IX Международная студенческая научная конференция Студенческий научный форум - 2017

Contact welding.

Contact welding concerns to kinds of welding with short-term heating a junction without flashing off or with flashing off and settlement warmed-over preparations. Prominent feature of these processes - plastic deformation during which welded connection is formed.

The junction is warmed up by an electric current taking place on metal, and the maximum quantity of heat is allocated in a place of welding contact.

On a surface of welded metal are available a film oxide and pollution with small electroconductivity which also increase electroresistance of contact. In result in points of contact metal is heated up to a thermoplastic condition or up to flashing off. At continuous squeezing the heated up preparations new things in common are formed, there will be no yet a full rapprochement up to internuclear distances, welding of surfaces.

Contact welding classify as the welded connection determining a kind of the welding machine, and on a sort of the current having the welding transformer. As welded connection distinguish butt welding, dot, seam.

Butt welding

Butt welding - a version of contact welding, at which preparation are welded on all surface of contact. Welded preparations fix in clips butt machines. The clip 1 is established on the mobile plate, moving in directing, a clip 2 solidified on a motionless plate. The welding transformer is connected to plates flexible trunks and eats from a network through including device. Plates move, and preparations are compressed under action of the effort developed by the mechanism deposits.

Butt welding with heating-up a joint up to a plastic condition and the subsequent upsetting name - flashing off welding.

Flashing off welding has advantages before welding by resistance. In process flashing off all roughnesses of a joint are leveled, and oxide and pollution leave, special preparations of a junction therefore are not required. It is possible to weld preparations with section, diverse metals.

The most widespread products, made butt welding, elements of tubular designs, wheels and rings, the tool, rails, ferro-concrete armature serve.

Spot welding.

Spot welding - a version of contact welding, at which preparation incorporate in separate points. At spot welding preparation collect lapped and clamp between the electrodes bringing a current to a place of welding.

Surfaces of welded preparations adjoining with copper electrodes are heated up more slowly their internal layers. Heating proceeds up to a plastic condition of external layers and before fusion of internal layers. Then switch off a current and remove pressure. In result the cast welded point is formed.

Spot welding depending on an arrangement of electrodes in relation to welded preparations can be bilateral and unilateral.

Multidot contact welding - a version of contact welding when for one cycle some points are welded. Spot welding carry out by a principle of unilateral spot welding. Multidot machines can have from one pair up to 100 pairs electrodes, accordingly weld 2-200 points simultaneously. Spot welding weld simultaneously and consistently. In the first case all electrodes at once press to a product that provides smaller warpage and the big accuracy of assembly. The current is distributed between pressing electrodes special sequence switch, including electrodes in pairs. In the second case of pair electrodes lower serially or simultaneously, and a current connect serially to each pair electrodes from the welding transformer. Spot welding apply basically in mass production where the big number of welded points on preparation is required.

Seam welding.

Seam welding - a version of contact welding at which between welded preparations strong and dense connection is formed. Electrodes carry out as flat rollers between which pass welded preparations.

In process seam sheet preparations lap weldings, clamp between electrodes and pass a current. At movement of rollers on preparations welded points overlapping each other therefore the seam turns out continuous vectorially are formed. Seam a point as well as dot, it is possible to execute at bilateral and unilateral arrangements of electrodes.

Seam welding apply in mass production at manufacturing various vessels. Thickness of welded sheets makes 0,3 - 3 mm. Seam welding carry out the same types of welded connections, as dot, but use for reception of a tight seam.

Welding

Welding is a process ofjoining together metallic parts by heating the place of contact to the fusion state. Welding processes are classified according to the source of energy employed for heating, the metals and the state of the metal at the place of welding. There are different types of welding such as hammer welding, thermit welding, electric arc welding, gas welding, etc. Hammer welding is a process in which two heated metal parts are joined and fused together by force from a power hammer. Thermit welding is a process consisting of a chemical reaction. It is used in repairing large sections such as rails, frames, etc. Resistance welding process forms a whole group consisting of many types of welding such as spot welding, butt welding and others. In arc welding the workpieces are not melted by a flame. They are melted by an electric arc. In order to create the arc, a powerful electric current must be provided. The current must be at least 60 A, otherwise the arc will not create enough heat. In gas welding, it is necessary to use a mixture of two gases. To create a hot flame, a combustible gas must be mixed with oxygen. Gas welding is normally used to join steel to steel.

Arc weiding

In arc welding the workpieces are not melted by a flame. They are melted by an electric arc. In order to create the arc, a powerful electric current must be provided. The current must be at least 60 A, otherwise the arc will not create enough heat. For thicker workpieces, the current may be 250 A. In order to carry this current, the cables from the transformer should be quite thick or else they will overheat. To supply the necessary current the transformer is used and to complete the electric circuit an earth clamp is used, which is attached to the workpiece. Then the current flows around the circuit and the arc appears. It must be securely attached, otherwise an arc will appear between the clamp and the workpiece. To strike the arc, the transformer should be switched first. The electrode holder contains an electrode rod which provides filler metal to join the workpieces. As the current flows between electrode and the workpiece, the tip of the electrode melts and falls onto workpiece. The electrode must be moved across the joint continuously, if is moved too quickly neither the electrode nor the workpiece will melt.

While choosing an electrode type it is necessary to know:a. Position to which the workpiece is to be welded.b. Type and thickness of metal used.c. Type of welding current.d. Class of work: deep penetration, surface quality, etc.

Laser and plasma welding

Welding is a process which provides a non-detachable joining of two like metal pieces by heating them till melting condition or fusion without or with mechanical pressure. Laser welding is quickly becoming a practical welding process. In its present stage of development, the laser can form welds up to about 1/32 inch deep. Pulsed lasers are often used in industry today. The laser’s heat input is very small, so the heat-affected zone around a joint is correspondingly small. The laser’s high power intensity permits welds between dissimilar metals of widely varying physical properties. Plasma arc welding is efficient for fusion welding stainless steels, titanium, nickel from 0.00 1 to 0.030 inch thick. The process is particularly well suited for repairing delicate parts, for joining thin structures, and for welding electronic components. With the exception of aluminium any metal or combination of metals can be welded with plasma arc process.

 

5

 

Код для цитирования: Скопировать