Method and apparatus for hybrid welding under shielding gas

A hybrid welding from a combination of laser beam welding with gas-shielded welding by electric arc uses at least two electrodes are used. The electrodes can be flooded by a common shielding gas curtain or separately or in groups. The hybrid welding increases the possibility of influencing the welding process and especially provides improved possibilities for automation.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German patent document No. 199 44 466.8, filed Sep. 16, 1999, the disclosure of which is expressly incorporated by reference herein.

The present invention relates to a method for gas-shielded hybrid welding by arc and laser beam. At least one focused laser beam is directed against a relatively moving workpiece, and an electric arc is produced by at least one electrode under a shielding gas.

The present invention furthermore relates to an apparatus for gas-shielded hybrid welding by laser beam and arc. The apparatus comprises a laser welding head for directing at least one focused laser beam against the workpiece; a welding torch for producing an electric arc by an electrode; means for supplying a shielding gas; and means for producing a relative movement between the laser welding head and the burner on the one hand and the workpiece on the other.

Laser beam and arc welding are widely employed in the field of industrial manufacturing. Each method has specific applications which are characterized by the physical processes of the delivery of energy to a material and the flows of energy produced.

Laser beam welding is characterized by low input of energy into the material and high working speeds, resulting in a comparatively narrow area affected by heat and a great ratio of seam depth to seam width. However, in laser beam welding the bridging of gaps that can be achieved is poor due to the small diameter of the laser beam.

The arc welding process produces low working speeds on account of the substantially lower energy density. Furthermore, the focal spot of the arc on the workpiece surface is larger than that of the laser beam. As a result, wider seams are produced by arc welding than by laser beam welding, so that the gap-bridging ability is greater for a comparable weld depth.

For some time, attempts have been made to combine laser beam welding with arc welding. Basically two variant methods are conceivable. The first possibility is serial processing, wherein the laser beam and arc are separate in time and place on the workpiece.

The second variant method is called hybrid welding, wherein the laser beam and arc act simultaneously in an interaction zone (plasma and molten metal) and mutually assist one another. The arc may be produced by gas metal arc welding (GMAW); tungsten inert gas welding (TIG); or plasma arc welding (PAW).

The present invention is directed to hybrid welding under a shielding gas, in which the laser beam and the arc strike the workpiece substantially at the same place. In hybrid welding, the arc delivers heat to the material in an upper seam area in addition to the laser beam, which leads to a wineglass shape in the seam. The mutual influence of the processes permits different appearances and alignments depending on the laser welding or arc welding process and the process parameters employed. The thermal stress on the workpiece in hybrid welding can be kept relatively small as it can in laser welding. The character of the particular process used in hybrid welding will predominate depending on the ratio of the power inputs from the laser beam or the arc.

Hybrid welding with the use of shielding gases is described in several variants, for example, in German patent document DE 43 34 568 A1.

In the known combinations of laser and gas-shielded welding methods in hybrid technology, there are few possibilities for influencing the welding process. In particular, due to the asymmetrical arrangement of the individual electrode and the laser beam, there are limited possibilities for automation.

Any departures from the relative positions of the two energy sources to one another and/or to the workpiece limit the repeatability of the welding process or result in unequal quality.

The present invention therefore is addressed to the problem of finding a method and an apparatus, through which a better possibility for influencing the welding process is provided, and especially an improved possibility for automation. Furthermore, a gas-shielded hybrid welding of good quality due to its repeatability and reliability is made possible.

This problem is solved by the present invention in that at least two electrodes are used.

DETAILED DESCRIPTION OF DRAWING

By increasing the number of electrodes to two or more electrodes, the possibility of influencing the welding process is substantially improved. For one thing, a better and repeatable seam quality is achieved, which manifests itself in a better penetration geometry and in a better seam surface. For another thing, the separate potentials permit a specific heat input. Both a directional and a nondirectional input of energy is possible.

In the scope of the present invention, consumable and/or non-consumable electrodes can be used. When consumable electrodes are used, higher ablation rates are possible. Also, different additive materials can be used. Fundamentally, consumable and non-consumable electrodes can be combined in any way with one another within the invention.

As shown in the FIGURE, each electrode may be flooded with a separate curtain of shielding gas. Alternatively, several electrodes are flooded with one common shielding gas curtain. It is also possible for all electrodes to be flooded with one common shielding gas curtain.

All of the known shielding gases or shielding gas mixtures can be used as the gases, and process gases or process gas mixtures can be fed in. Electrodes can be combined in groups in the shielding gas.

In an embodiment of the present invention, the electrodes are connected to an electrical potential and/or to separate electrical potentials. In particular, groups of electrodes can be connected to one electrical potential.

In an embodiment of the present invention, the electrodes are arranged in the same and/or different planes perpendicular to the laser beam axis and/or parallel to the workpiece surface. The term planes parallel to the workpiece surface is to be understood in the case of uneven workpiece surfaces to mean planes substantially parallel to the workpiece surface, in which the directional vector of the preferred direction of the relative movement lies. In particular, the electrodes can be arranged in planes at different distances from the working point on the workpiece surface. The penetration profile can be influenced by the arrangement of the electrodes.

The arc, or an arc, can burn between one electrode or a plurality of electrodes and the workpiece and/or between electrodes.

The term, focused laser beam, is to be understood within the scope of the present invention to refer to a laser beam substantially focused on the workpiece surface. In addition to the laser beam focused substantially on the workpiece surface in the predominantly used method, the present invention can also find application in the rarely used variant using an out-of-focus beam on the workpiece surface.

The present invention is not fundamentally limited to the use of special kinds of lasers. Suitable for laser beam welding are chiefly CO 2 lasers, Nd:YAG lasers or also diode lasers, especially high-power diode lasers (HDL).