DE102014220337A1 - Method for producing a connecting element and connecting element and CFRP component with such a connecting element - Google Patents

Abstract

In the method for producing a connecting element (16), in particular a screw, a rivet or a technical fastening spring, a jacketed blank (8) is provided which has a core (3) of a metallic core material, on which a jacket (4 ) is applied from a metallic sheath material. The sheathed blank (8) is brought to form the connecting element (16) by at least one forming operation in a desired final geometry with varying longitudinally cross-sectional geometry, wherein the core (3) with the shell (4) is connected together as a result of at least one forming operation.

Description

The invention relates to a method for producing a connecting element and a connecting element and a CFRP component with such a connecting element.

The connecting element is, in particular, a connecting element for connecting two components to one another. In particular, it is a screw.

Depending on the particular field of application, a wide variety of requirements are placed on connecting elements, some of which require material-technically contradictory properties of the connecting elements. Thus, a high strength is often required at the same time sufficient elongation and high corrosion resistance. In automotive often fasteners made of steel or aluminum are used for lightweight construction.

In the field of connection of components made of carbon fiber reinforced plastics (CFRP), these conventional fasteners can not be used. The reason for this is the high electrochemical potential differences between the bolting partners. When using fasteners or fasteners such as screws and rivets made of a metallic material, there may be contact corrosion on contact of the connecting element to the electrically conductive carbon fibers. Alloys made of titanium or nickel are more suitable, but they are very expensive to process and therefore lead to high production costs. Also, these materials often do not cover the required property profile and are also more expensive than, for example, aluminum or steel.

The DE 10 2007 003 276 B4 deals with such a problem of the connection of a CFRP component with a metal component by means of a connecting element. In order to prevent contact corrosion of the connecting element, these are made of a non-conductive material, for example of a fiber-reinforced plastic. In addition, they also consist of titanium or a titanium alloy or other materials that are neutral in the galvanic voltage series to metal and CFRP materials. The fasteners are rivets, bolts, pins or screws.

The use of titanium full metal fasteners is relatively expensive. In principle, it is also possible to provide titanium-coated fasteners. For example, from the JP 03261405 A To remove a tape on which, for example, a titanium coating is applied as corrosion and wear protection.

From the JP 2001214915 A Furthermore, it can be seen a self-tapping screw, which consists of aluminum, on which a nickel-containing hard coating is applied. In a similar way is also from the JP 11210728 A remove an aluminum screw with an applied nickel coating.

To the different z.T. In addition, materials that meet contradictory requirements are partially incorporated into the material reinforcing structures or the connecting elements are provided with a coating. However, this is often also associated with disadvantages, for example, processing is very limited and expensive.

From the DE 10 2009 032 990 A1 For example, a screw can be seen, which comprises a hollow metal shell element provided with an external thread and a core element made of a plastic-containing composite material incorporated therein.

Proceeding from this, the object of the invention is to specify an improved fastening or connecting element, in particular for CFRP components.

The object is achieved by a method having the features of claim 1. Furthermore, the object is achieved by a connecting element having the features of claim 11 and by a CFRP component with such a connecting element according to claim 15.

The connecting element is in particular a screw, but is not limited thereto. Alternatively, the connecting element is also a rivet or so-called technical spring, with the aid of which at least indirectly components are connected to one another. In particular, in the case of screws and rivets are basically bolt-shaped fasteners. The connecting element thus generally has a longitudinally varying cross-sectional geometry, in particular a varying diameter.

The connecting elements according to the invention are preferably used for connecting CFRP components to one another or to components made of other materials, preferably in the motor vehicle sector.

For producing the connecting element, first a sheathed blank is provided, which has a core of a core material, onto which a sheath of a metallic sheath material different from the core material is applied. The coated blank is finally brought to form the connecting element in a desired final geometry. This is done by at least one forming process of the coated blank. Preferably, several successive forming operations take place. Of particular importance now is that the sheath material is not applied as a coating, so not by means of a coating method on the core material. The connection between the sheath material and the core material is carried out rather by the at least one forming process. Before forming, therefore, the sheath preferably lies against the core only, without a cohesive connection being formed as a result of a coating or application method.

The jacket is applied to the core solely by mechanical processes and forming processes. For this purpose, for example, a composite of raw wire with coat attached thereto is pulled by a drawing process to a desired final dimension, in which case the desired coated blank is formed. Also by taking place in the course of the manufacturing process further forming operations is a solid permanent connection. For the production of the composite, for example, the raw wire made of aluminum is introduced into a jacket tube or the raw wire is wrapped with the jacket material, etc. There is no active cohesive bonding, for example, by a conscious welding. Also, no coating is done by a coating method in which cladding material is applied by a spray-spread or (galvanic) coating process. Depending on the selected mechanical process for connecting the core and the sheath, an example of a local cohesive connection can be formed, for example, by a heat generated during a press-fitting process in the manner of friction welding or diffusion welding. However, the active formation of a cohesive connection by active supply of a substance or of heat is not provided.

By this measure can be process technology in a simple way thick wall thicknesses of the shell form before forming, which are sufficient to perform even high degrees of deformation and at the same time to ensure a homogeneous continuous jacket in the finished fastener.

The connection between the core and the jacket is ultimately preferably formed exclusively by the at least one forming operation. In this case, forces are exerted on the sheathed blank, which also act in the radial direction, so that the sheath is pressed firmly against the core and an intimate connection is formed.

The core material is preferably a hardenable material, in particular a light metal. The core material is preferably aluminum or an aluminum alloy according to DIN EN ISO 573 used. Preferably, a particularly high-strength aluminum alloy is used. Alternatively, magnesium or a magnesium alloy. In principle, other materials, in particular, for example, steel or other iron alloys can be used.

The sheath material is preferably a noble metal compared to the core material, in particular titanium, a titanium alloy or else nickel or a nickel alloy or else a chromium-nickel steel. The term "noble" refers to the electrochemical series of voltages. Overall, therefore, a hybrid component is provided, which in particular has an aluminum core and a nobler metal shell or is formed by the aluminum core and the metal shell. Due to the jacket, only a small proportion of the nobler metal is needed, so that overall the connecting element can be produced inexpensively. In particular, the combination of the intended aluminum for lightweight construction with a titanium jacket is particularly suitable for use in CFRP components to prevent contact corrosion. The jacket material is preferably a self-passivating material, which therefore forms a protective layer.

By this measure, the sheathing of the (aluminum) blank with a nobler metal shell on the one hand, the particular advantage of avoiding contact corrosion is achieved.

At the same time only a small proportion of the more expensive metal is required by the hybrid design with the aluminum core and the noble metal shell, so that the connecting element can be made overall cost. A further advantage is also to be seen in that a comparatively low density for the desired lightweight construction is realized by the aluminum as the core material.

A sufficiently large wall thickness of the shell ensures reliable protection of the core. The combination of this thick jacket with the core also makes it possible to set the mechanical requirement profile in a targeted manner, such as, for example, one Desired low density, high strength, sufficient elongation, etc. By the forming process to form the final geometry is additionally achieved the advantage that the shell layer is additionally solidified by the pressure exerted and in particular also a work hardening occurs, so that overall improves the strength becomes.

Depending on the application, other materials are used for the jacket. For example, a material with good electrical conductivity, in particular copper or a copper alloy is used. The method described here is therefore also used for example for the formation of contact connection elements, such as a contact screw.

The sheathed blank is a strand-shaped body, in particular in the manner of a raw wire. The jacket is therefore applied in the manner of a cladding on an aluminum raw wire. To produce such a sheathed core wire, recourse is made to known production technologies, such as those used, for example, for the production of electrical conductor wires, for example so-called copper-clad conductor wires.

Depending on the selected materials and / or the requirement profile, a heat treatment is expediently carried out in order to achieve high strengths. In particular, for example, the aluminum core is subjected to a heat treatment, in particular before the forming process, before the cladding material is subsequently applied.

The jacketed blank is usually provided by the meter in the manner of a raw wire. For this, the connecting element is produced by cutting and forming. To form this sheathed raw wire is resorted to a conventional, known manufacturing method, as is known for example in copper-plated electrical conductor wires, for example, so-called "Copper Clad aluminum wires". In this case, for example, an aluminum starting raw wire is provided with a jacket, and the composite thus formed is then drawn by, for example, a drawing process to a desired final diameter, which is then further processed for the blank by this first cut to length and then later also formed several times.

Alternatively, the core is formed as an insert, which is inserted in an example preformed sleeve member of the shell material, in particular pressed. The insert and the sleeve member are preferably cylindrical. The sleeve member is preferably optionally tubular or pot-shaped or cup-shaped, thus has on one side a closed end face.

Alternatively, the insert and the sleeve member may already have a preform, and are provided for example in the case of a screw with a head and shaft part. The sleeve member is correspondingly preformed complementary, so that the insert rests accurately fit in the sleeve member.

Conveniently, a thread is formed in the forming process to form the final geometry in the sheathed blank. In this case, both the core and the sheath are expediently deformed.

The jacket expediently has a wall thickness in the range of 1 to 5 mm in the case of the sheathed blank. In the finished state, the jacket expediently still has a wall thickness in the range of 0.1 to 3 mm in the connection element. In particular, can be adjusted by the method described here, a high wall thickness, for example, up to 25% of the diameter of a shaft portion in the finished state. The wall thickness is for example at least 10% of the diameter of the shaft area in the finished state.

When forming to final geometry usually several forming operations are performed. In the case of a screw, for example, first a head region is formed with a subsequent shaft region. The same usually applies, for example, in a rivet. In the formation of a head region with adjoining shaft region usually a very large degree of deformation is required. By providing a sheathed core wire with a high sheath wall thickness is reliably ensured that despite this high degree of deformation of the jacket does not crack.

Due to the deformation of the blank with the sheath material, the connecting element in the finished state has a varying depending on a degree of deformation wall thickness of the sheath material over the length of the connecting element in a preferred embodiment. In general, the degree of deformation is understood to be the logarithm of the ratio of the initial geometry (length, thickness) to the transformed final geometry. In particular, for example, the logarithm of the initial diameter to the converted final diameter. Basically, fasteners have areas with different degrees of deformation. So In general, the head region, in particular in the transition to a shaft region, has a very high degree of deformation. In a threaded region of a screw, that is, as a result of introducing the thread, the connecting element, in contrast, a lower degree of deformation and thus also a different wall thickness of the sheath material.

In this case, overall, a strong deformation is preferably provided, in which the cross-section of the coated blank is changed by 25% to 75%, in particular by at least 50%.

The connecting element produced in particular according to this method therefore has a core of a core material, in particular aluminum, with a comparatively thick-walled jacket of a jacket material, in particular titanium or a titanium alloy, mounted thereon. A characteristic feature of this production method is to be seen in the fact that the jacket is not applied as a coating but is connected to the core by the at least one forming operation, that is, solely by a mechanical manufacturing step. For this purpose, recourse is made in particular to a prefabricated, sheathed raw wire. In the finished state, therefore, the core is open at least to one end face and preferably to both end faces. In the head and / or foot area, the core has an open, externally accessible end face without covering with the jacket material. However, this is not critical with respect to the input addressed corrosion resistance, since no contact with the CFRP workpiece occurs in these areas. In addition, the comparatively thick jacket material also sets a sufficient distance.

Such a connecting element is preferably attached to a CFRP component in order, for example, to connect two components to each other, at least one of which is a CFRP component. This CFRP component is used in particular in a motor vehicle.

In summary, the special manufacturing method provides a connecting element, in particular a screw, from the combination of two metals from different alloy systems. The sheath material almost completely encloses the core material (except for the front sides). The compound of the two materials is preferably produced exclusively by forming technology. As a core material, the comparatively cheap, lightweight aluminum or an aluminum alloy is used and as a shell material, the corrosion-resistant titanium or a titanium alloy. Overall, this makes the connecting element to a screw, for example, a titanium alloy lighter, less expensive and at the same time more resilient compared to a pure aluminum screw and compared to aluminum screw also resistant to corrosion in CFRP components. Due to the jacket material, damage to the surface due to the high layer thickness of the sheath material is tolerated, in contrast to conventional coatings, which are usually applied only in the micrometer range.

An embodiment of the invention will be explained in more detail with reference to FIGS.

1 illustrates a manufacturing method for producing the connecting element starting from a sheathed raw wire and

2 shows an alternative manufacturing method with the use of an insert.

At a first in 1 illustrated embodiment is first a raw wire 2 made of a core material, in particular aluminum or a high-strength aluminum alloy. At the raw wire 2 it is in particular a massive raw wire 2 , as can be seen from the cross-sectional view shown on the right side. Subsequently, this aluminum raw wire 2 from a coat 4 encased in a sheath material, leaving a sheathed blank 6 is trained. This turns into a jacketed raw wire 6 get with one through the raw wire 2 formed core 3 and the coat 4 , This is preferably still drawn to a desired diameter. The core 3 is generally considered a massive core 3 educated.

Preferably, a temperature treatment for curing takes place at most on an intermediate product, for example only on the raw wire 2 from the core material or also on the coated raw wire 6 , preferably after it has been pulled to the desired final diameter. A solidification of the jacket material is carried out by the subsequent forming process, ie by work hardening. A temperature treatment for curing therefore preferably does not take place on the finished connecting element.

From this jacketed raw wire 6 is then by cutting first a jacketed blank 8th produced by a first coarse-forming process to a jacketed preform 10 is trained. In the embodiment of a screw in this case is a header 12 and a shaft area 14 educated.

In particular, when using aluminum as a core material and / or as a sheath material coarse deformation takes place by a Extrusion and / or upsetting to achieve the desired high degrees of deformation can.

In a subsequent forming process then - in the case of a screw - a thread 18 in the shaft area 14 for the formation of the finished connecting element 16 brought in. This is usually done by a rolling process. In this manufacturing variant, the opposite end faces of the connecting element 16 each the core 3 with a free end which is concentric with the jacket 4 is surrounded. This subsequent forming process usually has lower degrees of deformation than the coarse deformation.

At the in 2 shown alternative variant (right half) is first a sleeve member 20 provided from the sheath material, which is preferably formed overall cup-shaped, so preferably has a bottom. However, this is not mandatory. Alternatively, it is also tubular, as shown on the left half of the picture, thus has no jacket material on its two opposite end faces. According to the variant shown in the figure, the sleeve member 20 overall cylindrical. Alternatively, it may also be preformed with a head portion and a shaft portion.

As an alternative to the arrangement of the bottom at the front end of the shaft, the bottom is formed at the opposite end, so that the head area 12 from the coat 4 is covered.

In the free interior of this sleeve element 20 becomes an insert part 22 used, in particular pressed. Depending on the selected mechanical process for connecting the core and the sheath, an example of a local cohesive connection can be formed, for example, by a heat generated during the press-fitting process in the manner of friction welding or diffusion welding. However, the active formation of a cohesive connection by active supply of a substance or of heat is not provided.

The insert 22 forms the later core 3 from the core material. This combined component of approximately cylindrical sleeve element 20 and insert inserted therein 22 is then a first forming process for forming the head area 12 and the shaft area 14 subjected. Then it will be - in 2 not shown in detail - on the shaft area 14 the thread 18 applied. Through the bottom part of the sleeve element 20 In contrast to the manufacturing variant described above, the core material does not emerge on the bottom end face on the surface.

In the cross-sectional representations of 2 is still in the header 12 an optional tool holder 24 represented, for example, an internal polygonal recording. Alternatively, this is also designed as external polygon. The design of the tool attack is done in a variant by a forming process below for pressing the insert 22 in the sleeve element 20 , Is the head area 12 closed with a bottom of the shell material, so in this preferred embodiment of the tool attack is provided with a layer of the shell material.

Generally, it is provided in a preferred embodiment that both the core material and the shell material is first homogenized prior to bringing into a composite element in order to achieve a uniform distribution of the various alloying elements, which are responsible for a mixed crystal formation and precipitation phases for the mechanical properties. As already mentioned, the composite is deformed together after assembly, in particular pulled to a desired final diameter. By forming a close connection between the core and sheath material is generally formed so that they are preferably connected directly to each other solely by the deformation. By the already mentioned heat treatment for the purpose of curing after formation of the composite, in particular after the drawing process, a chemical bonding, for example, a targeted alloying by diffusion of the alloy constituents of the shell on the core and vice versa is possible. In this curing, a predetermined temperature profile is subjected to the heat treatment to set a desired strength. Curing by thermal treatment of the entire finished connecting element 16 , So after the forming is preferably not.

For non-similar materials for the jacket 4 and the core 3 , In the heat treatment, a diffusion of the sheath material into the core material is specifically made possible, so that it is alloyed. As a result, a hardness gradient in the radial direction is preferably achieved by targeted alloying.

In addition, generally in a preferred embodiment between the jacket 4 and the core, if necessary, still arranged a barrier layer. This preferably consists of a metal which does not react with the materials of the core or of the jacket. For example, in the case of an Al core and a titanium shell, a reaction of titanium with Aluminum and thus prevents the formation of a titanium aluminide intermediate layer. Such can form crack germs in the case of a local overvoltage. Thus, for example, the barrier layer prevents cracks in the inner core from continuing into the cladding as cracking nuclei.

As can be seen from the preceding description, the cladding layer is already before the deformation, in particular the formation of the head region 12 , applied. The formation of the head area is carried out by cold forming and is also referred to as cold mass forming due to the high degree of deformation. During the forming, a cross-sectional reduction preferably takes place in the range of 25% to 75%, in particular of at least 50%. The coat 4 has a sufficiently thick wall thickness d for this purpose. In addition, the sheath material also has sufficient ductility to prevent cracking of the sheath material. The minimum wall thickness d is here at some 100 microns.

The wall thickness d varies over the extent of the connecting element 16 depending on the degree of deformation, which is position-dependent. This is how the coat shows 4 generally in areas of high degrees of deformation a smaller wall thickness d than in areas of low degrees of deformation.

The connecting element 16 is used in particular for the connection of CFRP components with other CFRP components or with metallic or other components, in particular in the automotive sector. In the assembled state are therefore CFRP components of a motor vehicle with the help of the connecting elements 16 attached.

LIST OF REFERENCE NUMBERS

2

raw wire

3

core

4

coat

6

jacketed raw wire

8th

coated blank

10

coated preform

12

head area

14

shaft area

16

connecting element

18

thread

20

sleeve member

22

insert

24

tool holder

d

Wall thickness

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007003276 B4 [0005]
• JP 03261405 A [0006]
• JP 2001214915 A [0007]
• JP 11210728 A [0007]
• DE 102009032990 A1 [0009]

Cited non-patent literature

• DIN EN ISO 573 [0018]

Claims (15)

Method for producing a connecting element ( 16 ), in particular a screw, a rivet or even a technical fastening spring, in which a sheathed blank ( 8th ), which has a core ( 3 ) of a metallic core material onto which a jacket ( 4 ) is applied from a metallic sheath material and the sheathed blank ( 8th ) for forming the connecting element ( 16 ) is brought by at least one forming operation in a desired final geometry with longitudinally varying cross-sectional geometry, wherein the core ( 3 ) with the coat ( 4 ) is joined together as a result of the at least one forming operation.  A method according to claim 1, wherein a curable material, in particular a light metal is used as the core material. The method of claim 1 or 2, wherein the core material is aluminum or an aluminum alloy is used. Method according to one of the preceding claims, in which a metal which is more noble in comparison to the core material, in particular titanium, a titanium alloy, nickel or a nickel alloy is used as the jacket material. Method according to one of the preceding claims, in which the encased blank ( 8th ) is provided as a meter, from which by cutting and forming the connecting element ( 16 ) will be produced. Method according to one of the preceding claims, in which the core ( 3 ) as an insert ( 22 ) is formed and the shell material by a sleeve member ( 20 ) is formed. Method according to the preceding claim, in which a preform with the insert ( 22 ) is provided, from which by the forming process, a desired end geometry of the connecting element ( 16 ) is formed. Method according to one of the preceding claims, in which in the coated blank ( 8th ) a thread ( 18 ) is formed. Method according to one of the preceding claims, in which the jacket ( 4 ) at the blank ( 8th ) has a wall thickness (d) in the range of 1 to 5 mm and further preferably in the finished state in the final geometry has a wall thickness (d) in the range of 0.1 to 3 mm. Method according to one of the preceding claims, in which the jacket ( 4 ) when the connecting element ( 16 ) has a varying depending on a degree of deformation wall thickness (d). Connecting element, in particular produced according to one of the preceding methods, comprising a core ( 3 ) of a core material with a shell applied thereto by means of a forming process ( 4 ). Connecting element according to Claim 10, in which the jacket ( 4 ) consists of a nobler material than the core ( 3 ). Connecting element ( 16 ) according to claim 10 or 11, wherein the core ( 3 ) consists of aluminum, magnesium, an aluminum alloy or a magnesium alloy, and the jacket ( 4 ) consists of titanium, a titanium alloy, nickel or a nickel alloy. Connecting element ( 16 ) according to one of claims 10 to 12, which has a front end with an open end face of the core ( 4 ). CFRP component, in particular of a motor vehicle with a connecting element ( 16 ) according to any one of claims 11 to 14.

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