CN107160713A - A kind of autoclave frame-type composite material shaping mould - Google Patents

Abstract

The invention relates to a frame-type composite material forming mold for hot autoclave, which comprises a frame-type base and a forming plate fixed on the base; the thickness of the forming plate away from the air inlet of the autoclave is less than or equal to the The thickness near the air inlet of the autoclave, and the thickness of the forming plate closest to the air inlet of the autoclave is greater than the farthest thickness of the air inlet of the autoclave. The mold can ensure that the curing degree of the composite material component is basically consistent and the structural deformation is small.

Description

A frame-type composite material molding die for autoclave

technical field

The invention relates to a frame-type composite material forming mold for hot-pressed tanks, which belongs to the technical field of mold forming.

Background technique

Advanced composite materials are widely used in the aviation field due to their significant advantages such as high specific strength and specific modulus, strong designability, and good fatigue resistance. The autoclave molding process is one of the main methods of forming composite parts. The autoclave molding process is to lay the prepreg on the tooling surface according to the layer design of the material, and then lay the adhesive layer, Air felt and other materials are put into a vacuum bag to evacuate. Finally, according to the curing process curve of the material, it goes through the stages of heating, pressurization, and finally cooling and depressurization, so that the prepreg blank is cured and formed into a composite material part that meets the design requirements. The method can be used as a forming method for the main load-bearing part and the secondary load-bearing part of the large complex curved surface in the field of aerospace.

Generally speaking, the curing of composite materials through an autoclave is a process of heating up, keeping warm, and cooling down, accompanied by pressurization and depressurization. The heat medium continuously heats the mold and components to ensure that the temperature of the components continues to rise and complete the curing and molding. When cooling down, turn off the heating device, and use water cooling at the same time to continuously cool down the air in the tank, and the fan circulates the air to ensure that the temperature in the tank is lowered.

During the autoclave curing process, the temperature change on the surface of the mold forming plate depends on the convective heat exchange between the mold surface and the fluid’s sweeping plate and the heat conduction between the frame base and the mold forming plate. When the fluid sweeps the forming plate, The contact surface between the forming plate and the fluid will generate a boundary layer. Due to the loss of kinetic energy due to the viscosity of the fluid, the velocity in the boundary layer will decrease along the flow direction, and as a result, the thickness of the boundary layer will continue to increase along the flow direction. According to the theory of convective heat transfer, the thicker the boundary layer, the greater the thermal resistance of heat conduction, and the lower the heat transfer efficiency, resulting in low temperature at the leeward end. Another reason for the low temperature at the leeward end is that due to the obstruction of the frame base on the windward side to the frame base on the leeward side, the intensity of jet impact heat transfer decreases with the flow direction, making the temperature of the grid frame at the leeward end lower. end, less heat is transferred to the forming plate.

When an actual forming plate was tested, the temperature distribution on the surface of the forming plate at the end of the heating phase was measured as shown in Figure 1. The maximum temperature difference on the forming surface reached 50.1 degrees, and the temperature difference from the windward side to the leeward side gradually increased. The area with the lowest temperature appears about 80% away from the windward end, and the low temperature area accounts for about 25% of the plane area of the mold. Therefore, the temperature distribution of the mold surface is quite uneven. The uneven temperature field will affect the molding quality of composite parts to a large extent, resulting in uneven heating of composite parts, inconsistent curing degrees, and structural deformation. Therefore, how to reduce the temperature gradient of composite components in the flow direction has become an urgent problem to be solved.

In order to improve the uniformity of the temperature field of the part, the existing technology mainly focuses on the following two aspects: one is to improve the existing curing process; the other is to propose a new process and new method to form the composite material part. The above improvement often involves the improvement of equipment, which is relatively complicated and has certain difficulties in actual production.

Contents of the invention

The technical problem to be solved by the present invention is: to overcome the disadvantages of the above-mentioned technologies, and to provide a frame-type molding die that can ensure that the solidification degree of composite material components is basically consistent and has small structural deformation.

In order to solve the above-mentioned technical problems, the technical solution proposed by the present invention is: a frame-type composite material forming mold for autoclave, including a frame-type base and a forming plate fixed on the base; The thickness far from the tuyere is less than or equal to the thickness near the air inlet of the autoclave, and the thickness of the forming plate closest to the air inlet of the autoclave is greater than the thickness farthest from the air inlet of the autoclave.

The applicant has found through long-term research that the influence of the external temperature field of the composite material component plays a leading role in the phenomenon that the temperature field of the composite material component presents a gradient change with the heating direction during curing. Therefore, the present invention improves the more commonly used composite material frame molds, and performs thickness-variable processing on the composite material contact plate, and according to the thermal resistance theory, thermal resistance is proportional to the length of the conduction path, that is, the thicker the formed plate thickness The higher the thermal resistance in this area, the more difficult it is to heat up. Therefore, according to this property, the present invention increases the thickness of the molded plate in the high-temperature region while reducing the thickness of the molded plate in the low-temperature region, so that the thermal resistance in the high-temperature region becomes larger and the thermal resistance in the low-temperature region becomes smaller, so that the surface of the mold plate The temperature distribution is more uniform.

Based on the above theory, the optimal technical means should be that the thickness of the formed plate decreases linearly along the heating direction, that is, the formed plate is trapezoidal as a whole, but in the actual forming test process, although the overall trapezoidal formed plate is very important for increasing the temperature of the part The field uniformity has some effect, but the applicant found that the effect of improving the uniformity is not very good, especially the temperature uniformity of the workpiece far away from the air inlet of the autoclave is very poor. The reason is that the applicant believes that the temperature change on the surface of the forming plate depends on the convective heat exchange between the surface and the fluid’s sweeping plate and the heat conduction between the bottom sash and the mold forming plate. When the fluid sweeps the forming plate, the forming plate A boundary layer will be generated on the contact surface with fluid, please refer to "Fundamentals of Fluid Mechanics (3rd Edition)" (Author: Wang Huimin, Tsinghua University Press, 2013). In this way, due to the loss of kinetic energy due to the viscosity of the fluid, the velocity in the boundary layer decreases along the flow direction, and as a result, the thickness of the boundary layer increases along the flow direction. In this way, when the formed plate is trapezoidal as a whole, the thickness of the boundary layer changes sharply near the windward end (close to the air inlet of the autoclave), and the thickness change is small after the boundary layer is fully developed, resulting in The temperature uniformity of the parts is very poor.

Just because the thickness of the boundary layer away from the air inlet of the autoclave varies little, in order to further improve the temperature uniformity of the workpiece, the present invention keeps the thickness of the forming plate unchanged at a distance away from the air inlet of the autoclave. There are two ways:

1) The profiled plate is in the shape of two steps, wherein the length of the thicker part of the profiled plate is 25% to 50% of the total length of the profiled plate. Preferably, the thickness of the thicker part of the forming plate (a section near the air inlet of the autoclave) is 1.5 to 3 times the thickness of the thinner part of the forming plate.

2) A section of the forming plate close to the air inlet of the autoclave is trapezoidal (that is, the part of the forming plate close to the air inlet of the autoclave is trapezoidal), and a section of the forming plate close to the air outlet of the autoclave has the same thickness. Preferably, the length of the trapezoidal portion of the forming plate accounts for 50% to 70% of the total length of the forming plate.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing.

Fig. 1 is a temperature distribution nephogram of an existing formed plate at the end of the heating phase.

Fig. 2 is a schematic structural diagram of an embodiment of the present invention.

Fig. 3 is a schematic cross-sectional view of Embodiment 1 of the present invention.

Fig. 4 is a schematic cross-sectional view of Embodiment 2 of the present invention.

Fig. 5 is a cloud diagram of temperature distribution during a comparative experiment in Example 1 of the present invention.

Fig. 6 is a cloud diagram of temperature distribution during the comparative experiment in Example 2 of the present invention.

detailed description

Embodiment one

The frame-type composite material molding die for the autoclave of the present embodiment, as shown in Figure 2, includes a frame-type base 2 and a forming plate 1 fixed on the base 2; the forming plate 1 is far away from the air inlet of the autoclave The thickness at the position is less than or equal to the thickness near the air inlet of the autoclave, and the thickness of the forming plate 1 closest to the air inlet of the autoclave is greater than the farthest thickness from the air inlet of the autoclave, that is The wall thickness of the forming plate 1 changes from thick to thin from its windward end (near the air inlet of the autoclave) to the leeward end (near the air outlet of the autoclave).

In this embodiment, the frame base 2 is in the shape of an "egg crate". Of course, other frame structures can also be used, as long as they can facilitate ventilation and meet the strength requirements of the supporting forming board, they can be applied to this example.

As shown in Figure 3, the forming plate 1 in this embodiment is in the shape of two steps, and four sets of stepped non-equal thickness plates were tested respectively, and the distances from the windward end were 400mm, 450mm, 500mm and 600mm respectively. The thickness of the thicker part of the forming plate 1 is 20 mm, and the thickness of the remaining positions is reduced to 10 mm.

In this embodiment, the size of the mold is 1500*1500*400mm, the material is Q235 carbon structural steel, the gas flowing in the autoclave is air, and the thermal properties of the mold and air are shown in Table 1. The autoclave has a diameter of 2500mm and a length of 7000mm.

Table 1 Thermal performance parameters of materials

The surface temperature cloud diagrams of the four groups of stepped non-equal-thickness forming plates are shown in Figure 5. The 400mm and 600mm groups have large temperature fluctuations in the thickness transition area, while the 450mm and 500mm groups have relatively small fluctuations in the transition area. The reason may be related to the change of boundary layer thickness. After many experiments, the applicant has determined that the effect is best when the length of the thicker part of the formed plate accounts for 30% to 35% of the total length of the formed plate.

In addition, experiments have shown that when the thickness of the thicker part of the forming plate 1 is 1.5 to 3 times the thickness of the thinner part of the forming plate 1, the temperature fluctuation in the transition region is also small.

Embodiment two

In this implementation, the parameters of the mold and the autoclave are all the same as in the first embodiment. The difference between the present embodiment and the first embodiment is that as shown in Figure 4, in order to reduce the sudden change of the thickness of the stepped forming plate 1 on the Due to the influence of the temperature in the transition area, a trapezoidal non-equal thickness plate is adopted, that is, in this embodiment, a section of the forming plate 1 near the air inlet of the autoclave is trapezoidal (that is, partly trapezoidal), and the forming plate 1 is close to the hot press. A section of the air outlet of the tank has the same thickness as the thinnest part of the trapezoidal plate.

In this embodiment, the thickness of the low-temperature area of the trapezoidal non-equal-thickness forming plate is changed to 10 mm, and the thickness of the high-temperature area decreases linearly (linearly) from 20 mm to 10 mm. In this embodiment, for six sets of trapezoidal plates with non-equal thickness, the distances from the windward end are 600mm, 700mm, 800mm, 900mm, 1000mm and 1100mm respectively. At the end of the heating stage of the six sets of trapezoidal non-equal-thickness forming plates, the surface temperature distribution of the forming plates is shown in Figure 6. It can be seen from Figure 6 that compared with the stepped shaped plate, the thickness of the high temperature area of the trapezoidal shaped plate is smaller, and the resistance to heat conduction becomes smaller, making the temperature difficult to be uniform. Therefore, increasing the length of the trapezoidal section makes the thickness of the high temperature area close to the windward However, if the distance is too large, the thickness of the low temperature region will increase, resulting in a lower temperature in the low temperature region.

Preferably, the length of the trapezoidal part of the forming plate accounts for 50% to 70% of the total length of the forming plate, which can ensure that the thermal resistance in the high temperature area will not become smaller due to the trapezoidal thickness, and can also ensure that the low temperature area will not Because the thickness of the trapezoid becomes larger, the thickness distribution on both sides is well balanced.

The present invention is not limited to the specific technical solutions described in the above embodiments. Besides the above embodiments, the present invention can also have other implementation modes. All technical solutions formed by equivalent replacement are within the scope of protection required by the present invention.

Claims (5)

1. a kind of autoclave frame-type composite material shaping mould, including framework type base and the shaping that is fixed on base Plate；It is characterized in that：The profiled sheeting is less than or equal to the air inlet from autoclave from the thickness of the air inlet distant place of autoclave Thickness nearby, and the profiled sheeting is more than the air inlet farthest of autoclave from the air inlet thickness most nearby of autoclave Thickness.

2. autoclave according to claim 1 frame-type composite material shaping mould, it is characterised in that：The profiled sheeting Stepped in two ranks, the length of wherein profiled sheeting thicker portion is the 25% ~ 50% of profiled sheeting total length.

3. autoclave according to claim 2 frame-type composite material shaping mould, it is characterised in that：The profiled sheeting The thickness of thicker portion is 1.5 ~ 3 times of the thickness of profiled sheeting thinner part.

4. autoclave according to claim 1 frame-type composite material shaping mould, it is characterised in that：The profiled sheeting Close to one section of trapezoidal, the one section of thickness one of the profiled sheeting at the air outlet of autoclave of the air inlet of autoclave Cause.

5. autoclave according to claim 4 frame-type composite material shaping mould, it is characterised in that：The profiled sheeting The length of trapezoidal part is the 50% ~ 70% of profiled sheeting total length.