METHOD FOR BONDING FIBER-REINFORCED PLASTIC COMPONENTS HAVING A THERMOSETTING MATRIX

Abstract

The present invention relates to a method for producing thermosetting components from two or more semifinished composite-material products with textile fibre reinforcement and matrix material, wherein the semifinished composite-material products are fully consolidated, with the exception of local regions, and are brought into contact at the partially consolidated (gelled) regions (201, 211, 221, 241) such that the matrix material of the partially consolidated regions (201, 211, 221, 241) bonds and the regions joined together in this way are subsequently fully consolidated. Furthermore, a device which is suitable for producing the semifinished composite-material products is disclosed.

Claims

1. A component part comprised of fiber-reinforced composite material having a thermosetting crosslinking plastic matrix system; characterized in that local regions in the component part (said regions being designated bonding locations because they are designed for later joining with other component parts) have a gelled morphological state of the resin system.

2. The component part according to claim 1; characterized in that the partially consolidated region has a degree of crosslinking, , between 1% and 99%, preferably between 2% and 90%.

3. The component part according to claim 1; characterized in that the partially consolidated region at room temperature is in a gelled and vitrified (glass-like) morphological state.

4. The component part according to claim 1; characterized in that the regions of the component part which are not designed for later joining with other component parts are nearly completely consolidated.

5. The component part according to claim 1; characterized in that the regions of the component part which are not designed for later joining with other component parts have the same degree of crosslinking as local regions of the component part which are designed for later joining with other component parts.

6. A device for fabrication of semifinished composite-material products from a fiber reinforcement means in textile form and a thermosetting thermally consolidatable matrix material, which device has a tool with at least two mold elements between which the textile fiber reinforcement is inserted, which textile has previously been impregnated with matrix material, or the device has channels for feeding the liquid matrix material; characterized in that the device further has heating elements for heating the mold elements, and has cooling elements for impeding or retarding the consolidation of the matrix material in sections of the textile fiber reinforcement at which in a gelled regions of the semifinished composite-material products are provided.

7. The device according to claim 6; characterized in that the cooling elements are in the form of channels for passage of a cooling liquid (cooling fluid), or in the form of electric Peltier elements.

8. The device according to claim 6; characterized in that the cooling or heating elements are attached to or mounted on the device from outside in order to achieve local temperature control of the matrix material, so as to at least partially impede consolidation in local regions.

9. The device according to claim 6; characterized in that the device has regions in which the heat capacity of the tool mold elements is changed so that cooled regions are produced.

10. A method for fabricating semifinished composite-material products; characterized in that semifinished products are fabricated from fiber reinforcing material and matrix material, wherewith the consolidation process of the entire semifinished product or of local regions of the product which are designed for later joining is maintained in a gelled morphological state.

11. The method according to claim 10; characterized in that the temperature in local regions of the semifinished composite-material products is changed, in order to obtain gelled regions.

12. The method according to claim 10 or 11; characterized in that the semifinished composite-material products are cut, pressed, temporarily stored, transported, or otherwise treated or handled, prior to further processing.

13. The method according to claim 12; characterized in that, during the described processes, the semifinished composite-material products are brought to a temperature which impedes or at least retards further consolidation of the gelled regions.

14. A method of fabricating thermosetting component parts from two or more semifinished composite-material products each of which semifinished products has a textile fiber reinforcing means and a matrix material; characterized in that that the two or more semifinished composite-material products at the gelled regions of at least one semifinished composite-material product are brought into contact in a manner such that the material of the gelled regions is bonded and the thus joined regions are subsequently completely consolidated.

15. The method according to claim 14; characterized in that the semifinished composite-material products are completely consolidated outside the regions which have been brought into surface contact.

16. The method according to claim 14; characterized in that the gelled regions of the semifinished composite-material products are brought into a generally flat surface contact.

17. The method according to claim 14-16; characterized in that the gelled regions of a plurality of semifinished composite-material products which are brought into contact are stitched, clamped, or stapled, or are fastened together by similar methods, before consolidation.

18. The method according to one of claims 14-17; characterized in that the gelled regions of a plurality of semifinished composite-material products which have been brought into contact are disposed such that they partially or completely surround inserts which are disposed between the said semifinished composite-material products.

Description

[0038] The above-described tool is provided with a stitching head, according to the prior art.

[0039] FIG. 1A is a schematic diagram showing the isothermal hardening of a typical reactive resin system according to the prior art (e.g. an epoxy resin system) versus the hardening time (after Flemming, (in German) Fiber composite construction, ISBN 3-540-58645-8, p. 210). It indicates the course of the hardening (corresponding to the degree of crosslinking of the reactive resin system) over time, at constant hardening temperature. After a hardening time of 15 hr, the maximum static degree of crosslinking is reached, which is also described by the static glass transition temperature Tg (static)=129 C. The diagram shows in particular the gel point, i.e. gelling wherewith the resin system passes from a liquid state into an infusible solid state.

[0040] FIG. 1B is a schematic diagram showing the dependence of the morphological state of a typical reactive resin system according to the prior art (e.g. an epoxy resin system equivalent to FIG. 1B) on the degree of crosslinking and the temperature. In the diagram, the different morphological states are indicated (in regions between the lines of delimitation). In addition to the line of delimitation between evaporation and thermal decomposition, gelling is indicated at a degree of crosslinking of ca. 48%. Also indicated is the line of delimitation comprising the glass transition temperature (Tg) of the resin system at the given crosslinking state. The Tg for complete crosslinking is 129 C., which is also designated Tg (static) (static glass transition temperature). Tg (static) is also represented in the literature as Tg (Tg infinity).

[0041] FIG. 2 shows the inventive tool during the execution of the inventive method. The two tool halves (11 and 12) enclose the fiber reinforcing material (2) impregnated with matrix material, and they re-form it. The heating elements (13) heat the lower tool part (12) and the upper tool part (11) over their entire surfaces (the surfaces of the tool parts), wherewith only local regions are defined by the cooling elements (14) in which regions the heating is reduced and the matrix material is partially consolidated (gelled). The joining between the two semifinished composite-material products (21, 22) according to FIGS. 3b and 4b is also shown.

[0042] FIG. 3a shows schematically the use of a gap tool (also called joining tool) in order to bond a completely consolidated semifinished product to a semifinished product which has a partially consolidated local region; and FIG. 3b shows the use of a gap tool to bond opposing partially consolidated, gelled local regiona.

[0043] FIGS. 4a and 4b show a curved hollow profile, in cross section (FIG. 4a) and in a perspective view (FIG. 4b), wherein the opposite edges of the semifinished product (21, 22) have been bonded by the inventive method.

[0044] FIGS. 5a and 5b show schematically the application of a bonding element (21) to a flat element (22).

[0045] FIGS. 6a to 6c show schematically the realization of various double strap joints by means of partially consolidated, gelled gap regions on the flat element (24) and/or the straps (21, 22), according to the inventive method. In FIG. 6a, the flat element (24) has a partially consolidated region (241) which is bonded with the upper (21) and lower (22) straps at bonding locations (23), as hardening occurs. In FIG. 6b, the straps have partially consolidated, gelled regions (211, 221) which are bonded to the flat element (24) at the bonding locations (23). In FIG. 6c, each of the elements of the gap (21, 22, 24) has a partially consolidated, gelled region (211, 221, 241), wherewith the elements are bonded together with consolidation, at the bonding locations (23).

[0046] FIG. 7 shows schematically the integration of an insert (4) and its bonding to a component part (22) with partially consolidated, gelled gap regions (221), according to the inventive method. The insert (4) is disposed between a second component part (21) and the below-disposed component part (22). Bonding locations (23) are formed between the two component parts (21 and 22) and between the lower component part (22) and the insert (4).

[0047] The inventive method, accomplished in the inventive tool, is illustrated by the following exemplary embodiment. At the same time, the scope of the invention is not limited by the below-described steps and parameters.

Step 1: Fabrication of a Semifinished Composite-Material Product Having Partially Consolidated Regions:

[0048] The description relates to fabrication of a plate-shaped component part comprised of 2 mm thick glass fiber reinforced epoxy resin with partially consolidated, gelled local regions. The epoxy resin system used gels at a degree of crosslinking of 48% (see FIGS. 1A and 1B) and has a glass transition temperature which depends on the degree of crosslinking, according to FIG. 1B.

[0049] First. 3 dry layers of fiberglass fabric with 220 g basis weight were inserted into an RTM infiltration tool, the tool was sealed to be air-tight, was heated to the infiltration temperature of 100 C., and was subjected to vacuum. (RTM=resin transfer molding.) The mixture of resin and hardener was heated to 100 C., and the infiltration was started. A holding pressure of 5 bar was used. After 10 min, the component part was completely infiltrated. The consolidation process was carried out, while continuing to maintain the holding pressure, according to the process variant described below, and then the tool temperature was reduced, the tool was opened, and the component part was removed from the mold. Following such removal, it is necessary to store the component part in a cool environment (depending on the particular process variant), so that the consolidation process is slowed very substantially (or nearly suspended).

[0050] To produce partially consolidated, gelled component part regions which later serve as bonding locations, the temperature in these regions was reduced during the consolidation, in order to slow the crosslinking reaction (or nearly suspend it) at these locations. This was accomplished by means of cooling elements (14) introduced into the RTM tool. FIG. 2 shows schematically a section of an RTM tool with the cooling elements (14) (which in the present instance were liquid-cooled channels).

Process Variant 1A:

[0051] Following the infiltration, the component part was held 15 hr at 100 C., to accomplish consolidation. This achieved a nearly complete crosslinking of the resin system, with a degree of crosslinking of nearly 100%, according to FIGS. 1A and 1B.

[0052] However, at the bonding locations, the resin system was crosslinked only to an un-gelled state (40% degree of crosslinking), wherewith after ca. 3.5 hrs. consolidation time the cooling was begun, and thereby the crosslinking was interrupted. By means of the cooling elements, the bonding locations were cooled to ca. 10 C.

[0053] Following the consolidation time of 15 hr, the bonding locations in the component part were in a prepreg state, wherewith at the time of a later joining the bonding locations could be re-melted by heating. Accordingly, ca. 60% of the original monomers in the thermosetting crosslinking reaction were still available as adhesive means for the later joining.

Process Variant 1B:

[0054] Following the infiltration, the component part was held 15 hr at 100 C. in the tool, for consolidation. A nearly complete crosslinking of the resin system was achieved, with a degree of crosslinking of nearly 100% (FIGS. 1 and 2).

[0055] At the bonding locations, the resin system was crosslinked up to a gelled state, with a degree of crosslinking of 60%, with cooling being started at ca. 4.5 hr consolidation time, resulting in subsequent interruption of the crosslinking. The effect of the cooling elements was to cool the bonding locations to ca. 10 C.

[0056] After the consolidation time of 15 hr, the bonding locations in the component part were at room temperature, in an un-meltable gelled solid state, so that when joining was attempted later, it was not possible to re-melt the bonding locations by heating. Only ca. 40% of the original monomers of the thermosetting crosslinking reaction were available for future joining; however, at the same time because of the un-meltability a possible soiling of the joining tools was avoided. At the time of the joining, the un-crosslinked monomers formed adhesive bonds beyond the borders of the component part, because they wetted the surfaces of the joining elements and adhesively bonded the latter.

Process Variant 1C:

[0057] Following the infiltration, the component part was held 5 hr at 100 C. in the tool, for partial consolidation. The resin system of the entire component part was thereby brought only to a partially consolidated degree of crosslinking of 70%.

[0058] Thus only ca. 30% of the monomers were available for future joining; on the other hand, joining was possible at any location on the component part, and as a result of the gelled and substantially crosslinked state of the resin, the component part had excellent stability (e.g. in the event of handling processes).

Step 2: Joining of Partially Consolidated Regions of Bonded Semifinished Products:

[0059] For the joining, the component part was disposed against a joining partner, so that the bonding location of the component part was located at the desired position of the joining partner. Then the respective bonding locations were subjected to pressure from a gap tool.

[0060] To activate the bonding location, it was heated to the specified process temperature, and adhesion was carried out, along with further consolidation. The heating was preferably by ultrasound waves, which were conducted through the gap tool to the bonding location, or otherwise by heatable welding heads according to the prior art.

[0061] To accomplish the joining, the region of the component part at the given bonding location was preferably heated to a temperature between the glass transition temperature corresponding to the given degree of crosslinking and Tg (static). For Process Variant 1A, this corresponds to a degree of crosslinking of 40% and a temperature range between ca. 20 and 129 C. (lower and upper temperature limits); for Process Variant 1B, this corresponds to a degree of crosslinking of 60% and a temperature range between ca. 40 and 129 C.; and for Process Variant 1C, this corresponds to a degree of crosslinking of 70% and a temperature range between ca. 50 and 129 C. To ensure reliable activation for the joining, preferably a brief starting period at 20 C. above the lowest temperature (thus 20 C. or 40 C. or 50 C.) was employed. With a higher heating temperature, the speed of the crosslinking at the bonding locations is increased. In order to increase the speed of the crosslinking reaction when performing joining, the upper temperature limit can be increased. However, the joining temperature should always be below the limiting temperature for thermal decomposition (and the evaporation temperature for the resin system) (see FIG. 2).

[0062] Also, the degree of crosslinking of the bonding location after the joining is determined by the holding time. Thus the degree of crosslinking of the resin system in the bonding location can be controlled via the holding time and the joining temperature. In an exemplary embodiment, the joining was carried out at 140 C. with holding time 1 hr, resulting in an increase in the degree of crosslinking in the bonding location of at least 10% (see FIG. 1).

[0063] Preferably, after the joining, the bonding location is brought to a temperature below the given glass transition temperature, while maintaining the pressing pressure. In this glass state (vitreous state), the resin system is inherently stable, so that the joints will remain effective after release of the pressing pressure (see FIG. 2).

[0064] If it is desired to bring about further crosslinking of the bonding locations and/or of the remainder of the component part following the joining, this can be accomplished by heating, and holding the joined component parts at a temperature below the given glass transition temperature. If the glass transition temperature is exceeded in the subsequent crosslinking, the bonding locations might not be damaged, but there is a risk of deformation of the pressed regions, which might lead to a negative effect on the load capacity.

[0065] Advantageously, the joining partners employed each comprise a component part having bonding locations according to the invention, so that during the joining there remains available additional adhesive material in the form of un-crosslinked monomer proportions, at the bonding locations.

[0066] Additional fabrication steps may be carried out between the fabrication of the semifinished product and the joining and/or the subsequent crosslinking.

LIST OF REFERENCE NUMERALS

[0067] 11 Upper tool half. [0068] 12 Lower tool half [0069] 13 Heating element. [0070] 14 Cooling element. [0071] 2 Semifinished composite-material product. [0072] 201 Partially consolidated local region of the semifinished composite-material product. [0073] 21 First semifinished composite-material product, for joining. [0074] 211 Partially consolidated local region of the first semifinished composite-material product. [0075] 22 Second semifinished composite-material product, for joining. [0076] 221 Partially consolidated local region of the second semifinished composite-material product. [0077] 23 Bonding location. [0078] 24 Third semifinished composite-material product, for joining. [0079] 241 Partially consolidated local region of the third semifinished composite-material product. [0080] 3 Joining tool. [0081] 4 Insert.