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Welding knowledge
Release time:2015-12-04    Author / source:    Read:4673count
At present the main welding method is resistance welding. Resistance welding (resistance welding) is to be pressed on two pieces of welding electrodes, and subjected to current resistance, use of the thermal effect of current flowing through the workpiece contact surface and the adjacent area will generate heat to melt or plastic state, so as to form a metal binding method.
Elements for judging the welding properties of metal materials:
The electric conductivity and thermal conductivity of the material, that is, the electrical resistivity is small and the thermal conductivity of the metal material, the welding is poor;
High temperature plastic and plastic temperature range of materials, that is, the high temperature yield strength of the material (such as heat-resistant alloy), plastic temperature
Materials (such as aluminum alloy) with a narrow range of degrees, are less welded;
The sensitivity of the material to the thermal cycle, that is, to generate the material with the thermal cycling effect on the defects (crack, hard tissue, etc.)
Material (such as 65Mn), its welding is poor;
The high melting point, linear expansion coefficient, high hardness of metallic materials, the welding is generally poor.
Of course, the evaluation of a metal material welding, should be integrated, comprehensive consideration of the above factors.
Copper and copper alloy can be divided into pure copper, brass, bronze and copper, the copper, copper, phosphorus deoxidized copper spot welding is poor (not recommended), brass, bronze, copper nickel alloy is excellent. High conductivity copper welding, more difficult, and poor bonding strength.
Resistance welding quality is determined by the following 4 elements:
1 welding current. The effect of electric current on the generation of heat is greater than that of resistance and time. Therefore, in the process of welding, it is a must be strictly controlled parameters. The main cause of the current changes is the voltage fluctuation of the power network and the impedance of the secondary circuit of AC welding machine. Impedance variation is due to changes in the geometry of the loop or the introduction of a different amount of magnetic metal into the secondary circuit. For DC welding machine, the secondary circuit impedance change, the current has no obvious effect. In addition to the total welding current, current density has a significant effect on the heating. The current density and the heat of welding can be reduced by the flow of the weld and the increase of the electrode contact area.
2 welding time. In order to ensure the weld size and the strength of the joint, the welding time and welding current can be added in a certain range. In order to obtain a certain strength of the solder joints, can be used for large current and short time (strong condition, also known as strong specification), can also be used for small current and long time (weak condition, also known as weak specification). The selection of strong and weak conditions, it depends on the performance of the metal, the thickness and the power of the welding machine. But for different performance and thickness of the metal required for the current and time, there are still a upper and lower limits, more than this limit, will not be able to form a qualified molten core.
3 electrode pressure. Electrode pressure on the total resistance of the two electrodes has a significant effect on R, with the increase of the electrode pressure, R significantly decreased. At this point, the welding current can be slightly increased, but it can not affect the reduction of the heat caused by R. Therefore, the strength of the solder joints decreases with the increase of the electrode pressure. At the same time, increasing the pressure of the electrode, increasing the welding current or the time to extend the welding time, to compensate for the influence of the resistance decreases, can keep the same strength of the solder joint. The stability of the joint strength can be improved by using this welding condition. The electrode pressure is too small, will cause the splash, also can make the solder joint strength reduce.
4 electrode shape and material properties. Since the contact area determines the electrode current density, electrode material resistivity and thermal conductivity between heat generation and dissipation, thus the electrode shape and material has a significant influence on the formation of nuclear fusion. With the deformation and wear of the electrode tip, the contact area will increase, and the strength of the joint will be reduced.
5 Effects of surface conditions of the workpiece. Oxide, dirt, oil and other impurities on the surface of the workpiece increases the contact resistance. A thick oxide layer can even cause the current to pass through. Local conduction, because the current density is too large, it will produce spatter and surface burning. The nonuniformity of oxide layer will affect the welding quality of the welding. Therefore, a thorough cleaning of the workpiece surface is necessary to ensure the quality of the necessary conditions.
Advantages of resistance welding:
1, the formation of the melt, always be surrounded by plastic ring, molten metal and air separation, metallurgical process is simple.
2, the heating time is short, the heat concentration, so the heat affected zone is small, the deformation and stress is also small, usually in the welding do not have to arrange the correction
And heat treatment process.
3, no need for welding wire, welding electrode and other metal, as well as oxygen, acetylene, hydrogen and other welding materials, welding low cost.
4, the operation is simple, easy to realize mechanization and automation, improve the labor conditions.
5, the productivity is high, and no noise and harmful gas, in mass production, and other manufacturing processes can be made to group
On-line But because of the flash butt welding spark splash isolation.
Resistance welding defect:
1, there is a lack of reliable non-destructive testing method, the welding quality can only rely on the process of test specimens and the destructive test of the workpiece.
Inspection, as well as by a variety of monitoring technology to ensure.
2, equipment, power, mechanization, automation degree is high, make the equipment cost is higher, maintenance is more difficult, and commonly used
Large power single phase AC welding machine is not conducive to the balanced operation of the power grid.
Application status of resistance welding in china:
Along with the development of aerospace, electronics, automobile, household appliances and other industrial development, more and more affected by resistance welding
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