1. Field of the Invention
This invention relates to a laser-arc hybrid welding head which can weld a base metal material, as an object to be joined, by combined use of laser welding and arc welding.
2. Description of the Related Art
Laser welding and arc welding are available as types of welding technologies for joining a base metal material, which is an object to be joined. Of these technologies, the laser welding process performs welding by focusing laser light on one point of the base material with the use of optical instruments such as a lens and a mirror. According to this process, the density of energy is so high that high speed, low strain welding providing a great depth of penetration can be performed in a narrow fusion range.
The arc welding process generates an arc between the base material and a welding wire, or between the base material and an electrode, fuses the base material by the heat of the arc, and performs welding while protecting the periphery of a zone of the base material, which is to be welded, by a shielding gas. According to this process, the depth of penetration is small, but the arc spreads over a relatively wide range, so that beads become broad, and welding with a high groove tolerance can be performed.
As a concrete method of arc welding, GAM welding or MIG welding using a consumable electrode is carried out, with an arc being generated between a welding wire as the consumable electrode and the base material in an inert shielding gas atmosphere such as argon or helium. With TIG welding using a non-consumable electrode, on the other hand, welding is carried out, with an arc being generated between a tungsten electrode as the non-consumable electrode and the base material in the above-mentioned shielding gas atmosphere.
With the aforementioned laser welding process, however, since laser light is focused, a groove tolerance is low, thus requiring a strict working accuracy for the groove. With the above-mentioned arc welding process, if welding is performed at a high speed, the arc may be unstable, or the large amount of heat input may result in a great thermal strain.
In recent years, a hybrid welding process comprising a combination of laser welding and arc welding has been studied in an attempt to solve the drawbacks of both technologies. Combining laser welding and arc welding coaxially permits welding with a broad range of welding and a great depth of penetration. A laser-arc hybrid welding head enabling coaxial welding by laser welding and arc welding is disclosed, for example, in JP-A-2002-59286.
With the above-mentioned conventional laser-arc hybrid welding head, entry of laser light into a head body takes place via an optical fiber. The optical fiber has to be wired with a great curvature in order to maintain its ability to transmit laser light. Moreover, the focal length of laser light focused is determined by the performance of optical instruments. Thus, the leading end of the head cannot be brought closer to the base material than required. Under these situations, when the conventional laser-arc hybrid welding head is used, the head has to be positioned at or moved to an arbitrary position in consideration of a wiring space and the focal length as well as the size of the head body.
That is, if a welding operation is performed within a narrow space with the use of the conventional laser-arc hybrid welding head, for example, when a floor surface or the like within a vehicle body is welded on a vehicle production line, the head may contact surrounding members, because the head itself is formed with a large longitudinal dimension, and has extensive wiring and piping. To solve such problems, it is conceivable to downsize the lenses and mirrors which are constituents of the laser-arc hybrid welding head. This may deteriorate the welding performance or decrease the welding efficiency, and downsizing of the constituents has its limits.
The present invention has been accomplished as a solution to the above-described problems. It is an object of the invention to provide a laser-arc hybrid welding head which can perform welding, without contacting surrounding members, even when used within a narrow space.