JP6905879B2 - Welding method and welding system - Google Patents

Description

The present invention relates to a welding method and a welding system for welding an object to be welded by temporarily applying heat to a welded portion of the object to be welded.

When arc welding is performed using a pulse current in which the first pulse and the second pulse, which have pulse peak current levels and pulse widths different from each other, are alternately repeated as a welding current, the welding arc is stabilized and the droplets are formed. A pulse arc welding method that improves transition regularity and significantly reduces spatter generation amount and fume generation amount is known (see, for example, Patent Document 1).

When the occurrence of a long-term short circuit is determined in the output control method of pulse arc welding in which the peak current during the peak period and the welding current with the base current during the base period as one pulse cycle are energized and welded, the long-term short circuit is released. A method of controlling the output of pulse arc welding that reduces the peak current and increases the base current during the transitional period until the subsequent welding voltage converges to a steady state is also known (see, for example, Patent Document 2).

This is an arc welding control method in which short-circuit arc welding is performed by repeating a short-circuit period and an arc period, and the peak current value of the initial short-circuit current or the output time of the peak current value for opening the short circuit at the start of the arc is set as the welding current. Also known is an arc welding control method that changes according to a value or a control parameter that adjusts the wire feed rate or the shape or heat input state of the tip of the welding wire (see, for example, Patent Document 3).

JP-A-2007-237270 Japanese Unexamined Patent Publication No. 2016-128186 Japanese Unexamined Patent Publication No. 2016-93842

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

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

For this purpose, the present invention is a welding method for welding a welded object by temporarily applying heat to the welded portion of the object to be welded, the amount of heat input when the heat is applied to the welded portion and the object to be welded. The temperature on the side opposite to the side to be heated, and the amount of heat input and the temperature to realize the temperature history in which the welded part is the target metal structure when welding the object to be welded are received and the received heat input amount. Provided is a welding method in which heat is input to a welded portion and the temperature on the side of the object to be welded opposite to the heat input side is adjusted to the received temperature.

Here, the heat input may be realized by arc discharge. Further, the amount of heat input may be given by a heat input pattern composed of pulses. Further, the heat input amount includes a first heat input amount when the welded portion is temporarily heated for the first time and a second heat input amount when the welded portion is temporarily heated for the second time. It may be a thing.

Further, in the present invention, a welding power source that supplies a welding current, a welding means that welds the work to be welded by temporarily applying heat to the welded portion of the work to be welded, and a side that receives heat from the work to be welded are used. The welding power supply is provided with an adjusting means for adjusting the temperature on the opposite side, and the welding power source is the amount of heat input when the welded portion is heated and the temperature on the side opposite to the heat input side of the work piece to be welded. When welding, it accepts the amount of heat input and temperature to realize the temperature history that makes the welded part the target metal structure, controls the welding means so that the received heat input amount enters the welded part, and controls the welded object. Welding systems that control the adjusting means to adjust the temperature on the side opposite to the heat input side to the accepted temperature are also provided.

Here, the welding means includes a first welding means that moves forward along the object to be welded and a second welding means that moves backward along the object to be welded, and the welding power source is used as a heat input amount. , The first heat input amount when temporarily inputting heat to the welded portion for the first time and the second heat input amount when temporarily inputting heat to the welded portion for the second time are accepted, and the first heat input amount is received. The first welding means may be controlled so as to enter heat into the welded portion, and the second welding means may be controlled so as to enter heat into the welded portion with the second amount of heat input.

According to the present invention, when the welded object is welded by temporarily applying heat to the welded portion of the workpiece, it is possible to realize a temperature history in which the welded portion has a target metal structure.

It is a figure which shows the schematic structure example of the welding system which concerns on 1st Embodiment (Example 1) of this invention. (A) is a diagram showing the target temperature history in Example 1, the temperature history when heat is input at the optimized heat input amount and the bottom surface temperature for this target temperature history, and the temperature history in the comparative example. b) is a figure which showed the evaluation function value with respect to the heat input amount and the bottom surface temperature of Example 1 and Comparative Example. It is a figure which shows the schematic structure example of the welding system which concerns on 2nd Embodiment (Example 2) of this invention. (A) is a diagram showing a target temperature history in Example 1, a target temperature history in Example 2, and a temperature history when heat is input at an optimized heat input amount and bottom surface temperature for these target temperature histories. Yes, (b) is a figure which showed the evaluation function value with respect to the heat input amount and the bottom surface temperature of Example 1 and Example 2. It is a figure which showed the example of the pulse which made the optimized heat input amount and the heat amount per cycle equal to this.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the embodiment of the present invention, in line welding, the temperature history of the welded portion for forming the metal structure at the time of welding according to the purpose by determining the amount of heat input to the welded portion and the temperature of the lower surface of the object to be welded. Is to be realized. Here, the line welding is welding performed by applying heat to the welded portion while moving with respect to the object to be welded. From the viewpoint of the welded portion, this can be regarded as welding performed by temporarily applying heat to the welded portion at least once.

[First Embodiment]
FIG. 1 is a diagram showing a schematic configuration example of a welding system 1 according to the first embodiment (Example 1) of the present invention. This welding system 1 welds the object to be welded 200 by a consumable electrode type (welding electrode type) gas shielded arc welding method.

This welding system 1 has 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 orientation of the welding torch 10. And have. Further, the welding system 1 includes a wire feeding device 30 for feeding the welding wire 100 to the welding torch 10 and a shield gas supply device 40 for supplying a shield gas (for example, carbon dioxide gas) to the welding torch 10. Further, the welding system 1 is a welding power supply device 50 as an example of a welding power source that supplies a DC welding current to the welding wire 100 and the object to be welded 200 via the welding torch 10 and controls the welding current, and a robot. It includes a robot control device 60 that controls the arm 20. Although not described in detail here, the welding power supply device 50 also 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 is input at a predetermined amount of heat input. Further, a metal plate 300 as an example of the adjusting means is attached to the lower surface of the object to be welded 200, and the power supply device 50 for welding of the metal plate 300 so that the temperature of the lower surface of the object to be welded 200 becomes a determined temperature. It also controls the temperature.

FIG. 2A shows the target temperature history of an arbitrary point on the object to be welded 200 in Example 1 with a thick solid line. As shown in the figure, in this target temperature history, the temperature is lowered at a rate of 175 ° C./s from 1500 ° C. near the melting point of the steel to 800 ° C. at which the γ-α transformation starts. By rapidly cooling this temperature range, the coarsening of dendrites and the coarsening of γ, which start to grow from the start of solidification, are suppressed. Further, it was decided to cool at 20 ° C./s below 800 ° C. By precipitating bainite at this cooling rate, a structure having a good balance between tensile strength and toughness can be obtained.

In order to determine the amount of heat input that realizes this target temperature history, a three-dimensional heat conduction simulation by the finite difference method was performed. The shape of the object to be welded 200 used in this simulation was a rectangular parallelepiped of 150 mm × 30 mm × 30 mm, and the rectangular parallelepiped was divided into meshes by dividing the rectangular parallelepiped at intervals of 3 mm in all directions. The time step was 0.5 seconds, and the welding speed was 5 mm / s. As for the physical properties, assuming steel, the thermal conductivity was 20 W / (mK), the density was 7870 kg / m ³ , and the specific heat was 435 J / (kgK). Further, as an initial condition, the intersections (mesh points) in all the meshes of the object to be welded 200 were set to 20 ° C. As the boundary conditions, the four surfaces other than the upper surface and the lower surface were set as heat insulating conditions. Regarding the upper surface, it was decided to exchange heat with the atmosphere by forced convection heat transfer with an outside air temperature of 20 ° C. and a heat transfer coefficient of 15 W / (m ^{2 K).} The heat input to the work piece 200 by the arc was applied as a heat flux to the mesh points (x, y) = (60 mm, 15 mm) on the upper surface and the four mesh points adjacent to the mesh points in the upper surface. Then, the bottom surface temperature was set to a constant condition of 300 ° C., the heat flux was used as an optimization parameter, and the amount of heat input was optimized using the conjugate gradient method. That is, the heat input amount closest to the heat input amount that realizes the target temperature history was obtained.

Here, there is no particular limitation on the method of optimizing the amount of heat input. In the above, the conjugate gradient method is used, but any optimization algorithm such as Newton's method or genetic algorithm widely used in various fields may be used for optimization.

FIG. 2A shows a thin solid line showing the temperature history of an arbitrary point on the work piece 200 when heat is input at the optimized heat input amount and the bottom surface temperature in Example 1. Comparative Example 1 shown by the alternate long and short dash line in FIG. 2A is a temperature history when the amount of heat input is optimized in the same manner as in Example 1 but the bottom surface temperature is 20 ° C., and FIG. 2A shows the temperature history. Comparative Example 2 shown by the alternate long and short dash line is a temperature history when the bottom surface temperature is the same as that of Example 1, but the amount of heat input is not optimized.

Further, FIG. 2B shows the heat input amount, the bottom surface temperature and the evaluation function value of Example 1, Comparative Example 1 and Comparative Example 2. Here, the evaluation function value is a value obtained by adding the deviations from the target temperature at each time in the time range where the target temperature is from 1500 ° C. to 400 ° C. The smaller the evaluation function value, the smaller the deviation from the target temperature. As shown in FIGS. 2A and 2B, by appropriately setting the bottom surface temperature and optimizing the amount of heat input as in Example 1, a temperature history close to the target temperature history could be obtained. .. In FIG. 2B, only 20 ° C. and 300 ° C. are shown as the bottom surface temperature, but this is also an evaluation function value when a plurality of bottom surface temperatures such as 100 ° C., 150 ° C., and 200 ° C. are set. Based on this, an appropriate bottom surface temperature may be obtained.

[Second Embodiment]
FIG. 3 is a diagram showing a schematic configuration example of the welding system 2 according to the second embodiment (Example 2) of the present invention. This welding system 2 also welds the object to be welded 200 by a consumable electrode type (welding electrode type) gas shielded arc welding method. However, this welding system 2 includes a welding system 1a and a welding system 1b having the same configuration as the welding system 1 shown in FIG.

Of these, the welding system 1a includes a welding torch 10a (hereinafter, also referred to as "preceding torch 10a") and a welding torch 10a as an example of a first welding means for welding an object to be welded 200 using a welding wire 100a. It is equipped with a robot arm 20a that holds and sets the position and orientation of the welding torch 10a. Further, the welding system 1a includes a wire feeding device 30a that feeds the welding wire 100a to the welding torch 10a, and a shield gas supply device 40a that supplies a shield gas (for example, carbon dioxide gas) to the welding torch 10a. Further, the welding system 1a includes a welding power supply device 50a as an example of a welding power source that supplies a DC welding current to the welding wire 100a and the object to be welded 200 via the welding torch 10a and controls the welding current, and a robot. It is provided with a robot control device 60a that controls the arm 20a. Although not described in detail here, the welding power supply device 50a also controls the welding speed, the feeding speed of the welding wire 100a, and the like in addition to the welding current. Further, the welding power supply device 50a controls the supply of the welding current to the welding wire 100a so that the heat is input at a predetermined amount of heat input. Further, a metal plate 300 as an example of the adjusting means is attached to the lower surface of the object to be welded 200, and the power supply device 50a for welding of the metal plate 300 so that the temperature of the lower surface of the object to be welded 200 becomes a determined temperature. It also controls the temperature.

Further, the welding system 1b includes a welding torch 10b (hereinafter, also referred to as "following torch 10b") as an example of a second welding means for welding the object to be welded 200 using the welding wire 100b. The portion of the welding system 1b including the robot arm 20b, the wire feeding device 30b, the shield gas supply device 40b, the welding power supply device 50b, and the robot control device 60b is the robot arm 20a, the wire feeding device 30a, and the shield of the welding system 1a. Since it is the same as the part including the gas supply device 40a, the welding power supply device 50a, and the robot control device 60a, the illustration is omitted.

FIG. 4A shows the target temperature history of an arbitrary point on the object to be welded 200 in Example 2 with a thick solid line. In FIG. 4A, for comparison, the target temperature history of an arbitrary point on the work piece 200 in Example 1 is also shown by a thick broken line. The target temperature history in Example 2 is different from the target temperature history in Example 1 only in the starting point, and the temperature lowering conditions and the like are the same.

In order to determine the amount of heat input that realizes this target temperature history, a three-dimensional heat conduction simulation by the finite difference method was performed. In Example 2, in order to bring the temperature closer to the target temperature than in Example 1, temperature control was performed using the preceding torch 10a and the trailing torch 10b as shown in FIG. The leading torch 10a and the trailing torch 10b were arranged so that their center points were 102 mm apart from each other. Further, the heat input by the trailing torch 10b was applied as a heat flux to the mesh points (x, y) = (60 mm, 15 mm) on the upper surface and 12 points around the mesh points. All the conditions other than those relating to the trailing torch 10b are the same as those in the first embodiment.

FIG. 4A shows a thin solid line showing the temperature history of an arbitrary point on the work piece 200 when heat is input at the optimized heat input amount and the bottom surface temperature in Example 2. In FIG. 4A, the temperature history of an arbitrary point on the work piece 200 when heat is input at the optimized heat input amount and the bottom surface temperature in Example 1 is also shown by a thin broken line.

Further, FIG. 4B shows the heat input amount, the bottom surface temperature and the evaluation function value of Example 1, and the first heat input amount, the second heat input amount, the bottom surface temperature and the evaluation function value of Example 2. Here, the first heat input amount of the second embodiment is the heat input amount by the preceding torch 10a, and is the heat input amount at the time of temporarily inputting heat to the welded portion for the first time when viewed from the welded portion. Further, the second heat input amount of the second embodiment is the heat input amount by the trailing torch 10b, and is the heat input amount at the time of temporarily inputting heat to the welded portion for the second time when viewed from the welded portion. The smaller the evaluation function value, the smaller the deviation from the target temperature. As shown in FIG. 4B, the evaluation function value of Example 2 is 1/3 or less of the evaluation function value of Example 1, and two welding torch, a leading torch 10a and a trailing torch 10b, are used. When the heat input amount was appropriately controlled by using the welding torch, the target temperature could be approached more than when the heat input amount of one welding torch was controlled.

[Modification example]
By pulsing the arc from the preceding torch 10a that melts the consumable electrode and promoting the droplet transfer, it is possible to improve the welding quality such as stabilizing the arc and suppressing spatter. At that time, the amount of heat generated in the unit time of the pulse (for example, one cycle) may be equal to the amount of heat generated at a constant heat input determined by the optimization method in the unit time.

FIG. 5 is a diagram showing an example of a pulse in which the optimized amount of heat input and the amount of heat per cycle are equal to this. _{In the figure, the peak value Q P} , the peak width t _P , the base value Q _B , and the base width t _B so that the amount of heat per cycle of the pulse is equal to the optimized amount of heat input in the time corresponding to one cycle. Has been adjusted. As a result, when focusing on a short time, the transfer of droplets is promoted, and when focusing on a long time, the temperature history of the welded portion is adjusted to the target.

At that time, the base value is preferably a calorific value that can maintain the arc. Although the period of the pulse is not limited, it is preferably about 1 ms to 500 ms in order to promote the droplet transfer, and more preferably about 1 ms to several tens of ms in order to realize a rapidly decreasing temperature history. In addition, there is no limit to the number of pulses created in one cycle. One pulse may be formed in one cycle, two pulses for promoting droplet growth and droplet detachment may be formed and combined, or three or more pulses may be formed and combined.

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

In the present embodiment, the welding torch 10 (welding torch 10a, 10b) is connected to the welding power supply device 50 (welding power supply device 50a, 50b) and is provided above, below, or beside the object to be welded 200. This is provided as an example of a device for applying heat to the object to be welded 200. Here, the mode in which heat is applied to the object to be welded 200 is not particularly limited. As described above, heating may be performed by arc discharge, laser heating, resistance heating, or the like.

Further, when two welding torches are used as in the second embodiment, it is preferable that the distance between the leading torch 10a and the trailing torch 10b is appropriately separated according to the welding member and the welding speed. As an example, when welding steel at a welding speed of 5 mm / s, the trailing torch 10b may be arranged about 50 mm to 150 mm behind the leading torch 10a. Further, in order to maintain the uniformity of the temperature history on the welding line, the moving speed of each welding torch is constant during welding, and it is preferable that the torches are always arranged at regular intervals.

Further, another welding torch may be provided behind the trailing torch 10b. Also in that case, it is preferable to appropriately separate the welding torches according to the welding member and the welding speed. By increasing the number of welding torches arranged at the rear and appropriately determining the amount of heat input, the deviation from the target temperature history can be further reduced.

Further, in the present embodiment, the metal plate 300 is attached to the object to be welded 200 in order to control the temperature of the lower surface of the object to be welded 200, but the present invention is not limited to this. For example, a halogen heater may be provided instead of the metal plate 300, and the welding power supply device 50 (welding power supply devices 50a, 50b) may control the amount of heat generated by the halogen heater.

Further, in the present embodiment, the welding power supply device 50 (welding power supply devices 50a and 50b) controls the temperature of the metal plate 300 and the amount of heat of the halogen heater, but the present invention is not limited to this. A control device other than the welding power supply device 50 (welding power supply devices 50a and 50b) may perform such control.

[Effect of this embodiment]
In the first embodiment and the second embodiment, the temperature history closer to the target temperature history than that of the comparative example can be reproduced. That is, the method for optimizing the heat input amount and the bottom surface temperature and the optimized heat input amount and the bottom surface temperature according to the present embodiment have an effect of controlling the structure of the welded portion.

1a, 1b, 2 ... Welding system, 10a ... Welding torch (preceding torch), 10b ... Welding torch (following torch), 20a, 20b ... Robot arm, 30a, 30b ... Wire feeder, 40a, 40b ... Shield gas Supply device, 50a, 50b ... Welding power supply device, 60a, 60b ... Robot control device, 100a, 100b ... Welding wire, 200 ... Welded object, 300 ... Metal plate

Claims (4)

In a welding method in which the welded object is welded by temporarily applying heat to the welded portion of the object to be welded.
The amount of heat input when heat is applied to the welded portion and the temperature on the side opposite to the heat input side of the work piece to be welded, and the welded part is designated as the target metal structure when the work piece to be welded is welded. Accepts the amount of heat input and temperature to realize the temperature history,
Heat is input to the welded portion with the received heat input amount, and the heat is input to the welded portion.
The temperature on the side opposite to the side where the heat is input to the work to be welded is adjusted to the received temperature.
The heat input amount includes a first heat input amount when the welded portion is temporarily heated for the first time and a second heat input amount when the welded portion is temporarily heated for the second time. A welding method characterized by that. The welding method according to claim 1, wherein the heat input is realized by an arc discharge. The welding method according to claim 1, wherein the heat input amount is given by an heat input pattern composed of pulses. Welding power supply that supplies welding current and
Welding means for welding the work piece by temporarily applying heat to the welded part of the work piece, and
It is provided with an adjusting means for adjusting the temperature on the side opposite to the side where the heat is input to the object to be welded.
The welding power source has a heat input amount when heat is input to the welded portion and a temperature on the side opposite to the heat input side of the welded object, and aims at the welded portion when welding the welded object. The welding means is controlled so as to receive the heat input amount and temperature for realizing the temperature history of the metal structure of the above, and to input heat to the welded portion with the received heat input amount, and the side to which the heat is input to the object to be welded. The adjusting means is controlled so as to adjust the temperature on the opposite side to the received temperature .
The welding means includes a first welding means that moves forward along the work piece and a second welding means that moves backward along the work piece.
The welding power supply has, as the heat input amount, a first heat input amount when temporarily inputting heat to the welded portion for the first time and a second heat input amount when temporarily inputting heat to the welded portion for the second time. The first welding means is controlled so that the first heat input amount receives heat and the first heat input amount enters the welded portion, and the second heat input amount receives heat into the welded portion. A welding system characterized by controlling the welding means of 2.

Images