Electric heating – Metal heating – By arc
Patent
1995-09-12
1998-03-31
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912151, 21912155, 219127, B23K 1000
Patent
active
057341443
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a plasma arc welding method of welding together a plurality of plate materials laid one over another and also to an apparatus for carrying out this method.
BACKGROUND ART
The plasma arc welding technique, especially, the plasma arc spot welding technique is favorably comparable with the conventional electrical resistance spot welding technique in that because of its ability to weld from one side, it is advantageously capable of dealing with large-sized workpieces as well as workpieces which are of an irregular configuration. For this reason, a research and development work has hitherto been extensively conducted for the plasma arc welding technique in respect of a variety of phases thereof.
In the conventional typical plasma spot welding technique, however, while a so-called thermal conducting process, i.e. a process in which workpiece materials are welded together by the thermal conduction of an arc heat, has inherently been adopted, due to an insufficient stability encountered in the plasma arc, a molten pool in a front side workpiece material may not stably be brought into contact with a rear side workpiece material. Accordingly in this technique, certain disadvantages have arisen that can be listed as follows: welding strength; formed between workpiece materials placed one over another to bring about a large fluctuation in the degree of a weld penetration formed, resulting in a lack of stability in the quality of a weld; and which are large in a thermal capacity thereof. Hence, being encountered with a problem arising in the reliability in the quality of a weld, the plasma arc welding technique has seldom been utilized in a workpiece welding operation in which the welding strength is especially important.
In an attempt to resolve this problem, the prior art has adopted as another technique a plasma arc spot welding method as disclosed in Japanese Unexamined Patent Publication No. Sho 51-142456 in which in spot-welding together two or more workpleces laid one over another, in addition to the use of a plasma arc in order to melt the workpiece materials by heating them, a keyhole action of the plasma arc is utilized to cause the plasma arc to completely penetrate into a rear side of a rear side workpiece material so as to allow the weld penetration formed to be reached thereto.
In FIG. 1 there is shown the sequence of a plasma arc spot welding method as set forth in the above noted prior art publication.
According to such a method, after a plasma arc 2 has first been generated by means of a torch 1, plasma arc 2; rear side workpiece material 3b; workpiece material 3b to form a keyhole extending through the two workpiece materials 3a and 3b; the keyhole is closed; and spot welding operation of keyhole type in the foregoing sequence, a weld penetration as formed will be reached into the rear sides of the workpiece materials 3a and 3b so as to form a complete nugget therein. Yet, since the weld penetration obtained is deep in this method, the technique can be applied to comparatively thick workpiece materials.
In a welding method of keyhole type in the above mentioned prior art, however, there arise inconveniences such as: workpieces 3aand 3b, a material may be blown off; consequently, since a portion which is of a weak strength may be created, or a blow-hole may be formed, the quality of a weld will not be stabilized; therethrough, a plasma unit which is of a considerably large output will be required; and that is inferior to those obtained by the above mentioned thermal conduction process.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is a primary object of the present invention to provide a plasma arc welding method as well as an apparatus for carrying out the same whereby a deep weld penetration welding operation is achieved without creating a keyhole; there is less susceptibility of being influenced from a spacing which may be formed between workpiece materials placed one over another; a stabilized welding operation can be achieved at all
REFERENCES:
patent: 4929812 (1990-05-01), Ivamikov et al.
patent: 5532453 (1996-07-01), Scheller
Kitahashi Masamitsu
Kurokawa Iwao
Minonishi Mikio
Yamaguchi Yoshihiro
Kabushiki Kaisha Komatsu Seisakusho
Kananen Ronald P.
Paschall Mark H.
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