RU2600762C1 - Method of producing parts from polymer composite material based on thermoplastic binders using industrial lasers - Google Patents

Abstract

FIELD: aviation; astronautics.

SUBSTANCE: invention relates to aircraft and aerospace engineering and can be used in aircraft and aerospace multiple use systems, rocket production, etc. According to the method of producing parts from a polymer composite material based on thermoplastic binders, onto a prepared forming tooling applied or wound are layers of a thermoplastic prepreg. Prepreg is heated during its applying or winding by layers onto the forming tooling with a laser beam within the temperature range of the molten thermoplastic binder with welding of every next layer of the prepreg formed as the result of applications or windings to the previous ones. Layers of the thermoplastic prepreg are compacted by a laying pressure element. Obtained by application or winding prepreg layers are cooled. Sealing the prepreg is performed by high-frequency short-pulse impacts of the laying pressure element with the help of ultrasound, pulse vibration of this element formed by a piezo element of a piezo converter.

EFFECT: invention provides higher quality of manufactured parts and increased reliability of the parts during their operation due to higher degree of integrity of applied or wound layers of the thermoplastic prepreg and due to considerable decrease of tendency to stratification of the applied layers of prepregs.

3 cl, 14 dwg

Description

Technical field

The claimed invention relates to aviation and space technology and can be used in all passenger and transport aircraft, from light to heavy aircraft, in unmanned systems, as well as in reusable space systems, orbital and suborbital space stations, in rocket science.

Also, the invention can be used in shipbuilding (in various swimming facilities from motor boats to cruise liners), automotive, in the production of high-speed trains, motorcycles and ATVs, in particular in the manufacture of elements that provide exceptional aerodynamic qualities and interiors; and, in addition, in various oil and gas transportation systems in industrial storages of gas and oil products as a reliable reinforcing and sealing coating; in building structures as power structural building elements, ensuring reliable performance in the most severe conditions for a long time operation.

Preferably, the invention is recommended for use in the manufacture of bulky, incl. double curvature of parts by layering or winding the prepreg tape impregnated with a thermoplastic binder (hereinafter thermoplastic prepreg), automated installation on the surface of the mold.

State of the art

The basis of the claimed invention is the manufacturing process of large-sized parts from thermoplastic polymer composite materials (PCM) using the principle of laser lay-out or winding, in which the thermoplastic prepreg is heated by a laser beam. This solution allows you to get large, including double curvature, parts of a monolithic structure that have the specified characteristics and the necessary geometry, and also practically do not require additional mechanical refinement.

Thermoplastic PCMs are heterogeneous systems that consist of a thermoplastic polymer matrix reinforced with high-strength, high-modulus filler fibers (carbon, glass, basalt, polymer, etc.).

Composite thermoplastic materials have the following advantages compared to traditional PCM based on thermosetting resins:

a) operational: resistance to shock and shock loads and local damage is 20–40% higher; high resistance to water and rain erosion; chemical resistance, including to aviation fuels and oils; fire resistance, reduced smoke emission and toxicity; maintainability (the material is easily welded);

b) technological: the possibility of forming parts on metallurgical equipment; short (from 10 to 60 min) molding cycle; the possibility of reforming defective parts and suitability for repeated use (can be reheated and re-molded); utilization of the material up to 95%; unlimited shelf life of the prepreg.

However, in this case, thermoplastic PCMs have the following features that must be taken into account when using them:

- high processing temperature (250-415 ° C);

- the difficulty of laying out a prepreg, which has no stickiness;

- thermoplastic binders are chemically inert in comparison with thermosetting binders and have a 1-2 melt higher melt viscosity; this leads to the fact that the filler is not wetted by polymer melts - therefore, sizing and modification techniques are used in the development of such composite materials, which increases the complexity and, consequently, the cost of the material.

Considering the specific properties of thermoplastic binders mentioned above, the main of which are their high heating temperature (250-415 ° C) and the difficulty of laying out a thermoplastic prepreg due to its reduced stickiness, it is most expedient to fabricate structural parts using laser radiation for laying thermoplastic prepregs.

The first time laser welding capabilities were demonstrated in the 70s. But the cost of the equipment was then very high, so this technology was not widely used. In the late 90s, when equipment prices became more affordable, the share of laser welding increased significantly.

It should be noted the following advantages from the use of laser radiation for forming PCM structures in comparison with traditional molding processes:

- reduction of energy consumption by 40%;

- reduction of the technological cycle of manufacturing parts by 30%;

- reduction of scrap material;

- reduction of the environmental load on production by 20%;

- reduction of labor intensity by 2-2.5 times;

- reduction of production area;

- reduction of the preparation cycle for the production of new products by 40%;

- the implementation of high-precision compounds; at the same time, an accurate, repeatable, stress-independent calculation process allows you to perform a reinforcement scheme at any angle;

- lack of direct contact of the connected parts with the equipment;

- the possibility of using manipulator equipment;

- strength of joints;

- the possibility of welding polymers of various compositions.

As a result of the analysis of the prior art in the manufacture of parts from thermoplastic PCM using the principle of laser heating when laying or winding PCM, the following is established.

It is widely known to use the energy of laser radiation to heat polymer composites with the aim of bonding them by heat sealing with each other (see, for example, US 5792301 A). In the process of bonding the materials disclosed in this patent, the materials are exposed after heating by two sealing rollers through the sting of which a duplicated bag passes.

As the closest analogue to the claimed technical solution, a method has been adopted for manufacturing parts from a polymer composite material using industrial lasers, which consists in the automated laying of a thermoplastic prepreg on a specially prepared forming mandrel, heating and softening the prepreg material with a laser beam, welding the prepreg layers, cooling and further machining the details. Heating is provided in the melt temperature range of the thermoplastic binder. The manufacturing process is accompanied by the use of a laying pinch roller acting on the prepreg simultaneously with the stages of softening and welding of the layers of the thermoplastic prepreg (see WO 2010031364 A1). The main disadvantage of this method is that when welding the layers of the prepreg does not occur sufficient required compaction of the molten thermoplastic when exposed to a laying roller. As a result, an increased porosity of the obtained parts is observed. This drawback has a significant impact on the operational properties of parts, reducing their strength characteristics and resistance to shock loads, rain erosion and chemical agents. In addition, the possibility of adhering to the roller residues of molten thermoplastic significantly affects the quality properties of parts and increases the number of defects.

It is advisable here to disclose in detail the mechanism of action of the roller on the prepreg in the method known in WO 2010031364 with reference to the individual figures of the drawings, which belong to the materials of this application, a full list of which will be given below in the section "Brief Description of the Drawings".

Roller sealing allows you to create highly concentrated pressure on a small area of the prepreg, sufficient for rapid laser heating, which does not require the use of powerful press equipment and, consequently, reduces the cost of power, electricity and increase the speed of the process. However, with the usual mechanical laying method, as the initial cross-sectional shape changes, rigid radius areas are formed along the edges of the prepregs due to increasing elastic forces and the formation of residual bending stresses. Moreover, the greater the degree of deformation of the prepreg and the smaller the radii at the edges of the prepreg, the more stressed the state of the radius regions becomes and the more rigid they become. As a result, due to the interaction of hard radius areas during the subsequent laying of a new adjacent layer, only a new layer is applied over the laid radius (at best after the subsequent rolling), without proper flow, and the formation of a void region (Fig. 1 and Fig. 1a, view A in Fig. 1). The presence of this void allows the layers to collide with each other at extreme loads, destroying the initial picture of the power reinforcement and the tightness of the applied prepreg layer, thereby opening the way for intensification of corrosion in a depressurized place. On an industrial scale, in order to avoid such consequences and improve sealing, reinforcement is carried out so that there is a constant small “collision” of a new layer on the previous one (Fig. 2, and Fig. 2a view B in Fig. 1). However, the presence of the void region still allows the layers to collide with each other, and even further at maximum loads, also destroying the initial picture of the power reinforcement and violating the tightness of the applied prepreg layer with the above consequences.

The task to which the claimed technical solution is directed is to develop such a method of manufacturing parts from a polymer composite material based on thermoplastic binders by lay-up or winding using industrial lasers, which would ensure the highest quality deposition of thermoplastic prepreg layers without the formation of technological voids.

The technical result achieved by the implementation of the claimed invention is to improve the quality of the manufactured parts and to increase the reliability of the parts during their operation by achieving a high degree of solidity of the laid or wound layers of the thermoplastic prepreg and by significantly reducing the tendency to delamination of the applied prepreg layers.

To achieve the technical result, a method for manufacturing parts from a polymer composite material based on thermoplastic binders is proposed, which consists in

- automated laying out or winding in layers of a thermoplastic prepreg on a previously prepared forming tool,

- heating the thermoplastic prepreg, in the process of laying it out or wrapping it in layers on the forming tool, with a laser beam in the temperature range of the thermoplastic binder melt, with welding of each subsequent layers of the prepreg formed as a result of laying out or winding, to the previous ones,

- compaction of the layers of the heated thermoplastic prepreg with a laying clamping element pressed to the surface of the mold,

- cooling obtained at the end of the calculation or winding of the prepreg layers.

The difference of the proposed method lies in the fact that the compaction of the prepreg is carried out by exposure to it with high-frequency short-pulsed strokes of the laying-down clamping element using ultrasonic, pulsed vibration of this element created by piezoelectric elements.

Preferably, a silicone rubber roller is used as the stacking pressing member. Advantageously, the roller is ceramic coated.

Thus, to solve the problem associated with the formation of void regions, which was indicated in the analysis of the prior art, it is proposed to use a high-frequency, short-pulse compaction of the layers with a styling clamping element, which is provided by ultrasonic, pulsed vibration of this element, created mainly by piezoelectric elements, which are ideal means of touch control, and therefore their application allows you to combine a sealing system and touch control, eliminating additional sensors and all related structural elements.

A brief description of the drawings.

In FIG. 1 and FIG. 1a shows the formed structure of the seam between the prepreg tapes, made by conventional laying known from the prior art;

In FIG. 2 and FIG. 2a is a diagram of a traditional solution for improving the quality of seams;

In FIG. 3a, 3b, 3c, 3d, 3e shows the sequence of propagation of shock waves when exposed to a laying clamping element;

In FIG. 4 and FIG. 4a - the formed structure of the seams between the prepreg tapes made using ultrasonic vibration;

In FIG. 5 - a device that implements the method, General view;

In FIG. 6 - node B in FIG. 5;

In FIG. 7 - node G in FIG. 5, top view.

Implementation of a technical solution.

A method for manufacturing parts from a polymer composite material on thermoplastic binders is proposed. According to the method, an automated laying out or winding in layers of a thermoplastic prepreg on a previously prepared forming tooling is performed. In the process of layering or wrapping the prepreg on the tool, the prepreg is heated by a laser beam in the temperature range of the thermoplastic binder melt (250-415 ° C). The result is the welding of each subsequent layer of thermoplastic prepreg, formed as a result of laying or winding, to the previous layer. Under the action of the laying clamping element, mainly the roller (and hereinafter referred to as the roller), each prepreg layer is densified in the section pressed to the mold surface and heated to the melt temperature of the binder, while in the preceding section (in a continuous process) softening occurs and welding layer. Moreover, the said compaction of the thermoplastic prepreg is carried out by exposing it to high-frequency short-pulse strokes of the stacking roller, which are provided by ultrasonic, pulsed vibration of the roller, created mainly by piezoelectric elements. The completion of the automated calculation process includes cooling the prepreg tape during installation, as well as laser cutting of the tape at the end of the deposition. Laser pruning allows you to melt the fibers and prevent them from breaking up, which is unavoidable during mechanical cutting.

A more detailed description of the method is given by the example of its implementation using the device shown in FIG. 5-7.

In FIG. 5 shows a main view of a device for manufacturing parts from polymer composite materials based on thermoplastic binders.

The device comprises a creel 2 located in the housing 1 with a thermoplastic prepreg 3, a laying clamping element, a predominantly freely rotating roller 4 (which, however, with certain structural additions of the device, can be driven), with a ceramic coating, a laser radiation generation system 5, a system 6 focusing the laser radiation, the guiding system 7, the laser absorber 8 for the segment of the prepreg. Next to the styling pinch roller 4 is a cooling roller 9 made of silicone rubber connected to the refrigeration device 10.

In contact with the ceramic surface of the stacking pressure roller 4 is a knife 11, and in close proximity to the roller 4 is a high pressure air supply pipe 12. On the other side of the roller 4, a trap 13 is installed opposite the tube 12. In FIG. 5, position 14 shows a moldable part, position 15 - a forming mandrel for lay-up or winding technology, position 16 - laser radiation and position 17 - laser contact area, 18 - an adjustable piezoelectric transducer system, 19 - a vibration transmitting coupling.

The implementation of the method using this device is as follows.

First of all, snap-in equipment is fixed in the spindles in accordance with the selected type of installation, in the case of choosing the winding technology it will be cylindrical equipment; and in the case of the choice of laying technology - equipment in the form of a swinging table. In this case, in the case of installing large-sized equipment, a laser system for controlling the exact position is used.

The creel is refilled in the stacking head of the robotic arm. The laser generation system is also turned on, the operation of the laser focusing system, the guide system, is checked. Then the process of manufacturing the part starts. The laying process by the robotic arm begins as soon as the laying head located on the robot arm touches the working surface of the equipment. The arm of the robotic arm begins to slide along the laid surface, laying the thermoplastic prepreg. In the process of automated laying out or winding (at the feed rate of the case with the nodes V _SUB under it), the prepreg 3 supplied from creel 2 is exposed to laser radiation 16, is heated to the melting temperature of the thermoplastic binder and falls under the action of the styling pinch roller 4. When this roller 4 with a given force presses on the molten thermoplastic base of the prepreg, repeating the curvature of the surface of the forming mandrel 15. The clamping force is formed as a result of controlled hands and the manipulator, and due to the operation of the piezoelectric transducers, the total vibrational force of which is transmitted through the coupling 19, which allows the transmission of vibration from the piezoelectric elements exclusively to the laying roller, excluding energy dissipation to the entire mass of equipment, in the absence of this coupling.

To prevent sticking of the molten thermoplastic, knives 11 slide on the surface of the laying roller 11. The remains of the thermoplastic binder are blown away by a directed stream of high pressure air into the trap 13 with a large cross section, and then the residues are removed into the cyclone filter. In order to prevent excessive sticking of the thermoplastic binder, a special ceramic coating is also applied to the surface of the stacking roller 4, to which the melted thermoplastic does not adhere.

Further, the stacked prepreg falls under the action of the cooling roller 9. The clamp is carried out by means of a height-adjustable spring, and the cooling of the roller 9 is provided by means of a special cooling device 10 operating on the principle of creating a cold air stream and blowing the ribs of the cooling roller from the inside. At the same time, there is also the possibility of a sufficiently wide temperature range not only by adjusting the power of intensive cooling, but also by installing additional small-sized heating elements in the air duct. The cooling roller 9 not only cools the molten prepreg and gives the final shape during the laying process, but also redistributes the residual stresses so that the stacked layers accurately repeat the specified curvature of the part. Also, part of only the cold air stream is sent to cool the piezoelectric transducers, preventing heat from the stacking roller 4, which is subject to constant thermal radiation from the laser radiation.

A laser system is also used to complete the process of laying the prepreg tape and cutting the tape at the moment the robotic arm stops. Thus, the fibers are melted and their disintegration is excluded, which is inevitable during mechanical cutting.

Figures 3a-3e show the following stages of shock wave propagation. FIG. 3a - stage of action of the primary impulse (F, F ₂ - impulse deformation force from the action of the vibrating roller 4; N, N ₂ - support reaction; R - radii of hard regions along the edges of the prepregs). FIG. 3b - stage of the appearance of the primary wave (V ₁ is the wave velocity of the primary pulse; N ₂ is the reaction of the support; R is the radius of the hard regions along the edges of the prepregs). FIG. 3c - stage of the emergence of the secondary wave, the effect of geometry, the sphere of reflection (V ₂ is the wave velocity of the secondary pulse; R is the radius of the hard regions along the edges of the prepregs). FIG. 3d - secondary sphere of reflection, the occurrence of regions of least resistance (V ₂ - wave velocity of the secondary impulse; N ₃ - reaction of the support; S - regions of least resistance). FIG. 3e - filling the areas of least resistance.

Due to the fact that in the process of a short-time, but sufficiently powerful pulse, generated by ultrasound, high pressure is formed, under the influence of which a powerful shock wave appears (Fig.3a), one radius overlaps and abuts against the already laid radius R ₁ , and the radius R ₂ remains free. In the process of exposure to an ultrasonic pulse and the creation of a shock wave, the following occurs: the shock wave begins to propagate in both directions, gradually stretching the cross section. Since the main principle of the propagation of any energy flow is the principle of least resistance, therefore, the radius R ₁ , abutting against the already laid radius, begins to intensively reflect the wave incident at this place, but at the same time there is intensive laying in the upper part. The reflected wave goes towards the free radius R ₂ and as it reaches it begins to lengthen the profile. The lengthening of the profile is accompanied by a decrease in the free radius R ₂ and an increase in mechanical stresses in this region, which leads to an increase in resistance and the free radius R ₂ begins to work like a sphere, reflecting the incoming wave in the direction of radius R ₁ . But since the upper part of the radius R _{1 is} not free and the wave propagates according to the principle of least resistance, in this case the void has the least resistance, i.e. under the influence of short-term powerful power pulses, the void is filled. This leads to the formation of the next interlayer pattern having a uniform structure (see Fig. 4, 4a). Now the layers are interlocked, and for a possible displacement of the layers, a much larger load will be required, which indicates an increase in tightness and will increase the operational loads.

Two more important factors of this stacking method also appear. First of all, under the action of shock waves, processes similar to ultrasonic welding occur. Since the shock wave also acts on the laid surface, partial destruction of the contacting surfaces occurs and the process of interpenetration into each other is observed. Thus, much better adhesion of the laid thermoplastic to the laid surface is ensured, as compared to conventional mechanical laying.

And most importantly, under the influence of shock waves, processes occur that lead to the fact that in all places of direct contact (thermoplastic - thermoplastic, thermoplastic - stacked surface) there arise G regions with increased density (Fig. 4), in which a kind of indentation of some polymer chains to others, which, in turn, leads to a decrease in the free expansion of the thermoplastic base, i.e. to reduce creep. The process is similar to the formation of a sewing seam with the only difference being that stitched materials and threads are the same polymer chains.

Thus, the use of a stacking roller with ultrasonic vibration and a system against sticking of thermoplastics makes it possible to provide significantly better contact with the surface, form more tight joints between the layers, reduce the fluidity of the thermoplastic binder base and provide a more resistant to mechanical stresses composite structure, which makes it possible to obtain better quality homogeneous, complex and more rigid spatial structures, for example, 3D - shells of aerodynamic surfaces to yla fuselage, different interior elements, etc.

Therefore, the most effective way to seal the molten thermoplastic binder is to combine rolling by the roller with simultaneous ultrasonic vibration of the roller itself. As you know, piezoelectrics (piezoelectric elements) under the influence of electric current and relatively low voltage, are slightly deformed. But as soon as the action of the electric current ceases, the piezoelectrics return to their original state, restoring shape. And the faster the action of the electric current stops, the faster the process of returning to the original form occurs. And since piezoelectrics have very large values of the elastic modulus, and therefore are very rigid, with a very rapid cessation of the electric current, very high acceleration values, high pressures are achieved in the process of shape restoration, despite the transience of the process and a small amount of deformation. This allows the formation of high-energy shock waves in various media (and the ability to form highly focused, concentrated flows): in gases, in liquids, in solids, which are used in various fields of technology.

Thus, due to the physical basis of the process of operation of piezoelectrics, it becomes possible to efficiently bond and harden a binder based on thermoplastics (which also have decent elastic modulus values), since high-energy shock waves arise in the structure of thermoplastics during cyclic exposure to high-pressure pulses, which leads to the occurrence of intense local deformations and a significant increase in temperature exceeding the glass transition temperature of thermoplastic ists. This, in turn, leads to the fact that a significantly greater mobility of the molecular chains is ensured at the working site, significantly better interpenetration of the molecular chains into each other for a short time, and to the appearance of significantly larger bending tau stresses, which also contribute to more intense tangling molecular chains, that is, to reduce the fluidity of thermoplastics, and increase the strength properties. And in the presence of intensive cooling, small thicknesses, fast fixation, and high speed of the process are provided. There is no need to warm all the equipment and press on the entire area of the molded part.

The sticking of the molten thermoplastic binder is prevented due to the removal of the settled part of the thermoplastic on the roller by the knife system and a powerful vacuum cleaner having two tubes: one of a smaller diameter, blowing off with large pressure, and the second, having a larger diameter, capturing with a vacuum, like an ordinary vacuum cleaner. In this case, an additional method of eliminating the sticking of thermoplastic is to apply a special ceramic coating to the roller.

The use of a ceramic-coated styling pinch roller with ultrasonic vibration to seal the molten thermoplastic base and the system of removing thermoplastic sticking during the manufacturing process of a part, which is molded using automated lay-out of a thermoplastic prepreg using industrial lasers, allows to achieve the following results.

Due to the ultrasonic pulsed vibration of the stacking roller, much better adhesion of the thermoplastic prepreg to the stacked surface is achieved, the resulting structure has greater uniformity, more tight joints between the layers are formed, boundary areas of increased density appear and therefore the fluidity of the thermoplastic binder base is reduced, which provides a more resistant to mechanical stresses composite structure. The use of a system of knives to remove the melted thermoplastic allows you to more efficiently optimize the process, increase its productivity and significantly reduce the number of rejects of finished parts. In this case, heating the roller under the action of ultrasound will significantly improve the quality of the part, because the prepreg tape, approaching the heated roller, will not be cooled, and as a result, reliable "setting" of the prepreg tape with the forming surface will be ensured.

All the above advantages make it possible to produce three-dimensional parts of any configuration with high surface quality, high strength, minimal creep, high accuracy of geometric dimensions, minimum weight and a long service life.

Claims (3)

1. A method of manufacturing parts from a polymer composite material based on thermoplastic binders,
consisting in
laying or winding in layers of a thermoplastic prepreg on a previously prepared forming tool,
heating the prepreg, in the process of laying it out or wrapping it in layers on the forming equipment, with a laser beam in the temperature range of the thermoplastic binder melt, with welding of each subsequent layers of the prepreg formed as a result of laying out or winding, to the previous ones,
compaction of the layers of thermoplastic prepreg with a laying clamping element,
cooling obtained by laying out or winding prepreg layers,
characterized in that
compaction of the prepreg is carried out by exposure to it
high-frequency short-pulse strokes of the laying-down clamping element using ultrasonic, pulsed vibration of this element created by the piezoelectric element of the piezoelectric transducer. 2. The method according to p. 1, characterized in that the pressure roller is used as the laying element. 3. The method according to p. 1, characterized in that the pressure roller is ceramic coated.

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