Capacitor welding allows installation of fittings (pins, needles, etc.) to a metal base (badges, orders, etc.).

The fastener material can be steel (black, stainless, nickel-plated, copper-plated, etc., brass, aluminum, silver, gold). The main advantage of capacitor welding is the ability to weld fasteners to thin sheet steel (less than 1 mm) without visible weld marks on the reverse side of the metal. During the welding process, neither heating of the parts nor their deformation occurs. Another advantage of capacitor welding is high productivity.

The speed is limited only by the time of insertion of the welded element into the welding holder, and the welding process itself takes a fraction of a second. The number of welds is 20-30 pieces per minute.

For capacitor welding, special needles and pins must be used. They must have a small cylindrical protrusion (less than 1 mm) at the base. This protrusion serves as a fuse.

Needle with lock

Needle without lock

Threaded stud

The connection using capacitor welding is durable. When working on a fracture, the fasteners do not fall off.

Fixation of electrochemical protection (ECP) terminals

FARADAY capacitor welding machines are used to fix electrochemical protection (ECP) leads to the base of main gas and oil pipelines. Capacitor welding allows you to weld fasteners (usually studs) to any steel base in a short time (0.001-0.003 seconds), with a very small penetration depth (approximately 0.3 mm). At the same time, the strength of the connection remains high - under loads, the body of the fastening element itself is deformed, and not the welding site. The studs themselves can be made of coated steel (copper plating, nickel plating, etc.) or stainless steel. A special feature of the fasteners for capacitor welding is the presence of an igniter (protrusion at the base), which lights up when the capacitor bank is discharged. The sizes of studs for fixing ECP terminals can be from M3 to M10. The studs themselves may have an enlarged flange to ensure better contact of the ECP leads. Power source - single-phase network. You can also use the FARADAY installation when connected to a generator.

One of the biggest advantages of the technology is its ease of installation:

1. The steel is cleaned of scale, rust and dirt.

2. Welding of studs with a capacitor discharge.

3. Installation of ECP terminals will be provided.

Welding studs come with a special enlarged flange for better contact:

Installation process video:

Stars from the Avenue of Champions at the Rosa Khutor resort

In 2016, the Alley of Olympic Champions appeared at the Rosa Khutor ski resort. Read more about this news at the link.

Originally, the brass star pieces were attached to the granite using a two-part epoxy adhesive. Six months later, the parts came unstuck and it was necessary to make an alternative mount. On the reverse side, steel studs were welded to the brass parts of the stars using a FARADAY CD 1400 capacitor welding machine.

Capacitor welding has a distinctive feature, namely, the penetration is minimal and there are no signs of damage on the back side of the base, which is especially important when working with thin metal. The alteration of the stars took place directly at the facility. Next, the brass parts were fixed on a granite slab and, in this form, were installed on the resort embankment.

The welding strength of capacitor welding, despite the minimum level of penetration, is very high: under loads, deformation of the pin itself occurs, and not the welding site. The material of the studs can be different - steel, stainless steel, brass, aluminum.

Installation of heat meters using capacitor welding

One of the areas where capacitor welding is used is the installation of thermal energy meters on heating radiators. The meter is mounted on two welded studs with a diameter of M3 at the required distance from each other. Before welding, the paint must be stripped down to the metal at those points where the fasteners will be welded. Welding studs by capacitor welding is used for mounting heat meters on panel radiators and some types of convectors. The need to use capacitor welding is explained by the low level of penetration when installing fasteners, which cannot be achieved with other types of welding.

Installation of insulation using capacitor welding

Capacitor welding is often used to install insulation on a metal surface. Almost any material can be used as insulation: any roll insulation, polystyrene foam, sound-absorbing material, etc. The advantages of capacitor welding are the speed and reliability of fastening. In many cases, capacitor welding is the only way to avoid damage (burning through) thin-walled metal structures, since the level of melting is minimal, which can be important for ventilation equipment.

The most common method is to weld insulating nails and then secure the insulation with locking washers. Installation takes place in 3 stages:

1. An insulating nail, which has a special protrusion and serves as an igniter for capacitor welding, is welded onto a metal base. Nails come in 2 and 3 mm in diameter and up to 200 mm in length. Depending on the thickness and density of the insulating material per 1 square
meter will require 1-5 nails.

2. Suitable insulation material is threaded onto the welded insulation nails.

3. The insulation is fixed with locking washers, which are threaded onto welded nails. The washers are made of spring steel, usually galvanized. It is enough to place them on a nail by 2-3 mm for durable
fastening. The washers can be made with or without a plastic cap. The protruding part of the nail may be cut off or bent if the length is not selected accurately.

For welding nails, a standard set of equipment FARADAY CD 1400 is suitable

Installing insulation material using CHP cup nails

Capacitor welding allows installation of insulating material on metalsurface.

Almost any material can be used as insulation: any roll insulation, polystyrene foam, sound-absorbing material, etc. The advantages of capacitor welding are speed, reliability of fastening and aesthetic appearance. In many cases, capacitor welding is the only way to avoid damage (burning through) thin-walled metal structures, since the level of melting is minimal, which can be important for ventilation equipment.

When installing insulating material with cup nails, it is necessary to use a CHP welding gun, complete with a magnetic holder.

This method allows for very quick installation, since the nail is welded directly through the insulation and does not require any additional actions. When using cup-shaped nails, the aesthetic appearance is maintained after installation.

What is capacitor welding

Capacitor welding is a welding method in which a short-term powerful current pulse received from banks of static capacitors. Several varieties of K are known. s.: resistance (point, suture, butt), impact (butt), etc. TO . With . It is especially effective when connecting small parts and metal sheets of small thickness, for example, in the manufacture of parts for electronic tubes, small-sized instruments and apparatus, metal toys, haberdashery items, etc.

General Information Basic Techniques

Technological methods include spot, seam and butt capacitor welding.

• Spot welding is commonly used to make connections in electronics, vacuum technology, and precision instrumentation. Additionally, spot welding can be used to join parts with a large thickness ratio.

• Seam (roller) welding is usually used for welding sensitive elements of membrane or bellows types and electric vacuum devices. At its core, it is a series of point, overlapping connections that are a continuous, sealed seam. The electrodes are made in the form of rotating rollers.

• Butt welding is divided into fusion and resistance welding. Technologically, during melting, the discharge of the capacitor due to the increased voltage occurs before the direct contact of the parts being welded, melts their ends, and the connection itself occurs during upsetting. In the case of resistance welding, the capacitor discharge occurs at the moment of contact of the welded ends of the parts.

A special case of capacitor flash welding is the welding of fasteners: studs, bushings, nails, etc. Their diameter usually varies from 2 to 12 mm. A prerequisite is the presence at the base of the welded elements of an axial protrusion in the form of a cylinder with a diameter of 0.6 to 0.75 mm and a height of 0.55 to 0.75 mm. This serves two purposes:

• Allows you to accurately determine, by preliminary punching, the welding location of the element on the surface of the workpiece.
• Provides ignition and stable burning of the welding arc over the entire surface of the welded element when discharging the capacitor.

Main advantages

1. High performance.
2. Minimum thermally affected zone due to high energy density and short pulse duration.
3. Connection strength.
4. Simplicity of technology that does not require highly qualified personnel.
5. Uniformity of the electrical load at high welding currents.

Some disadvantages

1. Limitations on maximum sections.
2. The need for special equipment.

Capacitor welding technology

In the process of manufacturing various products from sheet metal, during installation and repair work, the need arises to connect various parts through assembly.

Until now, production facilities in Russia use outdated technologies. There are few options. This is drilling holes for fasteners of various types (bolts with nuts, rivets of various types) or welding bolts and nuts using argon-arc welding or semi-automatic welding using welding wire and shielding gas. These technological processes have significant disadvantages: firstly, making holes in the supporting structures weakens their strength, secondly, many products require tightness, but with holes this is difficult to achieve, thirdly, the appearance of any device or equipment will be spoiled the presence of screw heads or rivet heads, and lastly, when welding, especially on a thin sheet, burnt spots and darkening appear. The technology of welding fasteners using capacitor welding does not have all these disadvantages.

Capacitor Discharge CD -This is the ability to very firmly and quickly weld fasteners to thin sheet metal with a thickness of 0.5 mm without visible damage on the back side of the sheet. A second equally important advantage is that welding fasteners to various metals does not require shielding gas or protective ceramic rings used in arc welding (ARC). The welding process is fully automated and no special qualifications are required to operate capacitor welding machines. Various equipment is produced for capacitor welding, from inexpensive manual models to fully automated lines, as well as a fairly large assortment of inexpensive welded hardware

The theory of capacitor welding (CD) welding process.

In this welding process, electrical energy stored in a high-capacity capacitor bank is discharged through the protruding tip of the base of the fastener being welded. The discharge period lasts 1-3 ms . (0.001-0.003 seconds). There are two methods for welding fasteners using the capacitor discharge (CD) method.

First way contact type includes the following sequential cycles:

1. The fastener to be welded is installed in a contact-type welding gun, positioned in the desired location and pressed against the surface. The required clamping force is set by a spring in the welding gun.

2. The welding process starts and an electric arc occurs between the base of the fastener and the metal surface, which melts the surface of the base of the fastener and the place on the metal surface under the base of the fastener.

3. The fastening element, after melting the protruding tip of the base under the force of the spring of the welding gun, is pressed against the metal surface and pressed into the melt formed under it.

Second way with preliminary lifting of the fastener:

1. The fastener to be welded is installed in a lift-type welding gun, positioned in the desired location and pressed against the surface. The required clamping force is set in the welding gun.

2. At the moment the welding process starts, the welding gun lifts the welded element above the metal surface, due to this the electrical contact is broken and electric potential is supplied to the fastening element from the capacitor battery of the power unit.

3. The raised fastener, under the action of the spring force in the welding gun, falls down and at the moment the protruding tip of the base touches the metal surface, an electrical contact appears, an electric arc occurs, which melts the surface of the base of the fastener and the place on the metal surface under the base of the fastener.

4. After melting the protruding tip of the base, the fastening element is pressed against the metal surface and pressed into the melt formed underneath

Capacitor welding using the contact method is used for welding fasteners made of ordinary and stainless steel, as well as brass.

Capacitor welding using the pre-lift method is used primarily for welding aluminum fasteners, but can also be used for steel, stainless steel, and brass fasteners.

Standard types of welded hardware

For welding using the capacitor welding method, special hardware is used, equipped with a special ignition tip. The following materials are used in their production: copper-plated steel, stainless steel, aluminum and brass. The industry produces both standard types of fasteners and special-purpose fasteners produced to order. A characteristic feature of hardware for capacitor welding is a special tip of calibrated size, which performs a dual task:

• Allows you to accurately determine the place where the hardware will be welded on the surface of the workpiece by preliminary core punching;
• Ensuring ignition and stable burning of the welding arc over the entire surface of the welded hardware when a capacitor discharge passes through it.

Setting up the FARADAY capacitor welding machine (Faraday)

The mechanical characteristics of the weld are determined by correctly setting the welding parameters, which includes:

• selection of the discharge energy value by changing the voltage of the capacitor bank,
• adjusting the pressure spring force of the welding gun and the gap between the hardware and the collet;
• proper organization of grounding;
• correct selection of combinations of materials to be welded;

Selecting the discharge energy value

The optimal welding voltages for the steel-steel material combination are given in the tables for both machines. For other material combinations, the optimum voltage may differ slightly from the recommended voltage and must be determined experimentally.

D, diameter	FARADAY CD 1400
	U, voltage	P, power
3 mm	70 V	162 J
4 mm	100 V	330 J
5 mm	115 V	436 J
6 mm	140 V	648 J
7 mm	180 V	1070 J
8 mm	200 V	1320 J

Setting up a gun for welding hardware

The force of the pressure spring of the welding gun affects the quality of welding significantly less than the voltage; the duration of the welding cycle mainly depends on it; the greater the force, the shorter the welding time.

Setting up the hardware collet

Collets for installing welding gun hardware DC same type. They differ only in the diameter of the internal hole to allow installation of hardware of different diameters. Collets for welding grounding tabs and nails have a different design.

1. Hardware

2. Collet

3. Lock nut

4. Locking screw

Different diameters of hardware require different collets. Set up the hardware collet as follows:

• Loosen the lock nut (3)
• Insert the hardware (1) into the collet.
• The distance between the leading edge of the hardware flange and the end of the collet should be within approximately 5 mm (as shown in the figure).
• The hardware must come into contact with the locking screw (4). (IMPORTANT!)
• Adjust the locking screw (4) in the hardware collet by rotating it until the distance from the leading edge of the hardware flange to the end of the collet is 5 mm.
• Secure the locking screw (4) with the locknut (3)
• For hardware from 20 to 40 mm long. The locking screw must be turned over with the threaded end inside the cage.

Installing a hardware collet into a welding gun

The illustration below shows how to install the collet into the gun DC for welding hardware. Welding gun DC may have a removable support pipe instead of support legs (1).

• Loosen the lock nut (3) with a socket wrench;
• Insert the hardware collet (2) into the spring piston (5) until it stops.
• Secure the collet (2) by tightening the lock nut (3).

The hardware flange must extend beyond the tops of the gun support legs or support tube. If this is not the case, remove the hardware clip from the gun and adjust the protrusion of the hardware using the collet locking screw!

Grounding rules

Due to the short welding time, in order to obtain a uniform weld over the entire base area of ​​the hardware, it is necessary to properly ground the working surface. All capacitor welding machines are supplied with two grounding cables. Grounding should be done on both sides of the welding site, and one should strive to ensure that the path for the welding current to pass is approximately the same for each grounding cable. If grounding is carried out only on one side, or there are massive metal parts in the path of the current, the distribution of the welding current will be asymmetrical relative to the base of the hardware and the quality of welding on different sides of the base may be different (the “arc blowing” effect).

Selecting material combinations for welding

When choosing combinations of base materials and welded products, you can use the following table:

MATERIAL BASICS	HARDWARE MATERIAL
	Mild steel Art.35	Stainless steel Cr-Ni	Aluminum Al 99.5, AlMg 1-5	Brass CuZn 37
Mild steel, St.35	Great	Great	Badly	Great
Medium carbon steel, St.60	Fine	Fine	Badly	Fine
Cink Steel	Fine	Fine	Badly	Badly
Stainless steel, Cr-Ni	Great	Great	Badly	Great
Brass, CuZn 37-30	Fine	Fine	Badly	Great
Copper, Cu	Fine	Fine	Badly	Great
Aluminum, Al 99.5, AlMg 1-5	Badly	Badly	Great	Badly
Excellent: the materials are fully compatible and the weld is very strong. Good: materials are conditionally compatible, weld quality is acceptable. Poor: materials are incompatible, weld is missing or very weak.

Methods for positioning hardware during welding

Core welding

The welding location can be indicated by punching the working surface. Since the welding process begins by igniting the welding tip of the hardware, punching too deeply will not provide optimal welding conditions. Welding will either not happen at all or the welding quality will be unacceptable. For high-quality welding, core punching should be carried out to a depth of no more than 0.3 mm. It is convenient to use a special tool for these purposes - an automatic core.

Pattern welding

In mass production, a template must be used for fast and accurate welding. In this case, a centering washer must be installed on the gun.

The template can be made of any non-flammable material to eliminate the possibility of fire, and there must be a gap of at least 3 mm between the template and the surface to be welded to remove welding gases and splashes of molten metal.

Welding sequence

• Connect the FARADAY power unit to mains and ground.
• Connect the welding gun.
• Set up the gun as described above.
• Connect the power supply to AC power.
• Set up the power supply for welding the hardware you intend to use.
• Insert the welding hardware into the collet.
• Hold the welding gun with both hands and place it in the working position on the workpiece and press vertically onto the surface of the workpiece.
• Hold the welding gun calmly and operate the trigger button. The welding process has begun.
• After welding, remove the welding gun vertically from the welded bolt, which will avoid expansion of the collet.
• Check the weld results according to the recommendations below.
• Upon completion of welding, disconnect the welding unit from the network and eliminate the possibility of operation by incompetent persons

1. Make sure there are good electrical connections at the power supply connectors, the collet mount in the gun, and the ground terminals.
2. Before welding, make sure that the welding cables do not form loops. This can avoid strong electromagnetic interference when large pulse currents pass through them.
3. Make sure the ground terminals are secured symmetrically and not too close to the welding area. This will avoid weld defects caused by the arc blowing effect.
4. Make sure that the workpieces are securely fastened and do not bend under the pressure of the welding gun. This applies especially to thin sheet materials.
5. The welding area must be cleaned down to metal; rust, grease or paint should not be present in the welding area. Anodized surfaces must be pre-treated with alkali. M The maximum roughness of the welding zone should not exceed 80 µm.
6. The materials of the surfaces to be welded must be compatible (see material compatibility table). If there are doubts about the compatibility of materials, it is necessary to carry out test welding with subsequent quality control.
7. There must be at least 40 mm around the welding area. free space for positioning the gun or centering attachment.
8. Make sure the welding voltage and gun settings are correct before welding.
9. At the time of welding, the gun and the workpiece must be motionless and positioned strictly perpendicular to each other.
10. Always make test welds to ensure all settings are correct.

1. Physical foundations of welding

Welding is a technological process of obtaining a permanent connection of materials due to the formation of an atomic bond. The process of creating a welded joint occurs in two stages.

At the first stage, it is necessary to bring the surfaces of the materials being welded closer to the distance of action of interatomic interaction forces (about 3 A). Ordinary metals at room temperature do not bond when compressed even with significant forces. The joining of materials is hampered by their hardness; when they come together, actual contact occurs only at a few points, no matter how carefully they are processed. The joining process is strongly influenced by surface contamination - oxides, fatty films, etc., as well as layers of absorbed impurity atoms. Due to these reasons, it is impossible to fulfill the condition of good contact under normal conditions. Therefore, the formation of physical contact between the joined edges over the entire surface is achieved either due to the melting of the material or as a result of plastic deformations resulting from the applied pressure. At the second stage, electronic interaction occurs between the atoms of the surfaces being connected. As a result, the interface between the parts disappears and either atomic metal bonds are formed (metals are welded) or covalent or ionic bonds are formed (when welding dielectrics or semiconductors). Based on the physical essence of the process of formation of a welded joint, three classes of welding are distinguished: fusion welding, pressure welding and thermomechanical welding (Fig. 1.25).

Rice. 1.25.

For fusion welding These are types of welding carried out by fusion without applied pressure. The main sources of heat in fusion welding are the welding arc, gas flame, beam energy sources and “Joule heat”. In this case, the melts of the metals being joined are combined into a common weld pool, and upon cooling, the melt crystallizes into a cast weld.

For thermomechanical welding thermal energy and pressure are used. The joining of the connected parts into a monolithic whole is carried out through the application of mechanical loads, and heating of the workpieces ensures the necessary plasticity of the material.

For pressure welding refers to operations carried out with the application of mechanical energy in the form of pressure. As a result, the metal becomes deformed and begins to flow like a liquid. The metal moves along the interface, taking the contaminated layer with it. Thus, fresh layers of material come into direct contact, which enter into chemical interaction.

2. Main types of welding

Manual electric arc welding. Electric arc welding is currently the most important type of metal welding. The heat source in this case is an electric arc between two electrodes, one of which is the workpiece being welded. An electric arc is a powerful discharge in a gaseous environment.

The arc ignition process consists of three stages: short circuit of the electrode to the workpiece, withdrawal of the electrode by 3-5 mm and the occurrence of a stable arc discharge. A short circuit is performed in order to heat the electrode (cathode) to the temperature of intense exo-emission of electrons.

At the second stage, electrons emitted by the electrode are accelerated in the electric field and cause ionization of the cathode-anode gas gap, which leads to the occurrence of a stable arc discharge. An electric arc is a concentrated source of heat with temperatures up to 6000 °C. Welding currents reach 2-3 kA at arc voltage (10-50) V. Covered electrode arc welding is most often used. This is manual arc welding with an electrode coated with an appropriate composition that has the following purpose:

1. Gas and slag protection of the melt from the surrounding atmosphere.

2. Alloying the weld material with the necessary elements.

The composition of the coatings includes substances: slag-forming substances - to protect the melt with a shell (oxides, feldspars, marble, chalk); forming gases CO2, CH4, CCl4; alloying - to improve the properties of the weld (ferrovanadium, ferrochrome, ferrotitanium, aluminum, etc.); deoxidizers - to eliminate iron oxides (Ti, Mn, Al, Si, etc.) Example of a deoxidation reaction: Fe2O3+Al = Al2O3+Fe.

Rice. 1.26. : 1 - parts to be welded, 2 - weld seam, 3 - flux crust, 4 - gas protection, 5 - electrode, 6 - electrode coating, 7 - weld pool

Rice. Figure 1.26 illustrates coated electrode welding. According to the above diagram, a welding arc is ignited between the parts (1) and the electrode (6). When melted, the coating (5) protects the weld from oxidation and improves its properties by alloying. Under the influence of the arc temperature, the electrode and the workpiece material melt, forming a weld pool (7), which subsequently crystallizes into a weld seam (2), on top of which the latter is covered with a flux crust (3), designed to protect the seam. To obtain a high-quality seam, the welder places the electrode at an angle of (15-20)0 and moves it downward as it melts to maintain a constant arc length (3-5) mm and along the axis of the seam to fill the seam groove with metal. In this case, the end of the electrode usually makes transverse oscillatory movements to obtain rollers of the required width.

Automatic submerged arc welding.

Automatic welding with a consumable electrode under a layer of flux is widely used. The flux is poured onto the product in a layer (50-60) mm thick, as a result of which the arc burns not in the air, but in a gas bubble located under the flux melted during welding and isolated from direct contact with air. This is enough to eliminate splashing of liquid metal and disruption of the shape of the seam, even at high currents. When welding under a layer of flux, a current of up to (1000-1200) A is usually used, which is impossible with an open arc. Thus, in submerged arc welding, the welding current can be increased by 4-8 times compared to open arc welding, while maintaining good welding quality and high productivity. In submerged arc welding, the weld metal is formed by melting the base metal (about 2/3) and only about 1/3 by the electrode metal. The arc under a layer of flux is more stable than with an open arc. Welding under a layer of flux is carried out with bare electrode wire, which is fed from a reel into the arc burning zone by the welding head of an automatic machine, which is moved along the seam. Ahead of the head, granular flux enters the weld through the pipe, which, melting during the welding process, evenly covers the seam, forming a hard slag crust.

Thus, automatic welding under a layer of flux differs from manual welding in the following indicators: stable quality of the seam, productivity is (4-8) times greater than with manual welding, thickness of the flux layer - (50-60) mm, current strength - ( 1000-1200) And, the optimal arc length is maintained automatically, the seam consists of 2/3 of the base metal and 1/3 of the arc burns in a gas bubble, which ensures excellent welding quality.

Electroslag welding.

Electroslag welding is a fundamentally new type of metal joining process, invented and developed at the Electric Welding Institute named after. Paton. The parts to be welded are covered with slag, heated to a temperature exceeding the melting point of the base metal and electrode wire.

At the first stage, the process proceeds in the same way as with submerged arc welding. After the formation of a bath of liquid slag, the burning of the arc stops and the melting of the edges of the product occurs due to the heat released when current passes through the melt. Electroslag welding allows you to weld large thicknesses of metal in one pass, provides greater productivity, and high quality welds.

Rice. 1.27. :

1 - parts to be welded, 2 - weld seam, 3 - molten slag, 4 - sliders, 5 - electrode

The electroslag welding diagram is shown in Fig. 1.27. Welding is carried out with a vertical arrangement of parts (1), the edges of which are also vertical or have an inclination of no more than 30 o to the vertical. A small gap is installed between the parts to be welded, into which slag powder is poured. At the initial moment, an arc is ignited between the electrode (5) and the metal strip installed below. The arc melts the flux, which fills the space between the edges of the parts being welded and the water-cooled copper forming slides (4). Thus, a slag bath (3) appears from the molten flux, after which the arc is shunted by the molten slag and goes out. At this point, electric arc melting turns into an electroslag process. When current passes through molten slag, Joule heat is released. The slag bath is heated to temperatures (1600-1700) 0C, exceeding the melting point of the base and electrode metals. The slag melts the edges of the parts being welded and the electrode immersed in the slag bath. The molten metal flows to the bottom of the slag pool, where it forms a weld pool. The slag pool reliably protects the weld pool from the surrounding atmosphere. After removing the heat source, the metal of the weld pool crystallizes. The formed seam is covered with a slag crust, the thickness of which reaches 2 mm.

A number of processes contribute to improving the quality of the weld in electroslag welding. In conclusion, we note the main advantages of electroslag welding.

Gas bubbles, slag and light impurities are removed from the welding zone due to the vertical position of the welding device.

High weld density.

The weld seam is less susceptible to cracking.

The productivity of electroslag welding for large material thicknesses is almost 20 times higher than that of automatic submerged arc welding.

It is possible to obtain seams of complex configuration.

This type of welding is most effective when joining large parts such as ship hulls, bridges, rolling mills, etc.

Electron beam welding.

The heat source is a powerful beam of electrons with an energy of tens of kiloelectronvolts. Fast electrons, penetrating into the workpiece, transfer their energy to the electrons and atoms of the substance, causing intense heating of the welded material to the melting point. The welding process is carried out in a vacuum, which ensures high quality seams. Due to the fact that the electron beam can be focused to very small sizes (less than a micron in diameter), this technology is exclusive to welding micro parts.

Plasma welding.

In plasma welding, the source of energy for heating the material is plasma - ionized gas. The presence of electrically charged particles makes plasma sensitive to the effects of electric fields. In an electric field, electrons and ions are accelerated, that is, they increase their energy, and this is equivalent to heating the plasma up to 20-30 thousand degrees. Arc and high-frequency plasma torches are used for welding (see Fig. 1.17 - 1.19). For welding metals, as a rule, direct plasma torches are used, and for welding dielectrics and semiconductors, indirect plasma torches are used. High-frequency plasma torches (Fig. 1.19) are also used for welding. In the plasmatron chamber, the gas is heated by eddy currents created by high-frequency currents of the inductor. There are no electrodes, so the plasma is highly pure. A torch of such plasma can be effectively used in welding production.

Diffusion welding.

The method is based on the mutual diffusion of atoms in the surface layers of contacting materials under high vacuum. The high diffusivity of atoms is ensured by heating the material to a temperature close to the melting point. The absence of air in the chamber prevents the formation of an oxide film that could impede diffusion. Reliable contact between the welded surfaces is ensured by mechanical processing to a high class of cleanliness. The compressive force required to increase the actual contact area is (10-20) MPa.

The diffusion welding technology is as follows. The workpieces to be welded are placed in a vacuum chamber and compressed with slight force. Then the workpieces are heated with current and kept for some time at a given temperature. Diffusion welding is used to join poorly compatible materials: steel with cast iron, titanium, tungsten, ceramics, etc.

Contact electric welding.

In electric resistance welding, or resistance welding, heating is achieved by passing an electric current from a sufficient needle through the weld site. Parts heated by electric current to a melting or plastic state are mechanically compressed or upset, which ensures the chemical interaction of metal atoms. Thus, resistance welding belongs to the group of pressure welding. Resistance welding is one of the high-performance welding methods; it can easily be automated and mechanized, as a result of which it is widely used in mechanical engineering and construction. Based on the shape of the connections being made, there are three types of resistance welding: butt, roller (suture) and spot welding.

Butt contact welding.

This is a type of contact welding in which the parts to be welded are connected along the surface of the butt ends. The parts are clamped in sponge electrodes, then pressed against each other by the surfaces to be joined and the welding current is passed through. Butt welding is used to connect wire, rods, pipes, strips, rails, chains and other parts over the entire area of ​​their ends. There are two methods of butt welding:

Resistance: plastic deformation occurs at the joint and the joint is formed without melting the metal (the temperature of the joints is 0.8-0.9 from the melting temperature).

By melting: the parts come into contact at the beginning at separate small contact points through which a high-density current passes, causing the parts to melt. As a result of melting, a layer of liquid metal is formed at the end, which, during sedimentation, along with contaminants and oxide films, is squeezed out of the joint.

Table 1.4

Parameters of Butt Welding Machines

Machine type	W,(kVA)	U slave,(B)	Welding per hour.	F,(kN)

Column designations: W - machine power, Uwork - operating voltage, productivity, F - compression force of welded parts, S - area of ​​the welded surface.

Heating temperature and compressive pressure during butt welding are interrelated. As follows from Fig. 1.28, the force F decreases significantly with increasing heating temperature of the workpieces during welding.

Seam contact welding.

A type of resistance welding in which the elements are overlapped with rotating disk electrodes in the form of a continuous or intermittent seam. In seam welding, the formation of a continuous joint (seam) occurs by sequentially overlapping points one after another; to obtain a hermetic seam, the points overlap each other by at least half their diameter. In practice, seam welding is used:

Continuous;

Intermittent with continuous rotation of the rollers;

Intermittent with periodic rotation.

Rice. 1.28.

Seam welding is used in mass production in the manufacture of various vessels. It is carried out using alternating current with a force of (2000-5000) A. The diameter of the rollers is (40-350) mm, the compression force of the welded parts reaches 0.6 tons, the welding speed is (0.53.5) m/min.

Spot resistance welding.

In spot welding, the parts to be joined are usually placed between two electrodes. Under the action of a pressure mechanism, the electrodes tightly compress the parts to be welded, after which the current is turned on. Due to the passage of current, the parts being welded quickly heat up to the welding temperature. The diameter of the molten core determines the diameter of the weld spot, usually equal to the diameter of the electrode contact surface.

Depending on the location of the electrodes in relation to the parts being welded, spot welding can be double-sided or single-sided.

When spot welding parts of different thicknesses, the resulting asymmetrical core is shifted towards the thicker part and, if there is a large difference in thickness, does not capture the thin part. Therefore, various technological methods are used to ensure the displacement of the core to the mating surfaces, increase the heating of a thin sheet due to overlays, create a relief on a thin sheet, use more massive electrodes on the side of a thick part, etc.

A type of spot welding is relief welding, when the initial contact of parts occurs along previously prepared protrusions (reliefs). The current, passing through the place where all the reliefs touch the lower part, heats them and partially melts them. Under pressure, the reliefs are deformed, and the upper part becomes flat. This method is used for welding small parts. In table 1.5 shows the characteristics of machines for spot welding.

Table 1.5

Characteristics of Spot Welding Machines

Machine type	W,(kVA)	U slave,(B)	D,(mm)	F,(kN)	Welding per hour

Column designations: W - machine power, irab - operating voltage, D - electrode diameter, F - compression force of welded parts, welds per hour - productivity.

Spot capacitor welding.

One of the common types of resistance welding is capacitor welding or welding with stored energy stored in electric capacitors. Energy in capacitors is accumulated when they are charged from a constant voltage source (generator or rectifier), and then, during the discharge process, is converted into heat used for welding. The energy stored in capacitors can be regulated by changing the capacitance of the capacitor (C) and the charging voltage (U).

There are two types of capacitor welding:

Transformerless (capacitors are discharged directly onto the parts being welded);

Transformer (the capacitor is discharged onto the primary winding of the welding transformer, in the secondary circuit of which there are pre-compressed parts to be welded).

The schematic diagram of capacitor welding is shown in Fig. 1.29.

Rice. 1.29. : Tr - step-up transformer, B - rectifier, C - capacitor with a capacity of 500 μF, Rk - resistance of the parts being welded, K - key switch

In switch position 1, the capacitor is charged to voltage U0. When the switch is moved to position. 2, the capacitor is discharged through the contact resistance of the parts being welded. This creates a powerful current pulse.

The voltage from the capacitor is supplied to the workpiece through point contacts with an area of ​​~ 2 mm. The resulting current pulse, in accordance with the Joule-Lenz law, heats the contact area to the operating temperature of welding. To ensure reliable pressing of the welded surfaces, a mechanical stress of about 100 MPa is transmitted to the parts through point electrodes.

The main application of capacitor welding is to join metals and alloys of small thicknesses. The advantage of capacitor welding is its low power consumption.

To determine the efficiency of welding, we estimate the maximum temperature in the area of ​​​​contact of the parts being welded (Tmax).

Due to the fact that the duration of the discharge current pulse does not exceed 10 -6 s, the calculation was carried out in the adiabatic approximation, that is, neglecting heat removal from the region of current flow.

The principle of contact heating of parts is shown in Fig. 1.30.

Rice. 1.30.: 1 - parts to be welded with thickness d = 5*10 -2 cm, 2 - electrodes with area S = 3*10 -2 cm, C - capacitor with a capacity of 500 μF, Rk - contact resistance

The advantage of capacitor welding is its low power consumption, which is (0.1-0.2) kVA. The duration of the welding current pulse is thousandths of a second. The range of welded metal thicknesses is from 0.005 mm to 1 mm. Capacitor welding allows you to successfully join thin metals, small parts and micro parts that are poorly visible to the naked eye and require the use of optical instruments during assembly. This progressive welding method has found application in the production of electrical measuring instruments and aircraft instruments, watch mechanisms, cameras, etc.

Cold welding.

The connection of workpieces during cold welding is carried out by plastic deformation at room and even at negative temperatures. The formation of a permanent connection occurs as a result of the emergence of a metallic bond when the contacting surfaces approach each other to a distance at which the action of interatomic forces is possible, and as a result of a large compression force, the oxide film breaks and clean metal surfaces are formed.

The surfaces to be welded must be thoroughly cleaned of adsorbed impurities and fatty films. Cold welding can be used to make spot, seam and butt joints.

In Fig. Figure 1.31 shows the cold spot welding process. Sheets of metal (1) with a thoroughly cleaned surface at the welding site are placed between punches (2) having projections (3). The punch is compressed with some force P, the projections (3) are pressed into the metal to their entire height until the supporting surfaces (4) of the punches rest against the outer surface of the workpieces being welded.

Rice. 1.31.

Cold welding is used to make overlapped and butt joints of wires, busbars, and pipes. The pressure is selected depending on the composition and thickness of the material being welded; on average it is (1-3) GPa.

Induction welding.

This method is used primarily to weld longitudinal seams of pipes during their manufacture on continuous mills and to deposit hard alloys on steel bases in the manufacture of cutters, drill bits and other tools.

With this method, the metal is heated by passing high-frequency currents through it and is compressed. Induction welding is convenient because it is non-contact; high-frequency currents are localized near the surface of the heated workpiece. Such installations work as follows. The high-frequency generator current is supplied to the inductor, which induces eddy currents in the workpiece, and the pipe heats up. Mills of this type are successfully used for the production of pipes with a diameter of (12-60) mm at speeds of up to 50 m/min. The current is supplied from tube generators with a power of up to 260 kW at a frequency of 440 kHz and 880 kHz. Pipes of large diameters (325 mm and 426 mm) with a wall thickness of (7-8) mm, with a welding speed of up to (30-40) m/min are also manufactured.

Features of welding various metals and alloys

Weldability is understood as the ability of metals and alloys to form a joint with the same properties as the metals being welded, and not to have defects in the form of cracks, pores, cavities and non-metallic inclusions.

When welding, residual welding stresses almost always occur (usually tensile stresses in the weld and compressive stresses in the base metal). To stabilize the properties of the connection, it is necessary to reduce these voltages.

Welding carbon steels.

Electric arc welding of carbon and alloy steels is carried out with electrode materials that provide the necessary mechanical properties. The main difficulty in this case lies in the hardening of the heat-affected zone and the formation of cracks. To prevent the formation of cracks, it is recommended:

1) heat products to temperatures (100-300) 0C;

2) replace single-layer welding with multi-layer welding;

3) use coated electrodes (welding is carried out using direct current of reverse polarity);

4) temper the product after welding to a temperature of 300 0C.

Welding of high chromium steels.

High-chromium steels containing (12-28)% Cr have stainless and heat-resistant properties. Depending on the content of chromium and carbon, high-chromium steels are divided according to their structure into ferritic, ferritic-martensitic and martensitic.

Difficulties in welding ferritic steels are associated with the fact that during the cooling process in the region of 1000 0C, chromium carbide may precipitate at the grain boundaries. This reduces the corrosion resistance of steel. To prevent these phenomena it is necessary:

1) use reduced current values ​​in order to ensure high cooling rates during welding;

2) introduce strong carbide formers (Ti, Cr, Zr, V) into the steel;

3) anneal after welding at 900 0C to level the chromium content in the grains and at the boundaries.

Ferrite-martensitic and martensitic steels are recommended to be welded with heating to (200-300) 0C.

Welding cast iron.

Welding of cast iron is carried out with heating to (400-600) 0C. Welding is carried out with cast iron electrodes with a diameter of (8-25) mm. Good results are obtained by diffusion welding of cast iron to cast iron and cast iron to steel.

Welding of copper and its alloys.

The weldability of copper is negatively affected by impurities of oxygen, hydrogen, and lead. The most common is gas welding. Arc welding with carbon and metal electrodes is promising.

Aluminum welding.

Welding is hampered by the Al2O3 oxide film. Only the use of fluxes (NaCl, RCl, LiF) makes it possible to dissolve aluminum oxide and ensure normal formation of the weld. Aluminum is welded well by diffusion welding.

Technical documentation is a kind of book for designers, planners, engineers, craftsmen and workers. It is compiled (written) according to certain rules and requirements. This is required for a correct understanding of the information presented. One area of ​​technical text is the identification of welds on drawings.

The welding process is a technological operation of forming a monolithic joint. The area where the material of the joined parts melted and solidified is called a weld.

Kinds

The welded joint is divided into:

• Stykova. The connection is formed along the end surfaces of the parts. It is carried out with or without edge processing. Marking "C".

• Overlapping. The planes of the parts are parallel to each other and partially overlap one another. Marking "N".

The seam is performed:

• Unilateral. Deposition is carried out on one side of the connection (joint).

• Bilateral. Processing occurs on both sides.

Necessity of welding designation

Any structure consists of individual parts (assemblies) connected to each other in one way or another. One of them is welding. The joint has its own characteristics that affect the performance of the product as a whole.

The welding designation in the drawing is an explanation of the joining method, the shape of the seam and its geometric parameters, the method of execution and other additional information. A competent engineer will gain additional information:

• about strength - the connection is continuous or intermittent; in addition, thermal stresses are formed in the weld zone;
• about the size and shape of the deposited metal;
• joint tightness;
• connection time - before installation or during its process, and others.

Explanation of technical abbreviation

Studying the designation of a weld in a drawing can be done in two ways:

• start with the basics - reading specialized literature, including GOSTs (analogue - learning letters in the ABC);
• go from the opposite, that is, start by looking at examples of how welding is indicated in the drawings, with a gradual deepening of your knowledge.

Examples

The marking of the welding joint is regulated by the ESKD. It includes:

• GOST 2.312-72.
• GOST 5264-80.
• GOST 14771-76.

According to GOST, a welded joint is indicated in the technical documentation by an extended arrow:

The location of the inscription above the arrow, below it, or on both sides indicates the location of the connection:

• from the front part of the part;
• from the reverse (invisible joint);
• two-sided processing.

The inscription and arrow indicate the back (closed) or front part, respectively.

Example 2.

• Made on one side, with a curved edge, open loop, according to GOST 5264-80 standards, electric arc welding.

Example 3.

• - the connection is made along a continuous line in the form of a ring;
• GOST 17771-76 - welding in a gas cloud;
• T3 - T-joint with processing on each side; there is no edge cutting;
• UP - gaseous carbon monoxide, molten electrode;
• 6 - the size of the welding joint leg is 6 mm;
• Periodic design with a welded continuous section of 50 mm in a checkerboard pattern (Z), pitch 100 mm.

Markings are conventionally drawn above (under) the shelf of the extension arrow:

Used auxiliary signs

Welding designations (excerpts from regulatory documentation) for different methods of operation (manual electric arc, argon) are summarized in the table:

Methods for making a weld are reflected in GOST:

• A - automatic joining with flux in the absence of a lining, pillow, without a preliminary seam;
• Af - automatic welding using flux and a pad based on it;
• IN - docking is carried out using a refractory tungsten alloy electrode in a cloud of gases without adding additional material;
• INP - docking is performed with a tungsten electrode in a cloud of inert gases with the addition of additional material;
• IP - the use of a melting electrode in a cloud of gases;
• UP - connection in a carbon monoxide environment through a melting electrode.

In general, deciphering and reading the designation of welds in documentation is almost the same as learning to read the ABC or Primer. It is required to remember the regulatory documents (GOST) and correctly decipher the symbols shown on the drawings.

Spot welding is a type of resistance welding. With this method, heating the metal to its melting temperature is carried out by heat, which is generated when a large electric current passes from one part to another through the place of their contact. Simultaneously with the passage of current and some time after it, the parts are compressed, resulting in mutual penetration and fusion of heated areas of the metal.

Features of resistance spot welding are: short welding time (from 0.1 to several seconds), high welding current (more than 1000A), low voltage in the welding circuit (1-10V, usually 2-3V), significant force compressing the welding site (from several tens to hundreds of kg), a small melting zone.

Spot welding is most often used for overlapping sheet metal workpieces, and less often for welding rod materials. The range of thicknesses welded by it ranges from a few micrometers to 2-3 cm, but most often the thickness of the welded metal varies from tenths to 5-6 mm.

In addition to spot welding, there are other types of resistance welding (butt, seam, etc.), but spot welding is the most common. It is used in the automotive industry, construction, radio electronics, aircraft manufacturing and many other industries. During the construction of modern airliners, in particular, several million weld spots are produced.

Well-deserved popularity

The great demand for spot welding is due to a number of advantages that it has. These include: no need for welding materials (electrodes, filler materials, fluxes, etc.), minor residual deformations, simplicity and convenience of working with welding machines, neat connections (virtually no weld), environmental friendliness, cost-effectiveness, susceptibility to easy mechanization and automation, high productivity. Automatic spot welders are capable of performing up to several hundred welding cycles (welded spots) per minute.

Disadvantages include the lack of sealing of the seam and stress concentration at the welding point. Moreover, the latter can be significantly reduced or even eliminated using special technological methods.

Sequence of processes for resistance spot welding

The entire spot welding process can be divided into 3 stages.

• Compression of parts causing plastic deformation of microroughnesses in the electrode-part-part-electrode chain.
• Turning on a pulse of electric current, leading to heating of the metal, its melting in the joint zone and the formation of a liquid core. As current passes, the core increases in height and diameter to its maximum size. Bonds are formed in the liquid phase of the metal. In this case, plastic settlement of the contact zone continues to its final size. Compression of the parts ensures the formation of a sealing belt around the molten core, which prevents metal from splashing out from the welding zone.
• Turning off the current, cooling and crystallization of the metal, ending with the formation of a cast core. When cooling, the volume of the metal decreases and residual stresses arise. The latter are an undesirable phenomenon that is combated in various ways. The force compressing the electrodes is released with some delay after the current is turned off. This provides the necessary conditions for better crystallization of the metal. In some cases, in the final stage of resistance spot welding, it is even recommended to increase the clamping force. It provides forging of metal, eliminating inhomogeneities in the seam and relieving stress.

At the next cycle everything repeats again.

Basic parameters of resistance spot welding

The main parameters of resistance spot welding include: the strength of the welding current (I SV), the duration of its pulse (t SV), the compression force of the electrodes (F SV), the dimensions and shape of the working surfaces of the electrodes (R - for a spherical shape, d E - for a flat shape ). For better clarity of the process, these parameters are presented in the form of a cyclogram reflecting their change over time.

There are hard and soft welding modes. The first is characterized by high current, short duration of the current pulse (0.08-0.5 seconds depending on the thickness of the metal) and high compression force of the electrodes. It is used for welding copper and aluminum alloys with high thermal conductivity, as well as high-alloy steels to maintain their corrosion resistance.

In the soft mode, the workpieces are heated more smoothly with a relatively low current. The duration of the welding pulse ranges from tenths to several seconds. Soft modes are shown for steels prone to hardening. Basically, it is soft modes that are used for resistance spot welding at home, since the power of the devices in this case may be lower than for hard welding.

Dimensions and shape of electrodes. With the help of electrodes, direct contact of the welding machine with the parts being welded is carried out. They not only supply current to the welding zone, but also transmit compressive force and remove heat. The shape, size and material of the electrodes are the most important parameters of spot welding machines.

Depending on their shape, electrodes are divided into straight and shaped. The first ones are the most common; they are used for welding parts that allow free access of electrodes to the welded area. Their dimensions are standardized by GOST 14111-90, which sets the following diameters of electrode rods: 10, 13, 16, 20, 25, 32 and 40 mm.

According to the shape of the working surface, there are electrodes with flat and spherical tips, characterized by diameter (d) and radius (R) values, respectively. The contact area of ​​the electrode with the workpiece depends on the values ​​of d and R, which affects the current density, pressure and size of the core. Electrodes with a spherical surface have greater durability (they can make more points before resharpening) and are less sensitive to distortions during installation than electrodes with a flat surface. Therefore, it is recommended to manufacture electrodes used in clamps with a spherical surface, as well as shaped electrodes that work with large deflections. When welding light alloys (for example, aluminum, magnesium), only electrodes with a spherical surface are used. The use of flat surface electrodes for this purpose results in excessive indentations and undercuts on the surface of the points and increased gaps between parts after welding. The dimensions of the working surface of the electrodes are selected depending on the thickness of the metals being welded. It should be noted that electrodes with a spherical surface can be used in almost all cases of spot welding, while electrodes with a flat surface are very often not applicable.

* - in the new GOST, instead of a diameter of 12 mm, 10 and 13 mm were introduced.

The landing parts of the electrodes (places connected to the electrical holder) must ensure reliable transmission of the electrical impulse and clamping force. They are often made in the form of a cone, although there are other types of connections - along a cylindrical surface or thread.

The material of the electrodes is very important, determining their electrical resistance, thermal conductivity, heat resistance and mechanical strength at high temperatures. During operation, the electrodes heat up to high temperatures. The thermocyclic operating mode, together with a mechanical variable load, causes increased wear of the working parts of the electrodes, resulting in a deterioration in the quality of the connections. To ensure that the electrodes are able to withstand harsh operating conditions, they are made from special copper alloys that have heat resistance and high electrical and thermal conductivity. Pure copper is also capable of working as electrodes, but it has low durability and requires frequent regrinding of the working part.

Welding current strength. Welding current strength (I SV) is one of the main parameters of spot welding. Not only the amount of heat released in the welding zone depends on it, but also the gradient of its increase over time, i.e. heating rate. The dimensions of the welded core (d, h and h 1) also directly depend on I SV, increasing in proportion to the increase in I SV.

It should be noted that the current that flows through the welding zone (I SV) and the current flowing in the secondary circuit of the welding machine (I 2) differ from each other - and the greater, the smaller the distance between the welding points. The reason for this is the shunt current (Iw), flowing outside the welding zone - including through previously completed points. Thus, the current in the welding circuit of the device must be greater than the welding current by the amount of the shunt current:

I 2 = I NE + I w

To determine the strength of the welding current, you can use different formulas that contain various empirical coefficients obtained experimentally. In cases where an exact determination of the welding current is not required (which is most often the case), its value is taken from tables compiled for different welding modes and different materials.

Increasing the welding time allows welding with currents much lower than those given in the table for industrial devices.

Welding time. Welding time (tSW) refers to the duration of the current pulse when performing one weld point. Together with the current strength, it determines the amount of heat that is released in the connection area when an electric current passes through it.

With an increase in t SV, the penetration of parts increases and the dimensions of the molten metal core (d, h and h 1) increase. At the same time, heat removal from the melting zone increases, parts and electrodes heat up, and heat dissipates into the atmosphere. When a certain time is reached, a state of equilibrium can occur in which all the supplied energy is removed from the welding zone without increasing the penetration of parts and the size of the core. Therefore, increasing t SV is advisable only up to a certain point.

When accurately calculating the duration of the welding pulse, many factors must be taken into account - the thickness of the parts and the size of the weld point, the melting point of the metal being welded, its yield strength, heat accumulation coefficient, etc. There are complex formulas with empirical dependencies, which, if necessary, carry out calculations.

In practice, most often the welding time is taken from tables, adjusting the accepted values ​​in one direction or another, if necessary, depending on the results obtained.

Compression force. The compression force (F SV) influences many processes of resistance spot welding: the plastic deformations occurring in the joint, the release and redistribution of heat, the cooling of the metal and its crystallization in the core. With an increase in FSW, the deformation of the metal in the welding zone increases, the current density decreases, and the electrical resistance in the electrode-part-electrode section decreases and stabilizes. Provided the core dimensions remain unchanged, the strength of the welded points increases with increasing compression force.

When welding in hard conditions, higher values ​​of F SV are used than in soft welding. This is due to the fact that with increasing rigidity, the power of current sources and the penetration of parts increases, which can lead to the formation of splashes of molten metal. A large compression force is precisely intended to prevent this.

As already noted, in order to forge the weld point in order to relieve stress and increase the density of the core, the technology of resistance spot welding in some cases provides for a short-term increase in the compression force after turning off the electrical pulse. The cyclogram in this case looks like this.

When manufacturing the simplest resistance welding machines for home use, there is little reason to make accurate calculations of parameters. Approximate values ​​for electrode diameter, welding current, welding time and compression force can be taken from tables available in many sources. You just need to understand that the data in the tables is somewhat overestimated (or underestimated, if you take into account the welding time) compared to those that are suitable for home devices, where soft modes are usually used.

Preparing parts for welding

The surface of parts in the area of ​​contact between parts and at the point of contact with electrodes is cleaned of oxides and other contaminants. If cleaning is poor, power losses increase, the quality of connections deteriorates and wear of the electrodes increases. In resistance spot welding technology, sandblasting, emery wheels and metal brushes are used to clean the surface, as well as etching in special solutions.

High demands are placed on the surface quality of parts made of aluminum and magnesium alloys. The purpose of preparing the surface for welding is to remove, without damaging the metal, a relatively thick film of oxides with high and uneven electrical resistance.

Spot Welding Equipment

The differences between existing types of spot welding machines are determined mainly by the type of welding current and the shape of its pulse, which are produced by their power electrical circuits. According to these parameters, resistance spot welding equipment is divided into the following types:

• AC welding machines;
• low-frequency spot welding machines;
• capacitor type machines;
• DC welding machines.

Each of these types of machines has its own advantages and disadvantages in technological, technical and economic aspects. The most widely used machines are AC welding machines.

AC resistance spot welding machines. The schematic diagram of AC spot welding machines is shown in the figure below.

The voltage at which welding is carried out is formed from the mains voltage (220/380V) using a welding transformer (TS). The thyristor module (CT) ensures the connection of the primary winding of the transformer to the supply voltage for the required time to form a welding pulse. Using the module, you can not only control the duration of the welding time, but also regulate the shape of the supplied pulse by changing the opening angle of the thyristors.

If the primary winding is made not of one, but of several windings, then by connecting them in different combinations with each other, you can change the transformation ratio, obtaining different values ​​of the output voltage and welding current on the secondary winding.

In addition to the power transformer and thyristor module, AC resistance spot welding machines have a set of control equipment - a power supply for the control system (step-down transformer), relays, logic controllers, control panels, etc.

Capacitor welding. The essence of capacitor welding is that at first electrical energy accumulates relatively slowly in the capacitor when charging it, and then is very quickly consumed, generating a large current pulse. This allows welding to be carried out while consuming less power from the network compared to conventional spot welders.

In addition to this main advantage, capacitor welding has others. With it, there is a constant, controlled expenditure of energy (that which has accumulated in the capacitor) per welded joint, which ensures the stability of the result.

Welding occurs in a very short time (hundredths and even thousandths of a second). This produces concentrated heat release and minimizes the heat-affected zone. The latter advantage allows it to be used for welding metals with high electrical and thermal conductivity (copper and aluminum alloys, silver, etc.), as well as materials with sharply different thermophysical properties.

Rigid capacitor microwelding is used in the electronics industry.

The amount of energy stored in capacitors can be calculated using the formula:

W = C U 2 /2

where C is the capacitance of the capacitor, F; W - energy, W; U is the charging voltage, V. By changing the resistance value in the charging circuit, the charging time, charging current and power consumed from the network are regulated.

Defects in resistance spot welding

When performed with high quality, spot welding has high strength and can ensure the operation of the product for a long service life. When structures connected by multi-point, multi-row spot welding are destroyed, the destruction occurs, as a rule, along the base metal, and not at the welded points.

The quality of welding depends on the experience gained, which comes down mainly to maintaining the required duration of the current pulse based on visual observation (by color) of the weld point.

A correctly executed weld point is located in the center of the joint, has an optimal size of the cast core, does not contain pores and inclusions, does not have external or internal splashes and cracks, and does not create large stress concentrations. When a tensile force is applied, the destruction of the structure occurs not along the cast core, but along the base metal.

Spot welding defects are divided into three types:

• deviations of the dimensions of the cast zone from the optimal ones, displacement of the core relative to the joint of parts or the position of the electrodes;
• violation of metal continuity in the connection zone;
• change in the properties (mechanical, anti-corrosion, etc.) of the metal of the weld point or areas adjacent to it.

The most dangerous defect is considered to be the absence of a cast zone (lack of penetration in the form of a “glue”), in which the product can withstand the load at a low static load, but is destroyed under the action of a variable load and temperature fluctuations.

The strength of the connection is also reduced when there are large dents from the electrodes, breaks and cracks in the overlap edge, and metal splashes. As a result of the cast zone coming to the surface, the anti-corrosion properties of the products (if any) are reduced.

Lack of penetration, complete or partial, insufficient dimensions of the cast core. Possible reasons: the welding current is low, the compression force is too high, the working surface of the electrodes is worn out. Insufficient welding current can be caused not only by its low value in the secondary circuit of the machine, but also by the electrode touching the vertical walls of the profile or by too close a distance between the welding points, leading to a large shunt current.

The defect is detected by external inspection, lifting the edges of parts with a punch, ultrasonic and radiation instruments for welding quality control.

External cracks. Reasons: too high welding current, insufficient compression force, lack of forging force, contaminated surface of parts and/or electrodes, leading to an increase in the contact resistance of parts and a violation of the welding temperature regime.

The defect can be detected with the naked eye or with a magnifying glass. Capillary diagnostics is effective.

Tears at lap edges. The reason for this defect is usually one - the weld point is located too close to the edge of the part (insufficient overlap).

It is detected by external inspection - through a magnifying glass or with the naked eye.

Deep dents from the electrode. Possible reasons: too small size (diameter or radius) of the working part of the electrode, excessively high forging force, incorrectly installed electrodes, too large dimensions of the cast area. The latter may be a consequence of exceeding the welding current or pulse duration.

Internal splash (release of molten metal into the gap between parts). Reasons: the permissible values ​​of the current or the duration of the welding pulse are exceeded - too large a zone of molten metal has formed. The compression force is low - a reliable sealing belt around the core has not been created or an air pocket has formed in the core, causing molten metal to flow out into the gap. The electrodes are installed incorrectly (misaligned or skewed).

Determined by ultrasonic or radiographic testing methods or external inspection (due to splashing, a gap may form between parts).

External splash (metal coming out onto the surface of the part). Possible reasons: switching on the current pulse when the electrodes are not compressed, the welding current or pulse duration is too high, insufficient compression force, misalignment of the electrodes relative to the parts, contamination of the metal surface. The last two reasons lead to uneven current density and melting of the surface of the part.

Determined by external inspection.

Internal cracks and cavities. Causes: The current or pulse duration is too high. The surface of the electrodes or parts is dirty. Low compression force. Missing, late or insufficient forging force.

Shrinkage cavities can occur during cooling and crystallization of the metal. To prevent their occurrence, it is necessary to increase the compression force and apply forging compression at the time of cooling of the core. Defects are detected using radiographic or ultrasonic testing methods.

Molded core is misaligned or irregularly shaped. Possible reasons: electrodes are installed incorrectly, the surface of the parts is not cleaned.

Defects are detected using radiographic or ultrasonic testing methods.

Burn-through. Reasons: the presence of a gap in the assembled parts, contamination of the surface of the parts or electrodes, absence or low compression force of the electrodes during the current pulse. To avoid burn-through, current should only be applied after full compression force has been applied. Determined by external inspection.

Correction of defects. The method for correcting defects depends on their nature. The simplest is repeated spot or other welding. It is recommended to cut or drill out the defective area.

If welding is impossible (due to undesirability or inadmissibility of heating the part), instead of the defective welding point, you can put a rivet by drilling out the welding site. Other correction methods are also used - cleaning the surface in case of external splashes, heat treatment to relieve stress, straightening and forging when the entire product is deformed.

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Capacitor welding

Metal welding

Capacitor welding

Capacitor welding is carried out by short-term pulses of welding current, lasting thousandths of a second; During the pulse time, heat is released in the welding zone, which spreads relatively slowly in the metal to the depth required for welding. With significant metal thicknesses, a difficult to overcome discrepancy arises between the duration of the welding pulse and the duration of the necessary heating of the metal. For small thicknesses this discrepancy does not exist.

For metal thicknesses less than 1 mm, the power of a capacitor machine is 50-100 times lower than the power of a conventional contact machine. As the thickness of the metal increases, the difference in the power of a capacitor machine and a conventional contact machine decreases, and welding on a conventional contact machine becomes more reliable. Therefore, the use of capacitor welding for metal with a thickness of more than 2 mm is rational only for special cases.

Capacitor machines for small thicknesses are simple, cheap, have low power, sometimes not exceeding the power of an ordinary table lamp, and they can be connected to a lighting network without power wiring. Capacitor welding for welding metal with a thickness of less than 0.1 mm is often irreplaceable with any other type of welding; for metal with a thickness of 1-2 mm it is acceptable, but can easily be replaced by other methods.

There are two main forms of capacitor welding: a) with direct discharge of capacitors for welding; b) with the discharge of capacitors to the primary winding of the welding transformer. An installation with direct discharge of capacitors is used for butt welding of wires and thin rods, for connecting a wide variety of and dissimilar metals, sometimes with completely different physical properties.

Machines with capacitor discharge to the primary winding of a welding transformer are designed for spot and seam welding and are of greatest industrial importance. The rapid development of capacitor spot welding began from the time it began to be used for welding metal of small thicknesses and small parts; here the quality of welded joints turned out to be excellent, the welding process is very productive and economically profitable.

Capacitor spot machines for welding metal of small thicknesses consume insignificant power from the network, 0.1-0.2 kea\ The electrical circuit of the machine (Fig. 204) is very simple. The current from the network, through a small step-up single-phase transformer T1 and rectifier B, is supplied to charge the bank of capacitors C. By means of switch P, the battery of capacitors is either switched on for charging or discharged to the primary winding of the welding transformer T2. All equipment is located in the machine body.

An example of a capacitor point machine is the TKM-4 machine. The machine is stationary, pedal; its weight is 165 kg; supply voltage 220 V; the average power consumed from the network is 0.1 kVA (Fig. 205). Oil-paper capacitors, total capacity 400 μF, charging voltage 600 V; The plug switch allows you to change the included capacitance from 10 to 400 microfarads. The welding transformer has four stages of regulation. The sedimentary pressure on the electrodes created by the load through a system of levers ensures strict constancy of the set pressure, which is very important for capacitor welding.

When welding two parts of different thicknesses, the decisive role is played by the part with a smaller thickness, which should not exceed the capabilities of the machine, while the second part can have an arbitrarily large thickness, which significantly expands the use of capacitor spot welding. For example, on a GKM-4 machine, metal 0.2 mm thick can be welded to metal 10 or 15 mm thick.

Rice. 1. Electrical circuit of a low-power capacitor machine

The electrical mode of the machine can be adjusted within wide limits by changing the number of connected capacitors and the stage of the welding transformer. You can change the amplitude of the welding current and the duration of its flow. The maximum value of the welding current is about 5000 A, the average duration of its flow is 0.6-0.8 -10~4 sec.

When you press the pedal, the load pressure is transferred to the electrodes, the capacitors are closed to the primary winding of the transformer, and one strictly defined pulse of welding current flows. When the pedal is released, the capacitors are charged again, the machine is ready for the next welding operation; when the pedal is pressed again, exactly the same pulse of welding current passes again.

Rice. 2. Point condenser machine TKM-4

For installation work on large-sized products, circuit assembly, etc., a portable point machine PTKM-1 Besom 34 kg was designed, welding metal with a maximum thickness of 0.3 mm. The welding part of the machine is made in the form of light hand pliers, connected to the machine with flexible wires 1-1.5 m long.

In the simplest point capacitor machines, the machine is driven by the force of the worker, which is acceptable when welding small parts with little effort and upsetting work and not very intensive production. For more difficult working conditions, a machine with a mechanized, for example electric, drive, type TKM-8, can be used. It has a cam spring compression mechanism driven by an electric motor through a clutch. When the pedal is pressed, the mechanism engages with the clutch and the current is turned on and the electrodes are compressed. If you press the pedal briefly, one point is welded, if you hold the pedal pressed, then 20-120 points are welded per minute, depending on the adjustment; The machine runs automatically continuously until the pedal is released. The machine is designed for spot welding of metal with a thickness of 0.05-0.5 mm; rated power of the machine is 0.3 kVA, electrode compression force is 6-40 kg.

Capacitor welding machines are often covered with a clear plexiglass cap, protecting the welding area from dust and other contaminants. The protective cap can be sealed, and a protective atmosphere of argon, hydrogen, nitrogen, etc. can be created in it.

Long-term operation of low-power capacitor machines revealed their significant advantages: high efficiency, low power consumption and accurate dosing for each welding. It is possible to conveniently and widely regulate the power of the machine, the duration and shape of each pulse. The short duration of welding minimizes heating of the product, its deformation, and the width of the influence zone. The welding process is very simple, fully automated and depends little on the qualifications of the worker, whose training only takes a few days.

Spot capacitor welding has found industrial application for many metals: aluminum and aluminum alloys, all kinds of copper alloys, nickel and nickel alloys, platinum, silver and its alloys, all kinds of steels, tungsten, molybdenum, etc.; Numerous combinations of dissimilar metals are possible. Spot capacitor welding replaces soldering, riveting, and folding. It is increasingly used in instrument making, in the production of electrical and aviation instruments, clock mechanisms, cameras, electrical equipment, optical instruments, radio tubes, electric lighting lamps, electronic equipment, radios and televisions, pens, metal toys, haberdashery, jewelry, etc. d.

Rice. 3. Continuous tight seam made by capacitor welding

A method of seam capacitor welding has also been developed and has been used in production. Seam welding is performed as spot welding, with such frequent placement of weld points that each subsequent point overlaps the previous one by 0.3-0.5 diameters, which creates a dense continuous seam, impenetrable to liquids and gases (Fig. 206). The electrodes of the machine are in the form of rollers that roll continuously along the seam at a constant speed and are driven by a small electric motor. The welding current is supplied in separate pulses from a bank of capacitors, as in spot welding. The electronic control system allows you to produce up to 50 complete charge-discharge cycles of capacitors in 1 second. Seam capacitor welding has found various applications in instrument making.

Capacitor welding has opened up a rather significant new area of ​​application for welding equipment: metals of small thickness, small parts and micro-parts that are poorly visible to the naked eye and require the use of optical instruments during assembly. Capacitor welding improves the quality of products and dramatically increases labor productivity; The cost of a capacitor machine usually pays off within a few months of operation. The extremely rapid development of instrument making requires the widespread use of capacitor machines, which free up a large number of workers by increasing labor productivity.

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Capacitor spot welding

One of the common types of resistance welding is capacitor welding or welding with stored energy stored in electric capacitors. Energy in capacitors is accumulated when they are charged from a constant voltage source (generator or rectifier), and then, during the discharge process, is converted into heat used for welding. The energy stored in capacitors can be regulated by changing the capacitance of the capacitor (C) and the charging voltage (U).

There are two types of capacitor welding:

Transformerless (capacitors are discharged directly onto the parts being welded);

Transformer (the capacitor is discharged onto the primary winding of the welding transformer, in the secondary circuit of which there are pre-compressed parts to be welded).

The schematic diagram of capacitor welding is shown in Fig. 1.29.

Rice. 1.29. Schematic diagram of a device for capacitor welding: Tr - step-up transformer, B - rectifier, C - capacitor with a capacity of 500 μF, Rk - resistance of the parts being welded, K - key switch

In switch position 1, the capacitor is charged to voltage U0. When the switch is moved to position. 2, the capacitor is discharged through the contact resistance of the parts being welded. This creates a powerful current pulse.

The voltage from the capacitor is supplied to the workpiece through point contacts with an area of ​​~ 2 mm. The resulting current pulse, in accordance with the Joule-Lenz law, heats the contact area to the operating temperature of welding. To ensure reliable pressing of the welded surfaces, a mechanical stress of about 100 MPa is transmitted to the parts through point electrodes.

The main application of capacitor welding is to join metals and alloys of small thicknesses. The advantage of capacitor welding is its low power consumption.

To determine the efficiency of welding, we estimate the maximum temperature in the area of ​​​​contact of the parts being welded (Tmax).

Due to the fact that the duration of the discharge current pulse does not exceed 10-6 s, the calculation was carried out in the adiabatic approximation, that is, neglecting heat removal from the region of current flow.

The principle of contact heating of parts is shown in Fig. 1.30.

Rice. 1.30. The principle of contact welding: 1 - parts to be welded with a thickness d = 5 * 10-2 cm, 2 - electrodes with an area S = 3 * 10-2 cm, C - a capacitor with a capacity of 500 μF, Rk - contact resistance

The advantage of capacitor welding is its low power consumption, which is (0.1-0.2) kVA. The duration of the welding current pulse is thousandths of a second. The range of welded metal thicknesses is from 0.005 mm to 1 mm. Capacitor welding allows you to successfully join thin metals, small parts and micro parts that are poorly visible to the naked eye and require the use of optical instruments during assembly. This progressive welding method has found application in the production of electrical measuring instruments and aircraft instruments, watch mechanisms, cameras, etc.

Cold welding.

The connection of workpieces during cold welding is carried out by plastic deformation at room and even at negative temperatures. The formation of a permanent connection occurs as a result of the emergence of a metallic bond when the contacting surfaces approach each other to a distance at which the action of interatomic forces is possible, and as a result of a large compression force, the oxide film breaks and clean metal surfaces are formed.

The surfaces to be welded must be thoroughly cleaned of adsorbed impurities and fatty films. Cold welding can be used to make spot, seam and butt joints.

In Fig. Figure 1.31 shows the cold spot welding process. Sheets of metal (1) with a thoroughly cleaned surface at the welding site are placed between punches (2) having projections (3). The punch is compressed with some force P, the projections (3) are pressed into the metal to their entire height until the supporting surfaces (4) of the punches rest against the outer surface of the workpieces being welded.

Rice. 1.31.Cold welding diagram

Cold welding is used to make overlapped and butt joints of wires, busbars, and pipes. The pressure is selected depending on the composition and thickness of the material being welded; on average it is (1-3) GPa.

Induction welding.

This method is used primarily to weld longitudinal seams of pipes during their manufacture on continuous mills and to deposit hard alloys on steel bases in the manufacture of cutters, drill bits and other tools.

With this method, the metal is heated by passing high-frequency currents through it and is compressed. Induction welding is convenient because it is non-contact; high-frequency currents are localized near the surface of the heated workpiece. Such installations work as follows. The high-frequency generator current is supplied to the inductor, which induces eddy currents in the workpiece, and the pipe heats up. Mills of this type are successfully used for the production of pipes with a diameter of (12-60) mm at speeds of up to 50 m/min. The current is supplied from tube generators with a power of up to 260 kW at a frequency of 440 kHz and 880 kHz. Pipes of large diameters (325 mm and 426 mm) with a wall thickness of (7-8) mm, with a welding speed of up to (30-40) m/min are also manufactured.

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Application of capacitor welding

One of the main types of resistance welding, widely used in industry, is capacitor welding. The rules for its implementation are regulated by GOST. Its principle is based on the discharge of an electrical charge accumulated on a block of capacitors onto the connected products. At the point of contact of the electrodes, a discharge occurs and a short electric arc is formed, sufficient to melt the metal.

Division into types

Capacitor welding is most widespread in instrument making. It is capable of welding metals up to 1.5 mm, and the thickness of the second part can be much greater. In welding thin products, capacitor welding has no competitors in terms of efficiency, productivity and quality.

It can be transformer or transformerless. In the first option, large energy can be stored on capacitors by using high voltage and discharging through a step-down transformer with high currents. The second option is simple and has a minimum of details.

Depending on the characteristics of the seam formation, capacitor welding is divided into:

• point;
• suture;
• butt.

The first, point method, is mainly used in instrument making and the production of electronic equipment. It is actively used for welding thin parts with thick ones.

Seam welding, also called roller welding, is used for welding membranes and electric vacuum devices. A continuous, sealed seam is obtained due to the fact that point connections are made with overlap. The role of electrodes is performed by rotating rollers.

Butt welding is carried out by flash or resistance. With the first method, a discharge first occurs between the parts being welded, the place of the future connection is melted under the action of the formed arc, and then they settle, after which the metals are joined. In the second case, the discharge and subsequent welding occurs at the moment the parts come into contact.

Advantages

The advantage of capacitor welding is that due to the high energy density and short duration of the welding pulse, the heat-affected zone is very small, stresses and deformations are minimal. The equipment is simple and productive. Due to the fact that at the moment of discharge the capacitor unit is disconnected from the network, it does not affect its parameters in any way. The only drawback is that it is only used when working with thin metals.

Another advantage of capacitive welding is its compactness. Capacitor welding does not require powerful power sources; the device can be charged between moving the electrode to the next point. There are practically no harmful gases during the welding process. The device is very economical; all the stored energy is used to melt the metals at the connection point. Due to the fact that the charge on the capacitors is constant, a high-quality and stable arc is obtained.

Capacitor welding allows you to weld non-ferrous metals of small thickness. In addition, it can connect dissimilar metals and alloys due to the high concentration of energy in a small area.

Due to the fact that the capacitor welding system operates in a discrete mode (first charge, then discharge), air cooling is sufficient for it, which simplifies the design of the welding unit.

The capacitive welding machine is used for joining all types of steels, parts made of brass, aluminum, and bronze. It can weld dissimilar metals, thin to thick sheets. The ability to adjust the discharge energy and pulse duration allows microwelding, for example, in a watch mechanism. The capacitor apparatus can weld refractory tungsten filaments and is used in jewelry.

Technological features

Depending on the technological process, capacitor-type welding is:

• contact;
• percussion;
• point.

During resistance welding, the energy accumulated in the container is discharged onto metal parts that were previously tightly connected to each other. At the point where the electrodes are pressed, an electric arc occurs, in which the current reaches 10-15 thousand amperes with an arc duration of up to 3 ms.

In the case of capacitor impact welding, the discharge occurs at the moment of a brief impact of the electrode on the workpiece. Duration of arc exposure is 1.5 ms. This reduces the thermal impact on the surrounding area and improves welding quality.

In capacitor spot welding, an arc appears between the electrodes and the workpieces located between them. The discharge process lasts from 10 to 100 ms (depending on settings), and the connection of metals occurs in a small area.

Transformerless device

Having decided to make a machine for capacitor welding yourself, first choose a design option. The simplest option is a transformerless circuit. It can be implemented with high or low voltage capacitors.

In the first case, you will need a step-up transformer and 1000 V capacitors with a capacity of 1000 μF. In addition, you will need a high-voltage diode bridge for rectifying alternating current, a switch, and electrodes with connecting wires. Welding occurs in two stages. At the first stage, the container is charged, at the second, after switching its leads to the welding electrodes and touching them to the welding site, a discharge occurs and the parts are connected. The flowing current reaches 100 A, the pulse duration is 5 ms. This option is dangerous for humans due to the high operating voltage.

The second option requires a step-down transformer, a bank of capacitors for voltages up to 60 V with a capacity of 40,000 μF or more, a diode bridge, and a switch. The welding process is identical to the first case, only currents of 1-2 kA and a duration of up to 600 ms pass through the welding point. The power of the transformer does not matter much; it can be 100-500 W.

DIY transformer circuit

When using a transformer circuit, you will need a step-up transformer and a diode bridge for charging at 1 kV, capacitors at 1000 μF and a step-down transformer, through the secondary winding of which the accumulated charge is discharged at the junction of the workpieces. With this design of the spot welding machine, the discharge duration is 1 ms, and the current reaches 6000 A. After charging the capacitor bank with a switch, they are connected to the primary winding of the step-down transformer. An EMF is induced in the secondary winding, which causes huge currents when the electrodes on the workpieces being connected are closed.

The quality of welding will greatly depend on the condition of the electrode block. The simplest option is clamps for fixing and pressing contactors. But a more reliable design is where the lower electrode is stationary, and the upper one can be pressed against the lower one using a lever. It is a copper rod with a diameter of 8 mm and a length of 10-20 mm attached to any base. The upper part of the rod is rounded to obtain reliable contact with the metal being welded. A similar copper rod is installed on a lever, when lowered, the electrodes should be tightly connected. The base with the lower electrode is isolated from the upper arm. The secondary winding is connected to the electrodes with a 20 mm2 wire.

The primary winding is wound with PEV-2 0.8 mm, the number of turns is 300. The secondary winding of ten turns is wound with 20 mm2 wire. A W 40 core with a thickness of 70 mm can be used as a magnetic circuit. To control charge/discharge, a PTL-50 or KU202 thyristor is used.

Preparing parts

Before starting capacitor welding, it is necessary to prepare the parts to be joined. Rust, scale and other contaminants are removed from them. The workpieces are properly aligned and then placed between the lower fixed electrode and the upper movable one. They are then strongly compressed by the electrodes. By pressing the start button, an electrical discharge is applied. Metal welding occurs at the point where the electrodes touch. It is necessary to release the electrodes after some time necessary for cooling and crystallization of the welding site under pressure. After this, the part moves, during which time the device has time to charge, and the welding process is repeated. The size of the welding site should be 2-3 times larger than the smallest thickness of the workpieces being joined.

When you need to weld a sheet up to 0.5 mm thick to other parts, regardless of their thickness, you can use a simplified welding method. One electrode is attached using a clamp to the thick part being welded in any convenient place. In the place where a thin part needs to be welded, it is pressed manually with a second electrode. You can use car clamps. Then welding is done. As you can see, the process is not too complicated and can be done at home.