GB2468011A

GB2468011A - Method for applying current for resistive welding

Info

Publication number: GB2468011A
Application number: GB201001545A
Authority: GB
Inventors: Toshinori Miyamoto; Masato Sasaki; Yuya Ishikawa; Katsushi Honda; Shinsuke Nakamura
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2009-02-20
Filing date: 2010-01-29
Publication date: 2010-08-25
Anticipated expiration: 2030-01-29
Also published as: JP2010188408A; GB2468011B; GB201001545D0

Abstract

A method for applying current for resistive welding that is less likely to generate sputter in a case of welding a high-tensile material or a hot-stamped material, and that can improve electrode life. The method including; Steps S1 and S2 of applying amperage of a magnitude that softens a surface of a joining location of the high-tensile material, continuously for an initial energizing period, a Step S3 of, when the initial energizing period has passed, switching an energization amount from the amperage to amperage that causes a nugget 6 to grow at the joining location; and Steps S4 and S5 of applying the amperage continuously for a latter energizing period.

Description

I

METHOD FOR APPLYING CURRENT FOR RESISTIVE WELDING

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2009-038009, filed on 20 February 2009, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for applying current for resistive welding.

* More specifically, the present invention relates to a method for applying current for resistive welding such as spot welding in cases of joining high-tensile materials or hot-stamped materials, and the like.

Related Art A spot weld is a weld in which overlapping steel plates are pressed and welding current is passed therethrough, and thus welding is performed by growing a nugget at a joining location of the two steel plates.

Among common current patterns in such spot welding, the square-waveform current pattern illustrated in FIG. 5A, the trapezoidal-waveform current pattern illustrated in FIG 5B, and the pulse-waveform current pattern illustrated in FIG. 5C are known (see Patent Document 1).

As illustrated in FIG. 5A, the square-waveform current pattern maintains a certain amperage for a certain duration from the beginning of energization to the end of energization, That is, energization with amperage ia starts at time tO. This amperage ia is continuously maintained until time ta. Then, the energization with the amperage ia ends at time ta.

In other words, the energization is performed such that the amperage ia is continued over an energizing period Ta.

As illustrated in FIG. 5B, the trapezoidal-waveform current pattern gradually raises amperage from the beginning of energization and, after a certain amperage is reached, maintains this amperage for a certain duration until the end of energization.

That is, from time tO to time tbl, the amperage rises at a certain rate from iO to ib.

This amperage ib is continuously maintained from time tbl until time tb2. Then, the energization with the amperage ib ends at time tb2.

In other words, the energization is performed such that the amperage rises at a constant rate through an energizing period Tbl, and the raised amperage ib is continued over an energizing period Tb2.

As illustrated in FIG. 5C, the pulse-waveform current pattern repeats energization and cutoff of a certain amperage from the beginning of energization to the end of energization.

That is, energization with the amperage ic starts at time tO and this amperage Ic is continuously maintained until time tcl. The energization with the amperage Ic ends at time tcl and amperage iO is maintained until time tc2. Thereafter, energization and cutoff of the amperage ic is repeated in the same manner.

In other words, the energization is carried out such that the amperage ic is continued through each of the energizing periods Tcl, Tc3, Tc5, Tc7 and Tc9. Energization pause. periods Tc2, Tc4, Tc6 and Tc8 are respectively interposed between the energizing periods Tcl, Tc3, Tc5, Tc7 and Tc9.

Patent Document 1: Japanese Unexamined Patent Publication No. 2006-181621

SUMMARY OF THE INVENTION

However, the square-waveform current pattern shown in FIG. 5A has the following problem.

A surface plating layer as in, for example, a hot-stamped material is very hard and coarse. Consequently, when joining a material for which it is difficult to obtain a stabilized energization path simply by overlapping and pressing, the energization is localized, more heat than required is generated, the nugget tends to grow very rapidly, and sputter tends to be produced.

The trapezoidal-waveform current pattern shown in FIG. 58 has the following problem.

When joining a hot-stamped material, for example, in conditions in which softening of a surface plating layer does not progress through energizing period Tbl, the nugget grows very rapidly in energizing period Tb2, and sputter tends to be produced.

The pulse-waveform current pattern shown in FIG. 5C has the following problem.

When joining a hot-stamped material, for example, the surface plating is repeatedly melted and solidified by the repetition of heating and cooling. Thus, plating at portions that touch against electrode tips adheres to the electrode tips and accumulates thereon. As a result, electrode life is greatly impaired.

The present invention has been made in consideration of the above situation, and it is an object of the present invention to provide a method for applying a current for resistive welding that is less likely to generate sputter in a case of joining a high-tensile material or a hot-stamped material and that can improve electrode life.

* The method for applying current for resistive welding according to the present invention is a method for applying current for resistive welding of a plate assembly in which the material of at least one plate is a high-tensile material (for example, a later-described high-tensile material 1 or 2), in which the method includes: a first step (for example, later-described Steps Si and S2) of applying a first amperage (for example, a later-described * amperage ip) of a magnitude that softens a surface of a joining location of the high-tensile material, continuously for a first predetermined duration (for example, a later-described initial energizing period Ip); a second step (for example, a later-described Step S3) of, when the first predetermined duration has passed, switching an energization amount from the first amperage to a second amperage (for example, a later-described amperage im), which causes a nugget to grow at the joining location; and a third step (for example, later-described Steps S4 and S5) of applying the second amperage continuously for a second predetermined duration (for example, a later-described latter energizing period Tm).

According to the present invention, due to the continuous energization with the first amperage for the first predetermined duration, the surface of the joining location of the high-tensile material is sufficiently softened before being joined, contact problems at the joining location are eliminated, and a stabilized energization path is assured.

Due to the continuous energization with the second amperage for the second predetermined duration, a stabilized welding state is assured at the joining location of the high-tensile material, the nugget grows properly, and sputter is unlikely to be produced.

The method for applying current for resistive welding according to the present invention is a method for applying current for resistive welding of a plate assembly in which the material of at least one plate is a hot-stamped material (for example, a later-described hot-stamped material 1 or 2), in which the method includes: a first step (for example, later-described Steps Sli and S12) of applying first amperage, of a magnitude that softens a plating layer at a joining location of the hot-stamped material, continuously for a first predetermined duration; a second step (for example, a later-described Step Si 3) of, when the first predetermined duration has passed, switching an energization amount from the first amperage to a second amperage, which causes a nugget to grow at the joining location; and a third step (for example, later-described Steps S14 and S15) of applying the second amperage continuously for a second predetermined duration.

According to the present invention, because of the continuous energization with the first amperage for the first predetermined duration, the plating layer at the joining location of the hot-stamped material is thoroughly softened, contact problems at the joining location are eliminated and a stable energization path is assured.

Due to the continuous energization with the second amperage for the second predetermined duration, a stabilized welding state is assured at the joining location of the hot-stamped material, the nugget grows properly, and sputter is unlikely to be produced.

In addition, since the plating of the hot-stamped material is not repeatedly melted and solidified, adherence of the plating to an electrode tip may be prevented, and electrode life can be improved.

According to the present invention, when high-tensile materials or hot-stamped materials are to be joined, surfaces at a joining location of the high-tensile materials or plating layers at a joining location of the hot-stamped materials are sufficiently softened, contact problems at the joining location are eliminated, and a stabilized energization path is assured. Thus, a stabilized welding state at the joining location is assured, the nugget grows properly, and sputter is unlikely to be produced. Moreover, because the plating of a hot-stamped material is not repeatedly melted and solidified, adherence of the plating to an electrode tip can be prevented, and electrode life can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a spot welding apparatus that implements a method for applying a current for resistive welding according to the present invention; FIG. 2 is a flowchart showing an embodiment of the method for applying a current for resistive welding according to the present invention; FIG. 3 is a time chart showing a current pattern related to the above embodiment of the method for applying a current for resistive welding; * FIG. 4 is a flowchart showing another embodiment of the method for applying a * current for resistive welding according to the present invention; and FIG. 5 is time charts showing current patterns related to a conventional method for applying a current for resistive welding.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, certain embodiments of the present invention are described, by way of example only, with reference to the drawings.

FIG. 1 is a schematic illustration of a spot welding apparatus 10 that implements the method for applying a current for resistive welding according to the present invention.

The spot welding apparatus 10 is provided with a pair of electrode tips 3 and 4 that press against overlapped welding object plates 1 and 2 and conduct welding current, a pressing device (not shown) that provides a required pressure force to the electrode tips 3 and 4, a power supply device (not shown) that supplies the required welding current through the electrode tips 3 and 4 to the welding object plates 1 and 2 that are being pressed by way of the pressing device, and a control device 5 that controls these.

With the spot welding apparatus 10 that is configured as such, welding is performed by growing a nugget 6 at a predetermined rate by way of flowing a welding current, which is set beforehand in accordance with welding conditions, through the electrode tips 3 and 4 into the welding object plates 1 and 2 only for a predetermined energizing duration set beforehand.

The control device 5 controls energization amount and energizing durations of the welding current in accordance with the flowchart of FIG. 2 or in accordance with the flowchart of FIG. 4.

FIG. 2 is a flowchart showing an embodiment of the method for applying a current for resistive welding according to the present invention. In the present embodiment of the energization method, the welding object plates 1 and 2 are both high-tensile materials.

Firstly, in Step SI, low amperage is applied by the control device 5 to the high-tensile materials 1 and 2 at a joining location. The low amperage serves as the first amperage of such a magnitude that softens surfaces of the high-tensile materials 1 and 2 at the joining location. This amperage is, for example, ip.

In Step S2, it is determined by the control device 5 whether or not an initial energizing duration, as a first predetermined period, has passed. This initial energizing duration is set to be a period required for the surfaces of the high-tensile materials 1 and 2 at the joining location to be sufficiently softened by the energization with the amperage ip. The initial energizing period is, for example, Tp.

In the case of the determination being "no", Step SI is returned to, and in a case of being "yes", Step S3 is advanced to.

In Step S3, the energization amount for the welding current is switched by the control device 5. That is, the energization amount is switched, just one time, from the amperage ip of the initial energizing period Tp to the amperage of a latter energizing period, which is described below.

In Step S4, high amperage is applied by the control device 5 to the high-tensile materials I and 2 at the joining location. The high amperage serves as the second amperage, which causes the nugget 6 to grow at the joining location of the high-tensile materials 1 and 2. This amperage is, for example, im.

In Step S5, it is determined by the control device 5 whether or not a latter energizing duration, as a second predetermined duration, has passed. This latter energizing duration is set as a period required in order for the nugget 6 at the joining location of the high-tensile materials I and 2 to be grown by the energization with the amperage im. The latter energizing period is, for example, Tm.

In a case of the determination being "no", Step S4 is returned to, and in a case of being "yes", the processing ends.

FIG. 3 is a time chart showing a current pattern related to the above embodiment of the method for applying a current for resistive welding.

As shown in FIG. 3, the control device 5 controls energization as follows, in accordance with the flowchart shown in FIG. 2.

That is, energization with the amperage ip starts at time tO. This amperage ip is maintained over the initial energizing period Tp until time tp.

Maintaining the amperage ip over the initial energizing period Tp indicates that pre-heating is applied to the joining location of the high-tensile materials 1 and 2. Therefore, the initial energizing period Tp as the first predetermined duration may also express a preparatory heating period.

Then, the energization amount is switched at time tp so as to change the amperage from ip to im.

Then, the amperage im thus switched is maintained over the latter energizing period Tm until time tm.

Maintaining the amperage im over the latter energizing period Tm indicates that main heating is applied to the joining location of the high-tensile materials 1 and 2.

Therefore, the latter energizing period Tm as the second predetermined duration can also express a main heating period.

The energization with the amperage im ends at time tm.

According to the present embodiment, the following effects are present.

(1) By the low amperage ip being maintained for the initial energizing period Ip, the surfaces of the high-tensile materials 1 and 2 at the joining location are sufficiently softened before being joined, contact problems at the joihing location are eliminated, and a stabilized energization path is assured.

* (2) By the high amperage im being maintained for the latter energizing period Tm, a stabilized welding state is assured at the joining location of the high-tensile materials I and 2, the nugget 6 grows properly, and sputter is unlikely to be produced.

* FIG 4 is a flowchart showing another embodiment of the method for applying a * current for resistive welding according to the present invention. In the present embodiment of the method for applying current, the target welding plates 1 and 2 are both hot-stamped * materials.

Firstly, in Step Sil, low amperage is applied by the control device 5 to plating layers of the hot-stamped materials 1 and 2 at a joining location. The low amperage serves as the first amperage of such a magnitude that softens plating layers of the hot-stamped materials 1 and 2 at the joining location. This amperage is, for example, ip.

In Step SI 2, it is determined by the control device 5 whether or not the initial energizing duration serving as the first predetermined duration has passed. This initial energizing duration is set to be a period required for the plating layers of the hot-stamped materials 1 and 2 at the joining location to be sufficiently softened by the energization with the amperage ip. The initial energizing period is, for example, Tp.

Iii a case of the determination being "no", Step Sli is returned to, and in a case of being "yes", Step S13 is advanced to.

In Step S13, the energization amount for the welding current is switched by the control device 5. That is, the energization amount is switched, just one time, from the amperage ip of the initial energizing period Tp to the amperage of the latter energizing period, which is described below.

In Step S14, high amperage is applied by the control device 5 to the hot-stamped materials 1 and 2 at the joining location. The high amperage serves as the second amperage, which causes the nugget 6 to grow at the joining location of the hot-stamped materials I and 2. This amperage is, for example, im.

In Step S15, it is determined by the control device 5 whether or not the latter energizing duration serving as the second predetermined duration has passed. This latter energizing duration is set as a required period in order for the nugget 6 at the joining location of the hot-stamped materials 1 and 2 to be grown by the energization with the amperage im.

The latter energizing period is, for example, Tm.

In a case of the determination being "no", Step S141s returned to, and in a case of being "yes", the processing ends.

In the present embodiment as well, the control device 5 controls the energization in accordance with the current pattern of the time chartshown in FIG. 3. Descriptions of this energization control that are the same as above are omitted.

In the present embodiment, more specifically, the amperage ip of the initial energizing period Tp is, for example, 4.0 kA. In this case, the amperage im of the latter energizing period Tm may be set in a range of, for example, 6.0 kA < im <9.0 kA.

In practice, the amperage im of the latter energizing period Tm is preferably set in a range of, for example, 6.5 kA �= im �= 8.0 kA. In other words, it is preferable to set the amperage im of the latter energizing period Tm in a range from 1.6 times to 2.0 times the amperage ip of the initial energizing period Tp.

In particular, it is especially preferable to set the amperage im of the latter energizing period Tm in a range of 7.0 kA �= im �= 8.0 kA. Which is to say, it is especially preferable to set the amperage im of the latter energizing period Tm in a range from 1.7 times to 2.0 times the amperage ip of the initial energizing period Tp.

According to the present embodiment, the following effects are present.

(3) By the low amperage ip being maintained for the initial energizing period Tp, the plating layers of the hot-stamped materials 1 and 2 at the joining location are sufficiently softened, contact problems at the joining location are eliminated, and a stabilized energization path is assured.

(4) By the high amperage im being maintained for the latter energizing period Tm, a stabilized welding state is assured at the joining location of the hot-stamped materials I and 2, the nugget 6 grows properly, and sputter is unlikely to be produced.

(5) Due to the plating of the hot-stamped materials 1 and 2 not being repeatedly melted and solidified, adherence of the plating to the electrode tips 3 and 4 can be prevented, and electrode life can be improved. : The present invention is not to be limited by the embodiments described above.

Modifications, improvements and the like in a scope within which the object of the present invention may be achieved are to be included in the present invention.

Claims

Claims: 1. A method for applying a current for resistive welding of a plate assembly in which a material of at least one plate is a high-tensile material, the method comprising: a first step of applying a first amperage of a magnitude that softens a surface of a joining location of the high-tensile material, continuously for a first predetermined duration; a second step of, when the first predetermined duration has passed, switching an energization amount from the first amperage to a second amperage that causes a nugget to grow at the joining location; and a third step of applying the second amperage continuously for a second * predetermined duration.
2. A method for applying a current for resistive welding of a plate assembly in which a material of at least one plate is a hot-stamped material, the method comprising: a first step of applying a first amperage of a magnitude that softens a plating layer of a joining location of the hot-stamped material, continuously for a first predetermined duration; * a second step of, when the first predetermined duration has passed, switching an energization amount from the first amperage to a second amperage that causes a nugget to grow at the joining location; and a third step of applying the second amperage continuously for a second predetermined duration.
3. A method for applying a current for resistive welding of a plate assembly in which a material of at least one plate is a high-tensile material, substantially as hereinbefore described with reference to Figs. 1, 2 and 3 of the accompanying drawings.
4. A method for applying a current for resistive welding of a plate assembly in which a material of at least one plate is a hot-stamped material, substantially as hereinbefore described with reference to Figs. 1, 3 and 4 of the accompanying drawings.