Often there is a need for spot welding, when you do not need to connect pipes or profiles, but simply need to attach a small but important detail. To do this will help capacitor welding with their own hands.
Electric circuit spot micro welding.
Contact welding is a fairly popular type of compound of metals, especially non-ferrous. Many seek to be able to carry it out at home. Condenser DIY welding is quite affordable and easy to do.
Variety of capacitor welding
Capacitor welding with capacitor discharge through the primary winding of a transformer: a — process diagram; b — current diagram.
Capacitor welding is a type of welding in which the metal is melted due to the stored electrical energy in the capacitors. According to the method of conducting capacitor welding can be divided into contact, impact and spot.
Contact welding implies that the capacitor is discharged onto two metal blanks previously pressed against each other. An arc arises at the point of contact, which melts and joins the workpieces in a small area of their contact. The welding current in the arc zone reaches 15 kA with an exposure time of up to 3 ms. During impact welding, the contact between the metal blanks, to which the discharge is applied, is made in the form of a short-term strike. The arc time does not exceed 1.5 ms, which further reduces the welding area.
In spot welding, the discharge is applied to two copper electrodes, which at points touch the surface of metals from two sides. An arc is formed between the electrodes within 0.01-0.1 s, depending on the adjustment. The strength of the welding current can reach 10 kA. Welding of metals occurs almost at the point.
The circuit of capacitor welding.
By the form of the formed discharge, capacitor welding is divided into transformerless and transformer welding. In the first form, the discharge from the capacitors goes directly to the metal surface. Such welding can be performed by a high-voltage discharge (voltage up to 1 kV) with a current up to 100 A for 0.005 s or a low-voltage discharge (voltage up to 60 V) with a current of 1-2 kA for up to 0.6 s.
The transformer type of capacitor welding consists in the discharge from the capacitor to the transformer winding, and from its secondary winding enters the welding zone. This type of welding expands the possibilities of adjusting the process. The discharge voltage reaches 1 kV, while in the secondary winding a welding current of up to 6 kA is achieved, which is supplied for up to 0.001 s.Back to table of contents
The principle of spot welding
The design of transformers for spot welding.
The most common type of household capacitor welding is spot welding of the transformer type. The basic principle of spot welding is that the welded workpieces, which are combined in the desired position, are clamped between two electrodes, to which a short-term welding current of a large magnitude is supplied. The electric arc formed between the electrodes melts the metal of the workpieces in the zone with a diameter of 4-12 mm, which leads to their connection.
The action of the welding pulse is provided for 0.01-0.1 s, which ensures the formation of a melt core common to both welded metals. After the current pulse is removed, a squeezing load continues to act on the workpieces, which ensures the formation of a common weld. Limiting the melting zone of metals is achieved by the fact that at the time of the impulse, the metals were in contact with each other, providing a heat sink.
The welding current (pulse) is supplied to the electrodes from the secondary winding, where a high current is provided at a low voltage. A pulse is generated to the primary winding when a capacitor (or a block of capacitors) is discharged. In the capacitor itself, the charge accumulates in the period between the supply of pulses to the electrodes, i.e. charging of the capacitor takes place while the electrodes are moved to another point for welding.
The scope of such welding is extensive by type of material. Particularly good results are obtained when welding non-ferrous metals, including copper and aluminum. The thickness of the welded sheets is a significant limitation - up to 1.5 mm. But spot welding perfectly showed itself in the case of attaching thin strips of wire to any massive structure. At the same time, the materials being joined may be heterogeneous.Back to table of contents
Requirements for capacitor welding
Types of resistance welding: a - butt; b - point; in - roller; 1 - welding seam; 2 - electrode; 3 - welded parts; 4 - movable plate with moving part; 5 - welding transformer; 6 - fixed plate.
In order for capacitor spot welding with your own hands to be of high quality, it is necessary to fulfill some conditions. A short pulse must be supplied for up to 0.1 s and a subsequent accumulation of energy from the network for a new pulse in a very short time.
The pressure of the electrodes on the parts to be welded at the moment the welding pulse is applied should ensure reliable contact between them. Decompressing the electrodes must be done with a delay in order for the melt to cool down under pressure, which improves the mode of crystallization of the metal in the weld.
As electrodes for spot welding, copper electrodes are most common. The diameter of the point at the point of contact should be 2-3 times the thickness of the thinnest workpiece to be welded.
The surface of the welded blanks before welding must be thoroughly cleaned so that oxide films and rust will not create a large resistance to current.
Condenser spot welding with your own hands can be performed only if the device is assembled with at least two units: the source of the welding pulse and the welding unit. In addition, it is necessary to provide for the possibility of controlling the mode of welding and protection.Back to table of contents
Simple spot welding design
Welding torches for spot welding.
When welding thin sheets (up to 0.5 mm) or when cooking thin elements to any parts, you can use a simplified design of the welding machine. In it, the welding pulse is supplied through a transformer. In this case, one end of the secondary winding is connected directly to the massive part, to which a thin part is welded, and the other end is connected to the electrode. In other words, the device provides for the use of only one (upper) electrode. It is pressed manually to a thin part. For fixing and holding the electrode, you can, for example, use standard clamping terminals for a car battery (a crocodile clip).
In the manufacture of a simple source of welded current (pulse), you can use the following scheme. The primary winding of the transformer feeding the welding unit is connected to the mains, with one end through one of the diagonals of the rectifier diode bridge. The signal from the thyristor, which is controlled by the start button, is sent to the other diagonal of this bridge.
Electrode position during welding.
The welding pulse accumulates in the capacitor, which is located in the thyristor circuit and is connected to the diagonal of the bridge with the output to the primary winding of the transformer. The capacitor is charged from an auxiliary circuit, which includes an input transformer and a rectifier diode bridge.
The source works in the following order. While the welding transformer is disconnected, the capacitor is charging from the auxiliary network. When you press the start button (turn on the welding transformer), the capacitor is disconnected from the auxiliary network and discharged to the primary winding of the transformer through a resistor. The discharge of the capacitor flows through the control thyristor. The duration of the discharge is changed using a regulating resistor. When the button is turned off, the discharge circuit is broken, and the auxiliary circuit is turned on, and the capacitor charging cycle begins.
The source of the pulse is a capacitor with a capacity of 1000 μF or 2000 μF for voltages up to 25 V. An important element of the circuit is a transformer. It can be made on the basis of the core W 40 with a thickness of 70 mm. The primary winding is made of wire PEV-2 with a diameter of 0.8 mm. The number of turns is 300. The secondary winding has 10 turns and is made of a copper bus with a cross section of 20 mm². For control, you can use a PTL-50 or KU202 thyristor. As an input transformer, you can use any 10 W transformer with a voltage on the secondary winding of 15 V. When using the recommended source, you can provide a current pulse of up to 500 A with a duration of up to 0.1 s.Back to table of contents
The device with increased power
Scheme of seam welding.
To increase the power of the welding current source, a design change should be recommended, allowing welding of sheets up to 1 mm thick or wire up to 5 mm. The signal is controlled using the MTT4K contactless starter for a current of 80 A and a reverse voltage of up to 800 V. The control module includes two parallel-connected thyristors, two diodes and a resistor. The response time is controlled by a time relay connected to the input transformer circuit.
Energy accumulation occurs in electrolytic capacitors assembled into a battery by parallel connection. Capacitors, usually in the amount of 6 pieces, are selected with the following rating: two capacitors with a capacity of 47 μF, two with a capacity of 100 μF, two with a capacity of 470 μF, for an operating voltage of at least 50 V. As a time relay, you can use reed relays RES42, RES43 for voltage up to 20 V.
Relief welding scheme.
The primary winding of the welding transformer is made of a wire with a diameter of 1.5 mm, and the secondary one is made of a copper bus or a wire with a cross section of at least 60 sq. Mm. The number of turns in the secondary winding is 4-7. At the same time, current in the welding zone is provided up to 1500 A.
The machine works as follows. When the start button is pressed, the relay is activated, which switches on the welding transformer through the thyristor control contacts. After discharge of the capacitors, the relay is turned off. Exact regulation of the pulse duration is a variable resistor.
Due to the increase in power, the welding unit should be made more reliable. It uses two copper electrodes. Quite often, welding pliers are used as electrodes, in which pressure up to 20 kg / cm² is provided. The diameter of the pads is selected the most minimal.Back to table of contents
Contact block designs
The welding unit is a contact block, i.e. a device that allows you to mount and move the electrodes. The simplest design provides for manual retention and squeezing of the electrodes. A more reliable system, providing a stationary lower electrode and a movable upper electrode. In this case, a copper bar of a small length (10-20 mm) with a diameter of at least 8 mm is fixed on any basis. The upper cut of the electrode is rounded. The top electrode of the same rod is fixed on the platform, which has the ability to move freely up or recline. Adjusting screws should be provided to create additional pressure after the top electrode contacts the surface of the workpiece. The base of the unit and the upper platform must be reliably isolated from each other before the contact of the electrodes.Back to table of contents
Conducting capacitor spot welding
The whole process of capacitor spot welding with your own hands can be divided into several stages. First, the surface preparation of the welded blanks is carried out. Then the blanks are combined in the required order, placed in the space between the electrodes and compressed by them. With the help of the start button, a welding pulse is applied. 1-2 min after the cessation of the pulse, the electrodes are moved apart. The welded part is removed and installed at another point.
The gap between the welding points depends on the thickness of the workpiece and usually ranges from 15-60 mm.
The welding process is repeated.
In order to do spot welding with your own hands you will need the following additional tool:
- emery circle;
- emery sandpaper;
Condenser welding with your own hands will help to connect thin sheets of any metal or weld small made to any metal structure. Such spot welding is quite simple and affordable.