DE102016208561A1 - Process for producing a leaf spring made of fiber-reinforced plastic - Google Patents

Abstract

The invention relates to a method of making a fiber reinforced plastic leaf spring, preferably for a vehicle, comprising the steps of: drawing reinforcing fibers through the opening of a pultrusion tool to make the leaf spring, wherein the reinforcing fibers provide resin before and / or in the pultrusion tool widening the opening during drawing, inserting a core between the reinforcing fibers, and pulling the core together with reinforcing fibers through the flared opening and then narrowing the opening to merge the reinforcing fibers surrounding the core.

Description

The present invention relates to a method for producing a leaf spring made of fiber-reinforced plastic, preferably for a vehicle. Furthermore, the invention relates to a leaf spring produced by the method according to the invention.

In the prior art, for example, a pressing method is used for producing a leaf spring made of fiber-reinforced plastic. Individual layers are stacked and pressed together. The resin can be added during the pressing process or in a second step. Subsequently, the leaf spring is reworked and excess material removed. In this production, relatively many process steps and long times for curing are necessary. Furthermore, the proportion of resin in relation to the proportion of reinforcing fibers is high, resulting in a high component weight.

It is an object of the present invention to provide a method for producing a leaf spring made of fiber-reinforced plastic that allows mass production of a very lightweight, small-sized and durable insertable leaf spring.

The object is achieved by the features of claim 1. The dependent claims have advantageous embodiments of the invention the subject.

Thus, the object is achieved by a method for producing a leaf spring made of fiber-reinforced plastic. The method comprises the following steps: (i) drawing reinforcing fibers through the opening of a pultrusion tool to make the leaf spring. The reinforcing fibers are provided with resin before the pultrusion tool and / or in the pultrusion tool. For this purpose, preferably the reinforcing fibers before the pultrusion tool are soaked in resin and / or it is preferably an injection of the resin in or immediately before the pultrusion tool. By using the continuous pultrusion process, the production time of the leaf spring is significantly reduced. Further, the pultrusion method allows the proportion of reinforcing fibers in the leaf spring to be much higher than in a pressing method or RTM method. This lowers the weight of the leaf spring while increasing rigidity.

(ii) The opening of the pultrusion tool through which the resinated reinforcing fibers are drawn is variable in its opening width. During the drawing, the opening is widened to (iii) insert a core between the reinforcing fibers. (iv) The core is drawn together with the reinforcing fibers through the flared opening. (v) Subsequently, the opening is narrowed again, so that a merging of the core enclosing reinforcing fibers takes place.

The variable orifice is always controlled so that the pultrusion tool exerts some pressure on the reinforcing fibers and the resin to shape the resulting leaf spring.

The leaf spring thus has a first section without a core, an adjoining second section with a core and an adjoining third section without a core. The resulting leaf spring is this continuously or quasi continuously drawn through the opening. It is not excluded that the pulling is temporarily interrupted.

The resulting leaf spring is pulled in the longitudinal direction of the leaf spring by the pultrusion tool. This direction corresponds to the pulling direction of the pultrusion. When the leaf spring is installed in the vehicle as a transverse leaf spring, the longitudinal direction of the leaf spring corresponds to a vehicle transverse direction. The spring direction of the leaf spring corresponds to a vehicle vertical direction. The core is preferably positioned centrally with respect to the longitudinal direction of the leaf spring or the vehicle transverse direction.

It is preferably also provided to incorporate more than one core during the pultrusion process in the leaf spring, then in each case between the cores by narrowing the opening, the reinforcing fibers are brought together again.

By inserting the core, the reinforcing fibers are displaced outward in the spring direction. As a result, the characteristic of the leaf spring and the stability of the leaf spring can be positively influenced. By a correspondingly lightweight construction of the core or by an at least partial removal of the core at the same time creates a very lightweight leaf spring.

In a preferred embodiment, it is provided that the core is removed again after pulling. This leaves a cavity within the leaf spring. The core can be completely or partially removed for this purpose.

Core removal occurs depending on the material of the core and how the core is surrounded by the reinforcing fibers. In particular, it is provided that the core is removed by a chemical process or by a mechanical process. In the chemical process, the nucleus can be dissolved. By mechanical means, the core becomes, for example removed by machining, by sandblasting or by simply squeezing out.

Furthermore, it is preferably provided that a support element is inserted into the cavity. This support element remains in the leaf spring and ensures that the geometry of the cavity is maintained during operation of the leaf spring. The support element is designed in particular in the form of a web, wherein the web extends substantially in the spring direction of the leaf spring. Furthermore, it is preferably provided that the support element has a truss structure or a honeycomb structure.

In an alternative variant, it is provided that the core is only partially removed after pulling, with part of the core remaining as a support element in the leaf spring.

The core, regardless of whether it is completely removed, partially remains or remains completely, may preferably be formed in one part or in several parts.

The core is preferably made of plastic, fiber reinforced plastic, metal or foam.

In a preferred embodiment, it is provided that the core is covered on both sides by reinforcing fibers and resin with respect to the spring direction. Depending on how and if the core is removed, the reinforcing fibers and / or the resin can also extend laterally on the core.

In a further preferred embodiment it is provided that the core in the pultrusion tool is completely and tightly enclosed by the reinforcing fibers and / or the resin. In this case, the core can not be removed. It is advantageous, however, that the core is securely positioned and protected from corrosion.

Advantageously, in the pultrusion process, the reinforcing fibers are braided around the core. This results in a very stable integration of the core in the leaf spring or a very stable embodiment of the cavity when the core is removed.

Furthermore, it is preferably provided that the core is thinner at both ends than in the middle. The center of the core is defined in the pulling direction of the pultrusion between the two ends of the core. By this configuration, a continuous and continuous expansion of the reinforcing fibers or the leaf spring takes place up to the thickest point of the core.

In a particularly preferred embodiment, it is provided that the core has an elliptical cross-section or a tapering to the ends form. This cross section is defined in a plane in which the longitudinal direction and the spring direction of the leaf spring lie.

An overall length is defined on the leaf spring in the pulling direction of the pultrusion, that is to say in accordance with the vehicle transverse direction. The core has a core length in the same direction. Experiments and calculations have shown that the core length should be between an upper limit and a lower limit for a stable design of the leaf spring.

The preferred upper limit of the core length is 90%, preferably 80%, most preferably 70%, of the total length.

The preferred lower limit of the core length is 10%, preferably 20%, most preferably 30%, of the total length.

Furthermore, the experiments and calculations have shown that the core thickness should be between an upper limit and a lower limit for a stable design of the leaf spring. The core thickness is defined in the spring direction of the leaf spring, being measured at the thickest point.

The preferred upper limit of the core thickness is 100 mm, preferably 70 mm, particularly preferably 60 mm.

The preferred lower limit of the core thickness is 5 mm, preferably 10 mm, particularly preferably 20 mm.

In particular, if the core is not or not completely removed, it is preferably provided that the core is structured on its surface. This structuring comprises in particular grooves, nubs or a rough surface. The structuring of the surface allows a very good, in particular positive, connection between the core and reinforcing fibers or resin.

The invention further comprises a leaf spring made according to the method just described. The leaf spring is preferably used in a vehicle. The vehicle is in particular a two-lane road vehicle. In particular, the leaf spring is used as a transverse leaf spring.

The transverse leaf spring is located in particular between two opposite wheel suspensions of the vehicle.

Further details, features and advantages of the invention will become apparent from the following description and the figures. Show it:

1 a longitudinal section of a leaf spring according to the invention according to an embodiment, prepared by the method according to the invention, and

2 a schematic representation of the method according to the invention.

1 shows a simplified schematic representation of a leaf spring 1 prepared by the process according to the invention. Shown is a sectional view of the leaf spring 1 ,

The leaf spring 1 used as a transverse leaf spring in a vehicle, extends in a vehicle transverse direction 9 which also acts as a longitudinal direction 9 the leaf spring 1 referred to as. A spring direction 10 the leaf spring 1 corresponds to a vehicle vertical direction 10 ,

The leaf spring 1 is made of a fiber-reinforced plastic 5 manufactured. This fiber reinforced plastic 5 includes reinforcing fibers embedded in a matrix of resin. The reinforcing fibers are preferably made of glass, carbon, ceramic or aramid fibers.

Along its longitudinal direction, the leaf spring 1 a first section 2 , a second section 3 and a third section 4 on. The first paragraph 2 and the third section 4 form the two opposite ends of the leaf spring 1 , These sections 2 . 4 are conventional pultrusion fiber reinforced plastic sections 5 ,

In the second section 3 became a nucleus during pultrusion 7 (please refer 2 ) between two strands 18 the reinforcing fibers used. This core 7 was removed after pultrusion so the cavity 6 originated. In the cavity 6 is a support element 8th in the form of a bridge according to 1 used.

Alternatively, it is also possible to use the core 7 in the leaf spring 1 to leave or the core 7 only partially removed.

1 shows a total length 11 the leaf spring 1 and a core length 12 of the core 7 or cavity 6 , Furthermore, in the spring direction 10 a core thickness 13 Are defined.

The core used 7 or the cavity 6 white in the sectional plane shown an elliptical cross section. This is the core 7 or the cavity 6 thicker in the middle than at its ends.

2 shows a schematic view of the manufacturing process for the leaf spring 1 , Here is a pultrusion tool 14 intended. The pultrusion tool 14 has an opening 15 on. A width of the opening 15 can be changed during pultrusion.

For the production of the leaf spring 1 become the reinforcing fibers, in the illustration according to 2 from right to left, through the opening 15 drawn. The reinforcing fibers are before and / or in the pultrusion tool 14 soaked in resin. Excess resin 16 will be at the entrance of the opening 15 away.

In the production of the first section 2 and the third section 4 is the opening 15 relatively narrow, so compact sections made of fiber-reinforced plastic 5 arise.

For the production of the second section 3 becomes the opening 15 widened. By means of a core tool 17 becomes the core 7 between the two strands 18 used. The core 7 gets along with the reinforcing fibers through the opening 15 drawn.

The width of the opening 15 will be according to the geometry of the core 7 always adjusted. When using the elliptical core described above 7 , the opening becomes 15 in the production of the second section 3 steadily widened and from the middle of the core 7 constantly narrowed.

As already described, after pultrusion the core becomes 7 partially or completely removed, or the core 7 remains in the leaf spring 1 ,

LIST OF REFERENCE NUMBERS

1

leaf spring

2

first section

3

second part

4

third section

5

fiber reinforced plastic

6

cavity

7

core

8th

support element

9

Vehicle transverse direction and longitudinal direction of the leaf spring

10

Vehicle vertical direction and spring direction of the leaf spring

11

overall length

12

core length

13

core thickness

14

pultrusion

15

opening

16

excess resin

17

core tool

18

strands

19

tensile direction

Claims (10)

Method for producing a leaf spring ( 1 ) made of fiber-reinforced plastic ( 5 ), preferably for a vehicle, comprising the following steps: • pulling reinforcing fibers through the opening ( 15 ) of a pultrusion tool ( 14 ) for producing the leaf spring ( 1 ), wherein the reinforcing fibers before and / or in the pultrusion tool ( 14 ) with resin, • widening of the opening ( 15 ) while dragging, • inserting a core ( 7 ) between the reinforcing fibers, and • pulling the core ( 7 ) with reinforcing fibers through the flared opening ( 15 ) and then narrowing the opening ( 15 ) to merge the core ( 7 ) surrounding reinforcing fibers. Method according to claim 1, characterized in that the core ( 7 ) after being pulled through the pultrusion tool ( 14 ) is removed and a cavity ( 6 ) remains. Method according to claim 2, characterized in that in the cavity ( 6 ) a support element ( 8th ), which is in the leaf spring ( 1 ) remains. Method according to claim 1, characterized in that the core ( 7 ) after being pulled through the pultrusion tool ( 14 ) is partially removed, with part of the core ( 7 ) as a support element ( 8th ) in the leaf spring ( 1 ) remains. Method according to claim 1, characterized in that the core ( 7 ) in the pultrusion tool ( 14 ) is completely and tightly enclosed by the reinforcing fibers and / or the resin. Method according to one of the preceding claims, characterized in that the reinforcing fibers before and / or in the pultrusion tool ( 14 ) around the core ( 7 ) are braided around. Method according to one of the preceding claims, characterized in that the core ( 7 ) at its two ends is thinner than in the middle, with the center of the core ( 7 ) in the pulling direction ( 19 ) of the pultrusion lies between the two ends. Method according to one of the preceding claims, characterized in that the leaf spring ( 1 ) in the pulling direction ( 19 ) the pultrusion has an overall length ( 11 ) and the core ( 7 ) in the pulling direction ( 19 ) the pultrusion has a core length ( 12 ), wherein • an upper limit of the core length ( 12 ) at 90%, preferably 80%, particularly preferably 70%, of the total length ( 11 ), and / or • a lower limit of the core length ( 12 ) at 10%, preferably 20%, particularly preferably 30%, of the total length ( 11 ) lies. Method according to one of the preceding claims, characterized in that the core ( 7 ) in a spring direction ( 10 ) of the leaf spring ( 1 ) a core thickness ( 13 ), wherein at the thickest point • an upper limit of the core thickness ( 13 ) at 100 mm, preferably 70 mm, particularly preferably 60 mm, and / or • a lower limit of the core thickness ( 13 ) at 5 mm, preferably 10 mm, particularly preferably 20 mm. Leaf spring ( 1 ), preferably for a vehicle, produced by a method according to any one of the preceding claims.

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