NL2022864B1 - Method for resistance welding and resistance welding apparatus - Google Patents
Method for resistance welding and resistance welding apparatus Download PDFInfo
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- NL2022864B1 NL2022864B1 NL2022864A NL2022864A NL2022864B1 NL 2022864 B1 NL2022864 B1 NL 2022864B1 NL 2022864 A NL2022864 A NL 2022864A NL 2022864 A NL2022864 A NL 2022864A NL 2022864 B1 NL2022864 B1 NL 2022864B1
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- longitudinal axis
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/10—Spot welding; Stitch welding
- B23K11/11—Spot welding
- B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/30—Features relating to electrodes
- B23K11/31—Electrode holders and actuating devices therefor
- B23K11/314—Spot welding guns, e.g. mounted on robots
- B23K11/315—Spot welding guns, e.g. mounted on robots with one electrode moving on a linear path
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/30—Features relating to electrodes
- B23K11/3063—Electrode maintenance, e.g. cleaning, grinding
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Robotics (AREA)
- Resistance Welding (AREA)
Abstract
The present invention relates to a method for resistance welding of workpieces, e.g. 5 aluminium workpieces, using a resistance welding apparatus. The resistance welding apparatus comprises electrodes with a respective electrode tip, a pressing device to press the workpieces in between the electrode tips, and a welding power supply to generate an electric current between the electrodes. The method comprises the steps of positioning the workpieces against each other 10 positioning the workpieces in between the electrode tips, pressing the workpieces in between the electrode tips, and generating, during the pressing, an electric current between the electrodes to form a weld between the workpieces. At least during the pressing of the workpieces, the electrodes are set at a non-right angle with respect to contact surfaces of the workpieces. 15 The present invention further relates to a welding apparatus of which, at least in a press configuration of a pressing device, the electrodes are adapted to be set at a non- right angle with respect to a contact surfaces of the workpieces.
Description
P33966NLOO/TRE Title: Method for resistance welding and resistance welding apparatus The present invention relates to a method for resistance welding by means of a resistance welding apparatus. The present invention further relates to a resistance welding apparatus.
In the field, it has been known to join workpieces by means of a resistance welding process. In particular in the automotive industry, such “spot-welding” processes are known for the welding of metal workpieces. For the welding, these workpieces are pressed between electrodes of a resistance welding apparatus. Then, an electric current is provided between the electrodes, which passes through the workpieces. The electric current causes local heating and melting of the workpieces and does, when the current is taken away, allow the metal of both workpieces to solidify and to join the workpieces together.
The electrodes of a resistance welding apparatus are generally provided with electrode tips that are configured to contact the workpieces. Generally, these electrode tips are made of a copper material, which may provide for the best possible conduction of the electric current. However, the copper material has the disadvantage that it may react with the workpieces during the welding process. These reactions may cause alloying of the electrode tip with the workpieces and may cause degradation of the electrode tips, an increased amount of wear and a reduced lifespan.
Several solutions are already provided for increasing the lifespan of the electrodes. From European patent application EP 0 384 484 A1, it is known to provide electrodes with a rotatable tip. In this publication, the tip is rotated with respect to the electrode during the weld, or after the forming of one or more welds. This rotation provides that the contact area of the electrode tip, where it contacts the workpiece, may be different after one or more welds. However, this rotation system makes the welding apparatus more complex. Furthermore, it is known from EP 1 838 484 A1 to rotate an entire welding tong during welding, in order to rotate the electrode tips with respect to the workpieces.
It is therefore an object of the present invention to provide a welding method, for which the lifespan of the electrode tips may be increased, but which may not require a significantly more expensive welding apparatus to carry out the method.
The present invention thereto provides a method for resistance welding of a first workpiece and a second workpiece, using a resistance welding apparatus, wherein the first workpiece comprises a first welding surface and an opposing first contact surface and wherein the second workpiece comprises a second welding surface and an opposing second contact surface, wherein the resistance welding apparatus comprises:
a first electrode, which comprises a first electrode tip with a first longitudinal axis, a second electrode, which comprises a second electrode tip with a second longitudinal axis, a pressing device, configured to move the first electrode and the second electrode with respect to each other, in order to press the first workpiece and the second workpiece in between the first electrode tip and the second electrode tip, and a welding power supply, which is electrically connected to the first electrode and the second electrode and which is configured to generate an electric current between the first electrode and the second electrode, and wherein the method comprises the steps of: - positioning the first welding surface of the first workpiece and the second welding surface of the second workpiece against each other, - positioning the first workpiece and the second workpiece in between the first electrode tip and the second electrode tip, - pressing the first workpiece and the second workpiece in between the first electrode tip and the second electrode tip, wherein the first electrode tip contacts the first contact surface and wherein the second electrode tip contacts the second contact surface, and - generating, during the step of pressing, an electric current between the first electrode and the second electrode in order to form a weld between the first workpiece and the second workpiece, wherein at least during the step of pressing the first workpiece and the second workpiece, the first longitudinal axis of the first electrode tip is set at a first non-right angle with respect to the first contact surface and the second longitudinal axis of the second electrode tip is set at a second non-right angle with respect to the second contact surface.
The method according to the present invention may be used to join a first workpiece and a second workpiece, wherein the joint is formed by a welded connection. For the welding, a welding surface of the first workpiece is positioned against a welding surface of the second workpiece. Each of the workpieces further comprises a contact surface, which opposes the respective welding surface. When the welding surfaces are positioned against each other, the contact surfaces may face away from each other.
Preferably, the workpieces are sheet-like elements, wherein the welding surfaces and the contact surfaces may be at least partially flat. When the welding surfaces are positioned on top of each other, these surfaces may become aligned parallel. Accordingly, the flat contact surfaces of both workpieces may thereby be aligned flat as well.
However, the workpieces do not need be flat, but may as well be provided as profiled elements. For the welding of these workpieces, it may be required that the welding surfaces can be positioned against each other and that the opposing contact surfaces may be contacted with the electrodes of the welding apparatus.
In an embodiment, the method may not only relate to the welding of a first workpiece and a second workpiece, but may further comprise the welding of a third workpiece. This third workpiece may comprise opposing welding surfaces and may be positioned in between the first workpiece and the second workpiece. As such, the first welding surface of the first workpiece may be pressed against a first one of the welding surfaces of the third workpiece and the second welding surface of the second workpiece may be pressed against a second one of the welding surfaces of the third workpiece, in order to provide that the first welding surface of the first workpiece and the second welding surface of the second workpiece are indirectly pressed against each other.
Alternatively, or additionally, an adhesive may also be present in between the first workpiece and the second workpiece during the welding. This adhesive may be provided on the first welding surface of the first workpiece and/or on the second welding surface of the second workpiece, before the respective welding surfaces are positioned against each other. The adhesive may contribute in the controlling of the formed weld and may be configured strengthen the connection between the first workpiece and the second workpiece.
The welding method according to the present invention may be carried out by means of a welding apparatus. The welding apparatus comprises a first electrode and a second electrode. Both of these electrodes may comprise shaft portions that have a cylindrical shape. Each of the electrodes comprises a respective electrode tip, which is connected to a respective shaft portion of the electrode and which extends along its respective longitudinal axis, wherein the electrode tips are configured to contact the contact surfaces of the workpieces. The electrode tips may be positioned on head ends of the electrodes and a first electrode tip of a first electrode may be arranged opposite to a second electrode tip of a second electrode. A passage may be defined in between the electrode tips, which may be arranged to receive the workpieces therein.
In an alternative embodiment, the shaft portions of the electrodes do not necessarily need to be provided as cylindrical electrodes. One or more of the electrodes may, for example, comprise a bent shaft portion and/or a cone-shaped shaft portion. Preferably, both of the shaft portions of the electrodes have the same shape and the electrode tips of both electrodes preferably face each other.
The welding apparatus for use in the method according to the invention further comprises a pressing device. The pressing device may comprise a set of lever arms, to which the electrodes are connected. The pressing device may be configured to move the lever arms, in order to move the electrodes with respect to each other between a released configuration and a press configuration.
In the released configuration of the pressing device, the electrode tips are set at a distance from each other. As such, a gap may be present in between the electrodes, which may allow for the receipt of the workpieces in between the electrode tips. In the press configuration of the pressing device, the electrode tips are moved towards each other. As such, the pressing device may press the workpieces in between the electrode tips.
Preferably, the pressing device comprises a motor device, which may be configured to initiate the movement of the electrodes and, preferably, to initiate the movement of the lever arms of the pressing device.
The lever arms of the pressing device may be in a C-type configuration, in which the lever arms together resemble the shape of a “C” and in which the electrodes are provided at the ends portions of the “C”. Alternatively, the lever arms of the pressing device may be in an X-type configuration, in which a rotatable joint is present at the crossing of both lever arms and wherein the electrodes are provided at a respective end portion of the opposing lever arms.
The welding apparatus further comprises a welding power supply, which is electrically connected to the first electrode and the second electrode. As such, an electric circuit may be formed by the electrodes and the power supply. In particular when the electrode tips are electrically connected, either by a direct connection or via one or more workpieces in between the tips, an electric current may be generated, which may flow between the first electrode and the second electrode. If the electric current flows through the workpieces, the current may initiate local heating of the workpieces, at least in the portions of the workpieces that are pressed in between the electrode tips. The local heating may cause local melting of the workpieces and fusion of the molten material of the workpieces. The molten workpiece material is allowed to solidify when the current is no longer applied, such that the workpieces become connected by means of a weld that is formed as a result.
For carrying out the method according to the invention, the welding surfaces of the workpieces are positioned against each other. The workpieces are thereby brought in a relative position and orientation that substantially corresponds to the final position in which they should be after welding. By the pasitioning, the welding surfaces face each other and both extend substantially parallel to each other. Accordingly, the opposing contact surfaces of the workpieces face away from each other in an outward direction.
Preferably, the contact surface of each of the workpieces extends parallel to the respective welding surface, which implies that the contact surfaces of both workpieces may be aligned parallel to each other as well, at least after the positioning of the workpieces.
The method further comprises the step of the positioning the workpieces in between the electrode tips. This step may take place after the workpieces have been positioned with respect to each other, but may as well take place before the relative positioning between the workpieces. During the positioning in between the electrode tips, the respective contact surfaces of the workpieces face towards the respective electrode tips. As such, the electrode tips may be positioned against the contact surfaces, in order to weld the workpieces.
The method further comprises the step of the pressing of the workpieces in between the 5 electrode tips. The electrodes are thereby moved towards each other, e.g. by means of the pressing device. The workpieces are arranged in between the electrodes, which implies that the first electrode tip contacts the first contact surface and that the second electrode tip contacts the second contact surface.
The pressing may take place at a certain pressing force that is applied by the electrodes. The pressing force may, amongst other welding parameters, be set in order to control one or more properties of the weld that is to be provided.
The method further comprises the step of generating an electric current between the electrodes to form a weld between the first workpiece and the second workpiece. This generating of the current takes place at least when the workpieces are pressed against each other by the electrode tips. The electric current locally causes melting of the workpieces, at least of the portions of the welding surfaces that are pressed between the electrodes. The melting of both workpieces may cause the molten metal to fuse together.
The magnitude of the electric current may be adapted in order to control properties of the weld that is formed. Accordingly, the duration for which the current is applied may be adapted in order to control the weld properties.
When the desired duration for the electric current has lapsed, the current is no longer applied. The heating of the workpieces is thereby cancelled, which may result in solidification of the molten metal. As a result of the fusion between the molten material of both workpieces, the solidification causes both workpieces to become fixedly connected to each other.
During the solidification, after the electric current has been cancelled, the pressing by the electrodes may continue during the solidification of the molten metal. As such, the relative orientation between the workpieces may be safeguarded until the welded material has been completely solidified. Furthermore, this ongoing pressing may influence the mechanical properties of the weld that is formed. The pressing force and/or duration of the pressing after cancelling the electric current may be adapted to control the weld properties.
According to the present invention, at least during the pressing of the workpieces, the first longitudinal axis of the first electrode tip is set at a non-right angle with respect to the first contact surface and the second longitudinal axis of the second electrode tip is set at a non- right angle with respect to the second contact surface. As opposed to known welding methods, the advantageous effect of the invention may be achieved when the electrodes are not set perpendicular to the contact surfaces of the workpieces.
The method according to the present invention may, for example, be carried out by means of a spot welding robot, but may as well be carried out by means of a stationary spot welding device.
The first longitudinal axis may be set at a non-right angle with respect to the plane of the first contact surface, and preferably also with respect to the plane of the first welding surface. Moreover, this angular orientation may also be characterized by a non-zero angle between the first longitudinal axis of the first electrode tip and the normal direction of the first contact surface. Similarly, the second longitudinal axis may be set at a non-right angle with respect to the plane of the second contact surface, and preferably also with respect to the plane of the second welding surface. Moreover, this angular orientation may also be characterized by a non-zero angle between the second longitudinal axis of the second electrode tip and the normal direction of the second contact surface.
The non-right positioning of the electrodes on the contact surfaces provides for an increased lifespan of the electrodes, and in particular of the electrode tips that contact the contact surfaces of the workpieces. It has been found by the applicant that the quality of the formed welds has been improved and has become more stable, e.g. a more constant weld quality over time for subsequent welds, for example a more constant diameter of the weld.
The applicant has surprisingly found that the lifespan of the electrode tips, e.g. the amount of welds that can be made until critical degradation of the tips would occur, could be increased by a factor three or more, when the welding is carried out by means of the method according to the invention. For example for the welding of 0.8 — 1 mm aluminium sheets, the normal lifespan of electrode tips could be 50 spots, whereas the inventive method may provide for at least 150 spots. For welding 1 — 2 mm aluminium sheets, the lifespan may even be increased to at least 250 spots.
The inventive method may provide for an increased lifespan of the electrode tips, and may thus provide for lower operational costs. Hence, the inventive method requires fewer replacements of the tips and/or fewer cleaning of the tips, since the amount of spots that lead to critical degradation may be significantly increased.
In an embodiment, the first electrode tip and the second electrode tip comprise a copper material. As such, the tips may be made of copper or of a copper alloy, such as a CuCrZr alloy, which comprises copper. Alternatively, the electrode tips may comprise a tungsten material.
In an embodiment of the method, at least during the step of pressing the first workpiece and the second workpiece, the first non-right angle between a normal direction of the first contact surface and the first longitudinal axis is larger than 4°. Accordingly, the second non- right angle between a normal direction of the second contact surface and the second longitudinal axis is larger than 4° as well. Similarly, these orientations may also be characterized in that the angle between the longitudinal axes of the respective electrodes and the planes of the respective contact surfaces is smaller than 86°.
This embodiment of the method provides for an offset of at least 4° with respect to a perpendicular orientation of the electrodes. It has been found by the applicant that this angular orientation may provide for an increased lifespan of the electrode tips. In particular, an angle of more than 5° may lead to a more economic, and therefore more advantageous manner of carrying out the inventive method.
In an embodiment of the method, at least during the step of pressing the first workpiece and the second workpiece, the first longitudinal axis of the first electrode tip is aligned parallel to the second longitudinal axis of the second electrode tip. For the pressing of the workpieces, one or both of the electrodes may be moved towards each other in respective directions that are parallel to each other. Preferably, the first longitudinal axis of the first electrode tip is in line with the second longitudinal axis of the second electrode tip.
This embodiment may provide, in particular when the contact surfaces of the workpieces are aligned parallel to each other, that the angle between the first longitudinal axis of the first electrode tip and the first contact surface is the same as the angle between the second longitudinal axis of the second electrode tip and the second contact surface. This embodiment of the method may lead to a weld that is properly arranged at the interface between the welding surfaces of both workpieces. Furthermore, the quality and/or appearance of the weld may be the same at both the first contact surface and the second contact surface.
This embodiment may provide, in particular when the first non-right angle between the first electrode and the first contact surface is the same as the second non-right angle between the second electrode and the second contact surface, for a slight deformation of the workpieces. At least the portions of the workpieces that are pressed in between the electrodes may, in dependence of the applied pressing force, undergo a deformation that may be large enough to contribute to an increased lifespan of the electrode tips, but which may be small enough to maintain a sufficient quality and/or appearance of the weld.
In an additional embodiment, at least during the step of pressing the first workpiece and the second workpiece, the first longitudinal axis of the first electrode tip is aligned in line with the second longitudinal axis of the second electrode tip. Hereby, the first longitudinal axis is formed by the same line that forms the second longitudinal axis.
In this configuration of the electrodes, the weld is formed on the same line as well, in between the electrodes. As such, the location of the formed weld may be accurately controlled. Furthermore, a current density of generated electric current, e.g. the amount of current per unit of intersectional area, may be constant across the entire contact area between the contact surfaces of the workpieces and the corresponding electrode tips. Additionally, the current may flow along the same line between the electrodes as well. In an embodiment of the method, a shaft portion of the first electrode and the first electrode tip and/or a shaft portion of the second electrode and the second electrode tip are substantially stationary with respect to each other. As opposed to the welding method in cited prior art document EP 0 384 484 A1, the method according to this embodiment provides that both electrode tips remain stationary with respect to the shaft portions of their respective electrodes and with respect to each other. The tips are at least held stationary during the pressing of the workpieces and during the generating of the electric current. This may provide for an improved weld quality and for a less complex, and therefore less expensive welding apparatus. Preferably, the stationary positioning between the electrode tips and the shaft portions is obtained by fixedly clamping the electrode tips on the shaft portions of the respective electrodes, for example by means of a cone-shaped press fit connection.
After the weld has been made, and the pressing has been cancelled, the electrode tips may be allowed to move with respect to each other again, but preferably remain stationary with respect to their respective electrodes. The allowed relative movement preferably only concerns the relative movement between the electrodes, to allow removal of the welded workpieces and to allow entrance of two subsequent workpieces that have not been welded. Preferably, the relative orientation between the electrode tips becomes the same again when the subsequent workpieces are pressed.
In an embodiment, the first electrode tip and/or the second electrode tip comprises a rounded end surface, wherein a radius of curvature of the rounded end surface may be in the range between 50 mm and 150 mm.
According to this embodiment, the end surface of at least one of the electrode tips is curved. The amount of curvature may vary, for example in between a spherical end surface and an almost planar end surface. The amount of curvature may be defined as the ratio between the radius of the electrode itself and the radius of curvature of the rounded end surface. The radius of the electrode may be the outer radius of the electrode tip, which is measured radially with respect to the respective longitudinal axis of the electrode.
In case the end surface were to be a spherical end surface, a radius of the electrode tip is equal to the radius of curvature of the end surface. If the end surface were to be close to a planar end surface, the radius of curvature would be much larger than the radius of the electrode tip.
In an embodiment, the first workpiece and/or the second workpiece comprises an aluminium material. It has been found by the applicant that the inventive method provides a significant advantage during the welding of workpieces that are made at least partially from an aluminium material. It was found that the method according to this embodiment, wherein the workpieces comprise the aluminium material, typically prevents the electrode tips from reacting and alloying with the workpieces during the welding. This advantageous effect was in particular noted during the welding with electrode tips that reach the end of their lifespan, before critical degradation.
The present invention further provides a resistance welding apparatus. This welding apparatus may comprise one or more of the features that are described above in relation to the resistance welding apparatus that is used for carrying out the method according to the present invention. Similarly, any feature that is described below in relation to the welding apparatus according to the invention may as well be provided in the welding apparatus that is used in the method according to the invention.
The resistance welding apparatus according to the present invention is configured for the resistance welding of workpieces and comprises: a first electrode, which comprises a first electrode tip with a first longitudinal axis, a second electrode, which comprises a second electrode tip with a second longitudinal axis, a pressing device, configured to move the first electrode and the second electrode with respect to each other between a released configuration and a press configuration, wherein, in the released configuration of the pressing device, the first electrode tip and the second electrode tip are set at a distance from each other to allow for the positioning of the first workpiece and the second workpiece in between the first electrode tip and the second electrode tip, and wherein, in the press configuration of the pressing device, the first electrode tip and the second electrode tip are moved towards each other to press the first workpiece and the second workpiece in between the first electrode tip and the second electrode tip, and a welding power supply, which is electrically connected to the first electrode and the second electrode and which is configured to generate an electric current between the first electrode and the second electrode, characterized in that at least in the press configuration of the pressing device, the first longitudinal axis of the first electrode tip is adapted to be set at a first non-right angle with respect to a first contact surface of a first workpiece and the second longitudinal axis of the second electrode tip is adapted to be set at a second non-right angle with respect to a second contact surface of a second workpiece.
The welding apparatus according to the present invention comprises a first electrode and a second electrode, which both comprise a respective electrode tip. The apparatus further comprises a pressing device, which is connected to the first electrode and the second electrode for moving the electrodes between the released configuration and a press configuration.
In the released configuration, the electrodes are moved away from each other and are set at a distance from each. The distance is selected such, that a passage may be defined in between the electrode tips. The passage is configured to receive the workpieces that are to be welded, which may be positioned in between the electrode tips of the electrodes.
Preferably, the passage is dimensioned such that it may receive contact surfaces of the workpieces and that the electrodes of the welding apparatus face these contact surfaces.
In the press configuration, the electrodes are moved towards each other with respect to the released configuration. The electrode tips of the electrodes may thereby be brought into contact with the respective contact surfaces of the workpieces. In the press configuration, the pressing device is configured to apply a pressing force on the workpieces, in order to safeguard a relative position between the workpieces and to pre-stress the workpieces in advance of the forming of the weld.
The welding power supply of the welding apparatus according to the invention is connected to the first electrode and the second electrode and may be configured to provide an electric circuit as soon as the first electrode is in electrical contact with the second electrode, wherein the circuit may extend via the workpieces that are pressed in between the electrodes. The power supply is configured to induce an electric current between the first electrode and the second electrode in order to locally melt portions of the workpieces that are provided in between the electrodes, in order to form the weld between the workpieces.
Preferably, the welding power supply is configured to generate the electric current when the pressing device is in its press configuration and when it presses the workpieces together.
In the welding apparatus according to the present invention, at least in the press configuration of the pressing device, the first longitudinal axis of the first electrode tip is adapted to be set at a first non-right angle with respect to the first contact surface and the second longitudinal axis of the second electrode tip is adapted to be set at a second non-right angle with respect to the second contact surface. The welding apparatus according to the present invention is thereby configured to contact first and second contact surfaces of first and second workpieces with electrode tips of respective electrodes, wherein the electrodes are aligned at a non-right angle with respect to the contact surfaces. The welding apparatus may thereby achieve an advantageous effect, since the electrodes are not set perpendicular to the contact surfaces of the workpieces, but are rather set at a non-right angle.
During operation of the welding apparatus according to the invention, the first longitudinal axis may be set at a non-right angle with respect to the plane of the first contact surface, and preferably also with respect to the plane of the first welding surface. Moreover, this angular orientation may also be characterized by a non-zero angle between the first longitudinal axis of the first electrode tip and the normal direction of the first contact surface. Similarly, the second longitudinal axis may be set at a non-right angle with respect to the plane of the second contact surface, and preferably also with respect to the plane of the second welding surface. Moreover, this angular orientation may also be characterized by a non-zero angle between the second longitudinal axis of the second electrode tip and the normal direction of the second contact surface.
The lifespan of the electrodes of the welding apparatus, and in particular of the electrode tips that contact the contact surfaces of the workpieces, may be increased when they are aligned at a non-right angle with respect to contact surfaces of the workpieces. It has been found by the applicant that the quality of the formed welds has been improved and has become more stable, e.g. a more constant weld quality over time for subsequent welds, for example a more constant diameter of the weld.
The applicant has surprisingly found that the lifespan of the electrode tips, e.g. the amount of welds that can be made until critical degradation of the tips would occur, could be increased by a factor three or more with the welding apparatus according to the invention. For example for the welding of 0.8 — 1 mm aluminium sheets, the normal lifespan of electrode tips could be 50 spots, whereas the welding apparatus with the non-right positioning of the electrodes may provide for at least 150 spots. For welding 1 — 2 mm aluminium sheets, the lifespan may even be increased to at least 250 spots.
The electrode tips of the welding apparatus according to the present invention have an increased lifespan, and may thus provide for lower operational costs of the welding apparatus. For the inventive apparatus, fewer replacements of the tips and/or fewer cleaning of the tips may be required, since the amount of spots that lead to critical degradation may be significantly increased.
In an embodiment, the first electrode tip and the second electrode tip comprise a copper material. As such, the tips may be made of copper or of a copper alloy, such as a CuCrZr alloy, which comprises copper. Alternatively, the electrode tips may comprise a tungsten material.
In an embodiment of the welding apparatus, at least in the press configuration of the pressing device, the first non-right angle between a normal direction of the first contact surface and the first longitudinal axis is adapted to be larger than 4° and the second non-right angle between a normal direction of the second contact surface and the second longitudinal axis is adapted to be larger than 4° as well. Preferably, one or more of the non-right angles between the electrodes and the respective contact surfaces is larger than 5°, which was found by the applicant to lead to an even further increased lifespan.
In an embodiment of the welding apparatus, at least in the press configuration of the pressing device, the first longitudinal axis of the first electrode tip is aligned parallel to the second longitudinal axis of the second electrode tip. This relative orientation of the electrodes may provide that the pressing device is, upon moving the electrodes between the released configuration and the pressed configuration, configured to move the electrodes parallel to each other.
In an additional embodiment of the welding apparatus, at least in the press configuration of the pressing device, the first longitudinal axis of the first electrode tip is aligned in line with the second longitudinal axis of the second electrode tip. Hereby, the first longitudinal axis is formed by the same line that forms the second longitudinal axis. Moreover, the longitudinal axes are arranged in line at least when the electrodes are arranged in the pressed configuration, during the pressing of workpieces and/or during the forming of the weld by generating the electric current.
In this configuration of the electrodes, the welding apparatus is configured to form a weld in between the electrodes, on the same line as the line that forms the first longitudinal axis of the first electrode tip and the second longitudinal axis of the second electrode tip. As such, the location of the formed weld may be accurately controlled. Furthermore, a current density of generated electric current, e.g. the amount of current per unit of intersectional area, may be constant across the entire contact area between the contact surfaces of the workpieces and the corresponding electrode tips.
In an embodiment of the welding apparatus, the pressing device comprises a set of lever arms, to which the electrodes are connected. The lever arms of the pressing device may be in a C-type configuration, in which the lever arms together resemble the shape of a “C” and in which the electrodes are provided at the ends portions of the “C”. Alternatively, the lever arms of the pressing device may be in an X-type configuration, in which a rotatable joint is present at the crossing of both lever arms and wherein the electrodes are provided at a respective end portion of the opposing lever arms. For both the C-type configuration as the X- type configuration, the longitudinal axes of the electrodes may, at least in the press configuration of the electrodes, be arranged in line.
In an embodiment of the welding apparatus, a shaft portion of the first electrode and the first electrode tip and/or a shaft portion of the second electrode and the second electrode tip are substantially stationary with respect to each other. Each of the electrode tips may be connected to its respective shaft portion by means of a press fit connection, which may provide for a secured position between the shaft portions and their respective electrode tips. According to this embodiment, each of the electrode tips is substantially fixed with respect to its shaft portion and both are not configured to move with respect to each other during normal use of the welding apparatus. As such, it is provided that the welding apparatus may be more rigid, less complex and therefore less expensive, in particular with respect to the welding apparatus that is disclosed in cited prior art document EP 0 384 464 A1.
In an embodiment, the first electrode tip and/or the second electrode tip comprises a rounded end surface, wherein a radius of curvature of the rounded end surface is preferably in the range between 50 mm and 150 mm. According to this embodiment, the end surface of at least one of the electrode tips is curved. The amount of curvature may vary, for example be in between a spherical end surface and an almost planar end surface.
In an embodiment, the welding apparatus further comprising a holding device, which is configured to hold the first workpiece and the second workpiece in a holding position. The first electrode is, at least when the first workpiece and the second workpiece are held in the holding position, configured to be positioned with respect to the holding device, such that the first longitudinal axis of the first electrode tip is set at the first non-right angle with respect to the first contact surface of the first workpiece. Furthermore, the second electrode is, at least when the first workpiece and the second workpiece are held in the holding position, configured to be positioned with respect to the holding device, such that the second longitudinal axis of the second electrode tip is set at the second non-right angle with respect to the second contact surface of the second workpiece.
Further characteristics of the invention will be explained below, with reference to embodiments, which are displayed in the appended drawings, in which: Figure 1 depicts an embodiment of the resistance welding apparatus according to the present invention, which is in a C-type configuration, Figure 2 depicts a different embodiment of the welding apparatus according to the present invention, which is in an X-type configuration, Figure 3 depicts a plurality of steps which are carried out with the method according to the invention, and Figure 4 schematically depicts embodiments of an electrode tip for use in the resistance welding apparatus.
Throughout the figures, the same reference numerals are used to refer to corresponding components or to components that have a corresponding function.
Figure 1 schematically depicts an embodiment of the resistance welding apparatus according to the present invention, to which is referred with reference numeral 1. The welding apparatus 1 comprises a first electrode 10 and a second electrode 20, which are arranged located to each other. The welding apparatus 1 further comprises a pressing device 30, which is associated with the second electrode 20, and a welding power supply 40.
In figure 1a, the pressing device 30 of the welding apparatus 1 is in a released configuration and in figure 1b, the pressing device 30 of the welding apparatus 1 is in a press configuration. In the released configuration, a spacing H is present in between the first electrode 10 and the second electrode 20. In the spacing H, one or more workpieces may be received, which may be welded together.
The first electrode 10 at least partially extends along a first longitudinal axis and the second electrode 20 extends along a second longitudinal axis. The first electrode 10 is aligned with the second electrode 20, in order to provide that the first longitudinal axis is aligned parallel to, and aligned in line with the second longitudinal axis, e.g. being aligned with longitudinal axis L.
The first electrode 10 comprises a first electrode tip 11 at its end, which faces towards the second electrode 20. The first electrode tip 11 is configured to form a contact surface between the welding apparatus 1 and a contact surface of a first workpiece that is to be received in the spacing H. The first electrode 10 has a bent shape, in order to provide for a so-called C-type welding apparatus, in which the electrodes are arranged in a configuration that mimics the shape of a “C”.
In the present embodiment, the first electrode tip 11 comprises a copper material and is releasable connected to a shaft portion 12 of the first electrode 10. The releasable connection provides that a worn out electrode tip 11 may be replaced by a fresh electrode tip, without requiring the entire electrode 10 to be replaced.
The second electrode 20 comprises a second electrode tip 21 at its end, which faces towards the first electrode 10. The second electrode tip 21 is configured to form a contact surface between the welding apparatus 1 and a contact surface of a second workpiece. The second electrode 20 has a substantially elongate shape, in order to allow for convenient movement thereof, upon moving the second electrode 20 with respect to the first electrode
10. In the present embodiment, the second electrode tip 21 comprises a copper material as well and is also releasable connected to a shaft portion 22 of the second electrode 20.
The first electrode tip 11 is releasable connected to the shaft portion 12 of the first electrode 10 and the second electrode tip 21 is releasable connected to the shaft portion 22 of the second electrode 20. However, during the welding, the electrode tips 11, 21 are adapted to remain substantially stationary with respect to their respective electrode 10, 20, and in particular with respect to their respective shaft portion 12, 22. For carrying out the method, the advantageous effect may be achieved without requiring a substantial relative movement, e.g. rotation, between the electrode tips and the electrodes.
The first electrode 10 is fixedly connected to a frame 2 of the welding apparatus 1, and is configured to remain stationary with respect to the frame 2 during the welding process. The second electrode 20 is connected to the pressing device 30 of the welding apparatus 1. The pressing device 30 is, in turn, fixedly connected to the frame 2 and is configured to move the second electrode 20 with respect to the frame 2.
The pressing device 30 is configured to move the second electrode 20 along the longitudinal axis L and to move the second electrode 20 with respect to the first electrode 10. The pressing device 30 is thereby configured to reduce the spacing H that is present in between the first electrode 10 and the second electrode 20. Upon further movement by the pressing device 30, the second electrode 20 eventually contacts the first electrode 10. In particular, the first electrode tip 11 will come in contact with the second electrode tip 21. As such, the welding apparatus 1 may end up in the press configuration, which is displayed in figure 1b.
The welding power supply 40 of the welding apparatus 1 comprises a transformer 40, which is connected to the frame 2 of the welding apparatus 1. The transformer 40 is electrically connected to the first electrode 10 and the second electrode 20, and is configured to apply an electric potential difference between the first electrode 10 and the second electrode 20. When the first electrode 10 and the second electrode 20 are, for example upon relative movement by the pressing device 30, brought in electric contact with each other, the potential difference may result in an electric current that may flow from the first electrode 10 to the second electrode 20, or vice versa. As such, the transformer is configured to generate an electric current between the first electrode 10 and the second electrode 20, in order to locally melt the workpieces in between the electrodes 10, 20.
In figure 2, another embodiment of the welding apparatus is displayed, which is a so- called X-type welding apparatus. This welding apparatus 1 also comprises a stationary first electrode 10 with a first electrode tip 11 and a movable second electrode 20 with a second electrode tip 21. The first electrode 10 is connected to a frame 2 of the welding apparatus 1 by means of a first lever arm 13, which extends between the first electrode 10 and the frame
2. The second electrode 20 is connected to the pressing device 30 by means of a second lever arm 23, which extends between the second electrode 20 and the pressing device 30.
In the embodiment of figure 2, the lever arms 13, 23 of the welding apparatus 1 mimic the shape of an “X”, having a central axis of rotation 3 between the first lever arm 13 and the second lever arm 23. Furthermore, this embodiment of the welding apparatus 1 also comprises a transformer 40, which is electrically connected to the first electrode 10 and the second electrode 20, and which is configured to generate an electric current between the first electrode 10 and the second electrode 20.
In figure 3, a plurality of steps is displayed in order to represent the method according to the present invention. In figure 3a, the first electrode 10 and the second electrode 20 of an embodiment of the welding apparatus 1 are displayed. The first electrode 10 comprises the first electrode tip 11 and the second electrode 20 comprises the second electrode tip 21. Both electrode tips 11, 21 are connected to a shaft portion 12, 22 of the respective electrode 10, 20 by means of a press fit connection.
In figure 3a, the pressing device of the welding apparatus is arranged in the released configuration and the first electrode 10 is set at a distance from the second electrode 20, in order to define a spacing H in between the first electrode tip 11 and the second electrode tip
21. The first electrode 10 extends along a first longitudinal axis L1 and the second electrode 20 extends along a second longitudinal axis L2. In the present embodiment, the first longitudinal axis L1 is aligned parallel to, and aligned in line with the second longitudinal axis L2.
In figure 3b, the pressing device of the welding apparatus is in its released position as well. The spacing between the first electrode 10 and the second electrode 20 remains present. However, a first workpiece 100 and a second workpiece 110 are positioned in the spacing between the first electrode 10 and the second electrode 20. This positioning may be done either by movement of the welding apparatus, in order to position the electrodes 10, 20 adjacent the workpieces 100, 110, or may be done by movement of the workpieces 100, 110 towards a location in between the electrodes 10, 20.
In the present embodiment, the first workpiece 100 and the second workpiece 110 are automotive components, which are intended to form part of the body of a vehicle. The first workpiece 100 and the second workpiece 110 are provided as substantially planar components, of which opposing surfaces extend substantially parallel to each other in a first and second orthogonal direction, and of which a dimension in a third orthogonal direction is very small in comparison to the dimension in the first and second orthogonal direction.
The first workpiece 100 comprises a first contact surface 101 and a first welding surface 102, which are located on opposite sides of the first workpiece 100. Similarly, the second workpiece 110 comprises a second contact surface 111 and a second welding surface 112, which are located on opposite sides of the second workpiece 110 as well. In figure 3b, the first welding surface 102 and the second welding surface 112 are displayed in magnified view on the first workpiece 100 and the second workpiece 110.
Upon positioning of the workpieces 100, 110 in between the electrodes 10, 20 of the welding apparatus, the first welding surface 102 is positioned against the second welding surface 112, in order to align the first workpiece 100 with the second workpiece 110. At least a portion of the first workpiece 100 thereby extends substantially parallel to at least a portion of the second workpiece 110 and both welding surfaces 102, 112 contact each other, in order to provide a weld in between them.
As a result of the facing welding surfaces 102, 112, the first contact surface 101 faces away from the second contact surface 111. In the present embodiment, the first workpiece 100 and the second workpieces 110 are at least partially planar, which implies that a normal direction of the first contact surface 101 is aligned anti-parallel to a normal direction of the second contact surface 111. In figure 3b, the normal direction of the first contact surface 101 is indicated by means of arrow N1 and the normal direction of the second contact surface 111 is indicated by means of arrow N2.
For the welding of the workpieces 100, 110, the pressing device is brought towards its press configuration, which implies that the first electrode 10 and the second electrode 20 are moved towards each other, e.g. by moving the second electrode 20 towards the first electrode 10. Figure 3c displays the movement of the electrodes 10, 20 by means of an arrow. This movement allows the first electrode tip 11 to contact the first contact surface 101 and allows the second electrode tip 21 to contact the second contact surface 111. The pressing device is configured to apply a pressing force on the electrodes 10, 20 in order to firmly press the workpieces 100, 110 in between the electrode tips 11, 21 and to assure a fixed relative position between the workpieces 100, 110.
In the press configuration in figure 3c, the first longitudinal axis L1 of the first electrode 10 is set at an angle 81 with respect to the normal direction N1 of the first contact surface
101. Furthermore, the second longitudinal axis L2 of the second electrode 20 is set at an angle 82 with respect to the normal direction N2 of the second contact surface 111. The angle 81 between the first electrode 10 and the first working surface 101 is equal to the angle 82 between the second electrode 20 and the second working surface 111, as a result of both electrodes 10, 20 and both workpieces 100, 110 being aligned parallel to each other.
The angles between the electrodes 10, 20 and the workpieces 100, 110 are non-right angles, which implies that the angles 81, 82 between the longitudinal axes L1, L2 of the electrodes 10, 20 and the normal directions N1, N2 of the contact surfaces 101, 111 are non- zero angles. In the present embodiment, the angles 81, 82 are set to be 5°, which has been found to be a value that gives rise to a significantly increased lifespan of the electrode tips 11,
21.
During the pressing of the workpieces 100, 110, the exerted pressing force on the workpieces 100, 110 may be increased further, when the electrode tips 11, 21 have already contacted the contact surfaces 101, 111 of the workpieces 100, 110, in order to form a welding force. In figure 3d, it is displayed that this welding force may induce a slight deformation of the workpieces 100, 110. At least the portions of the workpieces 100, 110 that are pressed in between the electrodes 10, 20 will, as a result of the applied welding force, undergo a deformation that may be large enough to contribute to an increased lifespan of the electrode tips 11, 21. However, this deformation of the workpieces 100, 110 is small enough to maintain a sufficient quality and/or appearance of the formed weld between the workpieces 100, 110.
Figure 4 displays an embodiment of an electrode tip that is to be used in a welding apparatus according to the present invention. Reference is made to this electrode tip by means of reference numeral 50. It is noted that this embodiment may be, but not necessarily needs to be, provided in the displayed embodiment of the welding apparatus. The electrode tip 50 comprises a cylindrical wall 51, which extends along a longitudinal axis Ld. The cylindrical wall 51 comprises a frustoconical portion 52, with which the electrode tip 50 is configured to be clamped around a corresponding frustoconical shaft portion of an electrode of a welding apparatus. The electrode tip 50 further comprises an end surface 53, which is arranged at the end of the cylindrical wall 51 that opposes the frustoconical portion
52. In the embodiment of figure 4, the end surface is a rounded end surface 53. The rounded end surface 53 is not flat, but comprises a curvature. As such, a central portion of the end surface, at or near the longitudinal axis Ld, may, depending on the amount of curvature, either form a protruded contact surface for the contacting of workpieces that are to be welded or may form an almost flat contact surface. The rounded end surface 53 has a certain amount of curvature, which is defined by a radius of curvature Rk of the end surface. In the present embodiment, the radius of curvature Rk of the end surface is approximately 4 inch (102 mm).
Claims (14)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2022864A NL2022864B1 (en) | 2019-04-04 | 2019-04-04 | Method for resistance welding and resistance welding apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2022864A NL2022864B1 (en) | 2019-04-04 | 2019-04-04 | Method for resistance welding and resistance welding apparatus |
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| NL2022864B1 true NL2022864B1 (en) | 2020-10-08 |
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| NL2022864A NL2022864B1 (en) | 2019-04-04 | 2019-04-04 | Method for resistance welding and resistance welding apparatus |
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Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0384464A1 (en) | 1989-02-23 | 1990-08-29 | Nippon Steel Corporation | Method and apparatus for resistance welding |
| JPH0475788A (en) * | 1989-07-26 | 1992-03-10 | Nippon Steel Corp | Resistance welding method and device thereof |
| JPH06198455A (en) * | 1993-01-11 | 1994-07-19 | Kikuchi Press Kogyo Kk | Resistance welding method |
| JP2000071078A (en) * | 1998-09-01 | 2000-03-07 | Honda Motor Co Ltd | Spot welding device and its method |
| JP2004330253A (en) * | 2003-05-08 | 2004-11-25 | Daihatsu Motor Co Ltd | Method and apparatus for spot-welding |
| EP1838484A1 (en) | 2005-01-11 | 2007-10-03 | KUKA Schweissanlagen GmbH | Method and device for electrical spot welding |
| WO2016181996A1 (en) * | 2015-05-11 | 2016-11-17 | 新日鐵住金株式会社 | Spot welding method |
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2019
- 2019-04-04 NL NL2022864A patent/NL2022864B1/en active
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0384464A1 (en) | 1989-02-23 | 1990-08-29 | Nippon Steel Corporation | Method and apparatus for resistance welding |
| JPH0475788A (en) * | 1989-07-26 | 1992-03-10 | Nippon Steel Corp | Resistance welding method and device thereof |
| JPH06198455A (en) * | 1993-01-11 | 1994-07-19 | Kikuchi Press Kogyo Kk | Resistance welding method |
| JP2000071078A (en) * | 1998-09-01 | 2000-03-07 | Honda Motor Co Ltd | Spot welding device and its method |
| JP2004330253A (en) * | 2003-05-08 | 2004-11-25 | Daihatsu Motor Co Ltd | Method and apparatus for spot-welding |
| EP1838484A1 (en) | 2005-01-11 | 2007-10-03 | KUKA Schweissanlagen GmbH | Method and device for electrical spot welding |
| WO2016181996A1 (en) * | 2015-05-11 | 2016-11-17 | 新日鐵住金株式会社 | Spot welding method |
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