JP7548131B2 - Arc stud welding method and arc stud welding device - Google Patents

Description

This disclosure relates to an arc stud welding method and an arc stud welding device.

In arc stud welding, a pilot arc is first generated between the stud and the base metal, and then a main arc is generated by passing a current larger than that of the pilot arc to melt the surface of the base metal. The stud is then welded to the base metal by pushing the stud toward the molten surface of the base metal (see, for example, Patent Document 1).

JP 2005-246395 A

When the base material is a thin plate, the melting may reach the back side of the base material in the main arc, a phenomenon known as strike-through. If the stud is pressed into the base material in this state, cracks may form on the back side of the base material.

This disclosure can be realized in the following forms:

(1) According to one embodiment of the present disclosure, an arc stud welding method is provided. This arc stud welding method includes a first step of setting a welding current flowing between a stud and a base metal to a first current value and generating a pilot arc, a second step of setting the welding current to a second current value greater than the first current value and generating a main arc, a third step of switching the welding current to a third current value smaller than the second current value and causing the main arc to be continuously generated after the second step and causing the welding current of the third current value to flow for a predetermined period, and a fourth step of pressing the stud into the base metal after the third step. According to this embodiment, in the third step before the fourth step of pressing the stud into the base metal, the current value is set small enough to generate a main arc, thereby suppressing heat input. As a result, even if the back surface of the base metal is melted, it cools and solidifies, so that even if the stud is pressed in the fourth step thereafter, the occurrence of cracks on the back surface of the base metal is suppressed.
(2) In the arc stud welding method of the above aspect, when the second current value is Im and the third current value is Ia, Ia may satisfy the following formula (1).
Ia=α×Im...Formula (1)
However, 0.1≦α≦0.3
According to this embodiment, since the heat input can be suppressed while the main arc is generated, the molten pool formed on the welding surface of the base metal can be maintained while the back surface of the base metal is solidified. Therefore, the stud can be welded while suppressing the occurrence of cracks on the back surface of the base metal.
(3) In the arc stud welding method of the above aspect, the predetermined period may be set to be equal to or greater than 2 ms and equal to or less than 10 ms. According to this aspect, even if the rear surface of the base metal is molten, the rear surface of the base metal can be reliably solidified.
(4) In the arc stud welding method of the above aspect, the fourth step may include a first moving step of moving the stud closer to the base metal at a first speed, and a second moving step of pushing the stud into the base metal at a second speed lower than the first speed. According to this aspect, by pushing the stud into the base metal at the second speed lower than the first speed, the kinetic energy that the base metal receives from the stud is reduced, so that the occurrence of cracks can be further suppressed. In addition, by setting the speed at which the stud is moved closer to the base metal to the first speed higher than the second speed, an increase in the time required for the fourth step can be suppressed.
(5) In the arc stud welding method of the above aspect, when the first speed is V0 and the second speed is V1, V1 satisfies the following formula (2).
V1=β×V0...Formula (2)
However, 0.1≦β≦0.5 and V1≦0.1 mm/ms
According to this embodiment, the occurrence of cracks in the fourth step can be reliably suppressed.
(6) According to one aspect of the present disclosure, there is provided an arc stud welding device. The arc stud control device includes a welding gun that drives a gripped stud into a base metal, a power supply device that supplies a welding current to the stud and the base metal, and a control device that controls the welding gun and the power supply device. The control device executes the following steps: a first step of setting the welding current to a first current value and generating a pilot arc, a second step of setting the welding current to a second current value that is greater than the first current value and generating a main arc, a third step of switching the welding current to a third current value that is less than the second current value and that causes the main arc to be continuously generated after the second step, and flowing the welding current at the third current value for a predetermined period of time, and a fourth step of driving the stud into the base metal after the third step. According to this aspect, in the third step before the fourth step of driving the stud into the base metal, the current value is set small enough to generate a main arc, thereby suppressing heat input. As a result, even if the rear surface of the base material is molten, it will cool and harden, so that even if the stud is pressed into the rear surface of the base material in the subsequent fourth step, the occurrence of cracks on the rear surface of the base material is suppressed.
The present disclosure may be realized in various forms other than the arc stud welding method and arc stud welding apparatus, for example, a control method for an arc stud welding apparatus, a computer program for implementing the control method, a non-transitory recording medium on which the computer program is recorded, etc.

FIG. 1 is a schematic diagram showing a configuration of an arc stud welding device. 4 is a flowchart showing an arc stud welding process. FIG. 1 is a diagram showing the relationship between welding current, welding voltage, and stud position and time in an arc stud welding process. FIG. 13 is a schematic diagram showing the molten state of a stud and a base material in a comparative example. FIG. 11 is a diagram showing the relationship between the position of a stud and time in a fourth step according to the second embodiment.

A. First embodiment:
A1. Configuration of the Arc Stud Welding Apparatus FIG. 1 is a schematic diagram showing the configuration of the arc stud welding apparatus 100. The arc stud welding apparatus 100 generates an arc discharge between a stud 10 and a base material 20, melts the base material 20 by the generated arc discharge, and then presses the stud 10 into the base material 20 to weld it. Specifically, the stud 10 is, for example, a stud bolt or a round bar. The base material 20 has a welding surface 20a to which the stud 10 is welded and a back surface 20b opposite to the welding surface 20a. For the base material 20, for example, various metal materials such as steel, aluminum, and aluminum alloys can be used. In this embodiment, a steel plate used for a vehicle body is used as the base material 20, and a stud bolt is used as the stud 10. The arc stud welding apparatus 100 includes a welding gun 40, a power supply unit 60, and a control unit 70.

The welding gun 40 has a chuck 41, a moving mechanism 42, and a leg 43. The chuck 41 is made of a conductor and holds the stud 10. The welding gun 40 is installed so that the axis of the stud 10 held by the chuck 41 is approximately perpendicular to the welding surface 20a of the base material 20. The chuck 41 moves forward and backward in the axial direction of the stud 10 by the moving mechanism 42. In this embodiment, the moving mechanism 42 is configured as a solenoid having a coil spring and a coil (not shown). The coil spring biases the chuck 41 toward the base material 20. When the coil is energized, the chuck 41 and the stud 10 are electromagnetically attracted to each other and positioned at the separation position P1 shown by the solid line in FIG. 1. When the chuck 41 and the stud 10 are positioned at the separation position P1, the coil spring is compressed. When the coil is de-energized, the magnetic attraction is released, and the chuck 41 and stud 10 move toward the base material 20 due to the biasing force of the coil spring. In FIG. 1, the stud 10 and chuck 41 are shown by dashed lines at contact position P0 where the stud 10 contacts the base material 20. The movement mechanism 42 may be configured to move the chuck 41 forward and backward using, for example, a linear motor. The legs 43 are provided to hold down the base material 20 during the welding process.

The power supply unit 60 and the chuck 41 are electrically connected by a first power cable 82. The power supply unit 60 and the base material 20 are electrically connected by a second power cable 83. The power supply unit 60 supplies DC power to the stud 10 and the base material 20, which are electrically connected to the chuck 41, through the first power cable 82 and the second power cable 83.

The control device 70 is configured as a computer having a CPU and memory. The memory stores a program for executing the arc stud welding process described below, and current values such as the first current value Ip and times such as the welding time Tm used in the arc stud welding process. The control device 70 has a position control unit 71 and a power control unit 72 as functional units. The position control unit 71 and the power control unit 72 are realized by executing a program stored in the memory. The control device 70, the position control unit 71, and the power control unit 72 may be realized by a hardware circuit, or may be realized by a combination of a computer and a hardware circuit. The position control unit 71 and the movement mechanism 42 are connected to be able to communicate with each other. The position control unit 71 controls the movement mechanism 42. The power control unit 72 and the power supply unit 60 are connected to be able to communicate with each other. The power control unit 72 controls the power supply unit 60 so that the current value of the power output from the power supply unit 60 becomes a target current value.

A2. Arc stud welding process:
FIG. 2 is a flow chart of the arc stud welding process according to the present embodiment. FIG. 3 is a diagram showing the relationship between the welding current, welding voltage, and stud position and time in the arc stud welding process. The upper part of FIG. 3 is a diagram showing the relationship between time and welding current. The middle part of FIG. 3 is a diagram showing the relationship between time and welding voltage. The lower part of FIG. 3 is a diagram showing the relationship between time and stud position. The times shown in the upper, middle, and lower parts of FIG. 3 indicate the same time, and are expressed in units of [ms]. The welding current is a current output from the power supply device 60, and is equivalent to the current flowing between the stud 10 and the base material 20. The welding voltage is a voltage output from the power supply device 60. As described above, the power supply device 60 is controlled so that the current value of the welding current becomes the target current value. During a period in which the welding current is constant, the voltage value of the welding voltage actually fluctuates depending on the electrical resistance value between the stud 10 and the base material 20, but in FIG. 3 and the following description, for convenience, the voltage value is assumed to be a flat voltage value. The stud position in Figure 3 is expressed based on the contact position P0 where the stud 10 and the welding surface 20a come into contact, with the direction in which the stud 10 moves away from the welding surface 20a being expressed as a positive direction and the direction in which the stud 10 is pressed further into the welding surface 20a being expressed as a negative direction.

In arc stud welding, a pilot arc is first generated between the stud 10 and the base material 20, and then a main arc is generated by passing a current larger than that of the pilot arc to melt the vicinity of the welding surface 20a of the base material 20. Next, the stud 10 is pressed toward the welding surface 20a of the molten base material 20 to weld the base material 20 and the stud 10. Here, if the base material 20 is a thin plate, the molten pool may reach the back surface 20b of the base material in the main arc, which is called back penetration. If the stud 10 is pressed in a state where back penetration has occurred, part of the molten metal on the back surface 20b of the base material 20 may scatter, and cracks may occur on the back surface 20b. Therefore, in this embodiment, the welding current in the main arc is devised. This makes it possible to suppress the occurrence of cracks on the back surface 20b of the base material 20. The arc stud welding process according to this embodiment will be described next.

For example, when a start switch for accepting the start of the arc stud welding process provided in the control device 70 is pressed, the arc stud welding process is started. In process P10 shown in FIG. 2, the stud 10 is gripped by the chuck 41 of the welding gun 40. As shown in FIG. 3, in process P10, the moving mechanism 42 positions the stud 10 at a distanced position P1 away from the welding surface 20a of the base material 20. In process P20 shown in FIG. 2, the moving mechanism 42 moves the chuck 41 so as to approach the base material 20, and the stud 10 contacts the base material 20. With the stud 10 and the base material 20 in contact, the power supply 60 starts outputting the welding voltage. In this embodiment, the current value of the welding current is set to the same current value as when the pilot arc is generated. As shown in FIG. 3, in process P20, the moving mechanism 42 moves the stud 10 to a contact position P0 where the stud 10 contacts the welding surface 20a of the base material 20. When the stud 10 is located at the contact position P0, a welding voltage of a first voltage value Ep is output from the power supply 60 so that the current value of the welding current becomes a first current value Ip.

In the first step P30 shown in FIG. 2, the stud 10 is moved away from the base material 20 by the moving mechanism 42. The welding current is set to a first current value Ip by the control of the power control unit 72. As shown in FIG. 3, when the stud 10 moves in a direction away from the base material 20 while current is flowing between the stud 10 and the base material 20, a pilot arc, which is an arc discharge through which a small current flows, is generated between the stud 10 and the base material 20.

In the second step P40 shown in FIG. 2, the welding current is set to a second current value Im under the control of the power control unit 72. The second current value Im is a current value that is greater than the first current value Ip and is large enough to generate a main arc. As shown in FIG. 3, in the second step P40, with the stud 10 positioned at the separation position P1, a welding voltage of a second voltage value Em is output from the power supply unit 60 so that the current value of the welding current becomes the second current value Im. As a result, a main arc, which is an arc discharge through which a large current flows, is generated between the stud 10 and the base material 20. The generation of the main arc melts the base material 20, and a molten pool is formed.

2, the set value of the welding current is switched to a third current value Ia that is smaller than the second current value Im under the control of the power control unit 72. The third current value Ia is a current value that is large enough to cause the main arc to be generated continuously and that satisfies formula (3).
Ia=α×Im...Formula (3)
However, 0.1≦α≦0.3
By satisfying the above formula (3), the rear surface 20b can be sufficiently cooled and solidified while stably maintaining the main arc. In the step P60, the supply of the welding current having the third current value Ia for a third current supply time Ta, which will be described later as a predetermined time, is continued, so that the main arc continues to be generated. The steps P50 and P60 are also referred to as the third step. As shown in FIG. 3, in the step P50, a welding voltage having a third voltage value Ea smaller than the second voltage value Em is output from the power supply device 60 so that the current value of the welding current becomes the third current value Ia. In the step P50, the current value of the welding current is set small, so that even if the base material 20 is melted up to the rear surface 20b, the heat input to the base material 20 can be suppressed, so that the vicinity of the rear surface 20b of the base material 20 can be solidified. Therefore, even if the stud 10 is pressed into the base material 20 in the next fourth step P70, the occurrence of cracks can be suppressed.

In the fourth step P70 shown in FIG. 2, the stud 10 is pushed into the base material 20 by the moving mechanism 42, the output of the welding voltage by the power supply 60 is stopped, and the welding step is completed. As shown in FIG. 3, in the fourth step P70, the stud 10 is moved further from the contact position P0 in a direction toward the base material 20. This causes the stud 10 to be pushed into the molten pool formed in the base material 20. The output of the welding voltage is stopped at the same time that the movement of the stud 10 starts. When the output of the welding voltage is stopped, the heat input is stopped, so the molten metal cools and solidifies, and the stud 10 and the base material 20 are joined.

The welding time Tm shown in FIG. 3, specifically, the time from when the current value of the welding current is switched from the first current value Ip to the second current value Im to when the stud 10 starts to be pushed in, is adjusted according to the material and thickness of the base material 20. The welding time Tm is determined in advance by experiments or the like according to the material and thickness of the base material 20, and is stored in advance in the memory of the control device 70. The control device 70 then controls the power supply device 60 using the stored welding time Tm. In this embodiment, the welding time Tm is about 40 ms. The third current supply time Ta, specifically, the period from when the current value of the welding current is switched from the second current value Im to the third current value Ia to when the stud 10 starts to be pushed in, is preferably about 30% or less of the welding time Tm. In this embodiment, the third current supply time Ta is 2 ms or more and 10 ms or less. By setting the third current supply time Ta within the above range, the rear surface 20b can be sufficiently cooled, and the molten metal on the rear surface 20b can be solidified while the molten pool formed in the base material 20 can be sufficiently grown. By reducing the current value of the welding current before starting to push the stud 10, even if the base material 20 is molten up to the rear surface 20b, the heat input to the base material 20 can be suppressed, so that the vicinity of the rear surface 20b of the base material 20 can be solidified. Therefore, the occurrence of cracks on the rear surface 20b can be suppressed.

The effect of the arc stud welding process according to this embodiment will be explained using FIG. 4. FIG. 4 is a schematic diagram showing the molten state of the stud 10 and the base material 20 when a pilot arc is generated, when a main arc is generated, and when welding is completed in a comparative example. (a) of FIG. 4 shows the molten state when a pilot arc is generated. (b) of FIG. 4 shows the molten state when a main arc is generated. (c) of FIG. 4 shows the molten state when welding is completed. In the arc stud welding process in the comparative example, the welding current when the main arc is generated is maintained at the second current value Im, as shown by the dashed line in FIG. 3.

As shown in FIG. 4(a), the pilot arc is generated near the axis of the stud 10. Therefore, heat is concentrated at the central part 20c of the base material 20, which is the intersection of the axis of the stud 10 and the welding surface 20a. As a result, a molten pool 200 is formed near the central part 20c. When the next main arc is generated, an arc discharge occurs from the entire surface of the stud 10 facing the base material 20. The molten pool 200 formed by the pilot arc grows due to the main arc. Therefore, the molten pool 200 near the central part 20c is closer to the back surface 20b than the molten pool 200 around the central part 20c. When the molten pool 200 grows further from the state shown in FIG. 4(b), the molten pool 200 near the central part 20c becomes exposed from the back surface 20b, resulting in a back-through state. As shown in FIG. 4(c), when the stud 10 is pushed in in the back-through state, part of the molten metal on the back surface 20b is scattered by the kinetic energy provided by the stud 10. When the back surface 20b is then cooled and solidified, cracks occur near the area where the molten metal was scattered. In this embodiment, the welding current is set to the third current value Ia before the stud 10 is plunged into the base material 20, and heat input is suppressed, so that the molten metal near the back surface 20b solidifies and the molten pool 200 shrinks to the position shown by the dashed line in Figure 4(c). Therefore, even if the stud 10 is plunged in thereafter, penetration to the back surface is suppressed, so the occurrence of cracks can be suppressed.

The arc stud welding method according to the first embodiment described above includes a first step P30 for generating a pilot arc, a second step P40 for generating a main arc, a third step including a step P50 for switching the welding current to a third current value Ia after the second step P40, and a step P60 for flowing the welding current at the third current value Ia until the third current supply time Ta has elapsed, and a fourth step P70 for forcing the stud 10 into the base material 20. In the third step, the welding current is switched to the third current value Ia, which is smaller than the second current value Im, which is the welding current in the second step P40. Therefore, the heat input to the base material 20 is suppressed, and even if the back surface 20b of the base material 20 is melted, the molten metal on the back surface 20b cools and solidifies, so that even if the stud 10 is pressed in the fourth step P70, the occurrence of cracks on the back surface 20b is suppressed.

The third current value Ia satisfies the above formula (3). Therefore, in process P60, the heat input can be suppressed while the main arc is generated, so that the back surface 20b can be solidified while maintaining the molten pool 200 formed on the welding surface 20a of the base material 20. Therefore, the stud 10 can be welded while suppressing the occurrence of cracks on the back surface 20b. In addition, the third current supply time Ta is set to 2 ms or more and 10 ms or less. Therefore, even if the back surface 20b of the base material 20 is melted, the back surface 20b can be reliably cooled and solidified.

B. Second embodiment:
5 is a diagram showing the relationship between the position of the stud 10 and time in the fourth step P70 according to the second embodiment. In the second embodiment, a further improvement is made in the fourth step P70 of the arc stud welding process compared to the first embodiment. The steps other than the fourth step P70 are the same as those in the first embodiment, so a description thereof will be omitted. Also, in this embodiment, the moving mechanism 42 is configured using a linear motor instead of a solenoid, and the moving speed of the chuck 41 is controlled by commands from a position control unit 71.

As shown in Fig. 5, in this embodiment, the speed at which the stud 10 is pressed into the base material 20 is adjusted in two stages in the fourth step P70. Specifically, the stud 10 is moved at a first speed V0 during the period from time t1 to time t2, and is moved at a second speed V1 lower than the first speed V0 during the period from time t2 to time t3. The step of moving the stud 10 closer to the base material 20 at the first speed V0 during the period from time t1 to time t2 is also referred to as a first movement step. The step of pressing the stud 10 into the base material 20 at the second speed V1 lower than the first speed V0 is also referred to as a second movement step. Here, the second speed V1 is expressed by the following formula (4).
V1=β×V0...Formula (4)
However, 0.1≦β≦0.5 and V1≦0.1 mm/ms
In other words, the second speed V1 when the stud 10 contacts the base material 20 is set to be smaller than the first speed V0 when the stud 10 starts to be pressed. This makes it possible to reduce the kinetic energy that the base material 20 receives from the stud 10. This further suppresses the occurrence of cracks. By making the second speed V1 satisfy the above formula (4), it is possible to suppress the scattering of molten metal while pressing the stud 10 into the base material 20 with sufficient force to ensure sufficient weld strength.

According to the second embodiment described above, the fourth step P70 includes a first movement step in which the stud 10 is brought closer to the base material 20 at a first speed V0, and a second movement step in which the stud 10 is pushed into the base material 20 at a second speed V1 that is smaller than the first speed V0. By pushing the stud 10 into the base material 20 at the second speed V1 that is smaller than the first speed V0, the kinetic energy that the base material 20 receives from the stud 10 is reduced, and the occurrence of cracks can be further suppressed. By setting the speed at which the stud 10 is brought closer to the base material 20 to the first speed V0 that is larger than the second speed V1, the increase in the time required for the fourth step P70 can be suppressed. In addition, the second speed V1 satisfies the above formula (4). This makes it possible to reliably suppress the occurrence of cracks in the fourth step P70.

C. Other embodiments:
(C1) In the first embodiment, in the fourth step P70, the output of the welding voltage is stopped at the same time as the movement of the stud 10 starts. In other words, the time when the output of the welding voltage is stopped is the same as the time when the movement of the stud 10 starts. In contrast, the time when the output of the welding voltage is stopped may be different from the time when the movement of the stud 10 starts. Specifically, for example, the output of the welding voltage may be stopped after the movement of the stud 10 starts. Regardless of the time when the output of the welding voltage is stopped relative to the time when the movement of the stud 10 starts, by performing step P50 and the subsequent step P60 in which the welding current of the third current value Ia is supplied until the third current supply time Ta has elapsed, the heat input to the base material 20 can be suppressed.

(C2) In the second embodiment, the movement mechanism 42 is configured using a linear motor. As another example of the configuration of the movement mechanism 42, it may be configured using a ball screw and a motor.

The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features of the embodiments corresponding to the technical features in each form described in the Summary of the Invention column can be replaced or combined as appropriate to solve some or all of the above-described problems or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

10... stud, 20... base material, 20a... welding surface, 20b... back surface, 20c... center, 40... welding gun, 41... chuck, 42... moving mechanism, 43... leg, 60... power supply, 70... control device, 71... position control unit, 72... power control unit, 82... first power cable, 83... second power cable, 100... arc stud welding device, 200... molten pool, Ep... first voltage value, Em... second voltage value, Ea... third voltage value, Ip... first current value, Im... second current value, Ia... third current value, P0... contact position, P1... separation position, P10, P20, P50, P60... process, P30... first process, P40... second process, P70... fourth process, Tm... welding time, Ta... third current supply time, V0... first speed, V1... second speed

Claims (6)

1. An arc stud welding method comprising:
A first step of setting a welding current flowing between a stud and a base metal to a first current value and generating a pilot arc;
a second step of setting the welding current to a second current value greater than the first current value and generating a main arc;
a third step of switching the welding current to a third current value that is smaller than the second current value and that allows the main arc to be continuously generated after the second step, and flowing the welding current of the third current value for a predetermined period of time;
a fourth step, after the third step, of pressing the stud into the base material. 2. The arc stud welding method according to claim 1,
2. An arc stud welding method, wherein, when the second current value is Im and the third current value is Ia, Ia satisfies the following formula (1).
Ia=α×Im...Formula (1)
However, 0.1≦α≦0.3 The arc stud welding method according to claim 1 or 2,
4. An arc stud welding method, wherein the predetermined period is greater than or equal to 2 ms and less than or equal to 10 ms. The arc stud welding method according to any one of claims 1 to 3,
The fourth step comprises:
a first moving step of moving the stud toward the base material at a first speed;
a second moving step of driving the stud into the base metal at a second speed that is slower than the first speed. 5. The arc stud welding method according to claim 4,
2. An arc stud welding method, wherein, when the first speed is V0 and the second speed is V1, V1 satisfies the following formula (2).
V1=β×V0...Formula (2)
However, 0.1≦β≦0.5 and V1≦0.1 mm/ms 1. An arc stud welding device comprising:
A welding gun that presses the held stud into the base material;
a power supply device for supplying a welding current to the stud and the base material;
a control device that controls the welding gun and the power supply device,
The control device includes:
a first step of setting the welding current to a first current value and generating a pilot arc;
a second step of setting the welding current to a second current value greater than the first current value and generating a main arc;
a third step of switching the welding current to a third current value that is smaller than the second current value and that allows the main arc to be continuously generated after the second step, and flowing the welding current of the third current value for a predetermined period of time;
and a fourth step of pressing the stud into the base material after the third step.

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