Self-made resistance welding allows you to solve many problems in the connection of various metal parts. At present, a lot of experience has been gained in the design and manufacture of welding machines in the home. They are based on the use of common parts.
Contact welding machine, made by hand, completely cope with minor repairs.
Welding of metals for domestic purposes usually does not provide for a high productivity of the process and the connection of large-sized products. This makes it much easier to make hand-made devices. A homemade machine will not meet the requirements of industrial use, but homemade products are simple and accessible to the home.
General principles and provisions
The process of resistance spot welding.
Any resistance welding is based on combining molten metals under compressive load. Melting of metals is achieved by short-term transmission of electric current through the contact area of the two blanks. An electric arc arises in the contact zone of metals, which ensures the size of the welding area. The power of such an arc depends on the magnitude of the applied current, the time of its action and the compressive force, which largely determines the length of the arc. The size of the arc impact area depends on the size of the electrodes.
There are three main types of home-made resistance welding: spot, seam and butt welding. Spot welding was the most common. With such welding, the minimum size of the welding zone is ensured by the use of appropriate electrodes. Butt welding is based on the contact of the ends of the parts, while they themselves serve as electrodes.Back to table of contents
Welding machine design
The design of the apparatus for resistance welding.
Self-made welding is performed on spot or butt welding machines assembled by hand. There are general rules for designing such devices. By type of use, they can be portable or stationary. In welding machines, the main parameters are set: current strength, duration of the welding pulse, type and dimensions of the electrode. Devices should be easy to manufacture and operate.
The device of resistance welding consists of two main blocks: a source of welding current and a contact block. The source of the welding current must ensure that a welding pulse arrives in the welding zone - a current of sufficient strength for a short time. In the contact block is directly welded zone. Consequently, the contact of metals, the application of an electrical impulse to them through the electrodes, the creation of a compressive load on the area of contact of metals should be ensured and recorded in this zone.Back to table of contents
Current source design
Figure 1. Diagram of a transformer for a welding machine.
Home-made contact-type welding uses, as a rule, an electrical circuit based on capacitors. The pulse of welding current in such sources is provided when the capacitor is discharged. One of the possible schemes is shown in Fig.1.
The pulse of welding current is formed in the secondary winding of the transformer Tr3. The primary winding of the transformer is connected to capacitors C8-C9, which provide the desired discharge. The capacitors are controlled by thyristors T1 and T2. The capacitor is charged on the auxiliary circuit from the input current transformer. The circuit provides for the rectification of the current diodes D6-D7.
Such a capacitor source works in the following order. When the main circuit is disconnected, the capacitors C8-C9 are charged from the transformer circuit Current. When the system is started, they are discharged to the secondary winding of the output transformer Tr3, in the control mode of the thyristors T1-T2. The pulse duration is controlled by the circuit Ru1-Ru2, R34 and C10. When you turn off the circuit, the process repeats.
Types and nominal values of details of the scheme are shown in Fig.1. Recommended parameters of the Transformer Current (220/220 V): the primary winding and both secondary windings are made of the PEV-2 wire with a diameter of 0.5 mm, the number of turns is 90.Back to table of contents
Homemade output transformer
Wiring of the output transformer.
The output transformer sets the strength of the welding current and is a very important element of the power supply design. To ensure the required welding parameters, it is advisable to make it yourself. First you need to pick up the transformer core. It can be used from any old power unit. The main thing is that the core should be made from steel plates, and the total cross-section of one rack should be about 65 sq. Cm. Steel plates fit tightly together and bolted with 8 mm diameter bolts. To increase the lateral strength of the core, it is advisable to strengthen the U-shaped profile or angle.
The primary winding is wound with a PEV or PETV wire with a diameter of 2.9 mm. The number of turns is 20. The core is wrapped with transformer or cable paper. Then coils of wire with tension are wound. You should strive for a uniform arrangement of coils along the length of the rack core. The ends of the winding are displayed on the upper part of the core and secured in the terminal block. A paper winding is applied over the wire and secured with tape.
The secondary winding is wound on the second rack of the core. The winding is made of a home-made flat-section tire assembled from 15-16 copper busbars. The total cross-section of the tire is about 200 square meters. mm The number of turns is 2. Before applying it to the core, the tire is wrapped with a fluoroplastic tape or a fabric insulating tape. Under the winding and on top of the winding paper is superimposed similarly to the primary winding. The ends of the winding are displayed on the upper part of the core. They make a hole for bolting the cable, departing to the contact block of the welding machine.
Such a transformer has the following characteristics: power 3000 W; the primary voltage is 220 V, the secondary voltage is 15 V. The welding current is up to 200 A.
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Current source assembly
The design of the current source.
It is advisable to assemble the welding current source inside one cabinet. The approximate size of such a metal cabinet is 50x80x40 cm. It is better to strengthen the bottom with corners, and install an output transformer on them. The electrical circuit (plateau) is assembled on a textolite panel, which is vertically fixed on the side inside the cabinet. The cabinet provides contact pads for electrical connection, as well as a bolt for grounding. All wire wiring inside the cabinet is collected in bunches and carefully laid along the wall. In the back wall, holes are drilled for the input of the electrical network and removal of the welding cable and cable (wire) to the start button.Back to table of contents
Contact block design
Depending on the type of resistance welding, several designs of the contact block can be recommended. The simplest design is provided for butt welding. In this case, the ends of the secondary winding are connected directly to the welded blanks. One end of the transformer winding is connected to one blank, and the other end to the other blank.
Spot welding involves the use of a contact block with electrodes. Designs can be used with one or two rod electrodes. In the case of using one electrode, the welding current is fed to one of the blanks, and the second end of the secondary winding of the output transformer is connected to the electrode.
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The use of a pistol type electrode holder is recommended.
The manufacture of the contact block type
Butt welding process.
The contact block for butt welding contains a stationary fastening of one of the welded blanks and a movable clip for the second blank. The block is assembled on the basis of a PCB with a thickness of at least 10 mm. Fixed clamp made of two steel parts. The lower case is a rectangular block 100x50x30 mm. In the upper part, a cutout of 50x20 mm is made to install the lower die and two threaded holes are drilled to secure the clip cover. Two threaded holes are drilled at the bottom of the case for attachment to the base.
The clamp cover is made of steel strip with a minimum thickness of 5 mm. The strip is attached to the U-shaped profile with bent ears for attachment to the body of the clip. U-shaped profile has dimensions equal to the size of the cutout in the body, and is designed to install the top plate. Holes are drilled in the ears. Dies are designed to clamp the workpiece to be welded and are made of steel bar size 50x20x30 mm. On the opposite sides of the dies, several (3-5 pieces) grooves are made parallel to each other according to the size of the intended blank. For fastening, the workpiece is installed between the dies, which are inserted into the body and the cover and clamped with screws.
The movable clamp is manufactured in the same way as a fixed clamp, but in the lower part of the body a longitudinal groove is made for installation in the guide runners. The runners themselves in the form of a U-shaped profile are mounted on the base of the block. The shift of the clamp itself is provided by an adjusting screw with a diameter of 10-15 mm and a length of up to 10 cm. The clip displacement unit is made of a steel strip with a minimum thickness of 5 mm. The strip bends at a right angle. Two threaded holes are drilled on the bottom for fastening to the base of the block. A threaded hole is drilled on the side surface to install the adjusting screw. This hole is drilled in the middle of the strip at a height of 20-25 mm from the base. The movement of the clamp along the guides is carried out due to the movement of the adjusting screw.Back to table of contents
The manufacture of the electrode unit
The scheme of the electrode unit for contact welding: a - butt; b - dotted; in - suture; 1 - welded product; 2 - electrodes; 3-transformer.
When using a contact block with a single electrode, a pistol type block is recommended. In this case, the clamping electrode is fixed in a homemade holder. Such a holder is made as follows. Two textolite plates with a thickness of about 10–15 mm are cut out in the form of a pistol 20–25 cm long. The barrel section is 40–45 mm wide, the handle is about 55 mm wide, and the handle is about 100 mm long. On the inner surface of the plates in the center of the barrel, a longitudinal circular groove with a radius of 5–8 mm for the electrode is made. The length of the groove, starting from the cut of the barrel, is 50-60 mm. At a distance of 35-40 mm from the cut of the trunk, a groove is made for installing a nut into which the electrode is twisted. In the kurkov part, two holes are drilled for fastening the starting button and a corresponding groove is made in the PCB to install the button body. To connect the plates together, they are drilled holes in them: four - in the handle, two each - in the receiver and rear parts of the gun. The handle is grooved for the institution of the welding cable.
The electrode is made of copper rod with a diameter of 8-10 mm. The end of the rod is sharpened on a cone. Electrode length about 50 mm. In the tail part of the carved.
The assembly is as follows. A fastening nut is screwed onto the electrode. The cable core is soldered to the end of the electrode. The electrode is installed in the groove of the plate so that its outreach from the holder is about 20 mm, and the nut enters the groove. The wire is laid on the groove. The start button is fixed. Plates of the holder are combined and fastened with screws.Back to table of contents
General assembly of the structure
The power supply is supplied from the mains. Connect the welding cable that connects the current source and the contact block. Clips of the free ends of the cable on the workpiece are carried out using "crocodiles", for example, from a car battery.
The tools needed to make a homemade welding machine:
- welding machine;
- soldering iron;
- electric drill;
- a set of taps and dies;
Resistance welding with your own hands is quite affordable and doable. Such welding greatly expands the capabilities of the home master.