RU2738650C1 - Method of moulding articles reinforced with continuous fibre carcass - Google Patents

Abstract

FIELD: foundry.

SUBSTANCE: invention relates to foundry. Method of moulding thermoplastic articles comprises preset arrangement, density and orientation of continuous fibre inside casting, wherein the continuous fibre frame and the thermoplastic preform are pre-synthesized by an additive method so that they form an integral whole. Surfaces and edges of the preforms serve as a fastener or a supporting element when the synthesized article is fixed in the working volume of the mould prior to the beginning of the moulding process. Then the entire working volume of the mould is filled with liquid thermoplastic or composite material injected into the mould. Thermoplastic material of the preform is combined with the matrix material of the thermoplastic composition or with a thermoplastic or composite material used in injection moulding. Besides, during moulding thermoplastic preform is sintered or completely alloyed with thermoplastic or composite material.

EFFECT: technical result is prevention of frame displacement during injection moulding by injection method.

1 cl, 14 dwg

Description

The invention relates to the field of foundry, and more precisely to injection molding of plastics. This method of molding plastics consists in injection under pressure into the working volume formed by the tightened parts of the mold, a liquid polymer material that fills the entire working volume, and then hardens, forms a casting and is removed from the machine.

The raw material, which is a polymer material, is loaded into the hopper of the injection molding machine. In this case, the polymer material can be presented both in the form of thermoplastic granules and in the form of thermosetting powders or thermoplastic elastomers.

The raw material comes from the hopper to the heated zone, through which it is transported to the gate. Heating is carried out to the temperature required to melt the polymer material. Thus, during transportation, the polymer material melts and homogenizes.

As the required volume of liquid polymer material accumulates, the latter is injected under high pressure (100-200 MPa) through the gate into the working volume, filling it.

The liquid polymer material that has filled the working volume is held in it for some time under pressure and hardens. The material is cooled down by heat exchange with the cooled mold.

As a result, a casting is formed, which is removed from the working volume after opening the mold.

To increase the strength characteristics of the castings, polymer materials filled with abrasives or short fibers can be used as raw materials. Various spinning techniques using continuous fiber composites have become widespread.

The state of the art discloses a method of forming chopped fiber-reinforced articles by means of injection of material under pressure. This method of molding products is described in patents US20080226892A1, publ. 18.09.2008. - "Fiber-filled molded articles" and US6558603B2 publ. 06.05.2003. - "Method of and apparatus for producing injection molded parts reinforced with long fibers".

This method is characterized in that a liquid polymeric material containing chopped fiber is injected into the mold. Chopped fiber can be added to the liquid polymer material through an additional hopper in the auger zone. In another case, raw material filled with chopped fiber is loaded into the hopper of the injection molding machine.

The disadvantage of this method is the lower mechanical properties of castings in comparison with methods where frames based on continuous fibers are used to strengthen the structure.

In addition, the disadvantage of this method is that the distribution of fiber in the volume of the product is random and uneven. The possibility of purposeful strengthening of individual units of the product is not presented.

There is also known a method of molding articles reinforced with a grating or sheets of continuous fiber by means of injection of material under pressure. This method is called RTM (resin transfer molding) and is described in patents US4891176, publ. 02.01.1990. - "Resin transfer molding process" and US5464337, publ. 11/07/1995. - "Resin transfer molding system".

This method differs in that at the first stage a dry reinforcing filler is prepared, which is a lattice or sheet of continuous fiber, for example, glass cloth. The reinforcing material is laid between the matrix and the punch, which are rigidly pulled together and give the sheet (s) the required shape. The required shape can be given to the reinforcing material before being placed in the mold. Then, a polyester resin is injected into the closed mold under pressure and at a predetermined temperature, which acts as a binder matrix. The impregnation process continues until the binder fills the mold. After curing, the finished product is removed from the mold.

The disadvantage of this method is the limited shape and size of the product due to the use of sheet reinforcing materials.

In addition, the disadvantages of this method are the complexity and multistage of its implementation, the high duration of the process, the need for a special binding material, the need for additional mechanical surface treatment.

In addition, the disadvantage of this method is the impossibility of purposefully setting the density and orientation of the reinforcing fibers in individual nodes of the finished product.

There is also known a method of forming articles reinforced with a lattice or sheets of continuous fibers by pressing. This method is known from patent US20100239856A1, publ. 23.10.2010. - "Continuous fiber reinforced thermoplastic parts with in-situ molded features".

This method differs in that at the first stage a thermoplastic composite material is prepared, which is a lattice or sheet of continuous fiber with a thermoplastic matrix. The composite material is placed in the mold. With the help of a punch, which is rigidly pulled together with the forming part, high pressure is applied to the composite material. At the same time, the material is heated. Thus, with the help of the temperature effect and the applied pressure, the casting is given the required shape. After curing, the finished product is removed from the mold.

The disadvantage of this method is the limited shape and size of the product due to the use of sheet composite materials.

In addition, the disadvantage of this method is the need for additional machining of the finished product.

In addition, the disadvantage of this method is the impossibility of setting the orientation and density of the reinforcing fibers in separate nodes of the finished product.

There is also known a method of forming articles reinforced with a continuous fiber frame by pressing. This method is known from patent US20180345605A1, publ. 6.11.2018. - "Aligned fiber reinforced molding".

This method differs in that the continuous fiber carcass is formed before the forming process in the form of rigid elements of a given shape. The frame, therefore, can consist of a plurality of individual elements, and of one element. These elements are formed from continuous fiber-based thermoplastic compositions obtained, for example, by pultrusion. The previously obtained rigid thread of the thermoplastic composition is heated to the glass transition temperature and is bent. Elements of a given shape, obtained by this method, in the amount of one or several pieces are installed in a mold. After that, the product is molded by pressing at a given temperature. The casting with the continuous fiber skeleton is then removed from the mold.

The disadvantage of this method is that the possibilities for fixing the frame elements are limited, and the supporting elements made of thermoplastic are manufactured separately. The lack of connection between the supporting elements and the frame elements does not ensure reliable fastening of the latter. As a result, the arrangement of the framework in a specific segment of the product is difficult, and it is also possible for the elements of the framework to be displaced during the molding process.

In addition, the disadvantage of this method is the narrow variation in the shape of the continuous fiber carcass, limited by the possibilities of bending the previously prepared rigid filament of the thermoplastic composition.

In addition, the disadvantage of this method is the use of a previously prepared homogeneous rigid thread of a thermoplastic composition as a frame material, which does not allow to fully set the density and orientation of continuous fibers in individual casting nodes.

In addition, the disadvantage of this method is the separate production of the frame and the supporting element, which significantly limits the possibilities of their pairing with each other, which leads to a narrowing of the possibilities of fixing the frame inside the mold.

In addition, the disadvantage of this method is the complexity and multi-stage implementation.

There is also known a method of molding products reinforced with continuous fiber by means of material injection under pressure or pressing. This method is known from patent US8617336, publ. 11/31/2013. - "Method for molding continuous fiber prepreg part".

This method is characterized in that continuous fiber and thermoplastic matrix strips are used to reinforce the molded article and are wound around a plurality of rods. The rods are used to stretch the fiber and then fix it with clamping devices and ultrasonic welding. Next, the resulting blank is placed in a mold. The molding step is carried out by pressing or injection of material under pressure.

The disadvantage of this method is the narrow variation in the shape of the continuous fiber carcass, limited by the need to wind the tape on the rods.

In addition, the disadvantage of this method is that after bonding and welding of the strips, they retain their mobility, which has a negative effect on the mechanical properties of the casting. In general, the mobility of the entire structure is maintained within the mold.

In addition, the disadvantage of this method is that the ability to set the orientation and density of continuous fibers in individual nodes of the finished product is limited by the features of the winding process.

The closest analogue to the claimed invention is a method of molding articles from thermoplastics reinforced with a continuous fiber carcass by means of casting at normal pressure, pressing or injection under high pressure. In this case, a continuous fiber frame is made by an additive method. Such a method for forming articles from thermoplastics reinforced with a continuous fiber frame is known from patent WO2017123726A1, publ. 20.07.2017. - "Embedding 3d printed fiber reinforcement in molded articles".

This method differs in that the continuous fiber frame is made on a 3D printer. Printing is carried out using a continuous fiber-based thermoplastic composition. After the printing process is completed, the composite material part is placed in a mold. The mold can also contain several of these parts, combined in advance. After that, the liquid polymer material is fed into the mold. In this case, the polymer material can be filled with short fibers, or additional composite sheets can be placed in the mold together with the part made of the composite material. The molding process can be carried out by pressing or injection under pressure, or casting at normal pressure. In this case, a piece of continuous fiber can be placed in a mold on a polymer blank, which is manufactured separately and is a separate piece that acts as a fastener or a supporting element.

The disadvantage of this method is that the lack of connection between the continuous fiber framework and the supporting elements does not allow for a rigid and reliable fastening of the continuous fiber framework during the forming process. This can lead to displacement of the carcass during the forming process, regardless of whether forming at normal pressure or at high pressure. The possibility of displacement of the frame not only reduces the repeatability of this technology, but also negatively affects the mechanical properties of the product.

In addition, the disadvantage of this method is the separate production of the frame and the supporting element, which significantly limits the possibilities of their pairing with each other, which leads to a narrowing of the possibilities of fixing the frame inside the mold.

In addition, the disadvantage of this method is the complexity and multistage of its implementation due to the separate production of the frame and supporting elements.

The technical result of the proposed solution consists in a method of injection molding of thermoplastic products reinforced with a frame of a given shape and density of continuous fiber (carbon fiber, glass fiber, nylon fiber, metal wire, etc.), which is rigidly fixed inside the working volume of the mold before work, which eliminates the displacement of the frame during injection molding and allows you to ignore the fasteners, which are automatically created preform from a thermoplastic material, when developing the casting model, as well as parts of the mold.

The technical result is achieved due to the fact that the frame made of continuous fiber and the preform from the thermoplastic material are synthesized by the additive method in the course of a single process so that the frame is fully or partially located in the volume of the preform and makes a single whole with it. The additive manufacturing process can be carried out using a 3D printer. The product is synthesized layer by layer in such a way that both thermoplastic material and continuous fiber can be laid in one layer. For this, a twin extruder or a pair of extruders is used, extruding one of the two materials in turn. If for the preform the main material is thermoplastic raw material, then for the frame, the raw material is a thermoplastic composition based on continuous fiber. Carbon fiber, glass fiber, nylon fiber, metal wire, etc. can be used as a fiber material.

The product is synthesized on the basis of pre-developed digital models of the frame and preform, based on the geometric requirements of the casting and parts of the mold.

In the process of designing a model of a continuous fiber skeleton, the location, density and orientation of the continuous fiber within the future casting are determined.

In the process of designing a preform model, the method of fixing the synthesized product in the working volume of the mold is determined. The relative position of the continuous fiber frame and the preform in the volume of the synthesized product is determined. The preform thus acts as a support or fastener for the continuous fiber framework. The preform is designed in such a way that, after fixing in the working volume of the mold, ensure the immobility of the continuous fiber frame before and during injection molding, ensure the specified location, density and orientation of the continuous fiber in the casting, and ensure that the entire working volume of the mold is filled liquid thermoplastic material during molding.

The material of the preform is a thermoplastic material, which is combined either with the matrix material of the thermoplastic composition, or with the thermoplastic or composite material used in injection molding.

The synthesized product is placed in the working volume of the mold, after which the mold is closed and the molding process begins, during which the working volume of the mold is filled with a liquid thermoplastic or composite material under pressure.

The fixation of the synthesized product is carried out by means of parts of the preform, its edges and surfaces abutting against the surface of the working volume of the mold. It is also possible to clamp the preform parts between the mold parts as they are closed.

During the molding process, the preform material is sintered or completely fused with a liquid thermoplastic or composite material injected into the mold. Due to this fact, it is not required to take into account the parts of the preform that are necessary for fixing the synthesized product in the working volume of the mold when designing the casting model or parts of the mold.

As a result of the described process, a casting is achieved by injection molding of thermoplastics under pressure, reinforced with continuous fiber with a given location, density and orientation within the casting.

The invention is illustrated by drawings of FIG. 1-13:

in fig. 1 shows an example of a continuous fiber scaffold synthesized by the additive method. The frame is made in the form of a solid piece of variable thickness. The frame can be made in the form of several elements, an example of which is shown in figure 5;

in fig. 2 shows an example of a continuous fiber scaffold and a thermoplastic preform made in a single process by the additive method and constituting a single whole;

in fig. 3 shows an example of a synthesized product in section shown in FIG. 2. This drawing illustrates the possible relationship between the continuous fiber scaffold and the preform relative to each other;

in fig. 4 shows an example of a synthesized product in section shown in FIG. This drawing illustrates the possible relationship between the continuous fiber scaffold and the preform relative to each other from a different perspective. Laying of continuous fiber on a previously synthesized thermoplastic layer is allowed;

in fig. 5 shows a second example of a synthesized product made in a single process by the additive method. The matrix of the thermoplastic composition allows the synthesis of a continuous fiber scaffold and a thermoplastic preform connected along the boundary surfaces. The synthesis of such a product involves the alternate laying of thermoplastic material and continuous fiber in one layer of the product;

in fig. 6a shows a method for securing a synthesized article from the first example. With the help of the preform ribs, the synthesized product is fixed between the walls of the mold;

in fig. 6b shows a method for securing a synthesized product from the first example. With the help of the lower surface of the preform, the synthesized product is placed on the bottom of the mold. The fixing of the preform can also take place without support on the bottom of the mold;

in fig. 7 shows the stage of preparing the injection molding machine for start-up. The mold shrinks. In its counterpart there is an opening representing channels for injection of liquid polymeric material;

in fig. 8 shows an example of a casting after the molding process is completed and removed from the mold. During molding, the thermoplastic material from which the preform was synthesized is sintered or completely fused with the thermoplastic or composite material used in the injection molding process;

in fig. 9 shows a sectional view of the casting. The continuous fiber frame is in a predetermined position in the volume of the casting. The preform ensured its reliable fixing before and during the molding process;

in fig. 10 shows an example of fixing the synthesized product shown in FIG. 5. Molds of this type are quite common and can be located both in vertical and in any other position. The synthesized product is installed on the forming protrusion of the mold and fixed on it with the help of the preform edges;

in fig. 11 shows the stage of preparing the injection molding machine for launch. The mold shrinks. In its counterpart there is a hole that represents channels for injection of a liquid thermoplastic or composite material. The drawing is given in section;

in fig. 12 shows an example of a casting after the completion of the molding process and its removal from the mold. During molding, the thermoplastic material from which the preform was synthesized is sintered or completely fused with the thermoplastic or composite material used in the injection molding process;

in fig. 13 shows a sectional view of the casting. The elements of the continuous fiber frame are in a given position in the volume of the casting. The preform provided a secure fixation of the frame elements before and during the molding process.

A method of injection molding of thermoplastic products, characterized by a given arrangement, density and orientation of continuous fibers inside the casting 1, while the skeleton 2 of continuous fiber and the preform 3 of thermoplastic material are preliminarily synthesized by the additive method in the course of a single process so that the skeleton of continuous fiber is completely or is partially in the volume of the preform and forms a single whole with it, while the surfaces and edges of the preform play the role of a fastener or a supporting element when fixing the synthesized product 4 in the working volume of the mold 5 before the start of the molding process, and so that they prevent the frame from displacement from the continuous fibers in the process of injection molding after closing the mold, provide filling of the entire working volume of the mold with a liquid thermoplastic or composite material through the sprue 6, injected into the mold, provide a given location, density and orientation continuous fiber inside the casting after the completion of the molding process with further opening of the mold, while the material for making the frame from continuous fiber by the additive method is a thermoplastic composition based on continuous fiber, while the thermoplastic material of the preform is combined with the matrix material of the thermoplastic composition, or with the thermoplastic or a composite material used in the injection molding process, while in the molding process the thermoplastic preform is sintered or completely fused with the thermoplastic or composite material used in the injection molding process, so that parts of the preform that are necessary for fixing the synthesized product in the working volume of the mold when designing the casting model or parts of the mold.

The method is carried out as follows:

1. For the manufacture of a product by injection molding, a mold is created.

2. In accordance with the required geometry of the product, a digital model of the continuous fiber skeleton is created.

3. In accordance with the geometry of the mold and taking into account the geometry of the digital model of the frame, a digital model of the preform is created. In this case, the frame must be fully or partially inside the preform.

4. Determine the type of thermoplastic or composite material that will be used for injection molding during the injection molding process.

5. The type of fiber that will be used for making the frame is determined.

6. The type of thermoplastic that will be used to create the preform is determined. The preform material must be combined with a continuous fiber thermoplastic matrix material, or with a thermoplastic or composite material that will be used as a raw material for molding.

7. The framework and preform are synthesized by the additive method, based on the prepared digital models, in the course of a single process. In this case, the frame is fully or partially in the volume of the preform and forms a single whole with it.

8. The synthesized product is fixed in the working volume of the mold before the start of the molding process. In this case, the ribs and surfaces of the preform act as support elements or fasteners for the continuous fiber framework. The ribs and surfaces of the preform allow the continuous fiber frame to be rigidly fixed in the working volume of the mold. The ribs and surfaces of the preform use the inner surfaces of the mold as support.

9. The mold is closed.

10. The raw material, which is a thermoplastic or composite material selected for casting, enters the heated zone, through which it is transported to the gate. Heating is carried out to the temperature required to melt the thermoplastic material.

11. Injection of a liquid thermoplastic or composite mass under pressure into the cavity of the mold is carried out.

12. Liquid thermoplastic or composite mass completely fills the working volume of the mold, surrounding the continuous fiber carcass and preform.

13. There is a complete or partial melting of the preform material.

14. Cooling and hardening of the finished product under pressure occurs.

15. The preform material is sintered or completely fused with the thermoplastic or composite material used in the injection molding process.

16. The mold is opened and the casting is removed, reinforced with a continuous fiber frame with a given arrangement, density and orientation of fibers in the volume of the casting.

Claims (1)

A method of injection molding of thermoplastic products, including a predetermined arrangement, density and orientation of continuous fibers inside the casting, while the continuous fiber scaffold and the thermoplastic material preform are preliminarily synthesized by the additive method in a single process so that the continuous fiber scaffold is completely or partially in the volume of the preform and forms a single whole with it, while the surfaces and edges of the preform act as a fastener or a supporting element when fixing the synthesized product in the working volume of the mold before the start of the molding process, and so that they prevent the displacement of the continuous fiber frame during the molding process by the injection method after closing the mold, provide filling of the entire working volume of the mold with liquid thermoplastic or composite material injected into the mold, provide the specified location, density and orientation of the continuous fiber inside casting after the completion of the molding process with further opening of the mold, while the material for making the frame from continuous fiber by the additive method is a thermoplastic composition based on continuous fiber, while the thermoplastic material of the preform is combined with the matrix material of the thermoplastic composition or with the thermoplastic or composite material used in the injection molding process, while in the molding process the thermoplastic preform is sintered or completely fused with a thermoplastic or composite material used in the injection molding process so that parts of the preform that are necessary for fixing the synthesized product in the working the volume of the mold when designing the casting model or parts of the mold.

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