JPH0527516B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a projection welding method for overlapping and joining metal plates, and particularly to prevention of indentations occurring on the plate surfaces.

[Prior Art] Fig. 5 is a block diagram showing a projection welding device for overlapping and welding a metal plate such as a mild steel plate to a top plate of a door or the like made of a metal plate in order to reinforce the top plate of a door or the like. In the figure, 1a is made of, for example, a mild steel plate and is used as a back plate.
The metal plate 1b is a second metal plate which is, for example, a front plate of a door, and the reference numeral 2 is a ring-shaped protrusion provided at the joint portion of the first metal plate 1a.

This annular protrusion 2 has been previously described, for example, in the document "Welding Data Book" (edited by Hiroshi Kihara, Sanpo Co., Ltd., published in 1964).
As described on page 100 of , the cross-sectional surface is formed in the shape of a circular arc.

3a is an upper electrode that presses the annular protrusion 2 against the second metal plate 1b and conducts electricity; 3b is a lower electrode fixed to the pedestal 4; 5 is an air cylinder fixed to the upper pedestal 6 and moves the upper electrode 1a. , the air cylinder 5 applies pressure between the first metal plate 1a and the second metal plate 1b via the rod 7 and the upper electrode 3a.

8 is a welding power source connected to the upper electrode 3a and the lower electrode 3b, and the welding power source 8 is a single-phase AC power source or a capacitor power source. Note that insulation is provided between the upper electrode 3a and the rod 7, and between the lower electrode 3b and the pedestal 4.

In the projection welding device configured as described above, the first metal plate material 1a and the second metal plate material 2a are overlapped and pressurized with a predetermined pressure by the air cylinder 5, and a constant current is applied for a certain period of time. Electricity is applied to the upper electrode 3a and the lower electrode 3b from the welding power source.

Figure 6 shows an example of the power waveform of a single-phase AC power supply with time (milliseconds) plotted on the horizontal axis and current KA on the vertical axis, and Figure 7 plots time (milliseconds) on the horizontal axis. , with the current KA plotted on the vertical axis, the time it takes for the current to reach its maximum value, that is, the current peak time ta, is, for example,
An example of the current waveform of a 10 ms capacitor power supply is shown.

The current shown in FIGS. 6 and 7 above is applied to the upper electrode 3.
When electricity is applied between the lower electrode 3b and the annular protrusion 2, the current concentrates on the annular protrusion 2 to generate Joule heat, and the heat is used to join the first metal plate 1a and the second metal plate 1b.

FIG. 8 shows a first metal plate 1a and a second metal plate 1b having the annular protrusion 2 having an arcuate cross-sectional shape.
The figure shows the progress of joining, where a shows the state at the start of joining, b and c show the state in which the joining progresses sequentially, and d shows the state when the joining is completed. In the figure,
9 is a current path, 10 is a welding nugget, 11 is the back side of the projection, 12 is a welding nugget 10
Indentations 13 are formed on the surface of the second metal plate material 1b due to the heat shrinkage force, 13 is dust in the middle caused by excessive heat input, and 14 is a hole caused by the dust.

[Problems to be Solved by the Invention] In conventional projection welding performed using a first metal plate 1a having an annular protrusion 2 having a uniform cross-sectional shape, a single-phase AC power source is used as the welding power source 8. When welding is used, the energization time is long, ranging from tens of milliseconds to hundreds of milliseconds, and excessive heat is also applied to the area around the weld, resulting in an indentation 1 as shown in Figure 8d.
2 usually reaches a depth of several tens of microns, which not only impairs the appearance of the second metal plate 1b, but also poses a problem in that if it is to be painted afterward, it is necessary to repair it by increasing the thickness of the paint film. .

In addition, to improve this problem, a method of bonding in a short time of about 10 milliseconds using a capacitor power supply has been proposed, but in this case, the skin effect of the current,
Due to the edge effect, almost no current flows inside the annular protrusion 2, and since the energization time is short, no temperature rise due to heat conduction can be expected, and an unbonded portion remains on the inner circumference of the annular protrusion 2. The problem was that the outer periphery generated heat and melted, making it easy to blow up. This phenomenon is particularly noticeable in materials such as stainless steel, which have low thermal conductivity, making stable joining difficult.

This invention was made to solve these problems, and provides a projection welding method that can prevent the formation of impressions on the surface of metal plates and form a good joint at the joint interface. The purpose is to propose the following.

[Means for solving the problems] The projection welding method according to the present invention includes:
The ring-shaped protrusion provided at the joining point of the first metal plate material to be joined to the second metal plate material has a radial cross section consisting of a convex curved surface, and a closed curve forming the outer periphery and inner periphery of the rising part of the convex curved surface. It is formed so that it has no inflection point, and the shape of the convex curved surface is such that the apex of the convex curved surface is
Located inside the center position between the closed curves on the inner circumference,
It is formed so that its height is constant over the entire circumference, and the first metal plate material and the second metal plate material are contacted and pressurized through this annular protrusion, and a current with a wave height time of 3 milliseconds or less is applied. The method is characterized in that the first metal plate material and the second metal plate material are joined by applying electricity to the annular projection.

[Function] In the present invention, the apex position of the radial cross section of the annular projection provided on the first metal plate material is located inside the center position of the radial cross section, and no inflection point is provided in the closed curve formed at the apex. By doing so, the current is concentrated inside the annular protrusion, and the current is applied in an extremely short period of time. By doing so, the bonding interface can be closed with only the heat generated by the concentrated resistance caused by the annular protrusion, while almost no conductive heat is generated. Can be joined.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention, and in the figure, 1a, 1b, 3a to 7 are the same as the conventional example shown in FIG. Reference numeral 15 denotes an annular projection provided on the first metal plate 1a, and the annular projection 15 is formed from a curved surface with a convex radial cross section as shown in FIG. The outer periphery and inner periphery of the rising portion from 1a are a large closed curve 16 and a small closed curve 17 that do not have an inflection point, respectively.
It is formed of. The curve formed by connecting the large closed curve 16, the small closed curve 17, and the vertex 18 is, for example, a circle with the same center and radii of ra, rb, and rc, and the radius rc from the center to the vertex 18 is large.
It is set to be smaller than the average of the radii ra and rb of the small closed curves 16 and 17 and larger than the radius rb of the small closed curve 17. Further, the height h of the annular projection 15 is, for example, 0.1 mm or more and less than the thickness of the first metal plate 1a, and the width ra-rb of the annular projection 15 is 3 mm of the thickness of the first metal plate 1a. It is set to be less than double.

The height h of the annular projection 15 is set to 0.1 mm or more as described above, for example, when joining large parts such as elevator door panels, the first metal plate material 1a and the second This is to prevent the two metal plates 2a from coming into contact with each other to prevent arcing and ineffective shunting from occurring. The reason why the height h of the annular protrusion 15 is set to be less than or equal to the thickness of the first metal plate 1a is because if the height h is made greater than the thickness of the first metal plate 1a and the second metal plate 1b after joining. This is because the gap between them becomes too large and sufficient reinforcement is not achieved, and the shape of the annular projection 15 is not formed stably.

In FIG. 1, 19 is a welding power source, and the welding power source 19 has a current wave height time ta of 3 as shown in FIG. It consists of a capacitor power supply that lasts less than a millisecond.

The reason why the current peak time ta is set to 3 milliseconds or less as described above is as follows. For example, in the case of a mild steel plate with a thickness of 1 mm, the time constant of heat conduction is 48 milliseconds.
Therefore, if the bonding interface is bonded within a time of 3 milliseconds or less, which is much shorter than this time, the generated heat will hardly be conducted, so the amount of heat input can be used effectively to bond the bonding interface. I can,
This is because excessive heat, which is one of the causes of indentation, is not applied. Note that as the current peak time ta is shortened, the current peak value naturally becomes higher compared to the conventional example.

The operation when welding the first metal plate 1a and the second metal plate 1b using the projection welding device configured as described above is the same as the conventional example shown in FIG. 5 except for the current waveform. Matsutaku is similar. Hereinafter, the features of the operation of this embodiment will be explained based on the progress of joining according to this embodiment shown in FIG.

In Fig. 4, a shows the start of welding, b and c show the state in which the welding is progressing in sequence, and d shows the state in which the welding is completed, 9 is the current path, 11 is the back side of the projection, and 20 is a thin weld. Shows the nugget part.

The first metal member 1a and the second metal plate material 1b are connected to each other via an annular projection 15 to an upper electrode 3a and a lower electrode 3b.
When welding current is applied from the welding power source 19 while pressurizing the upper electrode 3a, the current flows from the outer periphery of the upper electrode 3a to the first metal plate 1a due to the skin effect and edge effect.
and flows through the outer portion of the annular projection 15 to the second metal plate 1b. Since the annular projection 15 uniformly contacts the second metal plate 1b at the apex 18 near the inner circumference of the projection, the current path 9 is largely bent inward at the contact portion. After that, the vicinity of the inner circumference of the annular protrusion 15 softens and
Once melted, the annular protrusion 15 begins to collapse;
As shown in FIG. 4b, a new contact portion is formed closer to the outer periphery than the initial contact portion, and the current path 9 becomes closer to the outer periphery than the initial contact portion due to the above effect. Thereafter, the current path 9 gradually spreads to the outer periphery of the annular projection 15 as shown in FIG. A thin weld nugget 20 is formed and the bond is achieved.

In projection welding configured as described above, the current path 9 sequentially moves from the inner circumference to the outer circumference of the annular protrusion 15, so that the current density in each part of the joint becomes uniform, resulting in a uniform thin weld nugget. 20 can be formed. Therefore, it is possible to prevent explosions from occurring. Further, since the extremely thin weld nugget 20 is formed by applying electricity for a short time of 3 milliseconds or less, it is possible to prevent the formation of impressions on the surface of the second metal plate 1b without applying excessive heat.

Further, in the above embodiment, the width of the annular projection 15 is set to three times or less than the thickness of the first metal plate 1a in order to obtain uniform heat generation at the bonding interface, and the width of the annular projection 15 is made larger. This may cause the current distribution to become unbalanced, leaving unjoined parts near the inner periphery of the annular protrusion 15, or conversely causing explosions at the outer periphery, and this is to prevent this.

In addition, in the above embodiment, the case where the annular protrusion 15 has circular outer and inner circumferences and its width is constant is explained, but in this case, there is no anisotropy in the bonding strength, and the general bonding part has no anisotropy. However, for joints that need to have strength only against stress from a certain direction, it is possible to reduce the stress by providing an annular projection with variable width or an elliptical or oblong annular projection. can be dealt with.

Further, in the above embodiment, projection welding of mild steel plates has been described, but the first metal plate 1a and the second metal plate 1b may each be made of, for example, a stainless steel plate or a non-ferrous metal. The second metal plate material 1b may be made of different materials, such as a combination of a stainless steel plate and a mild steel plate.

[Effects of the Invention] As explained above, the present invention makes the apex position of the radial cross section of the annular projection provided on the first metal plate inside the center position of the radial cross section, and transforms it into a closed curve formed by the apex. By avoiding curved points, concentrating the energizing current inside the annular projection, and energizing in an extremely short period of time, the concentrated resistance caused by the annular projection is reduced while almost no conductive heat is generated. Since the bonding interface can be bonded only by heat generation, it is possible to prevent indentation from occurring on the surface of the second metal plate material, and also to prevent explosions and obtain a homogeneous bonded part.

Furthermore, since a homogeneous and thin joint can be obtained, the strength of the joint can be increased.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing a projection welding device according to an embodiment of the present invention, Fig. 2 is a side view showing a first metal plate material used in the above embodiment, and Fig. 3 is a diagram showing a side view of a first metal plate used in the above embodiment. Current waveform diagram of welding power source,
FIG. 4 is an explanatory diagram showing the welding progress process according to the above embodiment, FIG. 5 is a configuration diagram showing the conventional example, FIGS. 6 and 7 are current waveform diagrams of the welding power source of the conventional example, and FIG.
The figure is an explanatory diagram showing the progress of welding in a conventional example. 1a... First metal plate material, 1b... Second metal plate material, 2, 15... Annular projection, 3a... Upper electrode, 3b
...Lower electrode, 4... Frame, 5... Air cylinder, 6...
Upper frame, 7... Rod, 8, 19... Welding power source, 9
...Current path, 10, 20...Welding nugget. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Welding the first metal plate material and the second metal plate material by applying electricity while contacting and applying pressure to the protrusion formed at the joining location of the first metal plate material and the second metal plate material to be joined. In projection welding, between a large closed curve that has no inflection point on the circumference at the joining point of the first metal plate material and a small closed curve that is included in this large closed curve and has no inflection point on the circumference. is protruded with a curved surface having a convex cross section to provide an annular projection, the apex of the convex cross section of the annular projection is located inside the center position between the large and small closed curves, and the apex of the cross section is located on the first metal plate material. It is formed at a constant height from the surface, and presses the first metal plate material and the second metal plate material through contact through the annular projection, and the wave height time is 3.
A projection welding method characterized in that a first metal plate material and a second metal plate material are joined by applying a current of less than a millisecond to an annular protrusion. 2. The projection welding method according to claim 1, wherein the height of the annular projection is 0.1 mm or more and is less than or equal to the thickness of the first metal plate. 3. The projection welding method according to claim 1 or 2, wherein the annular projection has a constant cross-sectional width. 4. The projection welding method according to any one of claims 1 to 3, wherein the large and small closed curves of the inner and outer circumferences of the annular projection are each a circle, an ellipse, or an ellipse. 5. The projection welding method according to any one of claims 1 to 4, wherein the width of the annular projection is three times or less the thickness of the first metal plate.