Electric heating – Metal heating – By arc
Patent
1998-09-15
2000-05-09
Ryan, Patrick
Electric heating
Metal heating
By arc
21912172, 21912167, 21912165, 21912166, 2191216, B23K 2612
Patent
active
060606878
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for the laser cutting of metal workpieces.
BACKGROUND OF THE INVENTION
During the laser cutting of metal workpieces, a laser beam is focused onto the workpiece which is to be cut. Often, a cutting gas is simultaneously blown onto the cutting location by means of a nozzle. The cutting gas is intended to protect the nozzle of the cutting installation and the focusing lens contained therein from metal spatter and slag formed during the cutting process and, at the same time, to assist with flushing the molten material and the slag out of the cutting kerf. In many cases, the cutting gas used is oxygen or an oxygen-containing gas mixture. The chemical reaction of the oxygen with the cut material (for example steel) produces additional heat which assists the cutting process. Steel combustion then takes place.
During laser cutting, the person skilled in the art distinguishes between conventional laser cutting with a cutting speed of at most 10 m/min and high-speed cutting of thin metal sheets with cutting speeds of up to 100 m/min (Prei.beta.ig et al., High speed laser cutting of thin metal sheets, SPIE Vol. 2207, 96-110). In connection with high-speed cutting of thin metal sheets, it is already known from DE-A-4,123,716 to use a mixture of inert gas and hydrogen as the cutting gas. During high-speed cutting, the cutting speed is limited by so-called melt build-up phenomena. The high viscosity of the molten material which is formed during cutting limits the speed which can be achieved. DE-A4,123,716 teaches the person skilled in the art that the addition of hydrogen to the cutting gas reduces the surface tension of the molten material, thus counteracting a build-up thereof.
BRIEF SUMMARY OF THE INVENTION
The invention is based on the object of providing a process for laser cutting of metal workpieces which contain bonded oxygen that results in an untarnished and clean cut surface free of striation, burring or other contamination. This object is achieved according to the invention by the fact that a mixture of at least one inert gas and hydrogen is used as the cutting gas.
DETAILED DESCRIPTION OF THE INVENTION
In the context of the invention, the term inert gas denotes any gas and any gas mixture which under the conditions which arise during cutting does not undergo any, or undergoes only slight, chemical reactions with the workpiece to be cut, the reaction products formed during cutting and/or the surrounding atmosphere. Inert gases which may be used are, for example, noble gases, nitrogen and mixtures thereof. Amongst the noble gases, argon is particularly preferred.
The term "metal workpieces which contain bonded oxygen" comprises all metals which contain chemically bonded oxygen of oxidation number II at least in partial areas (for example on the surface). Typical examples are metals which maintain their resistance to environmental effects by means of a layer of oxide on the surface (for example aluminum and its alloys).
The invention has recognized that, in the case of such metals, the cutting-gas mixture according to the invention makes it possible to avoid a cut which is not clean and tarnishing of the material which is to be cut. Surprisingly, the addition of hydrogen avoids or reduces these undesirable effects.
The bonded oxygen in the metal clearly leads to a cut which is not clean (burring, for example), to oxidation reactions in the region of the cut edge and to the metal becoming tarnished in the region of the cut edge. Even this cannot be deduced from the prior art, since this generally actually adds oxygen in order to improve the cutting capacity.
The invention is furthermore based on the recognition that this undesirable effect caused by the oxygen bonded in the metal can be avoided or reduced by adding hydrogen to a cutting gas which is otherwise inert. This is surprising to the extent that it would actually be expected that the oxygen, which during the cutting operation may be released from its bond with the metal and woul
REFERENCES:
patent: 5380976 (1995-01-01), Couch, Jr. et al.
patent: 5578228 (1996-11-01), Beyer et al.
Preissig et al., "High speed laser cutting of thin metal sheets," SPIE 2207: 96-110 (1994).
AGA Aktiebolag
Elve M. Alexandra
Ryan Patrick
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