The excellent properties of aluminum, its excellent thermal conductivity, low weight have made such a material in demand in all areas of the production process. However, this material is very difficult to weld. Therefore, aluminum welding technology was specially developed to make it available to any industry.
Scheme argon welding of aluminum.
Factors complicating the welding process of aluminum parts
Aluminum and its alloys belong to the group of hard-to-weld metals. Several characteristic properties of this metal cause this feature: the surface is covered with an oxide film that tends to melt when the temperature reaches 2044 °. Directly aluminum has a melting point of 660 °.
Chemical properties of aluminum.
Due to its rapid oxidizability, a refractory film is formed during the appearance of the molten metal. This film does not allow to obtain a solid seam. To prevent the appearance of the film by fencing the welding zone from the ingress of air. Such protection became possible when automatic welding of aluminum using a protective gas environment is carried out. Aluminum has a high fluidity, so welding without heat-removing linings is practically impossible.
The possibility of some crystallization pores in the weld seam weakens aluminum. Regulates the appearance of pores hydrogen, which is dissolved in aluminum. He always seeks to leave the metal. The appearance of cracks mainly concerns aluminum alloys. They appear during the cooling of the metal due to the large amount of silicon.
Aluminum has a large shrinkage ability, this is affected by linear expansion, the value of which is incredibly high. As a result, during the hardening of the weld there are large deformations.
Huge thermal conductivity requires the use of welding current, which is several times greater than the current intended for steel parts, although the temperature of the molten steel is much higher than aluminum.
An additional complication of aluminum welding is the fact that, under domestic conditions, it is necessary to boil a variety of alloys of unknown grade. To obtain high-quality welds, a special welding technology is required.Back to table of contents
Inverter welding: features
The melting point of aluminum.
This welding technology is specifically designed for work with aluminum. This material is boiled in a protective gas sheath, most often argon. For the process of welding aluminum, tungsten non-consumable electrodes are used. For work, you must always clean the surface of the electrode. Its surface accumulates growths consisting of tungsten oxides. As a result, the quality of the seam suffers.
To remove such "crowns" with an abrasive disc, the electrode is sharpened. As a result, the surface of the electrodes becomes clean, there is no formation of burrs and grooves. For sharpening the electrode, a special disc is used, which is not used to clean other materials. It is quite possible to reduce the likelihood of growths if the electrode is subjected to strong gas cooling.Back to table of contents
Argon arc welding: the nuances
An electric arc during this welding process is formed between the electrode and the surface of the part. The torch holds the electrode, while the protective gas flows. At the same time the filler wire becomes a consumable material. Its submission can be carried out in two ways:
Table welding modes aluminum.
Aluminum welding with argon requires a special filler wire. The type of additive is directly dependent on the chemical elements in the alloy that will be welded. To make automatic welding, the following types of wire are used:
The size of this wire does not exceed 5 mm. When you have to boil other alloys that contain magnesium, similar types of wire are used. To compensate for the fainting during aluminum welding, filler wire is made with a large amount of magnesium.
Aluminum welding is performed in several ways:
TIG welding has low speed. The speed of the MIG welding process is several times greater. However, a more beautiful is a seam made by TIG-welding.Back to table of contents
Point method: preparatory work
The welding technology of a point type requires preparation before starting work. First, the aluminum surface is prepared. At this stage, it is required to completely clean the surface of the oxide film. To obtain high-quality welding using the point method, it will be quite enough to free the strip from the 50 mm wide film. Aluminum welding according to the point technology can occur in two ways:
The scheme of technology of spot welding of aluminum.
The most effective, giving excellent results, was a mechanical cleaning with the use of special tools. However, cleaning can also be done manually. In most cases, metal brushes are used, rotating at high speed.
When the surface is cleaned with hands, use sandpaper.
Of course, the best cleaning is considered chemical. It gives the greatest effect. Aluminum can be etched by various chemicals:
- caustic soda;
- phosphoric acid.
Before you start processing, workpieces degrease. After etching, aluminum can be stored in a warehouse for 3 days if welding with variable energy technology is carried out. One day is given to storage when using the welding process using accumulated energy.Back to table of contents
Spot Welding Technology
Such aluminum welding is available at a workpiece thickness of not more than 6 mm. Basically, the process is similar to welding a variety of metals. However, there are several differences. Point method can be cooked blanks:
Dimensions of spot welded joints.
When spot welding takes place, the parts are squeezed together with some effort to reduce the gap. If the gap is less than 0.2 mm, the welding area is minimally heated. For the welding process, a high current is used, its value is 1 kA / mm². This forms a welding point that connects the workpiece. Automatic welding is permissible only when hard modes are used. The welding time is adjusted depending on the metal thickness to be welded. To prevent overheating of aluminum, welding is done with short, strong pulses.Back to table of contents
Spot welding and electrodes
Due to the fact that aluminum alloys have a high thermal conductivity, they require the use of only specific types of electrodes. Usually they differ in several characteristic properties:
- electrical conductivity;
- heat resistance.
Copper has such properties, therefore electrodes are specially made for the work of spot welding from this non-ferrous metal. The composition may vary, it all depends on the type of alloy to be welded. The surface of the electrode may have a spherical shape.Back to table of contents
Technological nuances of the welding process
The conductivity of pure aluminum is much higher than steel. Aluminum welding has its own distinctive features. With its high thermal conductivity, aluminum does not allow for high-quality welding, it is impossible to melt the metal perfectly.
The scheme of gas welding aluminum.
The welding zone instantly crystallizes. To avoid this phenomenon, it is required to increase the welding current. The workpiece must be preheated. The protective gas is argon.
Sometimes a weak joint appears at the very beginning of the welding process. The reason is insufficient digestion, as the part was poorly heated. The four-stroke mode solves this problem. They are equipped with welding units "Merkle". At the initial stage, it is possible to create a current much larger than the main current, as a result of which the part will warm up faster.
The variety of aluminum alloys is huge. There is one basic requirement for aluminum wire: it must be used at the right time. When the packaging is opened, it can be stored for a very limited time. Due to the rapid oxidation, the properties of the wire will deteriorate. The most affected wire quality is high humidity.
Before welding, for better combustion of the electrode and obtaining a high-quality weld, the parts to be welded are cleaned of all kinds of contamination. Cleaning is done right before the start of the welding process. This is due to the property of aluminum to be very quickly covered with an oxide film.
Diagram of the process of aluminum welding semiautomatic.
As mentioned above, automatic welding of conventional aluminum occurs in the protective gas zone. Argon is most commonly used. The most preferred is a mixture of gases. Usually in this role argon plays along with helium. Thanks to helium, which has a high thermal conductivity, the welding bath acquires a particularly high temperature. This allows you to weld aluminum having a greater thickness. The mixture of gases contributes to a better gassing, it protects the seam from the appearance of pores.
It is possible to boil aluminum using classic MIG welding devices, but this is rather arbitrary. The best results are shown by synergistic impulse devices having a special program. With its help, automatic welding of the aluminum itself, numerous non-ferrous metals. To cook aluminum, the sheets of which have a thickness of 6 mm, requires welding equipment that has the ability to regulate the flow of welding current reaching 300 A.Back to table of contents
Pulsed welding: characteristics
Such synergistic impulse mechanisms have specially developed programs that help brew various types of materials. For each type of alloy the program has an individual setting. The manual controller displayed on the work panel allows you to customize the desired program. Push-button adjustment quickly selects the required current strength. Other parameters are configured automatically by the embedded microprocessor.
The latest pulse welding units support many welding modes. The four-stroke mode makes it possible to customize the individual welding parameters required at each technological transition. When welding starts, the initial cycle sends the highest current, resulting in accelerated heating of the welded workpieces. This mode allows you to get rid of all kinds of defects that occur at the very beginning of the welding process.
When welding works are completed, sometimes there are some defects, for example, an unfinished crater. When the metal is in the molten state, when it begins to cool, hot cracks may appear. The third cycle gives a reduced current, which allows you to completely get rid of these defects.Back to table of contents
Difficulties Welders Face
- When aluminum is being welded, its surface is covered with an oxide film. It does not allow to weld parts reliably, contaminates the seam, which becomes fragile. This film must be quickly removed.
- The weldability of aluminum is greatly influenced by the melting point.
- The expansion coefficient, which has high values when welding works are carried out, contributes to the appearance of serious deformations. Therefore, aluminum welding should occur with the utmost care.
- In the liquid state, aluminum has a high fluidity. Therefore, when it is boiled, the formation of stains is possible. To get rid of this phenomenon requires the mandatory use of gaskets, as well as other special devices.
- When the temperature rises when welding aluminum, the strength of the metal drops sharply, it quickly collapses.
- Aluminum is subject to warping. Therefore, aluminum welding requires reliable fastening of parts.
- To make the seams of high quality, durable and reliable, it is necessary to thoroughly clean the welding wire.
With regard to safety, then for welding aluminum alloys worker must have:
- protective mask;
- rubber boots.
There must be good insulation of all connecting wires. The room in which aluminum is being welded should not store explosive and combustible materials. It must be well ventilated so that the harmful gases evaporate quickly.