Method for simultaneous production of a plurality of leaf springs from a fiber composite material

Abstract

The invention relates to a method for producing leaf springs from a fiber composite material, for which a plurality of layers of fibers soaked or impregnated with synthetic resin in order to build up a not yet hardened unfinished leaf. The unfinished leaf spring is arranged in a compression mold, and the unfinished leaf spring is hardened under the influence of a predetermined pressing force and temperature curve over time to give a finished leaf spring. In order to reduce production costs, according to the invention a plurality of unfinished leaf springs are arranged vertically one above the other in the compression mold and the unfinished leaf springs are simultaneously hardened in the compression mold to give leaf springs.

Claims

1. A method for manufacturing leaf springs from a fiber-composite material, in which for the construction of a yet non-cured leaf-spring blank a plurality of layers of fibers which are soaked or impregnated with artificial resin are laid on top of one another, in which this leaf-spring blank is arranged in a compressive mold, and in which, in order to produce a finished leaf spring, the leaf-spring blank is cured under the influence of a predetermined temporal compression and temperature profile, characterized in that a plurality of leaf-spring blanks are vertically arranged on top of one another in the compressive mold, and in order to produce leaf springs, these leaf-spring blanks are simultaneously cured in the compressive mold, wherein prior to being laid up in the compressive mold, each of the leaf-spring blanks on the upper side and lower side thereof is covered with a release film, and wherein at least one release film is provided with at least one window-like cutout and is laid in such a manner onto the upper side of a leaf-spring blank that the next leaf-spring blank to be laid onto this release film in the region of the cutout comes into direct material contact with the lower leaf-spring blank and in that, on account of the material of the leaf-spring blanks, adhesive bonding of the leaf springs which are vertically directly adjacent takes place within this window-like cutout during curing of the leaf-spring blanks.

2. The method as claimed in claim 1, characterized in that such release films are composed of polyethylene terephthalate, acrylonitrile-butadiene-styrene, or aluminum.

Description

DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is further explained by means of exemplary embodiments and with the aid of a drawing which is appended to the description. In the drawing:

(2) FIG. 1 shows a schematic cross section through a compressive mold in which four leaf-spring blanks, which are separated from one another by release films, are arranged,

(3) FIG. 2 shows a plan view onto a stack having four leaf-spring blanks of various lengths, which are separated from one another by release films,

(4) FIG. 3 shows a side view of four leaf-spring blanks and assigned release films in the manner in which they are assembled to form the stack according to FIG. 2,

(5) FIG. 4 shows a side view of a stack of four cured leaf springs having various axial lengths, which are arranged on top of one another,

(6) FIG. 5 shows a side view as in FIG. 4, but with four cured leaf springs of identical length,

(7) FIG. 6 shows a side view of cured leaf springs from which the release films are being torn off in a method step,

(8) FIG. 7 shows a longitudinal section through a stack of cured leaf springs, in which in each case two adjacent leaf springs are interconnected in each case in one adhesive region, and

(9) FIG. 8 shows a plan view onto a release film having a centric, window-like cutout which enables adhesive bonding of two vertically adjacent leaf-spring blanks in the region of this cutout.

DESCRIPTION OF THE SELECTED EMBODIMENTS

(10) For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present invention may not be shown for the sake of clarity.

(11) The compressive mold 1 which is schematically illustrated in cross section in FIG. 1 is substantially composed of a molding box 2 having a base 3, two removable side walls 6, 7, and a cover 8. A first release film 4a, on which a first leaf-spring blank 5a has been deposited or constructed, has been arranged on the base 3 of the compressive mold 1. Thereabove, a second, third, fourth, and fifth release film 4b, 4c, 4d, 4e have been arranged in an alternating manner with in each case a second, third, and fourth leaf-spring blank 5b, 5c, 5d. The cross section through the stack 10 of the leaf-spring blanks 5a, 5b, 5c, 5d, and the release films 4b, 4c, 4d, 4e, corresponds to the section line A-A of FIG. 2.

(12) The four leaf-spring blanks 5a, 5b, 5c, 5d, are composed of a fiber-composite material having a duroplastic artificial resin which cures at a predetermined temperature. Fibers made from glass, carbon, aramid, or similar materials, may be employed as a fiber material. The leaf-spring blanks 5a, 5b, 5c, 5d, largely fill the interior space of the compressive mold 1, and the release films 4a, 4b, 4c, 4d, 4e, extend across the entire width B of the leaf-spring blanks 5a, 5b, 5c, 5d. The cover 8 of the compressive mold 1 bears from the very top onto this stack 10 composed of four leaf-spring blanks 5a, 5b, 5c, 5d, and five release films 4a, 4b, 4c, 4d, 4e which cover 8 exerts a preselected compressive pressure F on the stack 10. In order to be able to ensure a predetermined proportion of resin in the cured leaf springs 5a, 5b, 5c, 5d, excessive artificial resin preferably may be conveyed out of the compressive mold 1 in the direction toward the axial ends of the leaf-spring blanks 5a, 5b, 5c, 5d. A temperature T, which is selected in such a manner that the leaf-spring blanks 5a, 5b, 5c, 5d, can be cured according to their material properties to form finished leaf springs 5a, 5b, 5c, 5d, acts in the stack 10 of the four leaf-spring blanks 5a, 5b, 5c, 5d, and five release films 4a, 4b, 4c, 4d, 4e.

(13) Accordingly a plurality of leaf-spring blanks 5a, 5b, 5c, 5d, are compressed and cured in only one compressive mold 1, while until now, in the conventional manner, always only one leaf spring is arranged in a generic compressive mold in each compression and curing operation. As has been shown by investigations, the prevailing view among manufacturers of leaf springs made from fiber-composite material that in each case only one leaf spring of adequate quality can be compressed and cured in a compressive mold has proven to be a technical prejudice. On account of simultaneously compressing and curing a plurality of leaf-spring blanks 5a, 5b, 5c, 5d, which are arranged on top of one another in a stack 10, and at a temperature T which is adequate for curing the duroplastic artificial resin which is used in the leaf-spring blanks 5a, 5b, 5c, 5d, production time can be saved and the number of compressive molds to be made available in a factory for mass production can be considerably reduced, thus significantly reducing the manufacturing costs for such leaf springs.

(14) FIG. 2, in a schematic plan view, shows an exemplary embodiment of a stack 10 of four leaf-spring blanks 5a, 5b, 5c, 5d, of variable axis lengths, having a variable length L and an identical width B, which are separated from one another by four release films 4a, 4b, 4c, 4d. The four release films 4a, 4b, 4c, 4d, identifiably are also of variable axial lengths, wherein, however, each of these four release films 4a, 4b, 4c, 4d, is longer than the leaf-spring blank 5a, 5b, 5c, 5d, deposited thereon. On account of laying on top of one another variably long and/or wide leaf-spring blanks 5a, 5b, 5c, 5d, it is possible to manufacture leaf springs 5a, 5b, 5c, 5d, which are of variable lengths and/or widths in only one compressive mold 1.

(15) FIG. 3 shows this stack 10 in a schematic side view, in which the leaf-spring blanks 5a, 5b, 5c, 5d, and the release films 4a, 4b, 4c, 4d, for improved differentiation, are illustrated so as to be raised from one another, or as having a vertical spacing from one another, respectively. FIG. 3 thus also visualizes how the leaf-spring blanks 5a, 5b, 5c, 5d, are deposited on the respectively assigned release films 4a, 4b, 4c, 4d, namely vertically on top of one another, in order to form the stack 10. An axial projection 11 of the bottom-most release film 4a can be dispensed with or can be cut off. The projection 11 may also be folded up so as to be on the side walls 6, 7, of the compressive mold 1, on account of which molding of the leaf springs 5a, 5b, 5c, 5d, is facilitated.

(16) FIG. 4 shows a stack composed of four cured spring leafs 5a, 5b, 5c, 5d, which have just been removed from the compressive mold 1. These cured leaf springs 5a, 5b, 5c, 5d, are covered by five release films 4a, 4b, 4c, 4d, 4e, which are exactly as long as the respective leaf spring 5a, 5b, 5c, 5d, such that these leaf springs 5a, 5b, 5c, 5d, on their upper side and on their lower side are covered by a release film 4a, 4b, 4c, 4d, 4e. On account of a modest adhesive effect of the release films 4a, 4b, 4c, 4d, 4e, and/or because of cured excessive synthetic resin which has laterally remained, these four leaf springs 5a, 5b, 5c, 5d are still bonded and thus can be supplied as a stack to a further final processing station in a production line. However, it is also possible for the leaf springs 5a, 5b, 5c, 5d, of this stack to be interconnected by mechanical aids, in order to achieve a graduated leaf-spring package from fiber-composite material, which is composed of the four individual leaf springs 5a, 5b, 5c, and 5d. Such a mechanical aid may be a metallic clamp (not illustrated) which encompasses all individual leaf springs 5a, 5b, 5c, 5d, preferably in a centrically fixed and cushioned manner.

(17) In the stack of three cured leaf springs 5a, 5b, 5c, 5d, shown in FIG. 5 it is clearly identifiable that said leaf springs display in each case the identical axial length L. In order to manufacture finished leaf springs therefrom, they are initially separated from one another and subsequently the release films 4a, 4b, 4c, 4d, are torn off therefrom, as illustrated in FIG. 6. There remain three leaf springs 5a, 5b, 5c which are configured in a largely identical manner and are free from release film and which, in a manner saving manufacturing costs, have been simultaneously compressed and cured in only one compressive mold 1.

(18) However, the release films 4a, 4b, 4c, 4d, do not unconditionally have to be removed from the cured leaf springs 5a, 5b, 5c. Rather, they may remain as a protective film on the latter, in order to be able to absorb minor damage to the material of the finished leaf springs 5a, 5b, 5c, which may occur during assembly or during operation of the latter.

(19) FIG. 8, according to another variant, shows a release film 4b* which, in a centric manner, displays a rectangular window-like cutout 22. In the region of said cutout 22 this release film 4b*, in an arrangement between two vertically adjacent leaf-spring blanks 5a/5b, or 5b/5c, is not capable of preventing adhesive bonding of these adjacent leaf-spring blanks 5a/5b, 5b/5c, when the latter set and cure in the compressive mold 1. In the plan view, the cutout 22 may also be shaped so as to be round or oval, or may be formed from a plurality of small material clearances in the release film 4b*.

(20) FIG. 7 shows a schematic longitudinal section through a stack composed of three cured leaf springs 5a, 5b, 5c, and four release films 4a, 4b*, 4c*, 4d, in which the two release films 4b* and 4c* display the described cutout 22. At the location of these cutouts 22, the vertically directly adjacent cured leaf springs 5a/5b, 5b/5c, are fixedly interconnected in a first and a second adhesive region 21, 22. The narrated connection of the three leaf springs 5a, 5b, 5c, does not have to be able to transmit large forces. The cohesion is at least as great so that the leaf-spring package 23 composed of the individual leaf springs 5a, 5b, 5c, is maintained during downstream final processing steps and during shipping to the site of installation in the vehicle. Therefore, it is not considered to be disadvantageous if the leaf-spring package composed of three leaf springs 5a, 5b, 5c, separates into individual leaf springs after having been installed in a vehicle.

(21) While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the inventions defined by following claims are desired to be protected. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.