Patent Description:
It is known from the prior art to weld conductors to a workpiece. It may in this case be provided that the conductor has one or more cores, the one or more cores being enclosed by an insulating material. In order to weld the conductor to a workpiece, the conductor is stripped of its insulation in one region, that is to say the insulating material is removed. The stripped region of the conductor is subsequently pressed onto the workpiece, for example by means of holding-down devices. In the case of a multi-core conductor, it may be the case that for this purpose a number of conducting regions that are insulated from one another are arranged in the workpiece. After the pressing down of the conductor onto the workpiece, at least one core of the conductor is in mechanical contact with either the workpiece or at least one conducting region of the workpiece, and can thus be welded to the workpiece by means of a laser welding process.

On account of the conductor being at a distance from the workpiece as a result of the insulating material, the holding down of the conductor must take place in such a way that the core or the cores of the conductor is/are pressed against the workpiece with a certain expenditure of force. The holding-down devices must be equipped for this and, for this reason, can also only be used in the stripped region of the conductor.

Document <CIT>, on which the preamble of claim <NUM> is based, discloses a welding process in which a bead is formed in a stripped region of a conductor to allow for mechanical contact of the conductor with a workpiece.

One problem addressed by the invention is that of providing an improved welding process.

These problems are solved by the process for welding a conductor onto a workpiece of the independent patent claim. Advantageous configurations are specified in the dependent patent claims.

In a process for welding a conductor onto a workpiece, the conductor comprises a first metal and the workpiece comprises a second metal. In order to weld the conductor to the workpiece, the following steps are carried out. First, an insulation of the conductor is removed over a predetermined length. Subsequently, a bead is created in a stripped region of the conductor. The stripped region of the conductor may in this case be the region of the conductor in which the insulation has been removed.

The bead may be arranged in a manner that the conductor is displaced in the direction of the workpiece. This means that the conductor is not straight in the area of the bead, but bended in a way that the conductor in the area of the removed insulation is closer to the workpiece than in other areas of the conductor.

Subsequently, the conductor is held down on the workpiece, the holding down having the effect of producing a mechanical contact in a welding region between the conductor and the workpiece. The welding region is in this case arranged in the region of the bead. Subsequently, a laser welding of the conductor onto the workpiece takes place in the welding region.

The invention is therefore based on the central idea of reducing a distance between the conductor and the workpiece by means of a bead produced in the conductor, which is arranged in the stripped region of the conductor, by the necessary deforming of the conductor already taking place during the forming of the bead and not only when the holding down takes place. The bead may in this case be configured in such a way that a convexity of the conductor in the direction of the workpiece is produced on account of the bead and, as a result, the distance between the conductor and the workpiece is reduced. It may be provided that a further deformation of the conductor, occurring in addition to the bead, takes place during the holding down of the conductor. In particular, the welding process can be improved if a zero gap is produced, that is to say the conductor lies in direct contact with the workpiece.

After the laser welding, the conductor is welded to the workpiece in a further welding region by means of laser welding. The conductoris therefore respectively welded to the workpiece in a welding region and a further welding region, in order to provide a more secure welded connection.

The forming of the bead takes place in such a way that, during the holding down, the conductor initially lies in contact with the welding region and does not lie in contact with the further welding region. The thermal expansion of the conductor during the laser welding in the welding region has the effect that the conductor is deformed in such a way that the conductor subsequently lies in contact with the further welding region and can likewise be welded there to the workpiece. This may take place for example by the bead being configured in such a way that the conductor is arranged closer to the workpiece in the welding region than in the further welding region on account of the bead; the conductor is in contact with the workpiece in particular in the welding region and not in the further welding region.

As a result, the thermal expansion of the conductor during the laser welding can likewise be used to achieve the overall effect of the conductor lying even more advantageously in contact with the workpiece.

In one embodiment of the process, the workpiece comprises a number of conducting regions. The conductor is part of a multi-core conductor, an insulation being removed during the welding process on all of the cores of the multi-core conductor and a bead being formed in the case of all of the cores of the multi-core conductor. In the subsequent laser welding process, the cores are respectively welded one after the other to a conducting region.

This makes possible an efficient process for welding a multi-core conductor to conducting regions of a workpiece, such as is used for example in battery production.

In one embodiment of the process, the conductor is a flat conductor with a rectangular cross section. Such a conductor is particularly well-suited for the welding process described.

In one embodiment, the holding down takes place in a stripped region of the conductor. This may take place for example by means of a holding-down device, which contacts the conductor in the welding region and holds it down on the workpiece. Alternatively, the holding down may for example also take place by an air stream impinging in the stripped region.

In one embodiment of the process, the holding down takes place outside the stripped region. This may likewise take place for example by means of a holding-down device or an air stream. It may also be provided for example to use a holding-down device in the stripped region and a holding-down device in the non-stripped region of the conductor. If the conductor is held down outside the stripped region, as a result the stripped region can be of a reduced size.

In one embodiment of the process, the laser welding in the welding region takes place by means of a number of welding points. The same may also apply in the further welding region. In the case of laser welding, it is generally customary to set a number of welding points at a welding location, for example spirally. The bead allows this to be performed very efficiently in the described welding process, since for example no holding-down devices are necessary in the vicinity of the welding region.

In one embodiment of the process, a depth of the bead substantially coincides with a thickness of the insulation. In particular, the depth of the bead coincides with the thickness of the insulation. As a result, the conductor is in contact with the workpiece in the welding region when it otherwise lies in contact with the insulation on the workpiece and the bead is configured in such a way that a displacement of the conductor thereby initiated is facing the workpiece. This configuration is particularly well-suited for the holding down of the conductor on the insulation or the holding down of the conductor by means of an air stream.

In one embodiment of the process, the forming of the bead takes place by means of drop forging. In this case, the conductor is placed into a tool which comprises at least two moulds, the bead being created in the conductor by means of a forging operation. This makes possible a simple and efficient production process of the bead, good reproducibility of the forging result being possible due to the tool used in the drop forging.

In one embodiment of the process, the first metal comprises aluminium or copper or consists of aluminium or copper. In one embodiment of the process, the second metal comprises aluminium or the first metal is aluminium. In particular, these stated materials are well-suited for the use of the proposed laser welding process. Any light source capable of stimulating emission of which the energy and/or power and/or wavelength is suitable for welding together the metals to be welded may be used as the laser in the laser welding process. Such suitable laser welding processes are known from the prior art.

The problem addressed by the invention, the technical implementation of the solution and the advantages of the invention are clear from the exemplary embodiments, which are to be described below with the aid of figures, in the schematized representation of which:.

<FIG> shows a cross section through a conductor <NUM>. The conductor <NUM> in this case comprises a first metal <NUM>. An insulation <NUM> has been attached to the first metal <NUM> of the conductor <NUM> in such a way that the insulation <NUM> insulates the first metal <NUM>.

<FIG> shows the conductor <NUM> after the insulation <NUM> of the conductor <NUM> has been removed over a predetermined length <NUM>. The removal of the insulation <NUM> over the predetermined length <NUM> has had the effect that part of the first metal <NUM> of the conductor <NUM> is exposed.

This exposed region may also be referred to as a stripped region <NUM>.

<FIG> shows the conductor <NUM> from <FIG> after placing into a moulding tool <NUM>. The moulding tool <NUM> in this case comprises a lower part <NUM> and an upper part <NUM>. The moulding tool <NUM> serves the purpose of forming a bead in the stripped region <NUM> of the conductor <NUM>, by the upper part <NUM> of the moulding tool <NUM> being moved towards the lower part <NUM>.

<FIG> shows the conductor <NUM> once the upper part <NUM> of the moulding tool <NUM> has been moved towards the lower part <NUM> of the moulding tool <NUM> and a bead <NUM> has been created in the conductor <NUM>. This takes place for example by pressing the upper part <NUM> onto the lower part <NUM>. In one exemplary embodiment, the forming of the bead <NUM> takes place by means of drop forging, the moulding tool <NUM> then being a drop forging tool.

On account of the bead <NUM>, the conductor <NUM> is displaced in its position in the stripped region <NUM>. In this case, it may be provided that a depth <NUM> of the bead <NUM> substantially coincides with a thickness <NUM> of the insulation <NUM>. In alternative exemplary embodiments, not shown here, the depth <NUM> of the bead <NUM> does not coincide with the thickness <NUM> of the insulation <NUM>.

<FIG> shows the conductor <NUM> from <FIG> after it has been removed from the moulding tool <NUM>. The conductor <NUM> is held down on a workpiece <NUM> by means of holding-down devices <NUM>. The workpiece <NUM> in this case comprises a second metal <NUM>. In a welding region <NUM>, the first metal <NUM> of the conductor <NUM> is welded to the second metal <NUM> of the workpiece <NUM> by means of laser radiation <NUM>. The bead <NUM> has the effect that the holding-down devices <NUM> have to exert a smaller force on the conductor <NUM> than in the case of the welding processes known from the prior art, since, on account of the bead <NUM>, the first metal <NUM> of the conductor <NUM> already lies substantially in contact with the second metal <NUM> of the workpiece <NUM>, that is to say substantially forms a zero gap. This applies in particular in the welding region <NUM>.

The conductor <NUM> and the workpiece <NUM> form an arrangement <NUM> of a conductor <NUM> and a workpiece <NUM>, the conductor <NUM> comprising a first metal <NUM> and the workpiece <NUM> comprising a second metal <NUM>, the conductor <NUM> the workpiece <NUM> being welded in a welding region <NUM> and the conductor <NUM> being stripped of its insulation in the welding region <NUM> and comprising a bead <NUM>.

In this case, it may be provided by analogy with <FIG> that a depth <NUM> of the bead <NUM> substantially coincides with a thickness <NUM> of the insulation <NUM> outside the stripped region <NUM> of the conductor <NUM>.

<FIG> shows a multi-core conductor <NUM> in a plan view. In an insulation <NUM>, three cores <NUM> have respectively been stripped, the first metal <NUM> of the cores <NUM> being visible on account of the stripping of the cores <NUM>. In cross section, this may correspond to the representation of <FIG>, the cores <NUM> being arranged one behind the other and therefore only one being visible.

<FIG> shows the conductor <NUM> from <FIG> once a bead <NUM> has been formed in each core <NUM>. This may take place by analogy with the process described in <FIG> by means of the moulding tool <NUM>, for example by means of drop forging.

<FIG> shows the conductor <NUM> from <FIG> after it has been placed onto a workpiece <NUM>, in plan view. By means of holding-down devices that are not shown, the conductor <NUM> can be held down on the workpiece <NUM> in a way analogous to <FIG>. The workpiece <NUM> in this case comprises three conducting regions <NUM>, each core <NUM> being assigned a conducting region <NUM>. On account of the beads <NUM> of the cores <NUM>, it may be provided, by analogy with <FIG>, that the cores <NUM> lie in contact with the conducting regions <NUM>. Each core <NUM> comprises a welding region <NUM>, at which the conductor <NUM> or the core <NUM> of the conductor <NUM> is welded to the workpiece <NUM> or the conducting region <NUM> of the workpiece <NUM> in a way analogous to <FIG> by means of laser radiation <NUM>. Furthermore, the cores <NUM> respectively comprise a further welding region <NUM>, which is likewise arranged in the region of the bead <NUM> in the stripped region <NUM> and at which the cores <NUM> can likewise be welded to the conducting regions <NUM>.

It is analogously also conceivable to weld the conductor <NUM> from <FIG> additionally to the workpiece <NUM> in a further welding region <NUM>.

The conductor <NUM> and the workpiece <NUM> in this case again form an arrangement <NUM> of a conductor <NUM> on a workpiece <NUM>, in which the conductor <NUM> is welded to the workpiece <NUM>. In particular, each core <NUM> of the conductor <NUM> is welded to a conducting region <NUM> of the workpiece <NUM>. If the conducting regions <NUM> of the workpiece <NUM> are insulated with respect to one another, various contactings, for example of a battery, can thus be provided.

<FIG> shows a cross section through a further conductor <NUM> held down on a workpiece <NUM> by means of holding-down devices <NUM>. By contrast with <FIG>, the conductor <NUM> in <FIG> is held down by means of the holding-down devices <NUM> in the region of the insulation <NUM>, that is to say outside the stripped region <NUM> or the bead <NUM>. This is possible in particular whenever the depth <NUM> of the bead <NUM> coincides with the thickness <NUM> of the insulation <NUM>, as already described, since mechanical contact between the first metal <NUM> of the conductor <NUM> and the second metal <NUM> of the workpiece <NUM> is nevertheless possible. Thus, the first metal <NUM> of the conductor <NUM> can be welded in the welding region <NUM> to the second metal <NUM> of the workpiece <NUM> by means of laser radiation <NUM>. If a number of cores <NUM> are provided, as shown for example in <FIG>, each of the cores <NUM> may be welded by means of this process to a corresponding conducting region <NUM> of the workpiece <NUM>.

In a further welding region <NUM>, the bead <NUM> is configured in such a way that there is a distance <NUM> between the first metal <NUM> of the conductor <NUM> and the second metal <NUM> of the workpiece <NUM>. If, during exposure to the laser radiation <NUM>, the first metal <NUM> is heated on account of the laser radiation <NUM>, the first metal <NUM> expands.

<FIG> shows the conductor <NUM> and the workpiece <NUM> from <FIG> after the first metal <NUM> has been welded to the second metal <NUM> in the welding region <NUM> and the first metal <NUM> has expanded on account of the laser radiation <NUM> acting on it. The expansion has the effect that the first metal <NUM> of the conductor <NUM> then also lies in contact with the workpiece <NUM> in the further welding region <NUM> and can likewise be welded there to the workpiece <NUM> by means of laser radiation <NUM>. The conductor <NUM> and the workpiece <NUM> once again form an arrangement <NUM> as already described above.

It may be provided that the conductor <NUM> comprises a flat conductor with a rectangular cross section. In particular, the cores <NUM> may be flat conductors with a rectangular cross section, whereby the contact of the conductor <NUM> or of the cores <NUM> lying on the workpiece <NUM> is improved.

In <FIG>, the holding down of the conductor <NUM> by means of the holding-down devices <NUM> in the stripped region <NUM> of the bead <NUM> is shown. In <FIG>, the holding-down devices <NUM> are arranged in such a way that the holding down takes place on the insulation <NUM>. It is also conceivable in combination that one of the holding-down devices <NUM> holds down the conductor <NUM> in the region of the bead <NUM> or the stripped region <NUM>, while the other holding-down device <NUM> holds down the conductor <NUM> in the region of the insulation <NUM>. Furthermore, it is alternatively likewise conceivable to provide fewer or more holding-down devices <NUM>, for example only one holding-down device or three holding-down devices. Instead of the holding-down devices <NUM>, an air stream may also be used, by means of which the conductor <NUM> is pressed onto the workpiece <NUM>.

It may be provided that in the welding region <NUM> or in the further welding region <NUM> the first metal <NUM> is welded together with the second metal <NUM> by means of in each case a number of welding points, that is to say by means of respective multiple exposure to the laser radiation <NUM>. The welding points may for example be arranged in the form of a cross or spiral. The laser radiation <NUM> may in this case be any laser radiation suitable for welding the first metal <NUM> and the second metal <NUM>.

A cross section of the first metal <NUM> of the conductor <NUM>, and also of the cores <NUM> of the conductor <NUM>, may in this case be <NUM> millimetre on <NUM> millimetre. This means that, in the representation of <FIG> or <FIG>, a thickness of the first metal <NUM> of <NUM> millimetre is represented, and the cores <NUM> from <FIG> are represented in their width of <NUM> millimetre.

The thickness <NUM> of the insulation <NUM> may be between <NUM> and <NUM> millimetre, for example <NUM> millimetre. The depth <NUM> of the bead <NUM> may then likewise lie in this range and be for example <NUM> millimetre.

It may be provided that the first metal <NUM> comprises copper or aluminium, is copper or aluminium or comprises a laser-weldable alloy of the stated metals. The second metal <NUM> may comprise aluminium or a laser-weldable alloy with aluminium.

Claim 1:
Process for welding a conductor (<NUM>) onto a workpiece (<NUM>), wherein the conductor (<NUM>) comprises a first metal (<NUM>) and the workpiece (<NUM>) comprises a second metal (<NUM>), with the following steps: removing an insulation (<NUM>) of the conductor (<NUM>) over a predetermined length (<NUM>); forming a bead in a stripped region (<NUM>) of the conductor (<NUM>); holding down the conductor (<NUM>) on the workpiece (<NUM>), the holding down having the effect of producing a mechanical contact in a welding region (<NUM>) between the conductor (<NUM>) and the workpiece (<NUM>), wherein the welding region (<NUM>) is arranged in the region of the bead; laser welding of the conductor (<NUM>) onto the workpiece (<NUM>) in the welding region (<NUM>), characterized in that, after the laser welding, the conductor (<NUM>) is welded to the workpiece (<NUM>) in a further welding region (<NUM>) by means of laser welding, that the forming of the bead takes place in such a way that the conductor (<NUM>) initially lies in contact with the welding region (<NUM>) and does not lie in contact with the further welding region (<NUM>), that the thermal expansion during the laser welding in the welding region (<NUM>) has the effect that the conductor (<NUM>) is deformed in such a way that the conductor (<NUM>) subsequently lies in contact with the further welding region (<NUM>).