Electric heating – Metal heating – By arc
Reexamination Certificate
1999-03-30
2001-01-16
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121750
Reexamination Certificate
active
06175096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of processing a material with a first and a second surface by means of a laser beam which for instance by means of a multilens objective is focused in a number of focal points, where said focal points are approximately positioned on a common axis forming an angle with the first surface and are spaced apart.
2. Discussion of the Background
German Auslegeschrift No. 2,713,904 discloses a way of processing an article by means of a laser beam, said laser beam being focused in two focal points by means of a multilens objective. This processing method is used for drilling holes, whereby one focused bundle of rays is used for a melting of the surface of the article and the second bundle of rays presents a focal point positioned below the focal point of the first bundle of rays and is used for preheating the area surrounding the location of the article to be melted so as subsequently to be removed by way of evaporation. Such a processing method avoids to a certain degree formation of burrs at the edge of the hole. The lower focal point is, however, not utilized.
A growing demand has applied within the material processing industry employing lasers for a possibility of cutting in thick plates, such as steel plates of a thickness of 15 mm or more. As the cutting capacity of the laser beam is best on or adjacent the surface it is focused on, problems apply to transferring the effect to portions of the plate positioned below said surface. Moreover, the second surface of the material is encumbered with problems of an increased amount of adhering slags and a poor cutting quality, which inter alia results in a poor separation of the cut parts and may necessitate a finishing processing.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method of processing material by means of a laser, which ensures an improved processing quality in connection with thick materials. Furthermore, the expenditure of protecting gases must be low.
A method of the above type is according to the invention used for cutting plates, whereby several focal points are utilized for melting and cutting the plate material. The multilens objective has the effect that the total bundle of rays is relatively narrow, whereby the nozzle for protecting gases and consequently the expenditure of said protecting gases can be reduced correspondingly. It is well known that the protecting gases are very important for the quality and the cut.
According to a preferred embodiment of the invention, the focal points are positioned at a fixed distance relative to one another and to the first and the second surface.
It is advantageous for the complexity of the focusing optical instruments when the number of focal points is two.
It is furthermore advantageous when the distance between the head comprising the optical instruments and the first surface can be increased in such a manner that the focal point adjacent the second surface during the cutting can be caused to be positioned on the first surface, the so-called starting holes thereby being provided in an improved manner. In addition, the risk of the optical instrument being damaged by metal sprayings has been reduced.
A further advantage is found in connection with ignition, melting and removal of melt and slags by at least one of the focal points being positioned between the first and the second surface, adjacent the second surface or adjacent the first and the second surface, respectively,
In order to facilitate the penetration of the laser beam into the cutting notch it is furthermore advantageous when the focusing optical instruments focus the laser beam in several focal points, the distance of which from the second surface is increased concurrently with an increasing distance of the light from the central axis of the laser beam in such a manner that the central portion of the laser beam is focused in the focal point adjacent the second surface.
REFERENCES:
patent: 5063280 (1991-11-01), Inagawa et al.
patent: 5521352 (1996-05-01), Lawson
patent: 5690845 (1997-11-01), Fuse
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patent: 63-299881 (1988-12-01), None
patent: 64-48692 (1989-02-01), None
patent: 1-143783 (1989-06-01), None
Evans Geoffrey S.
Force Instituttet
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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