JPS6343775A - Spot welding method for galvanized steel sheet - Google Patents

Abstract

PURPOSE:To prevent the wear of an electrode by restraining the generation of a scattering body and to prevent the generation of a expulsion by removing the galvanized film of a spotting point part by a pressure electrification and forming a nugget with the pressure electrification again of this removed part. CONSTITUTION:Two sheets of galvanized steel sheets 5 are subjected to a pinching pressing by their overlapping by the electrode 4b fitted to the gun arm 4a of a pair of spot guns. An electrification is performed with the electrifying command placed from a timer contactor simultaneously with the pressing. The current of this time is adjusted so as to heat the galvanized steel sheet 5 at >= the temp. vaporizing the zinc plated film 5a formed on both faces of the galvanized steel sheet 5 and <= the temp. no nugget is formed. The pressing is then released simultaneously with cutting off the current after the electrification for a fixed time and the vaporized gas of the plated metal of a face mating part is released to the external part, then the plated film 5c of the electrification part of the galvanized steel sheet 5 is removed and the surface of the steel plate 5b is exposed. The same part with the 1st pressing point of two sheets of overlapped galvanized steel sheets 5 is then electrified by pressing it again, a nugget 11 is formed and the welding is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for spot welding plated steel plates, in which a plurality of steel plates having plated coatings formed on their overlapping surfaces are overlapped and spot welded.

[Conventional technology]

When spot-welding a plurality of steel plates, each of which has a plating film formed on the overlapping surfaces, by overlapping them, there is a problem in that explosions occur frequently and welding quality is degraded.

As a method to solve this problem, JP-A-50-104
As disclosed in Japanese Patent No. 742, a metal material having an insulating coating on both sides is sandwiched between a pair of electrodes, and before welding current is applied, a high frequency high voltage current and a low voltage are used to destroy the insulating coating. There is a known method in which a superimposed current is applied simultaneously with a frequency current to destroy the insulating film, and then a welding current is applied to this part using the same or separately sealed electrode.

Furthermore, as disclosed in Japanese Unexamined Patent Publication No. 55-36051, a method is also known in which a surface treatment film is removed in advance by a laser beam, and then an electrode is placed in the same position as the removed portion of the surface treatment film and welded.

[Problem that the invention seeks to solve]

However, according to the method disclosed in JP-A-50-104742, the arc generated between the metal material and the electrode further causes severe wear on the electrode due to the adhesion of an insulating film to the electrode, causing the welding current to flow. There was a problem that sometimes the flow was rapid and explosions occurred. Furthermore, the method disclosed in Japanese Patent Application Laid-Open No. 55-36051 requires a step of removing the surface treatment film with a laser beam, which has the problem of increasing equipment and man-hours. In addition, these conventional methods require the pressure to be strengthened, resulting in the gun and arm being large and often interfering with the workpiece.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for spot welding plated steel plates that can prevent explosions without using a high pressure gun.

[Means for solving problems]

In order to achieve the above object, the present invention provides a spot welding method for plated steel plates, in which a plurality of plated steel plates, each having a plated coating formed on their overlapping surfaces, are overlapped and spot welded. The first step is to remove the plating film at the spot dots by applying pressure and electricity to the steel plate by clamping it between the electrodes, and then applying pressure and electricity to the part where the plating film is removed using the same pair of electrodes. Spot welding is performed by a second step of forming and welding the nuggets 1-.

[Effect]

According to the method of the present invention, the plating film on the electrode contact portion and the facing portion of the overlapping steel plates is removed by pressurizing and energizing in the first step, and at the same time, the vaporized gas in the plating film is released to the outside. Next, in a second step, the portion from which the plating film has been removed is energized under pressure to form a nugget across the overlapping steel plates and welded without any explosion.

〔Example〕

Hereinafter, one embodiment of the method for spot welding plated steel sheets according to the present invention will be described with reference to the drawings.

'An embodiment of the present invention is shown in FIGS. 1 to 3.

FIG. 3 shows the configuration of the apparatus used in this example.

In the figure, a voltage supplied from a primary output power source 1 is set to an appropriate voltage by a transformer 2, and is applied to a pair of spot guns 4 via a power cable 3. This spot gun 4 has two plated steel plates 5 stacked on top of each other and is held under pressure by a pressure cylinder 7 operated by high-pressure air sent from an air valve 6. Electricity is supplied to the pressurized face-to-face portions of the two. Timer contactor 8
The welding sequence of pressurization and energization is stored in the
Commands for energizing and pressurizing the transformer 2 and pressurizing cylinder 7 are issued via signal lines 9 and 10, respectively.

Next, a welding method according to this embodiment will be explained. In step (a) of the flowchart shown in FIG. 2, the pressure command from the timer contactor 8 causes the electrodes 4b attached to the gun arms 4a of the pair of spot guns 4 to Two plated steel plates 5 are overlapped and clamped and pressed.

Next, in step (b), the eleventh step of energization is carried out in accordance with the energization command from the timer contactor 8 at the same time as pressurization. The current at this time is adjusted so that the plated steel plate 5 is heated to a temperature above about 906°C at which the galvanized coating 5a formed on both sides of the plated steel plate 5 vaporizes, and below 1,200°C at which no nuggets are formed. do. Next, in step (c) after energizing for a certain period of time, the current is turned off and at the same time the pressurization is released to release the vaporized gas from the plated metal in the facing area to the outside. As a result, as shown in FIG. 1(b), the plating film 5c of the current-carrying portion of the plated steel plate 5 is removed, and the surface of the steel plate 5b, such as SHP or SCP, is exposed. Next, in step (d), the same part of the two overlapping plated steel plates 5 as the first pressurizing point is again pressurized by a pressurizing command from the timer contactor 8, and in step (e), electricity is applied. The current at this time may be a normal current for spot welding ordinary steel sheets that are not coated with plating. and the first
A nugget 11 is formed as shown in Figure (c), and welding is completed in step (v).

According to this embodiment, the plating film 5c of the electrode contact portion and the face-to-face portion of the plated steel plate 5 is removed by the first pressurization of the two-step pressurization, and by releasing the pressure, the plating film 5c is removed. The vaporized gas in the coating 5c can be released to the outside. Next, when applying pressure for the second time using the same electrode 4b to the part 5C where the plating film 5a has been removed for the 11th time, since the surface of the ordinary steel plate 5b is exposed, the nugget 11 is welded under normal spot welding conditions. can be formed.

In the above-described embodiment, a case has been described in which two galvanized steel plates 5 are overlapped and spot welded, but the number of plated steel plates is not limited to two, and may be three or more. The heating temperature in the first step is
Needless to say, it varies depending on the material of the plating film that covers the steel plate 5.

〔Effect of the invention〕

According to the present invention, when plated steel plates are overlapped and spot welded, the plating film at the spot welding point is removed by applying pressure and electricity, and the vaporized gas is released to the outside, and then this removal is further performed. Since the nugget is formed by pressurizing and energizing the part again, it is possible to suppress the generation of flying particles, prevent wear of the electrode, and also prevent the occurrence of explosions.

Furthermore, nuggets can be easily formed and the joint strength of spot welding can be improved.

Furthermore, since the pressurizing force can be reduced, there is no need to use a high pressurizing gun, and interference between the workpiece and the gun arm can be prevented.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing an embodiment of the method for spot welding plated steel sheets according to the present invention, Figure 2 is a flowchart showing the steps of this embodiment, and Figure 3 is a diagram showing the apparatus used in this embodiment. FIG. 4...Subbot 1-gun, 4b...Spot gun electrode, 5...Plated steel plate, 5a, 5c...Plated film, 5b...Steel plate,
7... Pressure cylinder, 8... Timer contactor, 1.0... Transformer, 11... Nugget.

Claims (2)

[Claims] (1) In a spot welding method for plated steel plates, in which a plurality of steel plates with plated coatings formed on their overlapping surfaces are overlapped and spot welded, the plurality of plated steel plates are held between a pair of electrodes and energized under pressure. A first step is to remove the plating film at the spot dot portion, and a second step is to apply pressure and current to the removed portion of the plating film using the same pair of electrodes to form a nugget on the steel plate and weld it. A method for spot welding plated steel sheets, characterized by the following steps: (2) The method for spot welding plated steel sheets according to claim 1, wherein the applied current in the first step is adjusted so as to vaporize the plating film and not to form nuggets on the steel sheet. .