To obtain a permanent connection often use a technological process called welding, which is characterized not only by high quality of the welded joint, but also strictly follow the stages of the technology and safety at work. Recently on this site considered the welding spot belonging to the class of thermo-mechanical joining metals by welding. Therefore, in this article I propose to examine several types of welding, belonging to the class, which was already announced a little higher.
To start, decide that the thermomechanical class is characterized by the presence in his classification of the resistance welding, diffusion welding, forge welding, friction welding and welding using high frequency currents. These kinds of welding is performed by applying thermal energy and pressure. I propose to consider several types of welding: contact (butt and raised) and diffusion.
let’s Start with contact welding.
the Sequential process of heating products, which actually will be welding, to a plastic state and the subsequent deformation that accompanies the connection of these objects. To this type of welding include spot, seam and embossed.
Butt welding is characterized in that the process of obtaining the weld occurs by heating the surfaces and as a result, they are docking.
the Technological process is quite simple — in the jaws of the electrodes, we must consolidate and compress the axial force details that, in fact, want to connect. Further, by including a welding transformer, we get the following picture: there is the flow of electric current greater power and low voltage. As a result, heats up. Well, logically, at the junction of the parts, the heat is much more.
the Degree of heating of the ends helps to classify the technology of butt welding for the welding of resistance and welding technology. (the picture shows the sequence diagram of processes)
resistance welding is characterized by a tight contact of the ends, which contributes to the compressive axial force. If we want to produce such a weld, we need to apply an electric current. And then when we got the plastic state of the abutting surfaces, performed upset. This part of the process I’ll explain: at this stage you should get the connected solid phase. It should also be remembered that the current to be shut off directly before the end of the upsetting operation.
Usually, using this type of welding if you want to connect the parts having a round or rectangular cross-section (the area usually limited to 200 mm2). It is important to remember that before heating the ends of the section need to match exactly, and before starting work it is necessary to clear the surface by chemical or mechanical means.
welding melting is characterized by welding with melting and continuous melting discrete.
First consider the butt welding continuous melting. to carry out the welding, it is necessary gradually to bring together the details, the current source must be enabled. Next, you need to exercise touch the ends on certain ledges. Then, you can become a witness, as due to the small area of contact — bridges, flowing through them with a high current density, contributes to fast heat up and melt. And from the intersection of sparks fly, formed from the explosion of metal parts. If we continue to start to pull together the details, we get the formation and reflow of new contacts — jumpers. By itself, this continuous process forms the ends of the layer of liquid metal. After melting the ends on all the surface, you must make a Deposit. More force leads to a rapid convergence of the ends. As a result, the Burr, which is formed from extruding from the interface of the liquid metal to the outside, should be removed while it is hot.
For people faced with situations when you need to weld the parts having a large cross-sectional area, thus, reduce the capacity of the equipment, a nice butt welding with intermittent melting. Technological process assumes that the current should be turned on, and the details necessary to alternately compress with little effort, and dissolve again. Flowing current heats the surface. Formed at the open ends of the electric discharge, aplause ends on the surface. Repeating several times such an operation, a layer of liquid metal. Then, it is necessary to make a Deposit. From the junction, squeeze the liquid metal, and the ends connect. So it turns out the welded joint.
Welding is used if you need to connect the parts with complex cross-sectional shape (area up to 100 000 mm2). By the way, this welding does not require preliminary preparation of the same ends. Wonderful and convenient method for the manufacture of long products, parts with a closed form.
Next, consider the third type of resistance welding – projection welding.
Raised welding characterized by the fact that there is a connection of the parts having on its surface prepared or natural ledges (in other words, reliefs), under the influence of compression force and eyeliner current.
As mentioned just above, the surface of the workpieces should have reliefs. These reliefs are divided into types: overlap (have a forum spherical, conical, oval and circular shape) and brands. The technological process consists in clamping the parts between the electrodes in the form of a plate with subsequent efforts. Then, must be on the welding current.
Having done these simple steps, stage technology, projection welding, we find that the metal is subjected to intensive heating, which contributes to subsequent deformation. The contact area forms a zone of melting (as in spot welding). Further, we can notice that the area of melt increases, but the metal ledge during deformation, beyond the outer surface of the part. Next, shut off the current, and then, there will be a cooling of the melt and crystallization, which produces the nucleus, which is surrounded by a metal form of a belt, which actually happened the formation of a compound without melting.
What is the difference between the projection welding from other types of welding? Elementary fact that the shape and size of the ledge define a weld joint between the parts. The main advantage is probably that the electrodes have a long service life. As for the lack of it, of course, increased electrical power, which is used for welding presses.
having Considered all methods of contact welding, smooth transition to another type of thermomechanical welding class. the Following form will be considered by the diffusion welding.
Diffusion welding is characterized in that pressure and heat, or rather their joint effect form the weld bead. Accordingly, in order to get this thing welded connection it is necessary to apply high temperature and low pressure.
Before you start welding, you should carefully clean up the spot welded parts. Then, these same items must be placed in the working chamber. From this the camera is pumping atmospheric air pressure to become equal to 10‾5mm RT. the article Then with some small effort needs to be heated to 600 — 800°C. Usually, to obtain a weld by diffusion welding need 5 minutes. Heating of parts in vacuum leads to the cleansing of surfaces of oxides and organic contaminants.