Preparation method of fiber reinforced composite material molded structural member

Abstract

The invention relates to the field of preparation of fiber reinforced composite materials, in particular to a preparation method of a fiber reinforced composite material molded structural part. The preparation method of the fiber reinforced composite material mold pressing structural part comprises the following steps: placing a molding assisting material between a preformed blank and a mold, and then carrying out hot press molding, in the hot press molding process, the molding assisting material is heated to expand and deform, and the pressure generated by expansion of the molding assisting material and the deformation of the molding assisting material can improve the fitting property between the fiber reinforced composite material preformed blank and the mold, so that the molding rate is improved.

Description

Technical Field

[0001] The invention relates to the field of preparation of fiber reinforced composite materials, and more particularly to a method for preparing a fiber reinforced composite material molded structural component. Background Art

[0002] Compression moulding is a method for forming thermosetting composite materials. A certain amount of molding material is placed in a pair of metal molds (i.e., metal mold pairs), and the molding material is heated and plasticized in the mold cavity under a certain temperature and pressure, and then flows under pressure and fills the mold cavity to form a circle. The compression molding process requires heating and pressurization during the molding process, so that the molding material is plasticized and flows to fill the mold cavity, and the resin undergoes a curing reaction. In the process of the composite molding material flowing and filling the mold cavity, not only the resin flows, but also the reinforcing material flows, so that the resin and fiber fill all parts of the mold cavity at the same time.

[0003] The compression molding process can be divided into the following types according to the physical state of the reinforcing material and the type of molding material: fiber material molding, rag material molding, fabric molding, lamination molding, winding molding, sheet plastic (SMC) molding, preformed blank molding, etc.

[0004] In the process of forming composite materials by preformed blank compression molding, there is a problem of poor fit between the preformed blank and the mold, which leads to low forming rate and low forming accuracy of the formed component. Summary of the invention

[0005] Aiming at the problem of low forming rate in the process of composite material forming by preformed blank molding method, the present invention provides a method for preparing a fiber reinforced composite material molded structural part.

[0006] The present invention places an auxiliary forming material between a preformed blank and a mold, and then performs hot pressing forming. During the hot pressing forming process, the auxiliary forming material expands and deforms due to heat, and the pressure generated by the expansion of the auxiliary forming material and the deformation of the auxiliary forming material can improve the fit between the fiber reinforced composite material preformed blank and the mold, thereby improving the forming rate.

[0007] The object of the present invention is to provide a method for preparing a fiber reinforced composite material molded structural part.

[0008] The preparation method adopts a preformed blank molding method, including: placing a preformed blank made of a fiber-reinforced composite material in a mold, placing a molding aid material between the preformed blank and the mold to obtain a mold as a whole; and hot-pressing the mold as a whole to obtain a molded structural part.

[0009] In the preparation method provided by the present invention, during the hot pressing molding process, the auxiliary molding material expands and deforms due to heat. The auxiliary molding material is deformed and filled between the preform blank and the mold. At the same time, the expansion of the auxiliary molding material generates pressure on the mold and the preform blank, and the pressure between the mold and the preform blank increases, thereby fitting the preform blank to the mold surface. Under the combined action of temperature and pressure, the preform blank undergoes a curing reaction to form the required size and shape. Specifically, on the one hand, the pressure generated by the expansion of the auxiliary molding material squeezes the fiber reinforced composite material preform blank to one side of the mold, so that the fiber reinforced composite material preform blank fits the mold; on the other hand, the auxiliary molding material is deformed due to heat and fits the fiber reinforced composite material preform blank and the mold; thereby improving the fit between the fiber reinforced composite material preform blank and the mold.

[0010] The fiber-reinforced composite material refers to a fiber-reinforced resin composite material, and the fiber may be carbon fiber, glass fiber, basalt fiber, etc. The fiber-reinforced composite material may be made into a preformed blank by an existing method, for example, the fiber-reinforced composite material prepreg is cut, and then the preformed blank is prepared by paving and bonding.

[0011] The forming aid material includes a foaming material or a hydraulic bag.

[0012] The foaming material is a heat-expanding material; any existing heat-expanding material may be selected, such as foamed polyvinyl chloride (foamed PVC).

[0013] The hydraulic bag comprises a bag body and a filling liquid, wherein the filling liquid is filled in the bag body.

[0014] The bag body is made of high temperature resistant engineering plastics; high temperature resistant engineering plastics have the characteristics of high temperature resistance and high strength. The high temperature resistant engineering plastics are preferably selected from one or more of polyurethane (PU), thermoplastic polyurethane rubber (TPU), high temperature resistant nylon (PPA), and polyetherketone (PEK).

[0015] The filling liquid is selected from a liquid with stable high temperature performance. The liquid with stable high temperature performance refers to a liquid with certain high temperature stability. The liquid with stable high temperature performance does not undergo violent vaporization at 200-300°C. The filling liquid is preferably selected from a water glass solution with a mass concentration of more than 50%, a sodium benzoate solution, and a sodium silicate solution with a mass concentration of 60-70%. Preferably, a sodium silicate solution with a mass concentration of 60-70% is used.

[0016] The hydraulic bag is provided with a filling hole and a liquid outlet hole. When the filling hole and the liquid outlet hole are arranged on the side of the hydraulic bag, the filling hole and the liquid outlet hole do not directly contact the preform blank, thus avoiding being squeezed and broken; and it is also convenient to control the outflow and inflow of the filling liquid. Therefore, as a preferred solution, the filling hole and the liquid outlet hole are arranged on the side of the hydraulic bag.

[0017] The outer shape of the hydraulic bag can be any shape. However, in order to further improve the forming accuracy, the outer shape of the hydraulic bag is consistent with the basic shape of the preformed blank as much as possible.

[0018] Although both foaming materials and hydraulic bags can be used as auxiliary molding materials in the above method to improve the fit between the fiber reinforced composite preform blank and the mold, thereby improving the molding rate. However, compared with using foaming materials as auxiliary molding materials, using hydraulic bags as auxiliary molding materials can further improve the molding rate and molding accuracy; moreover, using hydraulic bags as auxiliary molding materials will not affect the structural strength and life of composite molded parts, and the production efficiency is higher.

[0019] During the hot pressing process, the foaming material foams and flows in an uncontrolled direction, and it is easy to flow to the weak position of the structure, resulting in uneven distribution of the foaming material, warping, local secondary foaming, and, for example, there are large cavity positions in the thin plate samples, which cause local secondary foaming. The flow of the filling liquid in the hydraulic bag is controlled by the hydraulic bag, and will not flow randomly, and there will be no problem of uneven distribution, and no warping.

[0020] The foaming material is in direct contact with the preform. The foaming material will penetrate into the surface of the preform. During the demolding process, the foaming material needs to be separated from the molded structural parts, and it is inevitable that there will be residual foaming material. The residual foaming material will cause secondary foaming problems, that is, during the use of the molded structural parts, as the external temperature increases, all foaming materials will expand twice or multiple times, resulting in local stress concentration and reduced dimensional accuracy, affecting the structural strength and life of the molded structural parts. Residual foaming material affects the weight of the molded structural parts. In addition, it takes time to separate the foaming material from the molded structural parts and clean up the foaming material, which reduces production efficiency.

[0021] The filling liquid in the hydraulic bag does not contact the preformed blank, and there will be no residue, which solves the technical problems of local stress concentration and reduced dimensional accuracy of molded structural parts caused by foaming material residue, as well as the technical problems that affect the structural strength and life of molded structural parts. During the demolding process, the liquid outlet on the hydraulic bag is opened to release the pressure in the entire mold, and the mold is gradually demolded to take out the prepared molded structural parts; compared with separating the foaming material from the molded structural parts, it saves more time.

[0022] Therefore, as a preferred solution, the forming-assisting material is a hydraulic bag.

[0023] The mold usually includes two parts that can be separated. Take the mold including the upper mold and the lower mold as an example: the preform blank is placed between the upper mold and the lower mold, so the space between the preform blank and the mold includes the space between the upper side of the preform blank and the upper mold, and the space between the lower side of the preform blank and the lower mold. Therefore, the "placing the auxiliary forming material between the preform blank and the mold" includes placing the auxiliary forming material between the upper side of the preform blank and the upper mold, placing the auxiliary forming material between the lower side of the preform blank and the lower mold, and placing the auxiliary forming material between the upper and lower sides of the preform blank and the upper and lower molds respectively.

[0024] When the auxiliary forming material is a hydraulic bag, the hydraulic bag is a liquid bag structure; if the hydraulic bag is placed on both sides of the preform blank, the precision of the molded structural parts will be reduced; if it is placed on only one side of the preform blank, although the molding precision of the side where the hydraulic bag is placed is reduced, the molding precision of the other side is significantly improved. Therefore, the above method is more suitable for molded structural parts with higher precision requirements on one side than on the other side. As a preferred solution, the auxiliary forming material is placed on one side of the preform blank; when the auxiliary forming material is placed on one side of the preform blank; the side is preferably the side with relatively lower precision requirements.

[0025] Consider the reusability of the mold. The contact surface between the mold and the hydraulic bag should be as smooth as possible without sharp angles and protrusions.

[0026] The preform blank molding method refers to first cutting the fiber reinforced composite material prepreg, then preparing the preform blank by laying and bonding, and then hot pressing the preform blank.

[0027] The hot pressing molding may adopt conventional operations of existing hot pressing molding, which may specifically include: placing the entire mold in a vacuum bag, placing the entire vacuum bag in a heating device for heating, and after the molding conditions are met, taking out the entire mold and demoulding.

[0028] The heating device can be any existing heating device that can be used for hot pressing molding, such as a hot press tank.

[0029] In the hot pressing forming, preferably, the vacuum bag is evacuated during the heating process. The specific operation can be: a vacuum pump is arranged outside the heating device, the vacuum pump is connected to the vacuum bag, and the vacuum bag is continuously evacuated by the vacuum pump. Since the preform blank is continuously discharged during the high-temperature curing process (hot pressing forming process), the discharged gas will gather in the vacuum bag. If the gas in the vacuum bag cannot be removed in time, it will affect the porosity of the molded structure. If the porosity is large, there are many gaps inside the molded structure, the strength of the molded structure decreases, and cracks and damage are prone to occur. The vacuum bag is evacuated by a vacuum pump, and the gas in the vacuum bag is pumped out of the vacuum bag, so that no gas is retained in the vacuum bag, thereby improving the compactness of the molded structure. The exhaust effect is related to the air pressure; if a vacuum pump is not used, the vacuum inside is continuously extracted, which will cause the internal air pressure to continue to rise, and the exhaust of the workpiece to be cured will be suppressed.

[0030] A method for preparing a fiber-reinforced composite molded structural component comprises: The preformed blank of the fiber reinforced composite material is placed in the mold, and the auxiliary molding material is placed between the preformed blank and the mold. One side of the preformed blank is in contact with the auxiliary molding material, and the other side of the preformed blank is fitted with the mold to obtain the mold as a whole; the mold as a whole is placed in a vacuum bag, and the vacuum bag as a whole is placed in a heating device for heating. During the heating process, the vacuum bag is evacuated, and after the molding conditions are met, the mold as a whole is taken out of the heating device and demolded. The auxiliary molding material is placed between the preformed blank and the mold, and specifically, the auxiliary molding material can be placed on the side of the preformed blank with relatively low molding accuracy.

[0031] According to an embodiment disclosed in the present invention, a method for preparing a fiber-reinforced composite molded structural part includes: Step 1: Preparation of hydraulic bag Use high temperature resistant engineering plastics such as PU, TPU, PPA or PEK as the bag body material of the hydraulic bag, and process the high temperature resistant engineering plastics into the bag body of the hydraulic bag according to the shape characteristics of the preformed blank. The shape of the bag body of the hydraulic bag is basically the same as the shape of the preformed blank or slightly larger than the preformed blank. Set a filling hole and a liquid outlet hole on the side of the hydraulic bag, select a liquid with stable high temperature performance as the filling liquid of the hydraulic bag, fill the filling liquid into the bag body, and obtain a hydraulic bag; the filling hole and the liquid outlet hole of the hydraulic bag are both in a closed state; Step 2: Mold preparation The mold is designed according to the shape characteristics of the preformed blank, and the mold includes an upper mold and a lower mold; a release agent is applied to the upper surface of the lower mold and the lower surface of the upper mold; Step 3: Preparation of the entire mold The preform is placed on the lower mold, the hydraulic bag is placed on the preform, and the upper mold is placed on the hydraulic bag; at this time, the hydraulic bag is located on one side of the preform and between the preform and the upper mold; the upper mold and the lower mold are pressed together and placed in a vacuum bag, the vacuum bag is sealed and evacuated to obtain the mold as a whole; Step 4: Molding The vacuum bag is connected to a vacuum pump, and the entire mold is placed in an autoclave or other heating equipment for heating. The vacuum pump is located outside the heating equipment and performs vacuuming while heating. Heating can expand the liquid in the hydraulic bag, exert pressure on the preform, and realize the forming and curing of the preform. Step 5: Cooling and demoulding After the molding conditions are met, the entire mold is taken out of the heating device, the vacuum bag is opened, the liquid outlet hole on the hydraulic bag is opened, the filling liquid flows out, the pressure of the mold is released, the mold is gradually demolded, and the prepared molded workpiece is taken out.

[0032] Compared with the prior art, the present invention has the following beneficial effects: The preparation method of the present invention has high forming rate and forming precision, will not affect the structural strength and life of the prepared molded component, and has higher production efficiency.

[0033] In the present invention, unless otherwise specified, the high temperature refers to 200-300°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the overall decomposition of the mold prepared in Example 1 of the present invention; Figure 2 This is a schematic cross-sectional view of the entire mold prepared in Example 1 of the present invention; Figure 3 This is a schematic structural diagram of a fiber-reinforced composite molded structural component prepared in Example 1 of the present invention; In the figure, A is a hydraulic bag, B is a preformed blank, C is a lower mold, D is an upper mold, and E is a vacuum bag. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0036] Example 1 Step 1: Prepare the upper and lower molds Prepare the upper mold D and the lower mold C strictly according to the size of the preformed blank B; Step 2: Preparation of Hydraulic Bag A Use high temperature resistant engineering plastics such as PU, TPU, PPA or PEK as the bag body material of hydraulic bag A; process the high temperature resistant engineering plastics into the bag body of hydraulic bag A according to the shape characteristics of preformed blank B, and the shape of the bag body of hydraulic bag A is basically the same as that of preformed blank B or slightly larger than that of preformed blank B. Set a filling hole and a liquid outlet hole on the side of hydraulic bag A, select a liquid with stable high temperature performance as the filling liquid of hydraulic bag A, fill the filling liquid into the bag body, and obtain hydraulic bag A; the filling hole and the liquid outlet hole of hydraulic bag A are both in a closed state; Step 3: Preparation of the entire mold like Figure 1 As shown in FIG. 1 , the upper surface of the preform blank B has a lower requirement for forming accuracy than the lower surface thereof. The preform blank B is placed on the lower mold C, the hydraulic bag A is placed on the preform blank B, and the upper mold D is placed on the hydraulic bag A. At this time, the hydraulic bag A is located on one side of the preform blank B, between the preform blank B and the upper mold D (as shown in FIG. 1 ). Figure 1 The upper mold D and the lower mold C are pressed together and placed in a vacuum bag E. The vacuum bag E is sealed and evacuated to obtain a mold as a whole (as shown in FIG. Figure 2 shown); Step 4: Molding The vacuum bag E is connected to a vacuum pump, and the entire mold is placed in the autoclave for heating. The vacuum pump is located outside the heating device, and vacuuming is performed while heating. Heating can expand the liquid in the hydraulic bag A, exert pressure on the preform B, and realize the forming and curing of the preform B. Step 5: Cooling and demoulding After the molding conditions are met, the mold is taken out of the autoclave as a whole, the vacuum bag E is opened, the outlet hole on the hydraulic bag A is opened, the filling liquid flows out, the pressure of the mold is released, and the mold is gradually demolded to take out the prepared molded structure (such as Figure 3 as shown).

[0037] Example 2 Step 1: Prepare the upper mold D and the lower mold C strictly according to the size of the preformed blank B; Step 2: The upper surface of the preform blank B has a lower molding accuracy requirement than the lower surface thereof. The preform blank B is placed on the lower mold C, an epoxy resin adhesive is coated on the upper surface of the preform blank B, and then PVC foam particles are laid on the upper surface of the preform blank B; the upper mold D is placed on the PVC foam particles, and the upper mold D and the lower mold C are pressed together and placed in a vacuum bag E. The vacuum bag E is sealed and evacuated to obtain the mold as a whole; Step 3: The vacuum bag E is connected to a vacuum pump, and the entire mold is placed in an autoclave for heating. The vacuum pump is located outside the heating device, and vacuuming is performed while heating. Heating can expand the liquid in the hydraulic bag A, exert pressure on the preform B, and realize the forming and curing of the preform B. Step 4: After the molding conditions are met, the entire mold is taken out of the autoclave, the vacuum bag E is opened, the mold is demolded, and the prepared workpiece is taken out. At this time, PVC foam is adhered to one side of the workpiece; the PVC foam on the workpiece is first cut off, and then the PVC foam remaining on the surface of the workpiece is wiped with degreased gauze dipped in anhydrous ethanol, and then cleaned with an air gun to obtain a molded structural part.

[0038] Comparative Example 1 Step 1: Prepare the upper mold D and the lower mold C strictly according to the size of the preformed blank B.

[0039] Step 2: Place the preformed blank B between the upper mold D and the lower mold C, press the upper mold D and the lower mold C together and place them in a vacuum bag E, seal the vacuum bag E, and evacuate it to obtain the mold as a whole; Step 3: Connect the vacuum bag E to the vacuum pump, and place the entire mold in the autoclave for heating. The vacuum pump is located outside the heating equipment, and vacuuming is carried out while heating. Step 4: After the molding conditions are met, the mold is taken out of the autoclave as a whole, the vacuum bag E is opened, and the mold is demolded to obtain a molded structure.

[0040] Quality inspection of molded structural parts Using the same prepreg, a round rod-shaped hollow preform blank B was prepared, the inner diameter of the round rod was 5 cm, and the length was 1 m; the molded structural parts were prepared by the methods of Examples 1, 2 or the comparative example respectively; 50 pieces were produced continuously by each method for calculating their molding conditions.

[0041] (I) Forming rate test: Measure the center alignment error at both ends of the hollow center of the molded structural parts. If the center alignment exceeds 3mm, it is considered as an unqualified product. Qualified rate = number of qualified products / number of products*%; the statistical qualified rate is shown in Table 1. The qualified rate is used to represent the molding rate. The higher the qualified rate, the higher the molding rate.

[0042] (II) Molding accuracy test: The arc error is used to characterize the forming accuracy. The smaller the arc error, the higher the forming accuracy.

[0043] Curvature error = [measured curvature radius - designed curvature radius] / designed curvature radius * %; the curvature error of the hollow center of the molded structural part is statistically calculated, as shown in Table 1.

[0044] Arc radius: take the average of the four maximum values ​​at the end.

[0045] (III) Post-processing time: The post-processing time is counted from the moment the mold is taken out of the autoclave, and the end point is when the molded structure and the upper mold D and the lower mold C are restored to a state where they can be hot-pressed for the next time. The post-processing time used in the methods of Examples 1 and 2 or Comparative Examples is shown in Table 1.

[0046] (iv) Mechanical strength test; Using the same prepreg, a round rod-shaped hollow preform blank B was prepared, the inner diameter of the round rod was 5 cm, and the length was 1 m; the molded structural parts were prepared by the methods of Example 1, 2 or the comparative example, and 3-5 molded structural parts were prepared by each method. The molded structural parts prepared by the three methods were placed in a tensile testing machine for quasi-static tensile testing. The static tensile test refers to the ASTMD3039 composite material tensile test standard; the test results are shown in Table 1.

[0047] Table 1 Example 1 Example 2 Comparative Example 1 Pass rate 94% 82% 36% Arc error 1.2% 7.4% 14.5% Post-processing time 24 seconds 145 seconds 12 seconds Tensile Strength 240MPa 216MPa 180MPa Compared with Comparative Example 1 (existing method), the qualified rate of Examples 1 and 2 increased by 161-128%, the curvature error decreased by 92-49%, and the tensile strength increased by 33-20%. That is, compared with Comparative Example 1 (existing method), the forming rate (characterized by the qualified rate), the forming accuracy (characterized by the curvature error) and the tensile strength of Examples 1 and 2 were significantly improved. This shows that the method of the present invention can significantly improve the forming rate, forming accuracy and tensile strength of molded structural parts. Example 1 uses hydraulic bag as the auxiliary forming material, and Example 2 uses foaming material as the auxiliary forming material. Compared with Example 2, the forming rate of Example 1 is further improved by 15%, the curvature error is further reduced by 84%, and the tensile strength is further improved by 11%; more obviously, the post-processing time of Example 1 is significantly shortened by 83%, thereby significantly improving the production efficiency. It can be seen that compared with the foaming material as the auxiliary forming material, the method of using hydraulic bag as the auxiliary forming material can further improve the forming rate, forming accuracy and tensile strength, and can also improve the production efficiency.

Claims

1. A method for preparing a fiber-reinforced composite molded structural part, characterized in that: The preparation method adopts a preformed blank molding method, including: placing a preformed blank made of a fiber-reinforced composite material in a mold, placing a molding aid material between the preformed blank and the mold to obtain a mold as a whole; and hot-pressing the mold as a whole to obtain a molded structural part.

2. The preparation method according to claim 1, characterized in that The forming aid material includes a foaming material or a hydraulic bag.

3. The preparation method according to claim 2, characterized in that: The hydraulic bag comprises a bag body and a filling liquid, wherein the filling liquid is filled in the bag body.

4. The preparation method according to claim 3, characterized in that: The bag body is made of one or more of polyurethane, thermoplastic polyurethane rubber, high temperature resistant nylon and polyether ketone.

5. The preparation method according to claim 3, characterized in that: The filling liquid is selected from a water glass solution with a mass concentration of more than 50%, a sodium benzoate solution, and a sodium silicate solution with a mass concentration of 60-70%.

6. The preparation method according to claim 2, characterized in that: The hydraulic bag is provided with a liquid filling hole and a liquid outlet hole; the liquid filling hole and the liquid outlet hole are arranged on the side of the hydraulic bag.

7. The preparation method according to claim 1, characterized in that: The hot pressing molding comprises: placing the entire mold in a vacuum bag, placing the vacuum bag in a heating device for heating, and after the molding conditions are met, taking out the entire mold and demoulding.

8. The preparation method according to claim 7, characterized in that: The heating device is a hot press.

9. The preparation method according to claim 7, characterized in that: During the heating process, the vacuum bag is evacuated.

10. The preparation method according to claim 1, characterized in that: A molding aid material is placed on one side of the preform blank; the side having relatively lower precision requirements.

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