JP4488838B2 - Spot welding method - Google Patents

Description

  The present invention relates to a series type spot welding method.

  When two plates to be welded are overlapped and welded to each other, spot welding (direct spot welding) is usually performed in which a pair of electrodes is sandwiched from above and below by a pair of electrodes.

  However, when it is difficult (or impossible) to sandwich the plate to be welded with a pair of electrodes, that is, there is a space for placing the electrode on one side of the plate to be welded, but on the other side the space is limited due to space constraints. Direct spot welding is not appropriate when it is difficult (or impossible) to place the electrodes.

  Series spot welding is known as a welding method when there is a restriction on the arrangement of the back electrode. In this series spot welding, a pair of protrusions are formed on one welded plate by embossing, and the other welded plate is overlapped so as to cover the pair of protrusions. A pair of electrodes are pressed against the pair of protrusions, and the pair of protrusions are melted and welded to the other welded plate by energizing between the electrodes in this pressurized state.

  However, since there is no back electrode in series spot welding, it is generally impossible to form a sufficiently large nugget and it is difficult to obtain the necessary welding strength. Therefore, an improved series spot welding method shown in FIGS. 3 to 5 has been proposed (see Patent Document 1).

3 to 5 show examples in which the floor panel 21 is spot-welded to the vehicle body frame 20. Since it is difficult to dispose a back electrode on the lower side of the floor panel 21, series spot welding is usually performed from the upper side of the floor panel 21. A reinforcing plate 22 is attached to the body frame 20 as necessary. As shown in FIG. 4, the floor panel 21 is press-molded with a plurality of circular protrusions 23, which are one level higher than the general portion, along the flange 22 a of the reinforcing plate 22. The reinforcing plate 22 is spot-welded to the vehicle body frame 20 at a plurality of points S1, as shown in FIGS. After the floor panel 21 is placed on the vehicle body frame 20 with the reinforcing plate 22 therebetween, the floor panel 21 is simultaneously pressed so that the pair of protrusions 23 are crushed by the pair of electrodes 24 and 25 on the R surface. When the pair of protrusions 23 are crushed by the electrodes 24 and 25, the protrusions 23 are deformed into a spherical shape 23a and hit the flange 22a of the reinforcing plate 22 at two points S2. By synchronizing the current between the electrodes 24 and 25 in synchronism with this, series spot welding is performed with the two points S2 as a set. Since the welding current flows through the energized path narrowed down to a dotted shape, the welding current density is increased and a sufficiently large nugget or welding strength can be obtained without a back electrode.

In the above welding method, since the protrusion 23 must be press-molded in advance on the floor panel 21 , the position of the protrusion 23 cannot be freely changed, and it is possible to respond quickly to changes in the production vehicle type, etc. Difficult to do.
In addition, although it is also conceivable that the three plates 20 to 22 are overlapped and directly spot welded at a time without forming such a protrusion 23, in that case, the vehicle interior side which is the upper surface side of the floor panel, Since it is sandwiched between a pair of electrodes from the outside of the passenger compartment, which is the lower surface side of the floor panel, a large welding gun is required, resulting in high equipment costs.

In order to solve the above problems, the present invention provides a method for spot welding by overlapping a third welded plate from the first welded plate side with respect to the superimposed first and second welded plates, A pair of electrodes that are opposed to each other on the same axis and are capable of approaching and separating, wherein one first electrode has a hole in the tip surface, and the other second electrode has a convex surface or a plane on the tip surface. Using the electrode, with the first and second welded plates overlapped, the first electrode is brought into pressure contact with the first welded plate side and on the second welded plate side. The second electrode is brought into pressure contact, and in this state, the first and second electrodes are energized to spot weld the first and second welded plates, and the first welded plate is a first step of forming a first projection that bulges toward the hole portion of the first electrode, the first and Said first and second welded plate with spot welding at the at a position spaced from said first projection and the second electrode is moved first step the same manner as in the first to-be-welded plate a second step of forming a second projection that bulges toward the said hole of the first electrode, the superposed third of the weld plate on the first of the welding plate, the first The first protrusion and the second protrusion are pressed simultaneously with the third electrode and the fourth electrode through the third welded plate and energized between the two electrodes, whereby the first and second protrusions are And a third step of welding the third welded plate to the third welded plate, the first welded plate and the second welded plate in the first step and the second step. A weld nugget formed therebetween, the first and second protrusions of the first welded plate in the third step, and the third welded plate And a weld nugget formed between, and forming by aligning the third thickness direction of the weld plate from the first.

  According to the present invention, when the first and second welded plates are spot-welded with the first and second electrodes, the projections of the welded plates necessary for the series spot welding are the first to the hole of the first electrode. Since the material of the welded plate can be formed at the same time, a press die for embossing the protrusion on the third welded plate as in the prior art is unnecessary, and the first The protruding portion of the welded plate can be formed at an arbitrary position.

  Moreover, since the protrusion is formed at the same position as the welded portion of the first and second welded plates and this protrusion is welded to the third welded plate, the welded portion overlaps the same position and is sufficient. Weld strength is obtained.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2.

  In the spot welding method of the present invention, as shown in FIG. 1 and FIG. 2, three welded plates 1, 2, 3 (steel plates) are welded, and at this time, protrusions are formed on the first welded plate 1. The perforated electrode 5 (first electrode) is used to form 4. This perforated electrode 5 is formed by forming a hole 6 extending a predetermined length in the axial direction of the electrode 5 in the plane of the tip of the electrode 5 or the center of the convex R surface. The diameter of the hole 6 may correspond to the required diameter of the protrusion 4, and there are no particular restrictions on the upper and lower limits of the diameter of the protrusion 4. In this embodiment, a hole 6 (round hole) having a diameter of 5 mm is formed in the center of the tip surface of an electrode having a flat tip (L-shaped electrode). The electrode 7 (second electrode) facing the perforated electrode 5 is an electrode having a convex or flat tip. In the present embodiment, an electrode having a tip radius of curvature of 8 mm is used. The first and second electrodes 5 and 7 are attached to, for example, a C-type welding gun supported on the tip of the robot arm.

  Using such a pair of electrodes 5 and 7, the first and second welded plates 1 and 2 are overlapped, and the welded plates 1 and 2 are paired as shown in FIG. 7 is sandwiched between the plates and pressurized and energized in the thickness direction. As a result, the pressed portions of the first and second welded plates 1 and 2 are melted by the resistance heat generation of the steel plates to form the weld nugget 8a, and the two welded plates 1 and 2 are spot welded. Further, the surface of the first welded plate 1 with which the first electrode 5 abuts is caused by a part of the softened material bulging out into the hole 6 of the first electrode 5 by applying a pressure, and FIG. A substantially hemispherical first protrusion 4a is formed as in (B) (first step). The inventor of the present application confirmed that the height of the protrusion 4 is constant when the pressure applied to the electrodes 5 and 7 is constant.

Next, the first and second electrodes 5, 7 are opened and moved along the welded plates 1, 2, and again in the same manner as described above at a position spaced apart from the first protrusion 4 by a predetermined distance. 2 protrusions 4b (see FIG. 2) are formed (second step). Next, as shown in FIG. 2, the third welded plate 3 is overlaid on the first welded plate 1, and the third electrode 9 and the fourth electrode are placed on the third welded plate 3. 10 is simultaneously pressurized toward the first and second protrusions 4a and 4b , and electricity is applied between both electrodes in this pressurized state. As a result, a welding current flows in the current path of the third electrode 9 → the first protrusion 4a → the second protrusion 4b → the fourth electrode 10, and the tips of the first and second protrusions 4a and 4b are melted. Then, the third welded plate 3 is spot-welded to the first welded plate 1 by forming the weld nugget 8b (third step). Since the tips of the first and second protrusions 4a and 4b hit the welded plate 3, the welding current flows through the energized path narrowed in a dot shape, so that the welding current density is increased and the back electrode is not required. A sufficiently large nugget or weld strength can be obtained.
When the present invention is applied to a method in which the floor panel 21 is spot-welded with the reinforcing plate 22 sandwiched between the body frame 20 and the three plates 20 to 22 are overlapped, a direct spot is formed at once with a pair of upper and lower electrodes. Compared with the conventional method of welding, since the method of the present invention does not require a large welding gun, the equipment cost can be greatly reduced.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible, for example, in the said embodiment, the 1st protrusion 4a and the 2nd protrusion 4b is formed in order, but two sets of the first electrode 5 and the second electrode 7 may be attached to the tandem C-type gun to form the first and second protrusions 4a and 4b at the same time.

The 1st and 2nd process of the spot welding method concerning this invention is shown, (A) is sectional drawing of the to-be-welded board just before welding, (B) is sectional drawing of the to-be-welded board after welding. The 3rd process of this invention is shown, (A) is sectional drawing of the to-be-welded board before welding, (B) is sectional drawing of the to-be-welded board after welding. Sectional drawing which shows the attachment structure of the floor panel with respect to the conventional vehicle body frame. The perspective view of the state which mounted the floor panel before welding on the conventional vehicle body frame. It is sectional drawing which shows the welding method of the floor panel with respect to the conventional vehicle body frame, Comprising: (A) is sectional drawing before welding, (B) is sectional drawing after welding.

Explanation of symbols

1, 2, 3 Plates to be welded 4a, 4b Projection 5 First electrode 6 Hole 7 Second electrode 8a, 8b Weld nugget 9 Third electrode 10 Fourth electrode 20 Body frame 21 Floor panel 22a Flange 22 Reinforcement plate 23 Protrusions 24, 25 electrodes

Claims (1)

In the method of spot welding by overlapping the third welded plate from the first welded plate side with respect to the superimposed first and second welded plates,
A pair of electrodes that are opposed to each other on the same axis and are capable of approaching and separating, wherein one first electrode has a hole in the tip surface, and the other second electrode has a convex surface or a plane on the tip surface. Using the electrode, with the first and second welded plates overlapped, the first electrode is brought into pressure contact with the first welded plate side and on the second welded plate side. The second electrode is brought into pressure contact, and in this state, the first and second electrodes are energized to spot weld the first and second welded plates, and the first welded plate is a first step of forming a first projection that bulges toward the hole portion of the first electrode,
The first and second electrodes are moved, and the first and second welded plates are spot welded to a position separated from the first protrusion by the same method as in the first step, and the first a second step of forming a second projection that bulges toward the hole portion of the first electrode to be welded plates,
A third welded plate is overlaid on the first welded plate, and the first and second protrusions are connected to the third electrode and the third welded plate via the third welded plate. A third step in which the first and second projections are melted and welded to the third welded plate by simultaneously applying pressure between the four electrodes and energizing both electrodes ;
A weld nugget formed between the first welded plate and the second welded plate in the first step and the second step, and the first welded plate in the third step. Forming a weld nugget formed between the first and second protrusions and the third welded plate in alignment with the plate thickness direction of the first to third welded plates; A spot welding method characterized by the above.

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