KR20240063441A - Fiber-reinforced composite material forming method and forming apparatus using VARTM process - Google Patents

Abstract

A fiber-reinforced composite material molding method and molding device using the VARTM process, which can reduce pores and increase fiber volume fraction, are disclosed.
The fiber-reinforced composite material forming method using the disclosed VARTM process is a method of forming a fiber-reinforced composite material by forming a vacuum pressure inside the vacuum bag film and transporting the liquid resin by the vacuum pressure. A first step of forming pneumatic pressure; A second step of injecting liquid resin into the vacuum bag film; It includes a third step of increasing the liquid resin injection pressure during the liquid resin injection.

Description

Fiber-reinforced composite material forming method and forming apparatus using VARTM process}

The present invention relates to a fiber-reinforced composite material molding method and molding device using the VARTM process, which can reduce pores and increase fiber volume fraction.

VARTM (Vacuum assisted resin transfer molding) is one of the representative polymer composite molding technologies that molds products by injecting resin in a vacuum.

The VARTM process belongs to the liquid composite molding (LCM) and out of autoclave (OoA) categories and is a technology that can produce large-area FRP (Fiber Reinforced Plastics) parts at a low cost of process construction. However, due to the low fiber volume fraction, it was difficult to apply it to high-reliability parts. However, recently, as process technology that compensates for these shortcomings has been developed, its application is expanding to the aviation industry.

In the VARTM process, it was difficult to achieve the fiber volume fraction at the autoclave level because the resin flow and the maximum compression pressure applied to the preform are molded by atmospheric pressure. Additionally, there was a significant loss in mechanical properties due to the high void content. Therefore, there is a need to develop technology that can reduce pores and increase fiber volume fraction.

Korean Patent Publication No. 10-2016-0071611

The purpose of the present invention is to provide a fiber-reinforced composite material molding method and molding device using the VARTM process, which can reduce porosity and increase fiber volume fraction.

The fiber-reinforced composite material molding method using the VARTM process according to an embodiment of the present invention,

A method of forming a fiber-reinforced composite material by forming vacuum pressure inside the vacuum bag film and transporting the liquid resin by the vacuum pressure, comprising: a first step of forming vacuum pressure inside the vacuum bag film; A second step of injecting liquid resin into the vacuum bag film; It includes a third step of increasing the liquid resin injection pressure during the liquid resin injection.

In the fiber-reinforced composite material molding method using the VARTM process according to an embodiment of the present invention, in the third step, it is preferable to increase the liquid resin injection pressure to form a step waveform.

The fiber-reinforced composite material molding device using the VARTM process according to an embodiment of the present invention,

A liquid resin supply unit that supplies liquid resin; a liquid resin molding unit that receives liquid resin from the liquid resin supply unit and molds a fiber-reinforced composite material; It includes a negative pressure forming unit that generates negative pressure in the liquid resin molding part. The liquid resin molding unit includes a lower mold and a back film installed on an upper part of the lower mold and having a resin injection port at one end and a resin discharge port at the other end. The liquid resin supply unit includes a first vacuum pump that creates negative pressure, an injection tube connecting the first vacuum pump and the resin injection port, a liquid resin supply tank connected to the injection tube and supplying liquid resin, and the injection port. It includes a pressure regulator that adjusts the injection pressure of the liquid resin injected into the resin injection port through the tube.

In the fiber-reinforced composite material molding apparatus using the VARTM process according to an embodiment of the present invention, it is preferable that the pressure regulator increases the injection pressure of the liquid resin to form a step waveform.

In the fiber-reinforced composite material molding apparatus using the VARTM process according to an embodiment of the present invention, the apparatus may further include an auxiliary pressure regulator that assists the pressure regulator to control the injection pressure of the liquid resin. The auxiliary pressure regulator includes a housing whose upper surface is connected to the injection tube and whose lower surface is connected to the resin injection port, a moving block installed to move forward and backward in the center direction within the housing, and a linear unit that moves the moving block forward and backward. It may include an actuator.

Details of other implementations of various aspects of the present invention are included in the detailed description below.

According to an embodiment of the present invention, it is possible to reduce pores and increase the fiber volume fraction, making it possible to manufacture highly reliable parts even with a low process construction cost.

Figure 1 is a flowchart showing a method of forming a fiber-reinforced composite material using the VARTM process according to an embodiment of the present invention.
Figure 2 is a diagram showing a fiber-reinforced composite material molding apparatus using the VARTM process according to an embodiment of the present invention.
Figure 3 is a graph showing the waveform of the liquid resin injection pressure controlled according to an embodiment of the present invention.
Figure 4 is a diagram showing a fiber-reinforced composite material molding apparatus using the VARTM process according to the prior art.
Figure 5 is a graph showing the waveform of liquid resin injection pressure according to the prior art.
Figure 6 is a table summarizing the experimental results according to VARTM process conditions.
Figure 7 is a graph showing the waveform of the liquid resin injection pressure according to the molding device equipped with the upper mold.
Figure 8 is a graph showing compression test results according to VARTM process conditions.
Figure 9 is a graph showing the fiber volume fraction results according to VARTM process conditions.
Figure 10 is a graph showing pore analysis results according to VARTM process conditions.
Figure 11 is a cross-sectional image of VARTM process samples.
Figure 12 is a cross-sectional image of sample H-08.
Figure 13 is a diagram showing a fiber-reinforced composite material molding apparatus using the VARTM process according to another embodiment of the present invention.
Figure 14 is a diagram showing the operation process of a fiber-reinforced composite material molding device using the VARTM process according to another embodiment of the present invention.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be exemplified and explained in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The terms used in the present invention are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as 'include' or 'have' are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that it does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof. Hereinafter, a fiber-reinforced composite material molding method and molding device using the VARTM process according to an embodiment of the present invention will be described with reference to the drawings.

Figure 1 is a flowchart showing a fiber-reinforced composite material forming method (hereinafter abbreviated as "composite material forming method") using the VARTM process according to an embodiment of the present invention.

Referring to FIG. 1, the composite material molding method according to an embodiment of the present invention is a method of forming a negative pressure (vacuum pressure) inside the bag film and molding a fiber-reinforced composite material while liquid resin is transported by the negative pressure. , a first step of forming negative pressure inside the back film (S100); A second step (S200) of injecting liquid resin into the back film; It includes a third step (S300) of increasing the liquid resin injection pressure during the liquid resin injection. And, in the third step, it is desirable to increase the liquid resin injection pressure so as to have a step waveform.

This will be described in detail with reference to the fiber-reinforced composite material molding device (hereinafter abbreviated as “composite material molding device”) using the VARTM process according to an embodiment of the present invention shown in FIG. 2.

Figure 2 is a diagram showing a composite material molding apparatus according to an embodiment of the present invention. Referring to FIG. 2, the composite material molding apparatus includes a liquid resin molding unit 100, a liquid resin supply unit 200, and a negative pressure forming unit 300.

The liquid resin molding unit 100 receives liquid resin from the liquid resin supply unit 200 and molds a fiber-reinforced composite material.

The liquid resin molding unit 100 includes a lower mold 110, a bagging film 120 installed on the upper part of the lower mold, and having a resin injection port 121 at one end and a resin discharge port 122 at the other end. , a peel ply 123 formed between the lower mold 110 and the back film 120 and assisting in demolding the fabric laminate (R), which is a molding object, with the lower mold 110, and the lower mold 110. It is formed between the fabric laminate (R) and the back film 120 and includes a resin distribution medium (124, flow meia) that assists in smooth supply of liquid resin between the fabric laminate (R) and the back film 120.

The liquid resin supply unit 200 supplies liquid resin to the liquid resin molding unit 100. In particular, the liquid resin supply unit 200 operates to increase the liquid resin injection pressure during liquid resin injection.

For this purpose, the liquid resin supply unit 200 includes a first vacuum pump 210 that generates negative pressure, an injection tube 220 connecting the first vacuum pump 210 and the resin injection port 121, and an injection tube 220. ) and includes a liquid resin supply tank 230 for supplying liquid resin, and a pressure regulator 240 for controlling the injection pressure of the liquid resin injected into the resin injection port 121 through the injection tube 220. Additionally, an inlet valve 250 is installed on the injection tube 220 to control injection of the liquid resin. The pressure regulator 240 may be a valve type that controls the opening degree of the injection tube 220.

The negative pressure forming unit 300 forms negative pressure inside the back film 120, so that the liquid resin injected through the resin injection port 121 is horizontally transferred along the surface of the fabric laminate (R) due to the pressure difference, It is transferred in the vertical direction of the fabric laminate (R) so that the liquid resin impregnates the fabric laminate (R) and forms the fabric laminate (R). In addition, the negative pressure forming unit 300 allows excess liquid resin after molding discharged through the resin discharge port 122 to be stored in the excess resin storage tank 310.

For this purpose, the negative pressure forming unit 300 includes a second vacuum pump 310 that forms negative pressure, a discharge tube 320 connecting the second vacuum pump 310 and the resin discharge port 122, and a discharge tube 320. ) and includes a surplus resin storage tank 330 that stores excess liquid resin discharged through the resin outlet 122. Additionally, an outlet valve 350 is installed on the discharge tube 320 to control discharge of the liquid resin.

An injection pressure meter 260 is installed in the liquid resin supply tank 230 to measure the injection pressure of the supplied liquid resin, and a discharge pressure meter 360 is installed in the surplus resin storage tank 330 to measure the discharge pressure of the surplus resin discharged. ) can be installed.

Next, a composite material molding method through operation control of a composite material molding device will be described with reference to FIG. 3. Figure 3 is a graph showing the waveform of the liquid resin injection pressure controlled according to an embodiment of the present invention.

As shown in FIG. 3, the composite material molding method and molding device according to an embodiment of the present invention starts injecting the liquid resin into the back film 120 through the resin injection port 121, and then injects the liquid resin. Gradually increase the liquid resin injection pressure. Preferably, the liquid resin injection pressure is increased to create a step waveform. In Figure 3, P1 is the pressure on the resin inlet 121 side, P2 is the pressure on the resin outlet 122 side, and Q is the liquid resin flow rate inside the bag film 120.

Before injecting the liquid resin, both the first vacuum pump 210 and the second vacuum pump 310 are operated so that the pressure difference between both sides of the bag film 120 (liquid resin supply unit 200 side and negative pressure forming unit 300 side) is increased. Make sure there is no such thing. Thereafter, when the liquid resin is injected, the pressure regulator 240 is controlled so that the negative pressure on the liquid resin supply unit 200 side is smaller than the negative pressure on the negative pressure forming unit 300 side, so that the liquid resin is gradually injected. After a certain period of time has elapsed, the magnitude of the negative pressure on the side of the liquid resin supply unit 200 is reduced through the pressure regulator 240 to increase the liquid resin injection pressure. This process is repeated until the preset negative pressure (for example, -0.2 bar) is increased to maximize the liquid resin injection pressure, and then the magnitude of the negative pressure on the liquid resin supply unit 200 is rapidly increased, and then the preset negative pressure is reached. After maintaining the negative pressure for a period of time, a curing process is performed to form the fiber-reinforced composite material.

After increasing the liquid resin injection pressure to the maximum, the liquid resin injection pressure is rapidly reduced to maintain negative pressure for a preset time because the resin injection port 121 side is convexly protruded by the injected liquid resin and the back film ( Since the upper surface of the back film 120 is non-uniform, the negative pressure on both sides of the back film 120 is set to a similar level and then injection is continued for a certain period of time to make the upper surface of the back film 120 uniform.

That is, as shown in FIG. 3, the liquid resin injection pressure is increased to create a step waveform during the [0 to t1] section, and the liquid resin injection pressure is maintained to decrease during the [t1 to t2] section to make the back film 120 uniform. , proceed with the hardening process.

By increasing the liquid resin injection pressure to form a step waveform during the [0 to t1] section, the liquid resin flow rate within the bag film 120 can be maintained constant.

In this way, by increasing the liquid resin injection pressure during liquid resin injection, pores can be reduced and the fiber volume fraction can be increased, making it possible to manufacture highly reliable parts even at a low cost of process construction.

Hereinafter, the porosity reduction and fiber volume fraction increase of the present invention will be described in comparison with the prior art. Figure 4 is a diagram showing a fiber-reinforced composite material molding apparatus using the VARTM process according to the prior art, and Figure 5 is a graph showing the waveform of the liquid resin injection pressure according to the prior art.

Referring to Figure 4, the composition of the liquid resin supply unit 200_2 in the composite material molding apparatus of the prior art is different from that of the present invention. In the prior art device, the liquid resin supply unit 200_2 includes only an injection tube 220 for supplying liquid resin, a liquid resin supply tank 230, and an inlet valve 250. Therefore, the liquid resin injection pressure cannot be controlled, and the liquid resin is injected into the bag film 120 at a level of 0 bar, which is atmospheric pressure, as shown in FIG. 5.

According to this prior art, since the pressures P1 and P2 are constant, the flow rate Q gradually decreases and flow rate control is impossible, making it difficult to reduce pores.

Figure 6 is a table summarizing the experimental results according to VARTM process conditions. The results are expressed as the average value and standard deviation of compression test, fiber volume fraction, and void analysis.

In Figure 6, type A is the experimental result according to the prior art in Figures 4 and 5, type B is the experimental result according to the present invention in Figures 2 and 3, and type C is the liquid resin injection as shown in Figure 7. These are the experimental results according to the pressure waveform (P1). Meanwhile, in the case of Figure 7, a molding device equipped with an upper mold is used, and liquid resin can be injected at an optimal flow rate, thereby minimizing voids by reducing the gap in dual-scale flow. However, in the VARTM process without an upper mold, It is not applicable.

Figure 8 is a graph showing compression test results according to VARTM process conditions, Figure 9 is a graph showing fiber volume fraction results according to VARTM process conditions, and Figure 10 is a graph showing pore analysis results according to VARTM process conditions.

It can be seen that the A type process shows relatively larger deviations than the B and C type processes. This cause can be interpreted as a deviation depending on the void content. In particular, in the case of the H-10 sample, the pressure inside the vacuum bag was slightly increased by closing the outlet for 20 minutes after completion of injection and additionally filling the resin. Despite the lower fiber volume fraction, voids were reduced and compressive strength was increased. It is confirmed that it was done.

Conversely, in the case of H-05, although the fiber volume fraction was relatively high, the compressive strength was somewhat low, which is expected to be due to the high void content. The reason for the high void content in the H-05 sample was that it was impossible to control the flow rate during injection, so a large amount of bubbles were generated and filled. After filling, the pressure at the injection port was set to -0.8 bar and maintained for 5 minutes, and the remaining voids were lowered. It is estimated that the volume increased significantly due to this.

Looking at the compression test graph in Figure 8, the H-08 sample produced by the B type process showed the highest average of 611 MPa. And in the A type process, the deviation of compressive strength was relatively large and low. The cause of these results is the result of the void content. In particular, the H-10 sample showed an average of 572 MPa. Looking at the optical microscopy results in Figure 11 (f), it can be seen more clearly that there are no voids. And although the H-09 sample was also produced using the C type process, it showed a low average of 458 MPa, which may be due to not maintaining enough time to increase the internal pressure after injection.

Looking at the fiber volume fraction analysis graph in Figure 9, the H-07 sample of the B type process that controlled atmospheric pressure showed the highest average of 56.77%, and the H-10 sample in which the pressure inside the vacuum bag was increased after injection had an average of 51.47%. It was the lowest in %. What is noteworthy in this graph is the variation in fiber volume fraction. In the case of the VARTM process, the variation in fiber volume fraction may increase due to the thickness variation between the inlet and outlet positions. The H-06~08 samples, whose flow rate was controlled through atmospheric pressure control, showed low deviation, and the H-10 sample, where the pressure inside the vacuum bag was raised after injection, also tended to be low. Fig. In the void analysis graph in Fig. 10, it can be seen that the sample controlled at atmospheric pressure has a relatively low deviation.

Figure 11 (a) is a cross-section of a specimen cut at the outlet of the H-02 sample observed at 50x magnification under an optical microscope. It was clearly observed that macro voids occurred due to the slow flow velocity at the outlet location. (b) is a cross-sectional image observed from the injection port of the H-02 sample. As the flow rate flows quickly, it can be seen that micro voids are formed inside the fiber bundle. (c) is a cross-sectional photograph of the H-05 sample in which a vacuum pressure of -0.8 bar was maintained for 5 minutes at the injection port location after resin injection was completed. As the pressure inside the vacuum bag decreased, the fiber volume fraction increased to 54.4%, but it was confirmed that the remaining void was elongated along the shape of the fiber bundle. (d) is a cross-sectional photograph of the H-09 sample with the outlet closed and held for 5 minutes to increase the pressure inside the vacuum bag after resin injection was completed. There is a high possibility that the pressure inside the vacuum bag did not increase sufficiently and a void remained. (e) is a cross-section of the H-08 sample produced by gradually increasing the atmospheric pressure. Although the fiber volume fraction was 55.5%, voids were significantly reduced and were not observed under an optical microscope. In other words, it was confirmed that the flow rate control method was effective. (f) is a cross-sectional photograph of the H-10 sample in which the pressure inside the vacuum bag was slightly increased by closing the outlet only and holding it for 20 minutes after completion of resin injection. Although the fiber volume fraction decreased, voids were not observed. In other words, it was confirmed that the increase in pressure inside the vacuum bag had a positive effect on reducing voids.

Figure 12 is a cross-sectional photograph of the H-08 specimen at 200x and 1000x magnification. Overall, it was observed that the resin impregnation was even without voids.

Next, a fiber-reinforced composite material molding apparatus using the VARTM process according to another embodiment of the present invention will be described with reference to FIGS. 13 and 14. Figure 13 is a diagram showing a fiber-reinforced composite material molding apparatus using the VARTM process according to another embodiment of the present invention, and Figure 14 is a diagram showing the operation process.

The composite material molding device according to the present embodiment includes a liquid resin molding unit 100, a liquid resin supply unit 200, and a negative pressure forming unit 300, similar to the above-described embodiment, but the liquid resin supply unit 200 Since the composition is partially different, only the different parts will be explained.

In this embodiment, the liquid resin supply unit 200 includes a first vacuum pump 210, an injection tube 220, a liquid resin supply tank 230, a pressure regulator 240, an inlet valve 250, Includes an injection pressure gauge (260) and an auxiliary pressure regulator (270).

The first vacuum pump 210, the injection tube 220, the liquid resin supply tank 230, the pressure regulator 240, the inlet valve 250, and the injection pressure gauge 260 are the embodiment described above. Since it is the same as , repeated explanation is omitted.

The auxiliary pressure regulator 270 may assist the pressure regulator 240 and control the liquid resin injection pressure together with the pressure regulator 240, or may independently control the liquid resin injection pressure instead of the pressure regulator 240.

The auxiliary pressure regulator 270 includes a housing 271 whose upper surface is connected to the injection tube 220 and the lower surface connected to the resin injection port 121, and a moving block installed to move forward and backward in the center direction within the housing 271. It includes (272) and a linear actuator (273) that moves the moving block (272) forward and backward. A plurality of moving blocks 272 are provided in the housing 271, and the plurality of moving blocks 272 may form a ring shape. The moving block 272 is formed in an upper-lower narrow shape with a wide upper part and a narrow lower part, and the wide upper part can perform a buffer function to temporarily store liquid resin that is continuously injected.

This auxiliary pressure regulator 270 is directly connected to the resin injection port 121 and adjusts the opening degree of the resin injection port 121 to control the liquid resin injection pressure.

As shown in (a) of FIG. 4, when the inlet valve 250 is closed, the linear actuator 273 moves the moving block 272 backwards so that it is closest to the inner wall of the housing 271, thereby increasing the opening degree of the resin injection port 121. Let be the maximum.

When the inlet valve 250 is switched from the closed state to the open state and the liquid resin injection process into the resin injection port 121 is started, after a preset time has elapsed, the linear actuator 273 moves the moving block 272 at a preset distance. The liquid resin injection pressure is increased by the first amount (P11) by advancing the resin injection port 121 to narrow the opening degree, and then maintaining that state for a certain period of time. After the preset time has elapsed, the linear actuator 273 moves the moving block 272 forward again by the preset distance so that the opening degree of the resin injection hole 121 becomes narrower, increasing the liquid resin injection pressure by the second size (P12). After increasing, maintain that state for a certain period of time. By repeating this process, the liquid resin injection pressure is increased to create a step waveform during the [0 ~ t1] section as shown in FIG. 3, and the liquid resin injection pressure is maintained decreased during the [t1 ~ t2] section to make the back film 120 uniform. After doing so, the curing process proceeds.

In this embodiment, the auxiliary pressure regulator 270 controls the liquid resin injection pressure together with the pressure regulator 240, thereby improving the increase rate of the liquid resin injection pressure, thereby shortening the overall process time. . In addition, the linear actuator 273 of the auxiliary pressure regulator 270 is adjusted to operate automatically by a control unit (not shown) according to the on/off of the inlet valve 250, so that the pressure regulator 240 is in an inoperable state. In this case, the liquid resin injection pressure can be adjusted.

Although the embodiments of the present invention have been described above, those skilled in the art will be able to understand the addition, change, deletion or addition of components without departing from the spirit of the present invention as set forth in the patent claims. The present invention can be modified and changed in various ways, and this will also be included within the scope of the rights of the present invention.

100: Liquid resin molding part
110: lower mold 120: back film
121: Resin inlet 122: Resin outlet
123: Peel ply 124: Resin distribution medium
200: Liquid resin supply unit
210: first vacuum pump 220: injection tube
230: Liquid resin supply tank 240: Pressure regulator
250: Inlet valve 260: Injection pressure gauge
270: Auxiliary pressure regulator
300: Negative pressure forming part
310: second vacuum pump 320: discharge tube
330: Surplus resin storage tank 350: Outlet valve
360: Discharge pressure meter

Claims (5)

A method of forming a fiber-reinforced composite material by forming a vacuum pressure inside the vacuum bag film and transporting the liquid resin by the vacuum pressure,
A first step of forming vacuum pressure inside the vacuum bag film;
A second step of injecting liquid resin into the vacuum bag film;
A third step of increasing the liquid resin injection pressure during the liquid resin injection;
Fiber-reinforced composite material molding method using the VARTM process, including.
In claim 1,
In the third step, a fiber-reinforced composite material molding method using the VARTM process, in which the liquid resin injection pressure is increased to form a step waveform.
A liquid resin supply unit that supplies liquid resin;
a liquid resin molding unit that receives liquid resin from the liquid resin supply unit and molds a fiber-reinforced composite material;
It includes a negative pressure forming part that creates negative pressure in the liquid resin molding part,
The liquid resin molding unit includes a lower mold and a back film installed on an upper part of the lower mold and having a resin injection port at one end and a resin discharge port at the other end,
The liquid resin supply unit,
a first vacuum pump that creates negative pressure;
an injection tube connecting the first vacuum pump and the resin injection port;
a liquid resin supply tank connected to the injection tube and supplying liquid resin;
A pressure regulator that adjusts the injection pressure of the liquid resin injected into the resin injection port through the injection tube.
Fiber-reinforced composite material molding device using the VARTM process, including.
In claim 3,
The pressure regulator is a fiber-reinforced composite material molding device using the VARTM process, wherein the pressure regulator increases the injection pressure of the liquid resin to form a step waveform.
In claim 3,
It further includes an auxiliary pressure regulator that assists the pressure regulator to control the injection pressure of the liquid resin, wherein the auxiliary pressure regulator includes,
a housing whose upper surface is connected to the injection tube and whose lower surface is connected to the resin injection port;
A moving block installed to move forward and backward in the center direction within the housing,
Linear actuator that moves the moving block forward and backward
Fiber-reinforced composite material molding device using the VARTM process, including.

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