Device and method for thermal joining using an energy beam

Abstract

Device for thermal joining of workpieces (7) by means of an energy beam (6), comprising a wire feed unit (1) and a beam head (5) with beam shaping, beam splitting and / or beam movement unit, wherein the wire feed unit (1) and the beam head (5) are connected to each other by means of a telescopic arm (4) which is displaceable along its telescopic axis (4.1) against a disengagement force, wherein - the wire feed unit (1) has a wire nozzle (1.1) with a wire strip channel for guiding at least one wire strip (3) made of parallel adjacent, individually longitudinally displaceable wires (2), which extends in a wire strip plane spanned by the wires (2) in the wire strip channel, wherein the parallel adjacent wires (2) in the wire strip (3) touch each other, - the wire tape channel has a shape adapted to the wire tape (3), wherein the wire tape (3) is guided in the wire tape channel with tight tolerances, - the beam head (5) is configured to widen, split or move the energy beam (6) about a mean beam axis (6.1) wherein the mean beam axis (6.1) and the telescopic axis (4.1) lie in a guide plane that is orthogonal to the wire tape plane, and - the wire nozzle (1.1) has an inner contour that tapers in a funnel shape towards the wire inlet of the wire strip channel.

Description

[0001] The invention relates to a device and a method for thermally joining workpieces using an energy beam with the addition of wire-shaped filler material. They are particularly suitable for producing large-volume welds or brazed seams.

[0002] Conventional wire-based automated joining processes, in which energy is introduced by means of an energy beam, particularly a laser or electron beam, regularly use individual wires as filler material. The wire is fed via exit nozzles or wire dies that completely enclose the individual wire. The filler wire is guided through a cylindrical feed tube into the wire die, from which it then preferably strikes the workpiece surface at an angle of 20° to 60°. The wire is subsequently struck by the energy beam at the so-called process point and, if necessary, melted together with sections of the workpiece. The feed tube and the wire die are usually designed as rotationally symmetrical turned parts.

[0003] According to the current state of the art, when replacing a wire nozzle, it is pushed over the individual wire protruding from the feed tube and then screwed into the feed tube by rotating it around the wire axis. The wire typically protrudes between 6 and 10 mm from the wire exit end of the wire nozzle before it reaches the processing point. The distance between the exit surface at the wire exit end of the wire nozzle and the processing point is also referred to as the "sickout." To improve accessibility to the workpiece and prevent collisions between the wire exit end of the wire nozzle and the workpiece(s), the wire nozzles are regularly tapered at the wire exit end.

[0004] For reliable process control, it is advantageous that the wire rests on the workpiece without gaps in the joining zone. This gap-free position of the wire on the workpiece is ensured by technical means, preferably by force-loaded telescopic mechanisms, for example, a telescopic arm. A release force acting along the telescopic axis of the telescopic mechanism is applied by means of spring force, air pressure, or an electric drive. The wire nozzle transmits the force introduced from the telescopic mechanism via the guide tube to the wire, which is consequently pressed continuously against the workpiece. Height deviations along the joint of the workpieces to be joined are thereby compensated for.

[0005] In single-wire welding, the process point, i.e., the focus of the energy beam, lies between the two contact points of the wire on the workpieces. Consequently, the filling of the weld volume in fillet or butt welds begins with the melting of the filler material at the root point located between the contact points and spreads from there towards the top of the weld or towards the contact points.

[0006] In conventional joining with a single filler wire, the energy beam is typically positioned in a fixed position. The intensity of the energy beam is set so that the filler material and, if necessary, parts of the workpieces to be joined are melted to form the desired metallurgical bond.

[0007] It is known that the compensating movement of the telescopic mechanism can be detected by means of a position sensor or displacement transducer. The position signal detected by the position sensor is used to adjust the focus of the energy beam in order to keep the coupled power of the energy beam at the process point constant. During single-wire joining, this correction is performed according to the relationships described above with respect to the root point of the weld seam.

[0008] DE 10 2017 112 849 A1 describes a method and a device for wire-based additive manufacturing, in which several comb-like individual wires arranged parallel to each other are fed as a wire package with individually controllable wire feed into a welding zone and melted there by means of an energy beam, in particular a laser or electron beam, and deposited layer by layer to form a shaped body, wherein the energy beam can, for example, be guided oscillating over the wire package by means of a scanner optic, expanded in a line shape or divided into several individual spots in order to melt the individual wires depending on their position and thus achieve a high build rate with simultaneous process stability of the additive manufacturing.

[0009] From KR 10 2018 0 028 977 A, a wire feed device for welding equipment, in particular for tungsten inert gas welding machines, is known, with which one, two or more wire strands can be fed simultaneously, so that several wires can be introduced into the welding area in parallel as required, whereby the selection and simultaneous feeding of several wires allows adaptation to different welding requirements.

[0010] DE 10 2019 103 350 B3 discloses a wire feeding device in which several directly adjacent individual wires are conveyed as a wire bundle through a guide channel of a nozzle body adapted to the bundle geometry into a process zone, wherein support elements are provided for transverse guidance and defined pre-bending of the individual wires in order to ensure reproducible, positionally accurate feeding with reduced nozzle wear.

[0011] From DE 10 2019 210 365 A1, a method and a device for laser cladding are known, in which at least two parallel, individually guided wires are fed to a laser beam by means of a wire positioning unit, wherein an electronically controlled relative movement between the focal spot of the laser beam and the wires causes a transverse displacement of the focal spot from one wire to another wire, so that the wires can be at least partially melted and their filler materials can be selectively mixed or locally incorporated differently into a coating.

[0012] One of the disadvantages of joining technology based on single wires is the potentially insufficient amount of filler material that can be introduced into the joining zone within a given time unit for specific joining tasks, since the conveying or feeding speed of the wire as well as the wire diameter are limited by process engineering.

[0013] If particularly large joints are required for geometric reasons, but especially for reasons of strength, single-wire joining technology is only applicable to a limited extent, possibly only in conjunction with a multi-layer technique - which is then often uneconomical.

[0014] Another disadvantage of single-wire thermal joining occurs when joining workpieces that can only be positioned at the joint with larger and / or varying gap widths, or between which thermal distortion during joining creates corresponding gaps. The wider the gap, the further the single wire, and with it the process point, is shifted into the gap. This can result in uneven melting of the workpieces to be joined and thus an uneven bond between the workpieces and the filler material. Furthermore, excessively large gaps can impair the stability of the weld pool.

[0015] It is therefore an object of the invention to avoid the disadvantages described above and to provide a device and a method for thermally joining workpieces using an energy beam, which makes it possible to produce large-volume joining connections, in particular single-layer weld or braze seams, with high positional accuracy and process stability, wherein the material distribution of the filler material and the possibly melted areas of the workpieces are variably adjustable.

[0016] This problem is solved by a device for thermal joining with the characterizing features according to claim 1 and a method for thermal joining with the characterizing features according to claim 6; advantageous embodiments of the invention are listed in claims 2 to 5 and 7 to 10.

[0017] According to the invention, the device for thermally joining workpieces using an energy beam, for example a laser or electron beam, comprises a wire feed unit and a beam head with a beam shaping, beam splitting, and / or beam movement unit. The wire feed unit and the beam head are connected to each other by means of a telescopic arm. The telescopic arm is displaceable along its telescopic axis against a disengagement force, i.e., the telescopic arm is subject to longitudinal compressive stress. The disengagement force is generated by known technical means, for example by a spring, a pneumatic device, or an electric drive.

[0018] The wire feeding unit has a wire nozzle with a wire strip channel for guiding at least one wire strip consisting of parallel, adjacent, individually longitudinally displaceable wires, wherein the wire strip extends in a wire strip plane spanned by the wires in the wire strip channel.

[0019] The beam head is designed to expand, split, or oscillate the energy beam around a central beam axis. According to the invention, the central beam axis and the telescopic axis lie in a guide plane that is orthogonal to the plane of the wire strip.

[0020] The thermal joining process can be carried out using the proposed device, or is carried out with it, whereby several wires fed into a joining zone are melted by means of the expanded, split, or oscillating energy beam and solidify as filler material, forming a metallurgical bond between the workpieces. In welding processes, in addition to the wire material, parts of the workpieces are also melted; in brazing processes, as a rule, only the wire material is melted. The filler material, which is essentially formed from the wire material, can therefore—depending on the type of joining process—contain material components from the melted workpiece material after melting.

[0021] The wires are individually fed into the joining zone, lying parallel to each other and allowing longitudinal movement within the wire strip. At least the two outermost wires of the wire strip are pressed against one of the workpieces to be joined at a contact point. The wire strip thus forms a bridge between the workpieces to be joined, in the simplest case bearing against the workpieces to be joined at two contact points.

[0022] According to the invention, the expansion, division, and / or movement of the energy beam are adjusted such that the energy beam encompasses the wire strip in its transverse extent. That is, in the case of beam expansion or beam division, the expanded or divided energy beam simultaneously covers the entire width of the wire strip; in the case of oscillating movement, the energy beam sweeps across the entire width of the wire strip in rapid succession. The central axis of the energy beam is preferably directed concentrically onto the wire strip.

[0023] One of the advantages of this process is that, by feeding the wires in the form of a wire strip, a relatively large quantity of filler material – compared to a single wire – can be introduced into the joining zone of the workpieces to be joined. The wire strip can be positioned very precisely relative to the workpieces using the wire nozzle. The telescopic arm, subjected to a release force, continuously presses the wire strip against the workpiece. This constant contact of the wires with the workpieces enables the formation of a precisely defined weld pool geometry, particularly when producing welds or brazed joints, and thus ensures high process stability during the joining process.

[0024] Furthermore, uneven gaps at butt or T-joints can be bridged by the wire strip without any loss of quality in the joint.

[0025] Large-volume welded and soldered joints, which can only be produced using multi-layer technology when using single wires, can often be manufactured using single-layer technology with the method according to the invention. Where necessary, however, the method can also be applied using multi-layer technology for particularly large-volume joints or for the additive manufacturing of shaped parts.

[0026] Furthermore, the wire strip can be variably positioned relative to the workpieces to be joined by tilting and shifting it. By selecting the position and spacing of the contact points, it is possible to predetermine the position and width of the joint to be created, as well as the respective connection widths to the workpieces. This allows, among other things, the stress-appropriate design of the weld and braze seam geometry.

[0027] The wire strip can be constructed in one or multiple layers. The wires positioned at the edges of the wire strip, which make contact with the workpieces, are determined by the arrangement of the workpieces to be joined and the position and orientation of the wire strip in relation to the workpieces.

[0028] According to one embodiment of the process, the energy beam is controlled so that the melting of the wires in the wire strip begins at the contact points. By initiating the melting at the contact points, it is possible to create a relatively small, stable melt pool with a rapidly following solidification front, despite the larger amount of filler material.

[0029] The process is preferably carried out with a sickout in the range of 5 mm to 12 mm. The sickout is the distance between the exit surface at the wire exit end of the wire nozzle and the point where the wire in contact with the workpiece is melted by the energy jet. Particularly good guidance and positioning of the wire strip can be achieved in this selected sickout area.

[0030] The wires lying parallel to each other in the wire strip preferably touch; this improves mutual guidance, especially when the wires are fed at different speeds. The method can also be carried out with small gaps between the wires or with deliberately set gaps. The use of wire strips with gaps is preferably in the sickout area specified above.

[0031] To improve wire strip guidance, the wire strip channel of the wire nozzle has a shape adapted to the wire strip. For example, in the case of a single-layer wire strip, the wire strip channel has an oval-rectangular cross-section in which the wire strip is guided with virtually no play.

[0032] According to one embodiment of the device, the wire feed unit has a feed tube that can be positively connected to the wire nozzle, the wire nozzle being lockable against rotation and displacement on the feed tube. The wire nozzle is, for example, positively pushed onto the guide tube and fixed to it by means of a clamping device.

[0033] The wire nozzle can have one or two flattened recesses or clearances designed such that, in the cutting plane perpendicular to the wire strip plane, the wire nozzle has an outer contour that tapers towards the wire exit point. These recesses or clearances prevent collisions between the wire nozzle and the workpieces and / or the energy jet in specific machining situations.

[0034] According to the invention, the wire nozzle has an inner contour that tapers in a funnel shape towards the wire inlet of the wire strip channel. The funnel angle is chosen to be as shallow as possible, i.e., significantly less than 90°. The funnel-shaped inner contour facilitates threading the wires when changing the nozzle.

[0035] The device can also include a swivel unit for positioning, aligning, and guiding the wire feed unit and the blasting head relative to the workpieces to be joined. The swivel unit is, for example, a robot arm to which the blasting head is attached. The swivel unit allows, in particular, adjustment of the angular position of the wire strip at the joint.

[0036] In one embodiment of the method, the contact forces acting on the wire strip at the contact points during joining can be detected by means of one or more force sensors, whereby the alignment and positioning of the wire strip and / or the power of the energy beam coupled into the joining zone are controlled and / or regulated depending on the detected contact forces.

[0037] The device can, for example, include one or more force sensors by means of which forces acting on the wire nozzle orthogonally to the wire feed direction can be detected. The wire feed direction is defined in a known manner as the direction along the longitudinal extent of the wires towards the joining zone. The force sensor(s) can, for example, be mounted on the telescopic arm. Since the contact forces acting on the wire strip during joining are transmitted to the telescopic arm via the wire feed unit, indirect force detection by the force sensors on the telescopic arm is possible.

[0038] In carrying out the method, the joint geometry and / or the joint position of the workpieces to be joined is continuously detected before joining by means of optical sensors, preferably by means of a light section sensor, whereby the orientation and positioning of the wire strip, the feed rate of individual wires into the joining zone and / or the power of the energy beam coupled into the joining zone are controlled and / or regulated depending on the detected joint geometry and / or joint position.

[0039] Furthermore, the formation of the joining zone during joining can be captured as a grayscale image using a camera, whereby the feed rate of individual wires into the joining zone and / or the power of the energy beam coupled into the joining zone can be controlled and / or regulated depending on the captured grayscale image.

[0040] The invention is explained in more detail below with reference to exemplary embodiments and the schematic drawings, wherein identical or similar features are designated with the same reference numerals. The drawings show: Fig. 1: the device for thermal joining in side view, Fig. 2: the wire feed unit in perspective view, Fig. 3: The wire feed unit in top view, Fig. 4: the position of the wire before joining using a single wire according to the state of the art in cross-section, Fig. 5: the position of the wires in cross-section before joining according to the inventive method, Fig. 6: the production of a fillet weld joint according to the state of the art using a single wire in cross-section, Fig. 7: the production of a fillet weld joint according to the inventive method with an oscillating energy beam in the cross-section, Fig. 8: the production of a fillet weld joint according to the inventive method with a widened energy beam in cross-section, Fig. 9: the production of a fillet weld joint according to the inventive method with a split energy beam in cross-section, Fig. 10: the position of the wires before joining according to the inventive method when using multilayer wire strips in cross-section, Fig. 11: the position of the wires before joining according to the inventive method when using wire strips with a gap in the cross-section, Fig. 12: various designs of fillet welds on a T-joint in cross-section, and Fig. 13: the forces when pressing the wire strip against workpieces arranged in a T-joint in cross-section.

[0041] The device for thermal joining according to the Fig. 1 comprises the beam head 5 and the wire feed unit 1, which are connected to each other via the telescopic arm 4. The telescopic arm 4 is displaceable along its telescopic axis 4.1.

[0042] The wires 2 are fed to the workpiece 7 as a wire ribbon 3 via the wire nozzle 1.1 of the wire feed unit 1. The telescopic arm 4 has a compression spring that generates a continuous release force along the telescopic axis 4.1. This presses the wires 2 exiting the wire nozzle 1.1 onto the workpiece 7 with a continuous force.

[0043] For joining, the wires 2 are melted by means of the energy beam 6, in the exemplary embodiment by means of a laser beam which is expanded, divided or moved oscillating around the central beam axis 6.1.

[0044] The force sensor 10 is installed on the section of the telescopic arm 4 connected to the beam head 5 in order to detect the forces acting on the wire strip 3 and introduced into the telescopic arm 4 via the wire feed unit 1. The force sensor 10 is, for example, a strain gauge, by means of which the bending forces acting on the telescopic arm 4 are determined by measuring the deformations of the telescopic arm 4.

[0045] The exit of the wire strip 3 from the parallel, adjacent, individually longitudinally displaceable wires 2 from the wire nozzle 1.1 of the wire feed unit 1 is illustrated Fig. 2. The energy beam 6 hits the wire strip 3 with its central beam axis 6.1.

[0046] The wire nozzle 1.1 and the wire strip 3, consisting of parallel, adjacent wires 2, are aligned such that the guide plane is orthogonal to the wire strip plane. The guide plane is shown in the top view according to the Fig. 3 perpendicular to the image plane and runs along the central beam axis 6.1 of the energy beam 6. The wire ribbon plane lies in the representation according to Fig. 3 in a flat plane that encloses the wire strip 3. The orthogonal orientation of the guide plane to the wire strip plane is clarified by the marking of the perpendicular angles.

[0047] For example, in Fig. Figure 4 shows the positioning of two workpieces 7 before joining using a single wire 2, according to the state of the art. Both workpieces 7 form a T-joint; the wire 2 lies in the gusset area of ​​this T-joint and is completely encompassed by the energy beam 6.

[0048] In the method according to the invention, - as shown in the example in Fig. 5 - A bridge is formed between the two workpieces 7 to be joined by the wire strip 3. The outer wires 2 of the wire strip 3 are in contact with each of the workpieces 7 at the contact points 8. By means of the energy beam 6, which oscillates around the central beam axis 6.1, the wires 2 and, if necessary, parts of the workpieces 7 are melted. After resolidification, the filler material 9 forms the joint.

[0049] The Fig. 6 and the Fig. Figure 7 illustrates the differences between the prior art single-wire joining method and the method according to the invention, with the respective sub-figure a showing the state before the melting of the wire 2 or wires 2 and the respective sub-figure b showing the state when the molten filler material 9 is present. In the conventional single-wire method, the melting begins in the core or root region of the joint, whereas in the wire strip method according to the invention, the melting starts at the contact points 8.

[0050] The Fig. 8 and the Fig. 9 correspond to the Fig. 7 with the difference that the energy beam 6 - instead of the oscillating motion - is in the Fig. 8 widened and in the Fig. It is divided into 9.

[0051] In the two sub-characters of the Fig. Figure 10 shows variants of multi-layered wire strips 3. In subfigure a, the edge wires 2 of the lower layer of the wire strip 3 contact the workpieces 7; in subfigure b, the edge wires 2 of the upper layer of the wire strip 3 lie against the workpieces 7.

[0052] The wire band 3 can - like the two partial figures of the Fig. 11 show - also be formed with gaps; the energy beam 6 is moved in a pendulum motion (partial figure a) or split (partial figure b).

[0053] The Fig. Figure 12 illustrates the variable possibilities of the inventive method for producing fillet welds at T-joints. The right fillet weld is symmetrical, i.e., the bonding width a of the filler material 9 on the upper workpiece 7 corresponds to the bonding width b on the lower workpiece 7. For this purpose, the (not shown) wire strip 3 and the (not shown) energy beam 6 were positioned such that the lateral angles α and β between the respective workpiece 7 and the central beam axis 6.1 are equal. The left fillet weld, on the other hand, is asymmetrical, with the bonding width a on the upper workpiece 7 resulting from the portion a1 located above the point of impact of the central beam axis 6.1 and the portion a2 located below it.

[0054] In the representation according to the Fig.Figure 13 shows the different contact forces F1, F2, F3 and F4 that occur when the wire strip 3 guided by the wire nozzle 1.1 is subjected to the force F emanating from the (not shown) telescopic arm 4. TA The wire strip 3 is pressed against the workpieces 7. It is positioned symmetrically at the T-joint, i.e., the lateral angle α corresponds to the lateral angle β; this results in identical connection widths a and b after joining. List of reference symbols used 1 wire feed unit 1.1 Wire nozzle 2 wires 3 wire band 4 telescopic arms 4.1 Telescopic axis 5 beam head 6 Energy beam 6.1 central beam axis 7 workpieces 8 Contact point 9 Additive material 10 Force sensor a, b Connection width a1, a2 proportional connection width α, β Lateral angles F1, F2, F3, F4 Contact forces F TA Power from telescopic arm

Claims

[1] Device for thermal joining of workpieces (7) by means of an energy beam (6), comprising a wire feed unit (1) and a beam head (5) with beam shaping, beam splitting and / or beam movement unit, wherein the wire feed unit (1) and the beam head (5) are connected to each other by means of a telescopic arm (4) which is displaceable along its telescopic axis (4.1) against a disengagement force, wherein - the wire feed unit (1) has a wire nozzle (1.1) with a wire strip channel for guiding at least one wire strip (3) made of parallel adjacent, individually longitudinally displaceable wires (2), which extends in a wire strip plane spanned by the wires (2) in the wire strip channel, wherein the parallel adjacent wires (2) in the wire strip (3) touch each other, - the wire tape channel has a shape adapted to the wire tape (3), wherein the wire tape (3) is guided in the wire tape channel with tight tolerances, - the beam head (5) is configured to widen, split or move the energy beam (6) about a mean beam axis (6.1) wherein the mean beam axis (6.1) and the telescopic axis (4.1) lie in a guide plane that is orthogonal to the wire tape plane, and - the wire nozzle (1.1) has an inner contour that tapers in a funnel shape towards the wire inlet of the wire strip channel. [2] Device according to claim 1, characterized by , that the wire feed unit (1) has a feed tube which can be positively connected to the wire nozzle (1.1), wherein the wire nozzle (1.1) can be locked on the feed tube against rotation and displacement. [3] Device according to claim 1 or 2, characterized by, that the wire nozzle (1.1) has one or two flattened recesses designed such that the wire nozzle (1.1) has an outer contour tapering towards the wire exit of the wire nozzle (1.1) in the section plane perpendicular to the plane of the wire strip. [4] Device according to one of claims 1 to 3, comprising a swiveling unit for positioning, aligning and guiding the wire feed unit (1) and the beam head (5) in relation to the workpieces (7) to be joined. [5] Device according to one of claims 1 to 4, comprising one or more force sensors (10) for detecting forces acting orthogonally to the wire feed direction on the wire nozzle (1.1). [6] Method for thermally joining workpieces (7), performable by means of a device according to one of claims 1 to 5, wherein several wires (2) supplied into a joining zone are melted by means of a widened, split or oscillating energy beam (6) and solidify as filler material (9) forming a material-bonded joining connection of the workpieces (7), wherein - the wires (2) are individually fed into the joining zone in a longitudinally displaceable manner in a wire strip (3) lying parallel to each other, - at least the two edge wires (2) of the wire strip (3) are pressed against each of the workpieces (7) to be joined at a contact point (8), whereby the wire strip (3) forms a bridge between the workpieces (7) to be joined by the contact of the two edge wires (2) at the two contact points (8), and - the widening, division and / or movement of the energy beam (6) are adjusted so that the energy beam (6) captures the wire strip (3) in its transverse extent, - the joint geometry and / or the joint position of the workpieces to be joined (7) is continuously detected by means of optical sensors before joining, whereby the alignment and positioning of the wire strip (3), the feed rate of individual wires (2) into the joining zone and / or the power of the energy beam (6) coupled into the joining zone are controlled and / or regulated depending on the detected joint geometry and / or joint position. [7] Method according to claim 6, characterized by , that the energy beam (6) is controlled in such a way that the melting of the wires (2) of the wire strip (3) begins at the contact points (8). [8] Method according to claim 6 or 7, characterized by, that the energy beam (6) is expanded, split or moved in a pendulum motion about a mean beam axis (6.1), wherein the mean beam axis (6.1) is directed centrally onto the wire strip (3). [9] Method according to any one of claims 6 to 8, characterized by , that the contact forces (F1, F2, F3, F4) acting on the wire strip (3) at the contact points (8) are detected during joining by means of one or more force sensors (10), whereby the alignment and positioning of the wire strip (3) and / or the power of the energy beam (6) coupled into the joining zone are controlled and / or regulated depending on the detected contact forces (F1, F2, F3, F4). [10] Method according to any one of claims 6 to 9, characterized by, that the formation of the joining zone during joining is captured as a gray image by means of a camera, whereby the feed rate of individual wires (2) into the joining zone and / or the power of the energy beam (6) coupled into the joining zone are controlled and / or regulated depending on the captured gray image.

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