RU2722494C1 - Method of striping of volume preforms - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the technology of making preforms of articles from polymer composite materials (PCM) - workpieces based on reinforcing fibres. Invention can be used in basic industries, such as aircraft engineering, space industry, power engineering, shipbuilding and automotive industry, for production of parts and their components from PCM, which can withstand extreme mechanical loads. Technical result of disclosed solution consists in elimination of deformation and damages of main reinforcing thread, as well as substrate due to non-use of sewing fixing thread, according to the proposed scheme of layer-by-layer strip of volumetric preforms and selection of substrate material, which leads to broader technological capabilities of the process of making fibrous blanks, and also selectively affects strength properties of target articles and their components from PCM. Proposed method consists in laying and fixing of main reinforcing thread on fixed substrate with subsequent build-up of layers of three-dimensional structure according to TFP technology on programmed embroidery machine. Fixation of the main thread is carried out by needle piercing with the substrate thread on the basis of the water-washing nonwoven with the clamp of the formed loop due to friction with the substrate material and further movement in the rectilinear direction of the stowing head with the needle to the next point specified by the program. In case of curved direction of laying in bending point or maximum stress, main thread loop is fixed additionally with suture filament by means of second needle operating in automatic mode synchronously with first, wherein in case of layers up to preset thickness of preform the perimeter of trajectory of every next layer of the main thread should exceed the previous one. Reinforcing threads used are carbon fibres, including in the form of roving, and the aramide fibres are used as the fixing threads.

EFFECT: proposed scheme of layers laying allows reinforcing preforms as straight and level as possible - without bends and waves, with threads, which allows to achieve the best characteristics of reinforcing filler when testing final products for bending and stretching.

4 cl, 6 dwg

Description

The invention relates to the field of manufacturing preforms of products from polymer composite materials (PCM) - blanks based on reinforcing fibers. The invention can be used in basic industries, such as aircraft, space, energy, shipbuilding and automotive for the production of parts and their components from PCM, which can withstand extreme mechanical loads.

Reinforced PCM products are made on the basis of a preform preform by laying the required number of layers of reinforcing fibers, placing the preform in a snap, impregnation with a binder based on polymers and / or resins and subsequent curing. Moreover, the fixed directivity of the reinforcing fibers has a decisive influence on the stiffness and strength of the target product.

One of the possible ways to ensure the requirements for the orientation of the fibers in accordance with the power load on the product as a whole and their structural elements is TFP-technology (Tailored Fiber Placement - directional fiber laying). TFP-technology includes laying fiber layers-strands ("bundles" or "bundles" of fibers), which, in turn, are formed from many separate reinforcing fibers that run parallel to each other along the desired, usually curved, trajectory, and their fastening with a fixing thread on the base layer of the workpiece. Typically, TFP technology is implemented using universal sewing or embroidery machines with numerical control (CNC). The consequence of the indicated mechanical reinforcement is the directional orientation of the individual fibrous strands, which optimally corresponds to the direction of the load acting on the product in working condition.

RU 2401740 describes a method for manufacturing a single or multilayer fibrous preform according to TFP technology. The method of forming a fiber preform preform includes the following operations: laying and securing the fiber strands on a flexible and elastic base by means of a fixing thread passed through the sewing head of a CNC sewing or embroidery machine; introducing the fixing thread into the base by means of a needle mounted on the sewing head, and as a result of introducing the fixing thread into the base, the formed loops of the fixing threads are tightly held in the base; removing the formed fibrous preform from the base. In order to form a finished composite component, after separation from the base, the fiber preform is cured using the well-known RTM technology ("Resin Transfer Molding" - "Transfer Molding Plastics"). To this end, the fiber preform is saturated or impregnated with a curable polymeric material, for example, polyester resin, epoxy resin or the like.

RU 2388599 describes a device by which, using TFP technology, it is possible to produce a fiber preform that has essentially any given surface geometry, in particular, different from a flat shape. In this case, the reinforcing fibers in the preform are substantially oriented according to the action of the load due to the fact that the sewing head and / or guiding means can be positioned in the spatial direction z.

US Pat. No. 7,942,993 proposes a method by which, using TFP technology, it is possible to produce preforms from a multilayer adapted fiber of any thickness. For this, reinforcing fibers are sewn to the support with fixing threads, as a result of which a predetermined preform structure is formed of reinforcing fibers. Then, the fixing threads in the fiber preform are chemically dissolved or thermally melted, and thereby the preform is separated from the carrier woven base.

In the application US 2010/0126652 A1 and US 2009/0229761 A1 describes a method and, accordingly, a device for the manufacture of fiber preforms, by which it is possible to fulfill the requirement of orientation of the fibers in the manufactured structural element in accordance with the load. In this case, the TFP-technology is applied, according to which the threads or bundles of fibers are laid out in a direction along an arbitrary force flow acting on the finished structural element, and are pre-fixed by means of fixing threads. For this, sewing and knitting machines with CNC are used, which are used in the textile industry.

It should be noted that the known methods of manufacturing fibrous preform preforms with complex three-dimensional structures are always technically laborious and expensive.

The patent RU 2583017 describes one of the possible ways of manufacturing fiber preforms, which is associated with the use of so-called non-woven materials with a multiaxial arrangement of fibers. These materials are understood to mean constructions of several thread layers located on top of each other, and these layers consist of a plurality of reinforcing threads arranged parallel to each other. The yarn layers located on one another can be connected to each other and fixed relative to each other by a plurality of adjacent or parallel to one another and forming loops of sewing or knitting threads, so that a nonwoven fabric with a multiaxial arrangement of fibers is thereby stabilized. In the multilayer nonwoven fabric of the present invention, reinforcing fibers or threads commonly used for the production of reinforced composite materials can be used as reinforcing fibers. Preferably, in the case of a complex reinforcing yarn, this is a carbon fiber yarn, as well as fiberglass or aramid yarn, or an elongated UHMW polyethylene yarn.

In the patent of the Russian Federation No. 2386534 it is indicated that technical reinforcing textile materials, such as aramid fibers, glass fibers or carbon fibers, can be used as fixing fibers. It is also noted that in order to ensure certain technological characteristics, yarns that do not have reinforcing properties, for example polyester yarns or the like, that is, yarns with elasticity, but capable of withstanding only small mechanical loads in the subsequent composite element, can be used, since in the region of the fixing yarns waves and / or gaps may appear, and microcracks can occur in the matrix region. To improve the mechanical properties of composite components, the method of using fixing threads, which can be dissolved, in particular, using TFP technology, is also known. One of the effects obtained from the use of fixing threads that dissolve at the end of the crosslinking operation is to reduce the waves of reinforcing fibers that are created by the fixing threads. However, according to the authors, soluble fixing threads are only conditionally suitable for TFP technology or other methods of crosslinking, since they do not have the required mechanical properties of conventional fixing threads, and therefore, tearing of the threads, peeling of the threads, separable ends, etc. may appear.

In the patent of the Russian Federation No. 2562490 it is noted that the disadvantage of the preform structures similar to those described above is the relatively high proportion of the material, which does not consist of reinforcing fibers and thus does not contribute to the strength of the resulting structural element. Matrix material refers to the total number of reinforcing fibers and the base material, so that relative to the volume of the structural element, a lower content of reinforcing fibers in the structural element and, accordingly, lower strength of the final product are obtained.

In the patent of the Russian Federation No. 2370368, selected as a prototype, a method for manufacturing a fiber preform is described, in the first stage of which the strands are first laid on a support layer using TFP technology using known automatic CNC sewing and embroidery machines, preferably so that they have an orientation, corresponding to the direction of the load, and are fastened with upper and lower fixing threads. The upper fixing thread forms loops under the support layer through which the lower fixing thread passes in order to reliably fix the fibrous preforms on the support layer or substrate to prevent them from moving.

The direction of the fiber strands to be laid and their fastening on the support layer are carried out by means of a sewing needle, the operation of which is controlled by a computer, in at least two spatial directions.

It was noted that with the fixing thread and the support layer, the TFP technology introduces two elements into the fiber preform, which in the subsequent composite component no longer perform any function, in particular, the support function. According to the authors, both the support layer and the fixing threads cause problems in terms of the implementation of the ideal sequence of layers, and, in addition, represent a fairly noticeable part in the total weight. Alternatively, the fibrous preform can also be stacked and stitched using the so-called “quilting” technology. In this case, only the upper fixing thread is used, which is directly fixed in the properly selected support layer by clamping therein. The lower fixing thread for fixing the upper fixing thread under the support layer by binding or looping with the upper fixing thread becomes superfluous. As a support layer, it is proposed to use, for example, a flexible and elastic rubber sheet, foam, etc., into which at least a needle is inserted into the surface. The loops of the upper fixing thread, which are formed in the rubber sheet after removing the needle, are firmly held inside the rubber sheet and as a result are fixed. This procedure has, in particular, the advantage that the support layer can be separated from the fiber preform in the fixing device before dissolving and washing out the fixing threads without any noticeable damage to the reinforcing fibers.

In accordance with a useful improvement of the method according to the invention, the fixing thread or fixing threads and / or the supporting layer or supporting layers are made of material that can be removed chemically or physically, in particular from a material that can be dissolved, for example, from a water-soluble polymer (however, specifically the polymer of which the substrate is made is not specified).

It is proposed to use distilled water as a possible solvent. As water-soluble fixing threads, for example, threads sold under the trademarks SOLVRON® Sewing Thread SX 100T / 1 × 3 and SOLVRON® SF62dtex from NITIVY Co. can be used. LTD. Tokyo, Japan.

The technical task of the invention is to minimize the effect of fixing threads on the reinforcing fibers in the process of stitching bulk preforms using TFP technology.

The technical result of the claimed solution is to eliminate the deformation and damage of the main reinforcing thread, as well as the substrate, due to the possible complete rejection of the use of stitching fixing thread, according to the proposed scheme of layer-by-layer sewing of bulk preforms and selection of substrate material, which ultimately leads to the expansion of technological capabilities of the manufacturing process of fibrous preforms, and also selectively affects the strength properties of the target products and their components from PCM.

The invention is illustrated by the following illustrative materials.

The figure 1 shows a fragment of the node of the sewing head with a laying foot and a needle for flashing - fixing thread (fiber), which implements the traditional method of forming preforms with an embroidery machine with CNC.

Figure 2 shows a General view of the embroidery machine with CNC, which implements the claimed method of forming preforms, Figure 3 shows part of its nodes, where the positions are indicated:

1 - a reel with a skein of the main carbon thread; 2 - substrate, water-washable; 3 - supporting frame; 4 - laying head;

5, 6 - blocks of an automated movement system in directions relative to the operator 0 ° (5) and 90 ° (6);

7 - control unit;

8, 9 - blocks of an automated shuttle movement system in perpendicular directions (0 ° and 90 °) for fixing an additional thread;

10 - needle with the main thread;

11 - needle with an additional fixing thread;

12 - laying foot.

The figure 4 shows a fragment of the node of the sewing head with a laying foot and two needles, one for the main thread, the second for the broaching - fixing thread.

The figure 5 shows the fixation of the main thread of the firmware thread at a given point in the program change the direction of the main thread.

The figure 6 shows the layout of the layers when building a given thickness of the preform.

The process of fixing the main thread firmware (Fig. 1) by traditional technology proceeds as follows. The needle with the additional thread passes through the substrate and, as on a regular sewing machine, clings to the hook of the lower hook (not shown, located under the mounting frame), the needle begins to rise and pulls the thread, at this time the shuttle rotates and forms a loop from the additional thread, the loop is tightened by tensioning the thread with a needle. Fixing the stitching thread with a loop using the lower shuttle is fully automated and synchronized between the movement of the needle and the rotation of the shuttle, the resulting loops have a certain pitch and density.

A common drawback of known methods with an additional firmware thread is the fact of deformation and damage to the main thread, as well as damage to the substrate, which can even lead to tearing off of the substrate and stopping the preform sewing process.

To solve the technical problem, a method is proposed for stripping preforms, which is implemented as follows: from a bobbin with a main thread - carbon thread (roving) (1), to a water-washed substrate (2), mounted on a supporting frame (3), the passage “there- back "needles with the main thread (10) through a water-based non-woven base-substrate, usually to a depth of 3-5 mm - sufficient to create a loop, and then moving the laying head (4) with the needle to the next point specified by the program, while the main thread is pressed by the laying foot (12), is regulated by an automated movement system in the directions 0 ° relative to the operator (5) and 90 ° (6) by the signal of the control unit (7), where it is again fixed by a loop (Fig. 4). From this point, the main thread is stretched and laid with a foot, after which at the next selected point it forms another loop.

If necessary: a significant change in the laying direction or local stress concentration, which can lead to strong tension and the danger of loops coming out of the substrate, the main thread is fixed with an additional thread, which with its needle (11) passes through the substrate-base, and is fixed according to the traditional technology by shuttle (as on a conventional sewing machine), which is located under a fixed substrate and moves in different directions using a mechanism of automated synchronized action of blocks (8.9) similar to blocks (5,6), at points defined and laid down in the program (Fig. . 5).

As an additional - fixing used aramid thread Rusar-S. Other high modulus threads such as CBM, Armos, Artec and ARUS can also be used.

It should be noted that the main carbon thread when piercing the substrate and rises back, forming a loop under the substrate, with special known devices, such as pressure “sponges”, is not fixed, but is held by the friction force. This effect is ensured by the selection of the substrate material, which is used as non-woven, where 100% polyvinyl alcohol is used as a stabilizer.

Non-woven paper-like non-woven material based on modified cellulose fibers. Due to the modification of the fibers and their chemical crosslinking during the molding of the final product, non-woven fabrics have greater tensile strength, abrasion resistance and stiffness than ordinary cellulose fibers. In this case, to give the required properties to the substrate material, the manufacturer applied the matrix with 100% polyvinyl alcohol (PVA, international name: PVA - artificial, water-soluble, thermoplastic polymer). Under the water-soluble non-woven base based on polyvinyl alcohol in the application refers to the above material. The authors of the application used non-woven fabrics based on polyvinyl alcohol of domestic and foreign manufacturers, mainly of type H and G (Allbiz, Westtext, Aurora, etc.). According to the characteristics of the manufacturers, the surface density of the water-soluble interlining used in this application was about 35-40 g / m ² . The properties of such a non-woven fabric were sufficient for clamping a loop of carbon fiber roving yarn due to friction, while in the prototype application (RF patent No. 2370368), the substrate material was specially selected - from rubber or foam. Optimal dissolution followed by leaching of the substrate is carried out at an initial water temperature of 80 ° C and holding the preform for 3 minutes.

One of the main features of preform design and programming of the patch process is the requirement not to sew the main thread with a fixing thread (in practice they often use the same main thread or one close to it in properties). In the proposed method, the main thread and the additional firmware do not go constantly along the direction of the main thread, constantly flashing it and thereby deforming it, but only flashing it at the programmed points. In addition, each new layer of the main thread should overlap the previous one in area so that new loops of the main thread do not deform the already laid main thread of the previous layer. It follows that each subsequent preform layer should occupy a large area, and the perimeter of the fixing loops of the main threads should be larger than the previous one (Fig. 6). Moreover, the laying direction of the reinforcing thread can be absolutely anything.

Upon completion of the laying of all layers of the main thread, it is possible to additionally flash the entire workpiece with fixing threads, if desired, not only in places of rotation or bending, but also where it is necessary, due to specific requirements, to increase resistance to shear loads and delamination of the final product.

The proposed layering scheme allows reinforcing the preforms as straight and straight as possible - without bends and waves, with thread stitches, which allows to obtain the best characteristics from the reinforcing filler during bending and tensile testing of the target products. And firmware in selected places leads to a local increase in stability with plasticity in this area.

At the same time, this method allows not only fixing the main thread at the moment of changing direction or transition from one layer to another, but also stitching several layers to increase the shear and delamination strength of the preform. At the same time, firmware only occurs at points previously planned and included in the embroidery machine's CNC program.

Claims (4)

1. The method of sewing bulk preforms, which consists in laying and fixing the main - reinforcing - thread on a fixed substrate and then building up the layers of the three-dimensional structure according to the TFP technology on a programmed embroidery machine, characterized in that the main thread is fixed by flashing with a needle and thread substrates based on water-washable interlining with a clamp of the formed loop and subsequent movement in the straight direction of the laying head with the needle to the next point specified by the program, and in the case of a curved direction of laying at the point of bending or maximum voltage, the loop of the main thread is additionally fixed with a second needle acting in automatic mode, synchronously with the first, while in the case of layers growing to a given preform thickness, the perimeter of the trajectory of each subsequent layer of the main thread should be larger than the previous one. 2. The method according to p. 1, characterized in that carbon fibers are used as reinforcing threads. 3. The method according to p. 2, characterized in that as the reinforcing threads use fibers in the form of roving. 4. The method according to p. 1, characterized in that aramid fibers are used as fixing threads.

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