JPS628269B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for performing indirect spot welding by overlapping a plurality of thin plates, such as when welding a door hem portion of an automobile.

For example, an indirect welding method has been adopted as a conventional welding method for a door hem portion formed by stacking three layers of thin steel plates and welding them. FIG. 4 schematically shows a state in which indirect spot welding is being performed on a welded object 3 in which two thin steel plates 1 and 2 are stacked one on top of the other. Two welding electrodes 5a, 5b are connected to a welding transformer 6, and back electrodes 4a, 4b made of copper are provided at respective positions facing each of the welding electrodes 5a, 5b. In between, the end of one thin steel plate 1 is folded back into a U-shape, one end of the thin steel plate 2 is positioned between them, and the end welded part of the three-layer welded body 3 is inserted into position. Moreover, between the other welding electrode 5b and the back electrode 4b,
The thin steel plate 2, which is bent in a direction away from the thin steel plate 1 and parallel to the thin steel plate 1, is inserted and welded. Electrode 5a and back electrode 4a
By applying pressure using a pressure means (not shown) and bringing the welding electrode 5b into contact with the thin steel plate 2, a predetermined welding current is passed between the welding electrodes 5a and 5b for a predetermined period of time. The contact portions of the thin steel plates 1 and 2 sandwiched between the welding electrode 5a and the back electrode 4a are spot welded.

In this welding process, the welding current flowing between the welding electrodes 5a and 5b takes two paths shown by broken lines in FIG. That is, the flow takes a route through the thin steel plate 2 and a route through the thin steel plate 1 on the back electrode 4a side, but most of the flow passes through the thin steel plate 2.

While welding, the thin steel plates 1 and 2
During this period, heat is generated, and heat is generated as a welding current flows through a part of the back electrode 4a, and as a result of repeated welding, the contact surface of the back electrode 4a with the object 3 to be welded is worn out. This causes a dent, and distortion and flaws occur in the thin steel plate 1 due to the pressure applied between the electrodes 5a and 4a during welding.

In cases where the properties of the steel plate surface are important, such as in a door hem portion corresponding to the door outer, such distortions and flaws cannot be ignored and rework is required.

Conventionally, as a method for preventing such distortions and flaws from occurring, an insulator 7 (shown by two-dot chain lines in FIG. 4) such as Bakelite or hard rubber is placed on the surface of the back electrode 4a facing the welding electrode 5a where the concave portion is formed. was established. According to this method, no dents are formed in the insulator 7 because no welding current flows, but the insulator 7 is thermally deformed due to repeated pressure during welding, and the surface of the thin steel plate 1 is also distorted. Scratches occur.

The present invention has been made in view of the above circumstances, and in the case of welding a door hem part, etc., when a plurality of plates to be welded are overlapped and indirect welded, the surface of the door hem part corresponding to the door outer, etc. The object of the present invention is to provide a spot welding method that can prevent distortion or flaws from occurring in areas where surface quality is important.

The spot welding method according to the present invention involves stacking a plurality of plates to be welded, disposing a welding electrode on one side, and disposing a ceramic support member at a position facing the welding electrode on the other side. Features.

The method of the present invention will be explained in detail below based on the drawings showing examples thereof. FIG. 1 is a schematic front view showing the implementation state of the method of the present invention, and the same parts as in FIG. 4 are given the same reference numerals.

1 is a thin steel plate that becomes the front side, and its end is U
The thin steel plate 2 is bent into a U-shaped portion, and one end of the thin steel plate 2 is inserted into the central space of the U-shaped portion to form a three-layer welded body 3. Then, indirect welding is performed using the spot welding machine described below. The thin steel plate 2 has one end inserted into the folded portion of the thin steel plate 1 as described above, is bent in a direction away from the thin steel plate 1, and is further bent in parallel to the thin steel plate 1.

5a and 5b are welding electrodes, and each welding electrode 5
a and 5b are spaced apart from each other by a suitable length on the lower surface of an upper platen (not shown) that moves up and down as a result of the advancing and retracting movement of a pressurizing cylinder (not shown), and one welding electrode 5b is positioned above. It is installed in the condition that it is installed. Further, the welding electrodes 5a, 5b are directly connected to a welding transformer 6 for supplying a predetermined welding current.

A support member 8 made of ceramic is provided at a position facing the welding electrode 5a located on the lower side, and a back electrode 4b made of copper is provided at a position facing the welding electrode 5b located on the upper side. There is.

As mentioned above, the material of the support member 8 is ceramic, and its characteristics are (a) good bending strength (impact resistance), (b) good workability, and (c) low price. It is best to use a material that has all three of these characteristics, such as alumina ceramic with an alumina purity of 92% or more, and silicon nitride ceramic with a bending strength of 45 kg/mm ^{2 or} more.

Attach the welding electrodes 5a and 5b as described above,
The upper platen, which is moved up and down by a pressure cylinder, the welding transformer 6 directly connected to the welding electrodes 5a and 5b, the support member 8, and the back electrode 4b constitute the main components of the spot welding machine, together with a welding condition control device (not shown). is an element.

Now, when performing spot welding of the three-layer end portion of the welded object 3, the three-layered end portion of the welded object 3 is placed between the welding electrode 5a of the spot welding machine described above and the support member 8. After inserting the end part and inserting the part of the thin steel plate 2 of the object to be welded 3 that is parallel to and apart from 1 between the other welding electrode 5b and the back electrode 4b, the pressure cylinder Move the upper platen downward and remove the welding electrode 5a and the support member 8.
Appropriate pressure is applied to the end portion of the object to be welded 3 via. In this case, the other welding electrode 5b only needs to come into contact with the upper surface of the thin steel plate 2, and the position of the back electrode 4b is determined so that excessive pressure is not applied to the thin steel plate 2. In such a state (FIG. 1 shows this state), a predetermined welding current is passed between the welding electrodes 5a and 5b for a predetermined period of time, and the thin steel plates 1 and 2 at the ends of the objects to be welded 3 are welded. Spot weld the contact area.

In such a method of the present invention, the supporting member 8
is made of electrically insulating ceramic and has excellent heat resistance and impact resistance, so no electricity is applied to the support member 8, and it has excellent heat removal properties, so the heat generated between the thin steel plates 1 and 2 prevents the support member from being energized. There is no risk that the member 8 will wear out, and therefore the supporting member 8 will not wear out even during long-term continuous welding, and the conventional problem of distortion and flaws occurring on the surface of the thin steel plate 1 can be solved. can.

In particular, when zinc chrome metal (coated with chromic acid and zinc paint) is used as a thin steel plate, the electrical resistance of the film is high, so the amount of heat generated is large, and as a support member, it has excellent heat resistance and little thermal deformation. Furthermore, it is necessary to have high thermal conductivity, large heat removal properties, and to withstand continuous impact, but by using the ceramic support member as in the method of the present invention, the above conditions are satisfied, and the thin steel plate can be used as a thin steel plate. Even when zinc chrome metal is used, welding can be performed without causing flaws, distortions, etc. in the zinc chrome metal.

FIG. 2 is a graph showing the results of considering the effects of the above-described method of the present invention from an appropriate range of welding conditions. That is, in Figure 2, the horizontal axis shows welding current, and the vertical axis shows welding time, and the appropriate conditions are shown for the conventional method (area surrounded by a solid line) and for the method of the present invention (area surrounded by a broken line). (area). The other main welding conditions in this case are that the pressurizing force is 80 kg in both cases, the distance between welding electrodes is 200 mm in both cases, and the curvature of the tip of the welding electrode is 20 mm in both cases. As is clear from the figure, in the case of the method of the present invention, since the support member 8 has heat resistance and impact resistance, the appropriate range can be wider than in the case of the conventional method, and stable operation is possible. .

FIG. 3 is a graph showing the results of considering the effect of the method of the present invention in terms of the wear depth of the back electrode or the support member. In other words, Figure 3 shows the number of dots on the horizontal axis and the wear depth on the vertical axis. This is a comparison with the method of the present invention using a member (broken line). In addition, the welding conditions in this case are that the welding current is 7000A, the energization time is 6cycles,
Pressure force is 80Kg. As is clear from the figure, the depth of wear of the support member corresponding to the conventional back electrode can be significantly reduced in the case of the present invention compared to the case of the conventional method.

The method of the present invention can also be applied to back electrodes for series spot welding.

As described in detail above, according to the method of the present invention, when a plurality of thin plates are overlapped and indirect welded, by using a ceramic bearing member, wear of the bearing member can be prevented and distortion of the thin plate can be prevented. , the occurrence of scratches is prevented. Therefore, the present invention provides indirect welding for parts where surface quality is important, such as the surface of the door hem corresponding to the door outer.
This provides an extremely powerful method.

[Brief explanation of the drawing]

FIG. 1 is a schematic front view showing the implementation state of the method of the present invention, FIGS. 2 and 3 are graphs showing the effects of the method of the present invention, and FIG. 4 is a schematic front view showing the implementation state of the conventional method. be. 1, 2... Thin steel plate, 3... Welded object, 4a, 4
b... Back electrode, 5a, 5b... Welding electrode, 6
... Welding transformer, 7 ... Insulator, 8 ... Supporting member.

Claims (1)

[Claims] 1. A spot welding method characterized in that a plurality of plates to be welded are stacked one on top of the other, a welding electrode is arranged on one side, and a ceramic support member is arranged on the other side at a position facing the welding electrode.