Abstract:
A welding electrode dressing device in particular in automated welding stations comprises an electrode treatment head ( 11, 111 ) equipped with upsetting members ( 15, 115 ) which reshape the tip of an electrode inserted in it without removing material. Advantageously the treatment head ( 11, 111 ) comprises two treatment seats ( 19, 119 ) arranged on opposite sides thereof to each receive the end ( 12 ) of a pair of welding gun electrodes.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for dressing welding electrodes and in particular in automatic welding stations. 
     It is known that the electrodes which make contact with the sheet metal to be welded are the consumable part of a resistance welding system. For reasons of conductivity and contact resistance the electrodes must be made of nearly pure copper which is well known to be a ductile and malleable material. During use the electrodes are subject cyclically to high pressures with high temperatures and undergo a plastic deformation process which changes their shape to the detriment of welding quality. To limit deterioration of quality beyond acceptable limits in practice devices termed electrode dressers which periodically mill the upset material with small shaped milling cutters to restore the original shape of the electrode tip are used. 
     Since the dressers work by material removal they can only intervene a small number of times. The dressing operations are therefore spaced in time and between one operation and the next the quality of the welding tips undergoes progressive deterioration to the limit of acceptability. However, the dressers removing material shorten considerably the useful life of the electrodes with resulting increase in operating costs. 
     The general purpose of the present invention is to overcome the above mentioned drawbacks by making available a dressing device which could be used frequently with optimal results and without limiting the useful life of the electrodes. 
     SUMMARY OF THE INVENTION 
     In view of this purpose it is sought to provide in accordance with the present invention a device for welding electrode dressing in particular in automated welding stations and comprising an electrode treatment head fitted with upsetting members which reshape the electrode tip inserted in it without removing material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     To clarify the explanation of the innovative principles of the present invention and its advantages compared with the prior art there are described below with the aid of the annexed drawings possible embodiments thereof by way of non-limiting examples applying said principles. In the drawings: 
     FIG. 1 shows a diagrammatic side view partially cross sectioned along plane of cut I—I of FIG. 2 of a device in accordance with the present invention, and 
     FIG. 2 shows a plan view of the device of FIG. 1, 
     FIG. 3 shows a side elevation view cross sectioned along plane of cut III of FIG. 4 of a possible variant of the device in accordance with the present invention, 
     FIG. 4 shows a plan view cross sectioned along plane of cut IV—IV of FIG. 3, and 
     FIG. 5 is a scrap view of another variant of the device of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the figures FIG. 1 shows a reshaping device indicated as a whole by reference number  10  comprising a treatment head  11  for dressing electrodes  12  of a robotized welding gun. The gun is not shown nor described here since it is essentially prior art. This gun can be part of an automated welding station where a plurality of robotized arms perform processing on an object such as for example an automobile body. The device  10  is supported by a support  13  appropriately arranged in the station so that the robotized arms can carry the electrodes and grasp the treatment head on the two sides. 
     An electric motor  14  drives upsetting members  15  located in the treatment head to do the electrode tip upsetting by exploiting the malleability and ductility of the material making up the electrodes. The upsetting members have a shape such as to define an upsetting seat  16 ,  17  for each electrode of the gun with the seat being shaped as desired for the electrode tip. 
     As may be seen also in FIG. 2 in the embodiment described the upsetting members are made in the form of three satellites  15  with periphery shaped with seats  16  and  17 . The satellites are arranged with rotation axis  18  at the vertices of an equilateral triangle to face each other opposite an opening  19  for introduction of the electrode tip in the reshaping device. The satellites  15  are supported by means of their own plain bearings  22  by a satellite holder  20  having bearings  21  supporting the body of the device. 
     The satellite holder  20  is rotated by the motor  14  by means of a drive belt  23 . 
     In use after a predetermined number of welds or even a single weld the welding gun closes on the head  11  so as to arrange the electrodes with the tips as shown in FIG.  1 . Rotation of the satellite holder and consequently of the satellites around the electrode tips perform the upsetting of the tips to reshape them in the original shape. It should be noted that the flat shape of the upsetting head  11  makes it perfectly compatible with the normal openings of welding guns. 
     FIG. 3 shows a second embodiment of a device in accordance with the present invention. For the sake of convenience details similar to those of the above embodiment are indicated by the same numbering increased by  100 . 
     The device of FIG. 3 indicated as a whole by reference number  110  comprises a treatment head  111  for dressing the electrodes  12  and is supported by a support  113 . 
     Differently from the device  10  the device  110  is supported in an intermediate position between its ends with the motor  114  arranged overhanging on the side opposite the treatment head. The motor  114  drives through a belt  123  upsetting members  115  located in the head  111 . 
     The upsetting head  111  is essentially similar to the head  11  described above to perform upsetting of the electrodes inserted in an opposing manner therein through the openings  119 . 
     Advantageously as may by seen in FIG. 3 the support for the device  110  is sprung by means of a spring units  130  and comprises pins  131  integral with the body  136  of the device  110  and running in seats  135  made in a plate  132  of the support  113 . On the two sides of the plate  132  are located springs  133 ,  134  each reacting between one end of the respective pin and the plate itself so as to provide a 2-way elastic support in the direction of thrust of the electrodes against the device. This elastic support allows the device to move adequately under the thrust of the welding guns which are brought into contact with the two processing heads. 
     In addition to the upsetting head  111  the device  110  has a second processing head or cleaning head indicated generally by reference number  125 . This second head  125  comprises a tool  126  designed for performing surface cleaning with negligible material removal. The tool is powered by the motor  114  through a second belt  127 . 
     The tool can be for example in the form of a lightly diamond-coated abrasive or some other tool suitable for the purpose for example with an appropriate cutting edge. 
     As may be seen in FIG. 4 the tool  126  projects from a protective hood  128  through an opening  129  so that the pair of electrodes  12  of one gun can rest on the work surface of the tool  126 . 
     Thus it is possible to perform cleaning of the electrode end which is a slightly flattened area (termed ‘lens’) remaining despite the action of the reshaping rollers. In this area are fixed oxides, zinc slag and the like which alloy with the metal of the electrodes and reduce passage of electrical current with resulting reduction of weld quality. 
     Advantageously the tool can be configured to maintain a slight curvature of the lens. This can be easily obtained with a tool shaped from a soft ‘floating’ disk or from a brush. 
     Bearing of the disk tool can take place first for one electrode and then for the other or simultaneously for both electrodes by partial closing of the gun on the disk. In the latter case it is necessary to check the gun closing force to have the right pressure necessary for smoothing. FIG. 5 shows a variant of the smoothing head indicated as a whole by reference number  225 . In this variant the head  225  comprises two cleaning disks  226   a,    226   b  mounted and keyed in a running manner on a shaft  240  rotated by the belt  127 . Between the two disks is arranged a spring  241  which pushes them apart. 
     The two electrodes draw near to the two disks from opposite directions and each electrode rests on the work surface of one of the two disks. 
     Support can take place first for one electrode and then for the other or simultaneously by partial closing of the gun. The support force of the electrode on the disk is determined by the spring  240 . It is thus easy to supply a predetermined support force even allowing for the variability of positioning of the electrode tip which also depends on consumption of the electrode due to welding work. 
     It is now clear that the preset purposes have been achieved. As no material is removed the possible number of operations on one electrode is theoretically unlimited and at each welding cycle the electrode appears practically like new with assured quality for the entire cycle. The useful life of the electrodes is considerably prolonged with considerable cost savings. 
     Even using the cleaning head, material removal is negligible since this head basically only removes the superficial oxides and does not reshape the electrode. 
     As another advantage, with assurance of welding tip quality it will be possible to reduce the quantity of redundant tips normally applied to the object being welded with resulting advantages in production times and costs. 
     Lastly, no chips which must be removed from the processing area are produced. 
     Naturally the above description of embodiments applying the innovative principles of the present invention is given by way of non-limiting examples of said principles within the scope of the exclusive right claimed here. 
     For example shapes and proportions of component parts of the device can vary with specific needs.