Single-sided spot welder

Abstract

Single-sided spot welding machine (1), comprising: a gun body (10) comprising an upper body (11) arranged at an end portion of an arm (5) of a robot (3) and a lower body arranged at a lower part of the upper body (11); a power supply part (20) arranged within the lower body (13); a welding electrode part (30) arranged on a lower side of the lower body (11), which is supplied with welding current from the power supply part (20) and which is arranged to weld welding base metals together by electric resistance welding; a coated metal strip (B) feeding part (40) which feeds a coated metal strip (B) between the welding base metal and the welding electrode (31); and a ground electrode part (50) electrically connected to the power supply part (20) and arranged on the other underside of the lower body (11) for contacting the welding base metal, the ground electrode part (50) comprising: a rotary holder (53) arranged on the other side of the lower body (11); a rotating motor (M3) arranged on one side of the rotary holder (53); a pressure control device connected to a shaft (33) of the rotary motor (M3) through a rotating block (55); and a ground electrode (51) arranged at an end portion of the pressure control device and making contact with the weld base metal.

Description

BACKGROUND OF THE INVENTION(a) Field of the Invention

[0001] The present application relates to a spot welding device. More specifically, the present invention relates to a single-sided spot welding device capable of generating high heat input to a weld metal base having high electrical conductivity, such as aluminum, and welding from a single side. (b) State of the art

[0002] Spot welding is typically widely used in joining different metal sheets, and spot welding requires electrical current to melt materials to be joined and pressure to be applied to maintain contact of the parts at the welding point during the application of the welding current, which forms electrical resistance to generate welding heat.

[0003] A spot welder is used to perform spot welding, and the spot welder can generally be divided into either a two-sided spot welder, which includes a fixed electrode and a movable electrode pressing a base metal together, or a single-sided spot welder (single-sided welder) including a single welding electrode.

[0004] In the case of spot welding aluminum, aluminum has a relatively high electrical conductivity, making it difficult to generate sufficient resistance. As a result, sufficient melting of the parts to be welded does not occur at the weld spot. Consequently, the tensile strength of the weld spot is relatively weak, and frequent dressing is required due to electrode contamination.

[0005] Meanwhile, for spot welding of an aluminum plate, a current greater than 25kA is supplied, and in this case, distortion of the welding spot may occur due to the high heat and a large amount of weld beads may be generated.

[0006] Mechanical joining methods for aluminum, such as self-piercing riveting or hemming, can also be used, but the joint integrity is relatively weak. Furthermore, self-piercing riveting requires heavy fixtures and expensive rivets.

[0007] From JP 3 996 737 B2 a single-sided spot welding device is known, comprising: a gun body comprising an upper body arranged at an end portion of an arm of a robot, and a lower hollow body arranged at a lower part of the upper body; a power supply part arranged within the lower body; a welding electrode part arranged at a lower side of the lower body, which is supplied with welding current from the power supply part and which is configured to weld welding base metals together by electric resistance welding, and a ground electrode part electrically connected to the power supply part and arranged at the other lower side of the lower body for contacting the welding base metal.

[0008] JP H04-322886 A discloses a method and apparatus for extending the electrode life in resistance welding a metallic material whose electrode life is short at the time of resistance welding, such as aluminum and aluminum alloys, aluminum and aluminum alloy sheets, and a metallic clad steel sheet, and for performing functional welding. The resistance welding method for a metallic plate continuously provides conductive strips between electrodes and materials to be welded and welds them through the conductive strips. Also, the resistance welding apparatus for a metallic plate is provided with feed rollers, backup rollers, winding rollers, and the electrodes, supports the conductive strips fed out of the feed rollers by the backup rollers, and continuously feeds them between the electrodes and the workpieces to be welded.

[0009] JP H05 - 77 061 A provides an electrode material made of aluminum oxide dispersion-reinforced copper for spot welding of Al and Al alloys, which improves the number of spots on Al and Al alloys. The electrode material contains 0.25 to 1.4 wt.% Al2O3 particles with a size of <=0.1 μm and 0.1 to 3.0 wt.% Al2O3 particles with a size of 0.5 to 5.0 μm, and the remainder consists of Cu and unavoidable impurities.

[0010] In US 4,481,401 A, a coating-compatible strip material is inserted between a coated plate to be welded and a welding electrode, which contacts this plate during the welding process in such a way that a coating-compatible film is applied to the plate during the welding process to prevent the removal of the plate's protective coating. An apparatus for carrying out the process comprises support means for supporting a supply of strip material and guides for inserting the strip material between the sheet and the welding electrode, which contacts the sheet during the welding process. The strip material can be contained in a cassette that can be attached to the apparatus.

[0011] EP 1 409 190 B1 also shows a method for controlling, in particular calibrating, an electrical, force- or position-controlled resistance welding device, consisting of a stationary or moving, preferably robot-guided, welding gun with one or more at least partially movable electrode arms with electrodes, an arm drive and a control system, wherein the welding gun is calibrated according to the electrode force by means of a sensor which can be inserted between the electrodes and which directly or indirectly measures the electrode force between the electrodes, wherein for calibration the electrodes are pressed against a force sensor located between them, wherein the force sensor emits measuring or switching signals to the control system for determining a characteristic curve, either continuously or at several individual, specific force thresholds.

[0012] The above information disclosed in this Background section is intended only to enhance the understanding of the background of the invention and may therefore contain information that does not constitute prior art already known to a person skilled in the art in this country. SUMMARY OF THE INVENTION

[0013] The present invention was made in an effort to provide a single-side spot welder having advantages in generating contact resistance using a coated metal strip fed during welding to generate a high heat input to improve the joinability of the weld area.

[0014] The present invention also eliminates the need for a conventional ground wire by equipping a gun body with a ground electrode together with a welding electrode to achieve a stable ground connection near the weld area.

[0015] A single-side spot welder according to an exemplary embodiment of the present invention may comprise: a gun body comprising an upper body disposed at an end portion of an arm of a robot, and a lower hollow body disposed at a lower part of the upper body; a power supply part disposed within the lower body; a welding electrode part i) disposed at a lower side of the lower body, ii) supplied with welding power from the power supply part, and iii) configured to weld welding base metals together by electric resistance welding; a coated metal strip feeding part that feeds a coated metal strip between the welding base metal and the welding electrode;and a ground electrode part electrically connected to the power supply part and arranged on the other bottom side of the lower body for contacting the welding base metal, the ground electrode part comprising: a rotary holder arranged on the other side of the lower body; a rotary motor arranged on one side of the rotary holder; a pressure control device connected to a shaft of the rotary motor through a rotating block; and a ground electrode arranged at one end portion of the pressure control device and making contact with the welding base metal.

[0016] The welding electrode part may include: a shaft attached to one side of the lower body and electrically connected to the power supply part to be supplied with a welding current; and a welding electrode arranged at an end portion of the shaft.

[0017] The welding electrode may comprise copper reinforced with an aluminum oxide dispersion.

[0018] The coated metal strip feeding part may include: a strip feeding motor arranged on one side of the upper body; a strip take-up motor arranged on the other side of the upper body; a strip feed pulley connected to the strip feed motor and feeding the coated metal strip; a strip take-up pulley connected to the strip take-up motor and taking up the coated metal strip discharged from the strip feed pulley; and a strip guide device arranged on the lower body and the welding electrode part for guiding the coated metal strip to the end portion of the welding electrode.

[0019] The strip guiding device may include: guide brackets formed on sides of the lower body and the welding electrode part for guiding the coated metal strip; and a guide cap arranged on the welding electrode for guiding the coated metal strip to an end portion of the welding electrode.

[0020] The tape feed motor and the tape take-up motor can be designed as a servo motor whose speed and direction of rotation can be controlled.

[0021] The coated metal strip can be designed as a steel strip coated with a nickel layer or a copper layer.

[0022] The rotating motor can be designed as a servo motor whose speed and direction of rotation can be controlled.

[0023] The pressure control device may include: a pressure housing connected to the shaft of the rotating motor through the rotating block; a worm gear connected to a screw shaft, disposed within the pressure housing, and rotating or reversely rotating according to control signals received from a controller; a movable block engaged with the screw shaft; a pressure sensor disposed below the movable block, measuring the pressure of the ground electrode on the weld base metal and outputting a pressure signal to the controller; a connecting rod disposed within the pressure housing and connected to the ground electrode through the pressure housing; and a compression spring disposed within the pressure housing and supplying elastic force to the pressure sensor and the connecting rod.

[0024] The worm drive can be designed as a servo motor whose speed and direction of rotation can be controlled.

[0025] The pressure sensor can be designed as a piezoelectric element.

[0026] The controller may include control logic that maintains constant the pressure of the ground electrode on the weld base metal by controlling the worm drive to rotate or reverse it according to the measured signals from the pressure sensor.

[0027] An upper part of the upper body of the gun body may be connected to the end portion of the arm of the robot through a robot mount and an upper part of the lower body may be connected to a lower part of the upper body.

[0028] According to the present invention, the single-sided spot welder can weld by inserting the coated metal strip to create additional resistance to generate high heat input. Consequently, the joinability of the weld area can be improved.

[0029] In addition, the ground electrode can be arranged close to the welding electrode and a stable ground connection can be made possible without a ground wire.

[0030] According to the present invention, the single-sided spot welder does not require a high current exceeding 25kA for welding materials with high electrical conductivity such as aluminum, can reduce contamination of the electrode, and can minimize distortion of the welding spot due to high heat and a large amount of weld spatter. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a perspective view of a welding robot system equipped with a single-side spot welder according to an exemplary embodiment of the present invention. Fig. 2 shows a top perspective view of a single-side spot welder according to an exemplary embodiment of the present invention. Fig. 3 shows a bottom perspective view of a single-side spot welder according to an exemplary embodiment of the present invention. Fig. 4 shows a cross-sectional side view of a single-side spot welder according to an exemplary embodiment of the present invention. Fig. Figure 5 shows a cross-sectional view along the line AA of Fig. 4. Fig. 6 shows a cross-sectional view along the line BB of Fig. 4. Fig. 7 shows an enlarged cross-sectional view of a coated metal strip used in a single-side spot welder according to an exemplary embodiment of the present invention. Fig. 8 and Fig. 9 show drawings illustrating operating states of a single-side spot welding machine according to an exemplary embodiment of the present invention. <Beschreibung der Bezugszeichen> 1 single-sided spot welder; 3 robots; 5 arms; 10 pistol bodies; 20 power supply unit; 30 welding electrode part; 40 Feeding part for a coated metal strip; 50 ground electrode part; 11 upper body; 13 lower body; 7 Robot mount 31 welding electrode; 33 wave; B coated metal strip; M1 tape feed motor; M2 tape take-up motor; P1 belt feed pulley; P2 belt take-up pulley; 61 guide angle; 63 guide cap; B1 steel band; B2 coated nickel layer B3 coated copper layer; 51 ground electrode; 53 rotary holders; M3 rotating motor; 55 rotating block; 71 pressure housing; M4 worm drive; 80 control; 73 movable block; 75 pressure cell; 77 connecting rod; 79 compression spring; and 91, 93 aluminum plate DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0032] Fig. 1 shows a perspective view of a welding robot system equipped with a single-side spot welder according to an exemplary embodiment of the present invention, and Fig. 2 shows a top perspective view of a single-side spot welder according to an exemplary embodiment of the present invention. Fig. 3 shows a bottom perspective view of a single-side spot welder according to an exemplary embodiment of the present invention and Fig. 4 shows a cross-sectional side view of a single-side spot welder according to an exemplary embodiment of the present invention.

[0033] A single-side spot welding apparatus according to an exemplary embodiment of the present invention, as shown in Fig. 1, which is arranged at an end portion of an arm 5 of a welding robot 3, is used for welding materials with a high electrical conductivity such as aluminum from a single side.

[0034] The single-sided spot welding device 1 comprises as in Fig. 2 to Fig. 4 shows a gun body 10, a power supply part 20, a welding electrode part 30, a feeding part 40 for a coated metal strip and a ground electrode part 50.

[0035] The gun body 10 comprises an upper body 11 arranged at an end portion of the arm 5 of the robot 3 and a lower hollow body 13 arranged at a lower part of the upper body 11.

[0036] An upper part of the upper body 11 is connected to the end portion of the arm 5 of the robot 3 via a robot bracket, and a spatial region S is formed within the upper body 11.

[0037] The lower body 13 is as in Fig. 4 is hollow and the power supply part 20 is arranged inside the lower body 13.

[0038] The welding electrode part 30 is arranged on a side of a lower part of the lower body 13 and receives a welding current from the power supply part 20 for electric resistance welding of a welding base metal, e.g., an aluminum plate, with a welding electrode 31.

[0039] The welding electrode part 30 comprises as in Fig. 5, a shaft 33 is provided on one side of the lower part of the lower body 13, and the shaft 33 is electrically connected to the power supply part 20 to receive a welding current.

[0040] The welding electrode 31 is arranged at an end region of the shaft 33 and the welding electrode may be formed, in a non-limiting manner, by a copper electrode reinforced with an aluminum oxide dispersion.

[0041] The coated metal strip feeding part 40 is arranged between the upper body 11 and the lower body 13 for feeding a coated metal strip B between the welding electrode 31 and the welding base metal, for example, an aluminum plate.

[0042] The feeding part 40 for a coated metal strip comprises, as in Fig. 5, a tape feed motor M1 arranged on one side of the upper body 11 and a tape take-up motor M2 arranged on the opposite side of the upper body 11.

[0043] The tape feed motor M1 and the tape take-up motor M2 may, in a non-limiting manner, be designed as a servo motor whose speed and direction of rotation are adjustable.

[0044] The coated metal strip feeding part 40 further includes the coated metal strip B fed between the welding electrode 31 and the welding base material, for example, aluminum plate.

[0045] The coated metal tape B is wound around a tape feed pulley P1, and the tape feed pulley P1 is connected to a shaft S1 of the tape feed motor M1 within the spatial area S of the upper body 11.

[0046] A tape take-up pulley P2 is connected to a shaft S2 of the tape take-up motor M2 within the spatial area S of the upper body 11, and the tape take-up pulley P2 takes up the coated metal tape B fed out from the tape feed pulley P1.

[0047] A strip guide device is arranged on the lower body 13 and the welding electrode part 30 for guiding the coated metal strip B at an end portion of the welding electrode 31.

[0048] The strip guiding device comprises guide brackets 61 formed on sides of the lower body 13 and the welding electrode part 30 to guide the coated metal strip B, and a guide cap 63 arranged on the welding electrode 31 to guide the coated metal strip B to the end portion of the welding electrode.

[0049] The coated metal strip B may be used in a non-limiting manner as in Fig. 7 can be designed as a steel strip which is coated with a nickel layer B2 or a copper layer B3.

[0050] The ground electrode part 50 is arranged on the other side of the lower body 13, electrically connected to the power supply part 20, and grounds (establishes a ground connection) the welding base metal such as an aluminum plate through the ground electrode.

[0051] The ground electrode part 50 comprises as in Fig. 3 and Fig. 6 shows a rotary holder 53 arranged below the lower body 13 and a rotary motor M3 arranged on one side of the rotary holder.

[0052] The rotating motor M3 may, in a non-restrictive manner, be designed as a servo motor whose speed and direction of rotation are adjustable.

[0053] The ground electrode part 50 further includes a pressure control device 70 connected to a shaft of the rotary motor M3 through a rotating block 55, and a ground electrode disposed at an end portion of the pressure control device 70 and making contact with the welding base metal.

[0054] The pressure control device 70 includes a pressure housing 71 connected to the shaft S3 of the rotating motor M3 through the rotating block 55.

[0055] A worm drive M4 is arranged within the pressure housing 71 and is connected to a screw spindle S4.

[0056] The worm drive rotates or rotates in the reverse direction according to control signals received from a controller 80 and may be implemented, in a non-limiting manner, as a servo motor whose speed and direction of rotation are adjustable.

[0057] In the pressure housing 71, a movable block 73 is engaged with the screw spindle S4, and a pressure sensor 75 is arranged below the movable block 73, and the pressure sensor 75 measures a pressure of the ground electrode 51 on the welding base metal and outputs a pressure signal to the controller 80.

[0058] The pressure control means 70 further includes a connecting rod 77 disposed within the pressure housing 71 and connected to the ground electrode 51 through the pressure housing, and a compression spring 79 disposed within the pressure housing 71, which applies an elastic force to the pressure cell 75 and the connecting rod 75.

[0059] The pressure sensor 75 may be a piezoelectric element.

[0060] The controller 80 includes a control logic that maintains constant the pressure of the ground electrode 51 on the weld base metal by controlling the worm drive M4 to rotate or reverse according to the detected signals of the pressure sensor 75.

[0061] In spot welding of the single-side spot welding machine 1 according to the exemplary embodiment of the present invention, the robot 3 is operated as shown in Fig. 8 shown for the ground electrode 51 to make contact with one side of a lower aluminum plate 91.

[0062] After the ground electrode 51 makes contact with the lower aluminum plate 91, the welding electrode 31 presses an upper aluminum plate 93 and a welding current is supplied from the power supply part 20 to the welding electrode 31.

[0063] The coated metal strip fed between the welding electrode 31 and the upper aluminum plate 93 creates an additional contact resistance to generate a high heat input to the parts of the upper and lower aluminum plates 93 and 91 to be welded.

[0064] After spot welding, the strip feed motor M1 and the strip take-up motor M2 are operated simultaneously to move the coated metal strip B, from which a welding nugget is formed corresponding to the welding electrode to prepare for the next spot welding.

[0065] In Fig. 9, operations of the ground electrode part 50 when a base surface F1 of the lower aluminum plate 91 is inclined are described.

[0066] When the base F1 is inclined against a welding surface F2, the rotating motor M3 is operated to rotate at an angle θ for the ground electrode 51 to vertically contact the base F1.

[0067] The robot 3 is operated (moved and arranged) for the ground electrode 51 to make contact with the lower aluminum plate 91, the welding electrode 31 presses the upper aluminum plate 93, and the welding current is supplied from the power supply part 20 to the welding electrode 31 for the upper and lower aluminum plates 93 and 91 so that they can be welded.

[0068] The ground electrode 51 presses the base surface F1 of the lower aluminum plate 91 with constant pressure by operating the pressure control device 70. That is, the worm gear M4 rotates or reverses according to the pressure changes detected by the pressure sensor 75 to control positions of the movable block 73.

[0069] And thus, the movable block 73 regulates the pressure amount of the compression spring 79 to maintain a pressure of the ground electrode 51 connected to the connecting rod 77 against the base surface F1.

[0070] Although this invention has been described in connection with what are presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

[1] Single-sided spot welding machine (1), comprising: a gun body (10) comprising an upper body (11) arranged at an end portion of an arm (5) of a robot (3) and a lower body arranged at a lower part of the upper body (11); a power supply part (20) arranged within the lower body (13); a welding electrode part (30) arranged on a lower side of the lower body (11), which is supplied with welding current from the power supply part (20) and which is arranged to weld welding base metals together by electric resistance welding; a coated metal strip (B) feeding part (40) which feeds a coated metal strip (B) between the welding base metal and the welding electrode (31); and a ground electrode part (50) electrically connected to the power supply part (20) and arranged on the other underside of the lower body (11) for contacting the welding base metal, the ground electrode part (50) comprising: a rotary holder (53) arranged on the other side of the lower body (11); a rotating motor (M3) arranged on one side of the rotary holder (53); a pressure control device connected to a shaft (33) of the rotary motor (M3) through a rotating block (55); and a ground electrode (51) arranged at an end portion of the pressure control device and making contact with the weld base metal. [2] A single-sided spot welding machine according to claim 1, wherein the welding electrode part (30) comprises: a shaft which is attached to one side of the lower body (11) and is electrically connected to the power supply part (20), and a welding electrode (31) arranged at an end region of the shaft. [3] A single-sided spot welder according to claim 1, wherein the welding electrode (31) comprises copper reinforced with an aluminum oxide dispersion. [4] A single-side spot welding machine according to claim 1, wherein the coated metal strip (B) feeding part (40) comprises: a tape feed motor (M1) arranged on one side of the upper body (11); a tape take-up motor (M2) arranged on the other side of the upper body (11); a tape feed pulley (P1) connected to the tape feed motor (M1) and feeding the coated metal tape (B); a tape take-up pulley (P2) connected to the tape take-up motor (M2) and receiving the coated metal tape (B) fed out from the tape feed pulley (P1); and a strip guide device arranged on the lower body (11) and the welding electrode part (30) for guiding the coated metal strip (B) to the end portion of the welding electrode (31). [5] A single-side spot welding machine according to claim 4, wherein the strip guiding device comprises: Guide angles (61) formed on sides of the lower body (11) and the welding electrode part (30) for guiding the coated metal strip (B); and a guide cap (63) arranged on the welding electrode (31) to guide the coated metal strip (B) to an end portion of the welding electrode (31). [6] Single-side spot welding machine according to claim 4, wherein the tape feed motor (M1) and the tape take-up motor (M2) are designed as a servo motor which is arranged to control a rotational speed and a direction of rotation. [7] Single-sided spot welding device according to claim 1, wherein the coated metal strip (B) is designed as a steel strip (B1) which is coated with either a nickel layer (B2) or a copper layer (B3). [8] Single-side spot welding machine according to claim 1, wherein the rotating motor (M3) is designed as a servo motor which is arranged to control a rotational speed and a direction of rotation. [9] A single-side spot welding machine according to claim 1, wherein the pressure control device comprises: a pressure housing (71) connected to the shaft (33) of the rotating motor (M3) through the rotating block (55); a worm drive (M4) connected to a screw spindle, arranged within the pressure housing (71) and rotating or rotating in the opposite direction according to the control signals received from a controller (80); a movable block (73) engaged with the screw spindle; a pressure sensor (75) arranged under the movable block (73) measures the pressure of the ground electrode (51) on the welding base metal and outputs a pressure signal to the controller (80); a connecting rod (77) arranged within the pressure housing (71) and connected to the ground electrode (51) through the pressure housing (71); and a compression spring (79) arranged within the pressure housing (71) which supplies an elastic force to the pressure cell (75) and the connecting rod (77). [10] Single-sided spot welding device according to claim 9, wherein the worm drive (M4) is designed as a servo motor which is arranged to control a rotational speed and a direction of rotation. [11] Single-sided spot welding device according to claim 9, wherein the pressure cell (75) is designed as a piezoelectric element. [12] A single-sided spot welder according to claim 9, wherein the controller (80) comprises a control logic which maintains the pressure of the ground electrode (51) on the welding base metal constant by controlling the worm drive (M4) to rotate or reverse the same according to the detected signals of the pressure sensor (75). [13] A single-side spot welding machine according to claim 1, wherein an upper part of the upper body (11) of the gun body (10) is connected to the end portion of the arm (5) of the robot (3) through a robot bracket (7), and an upper part of the lower body (11) is connected to a lower part of the upper body (11).

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