JPH071151A - Dc butt welding method for aluminum alloy sheets - Google Patents

Abstract

PURPOSE:To provide proper welding conditions by a two-stage pressurizing system in DC butt welding of aluminum alloy wheel rims. CONSTITUTION:In DC butt welding by the two-stage pressurizing system consisting of initial pressurization and second-stage pressurization, current density, initial pressurizing force (P1) and second-stage pressurizing force (P2) are made to 50-200A/mm<2>, 0.5-7kg/mm<2> and 3 X initial pressurizing force (P1)-50kg/ mm<2>, respectively and changeover from initial pressurizing force (P1) to second- stage pressurizing force (P2) is carried out in the range where the electrode moving quantity (L) is 0.1-2.0 times larger than thickness of the aluminum alloy sheets to be welded. Consequently, a weld zone excellent in workability which has not been attained in DC butt welding can be obtained and the aluminum alloy wheel rims can b eproduced in large quantities at the low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC butt welding method for rims used in automobile wheels, particularly aluminum alloy wheels.

[0002]

2. Description of the Related Art In recent years, the use of aluminum alloy wheels has been expanding as part of efforts to reduce the weight of automobile bodies.

Aluminum alloy wheels are manufactured by various methods. Among them, the two-piece wheel method, which is a method in which a rim and a disk are separately manufactured and then integrated by joining, is excellent in mass productivity. It is widely used in the manufacture of automobile wheels.

FIG. 4 is a diagram showing a rim manufacturing process in the two-piece wheel method. In this method, a rolled material is uncoiled and cut to form a cylindrical coil, and then both ends are abutted to each other to form a flash butt. Join by welding,
A processing method of trimming and then rim-forming by ring roll processing or spinning processing has been adopted.

However, in flash butt welding, there is a problem that the working environment is poor due to arc generation and the efficiency is low due to repeated heating by the arc. Therefore, recently, a DC butt welding method, which is more excellent in terms of efficiency and workability than flash butt welding, has been adopted for manufacturing rims.

Here, the DC butt welding is a method of welding and welding while applying a DC voltage to the welding surface of the materials to be welded while applying a DC voltage, and applying an AC current to generate a flash and pressurizing and welding. In principle, it is different from flash butt welding. For this reason, DC butt welding is a welding method which is advantageous in terms of workability and efficiency, since flashing and the like are less likely to occur and the welding time is short.

However, when DC butt welding is applied to an aluminum alloy plate, defects in welded joints are more likely to occur than when it is applied to steel plates. This is because the heat transfer coefficient of aluminum is about 3 times that of iron and the resistivity is about 2/7 times that of iron. This is because it has the characteristic. Therefore, when the DC butt welding is applied to the aluminum alloy plate, there are the following problems.

Since it is difficult to uniformly generate heat from an aluminum alloy plate, especially a large cross-section object such as an automobile wheel, it is difficult to obtain a uniform and sound joint in the production of a rim, and cracks occur in the welded portion. It easily occurs and causes processing defects.

In order to obtain a homogeneous and sound joint,
The range of appropriate current density becomes narrower under welding conditions. For example, when the current density is lower than the proper current density, a welding defect called so-called cold welding due to insufficient heat input to the bonding interface occurs in the bending test. On the other hand, if the current density exceeds the appropriate current density, cracks due to excessive heat input will occur in the bending test.

In addition, the range of the appropriate pressing force becomes narrower under the welding conditions. If the applied pressure does not reach the appropriate range, hammering noise will occur during welding and fusion defects will easily occur.If the applied pressure exceeds the appropriate range, the aluminum alloy plate will tend to soften especially at high temperatures. Buckling deformation will occur.

In order to solve the above problems, as a welding condition for DC butt welding on an aluminum alloy plate of an automobile wheel, a two-stage pressurizing type welding method is proposed in which squeeze pressure is applied and then upset pressure is applied. (See Japanese Patent Laid-Open No. 4-365831). However, welding conditions proposed therein, after which the pressure was early Sukuizu pressurized, it is desirable upset pressure of the second stage further adds 3~8kg / mm ² to Sukuizu pressure, up to even 15 kg / mm ² Upset pressure is to be applied. That is, it only suggests the range of the pressurization force of the two-stage pressurization, and does not disclose any timing for applying the upset pressurization force. In DC butt welding of aluminum alloy plates, the timing of switching from squeeze pressure, which is the initial pressure, to upset pressure, which is the second stage pressure, is an important factor that can control the heat input to the bonding interface, Since this timing is not set quantitatively, it is hard to say that the welding conditions are optimized.

[0012]

As described above, in the aluminum alloy plate, in particular, in order to uniformly heat a member having a large cross section such as an automobile wheel to obtain a uniform and sound joint, proper welding conditions are required. Is desired to be established.
In view of such a situation, an object of the present invention is to provide a method of DC flash butt welding an aluminum alloy plate for a wheel rim under appropriate conditions.

[0013]

The present invention is based on the following welding method as shown in FIG.

In the DC butt welding by the two-stage pressurization system consisting of the initial pressurization and the second pressurization, the current density is 50 to 20.
0A / mm ² , initial pressure (P ₁ ) is 0.5 to 7 kg / mm ² , second stage pressure (P ₂ ) is 3 x initial pressure (P ₁ ) to
And 50 kg / mm ^2, at an initial pressure ranging from 0.1 to 2.0 times switching the electrode moving amount (L) of the thickness of the aluminum alloy plate to be welded from (P ₁₎ to the second stage pressure (P ₂₎ And a method for welding an aluminum alloy plate for a rim of an automobile wheel.

[0015]

The aluminum alloy plate which is the subject of the method of the present invention is a non-heat treatment type 5000 series and a heat treatment type 6000 series (both JIS standards) which have been conventionally used as rim materials for automobile wheels.

The reason for setting the welding conditions in the method of the present invention will be described below.

First, as a method of welding an aluminum alloy plate, DC butt welding using a two-stage pressure system is adopted.
When DC butt welding is applied to a large cross-section that is difficult to heat uniformly with a constant pressure, the melted portion at the weld interface cannot be completely extruded, and trapped defects remain or lamellar defects in the base metal. Is sometimes left. If the initial pressure is increased, it is possible to extrude the melted part completely with one step of pressure, but in order to obtain a stable welded part under each condition, after welding with the initial pressure, the second step It is desirable to weld by pressure.

FIG. 1 is an explanatory view of the welding conditions of the present invention. The welding secondary current and welding pressure (P _{1 and} P
₂ ) and the amount of electrode movement (L). Simultaneously with the start of welding, P ₁ is added to the joint as initial pressure,
Further, a secondary welding current is passed to melt the joint. When the electrode movement reaches a predetermined amount, the applied pressure is switched, and P ₂ is added as the second stage pressurization, whereby a sound joint can be obtained. Hereinafter, each welding condition will be described.

The current density is represented by a value obtained by dividing the welding secondary current by the joining area (sheet thickness of the joint part × sheet width), and the appropriate range is determined by the correlation with the value of P ₁ . As will be described later, when P ₁ is set in the range of 0.5 to 7 kg / mm ² , the proper range of current density is 50 to 200 A / mm ² . For example, if the current density is less than 50 A / mm ² , heat input to the joint interface is insufficient, so-called cold welding occurs, or buckling deformation occurs and a sound weld cannot be obtained. On the other hand, in the range exceeding 200 A / mm ² , the amount of heat input to the joint interface increases too much, and a phenomenon called blasting occurs in which the interface melts and scatters. In addition, the current waveform during energization can basically be welded with a constant current as shown in Fig. 1, but up-slope energization and down-slope energization that are commonly used for current control can be used independently or in combination. Even if it is adopted, the effect of the present invention does not differ.

P _{1, that} is, the initial pressure is 0.5 to 7 kg / mm ² . If the range of P ₁ is smaller than 0.5 kg / mm ^2, the contact between the joint end faces at the weld interface becomes non-uniform, and the joint cannot generate heat uniformly. Further, when the range of P ₁ exceeds 7 kg / mm ² , the aluminum alloy is soft, so that after the start of welding, buckling deformation occurs and the welding itself cannot be performed.

P _{2, that} is, the second stage pressure is 3 × P _{1 to} 50 kg
/ mm ² If P ₂ is smaller than 3 × P ₁ , the effect of upset is hardly observed, the melted part cannot be completely extruded by the second stage pressurization, and entrained defects remain, or the base material is lamellar. Therefore, the sound joint cannot be obtained. On the other hand, when P ₂ is larger than 50 kg / mm ² , it is sufficient to discharge the molten metal at the joint interface, but the pressing force becomes too high, and the material buckles and the upset cost increases, which is not practical. . At the current practical level, the welding pressurizer is about 50 kg / mm ² (about 1 in absolute value).
00 tons) is the limit.

Next, the switching from the initial pressurization to the second-stage pressurization is decided by the electrode movement amount, and the switching timing is 0.1 to 2.0 times the plate thickness of the aluminum alloy plate to be welded. It's when.

FIG. 2 is a diagram schematically illustrating the electrode movement amount (L). There are two types of electrodes 1, a fixed type 1a and a movable type 1b, which hold both ends of a joint 2 of an aluminum alloy plate 3. FIG. 2 (a) shows a state of holding the aluminum alloy plate 3 by the electrode 1 before welding. The electrode 1 pressurizes the joint portion 2 at the same time when welding is started, and the amount of heat input increases and the welding shown in FIG. The movable electrode 1b moves inside. Here, the electrode movement amount (L) is expressed as the movement amount of the electrode in the pressing direction with the position of the movable electrode 1b before welding as the origin, as shown in FIG.

This electrode movement amount (L) has a strong correlation with the heat input amount to the joint interface, and is continuously measured during welding. Therefore, the switching timing is determined by the moving amount of the electrode because this moving amount (L) is an important parameter for controlling the heat input to the bonding interface.

Next, the reason why the switching timing from the initial pressurization to the second stage pressurization is performed when the electrode movement amount becomes 0.1 to 2 times the plate thickness will be described. Electrode movement is 0.1 of plate thickness
In the range smaller than twice, the heat input to the bonding interface is too small, so upsetting will be performed in the state where a uniform temperature distribution has not yet been obtained in the plate width direction.
Weld defects called cold welding occur. Also, if the second-stage pressure is applied in a range greater than twice the plate thickness, the amount of heat input to the vicinity of the weld increases, causing cracking due to excessive heat input, or causing buckling deformation. Will occur.

By adopting the welding conditions of the above two-stage pressurization method, it is possible to obtain a sound joint having an upset margin of about 4 to 5 times the plate thickness.

[0027]

EXAMPLES Examples of the present invention will be described by comparing Examples 1 to 10 of the present invention and Comparative Examples 11 to 18 under the welding conditions shown in Table 1.

The test material is the AA5454 alloy (JIS standard: Al-Mg 5000 series, 2.8
% Mg, 0.81% Mn, 0.16% Cr, 0.2% Si, 0.35% Fe, balance
Aluminum alloy) plate is used and its thickness is 5mm
And

FIG. 3 is a diagram showing an outline of a crack occurrence rate evaluation method in a bending test of a welded portion.

The crack generation rate evaluation method shown in the figure is the most severe evaluation method in consideration of the wheel processing method after rim welding.
No cracks occurred during the molding of the wheel.

A specific evaluation method is as follows: A plate-shaped test piece having a width of 160 mm and a length of 585 mm is sampled from the test material, bent into a cylindrical shape, and subjected to direct current butt welding. Cut into a width of 160 mm, a length of 200 mm and a thickness of 5 mm (a welding portion exists in the width direction), and collect a bending test piece 4. Then, in a bending test, 180 ° with a bending radius of 5 mm
After bending, the bending test piece 4 was visually cracked (I ₁ in the figure,
Check for I _2, I ₃ and I _4), measuring the total length of cracks. After that, the crack occurrence rate (D) is calculated by the following equation.

D = (ΣI _n / W) × 100 (%) where ΣI _{n is the} total length of cracks, W is the width of the bending test piece, and the cracking rate evaluation results in the bending tests of the present invention example and the comparative example are shown in Table 1. Put together.

[0033]

[Table 1]

As shown in Table 1, in each of the comparative examples, cracks were generated, and in particular, in Comparative Example 15, the heat input amount was excessive, so that the interface was melted and scattered to cause explosion. Buckling occurred in Comparative Example 16.

However, in the example of the present invention, no defect was generated by the bending test, and it is understood that a welded portion excellent in workability can be obtained under the welding conditions of the present invention.

[0036]

According to the present invention, it is possible to obtain a weld having excellent workability which cannot be achieved by the conventional DC butt welding. As a result, the aluminum alloy wheel rim can be mass-produced at low cost, which can greatly contribute to the weight reduction of the automobile.

[Brief description of drawings]

FIG. 1 is a diagram illustrating welding conditions of the present invention.

FIG. 2 is a diagram illustrating an electrode movement amount under welding conditions,
(A) is a figure before welding and (b) is a figure showing the situation during welding.

FIG. 3 is a diagram showing an outline of a crack generation rate evaluation method in a bending test of a welded portion.

FIG. 4 is a diagram showing a manufacturing process of a rim.

Front page continuation (72) Inventor Keizo Namba 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd.

Claims (1)

[Claims] 1. In DC butt welding by a two-stage pressurization system comprising an initial pressurization and a second stage pressurization, the current density is 50 to 20.
And 0A / mm ^2, the initial applied pressure and 0.5~7kg / mm ^2, the second-stage pressure as a 3 × initial pressure to 50 kg / mm ^2, the electrode switching from the initial pressure to the second stage pressure A method for welding an aluminum alloy plate for a rim of an automobile wheel, characterized in that the amount of movement is 0.1 to 2.0 times the plate thickness of the aluminum alloy plate to be welded.