JPH0324310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is aimed at improving the welding strength of base materials, as typified by joints of inlet pipes in fuel tanks for vehicles. This invention relates to a projection welding method for welding three layers.

(Prior art) In general projection welding, a welding protrusion is formed on one of two base materials, as shown in, for example, Japanese Utility Model Application No. 143990/1983. The welding protrusion is brought into contact with the flat surface of the other base material to create a two-layered state, and in this state, welding is performed by applying current at a predetermined current value and applying pressure.

(Problems to be Solved by the Invention) By the way, like the connection part of the inlet pipe in the vehicle fuel tank mentioned above,
When projection welding three base metals with different thicknesses, the welding process is performed due to the difference in the shape and size of the weld projections formed on two of the three base metals. Since the conditions were different, it was generally necessary to weld two layers together twice. In other words, three-ply projection welding is performed in two steps, resulting in duplication of equipment and work steps.

Therefore, it is conceivable to carry out this three-ply projection welding in one process by applying current once, but if this is done carelessly, an excessive current will flow through the abutting parts of each base metal, resulting in The occurrence of melt scattering and pinholes at the joint became noticeable, which could lead to deterioration in the quality and strength of the weld.

As another method, spot welding of the three-ply base metal with a large contact area may be considered. However, like the connection part of the inlet pipe in the fuel tank mentioned above, it is ring-shaped and has a small diameter (usually 120 mm or less).
In order to spot weld the base metal at multiple points (more than 5 points in the circumferential direction), it is difficult to line up the welding gun at each welding point at once, and welding must be done in several steps. Must be. As a result, an indexing device is required to correctly define the welding points, and a tack welding step is also added to prevent each base material from lifting up, resulting in an inconvenience that the cycle time of the welding operation is extended.

Incidentally, problems specific to spot welding include that the welding electrode must be managed more frequently to maintain the quality of the weld, and it is difficult to avoid indentations in the weld.

(Objective of the Invention) The object of the present invention is to be able to weld three-ply base materials in one step using standard welding equipment, and to improve productivity by avoiding duplication of work steps. In addition, it is possible to prevent excessive current from flowing in the contact area between the base metals, prevent melting spatter, pinholes, etc., and maintain appropriate quality and strength of the welded part. An object of the present invention is to provide a method for overlapping projection welding.

(Structure of the Invention) In order to achieve the above object, the present invention is structured as follows.

In other words, the reinforcing base material and the auxiliary base material are arranged in a three-layered state with the welding protrusions of the base material and the auxiliary base material in contact with each surface of the basic base material that does not have welding protrusions. Pressure is applied at the same time as current is applied at the current value and time required to melt and bond the abutting portion between the welding protrusion formed on the base material with the smaller thickness of the materials and the basic base material. After this, the current supply is stopped for the time required to cool down the fusion-bonded parts, and then the abutting parts between each fusion-bonded base metal and the welding protrusion formed on the remaining thicker base metal are removed. The current is applied again at the current value and time required for fusion bonding.

(Example) Hereinafter, the structure of the present invention will be specifically explained according to an example shown in the drawings.

Figure 1 shows the joining part of the inlet pipe in a fuel tank for a vehicle.The basic base material 1, which is the fuel tank upper, has a plate thickness.
It is thin at 0.8mm and has no welding protrusions. Note that an opening 2 communicating with an inlet pipe 10, which will be described later, is formed in advance in this basic base material 1. An auxiliary base material 5 and a reinforcing base material 3 having different thicknesses are provided on the upper and lower surfaces of the basic base material 1, respectively. The auxiliary base material 5 has the thickest plate thickness at 0.6 mm compared to the other base materials 1 and 3, and is formed into a ring shape with an outer diameter of 110 mm, and a weld with a diameter of 7 mm is applied along the circumferential direction. Protrusions 6 are formed at a total of seven locations. This auxiliary base material 5 is a retainer member for connecting a flange 10a of an inlet pipe 10, which will be described later, and is used to screw in a bolt 12, which will be described later, as is clear from FIG. A plurality of screw holes 7 are formed along the circumferential direction.

On the other hand, the reinforcing base material 3 has a plate thickness of 1.6 mm, which is thicker than the basic base material 1, and is formed into a ring shape with an outer diameter larger than the auxiliary base material 5.
A welding protrusion 4 having a different size and shape from the welding protrusion 6 of the auxiliary base material 5 is formed along its circumferential direction. Although the welding protrusions 4 of the reinforcing base material 3 are formed at almost the same pitch as the welding protrusions 6 of the auxiliary base material 5, both welding protrusions 4, 6
are formed with a deviation of 2 mm, which is the dimension L, in the radial direction of the base materials 3 and 5, respectively (see FIG. 1).

Next, the projection welding of the inlet pipe joint in the fuel tank will be explained. First, the three base materials 1, 3, and 5 are set in a stacked state as shown in FIG. In other words, the auxiliary base material 5 connects the welding protrusion 6 to the basic base material 1.
The reinforcing base material 3 is placed in contact with the top surface of the
Similarly, the welding protrusion 4 is placed in contact with the lower surface of the basic base material 1. At this time,
As described above, the welding protrusions 4 and 6 of the reinforcing base material 3 and the auxiliary base material 5 are offset from each other by 2 mm, which is the dimension L. In this state, electrodes (not shown) for projection welding are placed above and below the abutting parts of each base metal 1, 3, and 5, and a constant pressure of 900 kg is continuously applied as shown in Figure 3. Perform the first welding while adding. The welding conditions are a current value of 40 KA and a current application time of 40 seconds. After the first welding, the current is turned off for 30 seconds to allow the molten joint (nugget) to cool. The above is considered as one cycle, and a total of three cycles are performed under the same welding conditions and energization stop time. As a result, the three base materials 1, 3, and 5 are simultaneously projection welded in one process.

By this first energization in FIG. 3, the basic base material 1, which has the thinnest plate thickness, and then the welding protrusion 4 of the reinforcing base material 3, which has the thinnest plate thickness, are fused and bonded. Then, by stopping after the first energization, the above-mentioned molten joint (nugget) is cooled down, and as a result, the basic base material 1 and the reinforcing base material 3 become integrated (welded). Due to the second energization in FIG. 3, the welding protrusion 6 of the auxiliary base material 5, which has the largest plate thickness, is melted with respect to the basic base material 1 and the auxiliary base material 5, which have already been integrated by fusion bonding. be combined. After this, by energizing for the third time after a second pause, the auxiliary base material 5 sinks well, and the height H becomes uniform over the entire circumference as shown in Fig. 4. Welding is done.

In this way, by conducting short-cycle energization three times with a pause in between, the thin base materials 1 and 3 are first melted and bonded, and after cooling, the thin base materials 1 and 3 are bonded together. Since the thick auxiliary base material 5 is melt-bonded and the three sheets are finally welded together, an excessive current flows through the abutting portions of each base material, resulting in the occurrence of melting spatter, pinholes, etc. can avoid.

In addition, by shifting the positions of the welding protrusions 4 and 6 on the reinforcing base material 3 and the auxiliary base material 5, the concentration of heat on the mutual contact areas can be avoided, especially on the thin reinforcing base material 3 side. Melting and scattering due to abnormal heating can also be avoided.

Note that it is not necessarily necessary to shift the positions of the welding protrusions 4 and 6 by repeating short cycles of energization with pauses in between, and even if the positions of the welding protrusions 4 and 5 are aligned, three The overlapping welding protrusions are performed satisfactorily.

The inlet pipe joint portion of the fuel tank welded in this way has high rigidity and can sufficiently withstand even if abnormal bending force is applied from the inlet pipe or the like. Also,
Due to the above-mentioned reason, the height H shown in FIG. The contact surface is wide and uniform, resulting in good sealing properties.

As described above, this embodiment does not require any major changes to the projection welding equipment, and can perform good projection welding even with the small, small-capacity welding equipment that has been used up to now.

In the embodiment shown in FIG. 5, welding is completed by applying current twice, and the current value for the second welding is set higher than the current value for the first welding. In other words, the first welding condition is that the current value is
The energization time is 30 seconds at 30KA. After this first welding, the current supply is stopped for 30 seconds to allow the molten joint to cool. After this, the second welding will be performed, and the welding conditions for this welding are such that the current value is 50KA.
The energization time is set to 60 seconds.

In this way, in the embodiment shown in FIG. 5, the first energization melts and joins the basic base material 1 and the welding protrusion 4 of the reinforcing base material 3, as in the case described above. After the pause, the current value and energization time are increased and energization is performed for the second time, thereby completing projection welding.
In other words, at the time of the second energization, there is no thin wall part in the contact area between the two base materials, so even if a certain amount of current flows, there is no risk of melting and scattering. This embodiment takes advantage of this point and completes welding with two energizations.

(Effects of the Invention) As described above, the present invention can complete projection welding of three layers in one process, thereby avoiding duplication of work processes and improving productivity. Although the work can be completed in one step, excessive current flows through the contact parts of each base material, causing melting and scattering, pinholes, etc. This makes it possible to maintain appropriate quality of the welded part and increase its rigidity.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a cross-sectional view showing the inlet pipe joint in a vehicle fuel tank set before welding, and FIG. 2 is a part of an auxiliary base material that is a retainer. Fig. 3 is a characteristic diagram showing the energization and pressurizing force patterns of projection welding, Fig. 4 is a cross-sectional view showing the completed welding state of Fig. 1, and Fig. 5 is a different energization pattern. It is a characteristic diagram showing a pattern. 1...Basic base material, 3...Reinforcement base material, 4...Welding protrusion, 5...Auxiliary base material, 6...Welding protrusion.

Claims (1)

[Claims] 1. For each side of the basic base material, which has a thin plate thickness and does not have welding protrusions, a reinforcing base material and an auxiliary base material that have different plate thicknesses and both have welding protrusions, and each of these welding protrusions. A method of projection welding of three base metals by placing them in a stacked state in contact with each surface of the base metal, in which a predetermined pressing force is applied to each of the base metals, First, electricity is applied at the current value and time required to melt and bond the welding protrusion formed on the thinner base material of the reinforcing base material and the auxiliary base material to the basic base material. The current supply is stopped for the time required to cool down the fused joint, and then the abutting part between the two fused base materials and the weld protrusion formed on the remaining thicker base material is fused and joined. A three-ply projection welding method characterized by energizing again at the required current value and time.