JPH0890249A - Resistance spot welding method of aluminum - Google Patents

Abstract

PURPOSE: To improve the service life of a DC type electrode as long as that of an AC type electrode by employing a positive electrode made of copper of the prescribed purity which is connected to the positive electrode of a welding transformer to suppress the eccentric wear of the electrode attributable to the Peltier effect. CONSTITUTION: The phenomenon that a nugget is deviated in the direction of a positive electrode is observed when a chromium-copper electrode is used in the resistance spot welding of the DC inverter type. This is the phenomenon caused by the small cooling capacity of the positive electrode due to the Peltier effect, and is the main cause for the wear of the electrode due to the softening and alloying of the electrode tip to cause the eccentric wear of the positive electrode. Thus, the positive electrode is made of copper whose purity is >=99% which is excellent in the electric conductivity and the thermal conductivity and difficult to generate heat. As a result, the cooling capacity of the positive electrode is improved to suppress the heat generation of the positive electrode. The uneven wear of the positive electrode is prevented thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance spot welding method for spot welding by applying an electric current instantaneously while applying a pressure to an object to be welded through an electrode, and particularly a direct current resistance spot welding machine is used. The present invention relates to a resistance spot welding method for joining aluminum materials or aluminum alloy materials (hereinafter collectively referred to as aluminum materials).

[0002]

2. Description of the Related Art In recent years, in the body parts of automobiles, the use of aluminum materials tends to increase year by year for the purpose of improving fuel efficiency by reducing the weight and improving the efficiency of material recycling.
Generally, automobile bodies are assembled by spot welding, but in the welding of aluminum materials, there is a problem that the life of the electrode tip used for welding is significantly shorter than that of welding of steel plates. Replacement or maintenance (eg, dressing: polishing and shaping of electrode tip) takes a lot of time, which causes a significant decrease in productivity.

Further, in order to reduce power consumption and improve equipment efficiency in a production line, a DC resistance spot welder with less efficiency loss is often used in place of the AC resistance spot welder which has been widely used in the past. Has become. In particular, the inverter type DC spot welder is effective for mounting on a robot because the welding transformer can be made smaller and lighter, and is expected to be used as a welder for aluminum materials that requires a large capacity. .

However, in the DC resistance spot welding machine, there is a phenomenon in which the heat generated in the weld is biased toward the anode side due to the Peltier effect. When the materials are welded, the alloying of the electrodes is large, causing uneven wear, and the life of the electrodes is further shortened.

Therefore, as a measure for the electrode life as described above, the deviation of the electrode deterioration is averaged by switching the polarity (JP-A-1-118376) and the shape of the electrode tip (JP-A-4-46684). A technique for improving the electrode life has been proposed.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The above-mentioned techniques for suppressing uneven wear of the anode electrode are proposed in both publications.
Each of them has its own points of view, but these require problems such as requiring a device for switching the polarity and processing the electrodes into a special shape, which increases costs.

The present invention has been made to solve the above problems, and when copper is used for the electrodes when welding an aluminum material with a DC resistance spot welder, the electrodes due to the Peltier effect are formed. An object of the present invention is to provide a resistance spot welding method for an aluminum material that suppresses uneven wear.

[0008]

[Means for Solving the Problems] The gist of the invention is that when aluminum or an aluminum alloy material is welded using a DC resistance spot welder, at least the anode electrode connected to the anode of the welding transformer has a purity of 99% or more. This is a resistance spot welding method for aluminum materials using copper.

[0009]

Function: Chromium copper is generally used as the electrode material. Since chromium copper has high strength in addition to conductivity,
It can be used without buckling deformation even when welding steel materials. In welding aluminum materials, there is a document recommending cadmium copper, which has higher conductivity than chromium copper (Aluminum Association of America: T10 guideline), but it is considered that it is difficult to generalize due to the toxicity problem of cadmium.
Up to now, with respect to copper having a purity of 99% or more, it has not been used because it has a high electrical conductivity but a low strength, so it may not be able to withstand the pressure at the time of welding and may be buckled, but the present invention is to be welded. The effect is achieved by limiting the material to an aluminum material having a purity of 99% or more and a hardness lower than that of copper.

In the DC inverter type resistance spot welding, when a chromium copper electrode is used, a phenomenon in which the nugget is biased toward the anode side electrode is seen as shown in FIG. This is due to the heat generation of the anode side electrode due to the Peltier effect, which is a phenomenon that the cooling capacity of the anode side electrode is smaller than that of the cathode side electrode, indicating that the heat generation of the anode side electrode is remarkable.
This is a main cause of increasing the electrode wear due to the softening deformation and alloying of the electrode tip, and causes the uneven wear of the anode electrode.

Therefore, for the anode electrode, copper having a purity of 99% or more, which has high electrical conductivity and thermal conductivity and is hard to generate heat, is used. When copper having a purity of 99% or more is used for the anode electrode, the nugget is not biased toward the anode electrode as shown in FIG.
This is because by using copper having a purity of 99% or more for the anode electrode, the cooling capacity of the anode electrode is increased and the heat generation of the anode electrode can be suppressed. Therefore, uneven wear of the anode electrode is prevented. This effect does not change even when copper having a purity of 99% or more is used for both the anode electrode and the cathode electrode.

The reason why copper having a purity of 99% or more is used for the electrode is as follows. As shown in Table 1, it is considered that this effect is brought about by pure copper having 20% better thermal conductivity and conductivity than chromium copper. When searching for other materials applicable in that respect, there is pure silver, but since the hardness is lower than that of the material to be welded (aluminum material), buckling occurs during welding. Therefore, the material having high conductivity and harder than the aluminum material is limited to pure copper.

[0013]

[Table 1]

[0014]

EXAMPLES Examples of the present invention will be described below.
The aluminum material to be welded is A5182, a surface pickling material with a plate thickness of 1.0 mm. The welding conditions are as follows. The electrode shapes are the dome type electrode (DR40) and the R type electrode (R80) shown in FIG.
There are two types. The amount of cooling water circulating inside the electrode is 5 l / min. The pressurizing and energizing conditions are such that the initial pressurizing time is 20Hz, the pressurizing and holding time is 25Hz, the applied pressure is 2.9kN, and the welding current is 5mm. Table 2 shows the welding machine, electrode material, electrode shape and the number of continuous dots.

[0015]

[Table 2]

The number of continuous welding points indicates the electrode life in spot welding, and means the number of welding points that can be continuously welded while maintaining the initial welding quality obtained under the above welding conditions without exchanging the electrodes. In addition, here, the welding quality in the initial stage of the hitting point was set to the tensile shear strength JIS A class minimum value or more.

As is apparent from Table 2, in the case of the DC inverter type resistance spot welding machine, the method Nos. 7 and 8 of the present invention in which copper having a purity of 100% was used for the electrodes showed a continuous welding number of 5000 points or more. ing. On the other hand, in Comparative Examples Nos. 5 and 6, the electrode material is chrome copper, so the cooling capacity is small, the heat generation of the anode electrode cannot be suppressed, and the uneven wear of the electrode is severe.
The number of continuous runs for No. 5 is 2000, and the number of continuous runs for No. 6 is 1000.
It is a point.

On the other hand, in the case of the single-phase AC resistance spot welding machine, the Peltier effect is canceled because the direction of the current changes every half cycle, so that 5,000 or more points can be obtained regardless of the electrode material. The number of continuous hits is shown.

[0019]

As is apparent from the above description,
The resistance spot welding method of the aluminum material of the present invention is superior to the AC type in terms of workability and economical efficiency, and even if a DC resistance spot welding machine is used, the anode side electrode does not wear evenly Since it can be made as long as the formula, it is useful for various applications such as automobiles, vehicles, and aircraft.

[Brief description of drawings]

FIG. 1 is a diagram showing a nugget position in the case of welding with a DC resistance spot welding machine using chromium copper as an electrode.

FIG. 2 is a view showing a nugget position in the case where copper having a purity of 99% or more is welded by a DC resistance spot welding machine using an anode side electrode.

FIG. 3 is a diagram showing an electrode shape used in Examples.

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Claims (1)

[Claims] 1. When welding aluminum or aluminum alloy material using a DC resistance spot welder,
A resistance spot welding method for an aluminum material, characterized in that copper having a purity of 99% or more is used for at least an anode electrode connected to the anode of a welding transformer.