Patent GB-504505-A (GB)
Title: An improved apparatus for welding
IPC: B23K11/31
Filed: 1938-05-18
Abstract: 504,505. Welding motor vehicle frames &c. BUDD MANUFACTURING CO., E. G. May 18, 1938, No. 14832. Convention date, May 19, 1937. [Classes 83 (ii) and 83 (iv)] An electric-resistance spot welding machine, particularly for producing sheet-metal boxsection beams for automobile chassis, has a number of pairs of electrodes which are operated by hydraulic motors individual to each pair, fluid under pressure being supplied to the motors in sequence under the control of a common distributing valve which is driven step by step with a pause of predetermined duration between each step, means being also provided for closing and opening the welding circuit during the pause periods. A flanged channel section 59 to which a cover strip 101 is to be spot welded at each flange, is' placed in a channelled work holder 14 formed in four sections insulated from each other, the side walls of the section being formed with an outward flare so that when they are forced into the holder by clamp members 16, 17 carried by a ram 15, they are sprung into desired shape. The central portion 16 of the clamp is held in outward position by adjustable springs 19 and is connected by a slot 26 and pin 24 to the ram, the pin being connected by a clevis 23 to a high-speed hydraulically operated piston rod 22, so that after the central clamp pushes the cover plate on to the section and the section into the holder, the end clamps 17 are applied to the work. The cover plate is initially connected to the part 16 by spring pins 102 passing through holes in the strip. When the clamps 17 have been pressed against the work, final pressure is applied to the ram by fluid supplied through pipes 30 to high power cylinders 27, which have pistons secured at 28 to the ram. The upper ends of the cylinders 27 are surmounted by surge tanks 53 provided with spring closed valves 54, so that when the piston rod 22 is being moved downwards the valves 54 are opened to admit fluid from the surge tanks and thus prevent retardation of the piston rod. The lower ends of the cylinders 27 are connected by pipes 32, 32<1> to the surge tanks and also to exhaust through pipes 51, 47, 48 and sump 44, the pipes 51 being closed during upward movement of the ram so that they are only in communication with the surge tanks so as to prevent retardation of the piston rod 22 during its upward stroke. The supply to opposite ends of the cylinder 21 through pipes 41, 39 and 29 or 31 from a motor-operated pump 42 and its exhaust through pipes 46, 48, are controlled by a four way slide valve 33 operated through linkage by a hand lever 35, and the exhaust from the lower ends of the cylinders 27 through pipes 51, 47, 48, during the downward stroke, and the supply to the upper ends of the cylinders 27 through pipes 40, 30, and exhaust therefrom through pipes 30, 47, 48 are controlled by a four way slide valve 34 similarly operated by a hand lever 36. Mounted on each side of the clamping members 16, 17 are four cylinder blocks 60, Fig. 3, which are insulated from each other. Each block is provided with a number of pairs of cylinders 61, 62, in each of which slides an insulated spring-returned piston. To the inner piston of each pair is secured a holder 63 for an electrode 66, the holder being electrically connected by flexible braid 64 to a bus-bar 65, there being a bus-bar for each cylinder block. The bus-bars 65 carry the upper parts 76 of knife switches, the co-operating contacts 77 being fixed to one terminal 75 of its respective transformer 71. The outer piston has a head 69, which engages through an insulated pin 74 a rocker arm 68 carrying a co-operating electrode 67, the rocker arm being connected by a flexible braid 72 to a bus-bar 73 secured to the terminal 70 of the transformer 71. By this construction, when the ram 15 is raised the work may be inserted or removed laterally from the machine. Each pair of cylinders 61, 62 on opposite sides of the ram is connected by a pipe 78 to a common flexible tube 79, the tubes 79 being connected to separate ports 85, Fig. 11, in the casing of a distributing valve 80, there being a separate distributing valve for each pair of cylinder blocks 60 on opposite sides of the ram. The casing of each valve is connected by a port 82 and pipes 89 to the pump, the rest of the space 93 being connected to exhaust via pipes 95. The distributing arm 86 of the valve is mounted on a shaft 81 rotated by a Geneva gear 91, 92 from an electric motor 83, so that only one port 85 at a time is open to pressure. The arm has a passage 87 connected to the supply port 82 through a passage 88 in the shaft 81. On the shaft 99 of the Geneva pin wheel is carried a cam 98, which operates a switch 96 in timed relation with the movement of the valve. Thus each pair of electrodes of each cylinder block on opposite sides of the ram is operated in turn and each pair takes the whole of the current supply of its transformer. The finished article is removed from the work holder by ejectors 57.