Electric heating – Metal heating – By arc
Reexamination Certificate
2000-04-07
2002-04-02
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121720
Reexamination Certificate
active
06365870
ABSTRACT:
The invention relates to a method for processing
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workpieces with laser radiation that is focused on a to-be-processed workpiece surface by means of a laser beam that is not moved relative to the workpiece.
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TRANSLATOR'S NOTE: The German word “Bearbeitung” can be translated variously as processing, machining, treating or working. We have chosen “processing” over “machining” because it is more generic, and have rejected “treating” as implying some change in the properties of the material and “working” as implying deformation of it.
The aforesaid method is known from DE-A 33 44 709. Workpieces are deburred by this method. The laser beam is stationary. Its focal diameter is selected as so large that the entire area for deburring is covered. However, most of the beam energy fails to be used for burr removal because it falls on areas that are not intended for deburring or on areas where no workpiece is present, e.g. on holes in the workpiece. A large proportion of the energy of the laser radiation is therefore unused, and depending on the conformation of the workpiece, special measures may even be needed to ensure that the unused laser radiation is not harmful to the surroundings in areas of the workpiece not intended for deburring or areas adjacent the workpiece.
The task of the invention, by contrast, is to improve a method comprising the foregoing steps in such a way that a laser beam that is stationary relative to the workpiece can be used to process a workpiece surface diverging from the punctiform without wasting any of the available energy of the laser beam.
The aforesaid task is accomplished in that the laser beam is focused in a line-like manner and its beam spot corresponds practically exclusively and with full areal coverage to the workpiece surface to be processed.
It is essential to the invention that the beam spot of the laser beam be focused in a line-like manner in such a way that the workpiece surface for processing is irradiated as exactly as possible, specifically over its entire area. Consequently, the entire workpiece surface for processing is also simultaneously heated, and the heating simultaneously causes desirable processes to occur in the workpiece, e.g., melting of a parting line or a joint. Workpieces can also be processed over a larger area, however, provided that the laser beam functions in a line-like manner over the entire area, for example in the case of material transformations on hardened laser tracks.
The approach can be such that a focused line that is uniformly narrow over its entire length is used. Such uniformly narrow lines lend themselves especially well to joining and severing processes suitable for use in mass production. The narrow, focused line can be realized in such a way that high energy densities of the kind needed for joining or severing can be attained with the available laser sources. For example, metal foil or strips of thin or ultra-thin metal plate can be severed transversely. Such narrowly focused lines are also advantageous when there are problems in machining the material due to wear of the tool and/or impermissible mechanical stress on the strip material. Such severing processes are advantageously carried out such that the entire width of a plate or a traveling strip is severed in a pulsed manner by means of linear laser radiation.
A large number of processing operations on shapes and webs can be performed with the method described above. It is advantageous if the approach is such that the line extends over the entire width of the workpiece and/or forms a contour with an unirradiated center and/or follows an arbitrarily predetermined course and/or exhibits a nonuniform width over its course. Lines extending over the entire width of the workpiece are advantageous in particular in the severing or joining of workpieces. If a line forms a contour with an unirradiated center, recesses corresponding to the contour can be made in the workpiece. In such cases the shape of the line is of no consequence, as a rule. The line can follow any arbitrarily predetermined course, for example it can have curves. The nonuniform width of the line over its course can be advantageous when an influence is to be exerted on the shape of a parting line, joint line or recess.
If the output of the available laser sources is limited, it can be advantageous to perform the method in such a way that the line used is made up of component lengths that cover the entire length of the line simultaneously or in cycles consecutively. In this case the approach is to use laser radiation preferably emanating from a plurality of laser sources and consisting of an uninterrupted sequence of individual beams or groups thereof that simultaneously cover the entire line length or a component length. A plurality of laser sources can thus be used to irradiate the entire length of the line simultaneously. A single laser is sufficient if the line as a whole is to be worked through consecutively in cycles.
It is especially advantageous if the laser radiation is generated by means of diode laser bars and/or diode laser stacks. Diode laser bars and stacks each employ a plurality of laser diodes. Their laser radiation can be aligned and focused in linear form by suitable arrangement of the bars or stacks. They are especially well suited for focusing the laser beam—which then consists of a plurality of component beams from the individual laser diodes—in a line-like manner and allowing it to irradiate the entire area of the workpiece surface being processed.
The method can be performed in such a way that the laser radiation is used for severing. A processing operation similar to shearing takes place, since the workpiece is irradiated in a pulse-like manner and is disunited into its severed pieces. This is a contactless cutting operation that does not have the considerable disadvantages of mechanical severing methods performed with cutters. In particular, mechanical deformation of the workpiece is avoided.
For practical use, the above-described method is especially advantageous if a laser radiation source and/or at least one processing head delivering a laser beam are comoved with and at the same speed as a moving workpiece as the workpiece is being irradiated. The comovement of the laser radiation source with a moving workpiece makes it possible to use the method in particular for the transverse severing of sheet or strip material. The most frequently used method at present for the transverse severing of strip material consists in the use of mechanical means, so-called “flying shearing” or “eccentric shearing.” In this method, a cutter or a guillotine shear disposed transversely to the strip is comoved with the traveling strip for a short distance. The simultaneous process of raising the cutter and comoving it with the strip must be performed in such a way that the cutter travels exactly along with the strip while it is embedded in the strip material and then turns back oppositely to the direction of strip motion. The drives required for this arrangement, for example eccentric drives, must reach the highest possible cycle rates. This is limited by mechanical factors, however, particularly when the cutter or drive masses have a relatively high weight and the accelerative and decelerative forces are correspondingly high. In particular, this means that the eccentric needs a start-up and a run-down time, as well as a very high-cost, stable machine frame because of the high forces generated. The cutting process induces mechanical stresses in the workpiece material and can lead to burring and strain hardening in the region of the cut edge. The above-described severing methods do not have the disadvantages of the known mechanical severing arrangements. Particularly with the use of diode laser bars or diode laser stacks, the mass that must be moved is comparatively slight. Their rate of travel or that of the laser cutting heads can therefore be significantly higher than the speed of the strip. High cycle rates and short segments of strip between two processing operations can be o
Loosen Peter
Petring Dirk
Poprawe Reinhart
Treusch Hans-Georg
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Heinrich Samuel M.
Pandiscio & Pandiscio
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