Electric heating – Metal heating – By arc
Patent
1994-07-13
1997-07-29
Walberg, Teresa J.
Electric heating
Metal heating
By arc
21912167, 21912184, B23K 2614
Patent
active
056519044
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention refers to a method for removing material from metal workpieces moved relative to the removal tool, in particular for cutting sheet metal, comprising the step of preheating, without melting, the surface of the workpiece to a temperature at which ignition is triggered by a combustible gas which is blown onto the preheated section as a jet under pressure and by means of which burnt material of the workpiece is blown away from a cut recess produced by such burning.
Such a method is used in autogenous gas cutting processes. The preheating of the surface of the workpiece to the ignition temperature of said workpiece is carried out by means of a heating gas, e.g. a gas mixture consisting of acetylene and oxygen. The melting point is not reached during this preheating process. It is regarded as being essential that energy of the heating gas also penetrates into the kerf. The combustible gas used is oxygen by means of which the material of the workpiece is burnt to oxide. The oxide is blown away by the pressure of the combustible gas. A kerf or a cut recess having smooth walls is produced.
In the generally known laser beam gas cutting process, a jet of combustible gas and a laser beam which is coaxial with said gas jet are used for cutting sheet metal. When this laser beam gas cutting process is used for sheet metal thicknesses of less than 20 mm, the cutting speed can be increased in comparison with conventional autogenous gas cutting processes. The quality of cut faces of thicker plates, however, will be less good. When plates having a thickness of approx. 10 mm and higher are cut, the number of burnt-out cavities will increase and the averaged peak-to-valley heights will frequently exceed 100 .mu.m. Burnt-out cavities and surface roughnesses originate from turbulences caused on the removal front due to the incident laser radiation during melting and burning. The turbulences occurring will also reduce the cutting speed.
SUMMARY AND OBJECTS OF THE INVENTION
Hence, it is the object of the present invention to improve a method having the features mentioned at the beginning in such a way that also thick workpieces, i.e. steel plates having a thickness of more than 30 mm, can be subjected to a rapid material-removing process which will produce surfaces of the walls of the cut recess having a peak-to-valley height of less than 50 .mu.m.
This object is achieved by the feature that, in addition to the combustible gas, also laser radiation is irradiated into the cut recess where it impinges on the removal front.
The above-mentioned method step is known in connection with conventional laser beam gas cutting processes, but in these conventional processes it results in an increase of the peak-to-valley heights and in a reduction of the cutting speed with increasing plate thicknesses. The present invention, however, makes use of the important finding that, in the case of thick plates, an increase in the peak-to-valley height and a reduction of the cutting speed can be avoided when the surface of the cutting region is preheated before the laser radiation impinges on the removal front. Only then will it be possible to expect troublefree burning when the cutting process is started from the workpiece surface, such troublefree burning being known from autogenous gas cutting processes. In the case of the present method, the laser radiation irradiated onto the removal front serves to additionally couple thermal energy into the cut recess for increasing thus the cutting speed without causing any turbulences in the course of the melting processes. It follows that the laser radiation can especially produce an effect which will heat and straighten the removal front flattening at the lower cutting edge. If, however, no preheating is carried out, instabilities will occur, which originate from the first cut or rather from the points where the cutting operation is started, said instabilities being caused e.g. by variations in the introduction of the radiation en
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Franke Jorg
Herziger Gerd
Schulz Wolfgang
Advanced Technik GmbH
Mills Gregory L.
Walberg Teresa J.
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