METHOD FOR PRODUCING A TRANSITION BLANK The invention relates to a method for producing a transition blank comprising a first part made from a first metal and a second part made from a second metal, which is joined thereto. A transition blank of this nature is known from European patent application EP 0,745,449. A transition blank is a form of a tailor-made blank (TMB), which is understood to mean a blank composed of different materials and/or different material thicknesses, with the aim of obtaining the correct mechanical properties at the correct location in the finished product. TMBs are often used in the automotive industry. In the case of a transition blank, the two parts are made from two different materials, for example a first part is made from aluminium or an aluminium alloy, and the second part is made from steel, such as a high-strength steel or a sectional steel. The transition blank is then used, for example, to form a transition component, whether directly or by means of the product produced from the transition blank, between steel parts and aluminium parts of a means of transport. EP 0,745,449 describes a method for producing a transition blank in which the sides of the two parts are placed against one another in a contact plane, after which the first part is heated with the aid of a laser at a selected distance from the contact plane. The heat which is introduced propagates towards the contact plane and causes the second part, the melting temperature of which is lower than that of the first part, to melt. The two parts are joined together by the exertion of a force which is directed towards the contact plane.

A drawback of this method is that the two metal parts are in electric contact with one another. In the case of a transition blank made from steel and aluminium, this has the drawback that the aluminium part, and any aluminium components which are joined thereto during use, are affected by galvanic corrosion.

A further drawback of the known method is that it is not particularly suitable for the production of transition blanks of large dimensions, for example larger than 0.5 x 0.5 m, since the equipment required to do this then becomes excessively large and complicated.

Another drawback of the known method is that expensive and specialist equipment is required to carry out the method. Yet another drawback is that the contact

planes have to be treated to a very high level of accuracy in order to obtain a sufficiently low thermal resistance.

A further drawback is that the method is laborious and therefore time- consuming, so that only a small number of transition blanks can be produced per unit time.

The object of the invention is to provide a method which avoids these drawbacks or at least reduces them substantially and with which it is also possible to achieve other advantages. To this end, the method according to the invention is characterized in that the first and second parts at least partially overlap one another by means of an overlap area, and the first and second parts, at the location of the overlap area, are joined together by means of at least one layer of adhesive.

This results in the advantage of a joint which is easy to produce and can be applied to a wide range of materials, in particular steel, aluminium and aluminium alloys. The method requires little preparation of the parts which are to be joined together at the location of the overlap area. The simplicity of the method means that it can be carried out quickly and with simple means. The number of transition blanks which can be produced per unit time is high even for limited investment. With the invention, it is simple to make even transition blanks of large dimensions, since the method in principle comprises nothing more than applying a layer of adhesive and, if necessary, curing the adhesive from the layer of adhesive under pressure.

A more detailed embodiment of the method according to the invention is characterized in that the thickness of the layer of adhesive is selected as a function of at least one parameter selected from the list of parameters comprising thickness of the first part, thickness of the second part, extent of deformation applied, geometry of the product to be produced therefrom, and materials properties of the first and/or second part.

A first requirement which is to be imposed on the layer of adhesive is that it has a uniform thickness over the entire overlap area, at least where this area is subjected to any deformation of the transition blank. In the event of deformation to the transition blank, the layer of adhesive has to follow and to be able to follow the deformation of the two parts of the blank. This means, on the one hand, that the layer of adhesive must

not be too thick, in order to prevent the two parts from moving with respect to one another during deformation. The layer of adhesive must not be too thin, since in that case it becomes insufficiently deformable, and there is a risk that at least one of the two parts will tear open during deformation. Another problem with an excessively thin layer of adhesive or with a layer of adhesive with a thickness which is not homogeneous is that after deformation the two parts come into contact with one another, resulting once again in galvanic corrosion.

A particularly simple embodiment of the method according to the invention which, moreover, provides a transition blank of good quality is characterized in that the thickness of the layer of adhesive is set by means of spacer elements which are incorporated in the layer of adhesive.

The spacer elements ensure that the first part and the second part, at the location of the overlap area, are at a distance from one another which is defined by the dimensions of the spacer elements, and that the layer of adhesive therefore acquires a selected thickness.

A more detailed embodiment of the method according to the invention is characterized in that the spacer elements are incorporated in the adhesive from which the layer of adhesive is formed. In this embodiment, it is possible to distribute the spacer elements in a desired quantity and homogeneously in the adhesive.

Yet another more detailed embodiment of the method according to the invention is characterized in that the spacer elements are spherical elements. Generally, spherical elements are easy to produce. Owing to their symmetry, their orientation in the adhesive has no influence on the thickness of the layer of adhesive.

In yet a further refinement, the method according to the invention is characterized in that the spacer elements are made from vitreous and/or ceramic material. Materials of this nature are generally chemically inert and therefore do not react with the adhesive or with the metal from which the first and second parts are made. Moreover, these materials have a high compressive strength combined with a low deformation, so that the two metal parts which are to be joined together can be pressed towards one another at the location of the overlap area. In all embodiments of the method, the adhesive can be cured at elevated temperature.

A particularly advantageous embodiment of the method according to the invention is characterized in that the layer of adhesive is electrically insulating. This prevents conductive contact between the two metal parts and therefore galvanic corrosion.

An embodiment of the method according to the invention which is simple to use is characterized in that the layer of adhesive, whether or not it is provided with spacer elements, is applied in the form of a strip, tape or film. A strip, tape or film of adhesive can easily be applied, in an accurate position and rapidly. Known means can be used to apply the adhesive.

Preferably, the strip, tape or film is provided with an embedded network or embedded reinforcement elements, which, on the one hand, provides the strip, tape or film with the desired strength and manipulability during its application and, in addition, can act as a spacer element.

The invention is also embodied by a transition blank in an embodiment as obtained substantially by means of a method as described above. A transition blank of this nature has the advantage that galvanic corrosion is easy to prevent as a result of the possibility of providing electrical insulation between the two metal parts. In addition, the transition blank can be produced to any desired dimension, within reasonable limits.

In the case of a transition blank, it is known to join the two metal parts via the intermediary of an intermediate metal, for example nickel, in order to prevent galvanic corrosion. A method for applying an intermediate metal of this nature, which is often carried out by electrochemical means, is, however, a relatively slow process which is not easy to adapt to use on a transition blank of large dimensions.

The invention is also embodied by a component of a means of transport which is formed from a transition blank as described above. A component of this nature may, for example, be produced by pressing from a transition blank. A component of this nature may be used as a transition part between a steel ship's hull and an aluminium super structure, between a steel undercarriage of a train and an aluminium carriage superstructure, and between a steel car chassis and aluminium body parts. For automotive applications, the thickness of the steel part is of the order of 0.6 to 1.2 mm, while the thickness of the aluminium part is of the order of 0.8 to 1. 5 mm

The invention will be described in the following text with reference to the drawing, which shows a figure which depicts, in cross section, a non-limiting embodiment of a transition blank as obtained using the method according to the invention.

In Fig. 1, 1 denotes a first metal part and 2 denotes a second metal part which already overlap one another by way of an overlap area. A layer of adhesive 3 which joins the parts together is situated between the two parts 1 and 2. The layer of adhesive 3 incorporates spacer elements 4 which keep the two parts at a selected minimum distance from one another. It will be clear to the person skilled in the art that the layer of adhesive does not have to extend over the entire width of the overlap area.

Where the above text refers to a metal, this is also understood to include a metal-based alloy.