Forming method of special-shaped multi-cavity composite material part

Abstract

The invention provides a forming method of a special-shaped multi-cavity composite material part, which comprises the following steps of: manufacturing a plurality of core molds by adopting high-density PMI (Polymethacrylimide) foam, and assembling the core molds on a base to manufacture a mold tool; unfreezing the carbon fiber prepreg, and cutting the unfrozen carbon fiber prepreg into a plurality of material sheets; material sheets are laid on the surface of the mold tool to form a plurality of laying layers, vacuumizing and pre-compaction are carried out, and a rough part blank is manufactured; and the rough part blank is cured, demolded and finely machined to obtain a finished part product. The forming method can shorten the manufacturing period, reduce the manufacturing cost and improve the product percent of pass while ensuring the product profile precision, thereby improving the market competitive advantage of the product.

Description

Technical Field

[0001] The invention relates to the field of composite material parts manufacturing technology, and in particular to a molding method for special-shaped multi-cavity composite material parts. Background Art

[0002] Unmanned aircraft, or "drones" for short, are unmanned aircraft that are controlled by radio remote control equipment and self-contained program control devices, or are operated completely or intermittently autonomously by onboard computers. Compared with manned aircraft, drones are often more suitable for tasks that are too "dull, dirty or dangerous". In the civilian field, they have been widely used in aerial photography, agriculture, plant protection, micro selfies, express delivery, disaster relief, wildlife observation, infectious disease monitoring, surveying and mapping, news reporting, power inspections, disaster relief, film and television shooting, etc., which greatly expands the use of drones.

[0003] The fuselage of a drone is composed of multiple parts, among which the air intake is a key component of the drone's pneumatic system. It is used to provide the drone's engine with the air it needs to work, which directly affects the engine's working efficiency and plays a vital role in whether the engine works normally and the thrust size, thus having a great impact on the overall performance of the drone.

[0004] Conventional UAV air intake configurations include S-type, Y-type, and S-type or Y-type with wall panels. During the flight of the UAV, strong airflow will form strong internal pressure on it, so the air intake needs a smooth inner surface to ensure the air intake and gas flow under its working state. Such special-shaped multi-cavity parts are generally manufactured using molds. However, due to its complex structure, the mold structure used is also relatively complex, often consisting of a core mold and a base or cover plate, etc., so it is difficult and time-consuming to demold, and the efficiency is low. The resulting product has poor performance, low precision, and low product qualification rate. In addition, the design and assembly of traditional metal core molds are also relatively complex, with low production efficiency and high cost. Summary of the invention

[0005] The purpose of the present invention is to provide a molding method for special-shaped multi-cavity composite material parts. By using high-density PMI foam as a disposable core mold for overall molding, the mold design is simplified, the manufacturing cost of the mold is reduced, and the part production efficiency is improved. The surface of the product obtained is smooth, meeting the requirements of product performance and precision, and the product qualification rate is high, thereby improving the market competitiveness of the product.

[0006] To achieve the above object, the present invention proposes the following technical solutions:

[0007] A method for forming a special-shaped multi-cavity composite material part, specifically comprising the following steps:

[0008] Step 1: Take several core molds according to the part structure, machine the core molds according to the part surface structure, assemble the core molds on a base and perform positioning calibration, polish the surfaces of all the core molds to meet the precision requirements of the part surface, obtain the mold tooling, and lay a layer of adhesive release cloth on the surface of all the core molds; wherein, the material of all the core molds is high-density PMI foam;

[0009] Step 2: Take the carbon fiber prepreg, thaw it for 5-7 hours and cut it into several pieces;

[0010] Step 3: laying the sheet on the surface of the core mold of the mold tooling to form several layers to obtain a rough blank of the part, laying a layer of rubber soft film on the surface of the last layer, wherein after the first layer and every subsequent 3-4 layers are laid, vacuum pre-compacting is performed for bag making and packaging;

[0011] Step 4: placing the assembly formed by the mold tooling and the rough part blank in step 3 in an autoclave for curing, releasing the pressure and opening the autoclave after curing to obtain a rough part product formed by curing the rough part blank;

[0012] Step 5: destroy the core mold on the mold tooling, remove the rough part from the mold tooling, remove the burrs of the rough part, fine-process the rough part according to the part processing line, obtain the finished part, and test it.

[0013] As a preferred technical solution of the present invention, the base in step one is a metal base.

[0014] As a preferred technical solution of the present invention, a plurality of the core molds are positioned and connected by means of boss and groove engagement.

[0015] As a preferred technical solution of the present invention, the density of the high-density PMI foam is 110±10kg / m 3 , and the aperture is 0.1-0.3mm.

[0016] As a preferred technical solution of the present invention, the carbon fiber prepreg in the step 2 includes carbon fiber fabric prepreg and / or carbon fiber unidirectional tape prepreg.

[0017] As a preferred technical solution of the present invention, the number of the layers in step three is 15.

[0018] As a preferred technical solution of the present invention, in the step three, the pieces of material in the same layer of the ply are connected by overlapping, with an overlapping size of 15-30 mm, and the overlapping positions of the pieces of material in different layers of the ply are staggered by at least 20 mm.

[0019] As a preferred technical solution of the present invention, the vacuum degree of the bag-making vacuum pre-compaction in step three is above 950 mbar, and the pressure drop does not exceed 30 mbar within 5 minutes.

[0020] As a preferred technical solution of the present invention, the curing process in step 4 is vacuumed throughout the whole process. First, the temperature is raised to 81±3°C at a heating rate not exceeding 2°C / min and kept warm for 30±5min. When the temperature enters the insulation stage, pressurization is started to 0.3±0.03MPa, and then the temperature is raised to 125°C±5°C at a heating rate not exceeding 2°C / min and kept warm for 95min±5min. Then, the temperature is lowered at a cooling rate not exceeding 2°C / min. When the temperature drops below 60°C, the pressure is released and the can is opened.

[0021] As a preferred technical solution of the present invention, the curing process uses air or nitrogen as the curing medium.

[0022] The technical solution of the present invention provides a molding method for special-shaped multi-cavity composite material parts, which adopts high-density PMI foam as a disposable core mold, which is assembled with a base to form a mold tooling as an integral molding tool for laying product materials. After the product is cured and formed, the disposable core mold is destroyed to remove the product from the mold tooling. The demolding method is simple, which simplifies the molding process, is not easy to cause damage to the product, ensures the apparent quality of the product, shortens the product manufacturing cycle, reduces the manufacturing difficulty and manufacturing cost, and improves the product qualification rate, thereby improving the market competitiveness of the product.

[0023] It should be appreciated that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, may be considered to be part of the inventive subject matter of the present disclosure, provided such concepts are not mutually inconsistent.

[0024] The foregoing and other aspects, embodiments and features of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are not drawn to scale according to actual reference objects. In the accompanying drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For the sake of clarity, not every component is labeled in each figure. Now, embodiments of various aspects of the present invention will be described by way of example and with reference to the accompanying drawings, in which:

[0026] Figure 1 It is a front view of a mold tooling according to a specific embodiment of the present invention;

[0027] Figure 2 A side view of a mold tooling according to a specific embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the air intake structure of a UAV according to a specific embodiment of the present invention;

[0029] Figure 4 The figure is a flow chart of the molding process of a specific embodiment of the present invention.

[0030] The meanings of the reference numerals in the figures are as follows:

[0031] 1-Core mold one 2-Core mold two 3-Core mold three 4-Core mold four 5-Base DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs.

[0033] The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular form of "a", "an" or "the" and similar words do not indicate a quantity limitation, but indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before "include" or "comprise" include the features, wholes, steps, operations, elements and / or components listed after "include" or "comprise", and do not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0034] In order to solve the problems of difficult demoulding, long time consumption, low efficiency, poor performance and low precision of the obtained products, and low product qualification rate in the manufacturing and molding of existing special-shaped multi-cavity parts such as drone air intakes, an embodiment of the present invention provides a molding method for special-shaped multi-cavity composite material parts. By using PMI foam as a positive mold for paving and curing, the overall molding of such special-shaped multi-cavity parts can be achieved, the production process is simplified, the production cycle is shortened, the manufacturing difficulty and manufacturing cost are reduced, the product qualification rate is improved, and the market competitiveness of the product is improved.

[0035] An embodiment of the present invention provides a method for forming a special-shaped multi-cavity composite material part, which specifically includes the following steps:

[0036] Step 1: Take several core molds according to the part structure, machine the core molds according to the part surface structure, assemble the core molds on a base and perform positioning calibration, polish the surfaces of all the core molds to meet the precision requirements of the part surface, obtain the mold tooling, and lay a layer of adhesive release cloth on the surface of all the core molds; wherein, the material of all the core molds is high-density PMI foam, and the density of the preferred high-density PMI foam is 110±10kg / m 3 , and the aperture is 0.1-0.3mm; the base is preferably a metal base; in some specific embodiments of the present invention, several of the core molds are positioned and connected by means of bosses and grooves.

[0037] Step 2: Take the carbon fiber prepreg, thaw it for 5-7 hours, and then cut it into a plurality of sheets; wherein the carbon fiber prepreg includes carbon fiber fabric prepreg and / or carbon fiber unidirectional tape prepreg.

[0038] Step three: Lay the sheet on the surface of the core mold of the mold tooling to form several layers, preferably 15 layers, to obtain a rough part, lay a layer of rubber soft film on the surface of the last layer, wherein, after the first layer and every subsequent 3-4 layers are laid, perform vacuum pre-compaction for bag making and packaging. During the specific laying, the sheets of the same layer are connected in an overlapping manner, with an overlapping size of 15-30mm, and the overlapping positions of the sheets of different layers are staggered by at least 20mm. For vacuum pre-compaction for bag making and packaging, the vacuum degree is above 950mbar, and the pressure drop does not exceed 30mbar within 5 minutes.

[0039] Step 4: Place the assembly of the mold tooling and the rough part in step 3 in an autoclave for curing. After curing, release the pressure and open the can to obtain a rough part formed by curing the rough part. The curing process is vacuumed throughout. First, the temperature is raised to 81±3°C at a rate of no more than 2°C / min and kept warm for 30±5min. When the temperature enters the insulation stage, pressurization is started to 0.3±0.03MPa, and then the temperature is raised to 125°C±5°C at a rate of no more than 2°C / min, and kept warm for 95min±5min. Then, the temperature is lowered at a rate of no more than 2°C / min. When it drops below 60°C, the pressure is released and the can is opened. Air or nitrogen is preferably used as the curing medium in the curing process.

[0040] Step 5: destroy the core mold on the mold tooling, remove the rough part from the mold tooling, remove the burrs of the rough part, fine-process the rough part according to the part processing line, obtain the finished part, and test it.

[0041] Example 1

[0042] like Figure 1-3 As shown, it is a schematic diagram of the structure of the air intake duct of a UAV and its mold tooling. The embodiment of the present invention takes the air intake duct as an example to explain the technical solution of the present invention in detail. The specific manufacturing process steps are as follows:

[0043] Mold preparation: According to the structure of the air inlet, it is divided into 4 main parts, and then 4 core molds are selected and named as core mold 1, core mold 2, core mold 3 and core mold 4. In addition to the different structures, the four core molds are all made of high-density PM I foam, preferably with a density of 110±10kg / m 3 , and PM I foam with a pore size of 0.1-0.3mm. High-density PMI foam is a closed-cell rigid foam material based on polymethacrylimide, which is halogen-free, has small and uniform foam pores, and the processing technology can withstand temperatures up to 150°C and pressures up to 0.3MPa. In addition, high-density PMI foam can be easily hot-pressed, bonded with various adhesives, and processed at will using common CNC machine tools.

[0044] The core mold 1, core mold 2, core mold 3 and core mold 4 are assembled on a base 5 according to the structural layout of the air inlet duct. In order to meet the subsequent application requirements in the autoclave, a metal base is preferably used as a support for the mold tooling. During the specific assembly, the core mold and the metal base are preferably bonded with structural adhesive, because the structural adhesive can meet the temperature and pressure of the subsequent autoclave usage scenario and is easily available. The core mold 1, core mold 2, core mold 3 and core mold 4 are first machined into corresponding shapes respectively, and then the core molds are positioned and assembled with each other by means of bosses and grooves. For example, a boss is provided on core mold 1, and a groove matching the boss is provided on core mold 2. The core mold 1 and the core mold 2 are connected together by the engagement of the boss and the groove. Of course, the boss and the groove are not limited to any core mold, and can be designed according to actual conditions. At the same time, the positioning tool is used for auxiliary positioning to ensure that the position of each core mold is accurately installed, thereby ensuring the accuracy of the size of the manufactured product. Then, the laser tracker is used for combined calibration, the joints between the core molds are bonded with structural adhesive, and the joints are repaired and polished with putty to make them smooth. After all the core molds are assembled, the laser tracker is used again to scan the overall surface, and the local positions that do not meet the accuracy requirements are repaired with putty and then polished to obtain the mold tooling, and finally a layer of adhesive release cloth is laid on the surface of the core mold as a whole.

[0045] Material preparation: Take carbon fiber prepreg from the cold storage. Different types of carbon fiber prepreg are selected according to the fiber direction required by different products, which may include carbon fiber fabric prepreg and / or carbon fiber unidirectional tape prepreg. Thaw for 6 hours, and then design the cutting program in advance according to the product shape, and cut out the sheets with the correct fiber direction and shape accordingly, so as to ensure the fiber direction and the shape of the sheet.

[0046] Laying: Sheets cut from carbon fiber prepreg are laid on the surface of the core mold of the mold tooling to form multiple layers. The number of layers is preferably 15 to obtain a rough blank of the part. Of course, in actual laying, the appropriate number of laying layers can be selected according to the thickness requirements of different products, such as 20 layers, 30 layers, etc. After all the layers are laid, a layer of rubber soft film needs to be laid on the outer surface of the outermost layer to ensure its surface quality. Among them, the first layer and every subsequent 4 layers are vacuum pre-compacted for bag making and packaging. It should be noted that the sheets of the same layer are connected by overlapping, with an overlap size of 15-30mm, and the overlapping positions of the sheets of different layers should be staggered by at least 20mm. In addition, during laying, the R corner of the mold tooling and the narrow area around it need to be laid with auxiliary tooling such as long wedges to prevent bridging in the above-mentioned positions or areas, causing quality problems in the product.

[0047] When making bags and packaging, the assembly formed by the mold tooling and the rough blank of the parts is sealed with a vacuum bag, and release paper is placed at the R corner of the mold tooling. Then, the soft film wrapped with an isolation film is pressed against the R corner of the release paper to compact the R corner, so as to tightly press the carbon fiber prepreg at the R corner onto the mold tooling to avoid wrinkles in the R corner and its surrounding area. In the specific setting, two air nozzles are provided on the vacuum bag, and they correspond to the two ends of the metal base respectively. During the vacuuming process, "one pumping and one testing" is required. Specifically, one air nozzle is used for vacuuming, and the other air nozzle is used to detect the vacuum degree of the vacuum bag. Among them, the vacuum degree detection requires that the vacuum degree reaches above 950mbar, and the pressure drop does not exceed 30mbar within 5 minutes. In order to monitor the temperature of the rough part during curing, a leading thermocouple and a lagging thermocouple are placed at the diagonal positions of the rough part. The leading thermocouple is placed between the first and second layers of the bagging surface of the rough part margin area, and the lagging thermocouple is placed between the layers of the rough part margin area and the mold tooling. At the same time, a leading thermocouple and a lagging thermocouple are placed on the windward slope and leeward slope of the mold tooling to monitor the temperature of the mold tooling. The windward slope and leeward slope can be distinguished according to the wind direction inside the autoclave. After the vacuum bag is evacuated, it is tested for air tightness.

[0048] Curing: The assembly formed by the mold tooling and the rough blank of the part is placed in an autoclave for curing. The whole curing process is vacuumed, and the curing medium is preferably air or nitrogen. During curing, first heat the temperature to 81℃±3℃ at a rate not exceeding 2℃ / min, and keep it warm for 30±5min; when the temperature in the autoclave enters the insulation stage, pressurization begins, specifically to 0.3±0.03MPa; then heat the temperature to 125℃±5℃ at a rate not exceeding 2℃ / min, and keep it warm for 95min±5min; then the mold tooling is cooled at a cooling rate not exceeding 2℃ / min, and when the temperature of the mold tooling drops below 60℃, the pressure is released and the can is opened. Among them, the curing heating time and insulation time are based on the lagging thermocouple, and the heating rate should meet the requirements when measured within any 30min.

[0049] Demolding: Remove the vacuum bag, demoulding cloth and other auxiliary materials, destroy all the core molds on the mold tooling one by one, and then remove the rough parts formed by curing the rough parts from the mold tooling. This demoulding method can ensure that after the product is cured, it will not cause serious damage to the rough parts of the air intake duct. Finally, use a file and 80# sandpaper to remove the flash of the product.

[0050] Finishing: The rough parts are finished according to the processing line of the parts products to obtain the finished parts.

[0051] Inspection: Inspection of finished parts, including surface inspection and non-destructive inspection.

[0052] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A method for forming a special-shaped multi-cavity composite material part, characterized in that: The specific steps include: Step 1: Take several core molds according to the part structure, machine the core molds according to the part surface structure, assemble the core molds on a base and perform positioning calibration, polish the surfaces of all the core molds to meet the precision requirements of the part surface, obtain the mold tooling, and lay a layer of adhesive release cloth on the surface of all the core molds; wherein, the material of all the core molds is high-density PMI foam; Step 2: Take the carbon fiber prepreg, thaw it for 5-7 hours and cut it into several pieces; Step 3: laying the sheet on the surface of the core mold of the mold tooling to form several layers to obtain a rough blank of the part, laying a layer of rubber soft film on the surface of the last layer, wherein after the first layer and every subsequent 3-4 layers are laid, vacuum pre-compacting is performed for bag making and packaging; Step 4: placing the assembly formed by the mold tooling and the rough part blank in step 3 in an autoclave for curing, releasing the pressure and opening the autoclave after curing to obtain a rough part product formed by curing the rough part blank; Step 5: destroy the core mold on the mold tooling, remove the rough part from the mold tooling, remove the burrs of the rough part, fine-process the rough part according to the part processing line, obtain the finished part, and test it.

2. The method for forming a special-shaped multi-cavity composite material part according to claim 1, characterized in that: The base in the step 1 is a metal base.

3. The molding method of special-shaped multi-cavity composite material parts according to claim 1, characterized in that: The core molds are positioned and connected by means of boss-groove engagement.

4. The method for forming a special-shaped multi-cavity composite material part according to claim 1, characterized in that: The density of the high-density PMI foam is 110±10kg / m 3 , and the aperture is 0.1-0.3mm.

5. The molding method of special-shaped multi-cavity composite material parts according to claim 1, characterized in that: The carbon fiber prepreg in step 2 includes carbon fiber fabric prepreg and / or carbon fiber unidirectional tape prepreg.

6. The method for forming a special-shaped multi-cavity composite material part according to claim 1, characterized in that: The number of layers in step three is 15.

7. The molding method of special-shaped multi-cavity composite material parts according to claim 1, characterized in that: In the step three, the pieces of material in the same layer of the ply are connected by overlapping, with an overlapping size of 15-30 mm, and the overlapping positions of the pieces of material in different layers of the ply are staggered by at least 20 mm.

8. The method for forming a special-shaped multi-cavity composite material part according to claim 1, characterized in that: The vacuum degree of the bag making vacuum pre-compaction in the step 3 is above 950 mbar, and the pressure drop does not exceed 30 mbar within 5 minutes.

9. The method for forming a special-shaped multi-cavity composite material part according to claim 1, characterized in that: The curing process in step 4 is vacuumed throughout the whole process. First, the temperature is raised to 81±3°C at a heating rate not exceeding 2°C / min and kept warm for 30±5min. When the temperature enters the insulation stage, pressurization is started to be increased to 0.3±0.03MPa, and then the temperature is raised to 125°C±5°C at a heating rate not exceeding 2°C / min and kept warm for 95min±5min. Then the temperature is lowered at a cooling rate not exceeding 2°C / min. When the temperature drops below 60°C, the pressure is released and the can is opened.

10. The method for forming a special-shaped multi-cavity composite material part according to claim 9, characterized in that: The curing process uses air or nitrogen as the curing medium.

Images