WO2022171333A1

WO2022171333A1 - Welded joint capable of carrying current

Info

Publication number: WO2022171333A1
Application number: PCT/EP2021/085627
Authority: WO
Inventors: Friedrich Lupp; Christian Werner; Sven Schlosshauer
Original assignee: Siemens Aktiengesellschaft
Priority date: 2021-02-12
Filing date: 2021-12-14
Publication date: 2022-08-18
Also published as: DE102021201360A1

Abstract

The method according to the invention for producing a welded joint between two metal workpieces (10, 20) by means of laser-beam welding, the welded joint being capable of carrying current, comprises the following steps: placing joining surfaces (11, 21) of the workpieces (10, 20) together such that they form a joining gap (3) having a gap depth (T3), and guiding a laser beam (4) along the joining gap (3) at least twice, wherein, during each guidance, the workpieces (10, 20) are joined by means of an associated weld seam (1, 2), the weld seam depth (T1, T2) of which is less than the gap depth (T3). The laser beam (4) is guided such that at least two of the weld seams (1, 2) lie at different levels (T31, T32) with respect to the joining gap (3).

Description

description

Current-carrying welded connection

The invention relates to a current-carrying welded connection and a method for producing it.

DIN EN IEC 62271 "High-voltage switchgear and switchgear" specifies that current-carrying connections for currents with currents from 50 A must not show any aging over their service life, which is why a design as screw, rivet or purely form-fitting connections is not permitted. However, in the case of medium-voltage circuit breakers, care must be taken to ensure that components are not damaged by excessive heat, for example vacuum interrupters can have a plastic bearing whose maximum application temperature, e.g Welding processes such as MAG, TIG, plasma welding or electric welding with electrodes for the production of current-carrying connections are therefore ruled out in many cases because the workpieces become too hot (MAG = metal active gas welding; TIG = Tungsten-Inert-Gas-Welding) .Other common processes such as soldering can also be used because of Tem temperature restrictions can only be used to a limited extent.

Temperature restrictions and the requirement to prevent aging of a current-carrying material connection, e.g. B. between a moving contact rod of a vacuum interrupter and a power strip, can be met by using electron beam welding. Other manufacturers prefer to circumvent the standard by encapsulating the connection point with plastic by making the connection point non-destructively accessible from a metrological point of view. What both methods have in common is that they are very complex and expensive, which is not least due to the complex system technology they require. It is therefore the object of the present invention to provide a current-carrying connection which avoids the disadvantages mentioned above.

The object is achieved by a method according to claim 1. The method is used to produce a current-carrying welded connection between two metallic workpieces by means of laser beam welding. "Current-carrying capacity" is understood to mean a welded joint that can conduct a current of 50 A and more permanently without the welded joint being heated above the permissible operating temperature due to the current flow. The method has a step in which the joint surfaces of the Workpieces are placed one on top of the other in such a way that they form a joint gap that has a gap depth. whose weld seam depth is smaller than the gap depth The laser beam is guided in such a way that at least two of the weld seams are at different levels in relation to the joint gap.

The object is also achieved by a connection according to claim 7. The connection is a current-carrying laser beam welded connection between two metallic workpieces. The welded connection is formed by two or more weld seams, which run in a joint gap having a gap depth, which is formed by surfaces of the workpieces lying against one another. In this case, the two or more weld seams each have a weld seam depth that is smaller than the gap depth, and at least two of the weld seams are at different levels in relation to the joint gap.

The invention is based on a segmentation of a weld seam into two or more individual weld seams which, seen in the direction of the depth of the joint gap, lie one behind the other. On- instead of attempting to close a joint gap with a single weld seam with a large weld depth, the joint gap is closed with a plurality of weld seams, each with smaller weld depths, preferably in successive weld runs. In this way, a joint gap of any depth can be closed independently of the welding depth that can be achieved with a laser beam. The segmentation leads to a drastic reduction in the heat introduced during the connection process and thus to the fulfillment of any temperature restrictions.

In laser beam welding there is a correlation between the welding depth and the laser power required for this. For this reason, welding depths of more than 8 mm, for example, are not easy to achieve, since a very high laser power in the range > 16 kW is required with an NIR laser, see Andreas Heider: Expanding the process limits in laser beam welding of copper with welding depths between 1 mm and 10 mm , dissertation University of Stuttgart 2018, in the series: Prof. Dr.

Thomas Graf (ed.): Lasers in material processing - research reports from the IFSW, University of Stuttgart, Institute for Beam Tools (IFSW), Munich: Herbert Utz Verlag 2018, ISBN 978-3-8316-4738-5. The standard disk lasers recommended for copper welding due to their low susceptibility to back reflections are currently only available up to 16 kW (e.g. lasers from Trumpf GmbH & Co. KG, Ditzingen, DE), apart from the beam quality that decreases with increasing laser beam power (expanded , poorly focused beam), resulting in an even higher power requirement. This limits the technical availability of the system technology and leads to relatively high investment costs.

The invention circumvents these problems by dividing a weld seam to be produced in a joint gap of depth x with a weld seam depth x corresponding to the gap depth into N weld seams, each with smaller weld seam depths Xi, X ₂ , X ₃ , ... < x (integer N >= 2). It is therefore possible to work with a lower laser power than for production the total weld depth x would be required. The lower laser power required not only reduces the investment in the laser device, but also in its peripherals, such as e.g. B. cooler, optics, protective housing: overall, less complex system technology is required.

Further advantages of the invention are the low complexity of the required system technology, the low thermal and mechanical stress on the workpieces during the manufacturing process, an electrical conductivity of the welded connection approximately that of the workpieces, a thermal conductivity of the welded connection approximately that of the workpieces and the fact that no time-consuming seam preparation is necessary: a technical zero gap, i. H. neither fit nor wobble is sufficient. The heating of the workpieces during welding depends on the welding geometry and the geometry of the workpieces, as well as on the thermal connection of the workpieces to the clamping device. For typical workpieces for switchgear components such as e.g. B. vacuum interrupters, the temperature rise during welding is less than 100 °C, according to an estimate based on material constants and the typical welding process parameters without taking into account energy losses during welding.

Advantageous configurations of the invention are the subject matter of the dependent claims. The method according to the invention can also be further developed in accordance with the dependent device claims, and vice versa.

According to a preferred embodiment of the invention, at least two of the weld seams lie in non-overlapping deep sections of the joint gap. The advantage of this is that the weld seams fill the joint gap over their entire welding depth and thus promote the stability of the connection between the workpieces.

According to a preferred embodiment of the invention, an inlay, ie a metallic insert, is inserted into the joint gap. placed, which separates two or more welds from each other. In order to be able to carry out a laser welding in a joining gap that is relatively deep when viewed from a surface of the workpieces, it can be advantageous for the incidence of the laser beam if areas of the workpieces which lie in the beam path of the laser beam and which the laser beam is intended to reach of the level must be cleared, e.g. B. be removed by a machining process. After the laser welding is completed at the relatively deep level by producing a first weld seam, an execution of a laser weld at a less deep level of the joint gap, i.e. to produce a second weld seam "above" the first weld seam, can be simplified by the fact that in the cleared areas of the workpieces, which are also referred to as recesses, one or more metallic inserts, so-called inlays, are used, which are designed to correspond to the volume of the recesses, so that by inserting them into the recesses, sufficiently narrow joint gaps for laser welding he be witnessed, which are separated from each other by the inlay.

The inlays preferably correspond to the shapes of the joint gaps, i. H. an inlay can be designed as a ring in the case of a circular joint gap and as a rectangular strip in the case of a linear joint gap. The inlays as well as the recesses of the workpieces can have a rectangular cross-section in order to facilitate their manufacture.

According to a preferred embodiment of the invention, the weld seams are produced in a rough vacuum. The vacuum serves to calm the weld. In this way, high-quality weld seams can be produced, characterized by an almost homogeneous connection cross-section, no pores, no cracks and a resistance of < 100 pOhm. The vacuum is advantageously in a range of less than 200 mbar. The positive effect of the vacuum is more pronounced the lower the pressure. A particularly advantageous compromise There is a difference between the effort required to generate the vacuum and the welding result at a vacuum of approx. 20 mbar.

According to a preferred embodiment of the invention, the laser beam is generated by the simultaneous use of a laser in the NIR wavelength range, in particular l=780 to 3000 nm, and a laser in the green wavelength range, in particular l=520 to 565 nm. The use of such a "hybrid" laser beam calms the weld pool and, thanks to the additional green laser, improves the coupling of the laser beam into the workpiece material.

According to a preferred embodiment of the invention, the two metallic workpieces are made of copper or copper alloys. Both workpieces can be made of copper or of the same or different copper alloys. It is also possible that one of the workpieces is made of copper and the other workpiece is made of a copper alloy.

According to a preferred embodiment of the invention, the two metallic workpieces are made of aluminum or aluminum alloys. Both workpieces can be made of aluminum or of the same or different aluminum alloys. It is also possible that one of the workpieces consists of aluminum and the other workpiece consists of an aluminum alloy.

According to a preferred embodiment of the invention, heat management is practiced so that temperature restrictions are observed: After a first weld seam has been produced, the workpieces are preferably allowed to cool down sufficiently before a second weld seam is produced. The weld joint to be produced is preferably divided into as many smaller weld seams as are necessary to ensure that the workpieces do not overheat. Preferably, the workpieces are cooled, e.g. B. with liquid nitrogen. The properties, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood from the following description of the drawings. Here are shown in a schematic representation that is not true to scale:

FIG. 1 shows a section of an arrangement of two metal workpieces;

Figure 2 is a plan view of the arrangement of Figure 1;

Figure 3 is a sectional view of a conventional welded joint of the two metal workpieces of Figure 1;

Figure 4 is a plan view of the weld of Figure 3;

FIG. 5 shows a section of a welded connection according to a first embodiment of the invention; and

Figure 6 to 10

Sections and top views illustrating steps for producing a welded joint according to a second embodiment of the invention.

Figure 1 shows a section of an arrangement of two metallic workpieces 10, 20. A first workpiece 10 designed as a rod is inserted into a circular through-hole of a second workpiece 20 designed as a plate with a thickness D, so that an end face 100 of the rod 10 lies in one plane with an end face 200 of the plate 20 . In this way, a joint gap 3 is formed between the workpieces 10, 20, which gap has a depth T3 and a gap width B3. In this example, the gap depth T3 of the joining gap corresponds to the thickness D of the plate 20.

FIG. 2 shows a plan view of the end faces 100, 200 of the workpiece arrangement 10, 20 shown in FIG the joint gap 3 formed between the rod 10 and the plate 20 with the gap width B3 can be seen.

FIG. 3 and FIG. 4 show a section and a plan view of a conventional welded connection, with which the two metallic workpieces 10, 20 shown in FIGS. 1 and 2 are connected in a materially bonded manner. The weld seam 1 produced by a laser beam extends over the entire gap depth T3 of the joint gap 3. The greater the gap depth T3 of the joint gap 3 to be welded, the greater the laser power required for this. Relatively deep joining gaps 3 are therefore very expensive to weld with a laser beam.

FIG. 5 shows a section of a welded connection according to a first embodiment of the invention. Two workpieces 10', 20' designed as metal plates of the same thickness each have a plate edge which serves as joining surfaces 11, 21. Since the workpieces 10 ', 20' lie against one another in such a way that their joining surfaces 11, 21 laterally limit a joining gap 3 with a rectangular cross section. By the action of a laser beam 4 focused from the first side surfaces 100, 200 of the workpieces 10', 20' into the joint gap 3, a first weld seam 1 with a weld seam depth TI and in a dem first step subsequent second step at a second level T32 in the joint gap 3, which is closer to the first side surfaces 100, 200 than the first level T31, a second weld seam 2 drawn with a weld seam depth T2. The respective center point of the weld seams 1, 2, measured in the direction along the depth of the joint gap 3, is defined as the position of the weld seams 1, 2. The two welds 1, 2 are in non-overlapping Tiefenab sections DT31, DT32 of the joint gap 3, so are seen in Rich direction along the depth of the joint gap 3, one behind the other.

FIG. 6 shows a section of an arrangement of two metallic workpieces 10'', 20''. In this case, as a rod first workpiece 10" formed in a circular through-bore of a plate designed as a second workpiece 20" is inserted, so that an end face 100 of the rod 10'' lies in one plane with an end face 200 of the plate 20''. In this case, the lower half of the plate 20'' is brought up to the rod 10'', forming a joint gap, while the upper half of the plate 20'' is at a distance from the rod 10''. Relative to the longitudinal axis 12 of the rod 10'' having a radius 13, the plate 20'' ends in its upper half at a radius 23 which is larger than the radius 13 of the rod 10''; thus the rod 10'' is surrounded by an annular recess 5 µm in the upper half of the plate 20''.

In the lower half of the plate 20'', where the plate 20'' is guided up to the rod 10'', forming a joint gap, the workpieces 10'', 20'' are welded by an annular laser seam 1 '', which follows the longitudinal course of the cylindrical joint gap. FIG. 7 illustrates the geometry of the workpieces and weld seam shown in FIG. 6 using a plan view of the end faces 100, 200 of the workpieces 10'', 20''.

Figure 8 illustrates, starting from the in Figs. 6 and 7, a further step for producing a welded joint according to the invention between the workpieces 10'', 20''. An inlay 6 designed as a ring is inserted into the annular recess 5 surrounding the rod 10''. This creates a first joint gap 7 between the inlay 6 and the rod 10'' and a second joint gap 8 between the inlay 6 and the plate 20''. FIG. 9 illustrates the geometry of the workpieces and weld seam shown in FIG. 8 using a plan view on the end faces 100, 200 of the workpieces 10'', 20''.

Figure 10 illustrates, starting from the in Figs. 8 and 9 arrangement shown, a further step for producing a welded joint according to the invention between the workpieces corners 10'', 20''. In the first joint gap 7 formed between the inlay 6 and the rod 10'', a weld seam 31 is produced between the inlay 6 and the rod 10'' by means of laser beam welding. In the second joint gap 8 formed between the inlay 6 and the plate 20'', a weld seam 32 is produced between the inlay 6 and the plate 20'' by means of laser beam welding. The inlay 6 is arranged in such a way that an annular cavity 33 is formed on the bottom of the inlay 6 facing away from the end faces 100, 200. The cavity 33, which is formed due to the process in that the inlay 6 is not welded to the workpieces 10'', 20'' at its bottom facing away from the end faces 100, 200, should be as small as possible.

If one compares the arrangements shown in Figures 3 and 10, it can be seen that the conventional welded connection shown in Fig. 3 as a continuous weld seam 1 is divided into several weld seams 1'', 31 , 32 was segmented with a lower weld seam depth. This makes it possible to achieve relatively deep welding depths even with a laser with a lower beam power. Here is a concrete example: If a weld seam 1, for which a laser power of approx. 16 kW is required with a conventional design as a single continuous weld seam, is separated into two weld seam segments, each 4 mm deep, then there is only one NIR laser with a laser beam power of 8 kW and, if necessary, an additional laser with 1 kW in the green wavelength range is necessary in order to produce high-quality weld seams with a welding depth of 4 mm.

Claims

patent claims

1. A method for producing a current-carrying welded connection between two metallic workpieces (10, 20) by means of laser beam welding, having the following steps:

Laying joining surfaces (11, 21) of the workpieces (10, 20) together in such a way that they form a joining gap (3) having a gap depth (T3), and

Guiding a laser beam (4) at least twice along the joint gap (3), with the workpieces (10,

20) are connected by a respective weld seam (1, 2), the weld seam depth (TI, T2) of which is smaller than the gap depth (T3), the laser beam (4) being guided in such a way that at least two of the weld seams (1, 2) at different levels (T31,

T32) in relation to the joint gap (3).

2. The method according to claim 1, wherein at least two of the weld seams (1, 2) lie in non-overlapping depth sections (DT31, DT32) of the joint gap (3).

3. The method according to claim 1 or 2, wherein in the joint gap (3) an inlay (6) is inserted, which separates two or more welds (31, 32) from each other.

4. The method according to any one of the preceding claims, wherein the welds (1, 2) are produced in a vacuum of <200 mbar, in particular in a special range of <50 mbar, more preferably in a range of about 20 mbar.

5. The method according to any one of the preceding claims, wherein the laser beam is generated by a simultaneous use of a laser in the NIR wavelength range and a laser in the green wavelength range.

6. The method according to any one of the preceding claims, wherein the two metallic workpieces (10, 20) made of copper or copper feralloys, or made of aluminum or aluminum alloys.

7. Current-carrying laser beam welded connection between two metallic workpieces (10, 20), the welded connection being formed by two or more weld seams (1, 2) which run in a joint gap (3) having a gap depth (T3) and which passes through abutting joint surfaces (11, 21) of the workpieces (10, 20) are formed, which have two or more weld seams, each with a weld seam depth (TI, T2) that is smaller than the gap depth (T3), and at least two of the Welds (1, 2) are at different levels (T31, T32) in relation to the joint gap (3).