Welding gun trigger control circuit

Claim 1

In MIG welding apparatus including a welding gun, a welding wire source including a welding wire feed device and means for guiding the welding wire to the gun, a source of welding current and welding circuit means, in which the gun is incorporated, for supplying the gun with welding current, a source of shielding gas and conduit means connecting same to the gun for supplying shielding gas thereto, and a trigger switch and trigger control circuit controlled thereby for controlling the supply of welding wire, shielding gas and welding current to the gun, the improvement comprising: a source of direct current; a welding subcircuit connected in said trigger control circuit and including a normally open pre-welding switch and a normally open welding switch for initiating shielding gas, welding current, and welding wire feed upon activation; a gas purge subcircuit connected in said trigger control circuit for initiating shielding gas supply upon activation; said trigger switch including means for alternately connecting said source of direct current to said welding and gas purge subcircuits for activating said subcircuits and having a first position in which said direct current source is connected to said gas purge subcircuit and a second position in which said direct current source is connected to said welding subcircuit, said trigger switch being normally biased to said second position; separate control means responsive to activation of the welding and gas purge subcircuits for respectively controlling the supply of shielding gas, welding current and welding wire to the gun, each control means including an electromagneticcontrolled actuating means having a switch means in series therewith to initiate shielding gas, welding current, and welding wire feed upon the activation of the respective actuating means, said switch means comprising means for rendering the same conductive when said pre-welding or welding switch are closed and said trigger switch is in the second position, wherein when the respective switch means are conductive, the actuating means are activated; means for closing said pre-welding switch responsive to actuation of said trigger switch to said first position; timer means for limiting the time said pre-welding switch remains closed after being closed by said closing means, said timer means including time delay means to open said pre-welding switch a pre-determined time after said trigger switch has been actuated to said first position and released to said second position; and welding current actuated means responsive to welding current flow for closing said welding switch when said welding current switch means is conductive, whereby on initial actuation of said trigger switch to said first position from said second position, said shielding gas switch means is made conductive whereby pre-welding purging gas is available to the gun from said gas source without welding wire or welding current feed, and on release of said trigger switch, said trigger switch returns to said second position and all said switch means are conductive to supply shielding gas, welding current and welding wire feed, whereupon, if the welding arc is struck, shielding gas, welding current and welding wire are supplied to the gun, and on completion of welding, actuation of said trigger switch to said first position from said second position retains conductivity of said shielding gas switch means to supply post welding purge gas without welding for so long as the wire or current feed trigger switch is held in the first position, and whereby if the arc is not struck within a predetermined time initiating welding current flow, said timer means opens said pre-welding switch to render all said switch means non-conductive and ceasing all shielding gas, welding current and welding wire supply.