Consumable electrode type pulse arc welding method

In a consumable electrode type arc welding method, when short circuit shift welding is conducted at the start of an arc in the process of pulse arc welding and also when an inclinations of a rise or fall is decreased in the case of starting an arc in the process of pulse welding and also when an inclination of a short circuit current is increased, short circuit, which irregularly occurs at the start of an arc, can be released in a short period of time and the arc can be stabilized early. When the generation of a magnetic arc blow is suppressed, it becomes possible to form proper welding beads. Due to the foregoing, the efficiency of welding work can be enhanced.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a consumable electrode type pulse arc
 welding method by which welding is conducted in such a manner that at
 least one of the welding current and the welding voltage is superimposed
 like pulses between a welding wire and a welding base metal (work).
 2. Description of the Related Art
 Conventionally, in this type pulse arc welding method, an arc of pulse arc
 welding is started by using the same pulse parameter as that of main
 welding from the start of welding.
 However, when an arc of welding is started by the same pulse parameter as
 that of main welding, short circuit is irregularly caused because of an
 unstable arc at the start of arcing. Due to the foregoing, a period of
 time of short circuit is extended, and big pieces of spatter are
 generated, or the arc is suddenly cut off. Further, a change in the
 welding current per unit time at the rise and fall of pulses is so sharp
 that a value of the change is .+-.1000 to 1400 A/msec. Therefore, a
 magnetic arc blow occurs, and the arc becomes unstable. Accordingly, it is
 impossible to form proper welding beads.
 SUMMARY OF THE INVENTION
 The present invention has been accomplished to solve the above problems,
 and therefore an object of the present invention is to provide a
 consumable electrode type pulse arc welding method by which the occurrence
 of a magnetic arc blow is suppressed when short circuit, which has been
 irregularly caused in the process of starting an arc, is released in a
 short period of time, so that the arc can be prevented from cutting off
 and stabilized early and proper beads of welding can be formed.
 In order to accomplish the above object, a consumable electrode type pulse
 arc welding method of the present invention comprises: a first step for
 setting the welding current at a value lower than that of main welding in
 a first period of time which is a predetermined period of time from the
 start of welding; and a second step for increasing a setting value of the
 welding current to a value of main welding after the first period of time
 has passed. In this consumable electrode type pulse arc welding method,
 until the first point at which a setting value of the welding current
 reaches a predetermined setting value in the second step, not pulse
 welding but short circuit shift welding is conducted.
 Also, in this consumable electrode type pulse arc welding method, a
 consumable electrode type pulse arc welding method comprises: a first step
 for setting the welding current at a value lower than that of main welding
 in a first period of time which is a predetermined period of time from the
 start of an arc; and a second step for increasing a setting value of the
 welding current to a value of main welding after the first period of time
 has passed, wherein an inclination of pulses is decreased from the start
 of an arc to the end of the second step.
 In a consumable electrode type pulse arc welding method, a predetermined
 voltage is added to the welding voltage setting value and the thus
 obtained welding voltage setting value is outputted.
 In a consumable electrode type pulse arc welding method, an inclination of
 pulses is decreased in the second step after welding has passed through
 the first point.
 In a consumable electrode type pulse arc welding method, an inclination of
 a short circuit current is increased in the case of short circuit in the
 second step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Now, a description will be given in more detail of preferred embodiments of
 the invention with reference to the accompanying drawings.
 FIG. 1 is a flow chart showing a consumable electrode type pulse arc
 welding method of Embodiment 1 of the present invention, and FIG. 2 is a
 time chart showing a setting welding current, with a diagram of a waveform
 of a welding current. In the process of waiting, a welding device is not
 set in a pulse welding condition but in a short circuit shift welding
 condition. Next, when a welding start signal is turned on, an arc is
 generated.
 In this case, a first period of time is defined as a period of time from
 the start of the arc to a predetermined time, and a setting value of the
 welding current is set at a value lower than that of main welding until
 the first period of time has passed. This period of time is defined as a
 first step. A second step is defined as a period of time from a point of
 time at which the first period of time has passed to a point of time at
 which the setting value of welding is increased to a value of main
 welding. A first point is defined as a point of time at which the setting
 value of welding reaches a predetermined setting value in the second step.
 Pulse welding is started at this first point. That is, when short circuit
 shift welding is conducted until the welding current reaches the
 predetermined welding current, irregular short circuit occurring at the
 start of an arc can be released in a short period of time. Since it is a
 short circuit shift welding, a change in the welding current in the unit
 time is .+-.100 to 400 A/msec, which is not more than 1/2 of the welding
 current in the case of pulse welding. Therefore, it is possible to
 suppress the occurrence of a magnetic arc blow.
 FIG. 3 is a flow chart showing a consumable electrode type pulse arc
 welding method of Embodiment 2 of the present invention. FIG. 4 is a time
 chart of a setting welding current, and also FIG. 4 is a diagram of a
 waveform of a welding current. In this case, data is set so that a change
 in the welding current per unit time at a rise and fall of a pulse can be
 not more than .+-.1000 A/msec in the process of waiting. Next, when a
 welding start signal is turned on, an arc is generated.
 In this case, a first period of time is defined as a period of time from
 the start of the arc to a predetermined time, and a setting value of the
 welding current is set at a value lower than that of main welding until
 the first period of time has passed. This period of time is defined as a
 first step. A second step is defined as a period of time from a point of
 time at which the first period of time has passed to a point of time at
 which the setting value of welding is increased to a value of main
 welding. At the end of the second step, data of a rise and a fall of
 pulses is changed to data of main welding. That is, when a change in the
 welding current per unit time in the rise and fall of the pulse is
 decreased to a value not more than 1000 A/msec until the setting welding
 current reaches a current of main welding, it is possible to suppress the
 occurrence of a magnetic arc blow.
 FIG. 5 is a time chart of the setting welding current and the setting
 welding voltage showing a consumable electrode type pulse welding method
 of Embodiment 3 of the present invention. In the second step, a
 predetermined value of voltage is added to a value of welding voltage
 which is most appropriate for each welding current and can be unitarily
 set, and the thus obtained welding voltage is outputted. Due to the
 foregoing, irregular short circuit which occurs at the start of an arc can
 be released in a short period of time and the occurrence of short circuit
 itself can be suppressed.
 FIG. 6 is a time chart of the setting welding current and the setting
 welding voltage showing a consumable electrode type pulse welding method
 of Embodiment 4 of the present invention. In the second step, after the
 program has passed through the first point, an inclination of pulses is
 decreased. Due to the foregoing, it is possible to suppress the occurrence
 of a magnetic arc blow. When short circuit has occurred in the second
 step, an inclination of the short circuit current is increased. Due to the
 foregoing, even if an irregular short circuit occurs at the start of an
 arc, it is possible to release the short circuit in a short period of
 time, and the arc can be prevented from cutting off.
 As described above, according to the present invention, short circuit,
 which irregularly occurs at the start of an arc, can be released in a
 short period of time, so that the occurrence of a magnetic arc blow can be
 suppressed. Therefore, it is possible to prevent the arc from cutting off,
 and the arc can be stabilized early and proper beads can be formed. Due to
 the foregoing, welding work can be effectively performed.