SE501085C2 - Method for manufacturing bodies of fiber composites - Google Patents

Abstract

A method of manufacturing bodies of polymeric fibre composites, wherein a preformed fibre reinforcement (11, 21, 31, 41, 51) is placed in a cavity whereupon a liquid resin of a low-viscous polymer material is supplied to the cavity through one or more injection channels (13, 23, 33, 43, 53) provided in the fibre reinforcement, whereby the resin supply through the injection channel is controlled such that the flow front (19, 29, 39, 49, 59) of the resin during the mould filling propagates parallel to the axis of said injection channel through the cavity such that the fibre reinforcement is impregnated by the polymer material, the viscosity of the polymer material then being increased and the body being stripped.

Description

10 15 20 25 30 35 501 085 3, the mold is filled by injecting a liquid polymer into the tool, through one or more ingots, whereby the tool deaerated, through one or more deaeration points, 4, the polymeric material is cured in the tool, 5, the tool is opened and the molded part is demolded.

The process places demands on the polymeric matrix material physical properties and in good control of their change during the curing step. The form-filling requirement entails that the liquid polymeric matrix material must have a sufficiently low viscosity and maintain it until then that the entire mold is filled despite the hardening sometimes begins already during the mold filling. At the same time, the the detail after completion of mold filling quickly reaches a stiffness, by curing when such a level, so that the detail can removed from the tool without any extended residence time and deformed thereby achieving high productivity.

RTM tools consist of two or more tool parts as in mold filling and curing define a mold space with details jens geometry. The tool is always arranged to include at least one ingot for supplying the liquid polymeric feedstock rice material and at least one vent port for evacuation of air present in the tool at the mold filling. Positional ring and design of ingots and venting points are complete crucial to achieve a good form filling. It is usual to apply a negative pressure through the vent ports in the tool to increase the pressure difference between the ingot and flow front and thereby reduce the time for mold filling.

The use of vacuum, negative pressure, usually also lowers the content of air inclusions, pores.

Typically, the polymeric matrix material is pressed through the with a low pressure, injection pressure, 0.1 - 1 MPa, which means that the tool cohesive force, reading power may be limited. At the same time, it means that the ters acting on the tool surfaces become position thereby good geometric tolerances can be obtained even with relatively simple tool constructions. All in all, this means that 10 15 20 25 30 35 501 085 The costs of the RTM process are low in a comparative with other processes for forming fiber composites, especially processes for forming high-performance fibers composites.

The mold filling is a very critical process step during which it is required that the fiber reinforcement placed in the mold space completely filled without air inclusions, pores, remains in the shaped detail. In addition, the filling time is short to achieve high productivity.

Complete filling of the mold space and of the so-called the free volume of the fiber reinforcement is most easily achieved with simple and symmetrical geometries and with an even distribution in the mold load fiber content throughout the fiber reinforcement. For more complex geo- meters or in the case of a fiber reinforcement with varying fiber content or a fiber reinforcement unevenly distributed in the mold space often black to achieve a good form filling and / or low por- slippery.

Mold filling, pore content and filling time are thus affected by one several more or less cooperating parameters, such as inji- curing pressure, negative pressure in the tool, the polymeric matrix the viscosity of the material, its wetting properties relative fiber reinforcement and tool surfaces, injection rack and the permeability of the fiber reinforcement.

Furthermore, mold filling and mold filling time can be changed by choice of mold filling strategy. Two fundamentally different strategies giers are common: A. Point injection, by which is meant that one or more ingots placed close to the center of the part and to the flow front propagates from the ingot / ingöten in all directions towards the edges of the part where venting takes place through one or more vent ports.

B. Edge injection, by which is meant that one or more ingots placed along one or more of the edges of the mold space via one inlet or distribution channel. When the distribution channel is arranged 10 15 20 25 30 35 501 085 to supply polymer by casting which are essentially placed along an edge or side surface, propagate flow the front under the mold filling in a direction from this edge or side surface against the opposite side surface (s) where the vent ning happens. When the distribution channel and ingot are arranged to remove polymer from the edges or side surfaces which form the the outer limiting surface or periphery of the hoist propagates desfronten under the filling of form from the periphery towards the center where deaeration takes place.

In general, edge injection gives shorter filling time than point injection for the same detail and with the same process mêtrar.

The permeability of the fiber reinforcement, the permeability, is off crucial for the mold filling time. Permeability in The reinforcement is mainly determined by the volume content of fiber in the fiber reinforcement. the ring. High fiber levels which occur in high performance polymeric fiber composites provide great resistance to the the polymer mass, the resin, to impregnate the fiber reinforcement whereby the filling time becomes unacceptably long. At length filling time, the hardening is also affected in a negative way because the curing process must be adapted to meet the requirement for low resin viscosity during substantially the entire filling time. For many resin materials, the requirements of the hall low viscosity for a long mold filling time to ensure good filling and low pore content not combined with the requirements for a rapid curing process in a subsequent curing steps without usually having to compromise between these requirements.

This usually results in a constant injection of pressure, a decrease in the velocity of the flow front so that it total mold filling time is proportional to the square of the injection distance. In this way, large details are mold filling times unless a large number of ingots can arranged to shorten the necessary injection lengths. One however, large numbers of ingots complicate and make the tools more expensive.

One object of the invented method is to provide a during which a liquid polymeric material with a minimum 10 15 20 25 30 35 H31 085 row mold filling time is added and fills one of a cavity a mold tool defined shape and impregnates one in said shape arranged preform of fiber reinforcement. Furthermore, it offers invented the method a complete form filling with minimized pore content and a quality-repeatable mold filling below controllable conditions.

THE INVENTION In the production of polymeric fiber composite bodies with RTM technology, a molding tool is provided to define a molding, after which a preformed fiber reinforcement is placed in the mold space before a liquid resin of a low viscosity polymeric material is added to the mold space. The mold space is substantially completely filled polymeric material wherein said fiber reinforcement is impregnated substantially completely of the polymeric material. When polymer the viscosity of the material by curing has been increased to give the shaped composite body has a rigidity that allows it shaped fiber composite body can be handled demolded.

According to the invented method, the mold space is added below the mold filling resin through one or more of the fiber reinforcements arranged centrally located injection channels, wherein said resin is introduced into the mold by means of an injectable the injection side of the duct, the ingot heel and the injection duct len during the mold filling is extended in a controlled manner to control the supply of resin so that the flow front of the resin, below it that the mold space is filled and the fiber reinforcement is impregnated with resin, propagates substantially in parallel with said injection. axis of the duct through the mold cavity, as the injection the channel is extended into the mold space.

The invented method is particularly suitable for two types of composite products for which both the preformed fiber the ring includes cavities which result in heel bodies or details including both reinforced and unreinforced parts, sandwich constructions. Preferably arranged substantially cylindrical injection channels in said unreinforced heel cavity. with The injection channel can be defined by a tube, a liner, for the resin permeable walls or formed by the fiber reinforcement 10 15 20 25 30 35 5Û1 085 or as a cavity in a core permeable to the resin. Inji- can be straight and cylindrical but also arranged with contours which follow the geometry of the shaped body.

This is achieved in an embodiment of the invention by a piston is arranged in said injection channel and when resin below the mold filling is supplied through a casting heel in the injection box. one end of the valve is pulled out or pressed out of its inner part. pushed position through one at the other end of the injection channel arranged heel thereby extending the injection channel below the mold filling and the flow front of the resin substantially propagate gene parallel to the axis of said injection channel.

The same effect is achieved when said piston in another embodiment of the invention is arranged in the form of a hose which below the mold filling is turned inside out and pulled out of the injection the channel through an end of the ingot heel opposite injection channel arranged heel.

According to a further embodiment of the invention are provided said piston split in two with an inner stationary shaft, which remains in the mold cavity during the mold filling, in order to more injector volume, and an external concentric with said shaft arranged sleeve which during the mold filling on the above-mentioned method is pressed or pulled out of a heel device in the molded-in opposite end of the injection canal len.

In the manufacture of polymeric fiber composites accordingly invented method, the mold filling time is minimized by throughout the mold filling time the distance from free flowing resin in the injection channel to the flowing front that propagates through the fiber reinforcement is small and constant, which in comparison with conventional RTM technology greatly reduces filling time at; - large and / or long bodies, - bodies with a high fiber content, high viscosity matrix polymers. 10 15 20 25 30 35 .501 085 In addition, by the short distance from free flight resin in the injection channel to the flow front through the fiber reinforcement obtained by the invented method a good control over the mold filling process, which is thereby controlled with the movements of the piston.

With the invented method a material supply is obtained which during the filling of the mold is controlled from the injection the duct or ducts in the body, which is beneficial and to avoid air entrapment and other inhomogeneous activities that can be attributed to disturbed material flow through the fiber reinforcement.

The invented method is very advantageous for effect of long hollow products such as high performance tubes, as well as for integrated production of complex parts, such as tubes with integrated flanges and for drive shafts, control surfaces including shaft and attachment, in one step.

The invented method is also very valuable for manufacture of composites with highly viscous matrix systems such as high temperature resistant thermosets, high strength thermosets and thermoplastics.

FIGURES The invention will be explained in more detail below and exemplified by a number of preferred embodiments below reference to the accompanying figures. Figure 1 shows a procedure according to the invention where the distribution of the flow front is controlled by means of a piston arranged in the injection channel. IN Figure 2 shows an embodiment where the distribution of the flow front is controlled by a hose arranged in the injection channel during mold filling, it is inverted in and out of the injector. the ring channel. Figure 3 shows an embodiment through which the volume of the injection channel is minimized during the mold filling. 10 15 20 25 30 35 501 085 DESCRIPTION OF FIGURES In the manufacture of a polymeric composite body using RTM technology according to an embodiment of the invented method, which shown in figure 1. a preformed fiber reinforcement 11 is placed in a forming tool 12. In the fiber reinforcement 11 has a cylindrical injection channel 13 has been provided. A piston 14 has been inserted into the injection channel 13 through a heel 15 in the forming tool 12.

In the retracted position, the piston 14 fills up substantially whole the volume of the injection channel 13 and can be moved freely in the injection channel 13. A casting heel 16 is arranged in the mold the tool 12 and opens into one end of the injection channel 13, the casting side 17, while the outlet heel 15 of the piston is arranged in the other end of the injection duct 18. Venting points, no shown, are arranged as is the case with conventional according to RTM technology based on the geometry of the part. Resin is supplied during the mold filling by means of the the casting heel 16 of the lens 13 provided with a control rolled pressure and flow. At the beginning of the mold filling occupies the plunger 14 substantially the entire volume of the injection channel 13.

The piston 14 is then moved in a controlled manner so that a flow front 19 is formed which during the filling of the mold propagates with a constant and small lead, X, relative to that of the piston movement controlled the extension of the injection channel 13.

The flow resistance in the injection channel 13 is small and relatively relative to the flow resistance of the preformed fiber which causes the pressure drop in the injection canal len 13 is slightly below the mold filling. The pressure difference between the injection channel 13 and the flow front 19 are all the time large and constant, which is tantamount to adding resin. traveled through a ladle which essentially follows the flow front 19 during its propagation along the injection channel 13 below shape the filling. This large pressure difference over a short distance is maintained during substantially the entire mold filling.

When substantially the entire free volume of the fiber reinforcement 11 has replaced with polymeric material, the mold filling ends with the piston 14 is moved back to the initial position, which empties the injection channel 13 with a reverse flow out through 10 15 20 25 30 35 501 085 the casting hole 16. Then the curing step takes place during which the stiffness of the polymeric material is increased by the current polymer material relevant technique. When it formed the composite body achieved sufficient rigidity is formed with at conventional manufacturing using RTM technology accepted methods.

As shown in the embodiment shown in Figure 2, the piston function can the ring shape is achieved with a twisted hose. A preformed fiber reinforcement 21 is placed in a molding tool 22. In a fiber reinforcing ring 21 arranged in the ring 21 is inserted through a hole 25 in the forming tool 22 a hose 24. The hose 24 which in its shot end 241 is inverted and closed fills at molding the beginning of the filling, by applying an internal overpressure in the hose 24, substantially the entire volume of the injection channel 23.

A rod or rope 242 arranged inside the hose 24 is fastened the inverted end 241. By said rod 242 below the mold filling is pulled out through the hole 25, the hose 24 is turned out and likewise drawn in and out of the injection channel 23 through the hole 25. Hereby extended under the mold filling, as on the method described above is done by adding resin through the ingot hole 26. 29 propagates substantially parallel to the injection channel 23 so that the flow front the injection channel in the same way as under the previous one described embodiment. This embodiment is special advantageous in that no movement takes place in the interface 244 between the inner surface 231 of the injection channel and the tube 24.

Furthermore, it is allowed that the geometry of the injection channel 24 can be selected free. The internal overpressure applied in the hose 24 balanced against the casting pressure used in the resin to prevent the hose 24 from collapsing. After completing the form filling The hose is pressurized again so that the twist is successive returns while the excess resin in the injection box the needle 23 is pushed back through the ingot hole 26. The inner the overpressure in the hose 24 is maintained during the subsequent the curing step which, like demolding, is performed on earlier specified method using accepted methods.

The volume of the injection channel is minimized during the mold filling at using the embodiment shown in Figure 3 10 15 20 25 30 10 501 085 the finding. A preformed fiber reinforcement 31 is placed in one mold tool 32. In an injector arranged in the fiber reinforcement 31 ring channel 33, a two-part piston 34a, 34b is inserted through a heel 35 in the forming tool 32. The piston includes a stationary one shaft 34a, and one concentrically arranged about this axis sleeve 34b which runs along the entire injection channel 33 length. The sleeve 34b substantially fills in the retracted position the entire volume of the injection channel 33 and can be freely moved 33. To achieve a satisfactory seal, arrange outside the sleeve 34b one in figure sealing layer 34c, which is stationary anchored in the piston 34a, it seals the injection channel 33. along the stationary shaft 34a of the injection channel stationary flexible concentric sealing layer 34c, 3 shown as a hose. Sleeve 34b runs between this and the piston 34a for pressing out the sealing layer said that An ingot hole 36 is arranged in the mold jig 32 and opens into the injection channel 33 one end, the cast-in side 37, while the outlet heel 35 of the sleeve is arranged at the other end of the injection channel 38. Resin during the filling of the mold through that of the injection channel 33 casting side 37 provided the casting heel 36 with a controlled pressure and flow. At the beginning of the mold filling, the sleeve 34b occupies substantially the entire volume of the injection channel 33. Sleeve 34b then moved in a controlled manner so that a flow front 39 on described above and during the filling of the mold propagates substantially in parallel with the injection channel. smooth 33 axis through the mold space. When substantially the entire fiber the free volume of the ring 31 has been replaced with polymeric material the mold filling ends with the sleeve 34b being moved back to the initial position, which empties the injection channel 33 with a reverse flow out through the ingot hole 36. Then cured and the molded composite body is reshaped previously described manner.

Claims (4)

10 15 20 25 30 35 11 501 085 PATENT REQUIREMENTS A method of producing bodies of polymeric fiber composite in a molding tool which is arranged to define a mold space, where a preformed fiber reinforcement is placed in the mold space after which a liquid resin of a low viscosity polymeric material is added to the mold space so that the mold space is substantially filled with polymeric material. completely of polymeric material during the mold filling, after which the viscosity of the polymeric material is increased so that the body obtains a rigidity where the shaped fiber composite body can be deformed, characterized by - said resin being fed to the mold space by one or more in the fiber reinforcement (II, 21, 31, 41, 51 ) provided injection (13,23,33,43,53). - said resin is introduced into the mold through a casting heel (16, 26,36) arranged in injection channels of the ring channel (16, 27,37) and - the injection channel, during the filling of the mold, is extended in a controlled manner to control the supply of resin so that the resin flow front substantially parallel to the axis of said injection channel (19,29,39,49,59) during the mold filling propagates through the mold space. A method according to claim 1, characterized in that a piston (14,24,34) is arranged in said injection channel, wherein said piston is pulled out or pressed out during the mold filling through an end, the ring channel, in the injection side opposite end (18,28,38) of injection-arranged heel (l5,25,35) whereby the elongation of the injection channel is checked and the supply of the resin (19,29.39) the filling propagates substantially parallel to said guide so that the flow front of the resin below the axis of the injection channel through the mold space. A method according to claim 2, characterized in that said piston is arranged in the form of a hose which during the mold filling is turned in and out and pulled out through the injection side opposite end of the injection channel. 10 501 oss Ü A method according to claim 2, characterized in that said piston is arranged in two parts with an inner stationary shaft (34a) which remains in the mold space during the mold filling and an outer sleeve (34b) arranged concentrically with said shaft which is pressed or pulled out of a mold during the mold filling. in the injection side (37) opposite end (38) of the injection channel (33), arranged slider (35).