Electric heating – Metal heating – By arc
Patent
1997-02-28
1999-05-11
Mills, Gregory L.
Electric heating
Metal heating
By arc
21912167, 21912172, 83 53, 83177, B23K26/14;26/00
Patent
active
059024992
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an arrangement and method for processing material with a laser beam that is guided by a liquid jet.
2. Description of the Prior Art
Laser irradiation is used in a variety of ways for the material processing in the industry--cutting, drilling, welding, marking and material stripping. Nearly all types of material, e.g. steel, steel alloys, nonferrous metals, plastics and ceramics can be processed.
For nearly all of these methods, the laser beam is focused with the aid of an optical element, for example a lens, on the material to be processed in order to generate the intensity necessary for the processing operation. Due to this necessary beam focusing, a processing was possible only at the location of the focus point or the area immediately surrounding it.
From reference DE-A 36 43 284, a method for cutting a material with a laser beam is known, for which this beam was coupled with a water jet that was directed toward the material to be cut and was guided within this water jet. The feeding of the beam is by way of a beam guide (fiber), one end of which projected into the water jet that was produced in a nozzle. The diameter of the water jet was greater than that of the beam guide. The known arrangement had the disadvantage that the water jet diameter could never be smaller than that of the beam guide.
However, in order to achieve a high intensity at the processing location, a smallest possible beam diameter is necessary. The smaller the beam diameter, the lower the output of the laser radiation source with which it is possible to work. The smaller the output capacity of the laser, the lower the purchasing price.
Another disadvantage of the arrangement according to DE-A 36 43 284 resulted from the beam guide end that projected into the water jet. A dead water zone formed below the guide end which, among other things, produced interruptions in the flow that increased exponentially over the length of the water jet and finally resulted in a separation of the jet into drops. That is why it was impossible with this arrangement to achieve a laminar, compact beam length of more than 30 mm.
In the reference EP-A 0 515 983, an attempt was made to eliminate the above disadvantages by designing a water nozzle, which no longer contained the beam guide directly. In front of the nozzle that forms the water jet, there was a water chamber with a water intake and a focusing lens that closed off the chamber to the nozzle intake. This focusing lens is a component of an optical system, with which it was possible to focus the radiation emitted by the beam guide into the nozzle duct of the nozzle. The chamber was designed such that the water inside for the water jet was kept in a quasi standstill condition, that is in a relaxed condition.
However, it has proven that this second design variant of a laser beam to be coupled with a water jet causes uncontrollable damages to the nozzle wall in the area surrounding the nozzle duct intake.
It is the object of the invention to create an arrangement with which a laser beam can be coupled optimally with a fluid jet for material processing, without damage being caused to the nozzle that produces the fluid jet by the laser radiation.
The invention is based on the realization that the laser beam that is focused with the focusing optics into the nozzle range can heat up the liquid more or less strongly, depending on the intensity distribution. Liquid ranges with varied temperatures, a spatial temperature gradient, not only have a spatially specific density distribution, but also a spatial refractive index distribution. Meaning liquids with a spatial temperature gradient react optically as a lens and, as a rule, in the focusing cone of a focused laser beam as a dispersing lens.
An "optimally designed" coupling of the laser radiation with a liquid (water) jet produced in a nozzle duct, as shown in FIG. 2 of the EP-A 0 515 983, unfortunately does not work as assumed. For the arrangement as shown in the EP-A 0 515 983,
REFERENCES:
patent: 3503804 (1970-03-01), Schneider
patent: 4952771 (1990-08-01), Wrobel
patent: 5356081 (1994-10-01), Sellar
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