Electric heating – Metal heating – By arc
Patent
1991-07-15
1993-02-02
Albritton, C. L.
Electric heating
Metal heating
By arc
21912184, B23K 2600
Patent
active
051839911
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of welding a galvanized steel sheet with a laser beam, and more particularly to a method of welding a galvanized steel sheet with a laser beam while preventing porosity and weld bead defects including surface craters that are formed by an evaporated gas.
BACKGROUND ART
Welding metals with beams of high energy density (heat source), typically laser beams, is used in a wide range of metal welding applications since the welding process is clean, has a high degree of freedom, and can minimize thermal strains. Particularly, the laser beam welding process for metals finds growing use in the automobile industry or the like as a composite machining system composed of a laser oscillator and a numerically controlled apparatus or robot.
Automobiles employ a number of corrosion-resistant galvanized steel sheets as a highly durable material in their frames and other components. There is a demand for welding galvanized steel sheets with a laser beam.
FIG. 2 of the accompanying drawings shows a conventional process of welding galvanized steel sheets with a laser beam. A galvanized steel sheet 1 has plated zinc layers 2, 3 deposited on its opposite surfaces, and another galvanized steel sheet 4 also has plated zinc layers 5, 6 deposited on its opposite surfaces. When a laser beam 8 is applied to the galvanized steel sheets 1, 4 to weld them, a weld bead 10 is formed as a result of a weld pass.
Steel has a melting point of about 1545.degree. C. and a boiling point of about 2754.degree. C., whereas zinc has a melting point of 420.degree. C. and a boiling point of 903.degree. C. Because of the heat produced by the high-density energy of the applied laser beam, the zinc with a lower melting point is violently evaporated into a gas, thereby forming porosity (cavities) 11a, 11b, 11c in the weld bead 10. While only the surface porosity is shown, porosity is also formed within the weld bead 10. As a result, the weld bead 10 has irregular width dimensions, and the welded joint is rendered brittle. For the reasons described above, it has been infeasible to weld galvanized steel sheets with a laser beam.
DISCLOSURE OF THE INVENTION
In view of the aforesaid drawbacks of the conventional laser beam welding method, it is an object of the present envention to provide a method of welding a galvanized steel sheet with a laser beam while preventing porosity and weld bead defects.
To solve the above problems, there is provided a method of welding galvanized steel sheets to each other or a galvanized steel sheet and a sheet of another metal to each other with a laser beam, comprising the steps of forming an intermediate layer for suppressing evaporation of zinc, between said galvanized steel sheets or said galvanized steel sheet and said sheet of another metal, and applying a laser beam to said galvanized steel sheet or said sheet of another metal, thereby welding the sheets with the laser beam.
As a consequence, zinc layers are prevented from being violently evaporated. Porosity is prevented from being formed in a weld bead, and the weld bead has a constant width.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary perspective view showing a method of welding galvanized steel sheets with a laser beam according to an embodiment of the present invention; and
FIG. 2 is a fragmentary perspective view showing a conventional method of welding galvanized steel sheets with a laser beam.
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will hereinafter be described with reference to the drawings.
FIG. 1 shows a method of welding galvanized steel sheets with a laser beam according to an embodiment of the present invention. A galvanized steel sheet 1 has plated zinc layers 2, 3 deposited on its opposite surfaces, and another galvanized steel sheet 4 also has plated zinc layers 5, 6 deposited on its opposite surfaces. Each of the galvanized steel sheets 1, 4 has a thickness of 1 mm, and each of the zinc layers 2, 3, 5, 6 has a thickness ranging f
REFERENCES:
patent: 3969604 (1976-07-01), Baardsen
patent: 4642446 (1987-02-01), Pennington
patent: 4873415 (1989-10-01), Johnson et al.
Patent Abstracts of Japan, vol. 9, No. 63 (M-365)[1786], Mar. 20, 1985; & JP-A-59 197 390 (Toshiba K.K.) (Aug. 11, 1984) * Abstract *.
Albritton C. L.
Fanuc Ltd.
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