Device for removing electrode caps from electrode shafts

Description

[0001] The invention relates to a device for removing the electrode caps from electrode shafts in the resistance spot welding process.

[0002] Spot welding is often used to join metal sheets and strips.

[0003] In the automotive industry in particular, this process is used in body manufacturing in automated production lines.

[0004] Typically, a variety of welding robots are used to join the body sheet metal parts together by spot welding. These welding robots are equipped with welding guns, each of whose electrode shafts is equipped with a spot welding electrode, the so-called electrode caps.

[0005] These welding tongs are moved toward the positioned sheets to be welded. The precise positioning of the welding tongs relative to the sheets to be welded, as well as the alignment of the sheets relative to each other, is now automated and computer-assisted.

[0006] In such an automated production line, the welding processes are carried out as quickly as possible and without interruption.

[0007] This results in significant wear on the electrode caps, as their contact surfaces come into contact with the bodywork panels to be welded. During this welding process, current flows between the electrodes and the adjacent bodywork panels to be welded. This causes changes to the contact surfaces of the electrode caps in the weld-affected zone.

[0008] Often, burn-off beads form at the edge of the contact surfaces, which cause a change in the welding conditions by increasing the contact area.

[0009] In order to avoid having to counteract this change by uneconomically adjusting the current intensity, the electrode caps are regularly reworked by milling depending on their load and the resulting wear.

[0010] For this purpose, milling devices are arranged in such a way that the welding robots can reach them with their welding tongs and the electrode caps are brought into engagement with the respective installed milling device.

[0011] These electrode cap milling devices are regularly formed from a tool carrier with at least one milling tool mounted therein so as to be rotatable about a tool rotation axis and a drive for this milling tool.

[0012] Often, interacting electrodes of a welding gun will wear out to the same or a similar extent, so that they must be reworked regularly and simultaneously by milling.

[0013] After a number of reworking operations, material has been removed from the electrode cap to such an extent that it must be replaced.

[0014] To do this, the worn electrode caps are removed from the electrode shafts.

[0015] When removing the electrode caps from the welding electrode shafts, the electrode caps are clamped at their cylindrical outer surfaces using clamping jaws. The electrode cap is then rotated around its axis or the axis of the non-rotating welding electrode shaft and removed from the welding electrode shaft in the axial direction.

[0016] Manual pullers are known for this purpose, but they cannot be used in automated production lines due to the risk to workers.

[0017] Devices for removing electrode caps are known, for example, from DE20209401.

[0018] This describes a device for removing electrode caps, in which the electrode cap sits on an electrode shaft at a short distance from a collar on the electrode shaft. This creates a circumferential, groove-shaped space between the collar and the collar-side end of the electrode cap, into which a wedge engages, increasing in thickness tangentially in the direction of the width of the space.

[0019] From DE8808586 a device is known in which the electrode caps are pulled off the electrode cap shafts by means of a lever construction.

[0020] Pulling devices arranged in a tool carrier are also known. These pulling devices have a pulling tool mounted for rotation about a tool rotation axis and a drive for this pulling tool.

[0021] The electrode caps are secured by clamping jaws located in the removal tool. The electrode cap is then rotated around its axis or the axis of the welding electrode shaft, which is held securely against rotation, and removed from the welding electrode shaft in the direction of the shaft's axis.

[0022] DE patent 817231 describes a lathe chuck with clamping jaws for fine machining, which has a jaw protector (1) for roughing work that can be pushed tightly onto the clamping jaws (4) in the axial direction of the chuck and surrounds them like a frame, which has a clamping surface for the workpiece on one frame leg and a screw (3) on the opposite leg for fastening the jaw protector (1) to the clamping jaws (4).

[0023] In the German patent application DE 10 2014 209 828 A1, which forms the basis for the preamble of claim 1, a pulling tool for pulling electrode caps from cap carriers of spot welding electrodes is proposed, which comprises a tool body (24) which is rotatable about an axis of rotation (A) in the pulling operation and has an electrode cap receiving opening (56) which is open in the direction of the axis of rotation (A) for receiving the electrode cap, and two sets of clamping jaws for clamping engagement.

[0024] EP 2 647 462 B1 describes a welding electrode changer in which a removal station (12) for used electrodes outside the arms (11) of a welding gun comprises two skids (48, 50), is proposed in EP 2 647 462 B1.

[0025] These skids each have a contact surface (64) arranged opposite the other skids. Rack shafts are provided as the drive means for the skids.

[0026] US Patent US 6,971,283 B2 describes a gripping arrangement in which the teeth are arranged in at least two substantially rows, wherein at least one row of the teeth is offset in the longitudinal direction with respect to an immediately adjacent row of teeth.

[0027] The British patent GB 25830 proposes equipping the gripping surfaces in the jaws of chucks with definite serrations.

[0028] Another known solution is that instead of pulling the electrode cap from the electrode shaft, the electrode shaft is pulled out of the rotating cap by opening the welding gun.

[0029] In these devices, too, the cap is fixed by means of clamping jaws and rotated around its axis or that of the welding electrode shaft, which is held in a twist-proof manner, and the electrode shaft is pulled out of the electrode cap when the clamp is opened.

[0030] From DE 10 2014 209 828 A1 a pulling tool for pulling electrode caps from cap carriers of spot welding electrodes is known, comprising a tool body (24) which is rotatable about an axis of rotation (A) in pulling operation and has an electrode cap receiving opening (56) which is open in the direction of the axis of rotation (A) for receiving the electrode cap, a first set (26) of clamping jaws for clamping engagement with an electrode cap (20) positioned in the electrode cap receiving opening (56) at least when the tool body (24) rotates about the axis of rotation (A) in a first direction of rotation (R1), a second set (28) of clamping jaws for clamping engagement with an electrode cap (22) positioned in the electrode cap receiving opening (56) at least when the tool body (24) rotates about the axis of rotation (A) in a second direction of rotation (R2) opposite to the first direction of rotation (R1).

[0031] The known interchangeable head types according to the known state of the art are primarily equipped with either straight-toothed jaws or helical-toothed jaws.

[0032] Three jaws are commonly used. This design has the advantage of allowing tools or workpieces to be clamped to a precise centering position.

[0033] However, the disadvantage of the version with exclusively straight-toothed jaws is that there is little or no fixation against axial movement when removing the electrode caps from the pliers shaft. This can lead to premature, uncontrolled loss of the electrode caps after the removal process.

[0034] This problem does not occur with the further developed interchangeable head variant with exclusively helical-toothed jaws.

[0035] The helical toothing ensures that the pliers shafts are protected by the thread effect when removing the electrode caps. When cutting into the base material, the angled toothing forces the cap in an axial direction and thus away from the electrode shaft. Since the electrode cap is quickly moved away from its seat during the rotation of the replaceable head, less / shorter friction occurs between the contact surfaces of the electrode cap cone and the corresponding shaft, thus securing the electrode caps against axial movement.

[0036] This securely holds the loosened electrode cap. However, the disadvantage is that the required angle of rotation for the two-part process, consisting of cutting into the electrode cap until it is gripped and initiating a rotating movement, increases, and the effective angle of rotation in the "loosening phase" decreases.

[0037] The invention is based on the object of designing a pulling device of the above type in such a way that the difficulties of previously known solutions are avoided as far as possible and, in particular, to ensure that process reliability is guaranteed.

[0038] According to the invention, this object is achieved by a device and by the use of the device according to claims 1 and 2.

[0039] The device according to the invention will be explained in more detail below with reference to the figures and the following exemplary embodiment.

[0040] This shows Figure 1 the inventive puller device 1 in assembled, operational state in perspective as well as in sectioned top view Figure 2 the clamping devices 2 and 3 used and to be combined with each other with straight teeth 4 and with helical teeth 5. and Figure 3 an exploded view of the puller 1.

[0041] The electrode cap removal device according to the invention consists of at least one removal device 1 rotatably mounted about a tool rotation axis with clamping means 2 and 3 for fixing the electrode caps to be removed.

[0042] The electrode cap removal device according to the invention comprises a combination of straight-toothed and helical-toothed clamping means 2 and 3, wherein the helical-toothed clamping means have an oblique setting of the toothing in the axial direction.

[0043] When using a mixed assembly with at least one straight-toothed clamping means 2 according to the invention, this supports an earlier initiation of the rotary movement on the electrode cap to be released.

[0044] The use of at least one helically toothed clamping means 3 ensures a sufficient form fit by cutting into the copper material and thus a safeguard against uncontrolled loosening / loss of the loosened cap.

[0045] The combination of the toothing types enables process-reliable loosening, holding and placing of the electrode caps at the desired location.

[0046] In a particular embodiment of the solution according to the invention, it is possible to select these clamping means such that the majority of the clamping means used are the clamping means 2 or optionally the clamping means 3.

[0047] A particularly advantageous aspect of the use of the solution according to the invention is that it can also be used with stripping devices that are already in use.

[0048] Here, previously used identical clamping means can be varied so that at least one clamping means is replaced by a clamping means of the other embodiment.

Claims

1. System for removing the electrode caps from electrode shafts, consisting of at least one removing device (1) mounted rotatably about a tool rotary axis and having clamping means (2 and 3) for fixing the electrode shafts to be removed, characterized in that it comprises a combination of straight-toothed and helical-toothed clamping means (2 and 3), wherein the helical-toothed clamping means have an oblique tooth inclination in the axial direction.

2. Use of the device of claim 1 for removing electrode caps from electrode shafts.