Laser beam welding device

Abstract

Laser beam welding device for welding metallic workpieces with a vacuum chamber (12) in which a receptacle for a metallic workpiece (22) to be welded is provided, a laser beam source (16) which is arranged outside the vacuum chamber (12), and a vacuum window (20) which forms a beam inlet opening into the vacuum chamber (12), characterized in that at least one condensation surface (26) is provided in the area of ​​the beam path in the vacuum chamber (12) which has a certain minimum temperature difference to the temperature of the beam inlet opening, wherein the condensation surface (26) has a lower temperature than the beam inlet opening and the beam inlet opening is heated by means of a heating device.

Description

[0001] The present invention relates to a laser beam welding device for welding metallic workpieces, comprising a vacuum chamber in which a holder for a workpiece to be machined is provided, a laser beam source arranged outside the vacuum chamber, and a vacuum window forming a beam inlet opening into the vacuum chamber.

[0002] For cost reasons, fusion processing of materials using laser beams is usually carried out under atmospheric pressure and under a protective gas to prevent oxidation. A plasma cloud of ionized protective gas forms above the molten pool, forming a nail-shaped melt pool or solidification geometry that severely limits the penetration of the metal vapor capillaries created during deep penetration welding.

[0003] It has been shown that the plasma cloud above the vapor capillary can be minimized during laser melt processing under vacuum at certain pressures. This makes it possible to achieve the ideal of a lean molten pool, similar to electron beam welding, with a laser. Lasers offer the advantage of cost-effective availability of various laser beam sources with excellent beam quality, making them a suitable alternative to electron beam sources, especially since the use of laser beam sources in a vacuum chamber is advantageous in some applications.

[0004] When processing workpieces with lasers under atmospheric pressure, the necessary optics are additionally protected by a so-called cross-jet. This is an air stream that flows at very high speeds, for example, even in the supersonic range, preferably transverse to the beam exit of the optics opening. It removes contaminants, metal vapor, or splashes, thus preventing the lenses or mirrors from becoming contaminated and preserving their optical properties. In industrial applications, such protection of the optics is essential to ensure consistent welding parameters during continuous operation.

[0005] When welding in a vacuum, the problem is that the cross-jet described above cannot be used in this form.

[0006] This inevitably leads to increased contamination of the laser optics by metal vapor or splashes, making replaceable protective glasses or films necessary to regularly restore the optical properties to an optimum. Furthermore, sensors for continuous beam quality monitoring are required to detect contamination of the optics in a timely manner before disruptions to the production process occur. The constant replacement of protective glasses or films is time-consuming and costly and, in some cases, prevents the use of vacuum laser welding in mass production.

[0007] A device of the type mentioned above is known from EP 0 250 940 A1.

[0008] US 2006 / 0 199 475 A1 describes a device for processing organic layers for OLEDs with a condensation device.

[0009] DE 10 2005 034 155 B3 describes a device for the layer-by-layer production of a three-dimensional object, while EP 1 308 570 A2 shows a vacuum joining for in-vacuo produced vacuum containers and structures.

[0010] The object of the present invention is to provide a laser beam welding device with a vacuum chamber in which the contamination of the beam inlet opening or the vacuum window provided there is less noticeable.

[0011] According to the invention, the object is achieved in that at least one condensation surface is provided in the region of the beam path in the vacuum chamber, which condensation surface has a certain minimum temperature difference to the temperature of the beam inlet opening, wherein the condensation surface has a lower temperature than the beam inlet opening and the beam inlet opening is heated by means of a heating device.

[0012] It has been shown that the condensation of contaminants on the vacuum-side jet inlet surface can be significantly reduced by deliberately maintaining a temperature difference, since condensation then occurs primarily on the cooler condensation surfaces and correspondingly less condensation occurs at the vacuum window of the jet inlet opening.

[0013] The jet inlet opening is equipped with a heating device to specifically increase its temperature and thus further increase the temperature difference between the at least one condensation surface and the jet inlet opening. In principle, increasing the temperature difference leads to improved precipitation on the condensation surfaces, although economic considerations must be weighed against the technical measures used to achieve the temperature difference.

[0014] It is particularly advantageous to arrange the at least one condensation surface close to the jet inlet opening; in the simplest case, the wall of the chamber around the jet inlet opening can be kept correspondingly cooler.

[0015] Preferably, the at least one condensation surface is cooled by a cooling device. Active cooling makes it possible to specifically adjust the temperature level of the condensation surface, which can also effectively compensate for heating caused by the deposition of metal vapor. By controlling the temperature of the condensation surface, which is then configured as a cold surface, a pumping effect can also be achieved, which can improve the quality of the vacuum in the chamber.

[0016] Various designs are possible for the configuration of the at least one condensation surface. For example, the condensation surface can surround the beam, whereby it can be designed as the inside of a hollow cylinder, the surface of a coil surrounding the beam, or even the surface of a funnel through whose center the laser beam passes. Also conceivable are embodiments in which the at least one condensation surface is designed as a pinhole, through whose central opening the laser beam passes. To increase the effective surface, it is possible to arrange several pinholes one behind the other.

[0017] Irrespective of the type of formation of the condensation surface, it is, as already mentioned, advantageous to provide the body on which the surface is formed with a cooling device, wherein it is particularly preferred to provide the cooling device with a coolant circuit.

[0018] The coolant circuit is routed out of the vacuum chamber, with the coolant being cooled outside the vacuum chamber. This design allows for the provision of powerful cooling units, ensuring sufficient heat dissipation from the condensation surfaces even in challenging applications.

[0019] Further measures to improve the cooling effect can concern the condensation surfaces themselves, which can, for example, have scale- or disc-shaped structures to increase the effective surfaces and promote the precipitation of dirt, metal vapor or splashes.

[0020] An embodiment of the invention will be discussed in more detail below with reference to the accompanying drawing.

[0021] The figure schematically shows a vacuum welding device 10 with a vacuum chamber 12 surrounded by a wall 14. A vacuum pump 15 or a comparable device is provided to adjust specific pressure conditions in the vacuum chamber 12.

[0022] Outside the vacuum chamber 12, a laser beam source 16 is provided, the laser beam 18 of which is coupled into the vacuum chamber 12 via a vacuum window 20 serving as a beam inlet. A holder for a workpiece 22 is provided in the chamber, which is to be processed by means of the laser beam 18, in particular by means of a welding process.

[0023] Within the chamber, a cooled protective tube 24 is provided, on whose cylindrical inner surface a condensation surface 26 is formed. The jet passes centrally through the cooled protective tube 24. The protective tube 24 has internal channels (not shown) coupled to a coolant circuit 28. The coolant contained therein is maintained at a specific temperature level by means of a cooling device (not shown) provided outside the vacuum chamber and ensures that the condensation surface 26 of the cooled protective tube 24 is maintained at a significantly lower temperature level than the inner surface of the vacuum window 20 as the jet inlet opening.It has been shown that this formation of a cold surface, relative to the temperature level of the vacuum window 20, allows for condensation of contaminants, metal vapor, or splashes on the condensation surface 26, which reduces the amount of contamination on the inside of the vacuum window 20. This avoids downtime for cleaning the optics, for example, due to replacing the vacuum window 20, thereby saving time and money. The laser beam welding device 10 outlined is therefore also suitable for use in mass production, since significant quantities of workpieces 22 can be processed before cleaning the laser optics is required.

[0024] Further measures to promote condensation on a condensation surface may also consist of heating the vacuum window itself in order to increase the temperature difference between its inner surface and the condensation surface 26 or, in the absence of a cooling device, to ensure the temperature difference.

[0025] The design of the condensation surface 26 is merely exemplary. It can also be formed on the surface of a coil or funnel surrounding the laser beam 18. It is also possible to form condensation surfaces aligned vertically to the path of the beam 18 on the surface of pinhole diaphragms, several of which can be arranged in sequence around the laser beam 18. Of course, such diaphragms, coils, or funnels can also be coupled to a cooling circuit in order to set a specific temperature level of the condensation surface.

Claims

[1] Laser beam welding device for welding metallic workpieces, comprising a vacuum chamber (12) in which a receptacle for a metallic workpiece (22) to be welded is provided, a laser beam source (16) arranged outside the vacuum chamber (12), and a vacuum window (20) forming a beam inlet opening into the vacuum chamber (12), characterized by that in the region of the beam path in the vacuum chamber (12) at least one condensation surface (26) is provided which has a certain minimum temperature difference to the temperature of the beam inlet opening, wherein the condensation surface (26) has a lower temperature than the beam inlet opening and the beam inlet opening is heated by means of a heating device. [2] Device according to claim 1, characterized by that the condensation surface (26) is cooled by means of a cooling device. [3] Device according to one of claims 1 to 2, characterized bythat the at least one condensation surface (26) surrounds the jet (18). [4] Device according to claim 3, characterized by that the at least one condensation surface (26) is designed as a cylinder inner surface, as a surface of a helix or as a funnel surface, wherein the laser beam (18) runs centrally. [5] Device according to claim 3, characterized by that the at least one condensation surface (26) is designed as a perforated diaphragm. [6] Device according to claim 5, characterized by that several pinholes are arranged one behind the other. [7] Device according to one of claims 2 to 6, characterized by that the cooling device has a coolant circuit (28) which is led out of the vacuum chamber (12), wherein the coolant releases its heat via a heat exchanger outside the vacuum chamber (12). [8] Device according to one of the preceding claims, characterized bythat the at least one condensation surface (26) has a scale- or disc-shaped structure. [9] Device according to one of the preceding claims, characterized by that the at least one condensation surface (26) is arranged near the jet inlet opening.

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