Abstract:
A laser-arc hybrid welding head for performing laser light irradiation and arc discharge of a base material to weld the base material by combined use of laser welding and arc welding, comprising: an optical fiber for transmitting laser light used in laser welding; and an arc electrode for generating an arc between the arc electrode and the base material, wherein the optical fiber is disposed such that an optical axis thereof crosses an axis of the arc electrode at a predetermined angle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    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. 
         [0003]    2. Description of the Related Art 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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. 
         [0010]    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. 
         [0011]    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. 
       SUMMARY OF THE INVENTION  
       [0012]    A first aspect of the present invention is a laser-arc hybrid welding head for performing laser light irradiation and arc discharge of a base material to weld the base material by combined use of laser welding and arc welding, comprising: 
         [0013]    an optical fiber for transmitting laser light used in laser welding; and 
         [0014]    an arc electrode for generating an arc between the arc electrode and the base material, 
         [0015]    wherein the optical fiber is disposed such that an optical axis thereof crosses an axis of the arc electrode at a predetermined angle. 
         [0016]    In a second aspect of the present invention, the laser-arc hybrid welding head may further comprise: a collimating optical system for rendering parallel the laser light, which has been entered by the optical fiber, to deliver the laser light as parallel laser light; a splitting and deflecting optical system for splitting the parallel laser light, which has been delivered from the collimating optical system, into two split laser lights, and deflecting the two split laser lights to be parallel to each other and form the predetermined angle with an optical axis of the parallel laser light so that a space portion is formed between the split laser lights; and a focusing optical system for focusing the two split laser lights, which have been deflected by the splitting and deflecting optical system, on the base material, and the arc electrode may be disposed in the space portion to be closer to the base material than the focusing optical system. 
         [0017]    In a third aspect of the present invention, the splitting and deflecting optical system may comprise: a first reflecting mirror for reflecting part of the parallel laser light, which has been delivered from the collimating optical system, thereby splitting the parallel laser light into the two split laser lights consisting of first split laser light which has been reflected, and second split laser light which has not been reflected; and a second reflecting mirror for reflecting the second split laser light, which has not been reflected by the first reflecting mirror, to deflect the second split laser light so that the second split laser light parallels the first split laser light and the space portion is formed between the second split laser light and the first split laser light. 
         [0018]    The laser-arc hybrid welding head according to the present invention can deflect laser light efficiently, thereby performing welding, without contacting surrounding members, even when used within a narrow space. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING  
         [0019]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawing which is given by way of illustration only, and thus is not limitative of the present invention, and wherein: 
           [0020]      FIG. 1  is a schematic configurational drawing of a laser-arc hybrid welding head according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    A laser-arc hybrid welding head according to the present invention will be described in detail with reference to the accompanying drawing.  FIG. 1  is a schematic configurational drawing of the laser-arc hybrid welding head according to an embodiment of the present invention. 
         [0022]    As shown in  FIG. 1 , a laser-arc hybrid welding head  1  according to the present invention has a cylindrical head body  11  constituting a shell thereof. The head body  11  is crooked at its nearly intermediate part, and is composed of an inclined portion  11   a  on the proximal end side thereof, and a vertical portion  11   b  on the leading end side thereof, with the crooked region forming the boundary between them. The vertical portion  11   b  is disposed to have an axis orthogonal to the surface of a base material W, while the inclined portion  11   a  is disposed to have an axis crossing the axis of the vertical portion  11   b  at an angle of α (e.g., α=30°). 
         [0023]    To the proximal end of the inclined portion  11   a,  a YAG laser oscillator  12  is connected via an optical fiber  13 . The YAG laser oscillator  12  oscillates laser light L 0 , and the oscillated laser light L 0  is transmitted by the optical fiber  13  and entered to the proximal end side of the inclined portion  11   a.  The axis of the optical fiber  13  coincides with the optical axis of the laser light L 0 , and is placed coaxially with the axis of the inclined portion  11   a.    
         [0024]    A collimating lens group (collimating optical system)  14  is provided in a nearly intermediate part in the axial direction of the inclined portion  11   a.  The collimating lens group  14  is composed of a plurality of collimating lenses arranged in series, and allows the laser light L 0  entered by the optical fiber  13  to pass there through, thereby delivering it as parallel laser light L 1 . 
         [0025]    A first reflecting mirror  15  is provided on the leading end side of the inclined portion  11   a,  and a second reflecting mirror  16  is provided on the proximal end side of the vertical portion  11   b.  These reflecting mirrors  15  and  16  are placed with predetermined spacing in the axial direction of the inclined portion  11   a,  and placed with predetermined spacing in the axial direction of the vertical portion  11   b.  The reflecting mirrors  15  and  16  constitute a splitting and deflecting optical system. 
         [0026]    The first reflecting mirror  15  is a flat mirror for reflecting laser light, and is inserted up to a nearly central part of a cross section of the parallel laser light L 1 , which has been outputted from the collimating lens group  14 , in a direction orthogonal to the optical axis of the parallel laser light L 1 . The reflecting plane  15   a  of the first reflecting mirror  15  inclines downward. Thus, the first reflecting mirror  15  reflects an upper part of the parallel laser light L 1  downwardly, thereby splitting the parallel laser light L 1  into two parts, i.e., first split laser light L 2   a  which has undergone reflection, and second split laser light L 2   b  which has not undergone reflection. As a result, the first split laser light L 2   a  is deflected to have an optical axis crossing the optical axis of the parallel laser light L 1  at the angle of α, whereas the second split laser light L 2   b  proceeds, unchanged, in the direction of the optical axis of the parallel laser light L 1 . 
         [0027]    The second reflecting mirror  16  is a flat mirror similar to the first reflecting mirror  15 , and is disposed more remotely than the first reflecting mirror  15  from the collimating lens group  14  in the direction of the optical axis of the parallel laser light L 1 . The reflecting plane  16   a  of the second reflecting mirror  16  inclines downward so as to become parallel to the reflecting plane  15   a  of the first reflecting mirror  15 . Thus, the second reflecting mirror  16  reflects the remaining lower part of the parallel laser light L 1 , which has not been reflected by the first reflecting mirror  15 , downwardly as the second split laser light L 2   b.  As a result, the second split laser light L 2   b  is deflected to have an optical axis crossing the optical axis of the parallel laser light L 1  at the angle of α. 
         [0028]    A mirror adjusting portion  17  is annexed to the second reflecting mirror  16 , and the second reflecting mirror  16  is pivoted by adjusting the mirror adjusting portion  17 . By so doing, the inclination angle of the reflecting plane  16   a  is changed to adjust the deflection (reflection) angle of the second split laser light L 2   b.    
         [0029]    In this manner, the parallel laser light L 1  is reflected and deflected downward by the reflecting mirrors  15  and  16  as the split laser lights L 2   a  and L 2   b,  whereby the optical axes of the split laser lights L 2   a  and L 2   b  become parallel. As a result, a space portion  18  is formed between the split laser lights L 2   a  and L 2   b  along their optical axes. 
         [0030]    Furthermore, a focusing lens group (focusing optical system)  19  is provided in a nearly intermediate part in the axial direction of the vertical portion  11   b.  This focusing lens group  19  is composed of a plurality of focusing lenses arranged in series. The focusing lens group  19  allows the split laser lights L 2   a,  L 2   b,  which have been reflected and deflected by the reflecting mirrors  15 ,  16 , to pass therethrough, thereby focusing and directing the split laser lights L 2   a,  L 2   b  toward a zone of the base material W to be welded. By so focusing the split laser lights L 2   a,  L 2   b,  laser welding can be performed. 
         [0031]    Below the focusing lens group  19  in the space portion  18 , an electrode head  20  is supported by the vertical portion  11   b.  To the electrode head  20 , an arc welder and an electrode supply device (not shown) are connected via a guide pipe  21 . Thus, an electric power and an inert gas are supplied from the arc welder, and an MIG (metallic inert gas welding) electrode (arc electrode)  22  is supplied from the electrode supply device to make arc (MIG) welding possible. 
         [0032]    The MIG electrode  22  is supported by the electrode head  20  such that its axis crosses the axis of the optical fiber  13 , namely, the optical axis of the laser light L 0  at the angle of α. Thus, the optical axes of the split laser lights L 2   a  and L 2   b  and the axis of the MIG electrode  22  are disposed coaxially. The irradiation with the split laser lights L 2   a,  L 2   b  and the generation of an arc A between the MIG electrode  22  and the base material W make it possible to carry out coaxial welding using laser welding and arc welding in combination. 
         [0033]    According to the present embodiment, the MIG electrode  22 , which is a consumable electrode, is used as the arc electrode, but a TIG (tungsten inert gas welding) electrode, which is anon-consumable electrode, maybe used. In this case, the electrode supply device is unnecessary, and it suffices to hold the TIG electrode simply by the electrode head  20 . 
         [0034]    In the above-described configuration, therefore, the laser light L 0  emitted by the YAG laser oscillator  12  is transmitted by the optical fiber  13  and directed toward the collimating lens group  14 . The laser light L 0  entered into the collimating lens group  14  is passed through its interior, and thereby delivered as the parallel laser light L 1 . 
         [0035]    Then, part of the parallel laser light L 1  issued from the collimating lens group  14  is reflected by the first reflecting mirror  15  to become the first split laser light L 2   a,  which is deflected in a direction where it crosses the optical axis of the parallel laser light L 1  at the angle of α. On the other hand, the remaining part of the parallel laser light L 1 , which has not been reflected by the first reflecting mirror  15 , becomes the second split laser light L 2   b.  The second split laser light L 2   b  proceeds, unchanged, in the same direction as the optical axis of the parallel laser light L 1 . Then, the second split laser light L 2   b  is reflected by the second reflecting mirror  16 , and is deflected in a direction in which it crosses the optical axis of the parallel laser light L 1  at the angle of α. 
         [0036]    As described above, the parallel laser light L 1  is reflected and split in two by the reflecting mirrors  15 ,  16 , and the resulting split laser lights L 2   a,  L 2   b  are deflected in a direction in which they cross the optical axis of the parallel laser light L 1  at the angle of α. As a result, the first split laser light L 2   a  and the second split laser light L 2   b  proceed parallel. Moreover, the space portion  18  is formed between them along the directions of their optical axes. 
         [0037]    After the split laser lights L 2   a  and L 2   b  proceeding parallel are directed toward the focusing lens group  19 , they are focused by passing through its interior, and directed toward the zone of the base material W to be welded. Simultaneously, the electrode head  20  disposed in the space portion  18  is supplied with the electric power, insert gas and MIG electrode  22 . Since the optical axes of the split laser lights L 2   a,  L 2   b  and the axis of the MIG electrode  22  are placed coaxially, irradiation with the split laser lights L 2   a,  L 2   b  and arc discharge to the base material W by the MIG electrode  22  can be performed coaxially. Thus, coaxial welding using a combination of laser welding and arc welding takes place. 
         [0038]    In such coaxial welding, the irradiation with the split laser lights L 2   a,  L 2   b  evaporates the base material W, and a part of it is ionized (Fe ions, Cr ions, Ni ions, etc.), inducing an arc discharge. Even when the MIG electrode  22  moves at a high speed, therefore, the arc A stabilizes, thus forming continuous neat beads. Besides, the leading end of the MIG electrode  22  is heated not only by the heat of the arc discharge and Joule heat, but also by the irradiation with the split laser lights L 2   a,  L 2   b.  Consequently, welding can be performed at a high speed in comparison with MIG welding or TIG welding performed singly. 
         [0039]    If, in the laser-arc hybrid welding head, an error in assembly or the like occurs to cause a discrepancy between the focal lengths of the split laser lights L 2   a  and L 2   b,  the mirror adjusting portion  17  is adjusted to change the angle of deflection by the reflecting plane  16   a  of the second reflecting mirror  16 . By so doing, the focal length adjustment of a focused leading end part of the second split laser light L 2   b  can be made. Thus, coaxial welding can be always performed with a desired focal length. 
         [0040]    Thus, the optical fiber  13  is disposed such that its optical axis crosses the axis of the MIG electrode  22  at the angle α. The laser light L 0  entered by the optical fiber  13  is converted into the parallel laser light L 1 . Then, the parallel laser light L 1  is reflected by the reflecting mirrors  15 ,  16  as the split laser lights L 2   a,  L 2   b.  In this manner, the laser light L 0  entered by the optical fiber  13  can be deflected efficiently. As a result, the inclined portion  11   a  crooked relative to the vertical portion  11   b  on the leading end side can be formed on the proximal end side of the laser-arc hybrid welding head  1 . Thus, even if the laser-arc hybrid welding head  1  is positioned at or moved to an arbitrary position within a narrow space by a multi-axis NC robot or the like, it is capable of welding without contacting surrounding members, since it occupies a narrow space. Furthermore, there is no need for downsizing, such as using small lenses or mirrors as the constituents of the head. Thus, the deterioration of the welding performance or a decrease in the welding efficiency can be suppressed. 
         [0041]    In addition, the present invention can be applied to a laser-arc hybrid welding head which can enhance welding properties by pivoting or moving the reflecting mirror to adjust the spacing between the focused leading end parts of the split laser lights. 
         [0042]    The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.