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WIRE WELDING
Equipment
The basic elements in a complete equipment package for the Wire
Welding process are:
1. Power source with amperage or voltage control.
2. Welding current switch (contactor).
3. Power supply to wire feeder and gas valve.
4. Gas cylinder
5. Gas regulator with flow adjustment.
6. Gas valve (solenoid). 7. Wire spool.
8. Wire feed motor with drive rolls. 9. Wire feed control.
10. Torch cable package containing welding current cable, gas hose, control circuit cables and wire feed tube (liner).
11. Torch with contact tip for supplying current to the nozzle, and control switch.
In a welding sequence these elements function as follows when the welder points the torch towards the starting point of the weld and pushes the torch control switch:
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• Gas valve opens to supply gas. • Contactor closes to supply welding current from the power source to the torch contact tip and wire. • Wire feed motor starts, feeding wire through the torch. • The arc starts as the wire touches the workpiece, and welding proceeds.
When welding is to be stopped the welder releases the torch control switch and the following sequence of events take place: • Wire feed motor stops. • After a brief moment the contactor opens, preventing further current supply, and the arc is extinguished.
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• The gas valve closes, preventing further gas supply.
The sequence of events and the time delay between them is essential for a successful termination of the weld, first to avoid that the wire sticks in the weld deposit, secondly to ensure gas shield of deposit and wire tip until sufficient cooling has been obtained. Depending on the area of use the elements of the Wire Welding equipment are arranged in different ways, more or less suited to onboard use.
Most commonly used are constant voltage power sources where all elements 1-9 are assembled in one
unit, often even with the gas cylinder
mounted on the assembly. As the practical length of the torch cable package with wire feed liner is limited to 3–4 m (especially when welding aluminium) these units are limited to applications close to the machine. Another system is built around very small wire spools, incorporating elements 7–11 in the torch, and the other elements either in a control box or in the power source. This is a flexible system regarding distance from the power source, but limits the selection of wires to mainly aluminium alloys, due to the small wire spools.
Wire feeder principle
The most flexible system is to include elements 2 - 9 except gas cylinder regulator in a compact portable wire feeder unit, which has the ability to utilize power sources with constant voltage characteristic. Unitor Wire Feeder is based on this principle and requires only welding current as power supply.