CN100411853C - Pressure Shock Wave Degassing Device for Resin Transfer Molding Process - Google Patents

Abstract

A pressure shock wave degassing device for a resin transfer molding process, which belongs to the technical field of composite material manufacturing, and the device includes a shock wave generator (5), a shock wave generator power supply (6), an RTM mold (7), and the shock wave generator (5). The wave generator is composed of a light shell (1), a piezoelectric ceramic sheet (2), an end cover (3), and a terminal block (4); the specific implementation method adopts pulsed ultrasonic technology, and utilizes a shock wave generator (5 ) forms a pressure shock wave with instantaneous high pressure effect in the mold cavity, promotes the flow of the resin, improves the wettability of the resin to the fiber, removes excess gas and removes microbubbles. The invention is simple in structure and easy to use, and is an effective degassing device for resin transfer molding (RTM) of composite material components in the aerospace field, and is also applicable to the degassing requirements of other composite material mold molding processes.

Description

Pressure Shock Wave Degassing Device for Resin Transfer Molding Process

1. Technical field

The pressure shock wave degassing device of the resin transfer molding process of the present invention belongs to the degassing device and method of the RTM mold forming process.

2. Background technology

With the development of the polymer matrix composites industry, the resin transfer molding (RTM) process has been more and more widely used at home and abroad. The RTM process is to inject a liquid resin system under a certain pressure into a closed mold cavity pre-laid with fiber reinforced materials, and the resin infiltrates the fiber reinforced materials in the mold cavity and then solidifies and forms. Since the air is not easy to exhaust during the molding process, defects are prone to occur in composite products, thereby reducing their bending strength, tensile strength, impact strength and interlayer strength. Therefore, it is very important to improve the wettability of the resin to the fiber and reduce the porosity during the molding process.

In order to reduce the porosity of RTM molding composites and improve the wettability of resin to fibers during the molding process, researchers at home and abroad have done a lot of work.

If it is found that filling the mold under vacuum conditions can reduce the air bubble content of the product.

Through literature search, "Vibration Assisted Resin Transfer Molding" ( ^13th International Conference on Composite Materials, 2001), the influence of audio vibration on RTM molding process was studied. Experiments show that the audio frequency vibration is beneficial to the resin in the cavity to infiltrate the fibers, making the infiltration speed faster and reducing the air bubbles.

Through patent retrieval, the invention patent "Ultrasonic treatment of resin transfer molding method and device" (patent application number: 03132430.4) declared by Harbin Institute of Technology, in the RTM process, the fiber and resin in the cavity of the mold are ultrasonically treated to improve The wettability of the resin to the fiber and the reduction of the porosity of the composite material can improve the interfacial properties of the composite material.

The ultrasonic frequency used in the above-mentioned patented technology is 40~60kHz, the sound power is 0~400W, and the sound power density is not large. When the cross-section of the RTM mold cavity changes abruptly, the removal effect on microbubbles is not obvious.

In order to solve the degassing requirements of various RTM molds in engineering practice, it is necessary to further study the degassing device and method of new RTM molds.

3. Contents of the invention

The present invention aims at the current state of the prior art, and researches an effective method that can promote the flow of resin in the mold cavity, enhance the wettability of the resin to fibers, eliminate excess gas and remove microbubbles in the RTM process. The pressure shock wave degassing method of the resin transfer molding process of the present invention adopts the pulse ultrasonic technology, utilizes the piezoelectric shock wave generator to form a pressure shock wave with instantaneous high pressure effect in the liquid medium, and produces directional instant for the resin in the mold cavity. The pressure disturbance promotes the resin movement in the mold cavity, enhances the wettability of the resin to the fibers, and removes excess gas and microbubbles. The above method can not only promote the flow of resin in the mold cavity, but also not affect the stability of the process system, which is beneficial to improve the wettability of resin to fibers and reduce porosity during the molding process, and can be widely used in the field of RTM mold degassing technology.

The pressure shock wave degassing device for the resin transfer molding process to achieve the above goals is composed of a piezoelectric shock wave generator connected to the RTM mold and a high-power shock wave power supply. The piezoelectric shock wave generator includes a piezoelectric ceramic sheet bonded to the inner surface of the lightweight housing through a mounting hole, the end cover is connected to the upper end of the lightweight housing, sealed by a gasket, and the power inlet seat is located on the end cover. The shock wave generator is used as an integral part of the RTM mold, and by applying directional radiation pressure to the parts prone to defects to promote the resin flow in the RTM mold cavity, the function of liquid pressure shock wave to remove microbubbles can be realized.

Compared with the prior art, the present invention can generate high-energy ultrasonic waves with a frequency of (200-2000) kHz, and form a pressure shock wave with instantaneous high-pressure effect in the mold cavity to strengthen the resin against The wettability of fibers, the removal of excess gas and the removal of microbubbles.

According to the requirements of the RTM mold in actual production, the shape of the piezoelectric ultrasonic transducer can be changed accordingly. This article will propose a design scheme and implementation method for a special form of RTM mold structure.

The device of the invention has the advantages of simple structure, convenient use and low cost.

4. Description of drawings

Figure 1 is a partial cross-sectional view of an RTM mold cavity.

Note: porosity is easily generated in the annular area.

Fig. 2 is a structural schematic diagram of a piezoelectric shock wave generator, in which Fig. 2(a) is a schematic cross-sectional view of the front view, and Fig. 2(b) is a top view.

Label names in the figure: 1. Lightweight shell, 2. Piezoelectric ceramic sheet, 3. End cover, 4. Power inlet seat

Figure 3 is one of the schematic diagrams of the lightweight shell, in which the upper figure is a main sectional view, and the lower figure is a top view.

Figure 4 is the second schematic diagram of the lightweight shell, in which the upper figure is the main sectional view, and the lower figure is the top view.

Figure 5 Schematic diagram of liquid pressure shock wave degassing device

Label names in the figure: 5. Piezoelectric shock wave generator, 6. High-power shock wave power supply, 7. RTM mold

5. Specific implementation

The specific structure of the present invention is as follows: as shown in Figure 2, the piezoelectric ceramic sheet 2 is bonded to the inner surface of the lightweight housing 1, the end cover 3 is connected with the lightweight housing 1, and the two are sealed with a gasket. The lightweight housing 1 is shown in Figure 3, on the lightweight housing 1, the installation hole of the piezoelectric ceramic sheet 2 is designed; the distance d between the bottom surface of the installation hole and the surface of the lightweight housing 1 is determined according to the formula (1):

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; no</span>}\frac{\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where: f is the longitudinal resonance frequency of the piezoelectric ceramic sheet, c is the sound velocity in the material of the lightweight shell 1, f and c can be obtained through actual measurement, and n is a natural number.

The size, shape and number of piezoelectric ceramic sheets are designed according to actual needs, and thus determine the specific form of the lightweight housing 1 . Figures 3 and 4 show two specific forms of lightweight shells that meet the requirements of the RTM mold shown in Figure 1.

In order to ensure a good sound transmission effect, the mechanical processing method can be used to process all the piezoelectric ceramic mounting holes on the lightweight shell 1 through one clamping, so as to ensure the shape and position accuracy of each hole and meet the required surface processing accuracy And quality, so as to ensure the bonding quality and acoustic focusing effect.

A special bonding process is adopted to ensure the bonding quality of the piezoelectric ceramic sheet 2 and the light shell 1 .

Figure 5 is a schematic diagram of the use of the liquid pressure shock wave degassing device, that is, the high-power shock wave power supply 6 is connected to the piezoelectric shock wave generator 5 through the power inlet seat 4 on the end cover 3, and the piezoelectric shock wave generator 5 as an integral part of the RTM mold 7.

The specific working method:

The piezoelectric shock wave generator 5 is a component of the RTM mold 7 (the specific location depends on the actual demand), and with the cooperation of the high-power shock wave power supply 6, the working frequency is (200-2000) kHz, and the power is (0 ~2000) W, so as to realize the degassing function and improve the performance of composite products.

Claims (2)

1. the pressure shock wave depassing unit of a resin transfer molding (RTM) process, it is characterized in that, comprise piezoelectric type shock wave generator (5), high-power shock wave power supply (6), RTM mould (7), wherein high-power shock wave power supply (6) is connected in piezoelectric type shock wave generator (5), piezoelectric type shock wave generator (5) is connected in RTM mould (7), described piezoelectric type shock wave generator (5) comprises piezoelectric ceramic thin sheet (2), lightweight housing (1), end cap (3), sealing gasket (4), wherein piezoelectric ceramic thin sheet (2) is bonded in lightweight housing (1) inner surface by installing hole, and end cap (3) connects with lightweight housing (1), by sealing gasket (4) sealing, electricity-supply seat is positioned on the end cap (3).

2. the pressure shock wave depassing unit of resin transfer molding (RTM) process according to claim 1 is characterized in that, the installing hole bottom surface that lightweight housing (1) is gone up piezoelectric ceramic thin sheet (2) apart from lightweight housing (1) surface distance d according to formula $d=n\frac{f}{4c}$ Determine that wherein: n is a natural number, f is vertical resonant frequency of piezoelectric ceramics, and c is the velocity of sound in lightweight housing (1) material.

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