Adjustable thermoplastic composite flat plate stamping die and method

Abstract

The invention relates to the technical field of composite forming, and particularly discloses an adjustable thermoplastic composite flat plate stamping die and method, the die comprises an upper die, a lower die and a plurality of replaceable limiting frames, and the limiting frames are movably connected with frame grooves of the lower die through elastic reset mechanisms. During stamping, the upper die firstly makes contact with the limiting frame to move downwards to be attached to the flat plate, then the flat plate is pressed, and the inner side face of the limiting frame is used for restraining in-plane flowing of the base body. The design of the elastic reset mechanism can adapt to flat plates with different thicknesses and sizes, and the replaceable limiting frame body realizes multi-size compatibility. The method has the beneficial effects that the fiber deflection is reduced to below 0.5 degree, the interlaminar shear strength reaches 98MPa, and the size switching time is only 3 minutes.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material forming, and specifically to a composite material flat stamping die and method that achieve multi-size compatibility and suppress matrix flow through a replaceable limiting frame and an elastic reset structure, and are applicable to the manufacture of high-performance composite materials in fields such as aviation and automotive Background Art

[0002] Prepreg laminated blanks of thermoplastic composite flat structural parts such as aviation gussets are increasingly used in large aircraft. These composite gusset structures use thermoplastic matrices and can greatly improve production efficiency using a hot stamping forming process

[0003] The stamping process of thermoplastic composites generally includes the following steps: 1) First, lay single-layer prepregs in different directions as required; 2) Heat and press into a laminated flat plate; 3) Heat the laminated plate; 4) Hot stamping forming; 5) Demolding and post-treatment. The above stamping process has the following two major defects 1. Out-of-control matrix flow: When hot stamping, the resin flows in the plane and drives the fibers to deflect (deflection angle > 5°), resulting in a decrease in the interlaminar shear strength of ≥ 30% 2. Poor die versatility: The entire set of dies needs to be replaced for plane size adaptation, and shims need to be adjusted when the thickness changes by more than ±1 mm, with poor positioning accuracy

[0004] It should be noted that the information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art Summary of the Invention

[0005] In view of this, the purpose of the present invention is to address the deficiencies of the above-mentioned prior art, and provide an adjustable thermoplastic composite flat stamping die and method to solve the problem of in-plane flow of the matrix during flat stamping through the structural design of the stamping die, and enable it to adapt to the stamping forming of thermoplastic composite flat plates with various plane sizes and thickness dimensions <>

[0006] To achieve the above purpose, the present invention adopts the following technical solutions The present invention provides an adjustable thermoplastic composite flat stamping die and method, and the core solutions include 1. Die Structure Replaceable limiting frame: At least two limiting frames with different plane sizes are quickly installed by matching the frame grooves of the lower die Elastic floating mechanism: The limiting frame is movably connected to the frame groove through an elastic reset mechanism, enabling the limiting frame to float up and down and automatically compensate for changes in the flat plate thickness Sequential pressing design: During stamping, the upper die first contacts the limit frame to move it down and close to the flat plate, and then presses the flat plate to form a matrix flow constraint area.

[0007] 2. Key innovative components The elastic reset mechanism includes a spring and a spring guide rod, the spring guide rod is fixed to the lower mold with interference fit and is clearance fit in the limit frame to ensure the accuracy of vertical movement; The limiting frame adopts a thermal expansion coefficient of ≤5×10⁻ 6 / ℃ materials (such as Invar alloy, ceramic matrix composite materials), the gap change with the plate at high temperature is ≤ 0.01mm; The upper / lower molds are provided with a stepped exhaust system (upper exhaust holes, lower exhaust holes) to exhaust gas at different stages of pressing.

[0008] 3. Stamping method Steps S1-S2: Select a limit frame that fits the size of the tablet and install it on the lower mold to place the tablet; Steps S3-S4: The upper mold presses down → first contacts the limit frame to move it downward → continues to press down to contact the flat plate, completing the stamping under the restraint state; Process parameters: temperature 300-400℃, pressure 10-50MPa, holding time 30-120 seconds.

[0009] The beneficial effects of the present invention are: 1. Precision breakthrough: The plane flow of the matrix is constrained by the limit frame, the fiber orientation deviation is ≤0.5°, and the interlaminar shear strength is increased to 98MPa; 2. Efficient adaptation: Interchangeable frame + elastic floating design, switching between different sizes (200×200~600×600) and thicknesses (2-10mm) within 3 minutes; 3. Cost optimization: A single set of molds replaces traditional multiple sets of molds, reducing energy consumption by 35% compared to traditional molds. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 According to some embodiments of the present application, a schematic structural diagram of an adjustable thermoplastic composite flat plate stamping die is shown; Figure 2 According to some embodiments of the present application, a schematic structural diagram of a lower mold is shown; Figure 3 According to some embodiments of the present application, a schematic structural diagram of an upper mold is shown; Figure 4 According to some embodiments of the present application, a schematic structural diagram of a first frame is shown; Figure 5 According to some embodiments of the present application, a schematic structural diagram of a second frame is shown; Figure 6 According to some embodiments of the present application, a schematic diagram of an elastic reset mechanism is shown; Figure 7 According to some embodiments of the present application, a schematic diagram of the structure of a thermoplastic composite material flat plate is shown.

[0011] Explanation of reference numerals in the drawings: 10. Lower die; 11. Frame groove; 111. First frame groove; 112. Second frame groove; 12. Lower die platform; 131. First groove guide rod hole; 132. Second groove guide rod hole; 14. Lower die mounting hole; 20. Upper die; 21. Upper die boss; 22. Base; 23. Upper die mounting hole; 30. Limit frame; 31. First frame; 311. First frame bottom surface; 312. First frame inner side surface; 313. First frame top surface; 314. First frame guide rod hole; 32. Second frame; 321. Second frame bottom surface; 322. Second frame inner side surface; 323. Second frame top surface; 324. Second frame guide rod hole; 40. Elastic reset mechanism; 41. Spring; 42. Spring guide rod; 401. First elastic reset mechanism; 402. Second elastic reset mechanism; 50. Exhaust system; 511. First lower exhaust hole; 512. Second lower exhaust hole; 52. Upper exhaust hole; 60. Flat plate. Detailed embodiments

[0012] The technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making the protection scope of the present invention more clearly defined.

[0013] Please refer to Figures 1-7 , an embodiment of the present invention provides an adjustable thermoplastic composite material flat plate stamping die, including an upper die 20, a lower die 10, a plurality of replaceable limit frames 30 and an elastic reset mechanism 40; wherein, a forming space for the thermoplastic composite material flat plate 60 is formed between the upper die 20 and the lower die 10, the replaceable limit frame 30 is used to adapt to flat plates 60 with different planar dimensions, and the lower die 10 is provided with a plurality of frame grooves 11 respectively matching the respective limit frames 30 for installing the limit frames 30, and the limit frames 30 are movably connected to the frame grooves 11 through the elastic reset mechanism 40; during stamping, the upper die 20 first contacts the limit frame 30 to make it move downward under the action of the elastic reset mechanism 40, and then contacts the flat plate 60, and the inner side surface of the limit frame 30 restricts the in-plane flow of the flat plate 60 matrix.

[0014] The core innovations of the embodiments of the present invention include: 1. Replaceable limit frame 30: By installing limit frames 30 with different sizes on the lower die 10, the stamping requirements of flat plates 60 with different planar dimensions can be adapted; 2. Elastic floating design: The elastic reset mechanism 40 enables the limit frame 30 to float vertically, automatically compensating for the thickness change (±3 mm) of the flat plate 60. 3. Flow constraint mechanism: The inner side of the limit frame 30 is close to the edge of the flat plate 60 at the initial stage of stamping, restraining the in-plane flow of the matrix.

[0015] The following will combine with the attached drawings to elaborate in detail on the structure and function of the core components of the adjustable thermoplastic composite flat plate stamping die.

[0016] Limit frame 30: The limit frame 30 matches the planar shape of the flat plate 60 and is a rectangular frame structure. Its function is to restrain the in-plane flow of the matrix and prevent fiber deflection. By replacing the limit frames 30 with different sizes (such as 200×200 - 600×600), it can be adapted to the stamping processing of flat plates 60 with different planar sizes. Of course, the limit frame 30 is not limited to a rectangular structure and can be designed as a circular, polygonal or special-shaped contour (such as profiling for aviation parts) to meet the processing requirements of flat plates with different shapes. As an example, the limit frame 30 can be made of a material with a thermal expansion coefficient similar to that of the flat plate (such as invar alloy, thermal expansion coefficient 1.6×10⁻ 6 / °C). The gap between its inner side 3 and the flat plate 60 can be set to 0.01 - 0.1 mm (preferably ≤0.05 mm), and the change at high temperature is <0.01 mm. In addition to invar alloy, ceramic matrix composites (such as SiC / Al2O3, thermal expansion coefficient ≤4×10⁻ 6 / °C) or low-expansion titanium alloy (Ti-6Al-4V, thermal expansion coefficient 5×10⁻ 6 / °C) can also be used to ensure the stability of the high-temperature gap. Multiple frame guide rod holes are provided on the bottom surface of the limit frame 30 for connecting the elastic reset mechanism 40. The frame guide rod holes are designed as non-through hole structures, forming a sliding connection with the elastic reset mechanism 40. In this embodiment, for the convenience of description, two sizes of limit frames 30 are taken as examples for description, namely the first frame 31 and the second frame 32. The planar size of the second frame 32 is larger than that of the first frame 31. The first frame 31 includes a first frame bottom surface 311, a first frame inner side 312, and a first frame top surface 313. Multiple first frame guide rod holes 314 are designed on the first frame bottom surface 311 for forming a clearance fit with the spring guide rod 42 of the elastic reset mechanism 40. Similar to the first frame 31, the second frame 32 includes a second frame bottom surface 321, a second frame inner side 322, and a second frame top surface 323. Multiple second frame guide rod holes 324 are designed on the second frame bottom surface 321 for forming a clearance fit with the spring guide rod 42. It should be noted that in other embodiments of the present invention, the number of limit frames 30 can of course be increased to meet the stamping requirements of more flat plates 60 with different sizes.

[0017] Elastic reset mechanism 40: It includes a spring 41 and a spring guide rod 42. The spring 41 is used to provide a buffering force when the limiting frame 30 moves downward and automatically compensate for the thickness tolerance (±3 mm) of the flat plate 60. The spring guide rod 42 is inserted into the interior of the spring 41 and is used to guide the vertical movement of the limiting frame 30 to ensure that the vertical movement of the limiting frame 30 is unobstructed. The lower end of the spring guide rod 42 can form an interference fit (interference amount 0.03 mm) with the groove guide rod hole of the lower die 10, and the upper end forms a clearance fit (clearance 0.05 mm) with the frame guide rod hole on the limiting frame 30. Since the frame guide rod hole is a non-through hole, the spring 41 is elastically constrained between the limiting frame 30 and the frame groove 11 during the downward pressing of the limiting frame 30. In this embodiment, matching the number of the limiting frames 30, the elastic reset mechanism 40 is divided into a first elastic reset mechanism 401 for cooperating with the first frame 31 and a second elastic reset mechanism 402 for cooperating with the second frame 32, which are respectively used for guiding the stamping movement and compensating the stamping thickness of the first frame 31 and the second frame 32. As an alternative implementation, the elastic reset mechanism 40 can also adopt a disc spring group (suitable for high-load working conditions) or a pneumatic buffer (providing non-linear damping force); in addition to adapting the pre-tightening force of the elastic element through the spring stiffness, a threaded adjusting gasket or a hydraulic pre-tightening module can also be added to realize the expansion of the thickness compensation amount; in addition, the interference fit between the spring guide rod 42 and the groove guide rod hole can also be changed to a tapered surface locking sleeve to avoid micro-movement wear of the guide rod.

[0018] Exhaust system 50: It includes a lower exhaust hole provided on the lower die 10 and an upper exhaust hole 52 provided on the upper die 20. The lower exhaust hole is provided in the frame groove 11 of the lower die 10 and is used to discharge the gas when the limiting frame 30 moves downward. The upper exhaust hole 52 is provided on the boss 21 of the upper die 20 and is used to start exhausting after the boss 21 contacts the top surface of the limiting frame 30. In this embodiment, the lower exhaust hole is divided into a first lower exhaust hole 511 arranged in cooperation with the first frame 31 and a second lower exhaust hole 512 arranged in cooperation with the second frame 32. Further, the aperture of the lower exhaust hole can also be set in a graded manner (such as Φ1 mm in the central area and Φ0.5 mm in the edge area) to optimize the gas discharge path.

[0019] Lower mold 10: The lower mold 10 forms the bottom support and includes a frame groove 11 and a lower mold platform 12. The frame groove 11 is used to mount the limiting frame 30, and the lower mold platform 12 is used to place the thermoplastic composite flat plate 60. In this embodiment, to match the number of limiting frames 30, the lower mold 10 is provided with two frame grooves 11: a first frame groove 111 is used to mount the first frame 31, and a second frame groove 112 is used to mount the second frame 32. The first frame groove 111 is provided with a first elastic return mechanism 401 and a first lower vent hole 511, respectively used for elastic connection and stamping exhaust of the first frame 31; the second frame groove 112 is provided with a second elastic return mechanism 402 and a second lower vent hole 512, respectively used for elastic connection and stamping exhaust of the second frame 32. The lower mold 10 is provided with a lower mold mounting hole 14 for mounting and securing the lower mold 10. The depth of the frame groove 11 is 15mm. To facilitate the removal of the limit frame 30, the sidewalls of the frame groove 11 can be set at an angle of 0.5° to form a clearance fit with the limit frame 30 (single-side clearance of 0.02-0.05mm). The first groove guide rod holes 131 and the first lower exhaust holes 511 can be arranged alternately in the first frame groove 111, and the second groove guide rod holes 132 and the second lower exhaust holes 512 can be arranged alternately in the second frame groove 112. To ensure the surface quality of the thermoplastic composite plate 60, the surface flatness of the lower mold platform 12 is controlled to 0.01mm / m 2 In some embodiments, the surface of the lower mold platform 12 can be treated with a hard chrome layer (20 microns) and then impregnated with polytetrafluoroethylene to reduce the friction coefficient to below 0.1. Alternatively, the surface treatment of the lower mold platform 12 can be replaced with a laser-textured micro-pit array (50 μm diameter, 10 μm depth) and then impregnated with graphene to reduce the friction coefficient to below 0.05.

[0020] Upper mold 20: The upper mold 20 is used to generate top pressure and includes a base 22 with an upper mold boss 21 protruding from the base 22. The upper mold boss 21 is configured to contact the thermoplastic composite plate 60. Multiple upper vent holes 52 are provided on the upper mold boss 21 to allow for exhaust after the upper mold boss 21 contacts the top surface of the limit frame 30 and before contacting the thermoplastic composite plate 60. To facilitate connection to the pressurizing device, upper mold mounting holes 23 may be provided on the base 22. To improve wear resistance, the upper mold boss 21 may be surface treated, such as by laser cladding with a tungsten carbide coating (50 microns thick) with a temperature resistance of >500°C. In addition to tungsten carbide coating, multi-arc ion plating of TiAlN (hardness ≥3200 HV, temperature resistance of 700°C) is also possible.

[0021] Based on the inventive concept of the present invention, the embodiments of the present invention may also be expanded in the following ways: 1. Multi-frame synchronous stamping system: On the lower die 10, a plurality of frame grooves 11 are arranged side by side or in an array, and limit frames 30 of different sizes can be installed simultaneously; The upper die 20 is correspondingly designed with a split convex module to realize synchronous forming of multiple parts.

[0022] 2. On-line thickness monitoring and compensation: A pressure sensor can be integrated into the elastic reset mechanism 40 to be used for real-time feedback of the compression amount of the spring 41; Furthermore, it can be further connected to a PLC control system to be used for dynamically adjusting the downward pressing stroke of the upper die 20 and improving the tolerance compensation accuracy.

[0023] Based on the above structural design of the adjustable thermoplastic composite flat stamping die, the working principle of the embodiment of the present invention is as follows: 1. Matrix flow inhibition mechanism: During the downward movement stage of the limit frame 30, a closed constraint area is formed, enabling the matrix to flow only in the thickness direction; according to the experimental data of the applicant, the fiber deflection angle can be reduced from 5.2° in the traditional process to 0.4°.

[0024] 2. Thickness self-adaptation principle: Through the pre-tightening force F = k·Δx of the spring 41, it is ensured that flat plates of different thicknesses (2 - 10 mm) all obtain the same binding force (500 ± 50 N).

[0025] 3. Thermal deformation compensation mechanism: Select a material with a thermal expansion coefficient matching that of the flat plate matrix to manufacture the limit frame 30 to avoid an increase in the high-temperature gap.

[0026] Taking carbon fiber / PEEK prepreg as an example, during the specific stamping process based on the above die structure (temperature 380 °C, pressure 30 MPa): First stage, frame pre-pressing: The upper die 20 presses down to contact the top surface of the limit frame 30 → the spring 41 compresses → the limit frame 30 moves down 3 - 5 mm, and the inner side surface of the limit frame 30 presses closely against the edge of the flat plate 60 to form a flow barrier; Second stage, flat plate stamping: The convex of the upper die 21 presses into the flat plate 60 → hold the pressure for 30 - 120 s, and the matrix flows uniformly under the constrained state; Third stage, demolding and resetting: The upper die 20 is lifted → the spring 41 pushes the limit frame 30 to reset, preparing for the next cycle.

[0027] The typical application scenarios of the embodiment of the present invention include but are not limited to: 1. Aviation angle piece: 300×300×4 mm PEEK / carbon fiber plate, fiber orientation deviation ≤ 0.5°; 2. New energy vehicle battery panel: 500×800×6 mm PP / glass fiber plate, forming cycle shortened by 40%; 3. Medical implant preforming: Titanium fiber / PEEK composite material, size 100×100×2 mm, surface roughness Ra≤0.2 μm; 4. Ultra-thin fuel cell bipolar plate: 0.8-mm-thick carbon fiber / PPS flat plate, fiber deflection ≤0.2°.

[0028] Through the optimization of the mold structure, the beneficial effects of the embodiments of the present invention are reflected in: 1. Precision improvement: Fiber deflection angle ≤0.5°, control error of laminate anisotropy <3%; Flat plate thickness tolerance ±0.05 mm (traditional process ±0.15 mm).

[0029] 2. Efficiency breakthrough: Size switching time 3 minutes (traditional 45 minutes); Stamping cycle shortened to 42 s (traditional 68 s).

[0030] 3. Cost optimization: Reduce the number of mold sets: A single set of molds can replace multiple sets of traditional special molds; Energy consumption reduction: Due to rapid exhaust, the holding pressure time is reduced by 35% compared with the traditional process.

[0031] In the description of the embodiments of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "center", "top", "bottom", "top part", "bottom part", "inner", "outer", "inner side", "outer side", etc. are the orientation or positional relationships based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. Among them, the "inner side" refers to the internal or enclosed area or space. The "periphery" refers to the area around a specific component or a specific area.

[0032] In the description of the embodiments of the present invention, the terms "first", "second", "third", "fourth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first", "second", "third", "fourth" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0033] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installation", "connection", "linkage", and "assembly" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0034] In the description of the embodiments of the present invention, specific features, structures, materials, or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0035] In the description of the embodiments of the present invention, it should be understood that "-" and "~" represent the range between two numerical values, and this range includes the endpoints. For example, "A - B" represents a range greater than or equal to A and less than or equal to B. "A ~ B" represents a range greater than or equal to A and less than or equal to B.

[0036] In the description of the embodiments of the present invention, the term "and / or" herein is merely a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0037] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hot - plastic composite material flat stamping die, comprising an upper die (20) and a lower die (10). A forming space for a hot - plastic composite material flat plate (60) is formed between the upper die (20) and the lower die (10), characterized in that: The die is configured with at least two replaceable limiting frames (30) for adapting to flat plates (60) of different planar sizes; The lower die (10) is provided with a frame groove (11) matching the limiting frame; The limiting frame (30) is movably connected to the frame groove (11) through an elastic reset mechanism (40), so that the limiting frame (30) can float up and down to adapt to the thickness change of the flat plate (60); During stamping, the upper die (20) first contacts the limiting frame (30) to make it move downward, and then contacts the flat plate (60). The inner side surface of the limiting frame (30) restricts the in - plane flow of the matrix of the flat plate (60).

2. The stamping die according to claim 1, characterized in that: The elastic reset mechanism (40) includes a plurality of springs (41) evenly distributed on the bottom surface of the limiting frame (30); Each spring (41) is equipped with a spring guide rod (42). The spring guide rod (42) passes through the spring (41), and one end of it is fixedly connected to the frame groove (11), and the other end is slidably connected to the limiting frame (30). The spring (41) is elastically constrained between the limiting frame 30 and the frame groove 11 during the downward pressing of the limiting frame 30.

3. The stamping die according to claim 2, characterized in that: The frame groove (11) is provided with a groove guide rod hole, and the spring guide rod (42) and the groove guide rod hole are in interference fit.

4. The stamping die according to claim 2, characterized in that: The pre - tightening force of the spring (April 1) is adjustable to adapt to the thickness change of the flat plate (60).

5. The stamping die according to claim 1, characterized in that: The lower die (10) is provided with a plurality of lower exhaust holes arranged in the frame groove (11) for exhausting the gas in the frame groove (11) when the limiting frame (30) moves downward; The lower die (10) further includes a lower die platform (12) with a surface roughness Ra≤0.8μm for placing the flat plate (60).

6. The stamping die according to claim 1, characterized in that: The upper die (20) includes an upper die boss (21) for directly contacting the flat plate (60); The upper die boss (21) is provided with a plurality of upper exhaust holes (52) for exhausting gas after contacting the limiting frame (30) and before contacting the flat plate (60).

7. The stamping die according to claim 1, characterized in that: The limiting frame body (30) is made of a material with a coefficient of thermal expansion ≤ 5×10 -6 / °C to ensure a constant gap with the flat plate (70) during high-temperature stamping.

8. A stamping method using the stamping die according to any one of claims 1-7, characterized in that, It includes the following steps: S1 Select a limiting frame (30) adapted to the planar size of the flat plate (60) and install it on the lower die (10); S2 Place the flat plate (60) in the limiting frame; In S3, the upper die (20) presses downwards, first contacting the limiting frame body (30) to cause it to move downwards and compress the elastic reset mechanism (40); In S4, the upper die (20) continues to press down until it contacts the flat plate (60), and the inner side surface of the limiting frame body (30) restricts the planar flow of the matrix to complete stamping.

9. The method according to claim 8, wherein: The stamping temperature is 300 - 400 °C, the pressure is 10 - 50 MPa, and the pressure holding time is 30 - 120 seconds.

10. Application of the stamping die according to any one of claims 1 - 7 in the stamping of thermoplastic composite material flat plates.

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