TW201706065A - Spot welding method - Google Patents

Abstract

A spot welding method with which, when spot welding a group of plates including plated metal plates, it is possible to prevent cracks being generated in the overlaid surfaces of the metal plates, outside the corona bond diameter or at the corona bond nugget edge, thereby making it possible to form high-quality spot welded joints, the spot welding method being characterized in that, prior to welding, an angle between a central axis of an electrode tip attached to a distal end of a welding electrode and a normal line to the surface of the metal plate in contact with the electrode tip is adjusted to be less than 5 DEG from the perpendicular.

Description

Point welding method Field of invention

The present invention relates to a spot welding method for a plurality of sheet metal sheets comprising a plated metal sheet.

Background of the invention

As a member for an automobile, a galvanized steel sheet having excellent corrosion resistance is widely used from the viewpoint of high rust prevention of the vehicle body. From the viewpoint of weight reduction and high strength, a galvanized high-strength steel sheet is used as a galvanized steel sheet for automobiles, and the galvanized high-strength steel sheet is made of a high-strength steel sheet on a plated original plate.

In the car body assembly, parts installation, etc., mainly using point welding. However, when the galvanized high-strength steel sheet is subjected to spot welding, there is a problem that cracks occur in the nugget from the outer side surface of the steel sheet which is in contact with the welding electrode.

Fig. 1 shows an outline of cracks generated at the fusion joint when the galvanized steel sheet is spot-welded. When the galvanized steel sheet 1 is spot-welded, it is known that a crack 3 which progresses from the outer surface of the steel sheet 1 which is in contact with the electrode toward the nugget 2 and a crack 5 which progresses from the shoulder of the electrode toward the heat-affected portion 4 are generated.

It is generally believed that the crack is caused by the so-called liquid metal brittleness. The crack, the pressing force of the liquid metal brittle electrode and the tensile stress caused by the thermal expansion and contraction of the steel sheet are applied to the welded joint; the zinc, zinc and the electrode copper which are melted on the surface of the welded steel sheet invade the steel sheet to cause grain boundary strength Caused by the low. In the automobile body, when the crack generated at the welded joint is remarkable, there is a problem that the strength is low, and a technique for suppressing the occurrence of cracks at the welded joint by controlling the composition and structure of the steel sheet is known.

Patent Document 1 discloses a technique in which the iron phase of the Vostian formed at the time of spot welding is made into fine crystal grains by adjusting the composition of the steel sheet, and has an intricate metal structure formed with crystal grains of other phases. The technique of complicating the diffusion intrusion path of molten zinc to the crystal grain boundary and making the molten zinc not easily invade, thereby preventing liquid metal embrittlement cracking during spot welding.

Since the crystal grain boundary is complicated only by the structural control of the steel sheet, the crack in the welded portion cannot be sufficiently suppressed. Patent Document 2 discloses a technique in which the composition of the steel sheet is adjusted and hot rolling is performed. The grain boundary oxidation depth of the steel sheet is 5 μm or less, and the Fe-based plating treatment is performed on the cold-rolled steel sheet before the alloying hot-dip galvanizing treatment, so that the grain boundary corrosion depth of the alloyed hot-dip galvanized steel sheet is 5 μm or less, and the alloying is suppressed. A technique for generating cracks at the welded portion of a hot-dip galvanized steel sheet.

Patent Document 3 discloses a technique for preventing a liquid metal embrittlement prevention by removing a plating layer of an abutting portion of a strip-shaped end portion when an electric seam steel pipe is produced from a steel sheet subjected to galvanization or the like.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. 2006-265671

Patent Document 2: Japanese Patent Laid-Open Publication No. 2008-231493

Patent Document 3: Japanese Patent Laid-Open No. Hei 05-277552

Summary of invention

Although the countermeasures for cracking at the welded joints have been studied as described above, it is still impossible to weld the joints of the plated metal sheets or the welded joints of some of the non-plated metal sheets and the plated metal sheets. The desired tensile strength is obtained.

The inventors of the present invention investigated the reason. A cross section including the thickness direction of the nugget is shown in Fig. 2. As shown in Fig. 2, the point fusion joint in which the required tensile strength cannot be obtained is such that cracks 6 are formed just outside the plastic metal ring region (corona-bond) of the laminated surface of the metal sheet. Further, cracks are also generated at the nugget edge of the plastic metal ring region.

In view of such actual circumstances, the subject of the present invention is to provide a spot welding method capable of preventing the outer side of the plastic metal ring region of the laminated surface of the metal plate when the plate group including the plated metal plate is spot-welded. And the edge of the nugget of the plastic metal ring region generates cracks to form a high-quality point fusion joint.

The inventors of the present invention have conducted intensive studies on methods for solving the above problems. As a result, the inventors of the present invention found that even the member having the welded portion which is perpendicularly deviated from the angle of the axis of the electrode and the surface of the metal plate is welded. In the case where the normal line of the contact surface of the electrode tip attached to the tip end of the welding electrode and the normal angle of the surface of the metal plate are adjusted to be less than 5 degrees, the spot welding is performed, thereby preventing the plastic metal ring. Cracks occur on the outer side of the zone and cracks occur at the nugget edge of the plastic metal ring zone.

The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) A point welding method in which a laminate having a plurality of metal sheets is laminated, wherein the overlapping portions of the plurality of metal sheets are spot-welded, and a laminated surface of at least one of the plurality of metal sheets is subjected to execution In the plating, the above method is characterized in that it comprises a step of adjusting the angle of the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the surface of the metal plate to less than 5 degrees before the welding is performed.

(2) The point welding method according to the above (1), wherein the method of adjusting the angle of the normal line of the contact surface of the electrode end of the front end of the welding electrode and the normal to the surface of the metal plate to less than 5 degrees includes forming The aforementioned components.

(3) The point welding method according to the above (1) or (2), wherein the normal line of the contact surface of the electrode end of the front end of the welding electrode and the normal angle of the surface of the metal plate are adjusted to be less than 5 degrees. The method includes adjusting the shape of the fusion electrode.

(4) The point welding method according to the above (3), wherein the welding electrode includes: a holder, a shank assembled to the holder, and an electrode end attached to the shank; and adjustment of a shape of the fusion electrode By changing one or more of the above retainer, the handle, and the electrode end The shape to carry on.

(5) The spot welding method according to any one of the above (1) to (4), wherein at least one of the plurality of metal sheets is a galvanized steel sheet.

According to the present invention, even if the angle between the axis of the electrode and the surface of the metal plate is vertically deviated, the angle between the normal line of the contact surface of the electrode end attached to the tip end of the welding electrode and the normal to the surface of the metal plate is less than 5 degrees. Since the spot welding is performed, the residual stress generated at the outer side of the plastic metal ring region and the nugget edge of the plastic metal ring region becomes low, and liquid metal cracks can be prevented from occurring at the outer side of the plastic metal ring region and the nugget edge of the plastic metal ring region.

1‧‧‧Metal sheet

2‧‧‧Nuclear

3‧‧‧From the surface of the metal plate to the crack of the nugget

4‧‧‧The Ministry of Thermal Impact

5‧‧‧Cracks from the shoulders towards the heat affected zone

6‧‧‧ Cracks on the outer side of the plastic metal ring

7‧‧‧Cracks at the nugget of the plastic metal ring

8‧‧‧The normal of the metal plate

9‧‧‧weld electrode

9a‧‧‧weld electrode

9b‧‧‧fusion electrode

9c‧‧‧keeper

9d‧‧‧ handle

9e‧‧‧electrode end

10‧‧‧weld electrode shaft

11‧‧‧Higher weld residual stress on the surface of the steel plate

12‧‧‧Higher weld residual stress near the positive outer side of the plastic metal ring zone

13‧‧‧The normal to the contact surface of the electrode end mounted on the front end of the fusion electrode

Dn‧‧‧ nugget diameter

Dc‧‧‧plastic metal ring diameter

Fig. 1 is a schematic view showing cracks occurring at a welded portion when spot welding is performed on a galvanized steel sheet.

Fig. 2 is a view showing a section including a thickness direction of a nugget.

Fig. 3 is a view showing a state in which the angle of the shaft having the welded electrode and the surface of the metal plate is welded at a point where the angle of the vertically offset welding portion is welded at the time of welding.

Figure 4 is a graph showing the stress distribution at the weld after welding without cornering.

Fig. 5 is a graph showing the stress distribution at the welded portion after welding at an angle of 5 degrees. Fig. 5(a) shows the stress distribution of the entire welded portion, and Fig. 5(b) shows an enlarged view of the stress distribution near the outer side of the plastic metal ring region.

Fig. 6 is a view showing an outline of an angle adjustment of a shaft of a welding electrode and a surface of a metal plate. Figure 6 (a) shows the fusion electrode and the metal plate before the angle adjustment, Fig. 6(b) shows the welded electrode and the metal plate after the angle adjustment.

Fig. 7 is a view showing a state in which the angle between the shaft having the welded electrode and the surface of the metal plate is welded from the member of the welded portion which is vertically deviated when the space around the welded portion is restricted.

Fig. 8 is a view showing an outline of the angle adjustment of the axis of the welding electrode and the surface of the metal plate when the space around the welded portion is restricted. Fig. 8(a) shows the fusion electrode and the metal plate before the angle adjustment, and Fig. 8(b) shows the fusion electrode and the metal plate after the angle adjustment.

Fig. 9 is a view showing an example in which the shape of the holder is adjusted so that the angle between the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the surface of the metal plate is less than 5 degrees.

Fig. 10 is a view showing another example of the welding electrode in which the shape of the shank is adjusted so that the angle between the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the metal plate surface is less than 5 degrees. Fig. 10(a) shows an example in which the shank is bent in one step, and Fig. 10(b) shows an example in which the shank is bent into two stages.

Fig. 11 is a view showing another example of the welding electrode in which the shape of the electrode end is adjusted so that the angle between the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the metal plate surface becomes less than 5 degrees.

Form for implementing the invention

The spot welding method of the present invention (hereinafter referred to as "the welding method of the present invention") is to mount a metal plate having a plurality of sheets of metal sheets stacked thereon as a welded portion. At the front end of the fusion electrode The normal line of the contact surface of the electrode end and the normal angle of the surface of the metal plate are adjusted to be less than 5 degrees, and the metal plate is covered with one or more metal plates coated with the plating layer.

Hereinafter, the process of the welding method of the present invention and the welding method of the present invention will be described in detail.

The inventors of the present invention are directed to the outer side of the plastic metal ring region and the plastic metal ring region caused by the use of the galvanized steel sheet and the spot welding of the plated metal sheet on the inner surface side of the laminated metal sheet. The reason for the crack at the margin of the nugget is as follows.

Two sheets of steel sheets coated with a zinc-based plating layer and various component compositions or steel sheets not coated with a plating layer were used for spot welding under various welding conditions. Further, among the obtained spot welded joints, a cross section in the thickness direction of the nugget of the welded joint of the point where the tensile strength was lowered was observed.

As a result, the crack on the outer side of the plastic metal ring region of the steel plate superimposed surface and the crack at the nugget edge of the plastic metal ring region are obtained by using a so-called TRIP steel which is induced by the processing of a large amount of alloy containing components. It is produced at the same time; it is not easy to produce when the so-called DP steel which is formed by mixing the iron phase of the ferrite with less alloy composition and the granulated iron.

Moreover, this crack is also produced when a high-strength steel sheet having a tensile strength of 780 MPa or more and a Ceq of 0.15% by mass or more is used. Further, Ceq is represented by the following formula (1).

Ceq=[C]+[Si]/30+[Mn]/20+2[P]+4[S]. . . (1)

However, [C], "Si", [Mn], [P], and [S] are contents (% by mass) of C, Si, P, and S.

Further, in the case of the steel sheet in the case where the crack is generated, the steel sheet in the case where the two sheets are overlapped with each other is spot-welded.

Fig. 3 is a view showing a state in which the angle between the shaft having the welded electrode and the surface of the metal plate is welded from the member where the welding is vertically deviated at the time of welding. As shown in Fig. 3, when the angle θ between the normal line 8 of the metal plate 1 and the shaft 10 of the welding electrode 9 is 5 degrees or more, cracks directly on the outer side of the plastic metal ring region and cracks in the nugget edge of the plastic metal ring region are particularly generated. Hereinafter, the case where the axis of the welding electrode is perpendicular to the metal surface is expressed by the angle of the axis of the welding electrode and the normal line of the metal plate.

The spot welding of the welded portion is patterned to perform FEM analysis of the stress distribution (finite element method analysis). First, when calculating, the axis of the welding electrode is perpendicular to the surface of the metal plate (when there is no cornering), and the axis of the welding electrode and the surface of the metal plate are 5 degrees from the vertical (when the angle is 5 degrees) The point is the stress distribution at the weld after welding. In Fig. 4, the stress distribution at the weld after welding without the angle is shown. In Fig. 5, the stress distribution at the welded portion after welding at an angle of 5 degrees is shown. Fig. 5(a) shows the stress distribution of the entire welded portion, and Fig. 5(b) shows an enlarged view of the stress distribution near the outer side of the plastic metal ring region.

In FIGS. 4 and 5(a), both of them have a portion 11 having a high welding residual stress on the surface of the metal plate 1 which is in contact with the welding electrodes 9a and 9b. Further, in Fig. 5(a), there is a portion 12 (where surrounded by a broken line) where the welding residual stress is high on the outer side of the plastic metal ring region on the overlapping surface of the metal plate. Figure 5(b) shows an enlargement of the vicinity of the portion where the weld residual stress is higher near the positive outer side of the plastic metal ring region. Figure. The weld residual stress near the outer side of the plastic metal ring region is higher, and there is no stress distribution at the welded joint after welding without the angle shown in Fig. 4.

We believe that the weld residual stress on the outer side of the plastic metal ring region is higher at 12, which is in a compressed state during the welding of the welded electrode at the point of fusion welding, and becomes a tensile state when the welded electrode is separated, and after the welding is completed, During the cooling process, before the solidification of the galvannealed metal, as shown in Fig. 5, the tensile residual stress of the drawing becomes high. In this case, the inventors have speculated that cracks are generated on the outer side of the plastic metal ring region because the galvanized metal which is melted directly in the outer side of the plastic metal ring region during the spot welding process may invade the plastic metal after welding. The weld grain on the outer side of the ring region has a higher residual grain stress at the grain boundary of the metal plate at the portion 12, causing the grain boundary strength to be lowered.

Further, when the development of the plastic metal ring region is insufficient, it is presumed that the nugget residual stress at the nugget edge of the plastic metal ring region is high (not shown), and the galvanized metal is removed by melting from the nugget forming position. It is the crystal grain boundary of the metal plate which is invaded at the edge of the nugget of the plastic metal ring region, and the grain boundary strength is low, causing cracks at the nugget edge of the plastic metal ring region.

In the spot welding, basically, the electrode system for spot welding is in vertical contact with the surface of the metal plate. However, for example, in the assembly of an automobile, the space around the welded portion of the structural member that has been assembled is limited, so that the shaft having the electrode, the surface of the metal plate in contact with the electrode, and the surface of the metal plate in contact with the electrode are not vertically contacted at a place where the fusion gun is difficult to insert. The case of spot welding.

The present inventors have conducted research to prevent this in the case of this case. The crack on the outer side of the metal ring region and the crack at the margin of the nugget in the plastic metal ring region. It is considered that the crack is not caused by the angle between the axis of the welding electrode and the surface of the metal plate, but the normal line of the contact surface of the electrode end attached to the tip end of the welding electrode and the angle from the normal to the surface of the metal plate.

Therefore, the inventors of the present invention have found that the shape can be adjusted such that the normal line of the contact surface of the electrode end attached to the tip end of the welding electrode and the normal angle of the surface of the metal plate are less than 5 degrees to perform spot welding, thereby preventing plastic metal The crack on the outer side of the ring region and the nugget edge of the plastic metal ring region are cracked.

The present invention has been completed by the above-described research process. Hereinafter, the flow of the welding method of the present invention will be described.

An example of adjusting the angle between the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the surface of the metal plate will be described with reference to Fig. 6 . Fig. 6 is a view showing an outline of an angle between a normal line of a contact surface of an electrode end attached to a tip end of a fusion electrode and a normal line of a surface of a metal plate.

In Fig. 6(a), the fusion electrode and the metal plate before the angle adjustment are shown, and in Fig. 6(b), the fusion electrode and the metal plate after the angle adjustment are shown. The angle θ between the normal line 8 of the metal plate 1 of FIG. 6(a) and the axis 10 of the welding electrodes 9a and 9b is, for example, 5 degrees or more. In order to make the angle smaller than 5 degrees, the metal plate 1 is fixed. The welding electrodes 9a, 9b move in the direction of the black arrow. Thereby, as shown in FIG. 6(b), the angle θ between the normal line 8 of the metal plate 1 and the normal line of the contact surface of the electrode end attached to the tip end of the welding electrodes 9a and 9b can be made less than 5 degrees. Here, the welding electrode is moved, but the welding can also be performed. Extremely fixed to make a metal plate.

Fig. 7 is a view showing a state in which a member having a welded electrode and a member which is perpendicularly offset from the surface of the metal plate are welded to each other when the space around the welded portion is restricted. As in the case of Fig. 7, the portion of the metal plate 1 that has been subjected to press working or the like causes an obstacle to the angle adjustment, so that at least one of the fusion-bonding electrodes 9a, 9b and the metal plate 1 cannot be sufficiently moved, and there is no possibility that it will be mounted on the fusion-bonded electrode. The angle between the normal line of the contact surface of the electrode tip of the front end and the normal line of the surface of the metal plate is adjusted to be less than 5 degrees.

When the space around the welded portion is limited, an example of adjusting the angle between the normal line of the contact surface of the electrode end of the welded electrode tip and the normal to the surface of the metal plate will be described with reference to FIG.

Fig. 8 is a view showing an outline of an angle between a normal line of a contact surface of an electrode end attached to a tip end of a welding electrode and a normal line of a surface of a metal plate when the space around the welding place is restricted. Fig. 8(a) shows the electrode for spot welding and the metal plate before the angle adjustment, and Fig. 8(b) shows the electrode for spot welding and the metal plate after the angle adjustment.

In Fig. 8(a), the angle θ between the normal line 8 of the metal plate 1 and the shaft 10 of the welding electrodes 9a and 9b is, for example, 5 degrees or more. Therefore, in order to adjust the angle between the shaft of the welding electrode and the surface of the metal plate, the side of the shaft 10 of the welding electrode 9a inclined to the normal line 8 of the metal plate 1 is the metal plate 1 on the opposite side, in advance in the direction of the black arrow Formed into a convex shape and curved. Thereby, as shown in FIG. 8(b), the angle θ between the normal line 8 of the metal plate 1 at the welding place and the normal line of the contact surface of the electrode end attached to the tip end of the welding electrodes 9a and 9b is made smaller than 5 degrees.

(The angle between the fusion electrode and the metal plate is adjusted)

The spot welding method of the present invention is adjusted such that the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the surface of the metal plate become less than 5 degrees. The method of adjusting the angle is not particularly limited as long as the welding electrode or the metal plate can be adjusted by adjusting the normal line of the contact surface of the electrode end of the welding electrode tip and the normal to the surface of the metal plate to be less than 5 degrees. can.

Further, the space around the welded portion is restricted, and there is a case where the welding electrode or the metal plate cannot be moved to adjust the angle at the time of welding. In this case, the angle adjustment method can be such that the metal plate at the welded portion of the member is at least 5 degrees from the normal line of the contact surface of the electrode end of the welding electrode tip and the normal to the surface of the metal plate. Forming. The forming position is at least in the range of being spot-welded and having no influence on the product, and the forming method is not particularly limited.

When the angle between the normal line of the contact surface of the electrode end of the tip end of the welding electrode and the normal line of the surface of the metal plate is less than 5 degrees by the angle adjustment, the crack and the plastic metal ring on the outer side of the plastic metal ring region can be suppressed. Cracks occur at the margin of the nugget of the zone. The above angle is preferably 4 degrees or less, preferably 3 degrees or less, more preferably 2 degrees or less, and most preferably 0 degrees.

Next, the shape of the fusion electrode is adjusted so that the angle between the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the surface of the metal plate is less than 5 degrees, and the contact surface to be attached to the electrode end of the front end of the welding electrode The method of adjusting the normal line and the normal angle of the surface of the metal plate to less than 5 degrees will be described.

The member to be welded has a place where a plurality of metal plates are overlapped, The laminated surface of at least one metal plate among the metal plates is subjected to plating. As the metal plate, for example, a steel sheet coated with a zinc-based plating layer having a tensile strength of 780 MPa or more, a Ceq of 0.15% by mass or more, and a sheet thickness of 0.5 to 3.0 mm can be used.

In the case of spot welding, when the angle between the shaft having the welding electrode and the surface of the metal plate contacting the electrode is perpendicularly deviated from the welding, the normal line of the contact surface of the electrode end of the front end of the welding electrode and the normal to the surface of the metal plate are used. The fusion electrode whose shape is adjusted to have a shape of less than 5 degrees is attached to the fusion splicer.

In Fig. 9, one of the welding electrodes in which the shape of the retainer is adjusted by the normal line of the contact surface of the electrode end of the welding electrode and the normal to the surface of the metal plate is less than 5 degrees from the vertical. example. The welding electrode 9 has a holder 9c, a shank portion 9d assembled to the holder 9c, and an electrode end 9e attached to the shank portion 9d. Further, the shape of the welding electrode 9 is adjusted by bending the holder 9a so that the angle between the normal line 13 of the contact surface of the electrode end 9c and the normal line 8 of the metal plate is less than 5 degrees. Hereinafter, a description will be given of a case where the central axis of the electrode end is perpendicular to the metal surface, and the central axis of the electrode end is expressed at an angle to the normal line of the metal plate.

Next, spot welding is performed using a fusion splicing gun to which such a spliced electrode is adjusted. In the case of spot welding, two metal plates are laminated and sandwiched between two metal plates from both sides, while the front end is made of a copper alloy or the like, and the welding electrode adjusted to the above shape is energized. The molten metal is formed, and after the end of the energization, the water-cooled electrode is exhausted and heat is transferred to the metal plate itself, so that the molten metal is rapidly cooled and solidified, and formed between the metal plates. A nugget with an elliptical shape.

The spot welding condition at this time is not particularly limited. For example, the electrode has a tip diameter of a dome radius of 6 to 8 mm, and a pressing force of 150 to 600 kgf and an energization time of 5 to 50 cycles (power frequency). 50Hz), the current is 4~15kA. Thereby, liquid metal cracks can be prevented from occurring at the outer side of the plastic metal ring region and the nugget edge of the plastic metal ring region.

For the welding method, the necessary conditions and preferable conditions are sequentially explained.

First, a welding electrode in which the normal line of the contact surface of the electrode end of the welding electrode tip is adjusted and the angle of the normal to the surface of the metal plate is less than 5 degrees will be described.

(welding electrode)

The welding electrode is not particularly limited as long as the angle between the normal line of the contact surface of the electrode end of the welding electrode tip and the normal to the surface of the metal plate is less than 5 degrees. An example different from that of FIG. 9 will be described with reference to FIGS. 10 and 11 for the welded electrode in which the shape is adjusted.

Fig. 10 shows another example of the welding electrode in which the shape of the shank is adjusted so that the angle between the normal line of the contact surface of the electrode end of the welding electrode tip and the normal line of the surface of the metal plate becomes less than 5 degrees. Fig. 10(a) shows an example in which the bending of the shank is set to one stage, and Fig. 10(b) shows an example in which the bending of the shank is set to two stages. Further, Fig. 11 shows another example in which the shape of the electrode end is adjusted so that the angle between the central axis of the electrode end and the surface of the metal plate becomes less than 5 degrees from the vertical.

Figure 10 and Figure 11 show the fusion electrode 9 and the melting shown in Figure 9. Similarly, the electrode 9 has a holder 9c, a shank 9d, and an electrode end 9e. Further, the welding electrode 9 of Fig. 10 is shaped such that the shank portion 9d is curved so that the angle 13 between the normal line 13 of the contact surface of the electrode end 9e and the normal line 8 of the metal plate is less than 5 degrees. The bending of the shank 9d may be one segment as shown in Fig. 10(a) or two segments as shown in Fig. 10(b). Further, in the welding electrode shown in Fig. 9, the bending of the holder can be set to two stages as shown in Fig. 10(b).

In Fig. 11, the shape of the welding electrode 9 is adjusted such that the tip end of the electrode end 9e is inclined so that the angle 13 between the normal line 13 of the contact surface of the electrode end 9e and the normal line 8 of the metal plate becomes less than 5 degrees. In FIGS. 9 to 11 , the shape of either the holder, the handle, or the electrode end is changed. However, it is also possible to change the shape of the holder, the handle, and the electrode end by two or more shapes. Founder.

Further, the welding electrode may be moved, and the normal line of the contact surface of the electrode end attached to the tip end of the welding electrode may be moved so as to be less than 5 degrees from the normal to the surface of the metal plate. Further, it is also possible to combine the change in the shape of the welding electrode and the change in the shape of the member.

(member)

Next, the member to be welded by the point will be described.

The member is composed of at least a plurality of sheet metal sheets to which the welded portions are superposed, and is not particularly limited as long as the laminated surface of at least one of the metal sheets is coated with a plating layer. For example, a plurality of sheets of steel sheets in which all of the surface-welded metal sheets are coated with a zinc-based plating layer; and a steel sheet including a zinc-based plating layer on which the superposed surface of the steel sheet to be spot-welded is coated The spot welded steel sheet is not covered with a plurality of steel sheets of a steel sheet having a zinc-based plating layer.

Further, the metal plate coated with the plating layer on the surface to be welded by the spot welding may be coated on the surface opposite to the overlapping surface of the metal plate to be spot-welded, that is, the contact surface with the welding electrode. The coating may or may not be covered with a coating. However, in consideration of the corrosion resistance of the spot welded joint, it is preferable to coat the contact surface with the welded electrode with a plating layer.

The type of the plating layer of the metal plate coated with the plating layer used in the present invention is not particularly limited. The welding method of the present invention is suitable for welding a steel sheet coated with a zinc-based plating layer, but the same applies to the case of plating other alloys such as Al-plated or Cu-plated plating. Moreover, the same can be applied also when the metal plate other than the plated steel plate is welded.

As a plurality of sheet metal sheets that are spot-welded, two metal sheets are described in FIGS. 9 to 11, but it is also possible to form a plurality of sheet metal sheets of three or more sheets in accordance with the form of the joined structural members. The thickness of each metal plate to be spot-welded is not particularly limited. The welding method of the present invention is suitable for welding of steel sheets having a thickness of 0.5 to 3.0 mm. Further, the thickness of the entire sheet metal plate is not particularly limited. The welding method of the present invention is suitable for welding of a steel plate having an overall thickness of 1.0 to 7.0 mm.

Further, at least a part of the metal plate has a plate-like portion, and the plate-like portion may have a portion that is stacked on each other, or the entire plate may not be a plate member. Further, a plurality of sheet metal sheets are not limited to each of the metal sheets, and for example, a sheet of a metal sheet may be formed into a predetermined shape such as a tubular shape.

Further, the metal plate of the member to be spot-welded is not particularly limited in terms of its composition and metal structure. However, the steel sheet coated with the zinc-based plating layer on the laminated surface to be welded or the zinc-based plating layer and the When a steel plate laminated with a zinc-based plating layer is used, a TRIP steel plate and a high-strength steel plate having a Ceq of 0.15% by mass or more are used because of the nugget margin on the outer side of the plastic metal ring region and the plastic metal ring region. Since the crack is more likely to occur, in the welding method of the present invention, in particular, such a steel sheet can be set as a target.

Further, the plating layer to be coated on the metal plate to be welded is not particularly limited, and examples thereof include alloyed hot-dip galvanizing, hot-dip galvanizing, electro-galvanizing, and galvanizing. nickel. Also, galvanizing can be applied. aluminum. Magnesium. Moreover, aluminum plating and copper plating can also be applied.

(confirmation of crack)

Before applying the spot welding method of the present invention, spot welding may be performed in advance to confirm the occurrence of cracks. Although there is no problem in applying the present invention when cracks are not generated, when the present invention is applied to the welded position when cracks are generated, the effects of the present invention can be efficiently obtained.

When the shaft having the welded electrode and the member at the welded portion which is perpendicularly inclined from the surface of the metal plate are welded, it is preferable to perform spot welding in advance. In particular, when the shaft of the welding electrode is welded to the surface of the metal plate at a height of 5 degrees or more (an angle of 5 degrees or more), it is easy to be in the outer side of the plastic metal ring region and in the plastic metal ring region. Cracks are formed on the nugget side, and spot welding is performed in advance to confirm the presence or absence of cracks.

The point welding of the member is performed in advance, and the member is welded in a state where the axis of the welding electrode and the surface of the metal plate of the contact electrode are vertically deviated. The welding conditions at this time are not particularly limited, and ordinary welding conditions can be employed. For example, the electrode is set to a dome-shaped radial front end diameter of 6 to 8 mm. The pressure is 150~600kgf, the energization time is 5~50 cycles, and the current is 4~15kA.

(Confirmation of cracks at the nugget edge of the outer side of the plastic metal ring region and the plastic metal ring region)

By performing spot welding in advance, it is confirmed whether or not cracks occur at the outer side of the plastic metal ring region and the nugget edge of the plastic metal ring region of the obtained spot welded joint. The method of confirming whether or not the nugget of the nugget of the outer side of the plastic metal ring region and the plastic metal ring region is cracked is not particularly limited, and a method of observing a cross section including a thickness direction of the nugget can be used; and a tensile test for performing a splice joint And a method of determining whether or not a predetermined tensile strength can be obtained. Or, because the cutting position of the cross section including the thickness direction of the spot welded portion is included, whether or not the crack is formed on the outer side of the plastic metal ring region and the nugget edge of the plastic metal ring region is observed, and X-ray transmission is also possible. Test to confirm the crack.

Cracks occur at the outer side of the plastic metal ring region and at the nugget edge of the plastic metal ring region, either on the laminated surface of the metal plate coated with the plating layer or on the metal plated with the plating layer through the plating layer The face of the metal plate on which the plates are laminated is produced. Moreover, among the faces of the metal plates, they are generated in and around the plastic metal ring region. The plastic metal ring region and its vicinity refer to a range from about the nugget side end of the plastic metal ring region to about 1.2 times the diameter Dc of the plastic metal ring region.

Further, the above description has been made by arranging a galvanized steel sheet for automobiles as a center, but the present invention is not limited thereto. The object of the present invention can be achieved without departing from the gist of the present invention. For example, it can be applied to a composite material such as iron, aluminum, titanium, and stainless steel, and a metal-resin or a dissimilar metal other than a steel sheet. material. Further, it is not limited by the automobile, and can be applied to various vehicles, general machinery, home appliances, ships, and the like as long as it is spot-welded to the metal plate.

Example

Next, the examples of the present invention will be described, and the conditions of the examples are a conditional example employed to confirm the implementation possibilities and effects of the present invention, and thus the present invention is not limited by the above-described conditions. The present invention can adopt various conditions as long as the object of the present invention can be achieved without departing from the gist of the present invention.

[Example 1]

The zinc-based plating layer or the unplated steel sheet shown in Table 1 was laminated according to the plate group shown in Table 2, and a dome-shaped radiation type electrode having a front end diameter of 6 mm was used to be laminated from both sides. After the steel plate was clamped, a test piece was produced by performing a point welding by applying a pressing time of 8 kN and applying an electric current of 18 cycles and an electric current of 9 kA.

Set the angle of the electrode to 3 to 10 degrees to check for cracks after the spot is welded. In the confirmation of the crack, the test piece was cut in the thickness direction so as to include the nugget, and the cross section was confirmed. The results are shown in Table 3. "◎" in Table 3 indicates that there is no crack, "○" indicates that there is a microcrack of less than 100 μm, and "X" indicates that there is an internal crack of 100 μm or more.

As shown in Table 3, the smaller the angle, the less prone to cracking. When the angle of attack is less than 5 degrees, cracks of 100 μm or more are not generated in all the plate groups after the spot welding, and when the angle is 3 degrees, cracks do not occur in all the plate groups.

[Embodiment 2]

In Table 4, the metal plates used are shown. The metal plate is an alloyed hot-dip galvanized steel sheet, and a galvanized layer is coated on both sides of the high-strength steel sheet.

Two steel plates of each steel type were prepared, and the steel plates of the same steel type were superposed, and two steel plates were clamped from both sides using a dome-shaped radiation electrode having a front end diameter of 6 mm, and the electric power was set while being pressed at a pressure of 4 kN. A test piece was produced by performing 18-cycle and 9 kA current supply and spot welding. The angle of the electrode is set to 5 degrees. In addition, the crack was confirmed by cutting the test piece in the thickness direction so as to include the nugget. Further, the plate set of the galvanized steel sheet B and the cold-rolled steel sheet was also subjected to spot welding under the same conditions, and the presence or absence of cracks was confirmed by cross-sectional observation.

Although the corrosion resistance of the galvanized steel sheet A was good, it was confirmed that cracks occurred at the outer side of the plastic metal ring region and at the nugget edge of the plastic metal ring region. The corrosion resistance of the galvanized steel sheet B was good and cracks were not observed at the outer side of the plastic metal ring region and at the nugget edge of the plastic metal ring region. It was confirmed that cracks were formed in the galvanized steel sheet B, and it was considered that the system was associated with a low C content. On the other hand, cold rolling The steel plate has poor corrosion resistance, but since there is no galvanized layer, cracks are not observed at the outer side of the plastic metal ring region and at the nugget edge of the plastic metal ring region. Further, in the plate group of the galvanized steel sheet B and the cold-rolled steel sheet, it was confirmed that cracks occurred at the outer side of the plastic metal ring region of the cold-rolled steel sheet and at the nugget edge of the plastic metal ring region.

Next, two sheets of galvanized steel sheet A which were confirmed to have cracks on the outer side of the plastic metal ring region and cracks at the nugget edge of the plastic metal ring region were prepared, and two steel sheets were laminated and contacted at the electrode end of the front end of the welded electrode. The welding line is moved so that the angle between the normal to the surface and the normal to the surface of the steel sheet is less than 5 degrees, or the welded portion of the steel sheet is formed and spot-welded under the same conditions as the above-described spot welding. Subsequently, cracks were confirmed for the obtained test piece.

As a result, when the welding electrode was moved to have an angle of 2.5 degrees, cracks did not occur at the outer side of the plastic metal ring region and at the nugget edge of the plastic metal ring region. Further, when the welded portion of the steel sheet was formed to have an angle of 1.5 degrees, cracks did not occur at the outer side of the plastic metal ring region and at the nugget edge of the plastic metal ring region.

[Example 3]

In Table 5, the metal sheets providing the test are shown. The metal plate is an alloyed hot-dip galvanized steel sheet, and both sides of the high-strength steel sheet are coated with a galvanized layer.

Two sheets of steel sheets shown in Table 5 were prepared and laminated, and the test piece was produced by sandwiching with a welding electrode and holding it at a pressing pressure of 4 kN while providing an energization time of 18 cycles and an electric current of 9 kA to perform spot welding. Further, as the electrode end, a dome-radiation type made of copper having a curvature radius of 40 (mm) at the tip end and a tip end diameter of 8 (mm) was used. Further, the angle of the welding electrode was set to 5 degrees.

The crack was confirmed for the test piece. It was confirmed that the crack was cut so as to include a nugget, and the test piece was cut in the thickness direction to confirm the cross section. As a result, it was confirmed that cracks occurred at the nugget edge of the outer side of the plastic metal ring region and the nugget of the plastic metal ring region.

Next, a welded electrode in which the shape is adjusted so that the angle between the normal line of the contact surface of the electrode tip of the welding electrode tip and the normal line of the steel sheet surface is less than 5 degrees is prepared. Specifically, a fusion electrode that is adjusted to the shape of the holder shown in FIG. 9 is prepared; a fusion electrode that is adjusted to the shape of the handle shown in FIG. 10(a); and is adjusted to the electrode end shown in FIG. Shaped fusion electrode.

Further, in addition to the use of the welding electrodes, the spot welding is performed under the same conditions as the above-described spot welding conditions. Subsequently, cracks were confirmed for the obtained test piece. As a result, the spot welding is performed using a welded electrode having an adjusted retainer shape, a welded electrode having an adjusted shank shape, and a welded electrode having a shape of the adjusted electrode end, and is directly outside the plastic metal ring region and the plastic metal ring region. No cracks were observed at the nugget edge.

Industrial use possibility

According to the present invention, since the normal line of the contact surface of the electrode end mounted on the tip end of the welding electrode and the normal to the surface of the metal plate are less than 5 degrees The spot welding is performed, so that the residual stress at the nugget edge of the plastic metal ring region and the nugget edge of the plastic metal ring region is lowered, and the cracking of the liquid metal at the nugget edge of the plastic metal ring region and the plastic metal ring region can be prevented. . Therefore, the present invention is highly probable in industrial use.

1‧‧‧Metal sheet

8‧‧‧The normal of the metal plate

9a‧‧‧weld electrode

9b‧‧‧fusion electrode

10‧‧‧weld electrode shaft

Claims (5)

A point welding method is a method in which a plurality of metal plates are stacked, and the above-mentioned overlapping portions are spot-welded, and a laminated surface of at least one of the plurality of metal plates is plated, The method is characterized in that it comprises a step of adjusting the angle of the normal to the contact surface of the electrode end of the front end of the fusion electrode and the normal to the surface of the metal plate to less than 5 degrees before performing the fusion bonding. The point welding method according to claim 1, wherein the method of adjusting the angle of the normal line of the contact surface of the electrode end of the front end of the welding electrode and the normal line of the surface of the metal plate to less than 5 degrees comprises forming the member. The method of claim 1 or 2, wherein the normal line of the contact surface of the electrode end of the front end of the welding electrode and the normal angle of the surface of the metal plate are adjusted to be less than 5 degrees, including adjusting the welding electrode shape. The method of claim 3, wherein the welding electrode comprises: a holder, a handle assembled to the holder, and an electrode end mounted on the handle; the adjustment of the shape of the welding electrode is changed One or two or more shapes of the holder, the handle, and the electrode end are performed. The point welding method according to any one of claims 1 to 4, wherein at least one of the plurality of metal sheets is a galvanized steel sheet.