1. working principle and characteristics of non-melting argon arc welding
Non-melting electrode argon arc welding is that the arc burns between the non-melting electrode (usually tungsten electrode) and the workpiece, and inert gas (usually argon gas) which does not react with the metal flows around the welding arc to form a protective gas cover, so that the tungsten electrode tip, the arc, the molten pool and the metal already at high temperature are not in contact with air, which can prevent oxidation and absorb harmful gases. So as to form a dense welded joint with excellent mechanical properties.
2. Working principle and characteristics of 2.MIG welding.
The welding wire is fed through the wire wheel, and the conductive nozzle conducts electricity, so that an arc is generated between the base metal and the welding wire, so that the welding wire and the base metal are melted, and the arc and the molten metal are welded under the protection of inert gas argon. Different from TIG welding: one is that the welding wire is used as the electrode, which is continuously melted and filled into the molten pool, and then condensed to form a weld; The other is protective gas. With the application of MIG welding technology, shielding gas has developed from a single argon gas to a variety of mixed gases, such as argon-rich shielding gas with Ar 80%+CO 220%. Usually the former is called MIG and the latter is called MAG. Judging from its operation mode, semi-automatic MIG welding and argon-rich gas shielded welding are the most widely used at present, followed by automatic MIG welding.
Compared with TIG welding, MIG welding has the following characteristics.
(1) has high efficiency because of its high current density, concentrated heat, high deposition rate and fast welding speed. In addition, it is easy to arc.
(2) Protection needs to be strengthened. Due to strong arc and heavy smoke, protection should be strengthened.
3. Protective gas
(1) The most commonly used inert gas is argon. It is a five-color odorless gas, its content in air is 0.935% (calculated by volume), and the boiling point of argon is-186℃, which is between the boiling points of oxygen and helium. Argon is a by-product when liquid air is fractionated to produce oxygen in an oxygen plant.
Bottled argon gas for welding in China has a filling pressure of 15MPa at room temperature. The cylinder is painted with gray paint and marked with the words "argon". The chemical composition requirements of pure argon are: Ar ≥ 99.99%; he≤0.0 1%； O2≤0.00 15%； H2≤0.0005%； Total carbon content ≤ 0.001%; Moisture ≤ 30mg/m3.
Argon is an ideal protective gas, and its density is 25% higher than that of air. It is beneficial to protect welding arc and reduce the consumption of shielding gas during flat welding. Argon is a very inert gas, which will not react with metals even at high temperature, so there is no oxidation and burning loss of alloy elements and a series of problems caused by it. Argon is also insoluble in liquid metal, so it will not cause pores. Argon is a monatomic gas, which exists in atomic state, and there is no molecular decomposition or atomic endothermic phenomenon at high temperature. The specific heat capacity and thermal conductivity of argon are small, that is, the self-absorption is small, and the heat in the arc is not easy to be lost, which makes the welding arc burn stably and the heat is concentrated, which is beneficial to welding.
The disadvantage of argon is its high ionization potential. When the arc space is filled with argon, it is difficult to ignite the arc, but once it is ignited, it is very stable.
4. Disadvantages of argon arc welding: (1) Due to the large heat affected zone, defects such as deformation, hardness reduction, sand holes, local annealing, cracking, pinholes, wear, scratches, undercut or insufficient bonding force, internal stress damage, etc. often occur after argon arc welding. Especially in the process of repairing small defects of precision castings, the surface is prominent. In the field of precision casting defect repair, cold welding machine can be used instead of argon arc welding. Due to the small heat release of cold welding machine, the shortcomings of argon arc welding are well overcome and the repair problem of precision castings is made up.
Compared with covered electrode arc welding, argon arc welding is more harmful to human body. Argon arc welding has high current density and strong light ratio. The ultraviolet radiation produced by the arc is about 5 ~ 30 times that of ordinary covered electrode arc welding, and the infrared radiation is about 1 ~ 1.5 times that of covered electrode arc welding. The ozone content produced in the welding process is very high. So try to choose a ventilated place, otherwise it will be harmful to your health.
Application of argon arc welding;
Argon arc welding is suitable for welding non-ferrous metals and alloy steels that are easy to oxidize (at present, stainless steel is mainly welded with Al, Mg, Ti and their alloys); Suitable for single-sided welding and double-sided forming,
The above is the basic knowledge of argon arc welding.