Method and device for grinding welding electrode

Abstract

The invention relates to a method for grinding a rod-shaped welding electrode, in which a surface region of the welding electrode to be ground and an abrasive contact surface region of a rotating grinding tool are pressed against each other, a contact line is formed in the contact surface region of the grinding tool, and the rotating grinding tool and the welding electrode are moved relative to each other, in order to grind the entire surface of the welding electrode to be ground, the welding electrode is pressed in the axial direction on an abrasive contact surface region, and during a relative movement between the rotating grinding tool and the welding electrode, the grinding tool is moved in a curved trajectory in a movement plane which runs transversely to the contact line, the invention relates to a welding electrode for a grinding tool, comprising a longitudinal axis of the welding electrode, in which a holding device for a rotating grinding tool is arranged on a coupling transmission, which is provided with two actuating motors, which can move the holding device to any point within the adjustment range of the plane of movement.

Description

Technical Field

[0001] The invention relates to a method for grinding a rod-shaped workpiece, namely a welding electrode, wherein the surface area of ​​the welding electrode to be ground and the abrasive contact surface area of ​​a rotating grinding tool are pressed against each other. The invention also relates to a grinding device for carrying out this method. Background Art

[0002] When resistance welding metal sheets, a current of high current intensity is introduced into the sheet through two electrodes pressed on the outer surface of the sheet to be welded to each other. As a result, the metal of the sheet melts and forms a weld core, which firmly connects the adjacent sheets to each other. This applies to the welding of other metal components accordingly. Welding electrodes are usually made of copper or copper alloys. Especially in aluminum resistance welding, the ideal shape and purity of the surface of the welding electrode are important prerequisites for producing high and reproducible quality. Just by welding a few welds, for example ten to twenty welds, the surface of the welding electrode may be adversely affected by deposition and wear, so that the weld produced does not have the desired strength. Therefore, the welding electrode is reprocessed regularly so that its surface has the best shape and is not contaminated during each welding process. Grinding welding electrodes is a known method for reprocessing the surface of welding electrodes.

[0003] From the prior art, various methods and devices for machining welding electrodes are known. FR 2 738 518 A1 discloses a cutting head whose knives extend in an arc shape so that they produce the desired contour on the end face of the welding electrode when rotating about the axis of rotation of the cutting head. The surface of the welding electrode produced by cutting has the disadvantage of being too smooth. The surface produced by grinding has a certain roughness, which according to the invention leads to better welding results. The roughness is produced by the cutting of abrasive particles of the grinding tool, which form wear marks on the surface along their movement path.

[0004] For this reason, the applicant has developed a grinding method in which a grinding disk rotating about an axis of rotation performs an oscillating motion about the center of the end face of a welding electrode, the surface of the grinding disk extending radially relative to the axis of rotation forming an abrasive grinding surface. In this way, the end face of the welding electrode is ground into a convexly curved cap and has grooves in the surface produced by the grinding disk, which impart the desired roughness. The applicant's patent document US 9 573 237 B2 describes a mechanical rotary and oscillating drive for a grinding disk. The applicant's patent document US 9 579 770 B2 describes a rotary drive device that is coupled to a numerically controlled actuator in order to cause the grinding disk to perform the desired oscillating motion.

[0005] In practice, both systems have been shown to be able to be used to produce a defined cap-shaped electrode surface in a welding electrode. However, the production of the motion control device for the grinding disc is relatively complex.

[0006] DE 195 18 708 C2 and JP 2003071693 A describe a grinding method in which a workpiece is rotated about its longitudinal axis. WO 2020 / 106419 A1 describes a grinding method in which the axis of a grinding disc is moved along a circular path around the end face of the workpiece by a plotter drive or a pivot arm. Summary of the invention

[0007] The object of the present invention is to provide a method and a device for grinding rod-shaped welding electrodes which are easy to implement and can be used flexibly in practice.

[0008] This object is achieved by the features of the independent claims.

[0009] In the method described here for grinding a rod-shaped welding electrode, the surface area of ​​the welding electrode to be ground is pressed against the abrasive contact surface area of ​​a rotating grinding tool. A contact line is formed at the contact surface area of ​​the grinding tool, and the rotating grinding tool and the welding electrode are moved relative to each other in order to grind the entire surface of the workpiece to be ground.

[0010] The method is characterized in that the welding electrode is pressed against the abrasive contact surface area in the axial direction and during the relative movement between the rotating grinding tool and the welding electrode, the grinding tool moves on a curved trajectory in a movement plane, which extends transversely to the contact line and contains the longitudinal axis of the welding electrode. In other words, during grinding, the grinding tool, which contacts the end face of the welding electrode along the curved contact line, moves along a curved trajectory, especially a circular trajectory. The curved trajectory is located in a movement plane, which extends transversely to the contact line, especially at right angles to the contact line, and parallel to the longitudinal axis of the rod-shaped welding electrode. The curvature of the contact line is applied to the surface of the welding electrode in a direction parallel to the contact line. The curvature of the curved trajectory is applied to the end face in the direction of the movement plane. If the contact line and the curved trajectory are concavely curved relative to the end face, the two curvatures overlap and make the end face spherical after the grinding process. If, however, the contact line and the curved path are curved convexly relative to the end face of the welding electrode, a cavity is produced in the end face of the welding electrode, so that an annular contact area is available for welding.

[0011] The holding device for the rotating grinding tool is arranged on a coupling drive, which is equipped with two actuator motors, which can move the holding device to any point within the adjustment range of the movement plane. Such a coupling drive can be manufactured cost-effectively in a simple manner, requires little maintenance and can be controlled very reliably. Stepper motors or servomotors can be used as actuator motors for the two coupling devices.

[0012] In one embodiment, the abrasive contact surface area of ​​the grinding tool is formed by a concavely curved annular groove on the side of the grinding disk, in which embodiment the welding electrode is pressed parallel to the rotation axis of the grinding disk onto the concavely curved contact surface area of ​​the grinding tool.

[0013] In a variant design, the abrasive surface area of ​​the grinding tool is formed by the circumferential surface of the grinding disk, in which the welding electrode is pressed onto the circumferential surface of the grinding disk in the radial direction. The circumferential surface of the circular grinding disk is convexly curved along the circumference. The circumferential surface can be concavely curved along the axial direction to produce a contact line that is concavely curved. However, the circumferential surface can also be convexly curved to produce a contact line that is convexly curved. This can produce an annular end face of the welding electrode, which produces an annular contact during welding. In practical applications, an annular contact area may be very advantageous. For this purpose, the relative movement between the welding electrode and the grinding tool can be realized in the form of rotation around the axis of the welding electrode. A recess is then formed in the central area of ​​the end face, and the effective contact area during welding is annular. However, it is also feasible to move the spherically curved grinding disk along the end face of the welding electrode along a curve transverse to the curved contact line. In this case, an end face with a cavity is also produced on the welding electrode. The end face of the welding electrode is preferably rotationally symmetrical.

[0014] The abrasive particles are preferably formed of diamond particles or other high-strength grinding particles, such as cubic boron nitride (CBN). The grinding particles can be applied, especially electroplated, to a deformable metal foil. The metal foil itself can be applied, especially glued to a rubber-elastic deformable support layer of a grinding disc. DE 10 2016 119 746 A1 describes a manufacturing method for such a grinding disc. The flexible but high-strength fixation of the grinding particles on the metal foil enables an optimal processing tool for welding electrodes. The flexible grinding surface avoids hard impacts and collisions during the grinding process. At the same time, the grinding particles are firmly anchored to the metal foil. Such a grinding tool has a long service life.

[0015] However, it is also possible to arrange the drive motor for the grinding disc on a flexible holding device and in this way achieve certain elastic properties of the grinding surface. Alternatively or in addition, the drive shaft of the grinding disc can also be flexibly mounted, for example by magnetic forces acting on the rotor of the external rotor. The grinding disc can also be flexibly mounted on the shaft of the drive motor, for example by using elastic O-rings.

[0016] In order to implement the grinding method described here, a device for grinding a rod-shaped welding electrode is proposed, which has a grinding tool, a rotary drive for the grinding tool and a clamping device, which presses the surface area to be ground of the welding electrode and the abrasive contact surface area of ​​the rotating grinding tool against each other.

[0017] The contact surface area of ​​the grinding tool is the contact line, wherein the movement device moves the rotating grinding tool and the welding electrode relative to one another in order to grind the entire surface of the welding electrode to be ground.

[0018] This results in the advantages described above. With a simple design of the grinding device, a spherical end face provided with a uniform roughness due to the wear marks of the grinding particles can be reliably ground by the device if the contact line of the surface of the grinding disk is concavely curved and the grinding disk is guided along a concave path on the end face of the welding electrode. In the case of a convex curvature of the contact line, a cavity can be produced in the center of the welding electrode, so that the end faces make contact along the outer annular region of the welding electrode during welding.

[0019] The abrasive contact surface area of ​​the grinding tool can be formed by a, for example, concavely curved annular groove on the side of the grinding pad or by a concavely curved circumferential surface of the grinding pad.

[0020] The clamping device can be a mechanical arm or a welding tongs carrying the welding electrode. However, the clamping device can also be formed by a movable holding device for the grinding disk. With the help of this holding device, the welding electrode can be pressed onto the grinding disk. The clamping device can be provided for pressing the rod-shaped welding electrode onto the abrasive contact surface area in the axial direction, wherein the movement device can be provided for moving the grinding tool relative to the welding electrode on a curved trajectory in a movement plane, which extends transversely to the contact line and parallel to the longitudinal axis of the welding electrode.

[0021] The holding device for the rotating grinding tool is arranged in particular on a coupling transmission, which is equipped with two actuator motors that can move the holding device to any point within the adjustment range of the movement plane. This embodiment is described in detail below in conjunction with the accompanying drawings.

[0022] This embodiment can especially realize a particularly simple and compact construction of the grinding device. In fact, the grinding device with a drive motor for rotating the grinding disk and the motion device for generating relative movement between the grinding disk and the welding electrode can be designed as a component of the welding head or a component of the welding tongs with the welding electrode. In this way, the device for regrinding the welding electrode can be integrated into a fine welding head, especially for fixing small parts, so that the welding electrode can be regrinded without significantly interrupting the welding process or without intervention by the fitter. The device for welding small parts usually has a stationary welding head, to which the workpiece is transported. However, welding devices with movable welding heads are also known. Small parts are usually welded by welding electrodes with a diameter of 6mm to 8mm and a flat end face. The linear drive presses the end face of the welding electrode onto the workpiece. This welding electrode can be well formed into a preferably spherically curved shape by the device described here and the method described here, wherein the surface of the electrode obtains the desired structure by grinding. Good welding results can be achieved very reliably by this spherical end face of the welding electrode of the welding head of the small parts welding device. Slight inclinations of the welding electrode relative to the workpiece surface can be compensated by the spherical end surface.

[0023] Finally, the device described here can also be provided for elastically holding the abrasive contact surface area of ​​the rotating grinding tool relative to the welding electrode. As described above, the grinding surface with the abrasive particles can have an elastic base. The grinding tool can be elastically fixed to the drive motor or the holding device for the drive motor of the grinding tool can be designed elastically. The flexibility (or elasticity) of the grinding surface relative to the end face to be processed can prevent hard impacts on the end face and possible damage to the end face caused by the grinding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further specific embodiments and advantages of the present invention are described below in conjunction with the accompanying drawings.

[0025] Figure 1 A first embodiment of a grinding disc having a hub is shown in cross section.

[0026] Figure 2 A second embodiment of a grinding disc with a drive motor is shown.

[0027] Figure 3 Shows Figure 2 Holding device for the drive motor of the grinding disk in the embodiment of the present invention, with a schematically shown welding electrode.

[0028] Figure 4 Shown in front view Figure 3 The holding device in.

[0029] Figure 5Shown in side view Figure 3 and Figure 4 The holding device in.

[0030] Figure 6 Shown in the first position Figures 3 to 5 Coupling transmission device in.

[0031] Figure 7 Shown in the second position Figure 6 Coupling transmission device in.

[0032] Figure 8 Shown with Figure 5 The corresponding side view has Figure 7 The position of the coupling transmission in.

[0033] Fig. 9 The coupling transmission is shown in FIG. Figure 7 Schematic diagram of the positions corresponding to the positions shown.

[0034] Fig.10 The coupling transmission is shown Fig. 9 In the corresponding three views, the coupling drive is in three different positions for machining the upper welding electrode.

[0035] Fig.11 The coupling transmission is shown Fig.10 In the corresponding illustration, the coupling drive is in the position for machining the lower welding electrode. DETAILED DESCRIPTION

[0036] Figure 1 A first embodiment of a grinding disc 1 is shown, which constitutes a grinding tool for carrying out the method described herein. The grinding disc 1 is clamped in a rotationally fixed manner on a hub 2, which is rotated about its axis of rotation 3 by a drive motor (not shown). The grinding disc usually rotates at a speed of more than 1000 revolutions per minute. The grinding disc 1 is provided for side grinding and has a flat annular groove 4 on its upper side extending perpendicularly to the axis of rotation 3, which has a slightly concave extension. The grinding disc 1 is circular in a top view. The groove 4, which is concavely arched in the radial direction of the grinding disc 1, extends in an annular region on the circular grinding disc 1. In Figure 1 A rod-shaped welding electrode 5 is schematically shown in the right half of FIG. The welding electrode 5 has a longitudinal axis 6 and a cap-shaped end face which is pressed axially into an annular groove 4 with a concavely curved surface of the grinding disk 1. Grinding can remove contamination from the end face and produce a uniform surface with fine grooves, which are produced by the grinding particles.

[0037] Figure 2An alternative embodiment of a grinding disc 7 is shown. The grinding disc 7 is provided for circumferential grinding. This means that the grinding disc 7 has abrasive particles, preferably diamond particles or CBN particles, on its circumferential surface 9 which is curved concavely in the axial direction. A shaft 10 is integrally formed on the grinding disc 7 and is rotated at high speed about the axis of rotation 8 by a drive motor 11. Figure 2 Also shown is the welding electrode 5, which is pressed in the radial direction of the grinding wheel 7 onto the concavely curved circumferential surface 9 of the grinding wheel 7. As a result, a linear contact is also formed between the grinding wheel 7 and the welding electrode 5 along the concavely curved contact line.

[0038] Figure 3 An embodiment of a holding device for a drive motor 11 of a grinding disc 7 is shown. In this embodiment, the grinding disc 7 is guided along a curved path, which lies in a plane extending substantially perpendicular to the contact line. The curvature of the contact line between the grinding disc 7 and the welding electrode 5 overlaps with the curvature of the curved machining path and forms a spherical shape on the end face of the welding electrode 5. The curved machining path is generated by means of a coupling transmission (or coupling mechanism).

[0039] Figure 6 The components of the drive motor 11 for the grinding disc 7 are shown separately. In this embodiment, the holding device of the drive motor 11 is formed by the free end 14 of the first coupling device 15, the other end of which is connected to the first crank 16 of the first actuator motor 18 via a first joint 17. In the embodiment shown, the first coupling device 15 is in the shape of a bent rod. The second coupling device 19 is connected to the second crank 20 of the second actuator motor 22 at one end via a second joint 21 and is connected to the first coupling device 15 via a third joint 23. The third joint 23 is approximately located in the curved area of ​​the first coupling device 15. Figure 3 It can be seen that the stepper motors 18 and 22 are fixed to the support plate 24. By rotating the cranks 16 and 20 by means of the stepper motors 18 and 22, the free end 14 of the first coupling device 15, which forms a holding device for the drive motor 11 of the grinding disk 7, can be moved within an adjustment range in a plane parallel to the support plate 24.

[0040] The support plate 24 is located on the side of the electrode holding device 25 of the welding device. For the sake of clarity, the electrode holding device is Figure 3 , and has two welding electrodes 5, 5'. Since the grinding disc 7 can be moved substantially freely in a plane perpendicular to the rotation axis of the grinding disc 7 by means of a coupling drive, the grinding disc can be moved both toward the upper welding electrode 5 and toward the lower welding electrode 5', so that the end face can be processed by the grinding disc 7.

[0041] During the machining process, the coupling drive is approximately Figure 6 In the position shown, after processing, the coupling drive can be moved to Figure 7 In the position shown, the grinding disc 7 and its drive motor 11 are at their greatest distance from the welding electrodes 5, 5'. Figure 8 As shown, in this rest position, the grinding disc 7 does not interfere with the welding process performed by means of the welding electrode. If the end faces of the welding electrodes 5, 5' need to be re-processed, the grinding disc is moved back to Figure 3-Figure 5 in the position shown.

[0042] Fig. 9 shows the rotational position of the actuator motor which moves the grinding disc to Figure 8 in the position shown. Fig. 9 It is only a schematic diagram of the coupling transmission. The rotation axis 26 of the first actuator motor and the rotation axis 27 of the second actuator motor are shown here. The coupling devices 15, 19 and the cranks 16, 20 are shown only as lines. In addition, a processing trajectory 29 for the end face of the upper welding electrode 5 and a processing trajectory 30 for the end face of the lower welding electrode 5' are schematically shown. When the rotation axis 8 of the grinding disk moves along the processing trajectory 29 or 30, the concavely curved circumferential surface 9 of the grinding disk 7 has a linear contact with the corresponding welding electrode 5 or 5' to be processed. For the two cranks 16 and 20, the crank angle is shown with reference to the zero position extending horizontally to the right. Fig. 9 In the embodiment, the crank angle α between the first crank 16 and the zero position is 328.91°. Fig. 9 When in the middle position, the crank angle β of the second crank 20 has a value of 148.97°.

[0043] Starting from this position, the cranks 16 , 20 can be rotated in order to move the axis of rotation 8 of the grinding disk, for example, close to the machining path 29 of the upper welding electrode 5 .

[0044] Fig.10 A, B and C show three positions of the coupling drive when machining the upper welding electrode. It can be seen that the machining path 29 is curved concavely, so that the axis of rotation 8 of the grinding disk moves along the concave machining path 29. As a result, the circumferential surface is moved along the concave machining path 29 past the end face of the welding electrode 5. The concave contour of the circumferential surface of the grinding disk is superimposed on the concave movement path of the axis of rotation 8 of the grinding disk, and in this way a hood-like contour is generated at the end face of the upper welding electrode 5.

[0045] Fig.11 The three views A, B and C show three positions of the axis of rotation 8 of the grinding disk on the machining path 30 for the lower welding electrode 5 ′.

[0046] If the circumferential surface of the welding electrode does not extend concavely but convexly in the axial direction, the movement direction of the coupling drive can be the opposite, that is, during grinding, the grinding disk moves along a convex trajectory toward the welding electrode and is pressed into the end face of the welding electrode until the grinding disk reaches the center, and then the grinding disk is moved away from the welding electrode again in the axial direction. As a result, a spherical end face is not generated, but a cavity is generated in the center of the end face of the welding electrode. In this way, the end face of the welding electrode is provided with an axially protruding annular surface on the outer circumference, which contacts the workpiece during welding.

[0047] The features of the invention disclosed in this description, the drawings and the claims may be significant both individually and in any combination for realizing the invention in various embodiments. The invention is not limited to the above-described embodiments. The invention may be modified within the scope of the claims taking into account the knowledge of a person skilled in the art.

[0048] Reference numerals list

[0049] 1Grinding disc, grinding tools

[0050] 2 Hubs

[0051] 3. Grinding disc rotation axis

[0052] 4. Concavely curved annular groove

[0053] 5. 5' welding electrode

[0054] 6 Longitudinal axis of welding electrode

[0055] 7Grinding discs and grinding tools

[0056] 8 Axis of rotation of the grinding disc

[0057] 9 The circumferential surface is concavely curved

[0058] 10 Grinding disc axis

[0059] 11. Drive motor

[0060] 12Motor holding device

[0061] 14 The free end of the first coupling device, the holding device

[0062] 15 first coupling device

[0063] 16 First Crank

[0064] 17 First joint

[0065] 18 First actuator motor

[0066] 19 Second coupling device

[0067] 20 Second Crank

[0068] 21 Second joint

[0069] 22 Second actuator motor

[0070] 23 Third joint

[0071] 24 support plate

[0072] 25Electrode holding device

[0073] 26 Rotation axis of the first actuator motor

[0074] 27 Rotation axis of the second actuator motor

[0075] 28 Arrows

[0076] 29 Processing track for the upper welding electrode

[0077] 30 Machining track for the lower welding electrode

Claims

1. A method for grinding a rod-shaped welding electrode (5, 5'), in which a surface area of ​​the welding electrode (5, 5') to be ground and an abrasive contact surface area of ​​a rotating grinding tool (1, 7) are pressed against each other, in, A contact line is formed in the contact surface area of ​​the grinding tool (1, 7), and the rotating grinding tool (1, 7) and the welding electrode (5, 5') are moved relative to each other to grind the entire surface to be ground of the welding electrode (5, 5'), characterized in that the welding electrode (5, 5') is pressed axially against the abrasive contact surface area, and during the relative movement between the rotating grinding tool (7) and the welding electrode (5, 5'), the grinding tool (7) is moved on a curved trajectory (29, 30) in a movement plane, which extends transversely to the contact line and contains the longitudinal axis (6) of the welding electrode (5, 5'), wherein a holding device (24) for the rotating grinding tool (7) is arranged on a coupling transmission device, which is equipped with two actuator motors (18, 22), which can move the holding device (24) to any point within the adjustment range of the movement plane.

2. The method according to claim 1, characterized in that: The contact surface area of ​​the grinding tool (1, 7) is concavely curved, so that the contact line is also concavely curved.

3. The method according to claim 1 or 2, characterized in that: The abrasive contact surface area of ​​the grinding tool is formed by a concavely curved annular groove on the side surface of the grinding disk (1).

4. The method according to claim 1 or 2, characterized in that: The abrasive surface area of ​​the grinding tool is formed by the circumferential surface of the grinding disk (7).

5. The method according to claim 4, characterized in that The circumferential surface is concavely curved along the axial direction of the grinding disc (7).

6. The method according to any one of the preceding claims, characterized in that The surface area of ​​the welding electrode (5, 5') to be ground and the abrasive contact surface area of ​​the rotating grinding tool (1, 7) are elastically pressed against one another.

7. A device for grinding a rod-shaped welding electrode (5, 5'), the device comprising a grinding tool (1, 7), a rotary drive for the grinding tool and a clamping device, the clamping device pressing the surface area of ​​the welding electrode (5, 5') to be ground and the abrasive contact surface area of ​​the rotating grinding tool (1, 7) against each other, wherein: The contact surface area of ​​the grinding tool (1, 7) is a contact line, and wherein a movement device moves the rotating grinding tool (1, 7) and the welding electrode (5, 5') relative to each other to grind the entire surface to be ground of the welding electrode (5, 5'), characterized in that a clamping device is arranged to press the welding electrode (5, 5') onto the abrasive contact surface area in the axial direction, and the movement device is arranged to move the grinding tool (7) relative to the welding electrode (5, 5') on an arched trajectory (29, 30) in a movement plane, the movement plane extending transversely to the contact line and parallel to the longitudinal axis (6) of the welding electrode (5, 5'), wherein a holding device (14) for the rotating grinding tool (7) is arranged on a coupling transmission device, the coupling transmission device is equipped with two actuator motors (18, 22), which can move the holding device (14) to any point within the adjustment range of the movement plane.

8. The device according to claim 7, characterized in that The contact line is concavely curved.

9. The device according to claim 8, characterized in that The abrasive contact surface area of ​​the grinding tool is formed by a concavely curved annular groove on the side surface of the grinding disk (1) or by a concavely curved circumferential surface of the grinding disk (7).

10. Device according to any one of the preceding claims 7 to 9, characterized in that The abrasive contact surface area of ​​the rotating grinding tool (1, 7) is elastically held relative to the welding electrode (5, 5').

11. The device according to any one of claims 7 to 10, characterized in that The device is an integrated component of the welding head or an integrated component of the welding tongs.

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