Welding electrode reshaping device

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.

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.

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
 226a, 226b 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.