A continuous hot press forming process for composite parts

Abstract

This invention discloses a continuous hot-press molding process for composite material parts, belonging to the field of composite material molding technology. Our previous patent CN202423276696.9 disclosed a continuous compression molding machine, but the lack of supporting processes led to unstable quality in mass production. This invention, based on that equipment, provides the following: the mold is placed on a continuous conveyor device, sequentially passing through a preheating filling zone, a high-temperature curing zone, and a cooling and shaping zone; main pressure is applied when the temperature rises to a semi-cured state of 80-160°C at a rate of 1-5°C / min, causing the resin to cross-link and cure; finally, cooling and demolding are performed. This invention matches the heating rate and pressure application timing with the semi-cured state of the resin, avoiding defects such as insufficient resin and cracking, resulting in good curing quality consistency and increasing production efficiency by more than 30%.

Description

Technical Field

[0001] This invention relates to the field of composite material molding and processing technology, specifically to a continuous hot pressing molding process for composite material parts, which is particularly suitable for batch continuous hot pressing molding of carbon fiber reinforced resin matrix composite material parts. Background Technology

[0002] Composite material compression molding involves placing a certain amount of pretreated molding material into a preheated mold, applying high pressure to fill the mold cavity, and then curing the material under specific pressure and temperature. The product is then removed from the mold and further processed as needed. Traditional compression molding typically employs single-piece, intermittent operations, resulting in low production efficiency, high costs, and difficulty in achieving mass production and large-scale industrial production.

[0003] Our previous patent CN202423276696.9 (A Continuous Compression Molding Machine for Composite Materials) disclosed a production line operation method that uses an upper / lower traction system to drive the mold movement and apply heat and pressure in an integrated molding process. By setting up continuously and independently adjustable hot pressing zones I, II, and III, the temperature and pressure are adjusted and controlled for the softening, fusion, and curing of composite materials. This equipment solves the problem of low efficiency in traditional single-piece molding and realizes batch and automated production.

[0004] However, this equipment patent mainly discloses the mechanical structure and the basic temperature range and time of each hot pressing zone, without providing a corresponding refined process control method, especially: (1) The specific functional positioning of the preheating and filling area, the high-temperature curing area, and the cooling and shaping area, as well as the synergistic relationship between their parameters, are not disclosed; (2) The method for controlling the heating rate and its impact on the pressurization window are not disclosed; (3) The precise criteria for determining the timing of pressurization were not disclosed (i.e., how to determine that the resin is in a semi-cured state, and the consequences of pressurizing too early or too late). (4) The quantitative calculation method for pressure magnitude is not disclosed.

[0005] Therefore, in actual mass production, due to the lack of supporting processes, quality defects such as insufficient glue, pinholes, surface cracks, and internal pores still occur, resulting in poor consistency in curing quality and restricting the industrial application effect of the equipment.

[0006] To address the aforementioned issues, this invention provides a refined continuous hot pressing molding process that matches the equipment described in CN202423276696.9. By precisely controlling the heating rate, pressurization timing, and resin semi-cured state, high-quality and high-efficiency batch continuous production can be achieved. Summary of the Invention

[0007] This invention aims to provide a continuous hot pressing molding process for composite material parts. On the hardware platform of a continuous molding machine, through three-zone progressive temperature-pressure coordinated control, precise control of pressurization timing based on the semi-cured state, and matching of heating rate with resin rheological properties, it solves the problems of unstable curing quality and many defects in existing processes, thereby improving production efficiency and product consistency.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A continuous hot pressing process for composite material parts includes the following steps: (a) Prepreg cutting and laying: Cut the prepreg according to the template, remove the protective film, and lay it in the specified order and direction. Vacuum the air after each layer to ensure that there are no air bubbles between the layers. (ii) Mold loading and conveying: The mold with the prepreg laid on it is placed on a continuously operating conveyor. The conveyor is preferably a metal conveyor belt, through which heat and pressure are synchronously transferred to the mold; (III) Three-zone progressive hot pressing curing: (1) Preheating and filling zone: The mold enters the preheating and filling zone, and the heating temperature is 50-100℃. The pressure is calculated based on the contact area between the upper and lower surfaces of the mold to ensure mold closure. The heat preservation and pressure holding time is 20-60 minutes. In this zone, the synthetic resin softens when heated and becomes a viscous flow state. Under the action of pressure, it adheres to the fiber and flows to fill the mold, so that the material fills the cavity. (2) High-temperature curing zone: After the mold enters the high-temperature curing zone, the temperature is raised to 80-160℃ at a heating rate of 1-5℃ / min. When the synthetic resin is in a semi-cured state (i.e., the gel point where the resin changes from a viscous flow state to a solid state), the main pressure is applied, maintaining the temperature at 80-160℃, the pressure (calculated based on the mold contact area), and the heat and pressure holding time at 30-120min, so that the resin undergoes a chemical cross-linking reaction, forming a network structure, and finally becoming a non-flowing and non-melting three-dimensional structure. Applying pressure too early will cause the resin to remain in a flowing state, resulting in excessive resin extrusion and a dry composite material; applying pressure too late will cause the resin to harden and become uncompactable, resulting in surface defects. (3) Cooling and shaping zone: The mold enters the cooling and shaping zone and is cooled to 50-120°C at a cooling rate of 1-5°C / min. Then it is demolded to obtain composite material parts.

[0009] In the above process, controlling the heating rate to 1–5 °C / min is crucial: too fast a rate will shorten the pressurization interval and make it more difficult to select the pressurization point; too slow a rate will prolong the pressurization interval and increase costs. This heating rate ensures that the pressurization window in the semi-cured state matches the operating cycle of the conveyor device, guaranteeing accurate pressurization timing for each product during continuous production.

[0010] Compared with the prior art, the present invention has the following beneficial effects: (1) Stable curing quality: By precisely matching the heating rate, pressurization timing and the semi-cured state of the resin, defects such as insufficient glue, pinholes, surface cracks and internal pores are effectively avoided, and the product qualification rate is significantly improved. (2) High production efficiency: The continuous assembly line operation is adopted, and multiple molds pass through three functional areas in sequence, which improves the production efficiency by more than 30% compared with the traditional single-piece intermittent molding process. (3) Strong parameter controllability: This invention clearly provides quantitative parameters such as heating rate, pressurization temperature window, and pressure calculation method, which facilitates operators to quickly adjust the machine and ensure the consistency of batch production; (4) Synergistic protection with equipment: Based on the equipment patent, this process patent further limits the operating conditions, forming a combined technical barrier of "equipment + process". Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the continuous molding machine upon which the present invention is based (see CN202423276696.9). Figure 1 ).

[0012] Figure 2 This is a schematic diagram of the temperature-time curves of the preheating and filling zone, the high-temperature curing zone, and the cooling and shaping zone in the process of this invention.

[0013] Figure 3 This is a flowchart of the continuous hot pressing process for composite material parts of the present invention (including judgment of pressurization timing and quality feedback).

[0014] The markings in the diagram are: 1-Conveying device; 2-Mold; 3-Preheating and filling zone; 4-High temperature curing zone; 5-Cooling and shaping zone; T1-Preheating temperature; T2-Curing temperature; T3-Cooling temperature; t1-Preheating time; t2-Heating time; t3-Curing and holding time; t4-Cooling time. Detailed Implementation

[0015] The technical solution of this application will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0016] In the description of this application, it should be noted that the terms "center", "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to simplify the description of this application and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0017] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0018] In the following examples, unless otherwise specified, all reagents used are commercially available, and all process equipment used is conventional equipment in the art.

[0019] In the following embodiments, the meanings of the reference numerals are consistent with those in the description of the drawings.

[0020] In the following description, firstly, in conjunction with Figure 3 The flowchart illustrates the overall process steps of the present invention, and then combines them with... Figure 1 and Figure 2 The functions and parameters of each zone are described in detail, and finally, the implementation effect of the invention is further demonstrated through examples.

[0021] Figure 3 This is a flowchart of the continuous hot pressing process for composite material parts according to the present invention, showing the overall process steps and including key decision points. The specific steps are as follows: (1) Prepreg cutting and laying: Cut the prepreg according to the template, remove the protective film, and lay it in the specified order and direction. Vacuum the air after each layer is laid. (2) Mold loading: The prepreg is loaded into the mold and the mold is closed; (3) Conveying and positioning: placing the mold on a continuously running conveyor; (4) Enter the preheating and filling zone: heat to 50-100℃, keep warm for 20-60 minutes, and apply pressure to make the resin melt and flow to fill the mold; (5) Enter the high-temperature curing zone: Increase the temperature at 1-5℃ / min. Monitor the temperature inside the mold in real time to determine whether it has reached 80-160℃ (semi-cured state). If it has not reached this temperature, continue to increase the temperature; if it has, apply the main pressure and keep it at this temperature for 30-120 minutes to allow the resin to crosslink and cure. (6) Enter the cooling and shaping zone: cool down to 50-120℃ at 1-5℃ / min, and demold; (7) Quality inspection: Inspect the appearance and internal quality of the parts. If they are qualified, the finished products are put into storage; if they are not qualified, analyze the reasons (such as deviation of heating rate, improper timing of pressurization, etc.), adjust the process parameters and return to re-production.

[0022] This process fully demonstrates the invention's precise control over the timing of pressurization and its closed-loop quality feedback.

[0023] Figure 1 The diagram shows the structure of the continuous molding machine (CN202423 276696.9) upon which this invention is based. The equipment includes an upper conveyor belt, a lower conveyor belt, a pressure applying mechanism, a support mechanism, and hot pressing zones I, II, and III arranged sequentially along the conveying direction. This invention redefines these zones as a preheating and filling zone, a high-temperature curing zone, and a cooling and shaping zone.

[0024] Figure 2 This is a schematic diagram of the temperature-time curve of the process of this invention. The horizontal axis represents time, and the vertical axis represents the temperature inside the mold. The figure clearly shows the temperature changes in three zones: the preheating and filling zone (temperature rises from room temperature to T1=50~100℃ and is held for t1=20~60min); the heating transition zone (temperature rises at a rate of 1~5℃ / min to T2=80~160℃, time t2); the high-temperature curing zone (temperature is held for T2, and held for t3=30~120min); and the cooling and setting zone (temperature drops at a rate of 1~5℃ / min to T3=50~120℃, time t4). Figure 2 The document also indicates the pressurization point, which is when the temperature enters the 80-160℃ window and the main pressure is applied.

[0025] Example 1 Manufacturing carbon fiber reinforced epoxy resin composite material sheets (300mm×300mm×2mm): (1) Prepreg: T700 / epoxy unidirectional prepreg, 12 layers, layup angle [0 / 90] 3s; (2) Conveying device: metal conveyor belt, linear speed 0.2m / min; (3) Preheating of the mold filling area: temperature 80℃, pressure calculated based on the mold area (0.5MPa), time 35min; (4) High temperature curing zone: The temperature is increased to 115℃ at 2.5℃ / min, and a main pressure of 1.2MPa is applied at 115℃ and the temperature is maintained for 55min; (5) Cooling and shaping zone: Cool to 80℃ at 2.5℃ / min, then demold; (6) Quality inspection: The appearance is smooth and there are no defects in the internal ultrasonic testing.

[0026] Results: The parts have smooth, defect-free surfaces, internal porosity <1%, bending strength of 1250 MPa, and production efficiency is 40% higher than that of traditional autoclaves.

[0027] Example 2 Adjust the parameters to verify: (1) Preheating the mold filling area: temperature 70℃, time 30min; (2) High temperature curing zone: heating rate 2℃ / min, heating to 110℃, pressurizing 1.0MPa, and holding for 50min; (3) Cooling and shaping zone: cooling rate 2℃ / min, cooling down to 90℃.

[0028] Results: The quality of the parts was qualified, and the performance was comparable to that of Example 1, which verified the adaptability of the process parameters.

[0029] Compare with Example 1 All conditions of Example 1 were used, but the heating rate was changed to 6.6℃ / min. Results: The pressure point was difficult to control, and the main pressure was only applied to some molds after the resin had completely cured. Obvious glue shortages and dry spots appeared on the surface of the parts, and the flexural strength decreased by 18%.

[0030] Compare with Example 2 All conditions of Example 1 were used, but main pressure was applied when the temperature reached 75°C (before it entered the semi-cured state). Result: Excess resin was extruded, the parts became dry, the fibers were exposed, and the parts were scrapped.

[0031] Compare with Example 3 Using the same prepreg and curing parameters, but in a conventional flatbed hot press for intermittent single-piece production. Result: Single-piece cycle time is 45 minutes, and producing 10 pieces requires 450 minutes; in Example 1 of this invention, continuous production of 10 pieces requires only about 200 minutes (including transport time), an efficiency improvement of 56%.

[0032] Compare with Example 4 The process described in Example 1 was used, but post-demolding quality inspection and parameter adjustments were not performed. After continuous production of 100 parts, pinholes appeared on the surface of some parts. Analysis revealed that uneven temperature distribution was caused by slight wear on the conveyor belt, which was not adjusted in time. This invention can avoid batch defects through inspection and adjustment.

[0033] Definitions Semi-cured state: refers to the gel point stage in which thermosetting resins change from a viscous flow state to a solid state during the curing process. At this time, the resin has some fluidity but has begun to crosslink. The corresponding temperature range is usually 80 to 120°C (slightly different depending on the resin system).

[0034] Preheating and filling zone: Corresponds to the hot pressing zone I of the continuous compression molding machine. Its function is to melt the resin and allow it to flow and fill the mold cavity.

[0035] High-temperature curing zone: Corresponds to hot pressing zone II, its function is to cross-link and cure the resin.

[0036] Cooling and shaping zone: Corresponds to hot pressing zone III. Its function is to cool down the product to shape it for demolding.

[0037] Pressurization window: refers to the time period during which the resin is in a semi-cured state. This invention controls the heating rate to 1-5℃ / min and matches this window with the conveyor belt running rhythm to ensure that each product is pressurized at the optimal time.

[0038] Industrial applicability The continuous hot-pressing molding process for composite material parts provided by this invention can be widely applied to the mass production of carbon fiber, glass fiber, and other reinforced resin-based composite material parts. It is particularly suitable for medium-volume, high-quality molded products in the fields of automotive parts, drone structural components, and sporting goods. This process inherits the assembly line advantages of our company's previous equipment patents and adds refined process control methods, making it highly valuable for industrial applications.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A continuous hot pressing process for composite material parts, characterized in that, Includes the following steps: (1) Place the mold with the prepreg laid on it on a continuously running conveyor; (2) The mold passes through the preheating filling zone, the high-temperature curing zone, and the cooling and shaping zone in sequence; (3) In the preheating and filling zone, the mold is heated and pressurized to melt and flow the resin to fill the mold; (4) After the mold enters the high temperature curing zone, the temperature is raised to 80-160°C at a heating rate of 1-5°C / min, and the main pressure is applied when the synthetic resin is in a semi-cured state. The temperature and pressure are maintained to allow the resin to cross-link and cure. (5) The mold enters the cooling and shaping zone for cooling, and then the composite material part is demolded.

2. The continuous hot pressing process for composite material parts according to claim 1, characterized in that, In step (3), the heating temperature of the preheating filling area is 50-100℃, the pressure is calculated based on the contact area of ​​the upper and lower surfaces of the mold to ensure the mold is closed, and the heat preservation and pressure holding time is 20-60 minutes.

3. The continuous hot pressing process for composite material parts according to claim 2, characterized in that, The conveying device is a metal conveyor belt, through which heat and pressure are synchronously transferred to the mold.

4. The continuous hot pressing process for composite material parts according to claim 1, characterized in that, In step (4), the heat preservation and pressure holding time of the high temperature curing zone is 30 to 120 minutes, and the applied main pressure is calculated based on the contact area between the upper and lower surfaces of the mold.

5. The continuous hot pressing process for composite material parts according to claim 4, characterized in that, In step (4), the temperature at which the synthetic resin is in a semi-cured state is determined to be 80-160°C. The main pressure is applied within this temperature window. Applying pressure too early will result in excessive resin extrusion, while applying pressure too late will result in the resin being cured and unable to be pressurized.

6. The continuous hot pressing process for composite material parts according to claim 5, characterized in that, The heating rate of 1 to 5 °C / min ensures that the pressurization window in the semi-cured state matches the operating cycle of the conveying device. Too fast a heating rate will shorten the pressurization range and make it more difficult to select the pressurization point, while too slow a heating rate will extend the pressurization range and increase costs.

7. The continuous hot pressing process for composite material parts according to claim 1, characterized in that, In step (5), the cooling rate of the cooling and shaping zone is 1 to 5 °C / min, and the zone is demolded after cooling to 50 to 120 °C.

8. The continuous hot pressing process for composite material parts according to claim 7, characterized in that, The preheating and molding zone, the high-temperature curing zone, and the cooling and shaping zone are arranged sequentially and continuously along the length of the conveying device. The temperature of each zone is independently controlled. The length of the high-temperature curing zone is 1.2 to 2 times that of the preheating and molding zone, and the length of the cooling and shaping zone is 0.12 to 0.17 times that of the preheating and molding zone.

9. The continuous hot pressing process for composite material parts according to claim 1, characterized in that, Before step (1), there are also prepreg cutting and laying steps: cut the prepreg according to the template, remove the protective film, lay it in the specified order and direction, and vacuum the air after each layer is laid.

10. The continuous hot pressing process for composite material parts according to claim 1, characterized in that, The composite material is a carbon fiber reinforced resin matrix composite material, the prepreg is a carbon fiber prepreg, and the resin system is a thermosetting resin.

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