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2013-03-06, 6:02 PM
                             STUD WELDING

The stud welding is part of an arc welding process where a united body is produced by heating with an electrical arc between the metal studs or similar parts and base metals. The heating process is running till the base metal getting molten stage, after certain time the arc is stopped and stud is feed into the molten zone. Molten metal is shielded with a ferrule and flux or shielding inert gas. The Argon inert gas is used for joining the aluminium stud and flux is used for steel stud welding

Working principle of stud welding


                                       PRINCIPLE DIAGRAM OF STUD WELDING

The work or stud is held with collect chuck of welding gun and a porcelain or ceramic ferrule is placed around the welding zone of stud. The current and controller units are set for timing control. Now the welding gun is positioned wherein stud to be weld on the base metal. Then current supply is started and the stud lifted about 1mm to 1.5 mm. the arc is produced between the gap of stud and base metal. The arc melts the end of stud and base metal where it touches with flux. This flux provides protecting properties from atmosphere gases in the ferrule boundaries. Now current source is off as per schedule setting. The another additional spring loaded attachment is provided for exerted the force on stud during molten stage. This is an automated solenoid system. It has also setting time for released load after arc is completed. The end of stud and base metal fused together and solidify inside of the ferrule. Once welded joints are cooled, the ferrule may removed by breaking. Another one new ferrule used for new weld joint.




                     ELECTRO SLAG WELDING

The electro slag welding is group of an arc welding process. The electro slag welding define as, a welding process where weld joint is made by molten slag, which produce a heat and melt the filler metal or electrode and work piece which to be weld.

Electro slag welding principle:                               

A piece of steel wool is placed between the electrode and work piece to produce an arc. Some amount of flux is added in produced arc and it melts with heat of arc. The electrical arc is stopped when a sufficient amount of molten flux or slag is produced. Then electrical current is passed through the molten pool of slag. The molten slag is sufficient to melt the filler metal and work piece, because it contains temperature about 16000C-19000C . The electrode melts and fused also base metal, the melted metal deposited in beneath of the joint. It is slowly solidify and produce a weld bead. Thus the electro slag welding is a progressive process of melting and solidification from the bottom to upward.

The molten flux is also shielded the weld metal, which protects from atmospheric harmful gases. There are no need to providing continuously in welding zone. It reduce impurity of molten metal as a slag




                              SPOT WELDING

Spot welding joint is one type of electric resistance welding. Generally joining the sheet to sheet, sheet to rolled sections, wire to wire etc. by this spot weld process. The spot welding is very effectively, which can replace the rivet joints and is very speedy process, this spot welding machine does not need skilled operator, it can be operated by semi-skilled labour.



                                        PRINCIPLE DIAGRAM OF SPOT WELDING

The principle of spot welding is shown in the bellow diagram. In this machine basically having a transformer core (T) which is having a primary winding (PW). This primary winding tapped at a number of points. The secondary winding (SW)has the two ends of a circuit (C) which is connected two arms made of copper or bronze. Each side has a copper electrode, this electrode of spot welding produce the sufficient heat to fuse the joining metal. The lower arm is generally stationary and upper arm is movable (upward and downward). The technical terms are rocker arms or electrode arms. The electrodes of spot welding is cooled by water, the water is passing through the inter looped water line.



                               SEAM WELDING


                          PRINCIPLE DIAGRAM OF SEAM WELDING

Seam welding is the one type of resistance welding and also another modification of spot welding. The basic chief difference of spot weld and seam weld is that the formation of electrode. They are usually power driven and rotate whilst gripping the work. The current is supplied through the rotatable wheel and melt the metal. The edges of the two sheets must be overlap, so that the welding heat can be developed in joining interface of the sheet metal. The large manufacturing of cylindrical container, drum, pipe, etc. is best suited by these types of welding.

When the body is being performed into a tube, the overlapping edge made in united piece which is called longitudinal welding and the end position fitted of assembly work welding is called circumferential welding.

The use of seam welding is mainly designated for the thin sheet metal, the sheet metal often welded which should not exceed 1/8 inch. The welding speed may vary with the sheet gauge. The special machines are employed for the faster welding speed. In the bellow diagram shown the basic principle of seam welding.

Generally two types of seam welding machines found 1) Circumferential Seam Welding Machine 2) Longitudinal Seam Welding Machine. They are called because of the types of welding joint performance. Although the Universal Seam Welding Machine can perform both operation. By the changing of electrode assembly the circumferential welding can be converted into longitudinal welding.

In the seam welding operation, the sheets to be welded are properly overlapped and positioned between the both rollers. The clamp may be provided for the holding properly and applying the pressure. A current is provided through rollers to the material contact with them. The sufficient heat is produced and material reached in plastic stage. The welding operation done by pressure applied with both rollers and applied current.

The another important factor with roller cooling efficient. The huge amount of heat is developed through the rollers, so its required sufficient cooling system, which is increase the life of roller electrodes. The removal of heat from region of the work the special type roller is used. Which is cooling system is provided. After a short period of use the edges of the electrodes require trimming, the trimming operating can not be obtained by filling operation. The trimming or re-shaping operation of copper alloy electrode properly done with lath machining. The another process to reshaping the electrode fit into the roller machine, which have plus point is no material loss happened. The self trimming device is widely used which is which keeps the edge of electrode constantly good condition



                          PERCUSSION WELDING 

Percussion welding is one type of resistance welding method. In this welding process where a united body is made over the entire area of butt positioned work surfaces by heating is obtained from an arc produced by a rapid discharge of electrical energy and the pressure is applied same time of electrical discharge.

Principle of percussion welding:


                                    PRINCIPLE DIAGRAM OF PERCUSSION WELDING

  • The following steps are involved in percussion welding process—
  • The wok-pieces should be cleaned from dirt, grease, paint etc. foreign particles.
  • The wok-pieces are clamped rigidly in the machine table.
  • Which face to be weld, that brought together face to face and light forces applied.
  • The work-piece brought to touch in slightly and established a flow of current. Then electrical arc is produced in the interface of the work-piece.
  • At this time light force is applied each other as shown in the picture with arrow sign. After a certain time the switch of the current and hold the job till cool down.
  • Applied force is released from both end.
  • Work-pieces are unclamped.
  • Now work-piece made united


                               PROJECTION WELDING    

Projection welding is in group of resistance welding. In this welding process where weld joint is produced by heating is obtained from electrical resistance flow through the work, which held under electrode pressure. The localized welding joint is made by this welding method

 Projection welding principle:



The working principle of projection welding is more or less similar of spot welding.

The two surfaces of weld metal are held together in under pressure by the electrodes. When an electrical current flown through the weld electrode, it causes the projecting metals are melts and fuse the both material which is contacted. Thus the weld joint is made.

In single operation a number of joint is made. The joint strength is depend on nature of projection. There are three types of projections are used in projection welding process.

The button type projection is used for joining of thin flat sheet metals (24-13 gauge). The cone type projection is used on 12 to 5 gauge metal sheets. The spherical type projection is used on higher thickness of metal.



                          RESISTANCE WELDING

Principle of Butt or Welding



Butt welding is another type of electric resistant welding. The two weld metals are placed in a machine in face to face matching and both are clamped separately. These clamps are act as a electrode. These clamps are carry the current. The weld metals are matched correctly same axes and same line touching each other. Both weld metals are holding under pressure. The source current is given through the electrode to the weld metal and supply is continue until its reaching melting temperature. Previously load is applied to the metal and sufficient melting temperature, both are play master role for completed the butt weld.

During this welding process heavy current is required.Sheets 1.5 mm. thick and 250 mm. in diameter may be welded by butt weld. Pipes, tubing, bars, rods, light and medium weight structural shapes may be welded by butt weld.




                           FLASH BUTT WELDING

Principle of flash welding process


                                                  PRINCIPLE DIAGRAM OF FLASH BUTT WELDING

Flash welding is the another kind of butt welding process. This is different from other welding process is the arcing action, the heat is being generated at a number of points by a series of tiny arcs. The works does not coming into actual contact until the final forging pressure is applied. This welding process can be carried out in another theory that very light contact does occur at number of points. Such this a very small area contact each other face. Very intense heating takes place and causes melt the metal. After current applied, vaporization takes place between the metal joining portion. The liquid metals are flowing due to capillary action. At thesame time the final mechanical forging pressure is applied, then welding current supply is cut off. This entire operation is performed automatically. The heating effect is generally produced by the electrical resistance at the joint face. Flush welding process is very quick welding process than butt welding process. Due to less time radiation losses, relatively less current is required and a smaller volume of metal is heated. The principle of flush welding diagram is shown in the bellow picture.




                            FRICTION WELDING

The friction welding is one of the solid state welding process, where weld joint is made by heating is created from mechanically induced sliding motion between rubbing surface in under pressure.

The heat is generated by co-efficient of friction of the material. To get a quick heat from surface area, when the rotational speed is high.


Friction welding principle:


                                       PRINCIPLE DIAGRAM OF FRICTION WELDING

In this welding process the fusion is produced by rotating one of the weld parts to be joined against the fixed surface of the other part. Until fusion temperature is obtained in weld parts the rotation of rotating parts will be in high speed and under low pressure. Large amount of pressure will be applied in until both weld parts are welded.

Different types of material can be welding by this process. The materials are-

Carbon steel, alloy steel, copper to carbon steel, copper to aluminium, aluminium and its alloy, brass to bronze, tool steel, stainless steel, stainless steel to aluminium, tungsten, etc.





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