KR101595187B1 - Spot welding apparatus for preventing pressure mark of plate and spot welding method thereof - Google Patents

Abstract

According to an embodiment of the present invention, the spot-welding device to prevent a pressure mark on one surface comprises: a first electrode part positioned on one surface of an overlap part wherein a first panel and a second panel are overlapped; a second electrode part positioned on an other surface of the overlap part to electrically be connected to the first electrode part having one end which has a larger diameter than an end of the first electrode part, and a structure to support the overlap part; a current control part electrically connected to the first and the second electrode part to electrically connect the first and the second electrode part to each other when a current is applied; and a pressing part connected to the first and the second electrode part providing a pressure to the first and the second electrode part to press the overlap part until a temperature of the overlap part lowers to a recrystallization temperature or less from a time when the first and the second electrode part is electrically connected to each other. The end of the first electrode part has a smaller area than an area of a melted portion in the electrically connected portion, and an end of the second electrode part has a greater area than the melted portion in the electrically connected portion to support the other surface of the overlap part; thus preventing deformation of the other surface of the overlap part.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a spot welding apparatus for preventing one-sided indentation,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding apparatus for preventing single-sided indentation and a spot welding method for preventing single-sided indentation, and more particularly to a spot welding apparatus for preventing single- .

When appearance quality such as the outer plate of an automobile door is important, a hemming process is used in the prior art. The hemming process is a method of overlapping two sheets and folding the edges of one sheet to hold the other sheets.

The hemming process does not affect the surface condition of the plate, but it has a disadvantage that the strength is much lower than that of the spot welding process. Particularly, these disadvantages can cause serious problems in automobiles that emphasize occupant safety. Therefore, in automobile assembly, a spot welding process is used to increase the bonding strength of the plate material in a portion where the quality of the outer appearance is not important conventionally.

1 schematically shows a welding state diagram of a spot welding process according to the prior art.

As shown in FIG. 1, in the spot welding process, a plate material 10 and 20 placed between two electrodes 50 and 60 are brought into close contact with each other by applying pressure, and a large current is instantaneously applied thereto to melt .

The end of the electrode used in the spot welding process has a conical shape in order to reduce the contact area with the plate material. At this time, the diameters of the tips of the two electrodes 50 and 60 are set to be the same.

A current control unit (not shown) for controlling the amount of current is connected to the two electrodes 50 and 60. Each of the two electrodes 50 and 60 is connected to a pressing portion (not shown) for pressing the plate material.

When the current is supplied to the two electrodes 50 and 60, the overlapping portions of the two plates 10 and 20 located between the two electrodes 50 and 60 are melted as shown in FIG. A nugget 40 is formed as the two plate materials 10 and 20 are locally melted. At this time, the nugget 40 is formed larger than the diameter of the tips of the two electrodes 50 and 60.

As shown in FIG. 2, current is applied to the two electrodes 50, 60 until the temperature of the nugget 40 reaches the peak, and the pressure is applied to the two plates 10, 20.

In forming the nugget 40, due to the pressure applied to the surface of the plate and the deformation resistance due to melting, the surface of the plate is pressed by the tip of the electrode located at each of the upper and lower portions of the plate. During the cooling of the nugget 40 to room temperature, the plate material shrinks and further deformation such as grooves 11 and 12 formed in the upper and lower portions of the plate materials 10 and 20 occurs.

Thus, in spite of the excellent bonding strength, the spot weld is formed by melting the joint of the plate material in the process of welding for joining the overlapping portions of the two plate materials 10, 20. At this time, when the nugget 40 is formed, the strength of the nugget 40 is different from that of the other parts of the plate, and when the quality of the exterior of the automobile door is important due to the pressure applied to the electrode by the pressing part, Spot welding can not be used. Accordingly, the spot welding is used only for joining internal parts of the vehicle body in which the surface of the nugget 40 is not exposed to the outside.

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Korean Patent Laid-Open Publication No. 1994-0025696 discloses a shunt current measuring method and a shunt current detecting device in a spot welding process.

Accordingly, it is an object of the present invention to provide a spot welding apparatus and a method of manufacturing a spot welding apparatus for preventing surface indentation in which the quality of the outer appearance such as a shell plate of an automobile door is important, And to provide a method of spot welding for prevention.

According to an embodiment of the present invention, there is provided a spot welding apparatus for preventing single-sided indentation, comprising: a first electrode unit positioned on one surface of an overlapping portion in which a first plate and a second plate overlap; A second electrode part positioned on the other surface of the overlapping part so as to be electrically connected to the first electrode part, the end part having a larger diameter than the end part of the first electrode part and supporting the overlap part; A current controller electrically connected to the first electrode unit and the second electrode unit and configured to energize the first electrode unit and the second electrode unit when a current is applied; And supplying a pressure to the first electrode unit and the second electrode unit until the temperature of the overlapping unit is lowered to the recrystallization temperature or lower from the energization time of the first electrode unit and the second electrode unit, And the end portion of the first electrode portion has an area smaller than that of the portion to be melted in the portion to be energized and the end portion of the second electrode portion has an area larger than that of the portion to be melted in the portion to be energized It is preferable to support the other surface of the overlapping portion so as to prevent deformation of the other surface of the overlapping portion.

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In an embodiment of the present invention, it is preferable that the second electrode portion has a flat surface structure in which the portion in contact with the overlap portion is flat.

In one embodiment of the present invention, the current control unit controls the first electrode unit and the second electrode unit such that a portion where the first electrode unit and the second electrode unit are connected to each other is melted by resistance heating, When the melting temperature is exceeded, it is preferable to release the application of current to the first electrode portion and the second electrode portion.

On the other hand, in the one-surface indentation spot welding method in which the first plate and the second plate overlapping each other between the first electrode portion and the second electrode portion are spot-welded by using a spot welding device for preventing surface impression,

(a) the first plate and the second plate are pressed by the pressing portion;

(b) a current is applied to the first electrode unit and the second electrode unit by the current control unit, the first electrode unit and the second electrode unit are energized, and the energized part is melted by resistance heating;

(c) applying a current to the first electrode unit and the second electrode unit by the current control unit until the temperature of the energized portion exceeds the melting point of the first plate and the second plate; And

(d) after the step (c), the application of the current to the first electrode part and the second electrode part is canceled in the current control part, and the first plate and the second plate are pressed by the pressing part until the temperature of the part to be energized falls below the recrystallization temperature The end portion of the first electrode portion has an area smaller than the area of the portion to be melted in the portion to be energized and the end portion of the second electrode portion is larger than the area of the portion to be melted in the portion to be energized So that the second plate member is supported without being affected by the strength change due to the portion where the end of the second electrode portion is melted when the pressing portion is pressed so as to prevent deformation of the surface of the second plate member in the process of cooling the energized portion .

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1 schematically shows a welding state diagram of a spot welding process according to the prior art.
2 (b) is a time-current graph, and FIG. 2 (c) is a time-nugget temperature change graph in the prior art. FIG. 2 FIG.
FIG. 3 is a schematic view of a point welding apparatus for preventing single-sided indentation according to an embodiment of the present invention.
FIG. 4 schematically shows a state in which a nugget is formed on a superimposed portion in an embodiment of the present invention.
5 (b) shows a time-current graph according to the operation of the current control section, and FIG. 5 (c) shows a time- Temperature change graphs.
6 is a flowchart schematically illustrating a spot welding method for preventing single-sided indentation according to an embodiment of the present invention.

Hereinafter, a spot welding apparatus for preventing single-sided indentation and a spot welding method for preventing single-sided indentation according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

The spot welding apparatus 100 for preventing single-sided indentation according to an exemplary embodiment of the present invention includes a first electrode unit 110, a second electrode unit 120, a current control unit 130, and a pressing unit 150.

The one-sided indentation spot welding apparatus 100 applies pressure to the first plate 10 and the second plate 20 positioned between the first electrode unit 110 and the second electrode unit 120, 10 and the second plate 20 are brought into close contact with each other so that the first plate 10 and the second plate 20 are spot-welded by melting at the overlapping portion due to resistance heat generation by energizing a high current instantaneously.

The overlapping portion 30 refers to a portion where the first plate member 10 and the second plate member 20 overlap each other. The overlapping portion 30 is preferably disposed between the first electrode portion 110 and the second electrode portion 120. The first plate member 10 and the second plate member 20 are various types of steel plates requiring welding. In the present embodiment, the first plate member 10 and the second plate member 20 are specifically We do not restrict it.

As shown in FIG. 3, the first electrode unit 110 is located on one side of the overlapping unit 30. One side of the overlapping portion 30 is a portion where an even surface quality is not required.

The first electrode unit 110 has a conical shape with a pointed tip in order to minimize the area of the first electrode unit 110 with respect to the overlapping unit 30. The current control unit 130 and the pressing unit 150 are connected to the first electrode unit 110, respectively. The first electrode unit 110 is a member that is energized with the second electrode unit 120 to be described later when a current is applied to the current applying unit.

The second electrode portion 120 is located on the other surface of the overlapping portion 30. The other surface of the overlapping portion 30 is a portion where a uniform surface quality is required. The second electrode unit 120 is positioned to be energized with the first electrode unit 110 when a current is applied to the current controller 130. The current control unit 130 and the pressing unit 150 are connected to the second electrode unit 120, respectively.

The second electrode part 120 has a structure in which the second electrode part 120 abuts the lapping part 30 to support the lapping part 30. As shown in FIG. 3, the second electrode unit 120 preferably has a planar structure in which the portion in contact with the overlapping portion 30 is flat to support the overlapping portion 30.

The end portion 121 of the second electrode portion 120 has a diameter different from that of the end portion 111 of the first electrode portion 110. Specifically, the end portion 121 of the second electrode portion 120 has a larger diameter than the end portion 111 of the first electrode portion 110. The end portion 121 of the second electrode portion 120 preferably has an area larger than the size of the nugget 40 which is generated when the first plate 10 and the second plate 20 are melted when a high current is applied thereto.

The current control unit 130 is electrically connected to the first electrode unit 110 and the second electrode unit 120 as described above. As shown in FIG. 3, the power controller 140 is connected to the current controller 130.

5 (b), the current controller 130 applies a high current to the first electrode unit 110 and the second electrode unit 120. As shown in FIG. At this time, as the first electrode unit 110 and the second electrode unit 120 are energized, the lapping unit 30 is melted by resistance heating and forms a nugget 40 at the energized part. Thereafter, the overlapping portions 30 are joined to each other while cooling the nugget 40, so that the first plate 10 and the second plate 20 are connected to each other.

The current controller 130 cancels the current application to the first electrode unit 110 and the second electrode unit 120 when the temperature of the nugget 40 reaches a maximum point, as shown in FIG. 5 (b) . As shown in Fig. 5 (c), the maximum temperature of the nugget 40 formed in the lap 30 is a temperature exceeding the melting point of the plate material.

The nugget 40 is formed in the overlapping portion 30 of the first plate 10 and the second plate 20 and the strength of the first plate 10 and the second plate 20 is reduced, Are joined to each other by a pressing force.

Meanwhile, the pressing unit 150 is connected to the first electrode unit 110 and the second electrode unit 120. The pressing portion 150 is operated so that the first electrode portion 110 and the second electrode portion 120 press the first plate 10 and the second plate 20.

The operation of the pressing unit 150 is started when the current control unit 130 applies a current to the first electrode unit 110 and the second electrode unit 120. The first electrode unit 110 and the second electrode unit 120 press the lapping unit 30 while exerting forces in directions opposite to each other.

Unlike the case where the pressure applied by the pressing portion 150 to the plate member is removed when the application of the current to the plate member is canceled in the prior art, the pressing portion 150 according to the present embodiment is different from the first plate member 10, The first plate member 10 and the second plate member 20 are continuously pressed even after the two plate members 20 are bonded to each other.

As shown in FIG. 5 (a), the pressing force of the pressing portion 150 is the same from the starting point to the ending point of the pressing portion 150. The pressing unit 150 according to the present embodiment continuously presses the first plate 10 and the second plate 20 until the additional deformation of the plate surface disappears unlike the prior art.

5A, the ending point of the pressing portion 150 is until the temperature of the overlapping portion 30 between the first plate 10 and the second plate 20 falls below the recrystallization temperature . The nugget 40 is completely cooled when the lap 30 is melted due to current application between the first electrode unit 110 and the second electrode unit 120.

On the other hand, the recrystallization temperature refers to a temperature at which crystallization occurs again after the plate material is melted. The recrystallization temperature varies depending on the material. For example, the recrystallization temperature of steel is 500 ° C.

For example, in the case where the first plate 10 and the second plate 20 used for welding are formed of steel, the pressing portion 150 according to the present embodiment may be heated to 500 deg. C or lower So that deformation that may occur during the process of recrystallization of the first plate 10 and the second plate 20 as weld materials can be prevented.

Here, the first plate 10 and the second plate 20 made of steel are heated to a temperature of 1,520 ° C or higher, which is the melting point, while the resistance is generated by the high current applied by the current control unit during energization, thereby forming the nugget 40. Thereafter, the temperature of the nugget 40 is lowered when the current control unit 130 is de-energized.

The area of the nugget 40 generated in the overlapping portion 30 when the first electrode portion 110 and the second electrode portion 120 are energized is A2. The area of the first electrode unit 110 pressing the one surface of the overlapping unit 30 by the pressing unit 150 is A1 and the area of the second electrode unit 120 supporting and pressing the other surface of the overlapping unit is A3. At this time, the sizes of the areas A1, A2, and A3 are A1 <A2 <A3.

The first electrode unit 110 may be disposed on the overlapping unit 30 of the first electrode unit 110 because of the difference in contact area between the first electrode unit 110 and the overlapping unit 30 of the second electrode unit 120. [ Of the nugget 40 is smaller than the formed area A2 of the nugget 40 and the portion where the nugget 40 is formed is weaker than other portions of the plate due to melting, The surface of the first plate 10 deforms while press-fitting the one surface of the lapping portion 30. Here, one surface of the overlapping portion 30 is one surface of the first plate 10.

However, the second electrode unit 120 is formed such that the contact area A3 of the second electrode unit 120 with the other surface of the overlapping unit 30 is larger than the formed area A2 of the nugget 40, And the other surface of the overlapping portion 30 is supported without being affected substantially by the change in the strength of the plate material due to the nugget. Thus, deformation of the surface of the second plate member 20 can be prevented. Here, the other surface of the overlapping portion 30 is one surface of the second plate 20.

Therefore, unlike the portion where the first electrode portion 110 abuts the overlapping portion 30, the present invention minimizes the appearance damage at the abutting portion of the second electrode portion 120, It is possible to increase the strength of the product and improve the quality of the product.

Hereinafter, a spot welding method for preventing one-sided indentation will be described with reference to FIGS. 5 and 6. FIG.

The first plate member 10 and the second plate member 20 are positioned between the first electrode unit 110 and the second electrode unit 120. The first electrode unit 110 and the second electrode unit 120 press the first plate member 10 and the second plate member 20 by the pressing unit 150. [

When the first electrode unit 110 and the second electrode unit 120 are positioned in contact with the overlapping portions of the first plate member 10 and the second plate member 20, And the second electrode unit 120, respectively.

The first electrode unit 110 and the second electrode unit 120 are energized with each other. At this time, the portion to be energized is heated by resistance heating and melted to form nugget 40. At this time, the melting point of the portion to be energized varies depending on the material of the plate material. For example, if the material of the plate is steel (Fe), the melting point of the plate is 1,520 占 폚.

When the temperature of the nugget 40 exceeds the melting temperature as shown in FIG. 5C, the current controller 130 applies a current to the first electrode unit 110 and the second electrode unit 120 Release.

Even if the current application to the first electrode unit 110 and the second electrode unit 120 of the current controller 130 is released, the temperature of the nugget unit 40, that is, The first electrode unit 110 and the second electrode unit 120 are operated until the temperatures of the first electrode unit 110 and the second electrode unit 120 are lowered to the recrystallization temperature or lower. Here, the recrystallization temperature of the portion to be energized varies depending on the recrystallization temperature of the material. As described above, when the first plate and the second plate are made of steel, the recrystallization temperature of the portion to be energized is 500 ° C.

As shown in FIG. 5 (a), the pressing force is applied to the first plate member 10 (10) at the same intensity as when the current control unit 130 applies current to the first electrode unit 110 and the second electrode unit 120, And the second plate member 20 are pressed.

The pressing unit 150 according to the present embodiment continuously presses the first plate 10 and the second plate 20 until the additional deformation of the plate surface disappears unlike the prior art. Therefore, unlike the portion where the first electrode portion 110 abuts the overlapping portion 30, the present invention minimizes the appearance damage at the abutting portion of the second electrode portion 120, It is possible to increase the strength of the product and improve the quality of the product.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be clear to those who have knowledge.

100: Spot welder for preventing incidence of one surface 110:
120: second electrode unit 130: current control unit
140: power applying unit 150:

Claims (6)

A first electrode portion positioned on one surface of the overlapping portion where the first plate and the second plate overlap each other;
A second electrode part positioned on the other surface of the overlapping part to be electrically connected to the first electrode part;
A current control unit electrically connected to the first electrode unit and the second electrode unit to energize the first electrode unit and the second electrode unit when a current is applied; And
Wherein the first electrode unit and the second electrode unit are connected to the first electrode unit and the second electrode unit, and the first electrode unit and the second electrode unit are connected to each other until the temperature of the overlap unit falls below the recrystallization temperature, And a pressing portion for applying pressure to the two-electrode portion to press the overlapping portion,
The end portion of the first electrode portion has an area smaller than the area of the portion to be melted in the energized portion and the end portion of the second electrode portion has an area larger than an area of the portion to be melted in the energized portion, To thereby prevent deformation of the other surface of the overlapping portion.
delete The method according to claim 1,
Wherein the second electrode portion has a flat surface structure in which the portion contacting the overlap portion is flat.
The plasma display apparatus according to claim 1,
Applying a high current to the first electrode unit and the second electrode unit until the temperature of the energized part reaches the melting temperature so that the part where the first electrode unit and the second electrode unit are energized by the resistance heat generation,
And when the melting temperature is exceeded, the current application to the first electrode unit and the second electrode unit is canceled.
There is provided a spot welding method for one-sided indentation prevention in which a first plate and a second plate overlapping each other between a first electrode portion and a second electrode portion are spot-welded using the spot welding device for preventing surface indentation according to claim 1,
(a) pressing the first plate and the second plate by a pressing portion;
(b) a current is applied to the first electrode unit and the second electrode unit by the current control unit, the first electrode unit and the second electrode unit are energized, and the energized part is melted by resistance heating;
(c) applying current to the first electrode unit and the second electrode unit until the temperature of the energized portion exceeds a melting point of the first plate and the second plate; And
(d) the current control unit releases the current from the first electrode unit and the second electrode unit after the step (c), and stops the current application to the second electrode unit until the temperature of the current to be energized falls below the recrystallization temperature And continuing to pressurize the first plate and the second plate,
The end portion of the first electrode portion has an area smaller than the area of the portion to be melted in the energized portion and the end portion of the second electrode portion has an area larger than an area of the portion to be melted in the energized portion, The end portion of the second electrode portion supports the second plate member without being affected by the strength change due to the melted portion and prevents the surface deformation of the second plate member during the cooling of the energized portion A method of spot welding for preventing indentation on one surface.

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