DE19813105A1 - Molding fiber composite components avoiding air inclusions and rejects - Google Patents

Abstract

A porous membrane (32) is fixed in front of the vent holes (30) on the mold cavity side. Its pores are sized to release air freely, whilst the matrix material (21) is retained within. Preferred features: Membrane thickness is 10-60 mu m. Its attachment permits ease of removal when required. The vent holes taper outwardly from the cavity, support being provided to prevent bulging of the membrane into the holes. This takes the form of open-pored foam or honeycomb. The mold dies (13, 14) are clamped together then mixed fibers (20) and matrix (21) are injected. Alternatively the fibers are introduced first, followed by injection of the matrix, after which the dies are pressed together. In a further variant, mixture is introduced just before completion of closure. In a final variant, a fibrous blank is inserted with matrix material, into a die.

Description

The invention relates to a method for producing fiber composite components in which the fibers and the matrix material in at least two Parts comprising a mold forming a mold cavity are formed and openings from the mold cavity to the outside through which the in Air can escape from the mold cavity.

Fiber composite components have both in terms of their quantities produced their diverse areas of application have been extraordinarily strong in recent years gained in interest. The decisive factor for this is undoubtedly the large amount fold of processing possibilities. So there are several methods such. B. ver Different pressing and injection molding techniques are available to make fiber composite components One-off or series production versatile and with complicated shapes to ferti Even within these various processes, when the company multiple variations of the matrix and the matrix material are possible.

DE 196 30 840 describes a method for producing composite bodies a matrix material and a fiber body known in which to complete Filling and enclosing the fiber body the matrix material several times older is pumped by the fiber body located in a molded body. This process delivers composite bodies of very good quality without air conclusions and with complete enclosure of the fibers, but is due to the ex extremely long process time not for use in series production for  Fiber composite components suitable. In addition, due to the supply and discharge lines be worked with an excess of matrix material.

A process for the production of fiber composite components is from Otto Schwarz: "Glass fiber reinforced plastics", Vogel Verlag, Würzburg (1975) known. Two Partial tools form a mold cavity in which the fibers and the Matrix material are brought to their final form. To prevent Air pockets in the fiber composite component are located at certain points in determine distances holes in the tool through which the enclosed and transported through the fibers in front of the front of the flowing matrix material Air can escape. A disadvantage of this method is that with every molding process, matrix material collects in the bores, which during Removal process of the manufactured fiber composite component hardened and thus before the next molding process has to be laboriously removed from the hole, so that the bore can again contribute to the venting of the mold cavity. By removing the leftovers, the idle time between the one increases individual molding processes, which reduces productivity. Also goes through the holes also lost matrix material, which is then no longer for the filling of the fibers is available so that an excess of matrix material must be factored in.

It is therefore the task of a process for the production of fiber Specify bundle components that allow fiber composite components without air inlet conclusions and with complete encapsulation of the fibers in series production manufacture at a high clock rate so that the idle times between the Molding processes can be reduced to a small extent. Furthermore, a Excess matrix material can be prevented.  

A method of the type described in the introduction is invented to achieve the object appropriately characterized in that the mold cavity side in front of the opening a porous membrane is attached, the pores of which are dimensioned in this way are that the air is allowed to escape unhindered, but the matrix material in Mold cavity is retained.

The method according to the invention enables fiber composite components without To produce air pockets in series, with idle times between the one individual molding processes are minimized, which is compared to the conventional Procedure leads to an increase in output. In addition, the target time shortened between the individual processes since no openings are cleaned anymore Need to become. Because the mold cavity is closed, the matrix Compared to material there is no excess material, which means that the Her costs can be further reduced.

The multi-part tools that form the mold cavity can be made of art fabric or metal, depending on the temperature load at the Forming processes and number of pieces of the fiber composite components produced in a series. Metal tools exhibit at high temperatures and high numbers Advantages over plastic tools. The tools consist of several layers, so that only the one to be manufactured Layer facing the fiber composite component has a smooth and hard surface while the backing can be softer and rougher. For some Applications, it is beneficial if the multi-part tools Have guide bolts and crush or cutting edges. With the former can bring the different parts of the tool together precisely be, while the latter a closure of the mold cavity to the outside form.  

The preferred porous membranes are thin polyurethane foils (PU foils), thin Teflon films (PTFE films) or thin polyether block amide films in Be tracht that very well the contour of the fiber composite part to be manufactured and adjust the tool and thus ge an optimal manufacturing process guarantee.

PU, PTFE or polyether block amide films with a thickness in are advantageous Range between 10 microns and 60 microns used. Condition with such foils certain processes during the manufacture of the pores during production Use of these materials desired pore size, so that no additional Ar step is necessary to provide the foils with the pores, resulting in a Minimizing the effort leads.

Research has shown that the size of the pores in the por sen membrane on the viscosity of the matrix material and the material of the porö sen membrane, d. H. depends on the wetting behavior of these two materials. This shows that the viscosity of the material material is 50 mPas advantageously designed if the pores in the membrane have a diameter between 1 µm and 5 µm, in particular 3 µm. There are also pores bar, where due to the designs or geometry a restraint of the Ma terix material and an escape of air is accomplished.

As the porous membranes wear out or become worn with increasing use can be set in an advantageous embodiment of the method porous membranes attached so that they can be easily replaced if necessary can be. This can e.g. B. happen by the fact that they are from the molding surface of the tool, lowered by the membrane thickness, into a recess  and means are attached to prevent slipping. With the latter it is advantageously a circumferential adhesive layer or in the ver deepened recessed holding tips that cling to the film. Through the Introduction into a recess during the molding process the surface of the providing fiber composite component is not affected.

The openings through which the air from the mold cavity ge are preferred leads, at least in the cavity area on the outside appropriately attached. This facilitates the removal of the front of the matrix transported air bubbles because larger cross sections of the Openings are available and capillary effects are thereby reduced that can. In the case of circular openings, this tapering is caused by chamfering the mold cavity-side areas of the openings.

Because during the molding process high pressures on the walls of the tools and thus it also acts on the openings covered with porous membranes Stabilization of advantage, at least the cavity side area of the opening support. This is preferably done in that the addressed area of the openings with an open-cell foam (absorbent fleece) or is filled with a material with an open honeycomb structure. Prevent this filling prevents the porous membrane from slipping into the opening during the molding process without the air escaping from the mold cavity through the porous membrane to influence industries. In this way, impairments to the waiter area of the fiber composite component to be manufactured, as is the case with large openings can arise, prevented.

In principle, the method according to the invention can be used in every molding process be used in which a tool comprising at least two parts one  Form cavity forms through which the fibers and the matrix material in the ge desired shape, and with openings are made, by which can escape the air remaining in the mold cavity. The temperature of the Tools and materials are irrelevant.

There may be circumstances that require it, the fibers and that Matrix material together as a mixture in the clamped tool parts formed mold cavity or the matrix material alone in liquid form in the injected mold cavity with fibers via a channel. The one injection point in the mold cavity can be chosen arbitrarily, since in closed air can escape through the porous membrane and the openings.

However, the fibers and the matrix material are preferred in the mold cavity limiting area of the first tool part, after which the further Tool parts are then pressed onto the first one and the mold cavity is full delimit constantly. In this the fibers and the matrix material are attached finally formed into a fiber composite component. The trapped air that is located in front of the flowing front of the matrix material, escapes through the porö sen membranes and the openings while retaining the matrix material becomes. In this preferred method, the fibers and matrix mate introduced as a mixture or as a semi-finished fiber product covered with matrix material become. The matrix material can also be placed anywhere in the mold cavity space because it is homogeneously distributed in the liquid state.

The invention is described below with reference to an off shown in two figures management example described in more detail, from which further details, Merk color and advantages result.  

It shows

Fig. 1 shows a cross section through an apparatus for producing a fiber composite component by means of the method according to the invention.

Fig. 2 shows the enlarged section 1 of Fig. 1, showing a cavity-side opening including a porous membrane.

In Fig. 1, a device for wet pressing of fiber composite components is Darge, in which a preferred embodiment of the method according to the invention is applied. The two-part pressing tool 10 consists of a fixed to egg ner upper platen 11 upper tool part 13 and a lower platen 12 attached lower tool part 14 , which are pressed together with a force F. The spacers 15 define a formed by the upper tool part 13 and the lower tool part 14 th mold cavity. This is closed abge to the outside by the pinch edge 16 .

Before the molding process, the molding surface 14 a of the lower tool part 14 is designed with a semi-finished fiber 20 preformed from a carbon fiber multiaxial scrim. The liquid matrix material 21 is poured onto this. This happens here in the middle of the lower tool part, but can also be done at any other point in the tool part. Then the upper tool part 13 and the lower tool part 14 are pressed together with the force F until the end position, which is given by the spacers 15 , is reached, in this pressing process the liquid matrix material 21 is pressed into the semi-finished fiber 20 , whereby both takes the final shape of the fiber composite component.

The air enclosed in the semifinished fiber product 20 is pushed in front of the advancing front of the matrix material 21 during the pressing process.

In order to escape the air, openings 30 were drilled through the upper tool part 13 at certain intervals. In certain circumstances it can also be advantageous if the other tool parts contain further openings. The air is now allowed to escape through the porous membrane 32 between the mold cavity and the openings 30 , but prevents the matrix material 21 from penetrating into the openings 30 .

In FIG. 2, the mold cavity-side area of the openings is shown in enlarged form. So that the porous membrane 32 has no influence on the upper surface of the fiber composite part to be produced during the molding process, it was accommodated in this example in a recess in the upper tool 13 . In the case of very thin porous membranes 32 and less sensitive fiber composite component surfaces, the porous membrane 32 can also be applied directly to the molding surface 13 a of the upper tool part 13 without a recess. To fix the porous membranes 32 , these are stuck on adhesive part 33 on the upper tool part 13 .

For better ventilation of the mold cavity, the openings 30 in the mold cavity area were provided with a cone and lined with an air-permeable absorbent fleece 31 for stabilization. The porous membrane 32 together with adhesive strips 33 and absorbent fleece 31 can also be introduced in a composite, as a so-called pad, so that a change of these parts can be carried out in a simplified manner if necessary, since only a single component has to be replaced.

The porous membranes 32 allow ventilation of the mold cavity, but prevent the matrix material 21 from escaping into the openings 30 , so that all the matrix material 21 is available for filling the semi-finished fiber product 20 and the openings 30 do not stick together. By preventing the opening 30 from sticking, it is not necessary to remove hardened matrix material after the molding process, as a result of which the cycle times are considerably shortened.

Claims (9)

1. A process for the production of fiber composite components, in which the fibers ( 20 ) and the matrix material ( 21 ) are molded in at least two parts around a mold ( 10 ) forming a mold cavity and openings ( 30 ) are guided outwards from the mold cavity, Via which the air in the mold cavity can escape, characterized in that a porous membrane ( 32 ) is placed on the mold cavity side in front of the openings ( 30 ), the pores of which are dimensioned such that the air can escape unhindered, the matrix material ( 21 ) but is retained in the mold cavity. 2. The method according to claim 1, characterized in that a polyurethane (PU) film or a Teflon (PTFE) film or a polyether block amide film is used as the porous membrane ( 32 ). 3. The method according to claim 2, characterized in that the The thickness of the film is between 10 µm and 60 µm. 4. The method according to one or more of the preceding claims, characterized in that the porous membranes ( 32 ) are brought to such that they can be easily removed if necessary. 5. The method according to one or more of the preceding claims, characterized in that the openings ( 30 ) are tapered at least in the hollow region on the outside. 6. The method according to one or more of the preceding claims, characterized in that at least the mold cavity-side loading area of the openings ( 30 ) is lined with a support preventing the arching of the film into the opening. 7. The method according to claim 6, characterized in that at least the cavity side region of the openings ( 30 ) with an open-cell foam material ( 31 ) or with an open honeycomb structure made of permitted material is filled. 8. The method according to one or more of the preceding claims, characterized in that the tool parts ( 13 , 14 ) are clamped and a mixture of fibers ( 20 ) and matrix material ( 21 ) is injected or the fibers ( 20 ) before clamping the Tool parts ( 13 , 14 ) are placed in the mold cavity and the matrix material ( 21 ) is injected. 9. The method according to one or more of the preceding claims 1 to 7, characterized in that the tool parts ( 13 , 14 ) are pressed together with pressure and before closing a mixture of fibers ( 20 ) and matrix material ( 21 ) between the Tool parts is given or the fibers ( 20 ) as semi-finished products and the matrix material ( 21 ) are introduced into a tool part ( 14 ).