Arc-welding power supply

1. An arc welding power supply comprising:

an output control unit configured to output a welding voltage and a welding current in correspondence to each of a short-circuiting period and an arc period; and

a feeding control unit configured to increase a feeding rate of a welding wire in a forward feeding direction during a forward feeding acceleration period at a first positive acceleration, to reduce the feeding rate in the forward feeding direction during a forward feeding deceleration period, to increase the feeding rate in a reverse feeding direction during a reverse feeding acceleration period, and to reduce the feeding rate in the reverse feeding direction during a reverse feeding deceleration period,

wherein a short-circuit forcibly generating period is provided between the forward feeding acceleration period and the forward feeding deceleration period, and, during the short-circuit forcibly generating period, the feeding control unit increases the feeding rate with a change rate at a second positive acceleration larger than a change rate during the forward feeding acceleration period so that the second positive acceleration is greater than the first positive acceleration and maintains a predetermined forward feeding peak value when the feeding rate reaches the peak value, and

wherein the start of the second positive acceleration during the short-circuit forcibly generating period is continuous with the end of the first positive acceleration during the forward feeding acceleration period without any gap therebetween.

2. The arc welding power supply according to claim 1 , wherein during the reverse feeding acceleration period, the change rate of the feeding rate is increased by the feeding control unit to be larger than the change rate during the forward feeding acceleration period and the feeding control unit maintains a predetermined reverse feeding peak value when the feeding rate reaches the predetermined reverse feeding peak value.

3. The arc welding power supply according to claim 1 , wherein during the reverse feeding deceleration period, the feeding control unit reduces the feeding rate by a predetermined value from the reverse feeding peak value and thereafter reduces the feeding rate with a smaller change rate.

4. The arc welding power supply according to claim 1 , wherein the feeding control unit provides the short-circuit forcibly generating period in a case where an average value of the feeding rate is a predetermined reference feeding rate or more.

5. The arc welding power supply according to claim 1 , wherein the output control unit reduces the welding current during the arc period to a value smaller than a predetermined reference current value when the feeding rate enters into the short-circuit forcibly generating period.

6. The arc welding power supply according to claim 1 ,

wherein the output control unit includes a power supply main circuit, wherein the output control unit controls the power supply main circuit to output the welding voltage and the welding current to a welding torch; and

wherein the arc welding power supply further comprises:

a transistor; and

a current-reducing resistor connected between the power supply main circuit and the welding torch,

the transistor being connected in parallel to the current-reducing resistor and when turned on, places the current-reducing resistor into a current flow from the power supply main circuit to the welding torch, and

the current-reducing resistor reducing the welding current to the welding torch when the transistor is turned on.

7. The arc welding power supply according to claim 1 , wherein the feeding control unit controls the feeding rate so that the feeding rate is a linear function during forward feeding in the forward feeding direction, and a sinusoidal function for reverse feeding in the reverse feeding direction.

8. The arc welding power supply according to claim 1 , wherein the output control unit controls the welding voltage to be only a decreasing welding voltage during the arc period.