The present invention relates to a fastening arrangement for a structural element, in particular a lightweight structural element, with a housing that can be inserted into said structural element, having an internal thread and a screw element provided with an external thread, with the housing being embodied in one piece and with a threaded insert embodied as a helically wound wire being inserted into a bore of the housing with a force fit and/or a form fit, with its internal boundary forming the internal thread of the housing to screw in the threaded element.
Additionally, the invention relates to a method for producing such a fastening arrangement with the housing being inserted into the structural element, the threaded insert being inserted into the bore in the housing, and the screw element being inserted in the threaded insert.
A fastening arrangement of the type mentioned at the outset is known from GB 684 832. The known fastening arrangement serves to seal electric and other devices and to disclose any unauthorized opening of the device. In a sealed device, the threaded insert embodied as a helically wound wire is visibly anchored with one end in the bore of the device provided with a thread. When opening the device the anchored end of the threaded insert is visibly loosened from its engagement with the device and deformed. It is practically impossible to recreate the anchoring of the threaded insert in the device. The structural element at which the known fastening arrangement is mounted may be a part of the housing of the device, a bracket, or the like.
A fastening arrangement of the type mentioned at the outset is also known for various other special applications. In particular in aeronautics it is known that for mounting screw elements to a lightweight structural element, e.g., to a sandwich panel, said lightweight structural element is reinforced by the insertion of a housing. The housing typically produced from plastic is here produced via injection molding, having a metal part with a threaded bore, for which the metal part must be inserted through an expensive process into the injection mold.
Further, a threaded insert is known (DE 197 40 167 A1) that is screwed into a threaded bore of a work piece for reinforcement.
The object of the invention is to improve a fastening arrangement of the type mentioned at the outset such that when it is inserted into a lightweight structural element, the housing is produced without inserting a metal part with a threaded bore and which can be inserted into the lightweight structural element.
Additionally a method for producing such a fastening arrangement shall be provided.
This is achieved according to the invention in that another internal thread is formed in the wall of the bore, in which the threaded insert is incorporated, and/or by the threaded insert, upon being inserted into the bore of the housing, being incorporated in another internal thread formed in the wall of the bore. High extraction values in the connection of the housing and the threaded insert are particularly well achieved in the threaded insert having the same shape as the internal shape of the bore in the housing, which can be brought into a form-fitting contact with the housing as close as possible. By embodying the internal shape of the bore in the housing in form of another internal thread, the threaded insert can optimally be anchored in the housing and be fixed radially and axially. By screwing in the screw element, the threaded insert is additionally stressed in the housing and thus considerably increases the extraction values of the screw and the threaded insert from the housing. The shape of another internal thread can here be equivalent to any thread shape. By the one-piece embodiment of the housing, in particular made from a non-metallic material, weight and cost saving potentials are realized in the production of the housing. The production is particularly facilitated in that no additional part, such as e.g., a metallic threaded sheath or the like, needs to be inserted during injection molding in order to reinforce the thread. The fastening arrangement according to the invention is based on the screw element being mounted to a lightweight structural element in a simple manner with the help of two internally threaded parts. The structure of a lightweight structural element itself allows no direct connection to a screw element, because the structure is usually porous or has large hollow spaces. At the site of the fastening points, the lightweight structural element is provided with the housing of the fastening arrangement according to the invention, which is preferably made from a material with a low unit weight. In this manner, the requirements of minimum weight of the fastening arrangement are fulfilled to the extent possible. The object of the housing is to reinforce the lightweight structural element at the area where the fastening arrangement is to be mounted. By selecting the perimeter and the height of the housing, the fastening arrangement is designed in reference to the bore in the housing such that the extraction values between the lightweight structural element and the housing are of the same size as the ones between the housing and the threaded element.
Advantageous embodiments of the fastening arrangement according to the invention are the subject of the dependent claims.
In one embodiment the housing is provided with a lower strength than the threaded insert. The extraction values in the bore of the housing without any reinforcement are considerably lower when using material of the same strength values than between the lightweight structural element and the housing because the shearing area is correspondingly smaller. By using a threaded insert, the smaller area is compensated by the higher strength of the threaded insert. It is advantageous for the threaded insert to be anchored in the housing in a form-fitting manner. The threaded insert also contributes to higher extraction moments being achieved and thus the consequences of a potential shrinking of the housing, e.g., by aging or the like, can be compensated by a higher preliminary tension, which prevents any loosening of the threaded element.
In another embodiment, the housing is provided with a lower strength than the screw element. The screw element is designed such that the requirements to the fastening arrangement are fulfilled, but also result in a minimum weight. For this purpose, lightweight materials such as light metals, composite materials, or other plastics can be used for the screw element, which are characterized in high strength. By inserting a threaded insert into the housing, the connection between the screw element and the housing is reinforced such that the housing can be produced with a lower strength without becoming the critical element for the fastening arrangement with regard to material failure, e.g., by low extraction values or the like. In case of low requirements, the extraction values can at least be considerably enhanced by the features of the fastening arrangement according to the invention.
Further it is recommended that the housing is made from plastic. Plastics fulfill the features of a particularly low unit weight and thus can be used in a weight-saving manner. In spite of the low weight there is the chance to achieve good strength values, meeting the requirement of the fastening arrangement according to the invention. The housings can be produced in a more economical fashion by way of injection molding or the like and due to the simple production with higher process safety as well.
In particular polyetherimide (PEI), polyetheretherketone (PEEK), polyethersulphone (PES), GFK, carbon and fiberglass-reinforced plastic, composite material or the like are suggested for use. These materials are particularly suitable to produce components specifically adjusted to the application using conventional production methods. Plastics still show a wide range of potentially new combinations, in particular in combination with additional materials leading to a reinforcement and thus an improvement of the material features.
In another embodiment, the housing can be made from wood or the like. Instead of wood, the housing may also be made from another cellulose comprising man-made or natural product. Housings made from such porous materials are characterized in that the fastening arrangement can be connected to another structural element, such as the lightweight structural element, using an adhesive material, because the adhesive material diffuses into the porous structures of the housing and the lightweight structural element or penetrates it and hardens there. Furthermore, these materials are also particularly lightweight.
In another embodiment, the additional internal thread is simply formed by groove-shaped contours in the wall of the bore.
Another possibility comprises to provide the threaded insert with a self-cutting external thread for producing the other internal thread. This way, an additional simplification of the production and assembly process can be achieved, because during the injection molding of the housing, the interior shape of the bore can be produced without any grooves or threads and the threaded insert is designed such that it creates the additional internal thread automatically during the assembly in the housing. In addition to the simplified production process, an even better form fit can be achieved between the threaded insert and the housing.
Preferably the housing is inserted in a lightweight structural element made from Al-foam, light metals, or their alloys, GFK, sandwich panels, or the like. The use of the fastening arrangement according to the invention is particularly advantageous for the use in solutions designed to offer lightweight, highly stress-resistant fastening points. Particularly suitable for this purpose are lightweight structural elements, such as honey-comb shapes or the like made from materials, such as Al-foam, light metals, or their alloys or GFK or the like. Here, the honeycomb can be made from paper or the like, a curing foam, or any other material.
The fastening arrangement can be used particularly advantageous in aeronautics and aerospace technology. The search for increasingly lighter and more supportive materials is particularly influenced by the aeronautic and aerospace technology. The fastening arrangement according to the invention particularly targets high-value lightweight structural elements based on known and future materials.
Furthermore, the fastening arrangement is also particularly well suitable for the use in automobile construction, railway cars, or the like. By the increased use of lightweight construction materials in automotive technology, the fastening arrangement according to the invention provides the chance to economically and efficiently use fastening arrangements in lightweight structural parts, in particular in body construction. Presently used materials in prototype construction and small series, such as carbon, compound fibrous materials, such as GFK or the like will offer potential application fields for this fastening arrangement in the future, because the production costs can be lowered by the fastening arrangement according to the invention and the processing safety can be increased.
In one embodiment of the method for producing the fastening arrangement according to the invention, the housing is beneficially made in one piece, preferably by way of injection molding. In the subsequent preliminary assembly the insertion of the threaded insert occurs. In another step the preliminarily assembled housing is embedded in the lightweight structural element with epoxy resin or the like, and preferably adhered. Here, the zone around the housing is practically incompressible in the lightweight structural element, thus the extraction values of the housing made from the lightweight structural element increase and thus the fastening arrangement can be stressed more. The threaded bore created this way can now serve to allow screwing in a screw element, which is designed according to the specific requirements.
Exemplary embodiments of the invention are explained in greater detail in the following description using the drawings. They show:
In a variant of the embodiment according to
In another embodiment,
Number | Date | Country | Kind |
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102005026999.0 | Jun 2005 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP06/63036 | 6/9/2006 | WO | 8/7/2007 |