration curing condition of 90-30-10 g, the surface morphology of the skin section is flat, and no large-size pores or other curing defects such as delamination are generated. Only small pores are distributed in the layer at C, and the porosity of the workpiece is controlled to the lowest level and is all below 0.5%. At the same time, the resin cures into a well-shaped chamfer at area B of the skin-honeycomb core bonding, and the bonding performance of the skin-honeycomb core is excellent at this time. Under the vibration curing condition of 90-30-15 g, the morphology of the workpiece is relatively flat, but small round intra-layer pores and strip-shaped inter-layer pores are distributed at E and F, and at this time, the resin at area D of the skin-honeycomb core bonding forms an asymmetric chamfer, which will affect the bonding performance of the skin-honeycomb core to a certain extent.

[0112] Based on the above analysis, it can be seen that by adopting the vibration curing forming process conditions of 90-30-10 g, the obtained honeycomb sandwich structure workpiece has good micro-morphology, and its porosity can be controlled below 0.5%, which is better than other process conditions.

[0113] Drum peel strength test

[0114] Based on the test results of the porosity, the honeycomb sandwich structures prepared under the condition of 0.2 MPa autoclave (Comparative Example 1), 90-30-10 g vibration curing condition (Example 1) and 90-30-15 g vibration curing condition (Example 3) are further subjected to drum peel strength detection.

[0115] Test method: The drum peel strength test method of the honeycomb sandwich structure is carried out according to the "Test Method for Drum Peel Strength of Sandwich Structures" with the standard number of GB / T 1457-2022, and the testing machine used is an MTS universal tensile machine.

[0116] The test results are shown in detail in Figure 12 and Figure 13, based on the test results of the peel strength of the honeycomb sandwich structure drum and the metallographic analysis, it can be seen that an important factor affecting the bonding performance between the skin and the honeycomb core is the chamfer formed by the resin at the bonding site. Under the vibration curing condition of 90 - 30 - 10g, the bonding performance between the skin and the honeycomb core reaches 78.4 N·mm / mm, which is the optimal level. Secondly, under the condition of 0.2 MPa in the autoclave, the bonding performance is 74.7 N·mm / mm. When the vibration acceleration is increased to 15g, due to the increase in vibration acceleration, the resin inside the skin and the resin in the adhesive film will flow faster towards the cell wall of the honeycomb core during the curing process, and the chamfer shape of the glue tumor is irregular, thus affecting the bonding performance between the skin and the honeycomb core under this condition. At this time, the bonding performance is 71.6 N·mm / mm.

[0117] Compression strength test

[0118] Based on the test results of the porosity, the out-of-plane quasi-static compression strength tests were further carried out on the honeycomb sandwich structures prepared under the condition of 0.2 MPa in the autoclave (Comparative Example 1), the vibration curing condition of 90 - 30 - 10g (Example 1), and the vibration curing condition of 90 - 30 - 15g (Example 3).

[0119] Test method: The out-of-plane quasi-static compression strength test method of the honeycomb sandwich structure was carried out according to the "Test Method for Flat Compression Performance of Sandwich Structures or Cores" with the standard number GB / T1453 - 2022. Among them, the side lengths of the honeycomb sandwich structure in the W and L directions are both 50 mm, the honeycomb height is 10 mm, the loading speed of the testing machine is set to 0.5 mm / min, and the testing machine used is an MTS universal tensile machine.

[0120] The test results are shown in detail in Figure 14 and Figure 15 , under the vibration curing condition of Example 1 (90 - 30 - 10g), the out-of-plane compression strength of the honeycomb sandwich structure prepared is 2.237 MPa, which is the optimal level. Secondly, it is Comparative Example 1 (under the condition of 0.2 MPa in the autoclave), and the out-of-plane flat compression strength is 2.092 MPa. Under the vibration curing condition of Example 3 (90 - 30 - 15g), combined with Figure 10 and Figure 11 it can be seen that at this time, pores of different sizes are distributed in the in-plane and inter-layer regions of the skin layer. Among them, the in-plane pores will cause defects such as resin-rich or poor glue in the resin, while the inter-layer pores will cause delamination defects in the pre-impregnated fiber material. The superimposed effect of the in-plane and inter-layer defects will lead to poor forming quality of the skin of the formed honeycomb sandwich structure, and correspondingly, its out-of-plane load-bearing capacity will decrease. Therefore, the out-of-plane compression strength of the honeycomb structure under this condition is 1.858 MPa, showing the lowest level under the conditions of this group.

[0121] It should be noted that the resin in the present invention includes the resin of the adhesive film and the resin of the skin.

[0122] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions and substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A vibration curing forming method for a honeycomb sandwich structure, the honeycomb sandwich structure comprising a lower skin, a honeycomb core, and an upper skin stacked in the height direction, and the upper skin and the lower skin are both connected to the honeycomb core through adhesive films, characterized in that, The vibration curing forming method includes the following steps: Step (1): Provide the components of the honeycomb sandwich structure, encapsulation auxiliary parts, a vacuum bag, and a mold for carrying the components of the honeycomb sandwich structure and the encapsulation auxiliary parts. Among them, the components include an upper skin, a lower skin, a honeycomb core, and two layers of adhesive films. The pre-impregnated fiber materials of the upper skin and the lower skin are carbon fiber reinforced epoxy resin matrix composites. The honeycomb core is an aramid honeycomb core formed by compounding aramid paper and phenolic resin. The adhesive film is a toughened epoxy resin adhesive film; Step (2): Lay the components and the encapsulation auxiliary parts on the mold according to a preset method, and use the vacuum bag to encapsulate the components of the honeycomb sandwich structure and the encapsulation auxiliary parts to obtain an assembled component; Step (3): Provide a fixing part and a vibration device with a receiving cavity. First, place the assembled component in the receiving cavity and use the fixing part to fix the assembled component on the vibration table of the vibration device. Then, evacuate the vacuum bag and maintain the vacuum degree ≤ -0.098 MPa. Next, cure according to a preset vibration curing process to obtain the honeycomb sandwich structure. The preset vibration curing process includes first raising the temperature in the receiving cavity of the vibration device from room temperature to 90 °C and keeping it at 90 °C for 30 min. Then, raise the temperature from 90 °C to 130 °C and keep it at 130 °C for 2 h. When the insulation at 130 °C ends, cool down to a preset temperature to complete the curing. At the same time, when the temperature in the receiving cavity of the vibration device reaches 90 °C, turn on the vibration function of the vibration device and apply vibration excitation in three directions, namely the X direction, the Y direction, and the Z direction, to the vibration table according to a preset vibration acceleration, and the duration of the vibration excitation is 30 min. Among them, the preset vibration acceleration is 10g.

2. The vibration curing forming method of the honeycomb sandwich structure according to claim 1, characterized in that, The vibration device further includes a box body, a spring assembly for supporting the vibration table, and a vibration module. The vibration table is installed in the box body and divides the box body into the receiving cavity and the accommodating cavity. The vibration module is used to apply vibration excitation to the vibration table.

3. The vibration curing forming method of the honeycomb sandwich structure according to claim 2, characterized in that The vibration module includes a plurality of inclined pneumatic hammers arranged in a preset layout, a plurality of ventilation ducts, and an air compressor. The pneumatic hammer includes a first end and a second end. The first end of the pneumatic hammer is fixedly connected to the lower surface of the vibration table. One end of each ventilation duct is connected to one of the pneumatic hammers and the other end is connected to the air compressor. The preset layout is that a plurality of the pneumatic hammers are evenly distributed in multiple circles around the central axis of the vibration table.

4. The vibration curing forming method of the honeycomb sandwich structure according to claim 3, characterized in that The pneumatic hammer further includes a pneumatic hammer housing having a cavity, a piston located within the cavity and capable of sliding back and forth along the length direction of the pneumatic hammer housing, a cushion block provided on the inner wall of the pneumatic hammer housing and adjacent to the first end of the pneumatic hammer, a gas connector installed on the pneumatic hammer housing and communicating with the ventilation duct, and a gas delivery pipe provided on the piston and communicating with the gas connector. The output end of the gas delivery pipe faces the second end of the pneumatic hammer. The gas compressed by the air compressor sequentially enters the cavity through the ventilation duct, the gas connector, and the gas delivery pipe, driving the piston to move from the second end to the first end of the pneumatic hammer. After the piston collides with the cushion block, under the action of the reaction force and gravity, the piston moves from the first end to the second end of the pneumatic hammer.

5. The vibration curing forming method of the honeycomb sandwich structure according to claim 3 or 4, characterized in that, Based on the installation position, a plurality of the pneumatic hammers are classified into a first pneumatic hammer, a second pneumatic hammer, and a third pneumatic hammer. The specific preset arrangement method is as follows: a plurality of first pneumatic hammers are evenly arranged along a large square, a plurality of second pneumatic hammers are evenly arranged along a small square located within the large square, and a third pneumatic hammer is arranged at the center of the small square. The center points of the large square and the small square coincide. Among them, the first pneumatic hammer is a large pneumatic hammer, and the second pneumatic hammer and the third pneumatic hammer are small pneumatic hammers.

6. The vibration curing forming method of the honeycomb sandwich structure according to claim 5, characterized in that, The number of the pneumatic hammers is 13. The first ends of 8 first pneumatic hammers are located on the sides or vertices of the large square, the first ends of 4 second pneumatic hammers are located at the vertices of the small square, and the first end of the third pneumatic hammer is located at the center point of the small square.

7. The vibration curing forming method of the honeycomb sandwich structure according to claim 6, wherein, The angle between the central axis of the first pneumatic hammer and the plane where the vibration table board is located is 45 degrees, and the angle between the central axis of the second pneumatic hammer and the plane where the vibration table board is located is 45 degrees.

8. The vibration curing forming method of the honeycomb sandwich structure according to any one of claims 1 to 4, characterized in that, The encapsulation auxiliary includes a first isolation film, a second isolation film, a pressure equalizing plate, a breathable felt, two metal stoppers, and two rubber stoppers. Laying the components of the honeycomb sandwich structure and the encapsulation auxiliary on the mold according to the preset method is specifically as follows: First, lay the mold, the first isolation film, the lower skin, a layer of adhesive film, the honeycomb core, another layer of adhesive film, and the upper skin in sequence from bottom to top. Then, respectively set two metal stoppers at both ends of the assembled honeycomb sandwich structure and make them abut against each other. Next, respectively set two rubber stoppers on both sides of the assembled honeycomb sandwich structure and make them abut against each other. Finally, lay the second isolation film, the pressure equalizing plate, and the breathable felt on the upper skin in sequence.

9. The vibration curing forming method of the honeycomb sandwich structure according to claim 1, characterized in that The vibration excitation is a random vibration excitation.

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