Consumable-electrode AC gas shield arc welding method and apparatus therefor

A consumable electrode gas shield AC arc welding apparatus, comprising:

• a DC power source;
• an output setting means for setting the output current of said power source in at least four different levels, including a first higher current level than a specified critical level with the positive electrode, a second lower current level than the first with the positive electrode and a third current level with the negative electrode for generally periodically repeated three sequential periods, and a fourth higher current level than the first with the positive electrode for a period from an occasional detected time of a lower are voltage between the electrode and a base metal than a preset arc voltage in said period of the first current level until a recovered time when the detected arc voltage exceeds the preset arc voltage;
• a current control means connected to said output setting means, for controlling said DC power source;
• an inverter for inverting the output of said DC power source to AC power;
• duration period setting means for setting up said three sequential periods;
• a duration period control means with connections to said current control means and to said inverter, for periodically transmitting the duration period signals for said three sequential periods according to the signals from said period setting means;
• a voltage detection means for detecting the arc voltage between said consumable electrode and a base metal;
• a switching means for selectively switching said output current from said first level to said fourth level according to said detected arc voltage.

A consumable electrode AC-DC gas shield arc welding apparatus, comprising:

• a DC power source;
• a polarity switching means for supplying welding current to a welding wire as the consumable electrode from said DC power source connected thereto;
• an output current setting means for controlling said DC power source by selection of two current levels preset in two current reference setting means;
• an arc voltage detecting means for detecting the arc voltage between the electrode and a base metal;
• an arc voltage setting means for a reference;
• a duration period setting means for controlling respective polarity periods of said electrode with duration period references connected to said polarity switching means, the duration period including of a reversed polarity with a higher current level and of a straight polarity with a lower current level;
• a voltage error amplifier for regulating the value of the duration period reference of the straight polarity to square the detected value of said arc voltage detecting means with the value of said arc voltage setting means;
• and
• a polarity mode setting means for controlling said polarity switching means which changes the polarity mode from AC to DC when the regulated straight polarity duration period reaches to a preset value of a first AC/DC mode switching reference in the case of shortening the duration period, and from DC to AC when the straight polarity duration period reaches to a preset value of a second AC/DC mode switching reference in the case of prolonging the duration period.