Electric heating – Metal heating – By arc
Patent
1991-04-12
1993-06-01
Albritton, C. L.
Electric heating
Metal heating
By arc
B23K 2600
Patent
active
052162206
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods of welding coated metals such as steel coated with zinc, and to apparatus for welding such coated metals. More particularly, but not exclusively, this invention relates to processes for welding galvanized sheet steel as an integral step in the manufacture of various products, such as automobile body shells.
The use of welding in a wide variety of manufacturing processes is very familiar in industry. Typical equipment for performing one such process comprises, in addition to the workpieces to e welded, a blow torch with a supply of gas that can be regulated to provide a controllable heat source and, for some kinds of welding, an appropriate welding flux. The difficulties of controlling accurately the heat source in this process together with the inconvenience of having to make use of a suitable flux produce considerable limitations on the quality and neatness of a resulting weld. For these reasons, conventional gas welding processes have been larely superseded in many instances by laser welding processes, usually employing CO.sub.2 lasers which can serve as accurately focused and well controlled heat sources. Additionally, the use of a laser in a welding process enables the use of a welding flux to be dispensed with and this leads to very firm, sound and neat welds in the finished product. There are additional advantages in that smooth, efficient, accurate and swift processing can be achieved.
Steel sheets are often purchased as a processing material already coated with zinc to prevent corrosion. A basic difficulty arises when attempts are made to weld such galvanized steel sheets, especially when a laser welding process is to be employed.
Galvanized steel may be produced by one of the following methods: spraying a steel surface with molten zinc, electrolytic deposition of zinc on steel, heating steel in contact with zinc dust, and dipping steel into molten zinc. The zinc coated surface of the steel, when exposed to air, acquires a coherent inert oxide layer which prevents the steel from corroding. If the zinc layer on the surface of the steel if borken, some protection against corrosion is still obtained, as zinc is more electropositive than iron and the first stage of oxidation of zinc
It is for these reasons that galvanized steel is used extensively in industry. However, industrial production processes frequently require the lap welding of steel sheets, and, when galvanized steel sheets are used, the welding process has to cope with the layers of zinc between the steel substrates. Special difficulties arise with such sheets when welding by the use of a high-energy beam such as an electron beam or a laser beam. This is because zinc boils at a temperature of about 907.degree. C., but steels melt at somewhat higher temperatures of about 1372.degree. C., leading to explosive vaporization of the zinc layers sandwiched between the steel substrates of the sheets and consequent irregular distribution of (and loss of material from) the weld puddle of molten steel produced by the high-energy beam where it impinges on the sheets. The resulting weld is, in consequence, likely to suffer from voids and porosity and to be of poor quality.
One possibility for overcoming this problem is to machine the zinc coating off the steel sheet. This suffers from the disadvantages of being costly, time consuming and labour-intensive. Also there could be regions where the zinc coating is imperfectly removed by machining; inevitably problems would then be produced.
Another possibility is to follow the procedures suggested by the Ford Motor company in their U.S. Pat. No. 3,969,604. This describes a method of welding glavanized steel, using a high-energy welding beam, which attempts to prevent rapid vaporization of the zinc coating so as to avoid disrupting the weld puddle. In connection with the use of electron or laser beam welding with a power density of 6200 W/mm.sup.2, the patent proposed painting the galvanized steel workpieces, in the area adjacent the weld zone, with a coating of a flux materia
REFERENCES:
patent: 3604890 (1971-09-01), Mullaney
patent: 3969604 (1976-07-01), Baardsen
patent: 4642446 (1987-02-01), Pennington
patent: 4682002 (1987-07-01), Delle Piane et al.
patent: 4873415 (1989-10-01), Johnson et al.
patent: 4945202 (1990-07-01), Budenbender
Patent Abstract of Japan, vol. 9, 279 (M-427) (2002) Nov. 7, 1985, & JP-A-60 121093 (Mitsubishi Jukogyo K.K.) Jun. 28, 1985.
Davis Michael P.
Dowden John M.
Kapadia Phiroze D.
Rickwood Kenneth R.
Albritton C. L.
British Technology Group Ltd.
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