Spot welding head

Abstract: A spot welding head comprises a spot electrode (6), a spot electrode supporter (3) holding the electrode (6) on its tip, a base member (2) holding the supporter (3) in such a manner that the supporter can swing on a first pin (4), to move the spot electrode (6) into and out of contact with a steel strap workpiece (3) to be welded. A frame (1) and guide (17) hold the base member (2) so that it can swing on a second pivot pin (14) to move the spot electrode (6) in a first direction over the strap (S) and so that it can slide to move the spot electrode (6) in a second, perpendicular, direction over the strap (S). A first actuator (5) is connected at one end to the supporter (3) for swinging the supporter (3) relative to the base member (2) when a steel strap (S) is spot-welded, and a second actuator (9) is connected at its one end to the frame (1) and at its other end to the base member (2) for swinging and sliding the member (2) relative to the frame (1).

Description: The present invention relates to a spot welding head for spot-welding the overlapping portions of a steel strap wound and tightened around a steel strip coil, a wire coil, a group of pipes and rods/bars, a pile of plates, or the like which should be bound. Known is a conventional spot welding head of this type for spot-welding a steel strap longitudinally at one, two or three spots at regular intervals JP-A-H.2-274383. There is another spot welding head for spot-welding a steel strap laterally at two or more spots at one or more predetermined intervals Utility Model JP-A-H.7-31891. Before these spot welding heads are provided, spot welding heads exclusively for spot welding at only one spot or longitudinally in only one line were provided. With regard to the steel straps spot-welded each at only one spot or longitudinally in only one line, however, if tensile force is applied to each of the straps from both sides of weld spot, the minute welded area behaves in such a manner that it turns perpendicularly to the direction of tension. This causes a bending moment to act on the welded portion. As a result, a relatively small force broke some of such welded portions. Therefore, spot welding heads for multi-point spot welding as mentioned above have been provided, and measures have been taken so that no bending moment act on the spot-welded portions, or so that the portions are sufficiently proof against bending moments, if any. With regard to the above multi-point spot welding also, however, if tensile force is applied to a welded steel strap, a slight bending moment acts on the welded portions on both sides. In addition, because the strap is welded at multiple spots in a line within a size limited for compactness of the apparatus, the distances between the weld spots are shortened. Therefore, the spot welding temper hardening extremely reduces the allowable bending stress in the directions along the line connecting the weld spots, and also lowers the allowable stress in the direction of tension. It is the present situation that these reduced and lowered stresses are allowed within allowable ranges. In particular, for a steel strap of high-carbon material (with an equivalent carbon content of 0.2% or more), the above evils or ill effects of temper hardening due to spot welding are remarkable. Therefore, a steel strap may be spot-welded zigzag, square or rectangularly. Because a spot welding head needs to be compact, however, it has been practically impossible to provide a spot welding head for providing automatically a zigzag, square or rectangular spot welding pattern. In other words, it has been difficult to devise such a mechanism that can move spot electrodes into a zigzag, square or rectangular pattern as stated above in a spot welding head, which has only a relatively narrow space. Furthermore, the spot electrode of a conventional spot welding head for the foregoing multi-point spot welding is moved by a rotary actuator or the like through a gear mechanism. Therefore, the intervals between the spot welds due to gear back lash are not accurate. For example, it was originally necessary for welds to have intervals of 10 mm, but their actual intervals were 8 mm and 9 mm. In addition, a spot welding head with this type of mechanism is complicated in structure and therefore expensive, and it is structurally impossible to easily adjust the spot welding intervals from the outside. According to this invention a spot welding head for spot-welding overlapping portions of steel strap in an automatic strapping machine, comprises a spot welding head for spot-welding overlapping portions of steel strap in an automatic strapping machine, the head comprising a spot electrode as one of the electrodes for spot welding, a spot electrode supporter holding the spot electrode on its tip, a base member supporting the spot electrode supporter through a first pin in such a manner that the supporter can swing on the first pin, a frame supporting the base member in such a manner that the base member can swing or slide longitudinally relative to the frame, guide means for guiding the base member relative to the frame when the member slides longitudinally, and pivot pins moveable between different positions, acting as slide restraint means when they are in a first position for restraining the base member from sliding relative to the frame, or acting together with swing restraint means when they are in a second position for restraining the base member from swinging relative to the frame, so that the base member can slide longitudinally relative to the frame, a first actuator connected at its one end to the spot electrode supporter and at its other end to the base member for swinging the supporter relative to the base member and bringing it into contact with a steel strap when the strap is to be spot-welded, and a second actuator connected at its one end to the frame and at its other end to the base member for swinging or sliding the base member relative to the frame, whereby the base member slides relative to the frame due to the action of the second actuator to move the spot electrode in the Y-direction over the strap, by releasing the slide restraint means and engaging the swing restraint means, and whereby the base member is swung on the pivot pins relative to the frame due to the action of the second actuator to move the spot electrode over the strap in the X-direction, which is perpendicular to the Y-direction, by releasing the swing restraint means and engaging the slide restraint means; so that by moving the spot electrode in the X- or Y-direction over the steel strap, the head is able to spot-weld the strap in only the X- direction, or only the Y-direction, or in a combination of the X- and Y-directions. The base member may be held directly on the frame. Preferably the guide means is interposed between the base member and the frame for guiding and holding the base member when it slides longitudinally, swinging on the pivot pins, with the base member when it swings. If the second actuator is operated, with the slide restraint means restraining the base member from sliding longitudinally relative to the frame, and with the swing restraint means released, the base member swings on the pivot pins relative to the frame, so the spot electrode is moved in the X-direction. If the second actuator is operated, with the swing restraint means restraining the swing on the pivot pins, and with the slide restraint means released to make the base member slidable longitudinally relatively to the frame, the base member slides longitudinally relatively to the frame, while guided by the guide means, so the spot electrode is moved in the Y-direction. Therefore, as stated above, the spot electrode can be moved over the welding surface of a steel strap in any of the X- and Y-directions. It is consequently possible to spot-weld a steel strap at multiple spots longitudinally, laterally (widthwise) or in a combination of the longitudinal and lateral directions. According to the present invention, by simply operating the actuators, it is easy to spot-weld a steel strap only longitudinally or only laterally, or zigzag, square or obliquely by combining longitudinal welding and lateral welding. Therefore, in view of the nature of what is being bound and the nature of the steel straps or the desired binding strength, a single spot welding head can easily spot weld the strap in various patterns. Therefore, a single spot welding head is sufficient without providing an exclusive or special purpose spot welding head for longitudinal or lateral welding, dependently on the natures etc. of what should be bound and a steel strap, as was the case conventionally. Besides, a spot welding head according to the invention is simple in structure as compared with its function diversity, and can therefore be smaller than the conventional spot welding heads. Moreover, the spot welding electrode is shifted directly (through no gear mechanisms) by the direct acting pneumatic cylinders. It is therefore possible to make the spot welding intervals always accurate. Furthermore, more than anything, zigzag or square spot welding is possible, so it is possible to widen the spot welding intervals. It is therefore possible to prevent the ill effects on temper hardening, which were defects of the conventional multi-point spot welding. Specifically, it was found that the binding strength of a steel strap spot-welded zigzag at three spots improved by about 20-30%, in comparison with the conventional spot welding at three spots longitudinally in a line, under the same conditions. In addition, it is possible to use high carbon material with a relatively low equivalent carbon content, which was not able to be used in the past because the above ill effects on temper hardening were remarkable. Particular embodiments of the present invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is an exploded perspective view of a spot welding head according to the present invention from which the upper member of the frame has been removed, showing the structure of main part of the head; Figure 2 is a perspective view showing the part of the frame which is fitted over the upper sides (surface sides) of the components shown in Figure 1, the actuator fitted there, etc.; Figure 3 is a side view (perspective view seen from upper side in Figures 1 and 2) of the spot welding head shown in Figures 1 and 2, but in assembled condition; Figure 4 is an enlarged perspective view showing the guide sleeve and the base member held by the sleeve, with the member moved toward the spot electrode supporter; Figure 5 shows views showing the construction and operation of another embodiment (without a guide sleeve) of the present invention; Figure 5(a) is an enlarged perspective view showing the construction of the base member and adjacent parts of a spot welding head according to this embodiment; Figure 5(b) is a cross section taken along the line I-I of Figure 5(a), showing the sliding condition; Figure 5(c) is a cross section taken along the line I-I of Figure 5(a), showing the swinging condition; Figure 6 are enlarged partial cross sections showing the frame, guide sleeve and base member restrained by the pivot pins or the stop pin, with the connector omitted; Figure 7 shows views showing arrangements of spot welds which can be formed by a spot welding head according to the present invention; Figure 7(a) is a perspective view showing three-spot welding which is longitudinal of a steel strap; Figure 7(b) is a perspective view showing three spot welding which is lateral of the strap; Figure 7(c) is a perspective view showing three-spot welding which is zigzag on the strap; Figure 7(d) is a perspective view showing four-point welding which is square on the strap; Figure 7(e) is a perspective view showing three-spot welding which is oblique on the strap; Figure 7(f) is a perspective view showing three-spot welding which is zigzag on the strap reversely to Figure 7(c). As shown in Figure 1, the frame 1 includes a lower member 1A, which has a base surface 1a and side surfaces 1b standing from the surface la. Mounted movably on the base surface 1a is a base member 2, in such a condition that its surface which is upper in the drawing/s is positioned below the tops of the side surfaces 1b. The base member 2 supports a spot electrode supporter 3 through a pin 4, in such a manner that the supporter 3 can swing on the pin 4 in the direction R. The base member 2 has a flange 2c on its left end. Fixed to the flange 2c is the housing 5a of a pneumatic cylinder (third actuator) 5 for moving a spot electrode. The rod of the cylinder 5 is connected pivotably at its tip through a connector 24 to a point on the supporter 3 which is spaced from the pin 4, in such a manner that the telescopic motion of the cylinder 5 in the directions P swings the support 3. Fixed to the tip of the supporter 3 is a spot electrode 6. Connected to the root end of the support 3 is a current-carrying conductor 10 for supplying electricity. The base member 2 is surrounded partially by a guide sleeve 17 (guide means: see Figure 4 in which the sleeve is enlarged together with the base member 2) in the form of a rectangular pipe. The sleeve 17 is interposed between the base member 2 and the frame 1 adjacently to the flange 2c. In other words, the base member 2 is held slidably by the sleeve 17. As shown in cross section in Figure 6, the side surfaces 1b have through holes 7 extending toward the base member 2. The holes 7 are located near the flange 2c of the pneumatic cylinder 5, that is to say, around the guide sleeve 17. The sleeve 17 has through holes 18. The base member 2 has blind holes 8. The holes 18 and 8 are formed at a plurality of places (three in this embodiment) so as to be coaxial with the holes 7. The illustrated pivot pins 14 can move into and out of the through holes 7 and 18 and the blind holes 8. The pins 14 can be inserted and released (pulled out) by a pneumatic cylinder (fourth actuator), not shown, which is supported by the frame 1. As also shown in Figure 6, another through hole 19 is formed near and in parallel with the through holes 7. The sleeve 17 has another through hole 20 formed so as to be coaxial with the hole 19. The illustrated stop pin 21 can move into and out of the through holes 19 and 20. The pin 21 can be inserted and released (pulled out) by a pneumatic cylinder (fifth actuator), not shown, which is supported by the frame 1. As shown in Figure 2, the frame 1 includes another member 1B, which covers the side surfaces 1b of the frame 1 from upper side in Figure 1. A three (fixed) position type pneumatic cylinder 9 is fitted on the surface of the member 1B which is upper in the drawing/s. The cylinder 9 operates to move the spot electrode 6 longitudinally and laterally on the welding surface of a steel strap. The cylinder 9 corresponds to the second actuator. In this embodiment, the cylinder 9 includes two pneumatic cylinders coupled together in series, and is constructed so as to obtain three (fixed) positions. Specifically, the housing 9a of the cylinder 9 is fixed to the member 1B. As shown in Figure 3, the tip of the rod 9b of the cylinder 9 is connected through a spherical joint 26 to a hole 2d (Figure 1) of the flange 2c of the base member 2. A holder 11 for guiding and holding a steel strap S (as shown in cross section in Figure 3) is fixed with a screw 13 to the end of the frame member 1B on the left side in Figure 2. The holder 11 has a recess 1a formed at its end on the left side in Figure 2, through which the spot electrode 6 (Figure 1) passes during spot welding. A lower electrode supporter 22 (not shown) is supported pivotably on a pin 15 on the right side of the spot electrode supporter 3 in Figure 1, in such a manner that the supporters 3 and 22 face each other right and left. The supporter 22 supports a lower electrode 23 on its lower end. The electrode 23 and the spot electrode 6 face each other right and left. The lower electrode supporter 22 can be swung by a pneumatic cylinder (first actuator) 12, which is shown in Figure 3. The spot welding head thus constructed is controlled by a controller so as to operate as follows during spot welding. First, a steel strap S is wound by more than one turn round what should be bound. The wound strap is then tightened. The overlapping portions of the tightened strap are then held in the holder 11. In order to spot-weld the strap longitudinally (in X-direction) by the control of the controller, the pneumatic cylinder (fourth actuator), not shown, is kept extended to keep the pivot pins 14 in the holes 7, 18 and 8, as shown in Figure 6(b). At the same time, the pneumatic cylinder (fifth actuator) is retracted to keep the stop pin 21 out of the through hole 20 of the guide sleeve 17. Next, the pneumatic cylinder 12 is operated to position the lower electrode, which is fitted on the tip of the lower electrode supporter, under the spot electrode 6 through the strap (Figure 3). At the same time, the pneumatic cylinder 5 is extended to press the spot electrode 6 against the strap surface. Then, electric current is caused to flow for spot welding at the electrode position (see spot weld M1 in Figure 7(a)). Next, the pneumatic cylinder 5 is retracted to move the spot electrode 6 away from the steel strap surface. Then, by operating the pneumatic cylinder 9 to move it to the next (second) position, the base member 2 (spot electrode supporter 3) pivots on the pivot pins 14 by another predetermined angle. In this condition, the cylinder 5 is extended to press the spot electrode 6 again against the strap surface. In this condition, electric current is caused to flow for spot welding at the electrode position. Eventually, as shown in Figure 7(a), a second spot weld M2 is formed longitudinally on the strap 1g. Further, the pneumatic cylinder 5 is retracted to move the spot electrode 6 away from the steel strap surface. Then, by operating the pneumatic cylinder 9 to move it to the last (third) position, the base member 2 (spot electrode supporter 3) pivots on the pins 14 by a predetermined angle. In this condition, the cylinder 5 is extended to press the spot electrode 6 again against the strap surface. In this condition, electric current is caused to flow for spot welding at the electrode position. In other words, as shown in Figure 7(a), the spot electrode 6 moves in the X-direction over the welding surface, and a third spot weld M3 is formed longitudinal]y (in X-direction) on the strap 16. This spot welding head can weld a steel strap laterally (widthwise; in Y-direction) at three spots as follows. In order to spot-weld a steel strap widthwise at a number of (for example, three) spots, first, the strap S is wound by more than one turn round what should be bound. The wound strap is then tightened. The overlapping portions of the tightened strap are held in the holder 11. In this condition, the pneumatic cylinder (fourth actuator), not shown, is retracted to keep the pivot pins 14 out of the blind holes 8, as shown in Figure 6(c). As a result, the base member 2 can move relatively to the frame 1 in the direction P in Fig. 1 and direction L in Fig. 6(c). At the same time, the pneumatic cylinder (fifth actuator) is extended to keep the stop pin 21 in the through hole 20 of the guide sleeve 17. Next, the pneumatic cylinder 12 is operated to position the lower electrode, which is fitted on the tip of the lower electrode supporter, under the spot electrode 6 through the steel strap. At the same time, the pneumatic cylinder 5 is operated to press the spot electrode 6 against the strap surface. In this condition, electric current is caused to flow for spot welding at the electrode position (see spot weld M4 in Figure 7(b)). Next, the pneumatic cylinder 5 is retracted to move the spot electrode 6 away from the steel strap surface. Then, by operating the pneumatic cylinder 9 to move it to the next (second) position, the base member 2 (spot electrode supporter 3) slides relatively to the frame 1 by a predetermined distance in the direction L (the same as directions P), while guided by the guide sleeve 17. In this condition, the cylinder 5 is extended to press the spot electrode 6 again against the strap surface. In this condition, electric current is caused to flow for spot welding at the electrode position. Eventually, as shown in Figure 7(b), a second spot weld M5 is formed laterally (widthwise; in Y-direction) on the strap 16. Further, the pneumatic cylinder 5 is retracted to move the spot electrode 6 away from the steel strap surface. Then, by operating the pneumatic cylinder 9 to further move it to the last (third) position, the base member 2 (spot electrode supporter 3) slides relatively to the frame 1 by another predetermined distance in the direction L, while guided by the guide sleeve 17. In this condition, the cylinder 5 is extended to press the spot electrode 6 again against the strap surface. In this condition, electric current is caused to flow for spot welding at the electrode position. That is to say, as shown in Figure 7(b), the spot electrode 6 moves over the welding surface in the Y-direction, and a third spot weld M6 is formed laterally (widthwise;in Y-direction) on the strap 16. By properly combining the longitudinal and lateral movements of the steel strap, it is easy to spot-weld the strap zigzag as shown in Figs. 7(c) and 7(f), square or rectangularly as shown in Figure 7(d), or obliquely at three spots as shown in Figure 7(e). The pneumatic cylinders are used as the actuators of the above embodiment. Instead, hydraulic cylinders or electric, pneumatic or hydraulic motors may be used. By adjusting a screw 9c (Figure 3) of the pneumatic cylinders 9, and fitting the rod of the one of the cylinders 9 adjacent to the pneumatic cylinder 5 with a stopper which can be adjusted positionally to adjust the extended lengths of the cylinders 9, it is possible to adjust the intervals between the welds on the steel strap freely from the outside. The guide sleeve 17 is used as the means for guiding the sliding movement of the base member of the above embodiment. Instead, as shown in Figure 5(a), the base member 2 may have a guide groove G formed in its upper side. The through holes 8 are formed in a line within the groove G. Consequently, as shown in Figure 5(a), the sliding movement in the directions P (Figure 5(a)) can be guided by the pivot pins 14 and the stop pin 21. Besides, as shown in Figure 5(c), the base member 2 can pivot on the pivot pins 14 in the directions Q (Figure 5(a)). That is to say, it is possible to guide the sliding movement by providing a well known guide mechanism for longitudinal guiding, without providing a guide member such as the sleeve 17.

Claims: A spot welding head for spot-welding overlapping portions of steel strap in an automatic strapping machine, the head comprising a spot electrode (6) as one of the electrodes for spot welding, a spot electrode supporter (3) holding the spot electrode (6) on its tip, a base member (2) supporting the spot electrode supporter (3) through a first pin (4) in such a manner that the supporter (3) can swing on the first pin (4), a frame (1) supporting the base member (2) in such a manner that the base member (2) can swing or slide longitudinally relative to the frame (1), guide means (17) for guiding the base member (2) relative to the frame when the member slides longitudinally, and pivot pins (14) moveable between different positions, acting as slide restraint means (14) when they are in a first position for restraining the base member (2) from sliding relative to the frame (1), or acting together with swing restraint means (21) when they are in a second position for restraining the base member (2) from swinging relative to the frame (1), so that the base member can slide longitudinally relative to the frame, a first actuator (5) connected at its one end to the spot electrode supporter (3) and at its other end to the base member (2) for swinging the supporter relative to the base member (2) and bringing it into contact with a steel strap (S) when the strap is to be spot-welded, and a second actuator (9) connected at its one end to the frame (1) and at its other end to the base member (2) for swinging or sliding the base member (2) relative to the frame, whereby the base member (2) slides relative to the frame (1) due to the action of the second actuator (9) to move the spot electrode (6) in the Y-direction over the strap (S), by releasing the slide restraint means (14) and engaging the swing restraint means (21), and whereby the base member (2) is swung on the pivot pins (14) relative to the frame (1) due to the action of the second actuator (9) to move the spot electrode (6) over the strap in the X-direction, which is perpendicular to the Y-direction, by releasing the swing restraint means (21) and engaging the slide restraint means (14); so that by moving the spot electrode (6) in the X- or Y-direction over the steel strap, the head is able to spot-weld the strap in only the X- direction, or only the Y-direction, or in a combination of the X- and Y-directions. A spot welding head according to claim 1, in which the base member (2) is held directly on the frame (1). A spot welding head according to claim 1, in which the guide means (17) is interposed between the base member (2) and the frame (1) for guiding and holding the base member (2) when it slides longitudinally, swinging on the pivot pins (14), with the base member (2) when it swings. A spot welding head according to any one of the preceding claims, in which the slide restraint means comprise the pivot pins (14), holes (8) formed in the frame (1), the base member (2) and the guide means (17). A spot welding head according to claim 4, in which the pivot pins (14) are insertable into and releasable from the holes (8) by a fourth actuator. A spot welding head according to any one of the preceding claims, in which the swing restraint means (21) comprise a stop pin (21) extending parallel to the pivot pins (14) through a hole (19) in the frame (1) and into a hole (20) in the guide (17) or into a slot in the base member (2). A spot welding head according to claim 6, in which the stop pin (21) is insertable into and out of the holes (19, 20) by a fifth actuator. A spot welding head according to any one of the preceding claims, in which the X-direction is the longitudinal direction of the steel strap (S) and the Y-direction is the lateral direction of the steel strap (S) .

Inventors: KATOH KANAMI, KATOH, KANAMI
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1997
Main classification: B23K11
IPC codes: B23K11, B65B13