DE102007003596B4 - Method for producing a leaf spring made of a fiber composite material with a thermoplastic material - Google Patents

Abstract

Method for producing a leaf spring (25) from a fiber composite material, characterized by the following method steps:
Melting a thermoplastic (14),
Wetting a fiber strand (2) of at least parallel aligned fibers with the molten plastic (14),
Covering the fiber strand (2) on its upper side and on its underside, each with a covering material web (3, 4), wherein the plastic-wetted fiber strand (2) with the two Abdeckmaterialbahnen (3, 4) on a convexly curved and heated heating table (6) is merged,
Cutting off the fiber-reinforced fiber strand (2) covered with the two covering material webs (3, 4) and into prepregs (20) with predetermined lengths,
- depositing a predetermined number of prepreg layers (20 ', 20'',20''') on a support surface of a heated molding press (24), and
- Pressing the prepreg layers (20 ', 20'',20''') in the molding press (24) under the action of predetermined and material-dependent temperature and pressure gradients over time such that after the pressing process a cured fiber composite leaf spring. ..

Description

The The invention relates to a method for producing a leaf spring from a fiber composite material according to the preamble of the claim 1 and a leaf spring produced in accordance with the preamble of the claim 18th

For example, the EP 0 084 101 A2 It is known that leaf springs can be produced from a fiber composite material. Such leaf springs have over conventional leaf springs made of metallic materials the advantage of lower weight and a longer shelf life. By choosing the layer thicknesses of the laminate and by the respective orientation of the fibers in a plastic matrix, the spring characteristic can be influenced within wide limits.

in the In general, leaf springs made of fiber-reinforced materials are called so-called Wet laminates or prepregs prepared with the desired Fiber alignment on top of each other layered and then pressed and hardened become. The term prepreg is known to be a Semi-finished product or a precursor for the production of objects a fiber composite material understood. A prepreg is conventional made of fibers and an unhardened thermosetting plastic matrix. The continuous fibers can be unidirectional be aligned or present as tissue or scrim. A thermosetting plastic matrix usually exists from a mixture of a synthetic resin, a hardener and an accelerator. Examples of synthetic resins are resins based on epoxy resin or Vinyl ester resin for use.

to Production of prepregs with a thermosetting plastic matrix For example, the fibers are deposited on a carrier and then with wetted the resin. Also, an impregnation of the fibers with the still liquid Resin before it is deposited on the carrier is known. By cooling the Prepregs will be the chemical reaction of the hardener and the accelerator with the synthetic resin as long prevented until the prepreg for making a final product should be used. For example for producing a fiber composite leaf spring several prepreg layers one above the other layered and then tailored. By then heating this workpiece over the following Reaction temperature of the hardener In addition, the curing process begins, finally to the desired End product leads. Unless this warming in a press as well as in an autoclave at atmospheric Negative pressure carried out is, you can air-free end products with a very high fiber content and produce comparatively low plastic matrix content.

Around Prepregs produce in a continuous manufacturing process to be able to must be one of them Manufacturing device a strand of continuous fibers are supplied. It is important to ensure that the fibers in the desired spatial Orientation remain. The fiber distribution should therefore usually be homogeneous. In addition, in the supply and processing of the Strand of fibers as possible low fiber break occur.

In addition, should the fiber strand preferably with said thermoset plastic matrix, ie the mixture of at least resin, hardener and accelerator, wetted become. It is important that the distribution of the thermosetting plastic matrix evenly or all fibers of the fiber strand are impregnated by the plastic matrix. In addition, not too much of the plastic matrix on the fiber strand arrive, since this is a lateral drainage of the excess liquid to an undesirably large extent would result.

Provided the prepreg strand produced is cut into desired lengths or into a roll wound up and then is to be stored, is the fiber strand in the production of the prepreg strand is preferred at its bottom and at its Cover the top with a Abdeckmaterialbahn. When hanging up this Abdeckmaterialbahnen on the fiber strand it can come to that the fibers of the upper and / or the lower fiber layer of the fiber strand in an unwanted way transverse to the longitudinal extent of the fiber strand be folded. In a fiber composite end product, such folded fibers carry only a little to the desired Material properties, why such a fiber folding can be avoided should.

A leaf spring made of a fiber composite material, and a method for producing the same is for example from DE 10 2004 010 768 A1 known. Of particular importance in this fiber composite leaf spring is that the axial ends of a central longitudinal section with respect to the leaf spring width are tapered, wherein the axially aligned fibers of the fiber composite material are uncut out to the end edge of the leaf spring. In this document it is described that the manufacture of the leaf spring takes place with a duroplastic plastic matrix which cures when exposed to heat.

From the not pre-published DE 10 2006 052 136 A1 a method for the continuous production of prepregs is known in which a fiber strand of at least parallel aligned fibers wetted with a not yet set thermosetting plastic matrix and on its top and bottom are covered with a covering material web, and in which the plastic matrix-impregnated fiber strand covered with the covering material webs is finally cut to predetermined lengths as a prepreg or rolled up into a roll.

Around in the manufacture of prepregs to achieve that the fibers in a desired one Alignment in a related matter Get manufacturing device and there with a lower and an upper Covering material be occupied, that the not yet set Plastic matrix in sufficient quantity reaches all fibers of the fiber strand, that fiber breakage is minimized, and that a folding of the fibers transverse to the longitudinal extent of Fiber strand is avoided, it is also provided that the fiber strand with the unbound thermoset plastic matrix and the two Abdeckmaterialbahnen on a convex curved and heated heating table merged becomes.

the known method is based on the finding that at a bring together of the fiber strand with a lower and an upper plastic matrix occupied Covering material web or another flexible sheet on a heating table with a convex shaped surface all mentioned Requirements for the production of an optimal prepreg can be fulfilled.

• – Einen Heiztisch und eine Ablegrolle zur Führung und Ablage einer oberen Abdeckmaterialbahn auf den Faserstrang,
• – eine konvex gekrümmte Heiztischoberfläche zur Führung einer unteren Abdeckmaterialbahn und des Faserstranges, und
• – zumindest drei Heizzonen an dem Heiztisch zum Aufheizen der Abdeckmaterialbahnen, der duroplastischen Kunststoffmatrix und des Faserstrangs,
• – wobei die Krümmungsgeometrie der Oberfläche des Heiztisches sowie die Oberflächentemperaturen der zumindest drei Heizzonen derart gewählt sind, dass die Normalkraftkomponente einer auf den Faserstrang und die beiden Abdeckmaterialbahnen wirkenden Zugkraft die flüssige Kunststoff matrix von zumindest einer der Abdeckmaterialbahnen zu den Oberflächen aller Fasern im Faserstrang führt.

The DE 10 2006 052 136 A1 also discloses a device with which the production method just described can be carried out. Accordingly, the device for the production of prepregs from a fiber strand with at least parallel aligned fibers and with two plastic matrix-covering cover material webs is characterized by at least the following features:

• A heating table and an unloading roller for guiding and depositing an upper covering material web onto the fiber strand,
• - A convex curved Heiztischoberfläche for guiding a lower Abdeckmaterialbahn and the fiber strand, and
• At least three heating zones on the heating table for heating the covering material webs, the thermosetting plastic matrix and the fiber strand,
• - Wherein the curvature geometry of the surface of the heating table and the surface temperatures of the at least three heating zones are selected such that the normal force component of acting on the fiber strand and the two Abdeckmaterialbahnen traction the liquid plastic matrix of at least one of Abdeckmaterialbahnen leads to the surfaces of all fibers in the fiber strand.

Moreover, from the not previously published DE 10 2006 052 137 A1 a method for the production of leaf springs made of a thermosetting fiber composite material known to be produced with the high quality leaf spring. In particular, to be achieved with the local method that the fibers are present in the leaf spring a desired orientation that the not yet set thermosetting plastic matrix in the leaf spring in sufficient quantity to all fibers passes, that the extent of fiber breakage in the leaf spring is minimized, and that a folding of the fibers is at least largely avoided transversely to the longitudinal extent of the fiber strand.

• – Abdecken der Oberseite und der Unterseite eines Faserstranges, der aus zumindest parallel zueinander ausgerichteten Fasern besteht, mit zumindest einer Abdeckmaterialbahn.
• – Benetzen der Fasern des Faserstranges mit einer noch nicht abgebundenen duroplastischen Kunststoffmatrix.
• – Erwärmen des abgedeckten und kunststoffmatrixbelegten Faserstranges zur Imprägnierung der Fasern des Faserstranges mit der noch nicht abgebundenen duroplastischen Kunststoffmatrix.
• – Abkühlen des abgedeckten kunststoffmatriximprägnierten Faserstranges.
• – Abschneiden des abgedeckten kunststoffmatriximprägnierten Faserstranges zu einzelnen Prepregs.
• – Ablegen von mehreren Lagen Prepregs vertikal übereinander auf einer konvex gekrümmten Oberfläche zu einer Roh-Blattfeder.
• – Kühlen der Roh-Blattfeder auf einer konvex gekrümmten Oberfläche.
• – Pressen der Roh-Blattfeder in einer Presse zu einer gepressten Roh-Blattfeder.
• – Erwärmen der gepressten Roh-Blattfeder.
• – Endbearbeitung der gepressten Roh-Blattfeder zur fertigen Blattfeder, wobei bei allen Fertigungsschritten vorbestimmte Temperaturen an dem jeweiligen Werkstoff oder an dem jeweiligen Zwischenprodukt eingestellt werden, und bei dem die jeweiligen Temperaturen über vorbestimmte Zeiträume aufrechterhalten werden.

The known method comprises the following method steps:

• - Covering the top and the bottom of a fiber strand, which consists of at least parallel aligned fibers, with at least one Abdeckmaterialbahn.
• - Wetting the fibers of the fiber strand with a not yet set thermosetting plastic matrix.
• - Heating the covered and plastic matrix occupied fiber strand for impregnating the fibers of the fiber strand with the not yet set thermosetting plastic matrix.
• Cooling the covered plastic matrix impregnated fiber strand.
• - Cutting the covered plastic matrix impregnated fiber strand into individual prepregs.
• - Laying several layers of prepreg vertically above each other on a convex curved surface to a raw leaf spring.
• - Cooling the green leaf spring on a convex curved surface.
• - Pressing the green leaf spring in a press to a pressed raw leaf spring.
• - Heating the pressed raw leaf spring.
• - Finishing the pressed raw leaf spring to the finished leaf spring, wherein in all manufacturing steps predetermined temperatures are set to the respective material or to the respective intermediate product, and in which the respective temperatures are maintained for predetermined periods.

In addition, it is known to produce leaf springs made of a fiber composite material, which uses a thermoplastic material. That's how it describes DE 102 60 060 A1 a leaf spring for a motor vehicle, which may be made of various materials, which may include composites, metals, metal-metal castings and plastic-metal-hybrid materials. Although it is mentioned in this document that the leaf spring can be made of a thermoplastic composite material, as are the internal structure or No information was given on their production.

Finally, out of the JP 63 225 738 A a leaf spring for a vehicle is known, which is made of a multilayer fiber composite material. Certain layers of material of this leaf spring are used for vibration damping and consist of a viscoelastic material, such as a thermoplastic such as polyethylene, various foams, elastomers and rubber.

to Further development of this state of the art is the invention the object of a method for producing leaf springs from a fiber composite material, with the likewise the technical problems described above are mastered can and a high-quality leaf spring as inexpensive to produce is. So should be achieved in particular that the fibers in the Leaf spring in a desired orientation be present that the not yet set plastic matrix in the Leaf spring in sufficient quantity to all fibers passes that the extent of fiber breakage in the leaf spring is minimized, and that a folding of the fibers transverse to the longitudinal extent of the fiber strand at least largely avoided. Another task exists therein, the structure of a fiber composite leaf spring produced in this way to describe.

The solution These objects emerge from the features of the independent claims. advantageous Further developments and embodiments of the invention are assigned dependent claims removable.

Of the Invention is based on the finding that a leaf spring a fiber composite material then prevailing in the automotive industry very high quality requirements can be fair and also relatively inexpensive to produce is when their fiber composite using at least a thermoplastic material is produced.

As was described at the beginning, is the safe handling of a thermosetting Plastic in the production of a related fiber composite material or for producing a known fiber composite leaf spring adherence to many process parameters bound. These include the mixing ratio of synthetic resin, hardener and accelerator as well as the compliance of given upper and lower temperature limits, a useful for the manufacturing process viscosity of the thermoset To ensure plastic matrix and too early and unwanted hardening to avoid.

Of the Use of a thermoplastic in the production a fiber composite leaf spring, however, is relatively simple and therefore very advantageous because in the processing of this plastic only considered a solidification temperature or melting temperature must become.

• – Schmelzen eines thermoplastischen Kunststoffs,
• – Benetzen eines Faserstranges aus zumindest parallel zueinander ausgerichteten Fasern mit dem aufgeschmolzenen Kunststoff,
• – Abdecken des Faserstranges an seiner Oberseite und an seiner Unterseite mit jeweils einer Abdeckmaterialbahn, wobei der kunststoffbenetzte Faserstrang mit den beiden Abdeckmaterialbahnen auf einem konvex gekrümmten und beheizten Heiztisch zusammengeführt wird,
• – Abschneiden des mit den Abdeckmaterialbahnen abgedeckten und kunststoffbenetzten Faserstrangs als Prepreg in vorbestimmte Längen,
• – Ablegen einer vorbestimmten Anzahl von Prepreg-Lagen auf einer Ablagefläche einer beheizbaren Formpresse, und
• – Pressen der Prepreg-Lagen in der Formpresse unter Einwirkung von vorbestimmten und werkstoffabhängigen Temperatur- und Druckverläufen über die Zeit derart, dass nach dem Pressvorgang eine ausgehärtete Faserverbund-Blattfeder vorliegt.

The invention therefore initially relates to a method for producing a leaf spring made of a fiber composite material, which is characterized by the following method steps:

• Melting of a thermoplastic,
• Wetting a fiber strand of at least parallel aligned fibers with the molten plastic,
• Covering the fiber strand at its upper side and at its lower side, each with a covering material web, wherein the plastic-wetted fiber strand is brought together with the two covering material webs on a convexly curved and heated heating table,
• Cutting off the plastic-coated fiber strand covered with the covering material webs as prepreg into predetermined lengths,
• - depositing a predetermined number of prepreg layers on a support surface of a heated molding press, and
• - Pressing the prepreg layers in the molding press under the action of predetermined and material-dependent temperature and pressure gradients over time such that after the pressing process is a cured fiber composite leaf spring.

These Process features illustrate two essential to the invention Things. For one thing, by merging the fiber strand and the Abdeckmaterialbahnen on the convex curved and heated heating table ensures that the thermoplastic material optimally in the fiber strand can disperse without causing unwanted fiber breakage or to fiber folds or transverse orientations of fibers to the longitudinal extent the fiber strand comes. Furthermore becomes the fiber strand wetted with the thermoplastic through the at least one Abdeckmaterialbahn top, bottom and side wrapped so that the dimensional stability of such a manufactured Prepregs increased and a later one Flow away of excess thermoplastic Plastic is favored in a molding press.

According to a preferred development, it is provided that the molten thermoplastic material is applied to at least one of the two cover material webs prior to their contact with the fiber strand on the side facing the fiber strand. By this measure, the required amount of liquefied thermo targeted plastic plastic only then fed to the fiber strand when this and the Abdeckmaterialbahn are brought together on the surface of the heating table.

alternative to or in addition can be provided that the thermoplastic directly is applied to the fibers of the fiber strand, or that the Fiber strand through a container with pulled through a collection of thermoplastic material is before the fiber strand is merged with the Abdeckmaterialbahnen.

A Another embodiment provides that with the Abdeckmaterialbahnen Covered fiber strand on the heating table to temperatures above the melting temperature of the thermoplastic material heated or kept on this, as well as with one out of the on the fiber strand and the Abdeckmaterialbahnen acting tensile force and from the curvature of the table surface resulting normal force is applied so that the thermoplastic Plastic flows to all individual fibers and wets them.

Further is preferred that as a material for the Abdeckmaterialbahnen a thermoplastic material is used whose melting point is higher as the melting point of that thermoplastic, with all fibers of the fiber strand are wetted. This ensures that the Abdeckmaterialbahnen when merging with the other, molten hot thermoplastic Plastic still largely remain firm and so on the mechanical stability a prepreg produced in this way, for example for its further transport, is advantageous contribute.

According to one Another method feature may be that a lower Covering material on the surface of the heating table and an upper Covering material is passed around a Ablegrolle before these two Abdeckmaterialbahnen with the fiber strand in the range of the heating table in Get in touch.

there can be provided that the Auflegkraft the Auflegrolle smaller is the normal force component of the tensile force with which the Fiber strand together with the Abdeckmaterialbahnen over the Hot table is pulled. This division of forces causes the penetration the fiber strand with thermoplastic very gentle takes place, so that fiber breakage and fiber folding are kept low can.

Prefers is also provided that the heating table is heated and at least two, preferably at least three different heating zones with different Temperatures. This is a targeted influence on the temperature of the strand of fibers, thermoplastic and Abdeckmaterialbahnen in that crucial phase of Leaf spring production possible, in which these leaf spring materials are brought together.

In Embodiment of this method feature can be provided that where the lower Abdeckmaterialbahn first touches the heating table, the surface of the heating table has an average temperature lower is the coolest temperature Heating zone. Furthermore it is judged to be advantageous when passing through the Abdeckmaterialbahnen Covered and plastic-permeated fiber strand immediately behind the heating table, so behind the outlet end, an average temperature which is lower than the temperature in the hottest heating zone.

According to one Another feature of the method can be provided that by the Abdeckmaterialbahnen covered and plastic-permeated fiber strand in the transport direction behind the heating table along the surface of a cooling table guided and cooled down there becomes. It makes sense if the covered by the Abdeckmaterialbahnen and plastic-permeated fiber strand in the transport direction behind the cooling table one has mean temperature above the melting temperature of the all fibers wetting thermoplastic fibers lies.

The Transport speed V of the fiber strand and the Abdeckmaterialbahnen is for example between 0.05 m / s and 0.2 m / s.

Farther can be provided that covered by the Abdeckmaterialbahnen and plastic-permeated fiber strand in the region of the outlet side End of the heating table of at least one smoothing roller acted upon with a force is less than or equal to the bearing force F1 of the roll-up roll and smaller than the normal force component the tensile force on the covered fiber strand. The smoothing rollers just care for a smooth surface the deposited on the top of the fiber strand Abdeckmaterialbahnen.

The Fibers of the fiber strand are preferably aligned unidirectionally or as a woven or laid fabric, and as glass fibers, carbon fibers or aramid fibers formed.

According to another feature of the invention, it is provided that with closed and pressurized molding press in a certain period t0 to t1, the temperature of the stacked prepreg layers to above the enamel temperature T7 of the thermoplastic material wetting all the fibers is raised, that after a further specific period t1 to t2 the temperature of the stacked prepreg layers is raised above the melting temperature T8 of the thermoplastic Abdeckmaterialbahnen, and that thereafter in a further period t5 to t6 the temperature the prepreg layers is brought under the different melting temperatures T7 and T8 of the two thermoplastics. This ensures that the all-wetting thermoplastic material and the thermoplastic material of the Abdeckmaterialbahnen mix before the final curing of the leaf spring molten and so set no inhomogeneities in the leaf spring.

In addition can Run the procedure so that after heating all the fibers wetting thermoplastic over its melting temperature T7 the temperature of the prepreg layers over a period of time t3 to t4 below, preferably just below the melting temperature T7 held all the fibers wetting thermoplastic becomes.

Finally, concerns the invention, a leaf spring made of a fiber composite material, the has at least parallel aligned fiber in embedded in a thermoplastic material. This leaf spring is made up of several layers Layers of prepregs are constructed, the prepregs each consisting of one Fiber strand with in the longitudinal direction consist parallel to each other oriented fiber, which in the thermoplastic material are embedded, and where the top and bottom of the fiber strand of a respective Abdeckmaterialbahn from a thermoplastic is covered. Also, this leaf spring is provided that the melting temperature of the thermoplastic material the Abdeckmaterialbahnen over the melting temperature of that thermoplastic is with which all fibers of the fiber strand are wetted.

Of the all fibers wetting thermoplastic fibers is preferably made of polypropylene, polyamide, polyamide 6.6 or polybutylene terephthalate.

to Clarification of the invention, the description is a drawing accompanied with the one embodiment explained becomes. In this shows

1 a highly schematic production schedule for producing a fiber composite leaf spring, and

2 a temperature profile over time in the manufacture of the fiber composite leaf spring in the molding press according to 1 ,

1 shows therefore in a schematic representation of a production plant 1 for the production of leaf springs 25 from a fiber composite material. At the beginning of the production process, the production plant 1 a fiber strand 2 supplied continuously from parallel to their longitudinal extent aligned glass fibers. Before reaching the input-side section 16 a heating table 6 becomes the fiber strand 2 with a thermoplastic 14 occupied, which later all fibers of the fiber strand 2 will wet.

The melting of the thermoplastic material 14 takes place in the embodiment chosen here via a feeder designed as an extruder 13 to which the plastic is supplied on the input side in the form of a granulate, and the output side is equipped with a nozzle which provides optimum storage of the molten plastic 14 on the fiber strand 2 allowed. A second stream of molten plastic 14 is on an upper Abdeckmaterialbahn 3 filed, in such a way that the plastic 14 on the side of the Abdeckmaterialbahn 3 comes to rest, which later the fiber strand 2 is facing.

A second, lower cover material web 4 becomes the production plant 1 below the fiber strand 2 fed. While this lower Abdeckmate rialbahn 4 via the input-side section 16 of the heating table 6 to the fiber strand 2 guided there and optionally with a preferably above the melting temperature T7 of the thermoplastic material 14 lying table temperature T1 is preheated, passes the upper Abdeckmaterialbahn 3 about a roll-up roll 5 with a reversal of their direction of movement in the region of the fiber strand 2 ,

The two Abdeckmaterialbahnen 3 and 4 and the fiber strand 2 be on a convex curved surface 15 of the heating table 6 merged, with the Auflegrolle 5 the upper Abdeckmaterialbahn 3 with a comparatively low force F1 on the thermoplastic fiber strand 2 suppressed. The deflection force F1 of the Ablegrolle 5 is so small, so that it is ensured that no or only a relatively small fraction of fiber fraction is produced by the contact pressure.

Because of the combination of the thermoplastic fiber strand 2 and the two Abdeckmaterialfolien 3 . 4 at a velocity V and a tensile force F6 across the convex curved surface 15 of the heating table 6 are drawn from the tensile force F6, a normal force F2, which the two Abdeckmaterialbahnen 3 and 4 with the plastic 14 and the fibers of the fiber strand 2 in Direction to the surface 15 of the heating table 6 suppressed. This penetrates the heated thermoplastic 14 the fiber strand 2 so that all its fibers are gently and comparatively slowly impregnated with the same. A sufficiently large table length combined with a transport speed V adapted in this respect, for example from 0.05 m / s to 0.2 m / s, ensure that despite the comparatively low normal force F2 of the fiber strand 2 completely from the plastic matrix 14 is penetrated.

The merging of the fiber strand 2 and the two Abdeckmaterialbahnen 3 . 4 takes place on the convex curved surface 15 of the heating table 6 in the region of a first heating zone S1 of three heating zones S1, S2 and S3 thereof. These heating zones are equipped with an electric heater or hot water heater, not shown, which a comparatively accurate adjustment of the temperature of the hotplate surface 15 ensure in the respective heating zones S1, S2 and S3. This makes it possible to use the thermoplastic material 14 between the two Abdeckmaterialbahnen 3 . 4 To temper gradually so that it has, for example, in the first heating zone S1 and the second heating zone S2 temperatures T2 and T3, which are well above its melting temperature T7. The optimum temperature in the area of the heating zones depends on the selected materials of the leaf spring and can be set individually.

In any case, the three heating zones S1, S2 and S3 allow a systematic temperature control, in particular of the thermoplastic material 14 , wherein first a targeted increase in temperature and thus viscosity reduction is performed, which is the wetting of the fibers of the fiber strand 2 with the plastic 14 facilitated.

The transport of the plastic 14 from the upper and optionally the lower Abdeckmaterialbahn 3 . 4 into the depth of the fiber strand 2 Towards each individual fiber is essentially behind the Ablegrolle 5 if the composite structure of fiber strand 2 , Cover material webs 3 . 4 and plastic 14 with a tensile force F6 acting on it over the convexly curved heating table 6 with its three different heating zones S1, S2 and S3 is pulled.

Characterized in that in the wetting of the fibers of the fiber strand 2 with the plastic 14 no pressing or calender rolls are used with comparatively high contact pressures, the fiber breakage is advantageously small. Since all fibers of the fiber strand 2 as well as the upper cover material web 3 and the lower cover material web 4 with the same transport speed V over the heating table 6 are drawn, no or only negligible relative speeds of these elements against each other, so that the initially explained fiber folding does not occur or only slightly.

Subsequently, the temperature of the thermoplastic material 14 between the two Abdeckmaterialfolien 3 . 4 and in the fiber strand 2 in the third heating zone S3 are reduced to a value T4, which is lower than the temperatures T2 and T3 of the input-side and the middle heating zone S1 and S2, but still above the melting temperature T7 of the thermoplastic material 14 lies.

Because the Abdeckmaterialbahnen 3 and 4 consist of a thermoplastic material whose melting temperature T8 above the melting temperature of that thermoplastic 14 lies, with which all fibers of the fiber strand 2 were wetted, they initially remain intact and contribute to the mechanical stability of the prepreg strand to be produced 11 at.

Seen in the direction of transport behind the Ablegrolle 5 and in front of the outlet end of the heating table 6 , in the area of the third heating zone S3, has the manufacturing device 1 over three smoothing rolls 7 . 8th and 9 , with a comparatively low contact force or smoothing force F3, F4, F5 on the top of the upper Abdeckmaterialbahn 3 Press and smooth it out. Such a smoothing of the top of the upper Abdeckmaterialbahn 3 may be useful because the Ablegkraft F1 the Ablegrolle 5 is relatively low.

When leaving the heating table 6 is the average temperature T5 of the covered and plastic-impregnated prepreg strand 11 in this embodiment, slightly above the melting temperature T7 of the thermoplastic material 14 , To further lower this temperature and in particular easy to handle, from the prepreg strand 11 cut to length prepreg pieces 20 Being able to provide that strand becomes 2 made of fibers, Abdeckmaterialbah NEN 3 . 4 and thermoplastic 14 in a further process step on the cooled surface of a cooling table 10 drawn.

The one with the plastic 14 impregnated prepreg strand 11 indicates when leaving the cooling table 10 an average temperature T6, which is still slightly above the melting temperature T7 of all thermoplastic wetting the fibers 14 lies. One behind the cooling table 10 arranged cutting device in the form of a knife 23 separates sections of given length as prepregs 20 out of this endless strand 11 from.

The prepregs 20 are subsequently on intermediately stored convex curved storage surfaces or to a molding press 24 transported. In the molding press 24 becomes a desired number of prepreg layers 20 ' . 20 '' . 20 ''' on a convex curved die 21 stacked on top of each other and then by a patrix 22 the molding press 24 pressed into a geometry, which may also be finely machined fiber composite leaf spring eventually 25 equivalent.

To be in the molding press 24 a leaf spring 25 with the lowest possible plastic content, the highest possible fiber content and without producing any boundary layers in the plastic, the stack with the prepreg layers 20 ' . 20 '' . 20 ''' subjected to a temperature treatment during pressing, in 2 is illustrated. Accordingly, at the latest after closing the molding press in a period t0 to t1, the temperature of the prepreg layers 20 ' . 20 '' . 20 ''' raised to a value above the melting temperature T7 of all thermoplastic wetting the fibers 14 and is maintained until a time t3. This will make the thermoplastic 14 held molten or remelted so that excess plastic under the pressure of the prepreg layers 20 ' . 20 '' . 20 ''' exit and the molding press 24 can leave. If necessary, trapped air also exits the molded body.

Because the Abdeckmaterialbahnen 3 and 4 consist of a thermoplastic material whose melting temperature T8 above the melting temperature of that thermoplastic 14 lies, with which all fibers of the fiber strand 2 were wetted, they remain initially mechanically intact.

A beginning at time t2 lowering the temperature of the prepreg layers 20 ' . 20 '' . 20 ''' just below the melting temperature T7 of the plastic 14 in the period t3 to t4 can be used as a maturity phase, if desired or necessary.

Following this, the temperature of the prepreg layers 20 ' . 20 '' . 20 ''' in a period t4 to t6 raised to a value which is above the melting temperature T7 of that thermoplastic 14 lies, with which all fibers of the fiber strand 2 are wetted, and also in a sufficiently long period around the time t5 around the melting temperature T8 of the thermoplastic material of the two Abdeckmateriallagen 3 . 4 surpasses. As a result, the material melts the Abdeckmateriallagen 3 and 4 , so that this thermoplastic with the other thermoplastic 14 under the pressure of the molding press 24 merges molten.

Finally, the temperature of the prepreg layers 20 ' . 20 '' . 20 ''' until a time t7 below the melting temperature T7 of the thermoplastic material 14 lowered and the raw leaf spring 25 the molding press 24 taken to a possibly necessary finishing.

1

manufacturing device

2

Fiber strand; fiber

3

Upper cover material web

4

Lower cover material web

5

Auflegrolle

6

hot table

7

smoothing roll

8th

smoothing roll

9

smoothing roll

10

Refrigerated table

11

Prepreg strand

12

feeder for melted plastic

13

feeder for the melted plastic, extruder

14

Geschmozenen plastic

15

Heiztischoberfläche

16

Inlet check Section of the heating table

20

truncated prepreg

20 '

Prepreg layer

20 ''

Prepreg layer

20 '' '

Prepreg layer

21

Concave curved Die of the molding press

22

Convex curved Patrice of the molding press

23

knife

24

molding press

25

leaf spring

F1

Auflegkraft the Auflegrolle 5

F2

Normal force component of the tensile force F6 on the strand 11

F3

Pressing force of the smoothing roller 7

F4

Pressing force of the smoothing roller 8th

F5

Pressing force of the smoothing roller 9

F6

traction

S1

input-side Heating zone of the heating table

S2

middle Heating zone of the heating table

S3

Load-side Heating zone of the heating table

T1

Average temperature of the input-side section 16

T2

middle Temperature of materials in heating zone S1

T3

middle Temperature of materials in heating zone S2

T4

middle Temperature of materials in heating zone S3

T5

middle Temperature of the prepreg strand behind the heating table

T6

middle Temperature of the prepreg strand behind the cooling table

T7

Melting temperature of the plastic 14

T8

melting temperature the plastic of Abdeckmaterialbahnen

T

temperature

t

Time

Claims (19)

Method for producing a leaf spring ( 25 ) of a fiber composite material, characterized by the following process steps: - melting a thermoplastic material ( 14 ), - wetting a fiber strand ( 2 ) made of at least parallel aligned fibers with the molten plastic ( 14 ), - covering the fiber strand ( 2 ) at its top and at its bottom, each with a Abdeckmaterialbahn ( 3 . 4 ), wherein the plastic-wetted fiber strand ( 2 ) with the two Abdeckmaterialbahnen ( 3 . 4 ) on a convexly curved and heated heating table ( 6 ), - cutting off the with the two Abdeckmaterialbahnen ( 3 . 4 ) covered and plastic-wetted fiber strand ( 2 ) to prepregs ( 20 ) with predetermined lengths, - depositing a predetermined number of prepreg layers ( 20 ' . 20 '' . 20 ''' ) on a support surface of a heatable molding press ( 24 ), and - pressing the prepreg layers ( 20 ' . 20 '' . 20 ''' ) in the molding press ( 24 ) Under the action of predetermined and material-dependent temperature and pressure gradients over time such that after the pressing process, a cured fiber composite leaf spring is present. Method according to claim 1, characterized in that on at least one covering material web ( 3 . 4 ) before their contact with the fiber strand ( 2 ) on the to the fiber strand ( 2 ) facing side of the still molten thermoplastic ( 14 ) is applied. A method according to claim 1 or 2, characterized in that the thermoplastic material ( 14 ) directly onto the fibers of the fiber strand ( 2 ) or that the fiber strand ( 2 ) by a collection of thermoplastic ( 14 ) is pulled through. Method according to at least one of claims 1 to 3, characterized in that the with the Abdeckmaterialbahnen ( 3 . 4 ) covered fiber strand ( 2 ) on the heating table ( 6 ) above the melting temperature (T7) of the thermoplastic ( 14 ) is heated or held on this, and with a from the on the fiber strand ( 2 ) and the cover material webs ( 3 . 4 ) acting tensile force (F6) and from the curvature of the table surface ( 15 ) resulting normal force (F2) is applied in such a way that the thermoplastic material ( 14 ) flows to all individual fibers and wets them. Method according to at least one of claims 1 to 4, characterized in that as material for the Abdeckmaterialbahnen ( 3 . 4 ) is used, a thermoplastic whose melting point is higher than the melting point of that thermoplastic ( 14 ), with which all fibers of the fiber strand ( 2 ) are wetted. Method according to at least one of claims 1 to 5, characterized in that a lower covering material web ( 4 ) on the surface ( 15 ) of the heating table ( 6 ) and an upper cover material web ( 3 ) to a roll off ( 5 ) is guided before these two Abdeckmaterialbahnen ( 3 . 4 ) with the fiber strand ( 2 ) in the area of the heating table ( 6 ) get in touch. A method according to claim 6, characterized in that the Auflegkraft (F1) of the Auflegrolle ( 5 ) is smaller than the normal force component (F2) of the tensile force (F6) with which the fiber strand ( 2 ) together with the cover material webs ( 3 . 4 ) over the heating table ( 6 ) is pulled. Method according to at least one of claims 1 to 7, characterized in that the heating table ( 6 ) is heated in such a way that it has at least three different heating zones (S1, S2, S3) with three different temperatures (T2, T3, T4). A method according to claim 8, characterized in that where the lower Abdeckmaterialbahn ( 4 ) first time the heating table ( 6 ), the upper surface ( 15 ) of the heating table ( 6 ) has an average temperature (T1) lower than the temperature in the coolest heating zone (S1, S2, S3). A method according to at least one of claims 8 or 9, characterized in that the through the Abdeckmaterialbahnen ( 3 . 4 ) covered and plastic-permeated fiber strand ( 2 ) immediately behind the heating table ( 6 ) has a mean temperature (T5) lower than the temperature in the hottest heating zone (S1, S2 or S3). Method according to at least one of claims 1 to 10, characterized in that the material passing through the cover material webs ( 3 . 4 ) covered and plastic-permeated fiber strand ( 2 ) in the transport direction behind the heating table ( 6 ) along the surface of a cooling table ( 10 ) and cooled down there. A method according to claim 11, characterized in that by the Abdeckmaterialbahnen ( 3 . 4 ) covered and plastic Durchdrun gene fiber strand ( 2 ) in the transport direction behind the cooling table ( 10 ) has an average temperature (T6) which is above the melting temperature of the thermoplastic material which wets all the fibers ( 14 ) lies. Method according to at least one of claims 1 to 12, characterized in that the transport speed (V) of the fiber strand ( 2 ) and the cover material webs ( 3 . 4 ) is between 0.05 m / s and 0.2 m / s. Method according to at least one of claims 7 to 13, characterized in that the through the Abdeckmaterialbahnen ( 3 . 4 ) covered and plastic-permeated fiber strand ( 2 ) in the region of the outlet end of the heating table ( 6 ) of at least one polishing roller ( 7 . 8th . 9 ) is acted upon by a force (F3, F4, F5) which is less than or equal to the bearing force (F1) of the Auflegrolle ( 5 ) and smaller than the normal force component (F2) of the tensile force (F6) on the covered fiber strand ( 2 ). Method according to at least one of claims 1 to 14, characterized in that the fibers of the fiber strand ( 2 ) are unidirectionally aligned or arranged as a woven fabric or as a scrim, and are designed as glass fibers, carbon fibers or aramid fibers. Method according to at least one of Claims 1 to 15, characterized in that, when the molding press is closed and pressurized ( 24 ) over a certain period of time (t0-t1) the temperature of the stacked prepreg layers ( 20 ' . 20 '' . 20 ''' ) above the melting temperature (T7) of the thermoplastic material which wets all the fibers ( 14 ) is raised after a certain period of time (t1-t2), the temperature of the stacked prepreg layers ( 20 ' . 20 '' . 20 ''' ) above the melting temperature (T8) of the thermoplastic cover material webs (T8) 3 . 4 ) and that thereafter in a further period (t5-t6) the temperature of the prepreg layers ( 20 ' . 20 '' . 20 ''' ) is brought below the melting temperatures (T7, T8) of the two thermoplastics. A method according to claim 16, characterized in that after the heating of all the thermoplastic fibers wetting all the fibers ( 14 ) above its melting temperature (T7) the temperature of the prepreg layers ( 20 ' . 20 '' . 20 ''' ) is kept below this melting temperature (T7) and kept below this melting temperature (T7) for a certain period of time (t3-t4). A leaf spring made of a fiber composite material which has at least mutually parallel fibers which are embedded in a thermoplastic material ( 14 ) are embedded, characterized in that the leaf spring ( 25 ) of several layered layers ( 20 ' . 20 '' . 20 ''' ) of prepregs ( 20 ), that the prepregs ( 20 ) each consist of a fiber strand ( 2 ) in the longitudinal direction parallel to each other aligned fibers in the thermoplastic material ( 14 ) are embedded, that the top and the bottom of the fiber strand ( 2 ) each of a cover material web ( 3 . 4 ) are covered from a thermoplastic material, and that the melting temperature (T8) of the thermoplastic material from the cover material webs ( 3 . 4 ) above the melting temperature (T7) of that thermoplastic ( 14 ), with which all fibers of the fiber strand ( 2 ) are wetted. Leaf spring according to claim 18, characterized in that the thermoplastic material ( 14 ) consists of polypropylene, polyamide, polyamide 6.6 or polybutylene terephthalate.