JP2019005764A - Welding method and welding system - Google Patents

Abstract

To realize a temperature history which so makes a weld zone of a welded object as to be a target metallographic structure when welding the welded object by continuously inputting heat to the weld zone.SOLUTION: A welding system 1 comprises a power supply unit 50 for welding which supplies welding current, and a welding torch 10 which welds a welded object 200 by continuously inputting heat to a weld zone of the welded object 200. The power supply unit 50 for welding receives a heat input pattern, which is a heat input pattern when inputting heat to the weld zone, for the purpose of realizing a temperature history which so makes the weld zone as to be a target metallographic structure when welding the welded object 200, and controls the welding torch 10 so as to input heat to the weld zone in the received heat input pattern.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a welding method and a welding system for welding a workpiece by continuously applying heat to a welded portion of the workpiece.

  When arc welding is performed using a pulse current in which a first pulse and a second pulse having pulse waveforms having different pulse peak current levels and pulse widths alternately as a welding current, the welding arc is stabilized, There is known a pulse arc welding method that improves the transfer regularity and significantly reduces the amount of spatter and the amount of fume generated (see, for example, Patent Document 1).

  In the output control method of pulse arc welding, in which welding is performed by applying a welding current with the peak current during the peak period and the base current during the base period as one pulse period, when the occurrence of a long-term short circuit is determined, the long-term short circuit is released. There is also known a pulse arc welding output control method in which the peak current is reduced and the base current is increased during a transition period until the subsequent welding voltage converges to a steady state (see, for example, Patent Document 2).

  An arc welding control method in which short-circuit arc welding is performed by repeating a short-circuit period and an arc period, and a peak current value of an initial short-circuit current or an output time of the peak current value for opening a short-circuit at the time of arc start is determined by welding current. An arc welding control method is also known in which the value is changed according to a control parameter for adjusting a wire feed speed, a welding wire tip shape, or a heat input state (see, for example, Patent Document 3).

JP 2007-237270 A Japanese Patent Laid-Open No. 2006-128186 Japanese Patent Laid-Open No. 2006-93842

  In general, it is widely known that the metal structure of steel changes depending on the temperature lowering condition during solidification. Since mechanical properties such as toughness and strength change due to the change in the metal structure, it is important to change the metal structure (in this case, the solidified structure) of the weld according to the purpose.

  An object of the present invention is to realize a temperature history in which a welded portion is a target metal structure when the workpiece is welded by continuously applying heat to the welded portion of the workpiece.

  For this purpose, the present invention is a heat input pattern when heat is applied to a welded part in a welding method for welding the object to be welded by continuously inputting heat to the welded part of the work piece, Provided is a welding method for receiving a heat input pattern for realizing a temperature history having a weld metal as a target metal structure when welding an object to be welded, and inputting heat to the weld with the received heat input pattern.

  Here, the heat input may be realized by arc discharge. Further, the heat input pattern may be composed of pulses. Furthermore, the pulse may have a shape in which the amount of heat per unit time of the pulse matches the amount of heat per unit time of the heat input pattern. In that case, the shape may be obtained by adjusting the peak value, the peak period, the base value, and the base period in one cycle of the pulse.

  The present invention also includes a welding power source for supplying a welding current and welding means for welding the workpiece by continuously applying heat to the welded portion of the workpiece, and the welding power source enters the welded portion. A heat input pattern for heating, accepting a heat input pattern for realizing a temperature history with the weld metal as a target metal structure when welding the workpiece, and accepting the heat input pattern on the weld with the received heat input pattern A welding system is also provided for controlling the welding means to receive heat.

  ADVANTAGE OF THE INVENTION According to this invention, when welding a to-be-welded object by continuously inputting heat into the welding part of a to-be-welded object, the temperature history which makes a welded part the target metal structure is realizable.

It is a figure which shows the schematic structural example of the welding system which concerns on embodiment of this invention. (A) shows the first example of the target temperature history and the temperature history when heat is input in each heat input pattern, and (b) shows the optimized heat input pattern for the first example of the target temperature history. It is the figure which showed the heat input pattern of the pulse waveform. (A) shows the 2nd example of target temperature history, and the temperature history at the time of heat-input in each heat input pattern, (b) is the optimized heat input pattern with respect to the 2nd example of target temperature history. It is the figure which showed the heat input pattern of the pulse waveform. (A) shows the 3rd example of target temperature history, and the temperature history at the time of heat-input in each heat input pattern, (b) is the optimized heat input pattern with respect to the 3rd example of target temperature history. It is the figure which showed the heat input pattern of the pulse waveform. It is the figure which showed the example of the pulse which made the optimized heat input pattern and the calorie | heat amount per period equal to this.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  In the embodiment of the present invention, in spot welding, by determining a heat input pattern (time change of heat input amount) to the welded portion, the temperature of the welded portion for making the metal structure at the time of welding according to the purpose. A history is realized. Here, spot welding is welding performed by applying heat to the weld without moving with respect to the workpiece. From the viewpoint of the welded portion, this can also be regarded as welding performed by continuously inputting heat into the welded portion.

  FIG. 1 is a diagram showing a schematic configuration example of a welding system 1 according to an embodiment of the present invention. The welding system 1 performs welding of an object to be welded 200 by a consumable electrode type (melting electrode type) gas shielded arc welding method.

  The welding system 1 includes a welding torch 10 as an example of welding means for welding an object to be welded 200 using a welding wire 100, and a robot arm 20 that holds the welding torch 10 and sets the position and posture of the welding torch 10. And. The welding system 1 also includes a wire feeding device 30 that feeds the welding wire 100 to the welding torch 10 and a shield gas supply device 40 that supplies a shielding gas (for example, carbon dioxide gas) to the welding torch 10. Further, the welding system 1 includes a welding power supply device 50 as an example of a welding power source that supplies a direct welding current to the welding wire 100 and the workpiece 200 via the welding torch 10 and controls the welding current, and a robot. And a robot control device 60 for controlling the arm 20. Although not described in detail here, the welding power source device 50 controls the welding speed, the feeding speed of the welding wire 100, and the like in addition to the welding current. Further, the welding power supply device 50 controls the supply of the welding current to the welding wire 100 so that the heat input is performed with the determined heat input pattern.

  Hereinafter, three examples of target temperature history (target temperature history) will be described.

  FIG. 2A shows a first example of the target temperature history with a bold line. As shown in the figure, in the first example of the target temperature history, 2000 ° C. is maintained for 10 seconds, and the temperature is decreased at a rate of 175 ° C./s from 1500 ° C. near the melting point of steel to 800 ° C. at which the γ-α transformation starts. The By making this temperature range rapid cooling, dendrite coarsening and γ coarsening that start growing from the start of solidification are suppressed. Further, the temperature of 800 ° C. or lower is lowered at 50 ° C./s in the first example. In the first example, the material structure obtained by changing the temperature decrease rate in the temperature region where the γ-α transformation starts is made as martensite.

In order to determine the heat input pattern that realizes this target temperature history, a three-dimensional heat conduction simulation by the difference method was performed. The shape of the workpiece 200 used in this simulation was a cube of 30 mm × 30 mm × 30 mm, and the cube was divided into meshes by dividing the cube at intervals of 3 mm in all directions. The physical properties were assumed to be steel, with a thermal conductivity of 20 W / (mK), a density of 7870 kg / m ³ , and a specific heat of 435 J / (kgK). Furthermore, the intersection (mesh point) in all the meshes of the workpiece 200 was set to 20 ° C. as an initial condition. As the boundary conditions, the four surfaces other than the lower surface of the upper surface were set as heat insulating conditions. As for the upper surface, heat exchange with the atmosphere was performed by forced convection heat transfer with an outside air temperature of 20 ° C. and a heat transfer coefficient of 15 W / (m ² K). For the lower surface, the temperature was set to a constant 20 ° C. The heat input to the work piece 200 by the arc is the heat flux at the mesh point (x, y) = (15 mm, 15 mm) at the center of the upper surface and the four mesh points adjacent to the center mesh point within the upper surface. As given. The time increment was 0.5 seconds. The heat flux was optimized as an optimization parameter, and the heat input pattern was optimized using the conjugate gradient method. That is, the heat input pattern closest to the heat input pattern realizing the target temperature history was obtained.

  Here, there is no particular limitation on the method for optimizing the heat input pattern. In the above description, the conjugate gradient method is used. However, the optimization may be performed using any optimization algorithm such as a Newton method or a genetic algorithm widely used in various fields.

  FIG. 2 (b) shows the optimized heat input pattern for the first example of the target temperature history with a solid line, and FIG. 2 (a) shows the case where heat is input with the optimized heat input pattern. The temperature history of is shown by a thin solid line. When heat is input with a normal (non-optimized) pulse waveform indicated by a broken line in FIG. 2B, the temperature history greatly deviates from the target temperature history as indicated by the broken line in FIG. When heat was input with the optimized heat input pattern shown by the solid line in 2 (b), it was possible to match the target temperature history as shown by the thin solid line in FIG. 2 (a).

  FIG. 3A shows a second example of the target temperature history with a bold line. As shown in the figure, in the second example of the target temperature history, 2000 ° C. is maintained for 10 seconds, and the temperature is decreased at a rate of 175 ° C./s from 1500 ° C. near the melting point of steel to 800 ° C. at which the γ-α transformation starts. The By making this temperature range rapid cooling, dendrite coarsening and γ coarsening that start growing from the start of solidification are suppressed. Further, the temperature of 800 ° C. or lower is lowered at 1 ° C./s in the second example. In the second example, the material structure obtained by changing the cooling rate in the temperature region where the γ-α transformation starts is made as ferrite.

  In order to determine the heat input pattern that realizes this target temperature history, a three-dimensional heat conduction simulation by the difference method was performed. The conditions for this simulation are the same as those described in the first example. The heat flux was optimized as an optimization parameter, and the heat input pattern was optimized using the conjugate gradient method. That is, the heat input pattern closest to the heat input pattern realizing the target temperature history was obtained.

  FIG. 3B shows the optimized heat input pattern for the second example of the target temperature history with a solid line, and FIG. 3A shows the case where heat is input with the optimized heat input pattern. The temperature history of is shown by a thin solid line. When heat is input with a normal (non-optimized) pulse waveform indicated by a broken line in FIG. 3B, the temperature history greatly deviates from the target temperature history as indicated by the broken line in FIG. When heat was input with the optimized heat input pattern shown by a solid line in 3 (b), it was possible to match the target temperature history as shown by a thin solid line in FIG. 3 (a).

  FIG. 4A shows a third example of the target temperature history with a bold line. As shown in the figure, in the third example of the target temperature history, 2000 ° C. is maintained for 10 seconds, and the temperature is decreased at a rate of 175 ° C./s from 1500 ° C. near the melting point of steel to 800 ° C. at which the γ-α transformation starts. The By making this temperature range rapid cooling, dendrite coarsening and γ coarsening that start growing from the start of solidification are suppressed. In the third example, the temperature is lowered to 500 ° C. at 5 ° C./s, and then increased to 1100 ° C. at 50 ° C./s. After 1100 ° C. is maintained for 1 second, The temperature is lowered at / s. In the third example, after the γ-α transformation is started once, the γ transformation is caused again to obtain the effect of refining the structure.

  In order to determine the heat input pattern that realizes this target temperature history, a three-dimensional heat conduction simulation by the difference method was performed. The conditions for this simulation are the same as those described in the first example. The heat flux was optimized as an optimization parameter, and the heat input pattern was optimized using the conjugate gradient method. That is, the heat input pattern closest to the heat input pattern realizing the target temperature history was obtained.

  FIG. 4B shows the optimized heat input pattern for the third example of the target temperature history with a solid line, and FIG. 4A shows the case where heat is input with the optimized heat input pattern. The temperature history of is shown by a thin solid line. When heat is input with a normal (non-optimized) pulse waveform indicated by a broken line in FIG. 4B, the temperature history greatly deviates from the target temperature history as indicated by the broken line in FIG. When heat was input with the optimized heat input pattern shown by a solid line in FIG. 4B, the target temperature history could be matched as shown by a thin solid line in FIG.

  Moreover, in this Embodiment, you may make it accelerate | urge | promote transfer of a droplet by comprising the heat input pattern optimized with respect to the target temperature log | history with a pulse. The pulses constituting the heat input pattern may be constant during the welding time, but more preferably, the amount of heat per unit time (for example, one cycle) of the pulse is per unit time of the optimized heat input pattern. It is advisable to make it equal to the amount of heat.

FIG. 5 is a diagram showing an example of an optimized heat input pattern and a pulse in which the amount of heat per cycle is equal to this. In the figure, the peak value Q _P1 , peak width t _P1 , and base value of the first period are set so that the amount of heat per period of the pulse becomes equal to the amount of heat of the optimized heat input pattern in the time corresponding to one period. Q _B1 , base width t _B1 , second period peak value Q _P2 , peak width t _P2 , base value Q _B2 , base width t _B2 , third period peak value Q _P3 , peak width t _P3 , base value Q _B3 and base width t _B3 are adjusted.

  In that case, it is preferable that the base value is an amount of heat that can maintain the arc. The pulse period is not limited, but is preferably about 1 ms to 500 ms for promoting droplet transfer, and further preferably about 1 ms to several tens of ms for realizing a rapidly decreasing temperature history. Further, there is no limit on the number of pulses generated within one period. One pulse may be generated within one cycle, two pulses that promote droplet growth and droplet detachment may be generated and combined, or three or more pulses may be generated and combined.

  In the above description, the amount of heat per unit time of the pulse is described as being equal to the amount of heat per unit time of the optimized heat input pattern. However, the present invention is not limited to this. The former calorie need not be completely equal to the latter calorie, but may be substantially equal. That is, it is sufficient if the amount of heat per unit time of the pulse is matched with the amount of heat per unit time of the optimized heat input pattern.

  In the present embodiment, the welding torch 10 is connected to the welding power supply device 50 and is provided as an example of a device that is provided on the top, bottom, or side of the workpiece 200 and applies heat to the workpiece 200. It was. Here, the aspect which gives heat to the to-be-welded object 200 is not specifically limited. As described above, heating by arc discharge may be used, laser heating, resistance heating, or the like may be used.

  In the present embodiment, a temperature history closer to the target temperature history than the pulse heat input of the comparative example can be reproduced. That is, the heat input pattern optimization method and the optimized heat input pattern according to the present embodiment have an effect of controlling the structure of the welded portion.

DESCRIPTION OF SYMBOLS 1 ... Welding system, 10 ... Welding torch, 20 ... Robot arm, 30 ... Wire feeding apparatus, 40 ... Shield gas supply apparatus, 50 ... Power supply apparatus for welding, 60 ... Robot control apparatus, 100 ... Welding wire, 200 ... Cover Weldment

Claims (6)

In the welding method of welding the workpiece by continuously inputting heat to the welded portion of the workpiece,
It is a heat input pattern when heat is input to the welded portion, and accepts a heat input pattern for realizing a temperature history with the welded portion as a target metal structure when welding the workpiece.
The welding method, wherein heat is applied to the weld with the received heat input pattern.   The welding method according to claim 1, wherein the heat input is realized by arc discharge.   The welding method according to claim 1, wherein the heat input pattern includes a pulse.   The welding method according to claim 3, wherein the pulse has a shape in which a heat amount per unit time of the pulse matches a heat amount per unit time of the heat input pattern.   The welding method according to claim 4, wherein the shape is obtained by adjusting a peak value, a peak period, a base value, and a base period in one cycle of the pulse. A welding power source for supplying welding current;
Welding means for welding the workpiece by continuously applying heat to the welded portion of the workpiece,
The welding power source is a heat input pattern when heat is input to the welded portion, and a heat input pattern for realizing a temperature history with the welded portion as a target metal structure when welding the workpiece. And the welding means is controlled so as to input heat into the welded portion with the received heat input pattern.

Images