This invention relates to a consumable electrode type arc welding apparatus.
In order to carry out a welding operation by a gas shielded arc welding method, a welding apparatus shown in FIG. 1 has heretofore been used. Referring to the drawing, a reference numeral 1 denotes a base metal, 2 a welding power source, 3 a welding torch, 4 a tip of the welding torch, 5 a welding wire, 6 a welding arc, 11 wire feed rollers, 10 a motor for driving the wire feed rollers, 9 a wire wound spool, 7 an arm to which the welding torch 3 is fixed of a simplified carriage (not shown), or an arm of a welding robot, and 8 a conduit cable for feeding the wire 5 to the welding torch 3.
In order to carry out a welding operation by such a welding apparatus; first, a suitable voltage is supplied from the welding power source 2. Consequently, a welding arc 6 occurs between a free end of the welding wire 5 and the base metal 1, and the welding wire 5 is melted to form a droplet 22 as shown in FIG. 2. During this time, the welding arc 6 can be generated stably between the base metal 1 and the free end of the welding wire 5 by feeding the welding wire 5 by rotating the wire feed rollers 11 having the motor 10 as a driving power source therefor, by an amount sufficient enough to cause the droplet 22 to be transferred to the base metal 1.
Thus, in the welding operation which has heretofore been carried out, a feed speed of the welding wire supplied from the tip 4 to a weld zone is set so that the feed speed becomes constant at all times during the welding operation. For example, when a solid wire of 1.2 mm in diameter is used as the welding wire 5 with a welding current supplied at 200xcx9c300 ampere and with a carbon dioxide gas as a shielding gas supplied at 25 liters/min., the feed speed of the welding wire 5 is set to a constant level between 5xcx9c12 m/min.
On the other hand, the condition observed of the droplet 22 formed at the free end of the welding wire 5 and transferred to the base metal 1 with, for example, a carbon dioxide gas used as a shielding gas is as shown in FIG. 2. Namely, the droplet 22 starts being formed on a stage shown in FIG. 2A, and grows with the lapse of time on stages shown in FIG. 2B and FIG. 2C in order.
As is understood from FIG. 2, in a stage in which the droplet 22 starts being formed and grows, the droplet 22 is lifted up by an arc force since the arc occurs on a lower surface of the droplet 22. Therefore, the droplet 22 cannot be transferred easily to the base metal 1, i.e., the droplet 22 grows until it turns into the condition shown in FIG. 2C. The droplet 22 is transferred in an enlarged state to the base metal 1 as if it flew thereto as shown in FIG. 2D. When the enlarged droplet 22 thus transferred is taken in a molten pool in the base metal 1, it turns into a molten metal to contribute to the welding but, when the enlarged droplet 22 falls in a position other than the molten pool, it turns into a spatter, which does not contribute to the welding.
Thus, the related art gas shielded arc welding using a carbon dioxide gas as a shielding gas has the following inconveniences.
(1) Since a droplet 22 transferred from the free end of a welding wire 5 to the base metal 1 grows large, the droplet 22 is transferred to a position other than a molten pool to turn into a large-sized spatter in some cases.
(2) Since spatters occurring grow large, much time is needed to carry out an operation for removing the spatters deposited on the base metal 1. Moreover, an efficiency of deposition of droplets from a welding wire 5 to a weld zone lowers to cause a welding efficiency to decrease.
In order to eliminate these inconveniences, the following measures are employed in the methods disclosed in Japanese Patent Laid-Open No. 229682/1996 and Japanese Patent Laid-Open No. 85439/1997.
Japanese Patent Laid-Open No. 229682/1996 proposes welding method and apparatus rarely encountering the occurrence of a spatter, and having a high welding efficiency, which include varying the length of a passage for a welding wire in a welding torch by swinging a wire feed nozzle, which is provided in an inner portion of the welding torch, by an electromagnetic effect; and transferring a droplet, which occurs at a free end of the welding wire, to a base metal in a short-circuiting manner by changing a feed speed of the welding wire, which is sent out from a tip of the welding torch to a weld zone, from a predetermined level to a high level momentarily in a suitable cycle.
Japanese Patent Laid-Open No. 85439/1997 proposes welding method and apparatus rarely encountering the occurrence of spatters, which enable a droplet constituting a primary factor of the occurrence of a spatter to be transferred to a base metal regularly and reliably by varying a welding pule current synchronously with the changing of a feed speed of a welding wire, which is proposed in Japanese Patent Laid-Open No. 229682/1966, from a predetermined level to a high level momentarily in a suitable cycle.
FIG. 3 shows the construction of a welding torch of the apparatus disclosed in Japanese Patent Laid-Open No. 85439/1997. Referring to the drawings, a reference numeral 3 denotes a welding torch, 4 a tip, 5 a welding wire, 8 a conduit cable, 12 a base portion of the torch, 13 a shielding gas supply pipe, 14 a shielding gas injection port, 15 a spring, 16 a wire feeding nozzle, 17 a tip fixing member, 18A and 18B magnetic cores, 19A and 19B electromagnetic coils, 20A, 20B DC voltage generators, and 21 a voltage generator regulating unit.
As shown in FIG. 3, in the apparatus disclosed in Japanese Patent Laid-Open No. 85439/1997, the welding torch 3 has a special construction, and the voltage generator regulating unit 21 for swinging the wire feed nozzle 16, which is provided in an inner portion of the welding torch 3, by an electromagnetic effect is required. This apparatus was complicated and expensive. Moreover, a feed speed of the welding wire 5 can be varied only in a limited range corresponding to the swinging of the wire feed nozzle 16 in the inner portion of the welding torch 3.
In the related art welding apparatus, the techniques for suppressing the occurrence of a large sized spatter in a region (not higher than substantially 1.5 m/min) of a low welding speed are attained. However, in a welding operation carried out at a welding speed of not lower than substantially 2 m/min, a welding current is as high as 300Axcx9c400A, so that a wire melting speed becomes high to cause a large quantity of droplets to be formed, and an arc to become unstable.
The present invention has been made in view of the above-mentioned circumstances, and provides simple and inexpensive welding method and apparatus adapted to extremely reduce spatters occurring and scattering even during a welding operation carried out at a speed of not lower than substantially 2 m/min.
According to an aspect of the present invention, the consumable electrode type arc welding method has the steps of feeding a welding wire to a material to be welded, and carrying out a welding operation by generating an arc between the material to be welded and welding wire, the method including the steps, which are used during a welding operation, of reducing after the short-circuiting of the welding wire and material to be welded a wire feeding speed to a low level not higher than that of a wire feeding speed in a regular welding operation, and increasing the wire feeding speed to a level not lower than that of the wire feeding speed in a regular welding operation.
According to another aspect of the present invention, the consumable electrode type arc welding method has the step of carrying out a welding operation by using a consumable electrode type arc welding apparatus provided with a welding power source for canceling short-circuiting when short-circuiting occurs, by raising a short-circuiting current at a rate of increase of at least 500 A/ms by controlling a welding current and a welding voltage, a unit for feeding the welding wire to a material to be welded, a unit for giving the welding wire feeding unit in accordance with a signal from a short-circuiting/short-circuiting cancellation detector which is to be referred to below an instruction to feed the welding wire by reducing after the short-circuiting of the welding wire and material to be welded is detected after the occurrence of an arc a wire feeding speed to a low level not higher than that of a wire feeding speed in a regular welding operation, increasing after the cancellation of the short-circuiting the wire feeding speed to a level not lower than that of the wire feeding speed in a regular welding operation, and thereby setting equal to each other a shortage of an amount of the welding wire fed while the wire feeding speed is reduced and an excess of an amount of the welding wire fed while the wire feeding speed is increased, a welding condition setter, a welding speed setter, a unit for moving a welding torch in accordance with a welding speed, and a detector for detecting short-circuiting and the cancellation of the short-circuiting.
According to the present invention, a special structure is not needed in the welding apparatus used in the consumable electrode type arc welding, and the welding is done by reducing or increasing a welding wire feeding speed synchronously with the short-circuiting or the cancellation of the short-circuiting. Therefore, the present invention has the following effects, etc.
The welding apparatus is simple and inexpensive.
The cancellation of the short-circuiting can be carried out speedily, and spatters occurring and scattering during a welding operation decrease extremely.
The welding operation is transferred from the short-circuiting to the formation of an arc speedily, so that the breakage of an arc can be prevented.
An excellent bead can be obtained.
A stable arcing condition is obtained even at a welding speed of not lower than 2 m/min.