Welding apparatus with monitor means
BACKGROUND OF THE INVENTION 
     This invention relates to welding apparatus provided with a monitor, and more particularly it is concerned with a welding apparatus suitable for performing welding in narrow spaces. 
     Heretofore, in order to perform welding operations by remote control or effect their automation, it has been the usual practice to utilize fiberscopes or television cameras mounted in a position in a space remote from the welding torch to carry out welding while checking on the weld produced. In this welding system, it is necessary to provide a space for mounting a fiberscope or a television camera in addition to a space for accommodating the welding torch. Thus this welding system has suffered the disadvantage that when welding is to be carried out in narrow spaces not large enough to obtain space for mounting the monitor, it would become impossible to carry out monitoring, thereby raising the problem that the reliability of the welding operation performed might be reduced. 
     SUMMARY OF THE INVENTION 
     This invention has as its object the provision of a welding apparatus capable of monitoring the position of the welding torch and the condition in which welding is performed even in a narrow space, to thereby enable welding to be performed with increased precision and allow the reliability and quality of the weld produced to be improved. 
     To accomplish the aforesaid object, the invention provides an outstanding characteristic that a fiberscope serving as an image guide is built in an electric conductor of a welding torch of the welding apparatus. 
     In order to check on the welding position or the condition of the arc, the forward end of the fiberscope is advantageously located in a position in which an arc is generated or near the electrode. However, if the position of the fiberscope is too near the arc generating position, there would be the danger that the fiberscope might be damaged by the heat of the arc or the fumes and vapor of metals which are produced when welding is performed. To avoid this problem, the forward end of the fiberscope is cooled with gas, and at the same time the fumes and vapor of metals are removed by the gas in the welding apparatus according to the invention. This arrangement enables the forward end of the fiberscope to be located in close proximity to the electrode or in a position only 10 mm away from the electrode, with the temperature of the fiberscope only rising to about 100° C. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of the welding apparatus provided with a monitor according to the invention, showing the apparatus in its entirety; 
     FIGS. 2-4 are views showing the forward end portion of the welding torch in detail, FIG. 2 being a plan view, FIG. 3 being a sectional view taken along the line III--III in FIG. 2 and FIG. 4 being a sectional view taken along the line IV--IV in FIG. 2; and 
     FIG. 5 is a detailed view showing the welding torch shown in FIGS. 1-4 being used for welding a heat transfer tube to tube plates to produce a heat exchanger. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows one embodiment of the welding apparatus provided with a monitor in conformity with the invention. As shown, a welding torch 1 is supported by a welding head 2 serving as a drive source for actuating the welding torch 1 for performing welding. The welding torch 1 is usually required to move back and forth in reciprocatory movement along its longitudinal axis and in rotary movement thereabout. The welding torch 1 has mounted at its forward end an electrode 3 to which a pulse current is passed from a power source, not shown. The welding torch 1 has mounted therein an image guide 4 and a light guide 5 which are in the form of known fiberscopes. The image guide 4 has a filter 6 located at its rear end, so that a subject in front of the image guide 4 has its image formed on the filter 6. An industrial television camera 7 is mounted to process the image formed on the filter 6 and connected through a cable 8 to a television receiver 9 on an operational panel, so the image of the subject in front of the image guide 4 can be seen as a television image on the television receiver 9. The operation panel mounts thereon a switch of an optical light source device 10 which is turned on and off through an input cable 11. When the light source device 10 is turned on, light is transmitted to the light guide 5 through which it is transmitted to the welding head 2 and illuminates a weld being formed in the vicinity of the electrode 3 at the forward end of the welding torch 1. The input cable 12 is an input cable for a welding power source. 
     Monitoring is carried out by using the welding apparatus of the aforesaid construction as follows. When it is desired to check on the position of the welding torch 1 before performing welding, the light source device 10 is turned on to illuminate portions of metals to be welded by means of the light guide 5 and at the same time to form an image of the portions to be welded by means of the image guide 4. This enables television pictures of the portions to be welded to be watched on the operation panel, to enable information on the position of the electrode 3 relative to the portions to be welded to be obtained. This makes it possible to achieve correct positioning of the welding torch 1, thereby contributing to improved reliability of welding and production of sound welds of high quality. 
     During a welding operation, a welding arc is generated and provides illumination. Thus it is possible to watch the welding operation being performed as television pictures on the television receiver 9 through the image guide 4 irrespective of whether or not the light source device 10 is turned on. After the welding operation is completed, the weld formed can be checked on in the same manner as described by referring to the monitorning of the position of the welding torch 1 prior to the welding operation. 
     The welding torch 1 will be described in detail by referring to FIGS. 2-4. A principal member of the welding torch 1 is an electric conductor 13 which is generally in the form of a bar of copper. The electric conductor 13 is covered in its entirety with an insulating cap 14 which is only opened in the vicinity of the electrode 3. The insulating cap 14 is usually formed of ceramic material. The electrode 3 is secured to the electric conductor 13, which is formed with a bore 16 for feeding gas therethrough to a gas chamber 17 enclosing the electrode 3 fixed by a screw 15. The gas chamber 17 serves as a header for supplying gas to a plurality of gas ejecting ports 18 located about the electrode 3. When welding is carried out, shield gas, such as argon gas, is jetted out of the gas ejecting ports 18 and directed against the portions to be welded. The shield gas jetted out of the ports 18 may be 3-7 l/min as is usually the case with ordinary welding. The electric conductor 13 has two fiberscope mounted therein to serve as the image guide 4 and the light guide 5, with forward ends of the fiberscopes being positioned in the gas chamber 17. An image guide opening 19 and a light guide opening 20 are located around the electrode 3 so that the portions to be welded can be placed within the field of view of the image guide 4 and the light guide 5 through the openings 19 and 20. The openings 19 and 20 concurrently serve as gas ejecting ports. Thus as the shield gas is jetted out during welding operation, the image guide and the light guide 5 can be cooled satisfactorily with the gas. The shield gas also has the effect or removing fumes and vapor of metals generated during welding, thereby avoiding a reduction in resolving power which might otherwise be caused by the fumes and vapor of metals adhering to the image guide 4 or light guide 5. 
     In one example in which the invention was carried into practice, fiberscopes of 3 mm in diameter are used for the image guide 4 and the light guide 5. It has been found that a sufficiently large field of view can be secured when the guide openings 19 and 20 have the same diameter, and that cooperating with the gas ejecting ports 18 of 1.5 mm in diameter, the guide opening 19 and 20 are able to supply shield gas to the portions to be welded in an amount high enough to avoid oxidation of the weld. The welding torch 1 has defined therein a cooling water channel 23 through which cooling water is passed at a rate of 3-5 l/min from a cooling water supply source, not shown, in the welding head 2, to avoid a rise in temperature. 
     In the example of the aforesaid construction, transfer of heat generated by welding to the image guide 4 and the light guide 5 is avoided as follows: the heat that might be transferred by the conduction of heat is eliminated by the cooling water flowing through the welding torch 1 for the electric conductor 13; the heat of convection is eliminated by the shield gas ejected through the guide openings 19 and 20; and the heat of radiation is minimized by reducing the size of the openings 19 and 20 as much as possible. By this arrangement, a rise in the surface temperature of the fiberscopes 4 and 5 to a level above about 100° C. can be avoided even if the fiberscopes 4 and 5 are located in close proximity to the arc or only spaced apart therefrom by about 10 mm. 
     FIG. 5 shows the manner in which the welding apparatus according to the invention is used for producing a heat exchanger. As shown, the welding torch 1 is used for welding a heat transfer tube 22 to tube plates 21. In one example, the specifications of the heat exchanger included: thickness of the tube plate 21, 200 mm; outer and inner diameters of the heat transfer tube 22, 22.7 mm and 20.3 mm respectively; and inner diameter of a bore 24 of the tube plate 21, 23 mm. This means that the welding apparatus according to the invention is capable of carrying out welding in a small bore of about 20 mm in diameter. 
     In the embodiment shown and described hereinabove, the electrode 3 is located at one side of the axially extending electric conductor 13 (see FIG. 1). It is to be understood, however, that the invention is not limited to this specific position of the electrode and that the electrode may be located in the front or at the forward end of the electric conductor to enable illumination of the portions to be welded and check up of the weld being formed to be achieved by means of the fiberscopes through the guide openings serving concurrently as gas ejecting ports. 
     From the foregoing description, it will be appreciated that in the welding apparatus according to the invention the provision of fiberscopes in the electric conductor of a welding torch facilitates welding performed in narrow spaces which only admit the forward portion of the welding torch, thereby enabling a sound weld of high reliability to be produced.