JPH0825060A - Welding method for aluminum sheet metal and aluminum alloy sheet metal covered by organic matter - Google Patents

Abstract

PURPOSE:To improve the resistance spot weldability of aluminum sheet metal and aluminum alloy sheet metal covered by an organic matter. CONSTITUTION:Before applying a welding current, pre-energizing whose current value is within the range from 5 to 60% of the welding current, is performed. The energizing time of the pre-energizing must be within the range from 1 to 4 cycles. A time required from the completion of the pre-energizing to the energizing start of the welding current must be 100 cycles or below. Consequently, making a nugget warp and the generation of a blowhole are eliminated, the damage of an electrode is prevented, and an excellent welding zone and a sufficient electrode life are simultaneously attained.

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 technique in which welding is performed by instantaneously energizing a workpiece to be welded by electrodes, and particularly aluminum thin plates and aluminum alloy thin plates (hereinafter collectively referred to as "aluminum alloy"). Thin plate "
), A resistance spot welding method for satisfactorily welding an organic coated aluminum thin plate and an aluminum alloy thin plate (hereinafter collectively referred to as “organic coated aluminum alloy thin plate”).

[0002]

2. Description of the Related Art In resistance spot welding, generally,
As shown in FIG. 1, plates 1 and 2 to be welded are overlapped, and one point of the overlapped region is pressed by a pair of upper and lower electrodes 3 and 4 to be energized while being pressurized (5 to 10 cycles, 20 to 40 k).
By passing the current of A), a molten and solidified portion called a nugget 5 is formed in the portion sandwiched by the electrodes. The nugget 5 acts as a spot-shaped welded joint, and welding of the plates is achieved.

In resistance welding such as spot welding, the thermal conductivity and electrical conductivity greatly affect the welding conditions.
In the case of aluminum alloy, it is considered that large current and short time welding are necessary, and the recommended conditions of WES are also in line with this idea. However, since WES was created, many new alloys and new materials have been proposed, and accordingly various welding conditions different from the welding conditions of WES have been proposed. The welding method of the organic coating aluminum alloy thin plate which is the object of the present invention is also one of such techniques.

[0004]

The constitution of the organic coating referred to in the present invention is such that the surface of the aluminum alloy thin plate is chromate as the first layer and the organic resin coating containing the lubricant is provided as the second layer on top of it. For example, refer to JP-A-4-268038), or a general organic coating for automobiles, such as a resin of the second layer to which a conductive agent is added for the purpose of conducting electricity. The coating layer may be a single layer or multiple layers, and includes the case where the entire coating layer is made of an organic material. When welding such an organic-coated aluminum alloy thin plate, under the same welding conditions as those for welding an uncoated aluminum alloy thin plate, the weldability remarkably deteriorates due to the following two causes.

First of all, the organic coating layer between the plates makes the current path unstable, and the nugget can be located outside the position just below the electrodes. As a result, the shape of the nugget obtained becomes distorted and sufficient joint strength cannot be obtained. Moreover, since the molten liquid cannot be pressed by the pressure of the electrode, dust is generated during welding, and further, defects due to the organic resin remaining inside the nugget cannot be avoided.

Secondly, due to the presence of the organic coating layer, the resistance between the plate and the electrode is higher than that of the uncoated material, and during welding, the material is deformed due to the heat generated between the electrode and the plate due to this resistance, or directly under the electrode. The molten aluminum alloy and the copper electrode react with each other, causing severe electrode damage as compared with the uncoated material.

In order to obtain the joint strength of the organic coated aluminum alloy, the pressure of the electrode is increased to eliminate the resin,
A good weld can be obtained, but in that case the life of the electrode is significantly shortened.

Therefore, an object of the present invention is to prevent the nugget from becoming distorted and the formation of blowholes, to prevent the electrode from being damaged, and to provide a good welded portion and a sufficient electrode life at the same time. Another object of the present invention is to provide a welding method for aluminum alloy thin plates.

[0009]

According to a first aspect of the present invention, there is provided a resistance spot welding method for an aluminum thin plate or an aluminum alloy thin plate having a coating layer containing an organic substance, wherein the current value is prior to the application of welding current. It is characterized by pre-energizing within the range of 5 to 60% of the welding current.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the energization time for pre-energization is within a range of 1 to 4 cycles.

The invention according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the time from the completion of pre-energization to the start of welding current application is 100 cycles or less.

[0012]

From the above points, the inventors of the present invention have made intensive studies focusing on resin elimination, and as a result, as shown in claim 1, the current value is 5% or more of the welding current prior to the welding current being applied. It was found that by pre-energizing within the range of 60% or less, two problems of securing joint strength and securing electrode life can be solved at the same time. The welding current value here is WE
The conditions defined by S or other conditions may be used, and the type of welding machine is arbitrary.

The first energization, that is, the pre-energization in the present invention is to eliminate the resin existing between the plates to ensure stable energization. As a result, a nugget having a stable shape is obtained, and as a result, joint strength equivalent to that in the case where there is no organic coating can be obtained. Further, by completely removing the resin from the welded portion, it is possible to eliminate blowholes and cracks which are defects in the nugget due to the residual resin.

On the other hand, also between the electrode and the plate, the resin is removed to secure a stable energization path. Therefore, the resistance between the electrode and the plate is reduced, and excessive electrode damage due to the resin does not occur. As a result, the service life of the electrode is about the same as when there is no organic coating, and the service life of the welding electrode made of an organic coating aluminum alloy is remarkably long.

Here, the current value for pre-energization is set in proportion to the welding current because the energizing diameter to be ensured is small when the welding current is small, while it is large when a large current is passed. This is because a current-carrying diameter is required. Moreover, the reason why the current value for pre-energization is within the range of 5% to 60% of the welding current is that the resin is not sufficiently removed if it is less than 5%, while it does not differ from the welding current if it exceeds 60%. This is because there is no point in dividing the power supply into two.

In the invention as set forth in claim 2, the energization time is set within the range of 1 cycle or more to 4 cycles or less. Exclusion of the resin is not sufficient in less than 1 cycle, and the effect is saturated in more than 4 cycles. Therefore, it is meaningless to energize longer than this.

In the third aspect of the invention, the reason why the time interval is provided from the completion of the pre-energization to the start of the welding current energization is to cool the electrode which is heated by the pre-energization. The purpose is to extend the life of the electrode. However, the reason why the time from the completion of pre-energization to the start of welding current energization is 100 cycles or less is that productivity exceeding the characteristic of spot welding is impaired if it exceeds 100 cycles. Therefore, the upper limit is 100 cycles.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

[Example 1] Aluminum alloy thin plate (sample)
On the surface of, the first layer consisting of a chromate layer having a chromium amount of 10 mg / m ² and a lubricant of 30 wt. %, 1μ
An organic-coated aluminum alloy thin plate having a second layer made of an epoxy resin and having a thickness of m was used as a sample of the organic coating material. Further, for comparison, an aluminum alloy thin plate having an oxide film removed treatment on its surface was used as a specimen of an uncoated material. Then, the specimens of the organic coating material and the uncoated material were pre-energized for the time: t (cycle) and the current value: I (%) shown in Table 1 or were welded without pre-energization. , Joint strength was investigated. In the investigation, the welding current was 25
The joint strength at kA was evaluated by the result of comparison with the test piece of the uncoated material (Comparative Example 1). The evaluation method is based on JIS-Z3136, and the tensile shear strength of the specimen of the uncoated material (aluminum alloy thin plate) shown in Comparative Example 1 was 10
0%, and the strength compared with this is ◯ when 70% or more,
Less than 70% was marked with x.

The specifications are as shown below. Welding machine: Single-phase AC welding machine Electrode: DR type electrode (electrode diameter; 16 mmφ, tip diameter;
6mmφ, tip curvature; 40R, material chrome copper) Energization: 25kA-5 cycles (welding current) Aluminum alloy thin plate (sample): A5182-O material (plate thickness 1mm) specified in JIS Joint evaluation: JIS-Z3136 According to the above, the strength of 70% or more was marked with ◯, and the strength of less than 70% was marked with X.

[0021]

[Table 1]

It can be seen from Table 1 that the joint strength of the organic coating material specimen is increased by pre-energization. In addition, it is possible to perform welding by pre-energization even for the specimens of the uncoated material for comparison, in which case there is no problem. Thus, it is understood that the organic coating material can obtain the same strength as the uncoated material by pre-energizing the aluminum alloy thin plate.

Example 2 Using the same specimen and welding machine as in Example 1, the pre-current was changed and the joint strength at a welding current of 25 kA was evaluated by the same evaluation method as in Example 1.

The specifications are as shown below. Welding machine: Single-phase AC welding machine Electrode: DR type electrode (electrode diameter; 16 mmφ, tip diameter;
6mmφ, tip curvature; 40R, material chrome copper) Pressurizing force: 300kg Welding current: 25kA-5 cycles Post-heat current: 14kA-4 cycles Aluminum alloy thin plate (sample): JIS A5182-O material (plate thickness) 1 mm) Joint evaluation: According to JIS-Z3136, strength of 70% or more was marked with ◯, and strength of less than 70% was marked with x.

[0025]

[Table 2]

From Table 2, the pre-energization current value is 5 of the welding current.
It can be seen that if it is less than%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 60%, the difference from the welding current disappears and the effect cannot be obtained. Therefore, it is understood that the current value for pre-energization should be 5 to 60% of the welding current. Thus, it can be seen that the strength of the organic coating material is the same as that of the uncoated material by pre-energizing the aluminum alloy thin plate at 5 to 60% of the welding current.

FIG. 2 shows the relationship between the pre-energization current value (%) and the proper current range in this embodiment. Tensile shear strength is from current 7 to obtain JIS-B class minimum value to welding current 8
Was set to an appropriate current range 6. If the current value for pre-energization is less than 5%, no effect is observed, but if it is 5% or more, the appropriate current range is widened. Also, the optimum current range is 50%,
It can be seen that when it exceeds 60%, it sharply decreases.

[Example 3] Using the same specimen and welding machine as in Example 1, the energization time of pre-energization was changed and the joint strength of 25 kA was evaluated by the same evaluation method as in Example 1.

The specifications are as shown below. Welding machine: Single-phase AC welding machine Electrode: DR type electrode (electrode diameter; 16 mmφ, tip diameter;
6mmφ, tip curvature; 40R, material chrome copper) Pressurizing force: 300kg Welding current: 25kA-5 cycles Post-heat current: 14kA-4 cycles Aluminum alloy thin plate (sample): JIS A5182-O material (plate thickness) 1 mm) Joint evaluation: According to JIS-Z3136, strength of 70% or more was marked with ◯, and strength of less than 70% was marked with x.

[0030]

[Table 3]

From Table 3, it can be seen that a great effect can be obtained by precharging for one cycle or more. Further, FIG. 3 illustrates the relationship between the number of cycles of pre-energization (cycles / 50 Hz) and the proper current range in this embodiment. FIG.
In, the appropriate current range 6 is from the current 7 at which the tensile shear strength obtains the JIS-B class minimum value to the welding current 8. It can be seen from Table 3 and FIG. 3 that the proper current range is widened up to 4 cycles, but the effect is saturated even if it exceeds the range. Therefore, it can be seen that up to 4 cycles are more preferable.

Example 4 Using the same test piece and welding machine as in Example 1, the energization time (Table 4) or current (Table 5) for pre-energization was changed to evaluate the electrode life. The evaluation of the electrode life is 20 according to JIS-Z3136 (minimum value of class B).
Sampling was performed at every point. When the life was 1000 points or more, it was marked with O, and when it was less than 1000, it was marked with X.

The specifications are as shown below. Welding machine: Single-phase AC welding machine Electrode: DR type electrode (electrode diameter; 16 mmφ, tip diameter;
6mmφ, tip curvature; 40R, material chrome copper) Pressurizing force: 300kg Welding current: 25kA-5 cycles Post-heat current: 14kA-4 cycles Aluminum alloy thin plate (sample): JIS A5182-O material (plate thickness) 1 mm) Life evaluation: JIS-Z3136 (class B minimum value) was sampled every 20 points. With a life of 1000 points or more
The mark was marked with x when less than 1000 points.

[0034]

[Table 4]

From Table 4, the energization times 1 to 4 within the scope of the present invention.
It can be seen that continuous dot performance is also improved within the range of the cycle. Since the effect is saturated for 4 cycles or more, there is no meaning for long energization exceeding 5 cycles.

[0036]

[Table 5]

From Table 5, regarding the pre-energization current, as shown in Comparative Example 4 (welding current I: 1%), the welding current was 5
If less than%, no improvement can be obtained, but it can be seen that the effect can be seen within the range of 5% or more and 60% or less. However,
As shown in Comparative Example 3 (welding current I: 70%), 60%
If it exceeds, the effect will be saturated and conversely the life of the electrode will start to decrease.

[Embodiment 5] Using the same specimen and welding machine as in Embodiment 1, the influence of the time {time interval (cycle)} from the completion of pre-energization to the start of welding current energization on the electrode life was examined. investigated.

The specifications are as shown below. Welding machine: Single-phase AC welding machine Electrode: DR type electrode (electrode diameter; 16 mmφ, tip diameter;
6mmφ, tip curvature; 40R, material chrome copper) Pressure: 300kg Welding current: 25kA-5 cycles Post-heat current: 14kA-4 cycles Pre-energization: 2 cycles, 40% Aluminum alloy thin plate (sample): Specified in JIS A5182-O material (plate thickness: 1 mm) Life evaluation: JIS-Z3136 (Class B minimum value) Sampling was performed every 20 points. With a life of 1000 points or more
The mark was marked with x when less than 1000 points.

[0040]

[Table 6]

It can be seen from Table 6 that the number of hit points increases as the time interval becomes wider. However, it is meaningless to take 100 cycles or more for work efficiency.

[Example 6] Using the same welding machine as in Example 1, various aluminum alloy thin plates (samples) were subjected to the same organic coating as in Example 1 using organic coating material specimens, and joints The strength and electrode life were investigated. The joint strength was evaluated by the same evaluation method as in Example 1, and the electrode life was evaluated by the same evaluation method as in Example 4.

The specifications are as shown below. Welding machine: Single-phase AC welding machine Electrode: DR type electrode (electrode diameter; 16 mmφ, tip diameter;
6mmφ, tip curvature; 40R, material chrome copper) Pressing force: 300kg Welding current: 25kA-5 cycles Post-heating current: 14kA-4 cycles Pre-energization: 2 cycles, 40% Aluminum alloy thin plate (sample): Specified in JIS O material (A-1050, 1100, 5052, 5154,
5182) (Plate thickness 1 mm) Joint evaluation: In accordance with JIS-Z3136, strengths of 70% or more were marked with a circle, and less than 70% were marked with a cross. Life evaluation: Sampling was performed every 20 points according to JIS-Z3136 (class B minimum value). With a life of 1000 points or more
The mark was marked with x when less than 1000 points.

[0044]

[Table 7]

As can be seen from Table 7, regardless of the type of aluminum alloy thin plate, the welding strength and electrode life of the organic coated aluminum alloy thin plate were good.

[Embodiment 7] Using a specimen of an organic coating material having an organic coating similar to that in Embodiment 1, the welding machine was variously changed and joint strength and electrode life were investigated. The joint strength was evaluated by the same evaluation method as in Example 1, and the electrode life was evaluated by the same evaluation method as in Example 4.

The specifications are as shown below. Welding machine: Welding machine below (single-phase alternating current, single-phase rectification, three-phase rectification, three-phase low frequency, condenser) Electrode: DR type electrode (electrode diameter: 16 mmφ, tip diameter;
6mmφ, tip curvature; 40R, material chrome copper) Pressing force: 300kg Welding current: 25kA-5 cycles Post-heating current: 14kA-4 cycles Pre-energization: 2 cycles, 40% Aluminum alloy thin plate (sample): Specified in JIS A5182-O material (plate thickness: 1 mm) Joint evaluation: According to JIS-Z3136, a strength of 70% or more was marked with a circle, and a strength of less than 70% was marked with a cross. Life evaluation: Sampling was performed every 20 points according to JIS-Z3136 (class B minimum value). With a life of 1000 points or more
The mark was marked with x when less than 1000 points.

[0048]

[Table 8]

From Table 8, it can be seen that there are various types of applicable welding machines including the single-phase AC welding machine.

[0050]

As described above, according to the present invention, in resistance spot welding of organically coated aluminum thin plates and aluminum alloy thin plates, a spot welded joint having sufficient strength can be obtained, and the electrode life can be shortened. It is possible to secure an extremely long life as in the case of the uncoated material, and thus to bring about an industrially useful effect.

[Brief description of drawings]

FIG. 1 is a sectional view showing the principle of general resistance spot welding.

FIG. 2 is a graph showing a relationship between a pre-energization current value (%) and an appropriate current range in the example of the present invention.

FIG. 3 is a graph showing the relationship between the number of cycles of pre-energization and an appropriate current range in the example of the present invention.

[Explanation of symbols]

 1, 2: Plate to be welded 3, 4: Electrode 5: Nugget 6: Proper current range 7: Current at which tensile shear strength reaches JIS-B class minimum value 8: Welding current

Front page continuation (72) Inventor Masazo Asano 2-3-3 Shiba, Minato-ku, Tokyo Mitsubishi Aluminum Co., Ltd. (72) Hisao Tanigawa 2-3-3 Shiba, Minato-ku, Tokyo Mitsubishi Aluminum Within the corporation

Claims (3)

[Claims] 1. A method for resistance spot welding of an aluminum thin plate or an aluminum alloy thin plate having a coating layer containing an organic substance, wherein the current value is pre-energized within a range of 5 to 60% of the welding current prior to energizing the welding current. A method for welding an organically coated aluminum thin plate and an aluminum alloy thin plate, which comprises: 2. The method according to claim 1, wherein the energization time of the pre-energization is within the range of 1 to 4 cycles. 3. The time from the completion of pre-energization to the start of welding current energization is 100 cycles or less.
The described method.