Method for removing hard core material of composite material

Abstract

The invention belongs to the technical field of composite material processing, and provides a method for removing a hard core material of a composite material, which comprises the following steps of: determining a position close to a hole according to a defect range; covering a metal protective plate on the defect, and forming a through hole; primary holes are formed in the upper panel and the core material according to the positions of the through holes; removing tools including a spherical grinding tool and a cylindrical grinding tool are designed; the removing tool is used for conducting graded grinding till the core material is completely removed; core material powder is sucked out in a vacuum mode, and the metal protection plate is removed; and the initial hole is expanded to the final hole to facilitate the use in the subsequent process. The technical problem that no applicable maintenance scheme for the debonding defect of the existing foam sandwich structure exists is solved, and the selective removal of the core material is realized on the premise of ensuring the relative completeness of the panel interface.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material processing, and particularly relates to a method for removing a hard core material of a composite material. Background Art

[0002] In the aviation industry, debonding defects occur when the core and facesheet of honeycomb / foam sandwich structures separate, leading to interfacial failure. During service, the debonding area can gradually expand due to stress concentration, humid and hot environments, or vibration, causing a larger-scale interfacial failure. This can lead to a loss of composite material strength and stiffness, shortened fatigue life, and reduced impact resistance. Currently, repairing debonding defects in aviation composite materials requires adherence to process specifications, requiring local removal of core material in the debonded area for reinforcement.

[0003] Existing solutions: (1) Drill an access hole in the panel-core debonding area.

[0004] (2) Make a core removal cutting arm ("L" type hexagonal wrench).

[0005] (3) Insert the cutting arm into the access hole to remove the full depth core material under the panel. Use tweezers and a vacuum source with a nozzle to pick out the broken core material from the access hole.

[0006] (4) Reinforce the repair area by replacing the material through the access hole.

[0007] The existing core material removal method is not universal and is only applicable to honeycomb sandwich structure parts. For foam sandwich structure parts made of hard materials, the initial torque of the hand drill is insufficient, and thus it is impossible to drive the L-shaped cutting arm to complete the core material cutting and removal operation.

[0008] In the composite sandwich structure of a certain large passenger aircraft, honeycomb core materials are mainly used in the main aerodynamic surfaces and high-stress areas, accounting for more than 80% of the total core material of the sandwich structure. Foam core materials are used in secondary load-bearing structures and discontinuous areas, accounting for less than 20% of the total core material of the sandwich structure. Currently, there is no applicable repair solution for the debonding defects of the foam sandwich structure. Summary of the Invention

[0009] Aiming at the problem that there is no applicable repair solution for the debonding defects of the foam sandwich structure of a certain large passenger aircraft, the present invention provides a method for removing the hard core material of a composite material, which realizes the selective removal of the core material while ensuring the relative integrity of the panel interface.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions: A method for removing a hard core material of a composite material comprises the following steps: Determine the approach hole location based on the defect range; Covering the defect with a metal guard plate and opening a through hole; According to the through hole position, make the initial holes on the upper plate and core material; Design removal tools: spherical abrasives and cylindrical abrasives; Use the above removal tools to grind in stages until the core material is completely removed; Vacuum out the core powder and remove the metal guard plate; Expand the initial hole to the final hole to facilitate subsequent processes.

[0011] As a further solution of the present invention: the approach hole position is determined according to the defect range, specifically: the two farthest points of the debonding defect are used as the diameter to draw an envelope circle that can cover the defect, and the center position of the envelope circle is the approach hole position.

[0012] As a further solution of the present invention: the diameter of the access hole is determined by the wall panel thickness, the metal guard plate thickness, the core material thickness and the envelope circle diameter, specifically: access hole diameter = (wall panel thickness + metal guard plate thickness) / (wall panel thickness + metal guard plate thickness + core material thickness) * defect envelope circle diameter.

[0013] As a further solution of the present invention: covering the defect with a metal guard plate and opening a through hole, specifically: selecting a metal plate with a size larger than the diameter of the envelope circle as the guard plate material, and opening a through hole at its center position.

[0014] As a further solution of the present invention: align the center of the through hole of the metal guard plate with the center of the circle close to the hole, and use double-sided tape to stick the metal guard plate to the surface of the upper panel.

[0015] As a further solution of the present invention: the initial holes are made on the upper plate and the core material according to the positions of the through holes, specifically: at the positions of the through holes of the metal guard plate, the initial holes are made using a pneumatic grinding mechanism, and the diameter of the initial holes is slightly smaller than the diameter of the approaching holes.

[0016] As a further solution of the present invention, the drill bit is limited, and the limit height is consistent with the thickness of the upper panel and the core material, that is, the hole depth is the sum of the upper panel and the core material, avoiding damage to the lower panel.

[0017] As a further solution of the present invention: the designed removal tools: spherical grinding tools and cylindrical grinding tools, specifically: two removal tools are designed according to the properties of the core material, defects and approach hole size, the spherical grinding tool is a grinding tool with a round head straight rod, and the cylindrical grinding tool is a grinding tool with a cylindrical head bent rod, and there are multiple cylindrical grinding tools, and their bending lengths increase step by step.

[0018] As a further solution of the present invention: the step of using the above-mentioned removal tool for graded grinding until the core material is completely removed is specifically as follows: First, insert the spherical grinding tool into the access hole, allowing the grinding process to tilt the grinding tool until the core material is ground into a cone; Then replace the cylindrical grinding tool and insert it into the access hole to remove the core material under the panel step by step to the full depth.

[0019] As a further solution of the present invention, the vacuum suctioning out of the core material powder is specifically: using a vacuum source with a nozzle to remove the core material powder from the access hole.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This application uses a specific abrasive tool to achieve a conical hole expansion and graded full-depth core material removal method for hard core materials while ensuring the relative integrity of the panel interface.

[0021] 2. This application achieves full-depth removal of the foam core material under the panel while ensuring that the panel interface is relatively intact, avoiding the huge economic losses caused by the scrapping of foam sandwich structure composite parts due to the inability to repair debonding defects.

[0022] 3. This application has been used to repair the debonding defect of the foam sandwich structure inside the main landing gear door of a large passenger aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic flow chart of a method for removing a hard core material of a composite material according to the present invention; Figure 2 A schematic diagram of the approach hole position of the present invention; Figure 3 Schematic diagram of the tapered hole removal of the core material according to the present invention; Figure 4 Schematic diagram of the step-by-step removal of the core material according to the present invention.

[0024] Explanation of the accompanying symbols: 1. Debonding defect; 2. Access hole; 3. Core removal area; 4. Panel; 5. Metal guard plate; 6. Conical expansion hole; 7. Spherical grinding tool; 8. Cylindrical grinding tool. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] In the drawings, the same or similar reference numerals throughout the drawings represent the same or similar elements or elements having the same or similar functions. The described embodiments are only some of the embodiments of the present invention, but not all of the embodiments.

[0027] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0028] The following is combined with Figure 1-4 The embodiments of the present invention are described in detail.

[0029] Example 1 The present invention discloses a method for removing a hard core material of a composite material, which comprises the following steps: Determine the location of approach hole 2 based on the defect range; Cover the defect with a metal guard plate 5 and open a through hole; According to the through hole position, make initial holes on the upper plate 4 and the core material; Design removal tools: spherical abrasives 7 and cylindrical abrasives; Use the above removal tools to grind in stages until the core material is completely removed; Vacuum out the core powder and remove the metal guard plate 5; Expand the initial hole to the final hole to facilitate subsequent processes.

[0030] Preferably, the position of the approach hole 2 is determined according to the defect range, specifically: taking the two farthest points of the debonding defect 1 as the diameter to draw an envelope circle that can cover the defect, and the center position of the envelope circle is the position of the approach hole 2.

[0031] Preferably, the diameter of the access hole 2 is determined by the wall panel thickness, the metal guard plate 5 thickness, the core material thickness and the envelope circle diameter, specifically: the diameter of the access hole 2 = (wall panel thickness + metal guard plate 5 thickness) / (wall panel thickness + metal guard plate 5 thickness + core material thickness) * defect envelope circle diameter.

[0032] Preferably, a metal guard plate 5 is covered on the defect and a through hole is opened. Specifically, a metal plate with a size larger than the diameter of the envelope circle is selected as the guard plate material, and a through hole is opened at the center thereof.

[0033] Preferably, the center of the through hole of the metal guard plate 5 is aligned with the center of the circle close to the hole 2, and the metal guard plate 5 is adhered to the surface of the upper panel 4 using double-sided tape.

[0034] Preferably, the initial holes are made on the upper panel 4 and the core material according to the through hole positions, specifically: at the through hole positions of the metal guard plate 5, the initial holes are made using a pneumatic grinding mechanism, and the initial hole diameter is slightly smaller than the diameter of the approach hole 2.

[0035] Preferably, the drill bit is limited, and the limit height is consistent with the thickness of the upper panel 4 and the core material, that is, the hole depth is the sum of the upper panel 4 and the core material, to avoid damage to the lower panel 4.

[0036] Preferably, the designed removal tools include: a spherical grinding tool 7 and a cylindrical grinding tool. Specifically, two removal tools are designed according to the properties of the core material, defects and the size of the access hole 2. The spherical grinding tool 7 is a grinding tool with a round head straight rod, and the cylindrical grinding tool is a grinding tool with a cylindrical head bent rod. There are multiple cylindrical grinding tools, and their bending lengths increase step by step.

[0037] Preferably, the step of using the removal tool to grind in stages until the core material is completely removed is as follows: First, insert the spherical grinding tool 7 into the access hole 2, and allow the grinding process to tilt the grinding tool until the core material is ground into a cone; Then replace the cylindrical grinding tool and insert it into the approach hole 2 to remove the full depth core material under the panel 4 step by step.

[0038] Preferably, the vacuum suctioning out the core material powder is specifically performed by using a vacuum source with a nozzle to remove the core material powder from the access hole 2 .

[0039] Example 2 The present invention discloses a method for removing a hard core material of a composite material, comprising the following steps: (1) Determine the position of approach hole 2 like Figure 2 As shown in the figure, take the two farthest points of the debonding defect 1 as the diameter to draw an envelope circle that can cover the defect. The center of the circle is close to the position of hole 2.

[0040] The diameter of the access hole 2 is 6mm~12mm; (the following example uses 10mm); Diameter of access hole 2 = (wall thickness + metal guard plate 5 thickness) / (wall thickness + metal guard plate 5 thickness + core material thickness) * defect envelope circle diameter.

[0041] (2) Product protection Select a metal shield material that is larger than the enveloping circle and 2mm to 5mm thick. Create a hole with an 8mm diameter at the center of the metal shield 5. Use double-sided tape to affix the metal shield 5 to the surface of the panel 4, ensuring the center of the hole aligns with the center of the circle near hole 2. This protects the upper panel 4 to prevent damage during hole making and subsequent core material removal.

[0042] (3) Making the initial hole At the hole opening position of the metal guard plate 5, a pneumatic grinding machine is used to drill a hole with a hole diameter of 8 mm. The drill bit is limited, and the limit height is consistent with the thickness of the upper panel 4 and the core, that is, the hole depth is the sum of the upper panel 4 and the core material, to avoid damage to the lower panel 4.

[0043] (4) Homemade grinding tools Prepare core material removal tools spherical grinding tool 7, cylindrical grinding tool (take the core material removal diameter of 60mm as an example, Figure 4As shown, the cylindrical mold is bent step by step (such as 10mm, 20mm, 30mm).

[0044] (5) Conical expansion 6 Insert the spherical grinding tool 7 into the access hole 2 and allow the grinding process to tilt the grinding tool until the core material is ground into Figure 3 Cone shown.

[0045] (6) Complete removal of core material Tilt at a certain angle and insert the cylindrical grinding tool 8 (bent into L shape) into the access hole 2. Use 10mm, 20mm and 30mm cylindrical grinding tools 8 in sequence to remove the full-depth core material under the panel 4 step by step. If the resistance during the grinding process is large and the speed of the pneumatic grinder is insufficient, further classification can be performed.

[0046] (7) A vacuum source with a nozzle to remove the core material powder from the access hole 2 and remove the metal guard plate 5.

[0047] (8) Hole expansion The approach hole 2 is expanded to a diameter of 10 mm to avoid damage to the hole wall during the conical expansion process 6, which affects the hole quality.

[0048] So far, the purpose of the present invention has been accomplished.

[0049] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for removing a hard core material of a composite material, characterized in that: The following steps are involved: Determine the approach hole location based on the defect range; Covering the defect with a metal guard plate and opening a through hole; According to the through hole position, make the initial holes on the upper plate and core material; Design removal tools: spherical abrasives and cylindrical abrasives; Use the above removal tools to grind in stages until the core material is completely removed; Vacuum out the core powder and remove the metal guard plate; Expand the initial hole to the final hole to facilitate subsequent processes.

2. A method for removing a hard core material of a composite material according to claim 1, characterized in that: The approach hole position is determined according to the defect range, specifically: an envelope circle that can cover the defect is drawn with the two farthest points of the debonding defect as the diameter, and the center position of the envelope circle is the approach hole position.

3. The method for removing a hard core material of a composite material according to claim 2, characterized in that: The diameter of the access hole is determined by the wall panel thickness, metal guard plate thickness, core material thickness and envelope circle diameter, specifically: access hole diameter = (wall panel thickness + metal guard plate thickness) / (wall panel thickness + metal guard plate thickness + core material thickness) * defect envelope circle diameter.

4. The method for removing a hard core material of a composite material according to claim 1, characterized in that: The defect is covered with a metal guard plate and a through hole is formed, specifically, a metal plate with a size larger than the diameter of the envelope circle is selected as the guard plate material, and a through hole is formed at the center thereof.

5. The method for removing a hard core material of a composite material according to claim 4, characterized in that: Align the center of the through hole of the metal guard plate with the center of the circle close to the hole, and use double-sided tape to stick the metal guard plate to the surface of the upper panel.

6. The method for removing a hard core material of a composite material according to claim 1, characterized in that: According to the position of the through hole, the initial hole is made on the upper plate and the core material. Specifically, at the position of the through hole of the metal guard plate, the initial hole is made by using a pneumatic grinding mechanism, and the diameter of the initial hole is slightly smaller than the diameter of the approach hole.

7. A method for removing a hard core material of a composite material according to claim 6, characterized in that: The drill bit is limited, and the limit height is consistent with the thickness of the upper panel and the core material, that is, the hole depth is the sum of the upper panel and the core material to avoid damage to the lower panel.

8. The method for removing a hard core material of a composite material according to claim 1, characterized in that: The designed removal tools include: a spherical grinding tool and a cylindrical grinding tool. Specifically, two removal tools are designed according to the properties of the core material, defects and the size of the approaching hole. The spherical grinding tool is a grinding tool with a round head and a straight rod, and the cylindrical grinding tool is a grinding tool with a cylindrical head and a bent rod. There are multiple cylindrical grinding tools, and their bending lengths increase step by step.

9. The method for removing a hard core material of a composite material according to claim 1, characterized in that: The step of using the removal tool to grind in stages until the core material is completely removed is as follows: First, insert the spherical grinding tool into the access hole, allowing the grinding process to tilt the grinding tool until the core material is ground into a cone; Then replace the cylindrical grinding tool and insert it into the access hole to remove the core material under the panel step by step to the full depth.

10. The method for removing a hard core material of a composite material according to claim 1, characterized in that: The vacuum suctioning of the core material powder specifically includes: using a vacuum source with a nozzle to remove the core material powder from the access hole.

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