Existing types of the welding process depend on the use of certain energy sources that play an important role in the performance of this type of work. Spot welding with your own hands should be carried out under the control of the weld point through visual observation.
Spot welding is a welding process in which parts are joined at several points.
Often this type of welding is used at home. The level of its quality will be determined by the skill associated with a particular current pulse.
The use of capacitor spot welding technology
The scheme of capacitor spot welding.
Performing welding of thin parts (width 1-1.5 mm), apply the technology of capacitor welding. It is one of four ways to create welds using stored energy:
In practice, in industry and domestic life, capacitor welding is used. It is connected with the energy supply of the capacitor banks, which, after it has been saved, will be spent on the implementation of the weld for a certain time interval with a short duration. Two types of capacitor type welding:
- Due to the discharge of the capacitor to the part.
- For the area of the discharge capacitor take the primary winding of the transformer for welding.
If a direct discharge is provided, then butt welding is carried out. If you use the second method, it is just intended for the purpose of conducting spot welding, as well as suture. Their advantage is the ability to connect parts of various shapes with their thickness in the range of 0.005-1 mm. The level of power consumption varies in the range of 0.1-0.2 kVA, and the welding current operates with a short pulse, the duration of which is up to 0.001 sec. Capacitor spot welding is used in the manufacture of optical instruments, televisions, radios, measuring instruments, etc.Back to table of contents
How to do spot welding correctly: requirements for electrodes, devices
Manual spot welding device: 1 - base, 2 - fixed square, 3 - lever, 4 - hinge, 5 - square, 6 - screw, 7 - electrode.
For welding at home, various devices are used that are used without special skills, knowledge and experience. The simplest devices for spot welding have low power, they are desktop. These devices allow welding, connecting parts, the thickness of which can reach 0.2 mm. Devices are used for welding wire having a diameter of up to 0.3 mm. At the same time, welded joints are created for welding steel elements or parts made of foil.
Low-power devices are ideal for spot welding small parts. They do not require a significant clamping force, which is produced by pressing a hand. The type of electrode used in this device resembles the shape of a gun. The main element of the welding device may be a small-size welding transformer. The secondary winding of the transformer is used to securely connect electrodes to it. For carrying out welding in household use the device having small power. Use not only devices with low power, but also with higher. These devices operate on the basis of the following important elements:
- Powerful welding transformer.
- Thyristor semiconductor key.
- A special device that allows you to withstand time and provide control over the duration of the welding process.
This type of apparatus allows the welding of elements with the greatest thickness, providing the required level of pressure and suitable conditions during the welding process. You can buy a device with such power that will be needed. However, you can make an order for the manufacture of welding device, which will have advanced features. Electrodes must necessarily provide the necessary level of reliability in the framework of the appropriate temperature regime.
The advantage of the electrode is associated with its high thermal and electrical conductivity, easy machining. Bronze, used to create electrodes, contains cadmium or cobalt. Electrodes are made of electrolytic copper and its alloys, which contain chromium or tungsten. Copper has indicators of electrical and thermal conductivity, superior to the characteristics of bronze in its similar indicators, including its alloys. The indicator of the wear resistance of copper is 5 or 7 times lower, therefore, it is customary to manufacture electrodes mainly from a special alloy of EV, which is a pure type of copper, whose composition is up to 0.7% chromium and up to 0.4% zinc. Conducted spot welding in terms of quality is determined by the diameter of the electrodes used.Back to table of contents
How to properly observe welding safety precautions
Safety during welding.
For proper welding at home, you will need the following:
- The presence of a constant speed with which the movement of two electrodes.
- The required level of support for the indicator of pressure, which is associated with complete contact with the connected elements.
However, it is necessary to comply with the conditions of safety when conducting spot welding, which includes the following main points:
- Be sure to conduct insulation of each electrical and connecting wires.
- Apply protective equipment, that is, gloves or mittens that protect the hands from getting a possible burn.
- To protect the face, a special mask is used to prevent sparks and splashes of metal from reaching the face.
- There should be no materials or objects that are flammable near the work site.
- Wood flooring also requires special protection against fire.
- It is necessary to foresee the availability of special means to extinguish fires.
- In the room where the work is carried out, gases that are harmful to human health should not accumulate, so it should be ventilated.
Features of resistance spot welding technology
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What operations allows spot welding
Spot welding scheme.
This type of welding, as a spot, is used not only in domestic life, but also in industrial sectors. You can do spot welding by combining the following types of blanks:
- steel sheet;
- profile elements;
- metal rods.
To ensure a high-quality welded joint, it is imperative to carry out the preparatory work correctly. The surfaces of the parts are cleaned of various contaminants using special brushes, by sandblitting, etching in acids, etc. The scheme, which allows to do spot welding in everyday life, involves several steps. The welding machine can be used to connect various types of cable, aluminum parts, to repair kitchen utensils. Let us consider in more detail all the stages of welding.
- Parts requiring connections are placed in the correct position.
- Details are placed in the gap between the electrodes, followed by pressing together the blanks.
- The connected elements should be heated to a plastic state so that they can be deformed.
Industrial conditions for spot welding require appropriate equipment, providing for automatic operation.
Characteristics of spot welding.
600 points / min is the maximum level that the welding frequency can reach. Experts recommend leaving the speed at which the electrodes move at a constant level. At the same time, an appropriate amount of pressure should be provided with the mandatory contact of the elements to be connected. Resistance welding is the process by which a billet of metal is melted.
As a result, a cast structure is obtained, which is formed when the sediment pressure allows to overcome the prescribed stiffness of the parts subjected to deformation. The welding current when heated should be associated with a short pulse of duration from 0.01 to 0.1 sec. The duration of this pulse will depend on the welding conditions. This will allow the material to be melted by the electrodes, which will ensure for the blanks the formation of a liquid core, which is common, and its diameter can be from 4 to 12 mm.
If the current impulse ceases to act, then the blanks will be held in the device for a certain time, which will allow the core, which is in the molten state, to cool down, followed by crystallization. There are pros and cons of spot welding. For example, the mechanical strength of the created seams is associated not only with high efficiency, but also with the ability to automate the welding process with great accuracy.
Among the significant shortcomings are the lack of tightness of the resulting seams. If the thickness of the parts being welded increases, the pressure increases. This entails a reduction in the useful life of the electrodes. This type of work is used when connecting parts that are relatively small or small thickness up to 6.0 mm. At the same time, this type of welding is fairly safe, since the splash and spattering of the metal in these conditions does not occur after the creation of a sealing belt between them.Back to table of contents
Modes of spot welding
Modes of spot welding.
You can do spot welding in two modes, which depend on the current density:
- Soft (at a density of up to 100 A / mm²).
- Hard (at a density of up to 300 a / mm²).
Hard mode has the following characteristics:
- increased power level;
- large network load;
- increase in value.
The hard mode provides high welding performance with a short welding time. If, in the hard spot welding mode, there is a decrease in the strength index of the weld point, then this leads to the appearance of defects.
Defects of spot welding: a - undercut; b-crack; in - porosity; g - non-metal and slag inclusions; d - lack of penetration along the seam edge; e-not the thickness of the seam.
The occurrence of the inferior point represents a dangerous moment when the molten core is small or absent. Usually its size is not enough to ensure the strength of the seam. The presence of this defect can not be monitored every time, making a visual inspection, which is so dangerous. Defects can manifest as:
- The appearance of deep dents.
- Full burn metal.
- Melting surface parts.
- The presence of shells and deep dents.
- Strong porosity of the welded core.
The main characteristics of the soft mode are:
- Longer welding time.
- The smoothest heating at low power.
The possibility of reducing the power of the device consumed from the network is associated with a decrease in load and lower cost of the device itself. Using the soft mode, welding elements from alloyed steels and steel parts that contain carbon in large quantities are carried out. Hard mode is used when welding steels with the greatest strength. The pressure should be large, since cracks may form.