Aluminum resistance welding

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Semi-automatic and automatic welding are the most common techniques for soldering silver metal. There are many subtleties that need to be taken into account when metalworking.

Craftsmen are looking for the best method of joining aluminum and its alloys, because certain properties of the latter complicate the work. Nevertheless, this material has enough advantages: lightness, resistance to loads, good thermal conductivity, and therefore current.

Using autowelding it is possible to create different metal structures. You can also handle electric welding of an aluminum frame (for example, a bicycle frame).

In this article we will describe the intricacies of welding: what you need to know in order to weld winged metal and its alloys efficiently, so that the weld is strong and lasts a long time.

• Welding Characteristics
• Techniques for welding silver metal TIG welding
• MAG/MIG welding
• MMA Welding (arc welding)
• Dry welding

PROPERTIES OF ALUMINUM

The main difficulties when welding aluminum arise due to some of its features. For example, the melting point of metal is only about 650 degrees. It would seem not much, if not for one nuance. An oxide film appears on the surface of products made from this material. The cause of oxide is any contact with oxygen. So, it is quite difficult to melt this film. Its melting point reaches 2000 degrees.

Another nuance associated with the characteristics of aluminum is the absence of color change when heated. It turns out that it is very difficult to visually determine how hot the metal is. The result is burn-throughs, which significantly reduce the quality of welding.

The hygroscopicity of the substance leads to the fact that it quickly absorbs moisture from the air. As soon as heating occurs, it begins to evaporate. This can significantly reduce the quality of the resulting connection.

REMOVAL OF OXIDE FILM FROM ALUMINUM

The oxide film can be very disruptive when tig welding aluminum. Moreover, if it gets into the seam during work, this will affect its strength. Therefore, it is recommended to get rid of such a peculiar coating on the surface. There are two main methods for removing oxide from aluminum:

• Mechanical. This method is good if aluminum welding is carried out frequently and the master needs to connect only a few parts. Otherwise, such processing on an industrial scale will be very labor-intensive. To clean the material, you only need a small wire brush or sandpaper and a file. The latter is used for cleaning the ends. The wire on the brush should be no more than 0.15 mm. Thicker elements can lead to large, easily visible scratches that will significantly damage the surface. It is recommended to move in one direction during processing, otherwise there is a high risk of simply “rubing” the already removed film back into the metal.
• Etching. It is based on the use of various chemical compositions, as well as heating. It is used in industries where aluminum is boiled a lot and often.

If you can properly remove the film from the surface of the parts you are joining, this will significantly increase your chances of success. So don’t be lazy and carry out the recommended work in full.

Aluminum preparation

Raw materials must be prepared in advance, regardless of whether it is home or professional metalworking. Below are all the main steps:

The first step is to clean the surface of the aluminum and filler wire from any kind of contamination. You definitely need to go over them with a cloth, even if the materials seem clean.

The next step is degreasing with any solvent, such as acetone.

Edge cutting is a preliminary procedure, but is performed only when necessary.

For example, in the case of working with parts thicker than 5 mm, and when welding, coated rods are not used; if the metal thickness is more than 20 mm, and rods are used, then you should not bypass this preparation stage.

You need to remember about the oxide film. Some of it can be preliminarily eliminated before welding—partially, of course, but the number of residues will decrease. To do this you will need a file or a steel bristle brush.

After removing the film from the edges, you can begin to work. When welding aluminum at home, many craftsmen use gasoline or soda to remove the film. After processing, it is worth rinsing the edges with water.

At the end, cleanup is performed. To get rid of the remnants of frozen aluminum drops and slag, you need to clean the resulting weld seam with a stiff wire brush.

PREPARING THE WELDING MACHINE FOR WELDING ALUMINUM

In order to comply with all the conditions for welding aluminum, you will have to carry out a number of preparatory work. We already talked about what needs to be done in advance in the previous article. Let us recall only the main points. There are five steps required for successful welding:

1. Choose a large tip. It will help prevent the wire from jamming.
2. Take a guide spiral coated with Teflon. It will be able to ensure trouble-free wire feeding.
3. Use pure high quality argon. Many specialists who do not specialize in working with non-ferrous metals are interested in the question of whether it is possible to weld aluminum semi-automatically in a carbon dioxide environment. This is due to the fact that carbon dioxide is more common, and most welders working with steel have it. But the answer to this question is negative. To work with aluminum, you will have to buy pure argon with a percentage of the main substance of 98–99%.
4. Choose thick wire.
5. Adjust the rollers to make their pressure looser.

These steps alone will help you increase your chances of successful argon welding of aluminum. Almost unnoticed little things often lead to positive results, so don’t neglect anything.

EQUIPMENT FOR GAS WELDING OF ALUMINUM

It is clear that for any welding you will need a welding machine. In the case of processing aluminum parts, it is worth selecting it according to the following criteria:

• Category - TIG. We do not even consider other connection methods other than inverter argon arc.
• Availability of non-contact arc ignition function.
• Ability to adjust the current balance for aluminum welding.
• Setting the time period during which, even after the arc is turned off, argon will be supplied.

But it’s not just the tig machine for aluminum welding that needs to be selected with particular care. It is recommended to take into account the following nuances:

• View of the burner, or rather its collet holder. It would be good if a special mesh was installed on it. When argon passes through its cells, consumption is significantly reduced, but the level of protection is increased.
• Thickness of filler wire. It must exceed the dimensions of the parts being welded.
• The purity of argon and the quality of gearboxes. The more accurate the measuring equipment, the easier it will be to regulate the gas supply to the welding site.

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Is it possible to weld aluminum at home?
Aluminum is a metal whose own melting point is quite low - 657 degrees. At 1800 degrees, pure aluminum boils. But the oxides formed on the surface of aluminum parts are already much more refractory - their melting point is already 2500 degrees. These oxides are the main problem when welding aluminum, because their refractoriness prevents the formation of a weld pool, and the edges of the aluminum part melt before they can be welded. Oxides also have a high absorption capacity, which makes them a source of gases that dissolve in the metal - this partly affects the porosity of the weld.

Unfortunately, the high stability of aluminum oxide makes it impossible to restore the metal in the welding zone. In addition, welding is also complicated by the fact that it is impossible to visually distinguish the moment when the weld is fused due to the same color of the molten and solidifying metal. In addition, aluminum is several times more thermally conductive than steel, and during the welding process this leads to large internal stresses, cracks appear, and parts warp.

The Avaloninvest company (Kiev), having available materials of various profiles, manufactures metal structures for new buildings and reconstructs old ones, carries out the design and installation of metal structures. More details can be found on the website at https://avaloninvest.com.ua/.

It should be borne in mind that not all aluminum alloys are weldable. Those that are prone to the formation of hot cracks during welding disappear immediately. In principle, the weldability of an alloy is specified in its technical characteristics.

However, anything is possible, including welding aluminum at home. To do this, you will need a welding machine for AC argon-arc welding with a tungsten electrode (arc frequency of at least 10,000 Hz), an argon cylinder, aluminum wire that matches the alloy being welded, an oscillator, and a torch.

Welding aluminum at home with direct current of direct polarity is simply impossible, with reverse polarity it is possible, but this will cause severe overheating of the tungsten electrode, and the permissible current will drop to 30 A on an electrode with a diameter of 3 mm, which is enough for welding very thin parts. A current of 180-280 A will be sufficient.

Cleaning parts from oxides during argon-arc welding is not so necessary, because the arc breaks through the oxide film, however, for greater weld strength, it is necessary to preheat the parts with a torch to a temperature of 200-300 degrees. This especially applies to the beginning of the seam.

The aluminum wire used as an additive is soft, so the pressure of the rollers should be loosened as much as possible.

You also cannot do without an oscillator - it is responsible for maintaining the arc. It is clear that welding aluminum at home does not involve purchasing expensive equipment at a time, so you may have to make the oscillator yourself or order it from craftsmen. The only question is that everything ends well, given that we are talking about generating a voltage of several thousand volts.

It is possible that soldering, rather than welding, might be suitable for your specific case.

At home, the aluminum spot welding method , but in this case, a significant difficulty is the high thermal conductivity of aluminum and the rapid melting of the metal during welding. This method requires a relatively high speed when moving the electrode to maintain the same level of pressure and contact with the base metal.

Satisfactory results are obtained when resistance welding of aluminum . Aluminum resistance butt welding is carried out with continuous flashing on electric driven machines; there is also the possibility of aluminum seam welding, but it requires high-power machines with ion interrupters. Using the last two methods of aluminum welding at home will be very difficult for technical reasons. Cold welding of aluminum is completely excluded. Aluminum is superior to all metals used in technology in this regard .

Practical recommendations

Aluminum welding requires knowledge of metal welding techniques and certain dexterity. Welding of this metal occurs subject to certain conditions:

• filler wire and electrode should be positioned at an angle of 90°C
• It is necessary to apply the additive using short reciprocating movements
• it is necessary to avoid transverse vibrations of the tungsten electrode
• arc length must be maintained (1.5 to 2.5 mm)
• the electrode extension should be from 1 to 1.5 mm from the torch tip
• Welding should be done from right to left.

Safety precautions

When welding at home, strict adherence to safety precautions is a necessary condition. The first thing you need to pay attention to is the insulation of all connecting wires. When performing welding work at home, you need to use protective gloves or mittens that will protect you from burns. Rubber boots will protect you from electric shock.

When carrying out welding work, be sure to wear a special mask. Your face will be protected from embers or sparks. In the room where welding work is carried out, flammable and flammable materials must not be stored.

Wooden floors must be covered with sheet metal to protect against fire. Be sure to place a fire extinguisher or at least a bucket of water near the place where you plan to weld. Since the formation of harmful gases or compounds hazardous to health is possible, regular ventilation of the room is necessary.

Source: https://domashnih-usloviyah.ru/svarka-alyuminiya-v-domashnix-usloviyax.html, https://www.helpmaste.ru/artcl-sposobi_svarki_aluminia.html

WELDING METHODS OF ALUMINUM

As mentioned above, it is not worth trying to weld aluminum without argon, especially if you do not have the appropriate skills. But it’s still worth knowing that there are several ways to work with parts made of this non-ferrous metal. So let’s try to figure out which welding for aluminum is better and how, by examining the basic working methods:

• Classic, using a regular gas burner. To do this, you will need special rods and flux for welding aluminum. When heated, the aggressive substance attacks the film, corroding it. This allows access to the metal. After the parts are connected, they must be washed to remove any remaining flux.
• Electric arc. It will require special welding wire or electrodes. They cook with direct current. In such cases, the polarity for semi-automatic welding of aluminum is chosen to be reversed.
• Argon-arc. For it you will have to stock up on argon, tungsten electrodes and pure argon. Although this type of welding may seem the most difficult, it is also the most efficient. Under the influence of very high temperatures, even the most resistant film disintegrates, and thanks to the rapid movement of the electrode, aluminum simply does not have time to leak out of the welding zone.

Techniques for welding silver metal

There are several techniques for electric welding of aluminum, its alloys or stainless steel. Each of them involves the use of auxiliary components, such as gas, special. electrodes or glue.

We will consider the most well-known solutions in both industrial and home welding.

TIG welding

A particularly well-known method is TIG welding of aluminum. Tungsten electrodes are used here, and the process itself takes place under a shielding gas.

This is how gas-electric spot welding and plasma metalworking are carried out.

MAG/MIG welding

During MAG/MIG welding of aluminum, a semi-automatic welding device is used, and the gas is replaced with wire.

As a result, the weld turns out to be of quite high quality, because the filler metal is supplied automatically.

MMA Welding (arc welding)

Aluminum arc welding is the most common method of electric welding of aluminum at home.

This method is mainly used for minor repairs, since the quality of the seam is clearly lower than with TIG/MAG welding. But when working, you will only need electrodes with a special coating.

Dry welding

When dry (or so-called “cold”) welding of aluminum, parts are joined using auxiliary materials or mechanical manipulation, rather than heating.

SETTING UP THE WELDING MACHINE

The last step before starting work is setting up the equipment. The success of the entire event will largely depend on the correct implementation of all recommendations. The following tips should be taken into account:

• Polarity can be either direct or reverse. Usually from the start they set it to 50/50.
• It is better to cook on alternating current. Aluminum welding with direct current is carried out only using the electric arc method.
• Carefully regulate gas flow. It is better to immediately install it in the range of 6–12 liters. In the future, when you gain some experience, you will be able to adjust this indicator.
• Select the correct duration of arc decay, as well as argon supply after this. The first indicator is usually 2-4 seconds, the second - 5.

SELECTION OF FILLER MATERIAL AND TUNGSTEN ELECTRODES FOR ALUMINUM WELDING

When choosing an additive for aluminum, and in particular wire, it is worth remembering that the metal melts very quickly. Therefore, the material used must have a thickness no less than the parts being welded. But it is equally important to remember the chemical composition of the base and additive. If they do not correspond to each other, then a strong connection will not work. When selecting wire, you should be guided by the following data:

There are also special recommendations regarding the choice of electrodes. The main thing is that the diameter of the selected accessory is as close as possible to the thickness of the workpiece. It is recommended to choose WL 15 or WL 20. The electrode is sharpened as usual, but avoid creating a too sharp tip. In the very first seconds after heating, the end of the product takes on the shape of a drop, and already in this state the seam is made. In this case, the projection from the nozzle should be at least 3–5 mm.

ALUMINUM GAS WELDING TECHNOLOGY

Before starting work, we recommend that you familiarize yourself with the table containing information about aluminum welding modes.

Then you can proceed directly to connecting the parts. Follow a few simple rules and you are guaranteed success:

1. Place the workpieces in the most convenient position. To achieve even more comfort, they can be grabbed on both sides.
2. The wire begins to be fed only after a weld pool has formed. In this case, it is important not to delay and do everything on time.
3. The recommended arc length is 3 mm.
4. The electrode must be held at an angle of 80 degrees. But the wire is fed perpendicular to the position of the electrode.
5. To work with thin workpieces, it is enough to guide the electrode strictly along the seam. If the thickness of the product exceeds 3 mm, then it is quite possible to use a little zigzag movements.
6. The wire moves in front of the electrode.
7. To complete the seam, press the torch button. This starts the shutdown timer.
8. The device cannot be removed from the welding zone until the gas supply stops.

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Aluminum resistance welding

Of the existing resistance welding methods for aluminum and its alloys, spot welding and seam welding are widely used. Butt welding of aluminum alloys is used less frequently.

To obtain high-quality connections, special attention should be paid to the surface preparation of parts. Before spot and roller welding, sheet elements are cleaned on both sides to a width of 30-50 mm at the locations of weld points or seams. Parts prepared for butt welding must be cleaned at the ends and in areas where they are secured in the clamps of the welding machine. The best results are obtained by chemical cleaning - pickling parts in special baths after preliminary degreasing. It is recommended to carry out etching at 17-25° C in an aqueous solution of concentrated orthophosphoric acid (H3PO4) with the addition of 0.1-0.3% chromium (K2Cr2O7). The duration of etching is 10-15 minutes, then drying with hot air (T = 70÷80° C). After etching, parts can be stored before welding for up to 3 days when using AC machines and up to 24 hours when welding with stored energy.

Spot welding.

Figure 1. Scheme of spot welding of aluminum using gaskets made of stainless steel 12Х18Н9:1 - electrode; 2 - gasket; 3 - parts to be welded.

Spot welding of aluminum and its alloys presents some difficulties. Since aluminum has high electrical conductivity, welding is accompanied by overheating of the metal at the contact between the electrode and the part and, as a result, their welding. In order to eliminate this negative phenomenon, in some cases, heat-insulating gaskets made of steel 12Х18Н9 with a thickness of 0.2-0.5 mm are used between the electrode and the aluminum part. Such gaskets are not welded to parts. When welding aluminum alloys, it is necessary to ensure a small and, if possible, constant electrical resistance of the oxide film on the surface of the product: when welding on AC machines - 100-300 μOhm, when using stored energy - less than 100 μOhm. To control the quality of the surface, parts are clamped between the electrodes of a special press or pointing machine. When measuring contact resistance, you can use a micrometer type M246 or other instruments designed for measuring low resistances.

For aluminum and its alloys, spot welding is used for metal thicknesses from 0.04 to 5-6 mm. Elements assembled for welding must fit tightly to each other; Gaps of no more than 0.3 mm are allowed over a length of 100 mm.

Rice. 2. Types of connections for spot welding of aluminum to its alloys.

Table 1. Approximate modes of spot welding of aluminum alloys

Spot welding of aluminum and its alloys requires the use of welding currents of very high density - up to 1000 A/mm2 and higher, which significantly exceeds the current density when welding low-carbon steel. The currents used are 3-4 times higher than when welding steel. Recommended specific pressure is 59-98 MPa. The core diameter of the point when welding aluminum with a thickness of 2-3 mm is 8-11 mm. Since as a result of heating during spot welding, aluminum alloys soften, and the sizes of the softening zones depend on the welding time, alloys of this type are welded with relatively short current pulses lasting 0.08-0.3 seconds (hard modes). Depending on the thickness of the metal, the following radii of the electrode sphere are used:

When welding light alloys, minimal heat generation in the electrode-workpiece contact and intensive cooling of the electrode are ensured. In this regard, the electrical conductivity of the alloy for the manufacture of electrodes must be at least 85-90% of the conductivity of copper.

When spot welding high-strength aluminum alloys, starting with thicknesses of 1.5-2 mm, better compaction of the core and, accordingly, elimination of the tendency of the weld point to pores and cracks is achieved when using a variable force schedule with “forging” pressure Pk. Usually they take Pk = 1.5 + 3 Psv, where Psv is the force applied to the electrodes during welding heating. Thus, for the D16-AT alloy with a sheet thickness of 1.5 mm, Рсв = 6500 N, and Рк = 9810 ÷ 11800 N. In order to avoid overheating of the metal in the electrode-part contact, reduce wear of the electrodes and improve the surface quality of parts made of aluminum alloys , in some cases (for example, for critical parts), modulation of the welding current pulse is used with its gradual increase and decrease. For spot welding of metal of small thicknesses (0.02-0.5 mm), capacitor welding is used on TKM-4 type machines with a power of 100 W, etc.

Figure 3. Cyclogram of single-pulse spot welding of aluminum alloys with “forging” pressure.

Figure 4. Cyclogram of spot welding with a gradual increase and decrease in current

When welding aluminum alloys, the points, while having high shear strength, have relatively poor resistance to tearing.

Table 2. Average breaking force of precision welds on aluminum alloys

Figure 5. Basic typical connections for seam welding of aluminum and its alloys: a - lap; b - onboard.

Seam welding is successfully used in the manufacture of products from aluminum alloys up to 4 mm thick that require tightness. For light alloys based on aluminum and magnesium, such welding is carried out in two ways - intermittent and stepwise. In the first method, the parts to be welded move relative to the electrodes of the machine continuously, and the welding current is switched on by pulses of duration t alternating with pauses tn. Intermittent switching on of the current eliminates overheating of the surface of the parts being welded and sharply reduces wear of the electrodes. For aluminum alloys. In the second method, which is very effective for aluminum alloys, the switching on of the welding current and the movement of parts alternate: welding is carried out with stationary parts, and their movement is carried out with the current turned off and constant pressure.

The basic types of joints for seam welding aluminum are the same as for steel and other metals. Size C is taken depending on the thickness of the alloy:

The width of the working part of the rollers is 2-12 mm and increases with increasing thickness of the metal being welded. The electrode diameter is 150-200 mm. When the metal thickness is 0.5 mm, electrodes of a smaller diameter are used - 40-50 mm. For welding light alloys, rollers with a spherical working surface are used. When seam welding aluminum and its alloys, it is necessary to ensure the flow of significant current in the welding circuit. Therefore, high-power roller machines (250-350 kVA) are used.

Table 3. Approximate modes of intermittent seam welding of aluminum alloys

The compression forces of the electrodes are close to those for low-carbon steel of the same thickness. The welding speed is lower than for steel and lies in the range of 0.5-1.0 m/min. It decreases with increasing thickness of the parts being welded.

The condition of the alloy surface has a significant influence on the quality of the seam in seam welding, just as in spot welding.

Butt welding.

Butt welding of aluminum and its alloys is possible using both resistance and flash welding. When resistance welding aluminum, the current density is approximately twice as high as when welding low-carbon steel (for the same process duration). Heating is carried out at high speeds, exceeding the heating speed of steel parts. Aluminum requires significantly more power than steel. Thus, when resistance welding rods with a diameter of 8 mm, a power of 5 kVA is required for low-carbon steel, and 15 kVA for aluminum.

The most effective method for aluminum and its alloys is flash butt welding, since this process eliminates oxidation of the metal in the joint, the danger of which is very high when welding this metal. There are known examples of flash welding of products made of aluminum alloys on machines with a power of more than 500 kVA with an upsetting force above 150 kN, as well as welding of numerous simple sections of smaller sizes (rods, pipes, strips, etc.). In construction, butt welding is widely used to connect various complex profiles, which are welded at different angles to each other.

Butt welding is carried out at a high speed of continuous melting, reaching 8 mm/s or more (when welding steel it rarely exceeds 2-3 mm/s). Significant upsetting rates are required (150 mm/s and higher), greater than when welding low-carbon steel. Upsetting pressures for aluminum alloys can reach 196.1-215.7 MPa. Therefore, their welding requires machines of relatively higher power with automatic control.

Table 4. Approximate modes of flash butt welding of aluminum alloys.

Figure 6. Scheme of butt welding of aluminum billets with forced formation of a joint.

For aluminum alloys, flash butt welding with burr cutting with knives and forced formation of a joint is very effective. These methods provide favorable joint structure under elevated pressure while eliminating the delamination and looseness observed with conventional settlement patterns. When welding heat-treated parts with a large cross-section, heating is used (at an increased installation length and current density of 5-7 A/mm2) to 200-300 °C for 30-40 s (heating should not noticeably affect the softening of the alloy). The following welding process parameters are recommended: before heating, the ends are leveled by pre-melting, and then compressed at a pressure of 19.6-49.0 MPa. After heating, melting is initiated stepwise, at melting speeds of 0.5-1 mm/s, then at 3-5 mm/s and, finally, at 10-25 mm/s; upset pressure 147.2-245.3 MPa. Pulse reflow is also effective. The best results are obtained when welding aluminum alloys in a protective atmosphere of inert gases. However, experience shows that in many cases welding without gas protection is possible (especially for small sections).

The mechanical properties of joints made of a given alloy depend on the welding modes used. To ensure maximum strength, the pressure must be matched to the settling rate: as pressure increases, the settling rate decreases. The strength of aluminum joints averages 68.7-88.3 MPa. On an alloy of the AMg6 type, it is possible to obtain welded joints that are equal in strength to the base metal with satisfactory ductility. On high-strength alloys (for example, D16-AT), the strength and ductility of the joints is lower than that of the base metal. Heat treatment (annealing) has a significant effect on the strength and ductility of connections made from some alloys, for example AK6.

Table 5. Mechanical properties of joints of aluminum alloy plates made by flash butt welding

Wires made of aluminum and its alloys are joined end-to-end by capacitor welding. The mechanical properties of welded joints are determined for aluminum wire with a diameter of 2-3 mm by 6-8 bends at an angle of 180°.

Table 6. Approximate modes of capacitor butt melting of aluminum wires