1. Field of the Invention
This invention relates to a welding apparatus and, more particularly, to a welding apparatus suitable for use by multiple operators and for a welding apparatus suitable for use with a reduced input voltage.
2. Description of Related Art
There are numerous different welding processes utilized in the welding industry for welding various materials under different circumstances. These welding processes include stick arc welding, shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), flux core arc welding (FCAW), air carbon arc gouging and gas metal arc welding (GMAW). These several different welding processes are performed in numerous environments ranging from factories, construction sites to shipyards. Most arc welding operations are performed using direct current from either a DC power source or, more commonly, from an AC power source which has been converted from AC to DC.
Multiple operator welding machines were developed to permit several welding arcs to be struck from a single common power supply. The power supply typically has a transformer and rectifier to step down and convert the power from AC to an acceptable DC level. The known multiple operator welding machines are a saturable reactor type welding unit having a plurality of welding modules. Each welding module corresponding to a single welding arc requires a magnetic amplifier for generation of an acceptable arc. Such a saturable reactor type unit with magnetic amplifiers in each module is extremely heavy and very difficult to transport around a job site or to a new job site.
A further drawback of the known saturable reactor type multiple operator welding machine is that the welding processes which can be performed from the unit are limited. No known multiple operator welding machines can perform GMAW welding in addition to other welding processes such as stick, SMAW, GTAW or FCAW. GMAW operations on these welding machines must be performed with a voltage sensing wire feeder. In addition, none of the known multiple operator welding machines permit two or more different processes to be conducted from a single multiple operator welding machine at the same time absent the use of a voltage sensing wire feeder.
In light of the deficiencies, the known multiple operator welding machines are limited in their flexibility and versatility of use.
The arc voltage between a workpiece and a welding electrode is dependent upon the spacing between the two electrically charged members. As the spacing increases, the voltage increases and the current flow can decrease. When the spacing between the electrode and the workpiece is too great, an insufficient amount of current will flow, potentially resulting in defects such as spatter and lack of fusion. As the spacing increases, the arc will ultimately be extinguished.
Conversely, as the spacing between the electrode and the workpiece decreases, the voltage decreases and the current increases. If the spacing between the electrode and the workpiece is too small, the voltage will drop to an unacceptable level and excessive current will flow to the workpiece. This can result in gouging the workpiece or short circuiting the arc.
For most GMAW welding operations, it is desired to maintain a certain arc voltage and current flow, therefore, the spacing between the welding electrode and the workpiece must be maintained substantially constant. However, this spacing is constantly changing in light of globules of metal which drip from the welding electrode, the inability of the welder to hold the electrode steady and irregularities in the structure of the workpiece. Conversely, other welding procedures such as SMAW require varying the arc length to create different voltage, current and temperature levels. It is imperative that the arc not be extinguished or short circuit during these fluctuations in the arc length.
An additional problem with the known welding apparatus is that each welding module is based on a welding module input voltage of 80 volts DC from the rectifier of the transformer of the power frame. 80 volts DC is generally regarded as the voltage required to produce a relatively stable arc, i.e. the current fluctuation as a result of change in the arc voltage is acceptable. This input voltage is required even though the arc voltage is typically in the range of 25 to 35 volts. The 80 volt welding module input voltage is commonly reduced to the lower arc voltage by resistors or other suitable means. The power lost in reducing the voltage from 80 volts to 25 arc volts is significant. The lost power is converted into heat which must be vented from the machine. The power loss due to voltage reduction results in very uneconomical power usage and increases the likelihood of overheating of the welding units.