GB1597142A

GB1597142A - Resistance welding machines

Info

Publication number: GB1597142A
Application number: GB3860877A
Authority: GB
Original assignee: ARO Machinery Co Ltd
Current assignee: ARO Machinery Co Ltd
Priority date: 1977-09-15
Filing date: 1977-09-15
Publication date: 1981-09-03
Also published as: DE2840229A1; ES473417A1; JPS5453648A; DK404778A; FR2403153A1; FR2403153B3; FI782728A

Description

(54) IMPROVEMENTS IN OR RELATING TO RESISTANCE WELDING MACHINE (71) We, A.R.O. MACHINERY COM- PANY LIMITED, a British Company of 190 Castelnau, London SE13 9DJ, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to resistance welding machines and especially spot-welding machines.

Conventional hand-operated spot welding guns and foot-operated spot welding machines use arrangements of levers to provide mechanical advantage from muscle power to create electrode tip forces sufficiently high for spot welding. There are also, air-operated spot welding guns and machines which employ air cylinders to provide the electrode tip force.

Each system has its inherent and distinct advantages. Hand or foot-operated mechanims are highly accurate and safer, while airoperated guns and machines are faster and fatigue-less.

It is an object of the invention to achieve an arrangement wherein substantially all the desirable features of both prior systems are attained.

According to the present invention, there is provided a welding machine having electrodes movable toward one another to apply gripping and welding pressure to the work to be welded and away from one another to release the work, and comprising hand or foot powered means to effect relative movement of the electrodes toward one another by manuaI or pedal effort until the electrode tips are closed upon the work to be welded substantially without pressure, and fluid-pressureoperated means operative only after the electrode tips have been closed as aforesaid to apply the electrodes forcibly to the work to create the gripping and welding pressure between the electrode tips.

The expression 'substantially without pressure' means that, while the electrodes are brought up close to the work, nevertheless if the electrode tips actually touch the work they exert only minimal pressure thereon.

In such an arrangement, accuracy and safety can be ensured by a simple, positive hand or foot-operated lever mechanism, to bring together the electrode tips without any force between them. Immediately after closing the tips an air cylinder can be. automatically activated to press the electrode tips together with great force.

In addition to being fast and effortless in operation, welding guns and machines incorporating the invention give the operator complete control in placing spot welds most accurately by sight, since the electrode tips can actually touch the workpiece before the squeeze pressure is applied.

Two embodiments of the invention will now be described by way of example. with reference to the accompanying drawings, in which: Figures 1 and 2 are, respectively, a side elevation and a plan of a hand-held' spotwelding gun, and Figure 3 is a diagrammatic side elevation of a foot-operated pedestal spot-welding machine.

Figures 1 and 2 show a hand-held spotwelding gun. The upper electrode I0 is carried by a bar 11 fixed at the front end of the main body of the gun while the lower electrode 12 is carried by a similar bar 13 fixed in a movable jaw 14 that is pivotally mounted on the main body of the gun at. 15.

Swinging ofthejaw 14 clockwise and counterclockwise as seen in Fig. 1, causes the tip of the lower electrode to move toward and away from the upper electrode tip. On the gun main body is mounted the usual transformer t6 for supplying the welding current to the electrodes.

An operating handle 17 for opening and closing the electrodes overlies the main body of the gun and has a pivotal mounting: i8. on the gun body at the back end thereof opposite the electrodes. The handle 17 acts through an operating rod 19 extending along the gun body and having its forward end pivotally connected at 20 to a bifurcated arm 21 of the jaw 14 that extends above the pivot 15.

The length of the rod 19 is adjustable by knurled adjusters 22. To form the coupling between the handle 17 and the operating rod 19, the rear end portion of the rod has a longitudinal slot 23 and the handle 17 is formed substantially as a bell-crank lever with an arm 24 extending down below the handle pivot 18 and bifurcated to embrace the slotted portion of the rod 19. A cross bar 25 has its ends engaged in nearly vertical slots 26 in the two portions of the bifurcated arm 24, and its middle portion is of rectangular section and is slidably engaged in the slot 23 of the rod. When the handle 17 is lifted, the arm 24 swings forward and the cross bar 25 engages the forward end of the slot 23 and pushes the rod 19 forward endwise to lower the jaw 14 and open the electrodes 10, 12.

When the handle 17 is lowered, the rod 19 is shifted back to raise the jaw 14 and close the electrode tips together but this is brought about by the cross bar 25 acting on the rod 19 through a spring 27 and therefore when the electrode tips engage the spring 27 yields and only a very light pressure can be exerted between the electrode tips manually before the handle 17 encounters a stop on the gun body.

The electrode tip force needed during welding is applied, after the tips have been closed manually by the handle 17, by a pair of air cylinders 28 mounted side by side on the gun body. The piston rods of these air cylinders are coupled together by a yoke bar 29 that is engaged in a keyway 30 in the operating rod 19. When the handle 17 reaches its fully lowered position, and the electrode tips are closed, the air cylinders are pressurised as the result of operation of a valve 31 by a cam face 32 on the arm 24. The welding current cycle is also initiated by operation of a microswitch 33.

The yoke bar 29 is normally maintained in engagement with the keyway 30 by a spring 34 pulling up on the back end of the operating rod 19. With the yoke bar thus engaged, the handle 17 can only be raised to an angle of roughly 45". If it is desired to open the electrodes wider, a trigger 35, pivotally mounted on the handle 17 at 36, can be operated to cause its tail 37 to press down the rod 19 against the action of the spring 34 and disengage the yoke bar 29 from the keyway 30.

The handle 17 can then be raised to, say, 90" to open the electrodes to a much wider distance apart. When the handle is lowered to close the electrode tips, the yoke bar 29 and keyway 30 automatically reengage.

Referring now to Figure 3, this shows a foot operated pedestal spot-welding machine. The lower electrode 40 is carried by a fixed arm 41 and the upper electrode 42 is carried on a movable lever arm 43 pivotally mounted on the machine frame at 44. The electrodes are opened and closed by lowering and raising of a rod 45 that extends down the back of the machine and has its upper end pivotallyconnected at 46 to the back end of the arm 43.

The lower end of the operating rod 45 is pivotally connected at 48 to a short link 47 that has its other end pivotally mounted on the machine frame at 49 to form a toggle linkage. Generally parallel links 50 and 51 extend toward the front of the machine frame from the pivots 48, 49 respectively. At the front of the machine, the links 50 and 51 are pivotally coupled by one arm 52 of a bell crank lever 53, the links 47, 50, 51 and the arm 52 together forming a parallelogram linkage. The other arm of the bell crank lever 53 extends in front of the machine frame and bears an operating pedal 54. Pivotally mounted at 55 on the pedal arm is a latch 56 that engages under the end of a forward extension 57 of the link 51 after the pedal has been depressed through a certain distance. This latch has a foot-operated release pad 58. The forward end of the link 51 is pulled upward by a pair of springs 59, and the pedal bell crank 53 is urged in a clockwise direction about its pivot, as viewed in Figure 3, by a spring 60 connecting the upper and lower parallel links 50, 51. With the pedal 54 and parallelogram linkage in the raised position, i.e. the electrode tips open, pedal movement upward is limited by an adjustable stop 61.

When the pedal 54 is initially depressed by the machine operator's foot, the pedal bell crank turns anticlockwise about its pivot and pulls the link 50 forward. This acts on the toggle linkage 45, 47 and causes the rod 45 to rise thereby swinging the forward end of the arm 43 down and closing the electrodes 40, 42.

When the electrodes are closed the pedal 54 is depressed far enough for the latch 56 to engage the link extension 57. At this point a valve is operated and air pressure is admitted to an air cylinder incorporated in the link 50 at 62. The cylinder 62 then tends to shorten the effective length of the link 50 which consequently urges up the rod 45 and applies the high force required between the electrode tips during welding. A yielding spring strut 63 in the rod 45 is set by an adjuster 64 to yield at a predetermined load, and as this strut contracts a link 65 operates a switch 66 to initiate the welding current cycle.

It will be understood that the foot-operated linkage is so adjusted that only a fairly light force can be applied to the electrode tips by the muscle power of the machine operator.

When the pedal 54 is depressed there is not only turning of the pedal bell crank 53 about its pivot but also the whole parallelogram linkage 47, 50, 51, 52 begins to turn about the pivot 49 the ratio of these two motions depending on the relative forces of the springs 59, 60. Depression of the latch pad 58 to release the latch 56, and release of foot pres sure on the pedal 54, causes the air to exhaust from the cylinder 62 and allows the springs to return the linkage to the position shown in the drawing.

WHAT WE CLAIM IS 1. A welding machine having electrodes movable toward one another to apply gripping and welding pressure to the work to be welded and away from one another to relase the work, and comprising hand or footpowered means to effect relative movement of the electrodes toward one another by manual or pedal effort until the electrode tips are closed upon the work to be welded substantially without pressure, and fluid-pressureoperated means operative only after the electrode tips have been closed as aforesaid to apply the electrodes forcibly to the work to create the gripping and welding pressure between the electrode tips.

2. A machine according to claim 1, and which is a hand-held spot-welding machine comprising a body having a fixed jaw carrying a first electrode, a movable jaw pivotally mounted on the body and carrying a co operating second electrode, an operating rod extending along the body and coupled at one end to the movable jaw, a handle pivotally mounted on the body and coupled to the other end of the operating rod through a resiliently yielding connection so that when the handle is operated to close the jaws the electrode tips are brought together substan tially without pressure, fluid-operated piston and-cylinder means also connected to the operating rod and operable to apply the welding pressure, and a control valve for the piston-and-cylinder means arranged for oper ation by the handle when the handle has been moved far enough to close the electrode tips.

3. A machine according to claim 2, wherein the control valve is operated by a cam on the handle.

4. A machine according to claim 2 or claim 3, wherein the handle also operates switch to initiate the welding cycle when the welding pressure has been applied.

5. A machine according to claim 2 or claim 3 or claim 4, wherein the connection between the operating rod and the pistonand-cylinder means can be disengaged to enable the jaws to be opened to a wider than normal extent.

6. A machine according to claim 5, wherein the connection between the operating rod and the piston-and-cylinder means is arranged to be disengaged by a trigger lever on the handle.

7. A machine according to claim 1, and which is a foot-operated pedestal spotwelding machine, wherein one electrode is mounted on a pivotally-mounted arm so that it can be moved toward and away from a cooperating fixed electrode, a substantially vertical operating rod is coupled at its upper end to said arm, a foot pedal is connected through a linkage to the lower end of the operating rod, and the linkage includes a fluidoperated piston-and-cylinder unit arranged to apply the welding pressure after the foot pedal has been operated to close the electrodes.

8. A machine according to claim 7, wherein the linkage is substantially a parallel gram linkage and the piston-and-cylinder unit acts to shorten one link of the parallelogram.

9. A machine according to claim 7 or claim 8, wherein the operating rod includes a yielding spring strut that limits the welding pressure, the welding cycle being initiated by operation of a switch as the strut yields.

10. A welding machine substantially as described with reference to Figures 1 and 2, or Figure 3, of the accompaying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sure on the pedal 54, causes the air to exhaust from the cylinder 62 and allows the springs to return the linkage to the position shown in the drawing. WHAT WE CLAIM IS

1. A welding machine having electrodes movable toward one another to apply gripping and welding pressure to the work to be welded and away from one another to relase the work, and comprising hand or footpowered means to effect relative movement of the electrodes toward one another by manual or pedal effort until the electrode tips are closed upon the work to be welded substantially without pressure, and fluid-pressureoperated means operative only after the electrode tips have been closed as aforesaid to apply the electrodes forcibly to the work to create the gripping and welding pressure between the electrode tips.