METHOD AND DEVICE FOR GRINDING WORKPIECES, IN PARTICULAR WELDING ELECTRODES

Abstract

The invention relates to a method and a device for grinding rod-shaped workpieces, in particular welding electrodes (5, 5'), in which a surface area of ​​the workpiece (5, 5') to be ground and an abrasive contact surface area of ​​a rotating grinding tool (7) are pressed against each other. The object of the invention is to create a method and a device for grinding rod-shaped workpieces that are easy to implement and flexible to use in practice. This task is solved by the contact surface area of ​​the grinding tool (7) forming a contact line that is particularly concave, and by moving the rotating grinding tool (7) and the workpiece (5, 5') relative to each other in order to grind the entire surface of the workpiece (5, 5').

Description

Technical area

[0001] The invention relates to methods for grinding rod-shaped workpieces, in particular welding electrodes, in which a surface area of ​​the workpiece to be ground and an abrasive contact surface area of ​​a rotating grinding tool are pressed against each other. The invention further relates to a grinding device for carrying out such a method. State of the art

[0002] In resistance welding of metal sheets, high-intensity electric currents are introduced into the sheets through two electrodes pressed against the outer surfaces of the sheets to be welded. This melts the metal of the sheets, forming a weld nugget that firmly bonds adjacent sheets together. The same applies to welding other metallic components. The welding electrodes are typically made of copper or copper alloys. Especially in aluminum resistance welding, the ideal shape and clean surface of the welding electrodes are essential for producing a weld spot of high and reproducible quality.Even just welding a few spot welds, say ten to twenty, can damage the surfaces of the welding electrodes due to deposits and wear, resulting in welds that do not have the desired strength. For this reason, welding electrodes are reworked at regular intervals to ensure their surfaces retain their optimal shape and are free of contaminants after each welding operation. Grinding the welding electrodes is a well-known method for reworking the surfaces of welding electrodes.

[0003] Several methods and devices for processing welding electrodes are known from the prior art. For example, FR 2 738 518 A1 discloses a cutting head whose cutting edges are curved so that, when rotated about the cutting head's rotational axis, they create the desired contour on the end face of the welding electrodes. A welding electrode surface produced by cutting has the disadvantage of being too smooth. Surfaces produced by grinding exhibit a certain roughness, which experience has shown to lead to better welding results. This roughness is caused by the cutting edges of the abrasive particles of the grinding tool, which create grinding marks on the surface along their trajectory.

[0004] For this reason, the applicant has developed a grinding process in which a grinding wheel rotating around a rotational axis, the surfaces of which extend radially to the rotational axis forming the abrasive grinding surfaces, performs a wobbling motion around the center of the end face of the welding electrode. In this way, the end face of the welding electrode is ground in the form of a convexly curved cap and has grooves in the surface created by the grinding wheel, which impart the desired roughness. The applicant's publication US 9 573 237 B2 describes a mechanical rotary and wobbling drive for the grinding wheel. The applicant's publication US 9 579 770 B2 describes a rotary drive coupled to a digitally controlled actuator to impart the desired wobbling motion to the grinding wheel.

[0005] Both systems have proven effective in producing the specified cap-shaped electrode surface for welding electrodes. However, the motion controls for the grinding wheels are somewhat complex to manufacture. Summary of the invention

[0006] The object of the invention is to provide a method and a device for grinding rod-shaped workpieces which are easy to implement and flexible to use in practice.

[0007] This problem is solved by the features of the independent patent claims.

[0008] The method described here for grinding rod-shaped workpieces, in particular welding electrodes, in which a surface area of ​​the workpiece to be ground and an abrasive contact surface area of ​​a rotating grinding tool are pressed against each other, is characterized in that a contact line is formed at the contact surface area of ​​the grinding tool and that the rotating grinding tool and the workpiece are moved relative to each other in order to grind the entire surface of the workpiece to be ground.

[0009] Similar to FR 2 738 518 A1, the machining tool at least partially defines the contour that the workpiece to be machined will have. However, unlike FR 2 738 518 A1, the machining tool is not a face milling cutter but a grinding wheel with a contact surface area that forms linear contact with the end face of the welding electrode and can be concavely curved to form a spherical end face. By machining with a grinding wheel, small grooves and score lines can be created on the machined surface. These are generated by the grinding particles and give the surface the desired roughness. Such finely structured surfaces are ideal as the contact surface of a welding electrode because they ensure conductive contact with a metallic material against which it is pressed.However, when a spherically curved or otherwise shaped end face of a rod-shaped welding electrode is pressed against an abrasive contact surface, only a linear contact is created. This method does not allow for full-surface machining of the spherical surface of the welding electrode.

[0010] For this reason, the rotating grinding tool and the workpiece are moved relative to each other in order to grind the entire surface of the workpiece to be ground. A hybrid servomechanical grinding process is therefore proposed in which, in one plane, the curvature is mechanically imposed by the curvature of the contact area between the workpiece and the tool, and in the other plane, the curvature is caused by the relative movement between the workpiece and the tool. In one embodiment, the generated contour of the end face of the welding electrode can be spherical, i.e., convexly curved. In this embodiment, the contact surface area of ​​the grinding tool can be concavely curved, so that the contact line is also concave.

[0011] In an embodiment in which the abrasive contact surface area of ​​the grinding tool is formed by a concave, annular groove on the side surface of a grinding wheel, the welding electrode is pressed against the concave contact surface area of ​​the grinding tool parallel to the axis of rotation of the grinding wheel.

[0012] In one design variant in which the abrasive surface area of ​​the grinding tool is formed by a circumferential surface of a grinding wheel, the welding electrode is pressed radially against the circumferential surface of the grinding wheel. The circumferential surface of the circular grinding wheel is convexly curved in the circumferential direction. In the axial direction, the circumferential surface can be concavely curved to create a concavely curved contact line. However, it can also be convexly curved to create a convexly curved contact line. This then creates an annular end face of the welding electrode, which creates annular contact during welding. An annular contact area can be very advantageous in practical applications. For this purpose, the relative movement between the welding electrode and the grinding tool can take place as a rotation around the axis of the welding electrode.A depression then forms in the center of the face, and the contact area effective during welding is ring-shaped. However, it is also possible to move a spherically curved grinding wheel along an arc perpendicular to the curved contact line along the face of the welding electrode. In this case, too, a face with a depression is created on the welding electrode. The face of the welding electrode is preferably rotationally symmetrical.

[0013] The abrasive particles are preferably formed from diamond particles or other high-strength grinding particles such as cubic boron nitride (CBN). The grinding particles can be applied, in particular electroplated, to a deformable metal foil. The metal foil, in turn, can be applied, in particular glued, to a rubber-elastic, deformable support layer of the grinding wheel. A manufacturing process for such a grinding wheel is described in DE 10 2016 119 746 A1. The flexible, yet high-strength attachment of the grinding particles to the metal foil allows for an optimal processing tool for welding electrodes. The flexible grinding surface prevents hard impacts and shocks during the grinding process. At the same time, the grinding particles are firmly anchored to the metal foil. Such grinding tools have a long service life.

[0014] It is also possible to mount the grinding wheel drive motor on a flexible mount, thus achieving a certain springiness of the grinding surface. Alternatively or additionally, the grinding wheel drive axle can be mounted flexibly, e.g., by the magnetic forces acting on the rotor of an external rotor. Likewise, the grinding wheel can be mounted flexibly on the drive motor axle, e.g., by using elastic O-rings.

[0015] In a practical embodiment of the method, the rod-shaped workpiece can be pressed axially against the abrasive contact surface area, and during the relative movement between the rotating grinding tool and the workpiece, the grinding tool can be rotated about the longitudinal axis of the workpiece. The welding electrode can be rotated about its own longitudinal axis while its end face is pressed against the, for example, concavely curved contact surface area of ​​the grinding tool, making contact with it along the contact line. The aim should be for the longitudinal axis of the welding electrode to be perpendicular to the contact surface area during the pressing process. In this case, the contact line runs through the center of the end face of the welding electrode. By rotating through an angle of 180°, the contact line sweeps across the entire end face of the welding electrode.A 180° rotation of the welding electrode is possible if the welding electrode is held in a movable manner. For example, the welding electrode can be attached to a welding gun carried by a robot arm. The robot arm is digitally controlled and can perform any movement in space. The robot arm can be controlled such that it presses the welding electrode axially against the contact surface area of ​​the grinding tool, thereby rotating the welding electrode 180°. In practice, however, it may be necessary to leave the welding electrode at rest during the grinding process and move the grinding tool. Again, the grinding tool must be rotated such that the contact line, which runs diametrically across the end face of the welding electrode, sweeps over the entire end face.If the contact line is concave, a 180° rotation of the concave contact surface area of ​​the grinding wheel relative to the stationary face of the welding electrode creates a spherical face with a convex curvature that corresponds to the concave curvature of the contact surface area of ​​the grinding wheel. If the contact line is convex, however, a concavely curved face is created, with a depression in the center and an annular contact area at the edge of the welding electrode.

[0016] In an alternative embodiment, in which the rod-shaped workpiece is also pressed in the axial direction against the abrasive contact surface area, the relative movement between the rotating grinding tool and the workpiece can be brought about by the grinding tool being moved on a curved path in a plane of movement that runs transversely to the contact line and parallel to the longitudinal axis of the workpiece. In other words, the grinding tool, which contacts the end face of the welding electrode along the curved contact line, is moved along a curved path, in particular a circular path, during grinding. This curved path lies in a plane of movement that runs transversely and in particular at right angles to the contact line and extends parallel to the longitudinal axis of the rod-shaped workpiece. In the direction parallel to the contact line, the curvature of the contact line is impressed on the end face of the welding electrode.In the direction of the plane of movement, the curvature of the curved path is imprinted on the end face. Both curvatures overlap and, after the grinding process, result in a spherical shape of the end face if the contact line and the curved path are concavely curved relative to the end face. If, however, the contact line and the curved path are convexly curved relative to the end face of the welding electrode, a depression is created in the end face of the welding electrode, creating a ring-shaped contact area for welding.

[0017] Movement along a curved path can be achieved in various ways. For example, a mount for a drive motor, whose motor shaft drives the grinding wheel, can be attached to a motor-driven swivel arm that pivots around a specified radius. The entire mount with the grinding wheel then moves along a circular path. An XY drive, such as those found in plotters, can also be used to move the grinding wheel along a desired path along the surface of the workpiece.

[0018] In an alternative embodiment of the method, a holder for the rotating grinding tool can be arranged on a coupling gear equipped with two servomotors that allow the holder to be moved to any point within the adjustment range of a movement plane. Such a coupling gear can be manufactured inexpensively using simple means, requires little maintenance, and is very reliable to control. Stepper motors or servomotors can be used as servomotors for the two couplings.

[0019] To implement the grinding method described here, a device for grinding rod-shaped workpieces, in particular welding electrodes, is proposed, which device has a grinding tool, a rotary drive for the grinding tool and a pressing device which presses a surface area of ​​the workpiece to be ground and an abrasive contact surface area of ​​the rotating grinding tool against each other.

[0020] This device is characterized in that the contact surface area of ​​the grinding tool is a contact line, wherein a moving device moves the rotating grinding tool and the workpiece relative to each other in order to grind the entire surface of the workpiece to be ground.

[0021] This results in the advantages described above. With a simple grinding device design, this device can reliably produce a spherical end face with a uniform roughness due to the grinding marks of the grinding particles. This is done if the contact line on the surface of the grinding wheel is concavely curved and the grinding wheel is rotated around the axis of the welding electrode or guided along a concave path over the end face of the welding electrode. With a convex contact line, a depression can be created in the center of the welding electrode, allowing the end face to contact the workpiece along an outer ring area during welding.

[0022] The abrasive contact surface area of ​​the grinding tool can be formed by, for example, a concavely curved, annular groove on the side surface of a grinding wheel or by a concavely curved peripheral surface of a grinding wheel.

[0023] The pressing device can be a robot arm or a welding tongs that carries the welding electrode. However, it can also be formed by a movable holder for the grinding wheel. By means of this holder, the welding electrode can be pressed against the grinding wheel. The pressing device can be configured to press the rod-shaped workpiece in the axial direction against the abrasive contact surface area, wherein the moving device is configured to rotate the grinding tool relative to the workpiece about the longitudinal axis of the workpiece. Alternatively, with an axially acting pressing device, the moving device can be configured to move the grinding tool relative to the workpiece on a curved path in a movement plane that runs transversely to the contact line and parallel to the longitudinal axis of the workpiece.

[0024] In one embodiment, a holder for the rotating grinding tool can be arranged on a coupling gear provided with two servomotors that enable movement of the holder to any point within an adjustment range of a movement plane. This embodiment is explained in more detail in conjunction with the drawings.

[0025] In particular, this design enables a particularly simple and compact design of the grinding device. In practice, the grinding device, with the drive motor that rotates the grinding wheel and the movement device that generates the relative movement between the grinding wheel and the workpiece, can be designed as an integral component of the welding head or welding gun that houses the welding electrodes. Especially in precision welding heads for fastening small parts, the device for regrinding the welding electrodes can be integrated into the welding head in this way, allowing the electrodes to be regrinded without significant interruption to the welding process or requiring intervention by a technician.

[0026] Finally, the device described here can also be designed so that the abrasive contact surface area of ​​the rotating grinding tool is held resiliently relative to the workpiece. As described above, the grinding surface with the abrasive particles can have a resilient base. The grinding tool can be resiliently attached to the drive motor, or the mount for the drive motor of the grinding tool can be resiliently designed. The flexibility of the grinding surface relative to the end face to be machined prevents hard impacts against the end face and possible damage to the end face during the grinding process. Short description of the drawings

[0027] Further practical embodiments and advantages of the invention are described below in conjunction with the drawings. Fig. 1 shows a sectional view of a first embodiment of a grinding wheel with hub. Fig. 2 shows a second embodiment of a grinding wheel with drive motor. Fig. 3 shows a first embodiment of a mounting for the drive motor from Fig. 2 in a first rotational position. Fig. 4 shows the mount for the drive motor from Fig. 3 in a second rotation position. Fig. 5 shows a second embodiment of a holder for the drive motor of the grinding wheel from Fig. 2 with schematically shown welding electrodes. Fig. 6 shows the bracket made of Fig. 5 in front view. Fig. 7 shows the bracket from the Fig. 5 and Fig. 6 in side view. Fig. 8 shows the coupling mechanism from the Fig. 5-7 in a first position. Fig. 9 shows the coupling gear from Fig. 8. a second position. Fig. 10 shows one of the Fig. 7 corresponding side view with the position of the coupling gear from Fig. 9. Fig. 11 shows a schematic representation of the coupling mechanism in a position corresponding to that shown in Fig. 9 corresponds to the position shown. Fig. 12 shows three of the Fig. 11 corresponding representations of the coupling gear in three different positions for processing the upper welding electrode. Fig. 13 shows the Fig. 12 corresponding representations of the coupling gear in positions for processing the lower welding electrode. Description of the embodiments

[0028] The Fig. 1 shows a first embodiment of a grinding wheel 1, which forms the grinding tool for carrying out the method described here. The grinding wheel 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). Grinding wheels are usually rotated at speeds of over 1,000 revolutions per minute. The grinding wheel 1 is intended for side grinding and has, on its upper side surface running perpendicular to the axis of rotation 3, a flat annular groove 4 with a slightly concave curve. The grinding wheel 1 is circular in plan view. The groove 4, which is concave in the radial direction of the grinding wheel 1, extends in an annular region on the circular grinding wheel 1. In the right half of the Fig. 1 schematically shows a welding electrode 5 which forms the rod-shaped workpiece. The welding electrode 5 has a longitudinal axis 6 and a cap-shaped end face which is pressed axially into the annular groove 4 of the grinding wheel 1 with a concavely curved surface. If the welding electrode 5 is attached to welding tongs, which in turn are attached to a robot arm, the welding electrode 5 can be rotated about its longitudinal axis 6 so that the concave curvature of the annular groove 4 is impressed on the entire end face of the welding electrode 5, giving this end face the shape of a uniformly curved cap. Grinding removes contaminants from the end face, creating a uniform surface with fine grooving caused by the grinding particles.

[0029] The Fig. Figure 2 shows an alternative embodiment of a grinding wheel 7. This grinding wheel 7 is intended for peripheral grinding. This means that the grinding wheel 7 has abrasive particles, preferably diamond particles or CBN particles, on its axially concave peripheral surface 9. A shaft 10 is integrally formed on the grinding wheel 7 and is rotated at high speed about the rotational axis 8 by a drive motor 11. Fig. 2 also shows the welding electrode 5, which is pressed in the radial direction of the grinding wheel 7 against its concavely curved circumferential surface 9. This also creates a linear contact along a concavely curved contact line between the grinding wheel 7 and the welding electrode 5. Again, by rotating the welding electrode 5 about its longitudinal axis 6 by a rotation angle of 180°, the entire end face of the welding electrode 5 is machined by the circumferential surface 9 of the grinding wheel 7. As an alternative to rotating the welding electrode 5, the grinding wheel 9 can be Fig. 2. If a grinding wheel with a convex circumferential surface in the axial direction is used (not shown in the drawing), a central depression can be created on the end face of the welding electrode so that only the annular outer region of the end face of the welding electrode contacts the workpiece during welding.

[0030] This is shown schematically in the Fig. 3 and Fig. 4. The drive motor 11 is mounted on a turntable 13 by a motor mount 12. The turntable 13 can be moved from the first Fig. 3 shown position by 180° into a second, in Fig. 4. This rotation is shown in Fig. 3 by the arrow 28. It can be seen that the center of the turntable 13 lies on the longitudinal axis 6 of the welding electrode 5. The rotation causes the contact line between the grinding wheel 7 and the welding electrode 5 to sweep over the entire end face of the welding electrodes 5 once. In this way, the curvature of the peripheral surface 9 of the grinding wheel 7 is transferred to the end face of the welding electrode 5, which thereby takes on a spherical cap shape with regular grooves. While the grinding wheel 7 is rotated at high speed, the rotation of the turntable through 180° takes place slowly, e.g., over a period of one or more seconds.

[0031] The Fig. Figure 5 shows an alternative embodiment of a mount for the drive motor 11 of a grinding wheel 7. In this embodiment, the grinding wheel 7 is not rotated about the longitudinal axis of the welding electrode 5, but rather is guided along a curved path that lies in a plane substantially perpendicular to the contact line. The curvature of the contact line between the grinding wheel 7 and the welding electrode 5 and the curvature of the curved machining path overlap, imparting a spherical shape to the end face of the welding electrode 5. The curved machining path is generated by means of a coupling gear.

[0032] The components of the holder of the drive motor 11 for the grinding wheel 7 are optional in Fig. 8. The holder for the drive motor 11 is formed in this embodiment by a free end 14 of a first coupling 15, the other end of which is connected via a first joint 17 to a first crank 16 of a first servomotor 18. In the illustrated embodiment, the first coupling 15 has the shape of a cranked lever. A second coupling 19 is connected at one end via a second joint 21 to a second crank 20 of a second servomotor 22 and via a third joint 23 to the first coupling 15. The third joint 23 is located approximately in the region of the crank of the first coupling 15. In Fig. 5 shows that the stepper motors 18 and 22 are attached to a support plate 24. By rotating the cranks 16 and 20 by means of the stepper motors 18, 22, the free end 14 of the first coupling 15, which forms the holder for the drive motor 11 of the grinding wheel 7, can be moved within an adjustment range in a plane parallel to the support plate 24.

[0033] The support plate 24 is located to the side of an electrode holder 25 of a welding device, which is used as Fig. 5 is shown as a transparent plate for reasons of clarity and carries two welding electrodes 5, 5'. Since the coupling mechanism allows the grinding wheel 7 to be moved essentially freely in a plane perpendicular to the axis of rotation of the grinding wheel 7, it can be moved both toward the upper welding electrode 5 and toward the lower welding electrode 5' in order to machine the end face with the grinding wheel 7.

[0034] After machining, in which the coupling gear has approximately the Fig. 8 shown position, the coupling gear can be moved to the position shown in the Fig. 9, in which the grinding wheel 7 and its drive motor 11 are at the maximum distance from the welding electrodes 5, 5'. In this rest position, the grinding wheel 7 does not interfere with the welding process by means of the welding electrodes, as in Fig. 10. If reworking of the end faces of the welding electrodes 5, 5' is required, the grinding wheel is returned to the position shown in Fig. 5 - 7 recognizable position moved.

[0035] The Fig. 11 shows the rotational position of the servomotors which move the grinding wheel to the Fig. 10 shown position. The Fig. Figure 11 is only a schematic representation of the coupling mechanism. The rotational axis 26 of the first servomotor and the rotational axis 27 of the second servomotor are shown here. The couplers 15, 19 and the cranks 16, 20 are shown only as lines. Furthermore, the machining path 29 for the end face of the upper welding electrode 5 and the machining path 30 for the end face of the lower welding electrode 5' are shown schematically. When the rotational axis 8 of the grinding wheel moves along the machining path 29 or 30, the concavely curved circumferential surface 9 of the grinding wheel 7 makes linear contact with the respective welding electrode 5 or 5' to be machined. For both cranks 16 and 20, the crank angle is shown relative to a zero position extending horizontally to the right. Fig. 11, the crank angle α between the first crank 16 and the zero position is 328.91°. The crank angle β of the second crank 20 in the position of the coupling gear in Fig. 11 has a value of 148.97°.

[0036] Starting from this position, the cranks 16, 20 can be rotated to move the rotational axis 8 of the grinding wheel, for example, close to the machining path 29 of the upper welding electrode 5.

[0037] The Fig. 12 A, B, and C show three positions of the coupling gear during machining of the upper welding electrode. It can be seen that the machining path 29 is concavely curved, so that the rotational axis 8 of the grinding wheel moves along a concave machining path 29. As a result, the peripheral surface is moved along the concave machining path 29 past the end face of the welding electrode 5. The concave contour of the peripheral surface of the grinding wheel overlaps the concave movement path of the rotational axis 8 of the grinding wheel, thus creating a cap-shaped contour on the end face of the upper welding electrodes 5.

[0038] The Fig. 13 shows in the representations A, B and C three positions of the rotational axis 8 of the grinding wheel on the machining path 30 for the lower welding electrode 5'.

[0039] If the peripheral surface of the welding electrode is convex rather than concave in the axial direction, the motion sequence of the coupling gear can be reversed. This means that the grinding wheel is moved along a convex path toward the welding electrode during grinding and pressed into its end face until it reaches the center. It is then moved away from the welding electrode again in the axial direction. This results in a hollow in the center of the end face of the welding electrode rather than a spherical end face. This gives the end face of the welding electrode an axially projecting annular surface on its outer circumference, which contacts the workpiece during welding.

[0040] The features of the invention disclosed in the present description, the drawings, and the claims may be essential, both individually and in any combination, for the realization of the invention in its various embodiments. The invention is not limited to the described embodiments. It may be varied within the scope of the claims and taking into account the knowledge of the person skilled in the art. List of reference symbols 1 grinding wheel, grinding tool 2 Hub 3 Rotation axis of the grinding wheel 4 concave annular groove 5, 5' welding electrode, workpiece 6 Longitudinal axis of the welding electrode 7 Grinding wheel, grinding tool 8 Rotation axis of the grinding wheel 9 concavely curved peripheral surface 10 Shaft of the grinding wheel 11 Drive motor 12 Engine mount 13 turntables 14 free end of the first coupling, bracket 15 first paddock 16 first crank 17 first joint 18 first actuator 19 second paddock 20 second crank 21 second joint 22 second actuator 23 third joint 24 Support plate 25 electrode holders 26 Rotation axis of the first servo motor 27 Rotation axis of the second servo motor 28 Arrow 29 Processing path for the upper welding electrode 30 Processing path for the lower welding electrode QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] FR 2 738 518 A1 [0003, 0009] US 9 573 237 B2

[0004] US 9 579 770 B2

[0004] DE 10 2016 119 746 A1

[0013]

Claims

[1] Method for grinding rod-shaped workpieces, in particular welding electrodes (5, 5'), in which a surface area of the workpiece (5, 5') to be ground and an abrasive contact surface area of a rotating grinding tool (1, 7) are pressed against each other, characterized by that a contact line is formed at the contact surface region of the grinding tool (1, 7), and that the rotating grinding tool (1, 7) and the workpiece (5, 5') are moved relative to each other in order to grind the entire surface of the workpiece (5, 5') to be ground. [2] Method according to claim 1, characterized by that the contact surface area of the grinding tool (1, 7) is concavely curved, so that the contact line is also concavely curved. [3] Method according to claim 1 or 2, characterized by that the abrasive contact surface area of the grinding tool is formed by a concave, annular groove on the side surface of a grinding wheel (1). [4] Method according to claim 1 or 2, characterized by that the abrasive surface area of the grinding tool is formed by a peripheral surface of a grinding wheel (7). [5] Method according to claim 4, characterized by that the circumferential surface is concavely curved in the axial direction of the grinding wheel (7). [6] Method according to one of the preceding claims, characterized by that the rod-shaped workpiece (5, 5') is pressed in the axial direction against the abrasive contact surface area and during the relative movement between the rotating grinding tool (1, 7) and the workpiece (5, 5') the grinding tool (1, 7) is rotated about the longitudinal axis of the workpiece (5, 5'). [7] Method according to one of the preceding claims, characterized bythat the rod-shaped workpiece (5, 5') is pressed in the axial direction against the abrasive contact surface area and during the relative movement between the rotating grinding tool (7) and the workpiece (5, 5'), the grinding tool (7) is moved on a curved path (29, 30) in a plane of movement which runs transversely to the contact line and contains the longitudinal axis of the workpiece (5, 5'). [8] Method according to claim 7, characterized by that a holder (24) for the rotating grinding tool (7) is arranged on a coupling gear which is provided with two servomotors (18, 22) which enable movement of the holder (24) to any point within an adjustment range of a movement plane. [9] Method according to one of the preceding claims, characterized bythat the surface area of the workpiece (5, 5') to be ground and the abrasive contact surface area of the rotating grinding tool (1, 7) are pressed resiliently against each other. [10] Device for grinding rod-shaped workpieces, in particular welding electrodes (5, 5'), with a grinding tool (1, 7), a rotary drive for the grinding tool and a pressing device which presses a surface area of the workpiece (5, 5') to be ground and an abrasive contact surface area of the rotating grinding tool (1, 7) against each other, characterized by in that the contact surface area of the grinding tool (1, 7) is a contact line, wherein a moving device moves the rotating grinding tool (1, 7) and the workpiece (5, 5') relative to each other in order to grind the entire surface of the workpiece (5, 5') to be ground. [11] Device according to claim 10, characterized by that the contact line is concave. [12] Device according to claim 11, characterized by that the abrasive contact surface area of the grinding tool - is formed by a concave, annular groove on the side surface of a grinding wheel (1) or - is formed by a concavely curved peripheral surface of a grinding wheel (7). [13] Device according to claim 10, 11 or 12, characterized by that the pressing device is designed to press the rod-shaped workpiece (5, 5') in the axial direction against the abrasive contact surface area, and that the moving device is designed to rotate the grinding tool (1, 7) relative to the workpiece (5, 5') about the longitudinal axis of the workpiece (5, 5'). [14] Device according to one of the preceding claims 10-13, characterized byin that the pressing device is designed to press the rod-shaped workpiece (5, 5') in the axial direction against the abrasive contact surface area, and in that the moving device is designed to move the grinding tool (7) relative to the workpiece (5, 5') on a curved path (29, 30) in a plane of movement which runs transversely to the contact line and parallel to the longitudinal axis of the workpiece (5, 5'). [15] Device according to claim 14, characterized by that a holder (14) for the rotating grinding tool (7) is arranged on a coupling gear which is provided with two servomotors (18, 22) which enable the holder (14) to be moved to any point within an adjustment range of a movement plane. [16] Device according to one of the preceding claims 10-15, characterized bythat the abrasive contact surface area of the rotating grinding tool (1, 7) is held resiliently relative to the workpiece (5, 5'). [17] Device according to one of claims 10-16, characterized by that it is an integrated part of a welding head or welding gun.

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