Method of MAG arc welding and welding apparatus

A pulse MAG arc welding apparatus for carrying out an arc welding operation by supplying a pulse welding current while switching the same between a first pulse current group for generating a short arc length and a second pulse current group for generating a long arc length, said apparatus comprising:

• an arc voltage detection circuit for detecting an arc voltage value and outputting an arc voltage detection signal corresponding thereto;
• an arc voltage setting circuit for setting a value of arc voltage in according with welding conditions and outputting an arc voltage setting signal corresponding thereto;
• a comparison circuit for comparing said arc voltage detection signal and arc voltage setting signal and outputting a difference between said two signals as an arc voltage control signal;
• a pulse condition control signal generation circuit for generating a pulse condition control reference signal for controlling one preselected among four pulse control conditions in common with said first and second pulse current groups in accordance with said arc voltage control signal, said four pulse control conditions comprising pulse frequency, pulse width, base current value and peak current value;
• a first pulse current setting circuit for setting remaining three pulse control conditions for said first pulse current group which have not been preselected and for outputting first pulse current group setting signals including setting signals corresponding to said remaining three pulse control conditions other than said pulse condition control signal;
• a second pulse current setting circuit for setting remaining three pulse control conditions for said second pulse current group which have not been preselected and for outputting second pulse current group setting signals including setting signals corresponding to said remaining said three pulse control conditions other than said pulse condition control signal;
• a switching circuit for generating a switching signal for switching said first and second pulse current setting circuits alternatively at a frequency ranging from 0.5 to 25 Hz;
• a pulse frequency signal generation circuit for generating a pulse frequency signal in response to either the pulse frequency control reference signal if output from said pulse condition control signal generation circuit, or, the pulse frequency setting signal output alternatively from selected each of said first and second pulse current setting circuits if said pulse frequency control signal is not output from said pulse condition control signal generation circuit;
• a pulse frequency and width signal generation circuit for outputting a pulse frequency and width signal in response to
• the pulse frequency control signal and pulse width setting signal if the pulse frequency control reference signal is output from said pulse condition control signal generation circuit,
• the pulse frequency signal and pulse width control signal if the pulse width control signal is output from said pulse condition control signal generation circuit, or
• the pulse frequency signal and pulse width setting signal if the peak current control signal or base current control signal is output from said pulse condition control signal generation circuit;
• a pulse current control circuit for outputting first pulse control signal and second pulse control signal alternatively in response to
• the pulse frequency and width signal, the peak current setting signal and base current setting signal if the pulse frequency control reference signal or the pulse width control signal is output from said pulse condition control signal generation circuit,
• the pulse frequency and width signal, the peak current control signal and base current setting signal if the peak current control signal is output from said pulse condition control signal generation circuit, or
• the pulse frequency and width signal, the peak current setting signal and base current control signal if the base current control signal is output from said pulse condition control signal generation circuit;
• and,
• a welding power source control circuit for outputting the first pulse current group when the first pulse control signal is output from said pulse current control circuit and the second pulse current group when the second pulse control signal is output from said pulse current control circuit.