Electric heating – Metal heating – By arc
Patent
1992-05-26
1996-07-23
Evans, Geoffrey S.
Electric heating
Metal heating
By arc
21912184, B23K 2612, B23K 2614
Patent
active
055391800
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a laser apparatus and a laser beam welding method of welding a surface-treated metal, and more particularly, to a laser apparatus and a laser beam welding method of welding a zinc-plated steel sheet with laser beams.
BACKGROUND ART
The increasing output of laser oscillators has led to an expansion of the fields of application for laser beam welding, which uses laser beams in place of the conventional gas welding or electrical welding. In particular, there is a strong demand for the capability to weld superimposed steel sheets and the like in the automobile industry. Namely, the steel sheets used in the automobile industry are zinc-plated steel sheets treated with zinc plating for the purpose of rust prevention, and a stable and high-speed laser beam welding of such zinc-plated steel sheets and the like is now required.
When welding superimposed zinc-plated steel sheets, however, a surface plating layer on the steel sheet is evaporated when irradiated with a laser beam, causing the generation of many blowholes. In particular, if there is no gap between the steel sheets, the steam of evaporated zinc blows off the molten base metal, making welding impossible. This is considered to be because zinc has a lower boiling point than the melting point of iron, and because the evaporating pressure is high, thus causing the molten iron to be blown off.
Accordingly, when welding superimposed zinc-plated steel sheets, a gap of few hundred microns is provided between the steel sheets to allow the zinc steam generated on the surfaces thereof to escape. Nevertheless, it is extremely difficult to maintain the gap at a fixed value, at an actual production site, and thus the laser beam welding must be carried out while the steel sheets are in close contact with one another.
DISCLOSURE OF THE INVENTION
The present invention is intended to solve the foregoing problems, and an object of the present invention is to provide a laser apparatus capable of producing a stable welding of surface-treated metals such as zinc-plated steel sheets while such sheets are in close contact with one another.
Another object of the present invention is to provide a laser beam welding method permitting a laser beam welding during which the occurrence of blowholes on surface-treated metals such as zinc-plated steel sheets is kept to a minimum.
To fulfill the above-mentioned object, the present invention provides a laser apparatus designed to weld a surface-treated metal coated with a material having an evaporation temperature lower than the melting point of the metal, by using continuous wave or pulse wave laser beams, the laser apparatus comprising a gas supply unit for supplying oxygen or oxygen and another gas as an auxiliary gas, and an auxiliary gas jetting unit for jetting the auxiliary gas onto a welding spot.
Further, a laser beam welding method of welding surface-treated metals coated with materials having an evaporation temperatures lower than the melting points of the metals, by using continuous wave or pulse wave laser beams is provided, wherein oxygen or a mixture of oxygen and another gas is used as an auxiliary gas for the welding.
Conventionally, oxygen gas is not used for welding because it will ignite the iron, but when a laser beam is irradiated onto a surface-treated metal such as a zinc-plated steel sheet in an atmosphere of an auxiliary gas including oxygen gas or a mixture of oxygen gas and another gas, the material is ignited and forms a molten pool of a mixture of oxygen and iron. Such a molten pool has a low viscosity, allowing an easy escape of zinc steam.
Further, oxygen and zinc react to produce zinc oxide or zinc peroxide rather than steam, and therefore, when a laser beam passes therethrough, the iron oxide is separated as slag on the surface of the steel sheet, and an unoxidized part of the molten iron is solidified, to thereby obtain a strong weld. The zinc layer of the zinc-plated steel sheet is thinner than the steel sheet, and thus has no affect on the strengt
REFERENCES:
patent: 4684779 (1987-08-01), Berlinger et al.
patent: 4945207 (1990-07-01), Arai
patent: 5142119 (1992-08-01), Hillman et al.
Mori Atsushi
Nakata Yoshinori
Yamazaki Etsuo
Evans Geoffrey S.
Fanuc Ltd.
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