Electric heating – Inductive heating – Metal working
Patent
1996-03-26
1998-06-16
Leung, Philip H.
Electric heating
Inductive heating
Metal working
219614, 219659, 219645, H05B 606
Patent
active
057674906
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for the fusion in a joint of two workpieces produced from sheet metal, by induction heating thereof, the apparatus comprising means for positionally fixing the workpieces in a joint region and an induction device connectable to a current source for heating the workpieces.
BACKGROUND ART
Increasingly far-reaching demands are placed in the automotive industry on the possibility of employing rational welding processes to fuse together sheet metal parts which later constitute the blanks in a pressing process. By such means, considerable material waste is avoided in that the blank may be given a configuration which corresponds to that of the finished part.
Those blanks which are under consideration here may many times consist of sheet metal materials of different thicknesses, and the sheet material may have different types of surface coatings. In such instance, it is then important that the surface coatings are damaged as little as possible, and that the effects of heat on the material are also kept within very narrow limits.
The prior art technology employed for welding in similar or identical practical applications to the present one has previously been resistance welding using copper wheels as electrodes (seam welding). Such a method is relatively simple and economical but does not guarantee high and uniform quality, since an overlap joint must be employed.
Laser welding has also previously been tried in practical applications of the type under consideration here. This welding method results in superior quality because of welding in a butt joint. However, productivity is low and investment costs are so high that this method can only be employed in exceptional cases.
U.S. Pat. No. 4,947,462 discloses an apparatus of the type mentioned by way of introduction. The apparatus according to this patent specification is designed for fusing tubes end-to-end. Since the workpiece is accommodated interiorly in the coil, favourable electric/magnetic conditions are created, but the coil must be dimensionally adapted wholly to suit the workpieces which are to be welded.
The technology disclosed in the above-considered US patent specification cannot, therefore, be applied in the fusion of sheet metal blanks in which the joint lengths may be considerable, up to 1 meter or more. Furthermore, considerable problems would occur at the ends of the joint, since it would be extremely difficult to achieve sufficiently great current density in the corner regions of the workpieces located there.
One variation of resistance welding is also previously known in the art in which electric terminals are directly connected to the workpieces at opposing ends of the joint and on both sides thereof. In order to concentrate the current paths to strip-shaped regions along the joint, use is made of high frequency current, which also passes through a conductor which is disposed in parallel with and along the joint a short distance therefrom.
This welding method gives better welding quality right out in the end regions of the joint, but presents considerable practical problems because of the demand on good electric contact direct with the workpieces. These problems are particularly manifest when the workpieces do not have exactly the same width or when they are of different thicknesses or carry different surface coatings.
PROBLEM STRUCTURE
The present invention has for its object to realise an apparatus of the type disclosed by way of introduction, the apparatus being designed in such a manner that it is capable of fusing sheet metal parts in a butt joint, with superior quality, at high productivity and reasonable cost, even if the sheet metal parts are of different thicknesses or are surface coated. The present invention further has for its object to realise an apparatus which affords satisfactory weld quality right out in the end regions of the joint. Finally, the present invention has for its object to realise an apparatus in which one and the same induction device may be employ
REFERENCES:
patent: 2678370 (1954-05-01), Denneen
patent: 2862092 (1958-11-01), Cowan
patent: 2964607 (1960-12-01), Frumkin
patent: 3395261 (1968-07-01), Leatherman et al.
patent: 4224494 (1980-09-01), Reboux et al.
patent: 4947462 (1990-08-01), Moe
patent: 5240167 (1993-08-01), Ferte et al.
AB Volvo
Leung Philip H.
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