CN112406140A

CN112406140A - Molding method of die-pressing heat setting type polyurethane foam

Info

Publication number: CN112406140A
Application number: CN202010961279.5A
Authority: CN
Inventors: 王红丽; 路建军; 方旭东; 毕向军
Original assignee: Aerospace Research Institute of Materials and Processing Technology
Current assignee: Aerospace Research Institute of Materials and Processing Technology
Priority date: 2020-09-14
Filing date: 2020-09-14
Publication date: 2021-02-26
Anticipated expiration: 2040-09-14
Also published as: CN112406140B

Abstract

The invention provides a molding method of molded thermosetting polyurethane foam, belonging to the field of molding methods of composite material parts, firstly preliminarily polishing the surface of the polyurethane foam, then placing the polyurethane foam into a cavity of a molding die for thermoforming, and polishing the surface of the polyurethane foam again after demolding to make the surface rough; and wrapping the composite material skin outside the rough polished polyurethane foam, and putting the polyurethane foam skin into the die cavity again for hot forming to obtain the final polyurethane foam skin sandwich part. The method utilizes the good extension characteristic of polyurethane foam at high temperature under the condition of less product development quantity, and uses a forming die of the product to carry out heat setting forming on the foam instead of machine addition forming.

Description

Molding method of die-pressing heat setting type polyurethane foam

Technical Field

The invention belongs to the field of composite material part forming methods, and particularly relates to a forming method of die pressing heat setting type polyurethane foam.

Background

The typical structure form of the composite material product is a sandwich structure form (see figure 1) in which composite material skins and foams are co-cured, and the structure form is generally that prepreg skins are cut into sample plates, then the sample plates are paved on the upper airfoil surface and the lower airfoil surface of a forming mold layer by layer, then the prepreg skins are bonded with foam core materials through structural adhesives, and the foam core materials are buckled on the mold and then heated, pressurized and cured on a press to form the composite material product. The polyurethane foam core material can be precisely processed in a foam shape through a machining mode, and the machining cost is high.

When the product is in the initial stage of development and the quantity of development is less, in order to reduce the machining cost of foam, the precise shape of the foam core layer can be cured and formed in a forming die of the product in a heating, pressurizing and other modes by utilizing the characteristic that the polyurethane foam board has good ductility at high temperature and the structural characteristics of a composite material product. The shape of the formed foam is slightly larger than the theoretical shape, which is just a compression allowance left when the foam is heated, pressurized and cured in a secondary mold feeding process, and provides internal pressure for the compaction of the prepreg skin, so that the internal pressure and the external pressure applied by a press act together to compact the prepreg skin.

Disclosure of Invention

The invention aims to provide a molding method of die pressing heat setting type polyurethane foam, which utilizes the good extension characteristic of the polyurethane foam at high temperature under the condition of less product development quantity, uses a molding die of a product to heat setting and molding the foam, and replaces machine adding molding.

In order to achieve the purpose, the invention adopts the technical scheme that:

a molding method of die pressing heat setting type polyurethane foam is based on a molding die, the die comprises an upper female die, a lower female die and a combined edge strip, and the upper female die, the lower female die and the combined edge strip can enclose a cavity for heat molding of the polyurethane foam; the method comprises the following steps:

1) primarily polishing a polyurethane foam plate, wherein the vertical thickness of the polished polyurethane foam is greater than the thickness of a mold cavity, the transverse maximum profile of the polished polyurethane foam is less than or equal to the transverse maximum profile of the mold cavity, the vertical direction is the direction of an upper female mold and a lower female mold, and the transverse direction is the direction perpendicular to the vertical direction;

2) putting the polished polyurethane foam into a cavity defined by a lower female die and a combined edge strip, buckling an upper female die with the lower female die, heating through an upper press, then preserving heat, pressurizing to enable the upper female die and the lower female die to be in place for mold combination, continuing to preserve heat, cooling, and then demoulding through a lower press;

3) polishing the surface of the demolded polyurethane foam to make the surface rough;

4) and wrapping the composite material skin outside the rough polished polyurethane foam, putting the composite material skin into a mold cavity again for mold assembly, heating and pressurizing to realize bonding and curing, and obtaining the final skin sandwich part of the polyurethane foam.

Further, the forming die is made of steel.

Further, primarily polishing the polyurethane foam plate according to a section sample plate, wherein the shape and the size of the section sample plate are similar to or the same as those of the maximum section of the die cavity (or a final molded product), and controlling the weight of the polyurethane foam in the polishing process so that the polished weight is larger than the weight theoretically calculated according to the size of the die cavity.

Further, the thickness of the primarily polished polyurethane foam is 1-2 mm larger than the vertical thickness of the mold cavity.

Further, heating the mixture to 120-130 ℃ by using a pressing machine, and then preserving heat.

Further, the heat preservation time is not less than 2 h.

Further, the temperature is reduced to below 60 ℃.

Compared with the prior art, the invention has the beneficial effects that: for the skin sandwich part of polyurethane foam, because of the material characteristics of polyurethane foam, the traditional method is to use the machining form for forming, the cost for forming the part by adopting the traditional method is very high in the early development stage of the product, and the product is not applicable.

Drawings

FIG. 1 is a schematic diagram of a typical polyurethane foam core sandwich.

Fig. 2 is a schematic structural view of a forming mold.

FIG. 3 is a schematic view of a polyurethane foam primary sanding.

Fig. 4 is a schematic flow chart of heat-setting of polyurethane foam by the forming mold.

FIG. 5 is a schematic view of the polyurethane foam skin sandwich component heat setting.

Detailed Description

In order to make the technical solution of the present invention more comprehensible, embodiments accompanied with figures are described in detail below.

Fig. 2 is a schematic structural diagram of a forming mold, which includes an upper female mold 1, a lower female mold 2, and a combined edge 3, which enclose a cavity, the shape and size of which are determined according to the shape and size of a final product to be obtained, that is, according to the shape and size of the product design, all of which are made of steel, and are formed by machining.

The embodiment discloses a molding method of mold pressing heat setting type polyurethane foam, which uses the molding mold to heat set the accurate shape of core material polyurethane foam and comprises the following steps:

1) the polyurethane foam board is primarily polished according to a section sample plate, the polished outline is larger than 1-2 mm (slightly smaller and neglectable) of the product design size thickness on the wing profile thickness, the transverse length and width maximum size are smaller than or equal to the product outline size, the product design size is consistent with the size of a cavity of a forming die, the polishing degree can be controlled according to the foam weight requirement, the polished weight is larger than the weight theoretically calculated according to the size of the die cavity, the filling and compression in the die are ensured, and the situation that the foam is not filled or is just filled in the die cavity is avoided. As shown in fig. 3.

2) Putting the polyurethane foam piece subjected to primary polishing into a cavity formed by a lower female die 2 and a combined edge 3 of a die, buckling an upper female die 1 and the lower female die 2, heating by an upper press, pressurizing after the temperature reaches 120-130 ℃, enabling the upper female die 1 and the lower female die 2 to be matched in place, keeping the temperature for 2 hours, cooling to below 60 ℃, and then demoulding by a pressing machine. The whole process is shown in fig. 4.

3) The polyurethane foam after demoulding has accurate appearance and smooth surface, and needs to be integrally polished before the next combined bonding procedure, so that the surface is rough and is beneficial to bonding.

4) Wrapping the composite material skin outside the ground polyurethane foam, putting the composite material skin into a forming die again for thermoforming, and pressurizing, heating, bonding and curing the composite material skin as shown in figure 5, wherein the heating temperature is determined according to the curing temperature of the skin prepreg, so as to obtain the final skin sandwich part of the polyurethane foam (shown in figure 1).

The above embodiments are only intended to illustrate the technical solution of the present invention, but not to limit it, and a person skilled in the art can modify the technical solution of the present invention or substitute it with an equivalent, and the protection scope of the present invention is subject to the claims.

Claims

1. A molding method of die pressing heat setting type polyurethane foam is characterized in that based on a molding die, the molding die comprises an upper female die, a lower female die and a combined edge strip, wherein the upper female die, the lower female die and the combined edge strip can enclose a cavity for heat molding of the polyurethane foam; the method comprises the following steps:

1) primarily polishing polyurethane foam, wherein the vertical thickness of the polished polyurethane foam is greater than the thickness of a mold cavity, the transverse maximum profile of the polished polyurethane foam is less than or equal to the transverse maximum profile of the mold cavity, the vertical direction is the direction of an upper female mold and a lower female mold, and the transverse direction is the direction perpendicular to the vertical direction;

4) and wrapping the composite material skin outside the rough polished polyurethane foam, putting the composite material skin into a mold cavity again for mold assembly, and heating and pressurizing to realize bonding and curing to obtain the final skin sandwich part of the polyurethane foam.

2. The method of claim 1, wherein the forming die is formed of steel.

3. The method as set forth in claim 1, wherein the polyurethane foam sheet is preliminarily ground in a section template having the same shape and size as the maximum section of the mold cavity, and the weight of the polyurethane foam is controlled during the grinding so that the ground weight is greater than the theoretically calculated weight for the size of the mold cavity.

4. The method of claim 1, wherein the thickness of the polyurethane foam after the initial sanding is 1 to 2mm greater than the vertical thickness of the mold cavity.

5. The method of claim 1, wherein the upper press is heated to a temperature of 120-130 ℃ and then kept warm.

6. The method of claim 1 or 5, wherein the incubation is not less than 2 hours.

7. The method of claim 1, wherein the temperature is reduced to below 60 ℃.

8. The method of claim 1, wherein the post-clamp temperature heating temperature in step 4) is determined based on the curing temperature of the prepreg of the skin.