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 xe2x80x9chybrid welding,xe2x80x9d 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.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.