welding and welding transformer

i have made a presentation on welding and welding transformer, here i included types of weldings and their advantages and types of welding transformer and their working, construction, application, advantages..

1. Welding and Welding transformers Prepared By; Hanif Pathan [email protected]

2. Introduction Types of welding Classification of welding processes Construction Working Types of welding transformer Auxiliary equipment Advantages- Disadvantages Application Flow of Presentation

3. Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material. Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames , railway wagons, machine frames, structural works, tanks , furniture, boilers, general repair work and ship building. Introduction

4. 1. Pressure Welding The piece of metal to be joined are heated to a plastic state and forced together by external pressure (Ex ) Resistance welding. 2. Non-Pressure Welding The material at the joint is heated to a molten state and allowed to solidify. (Ex ) Gas welding, Arc welding. Types of welding

5. 1. Arc welding Carbon arc Metal arc Metal inert gas Tungsten inert gas Plasma arc Submerged arc Electro-slag 2.Gas Welding Oxy-acetylene Air-acetylene Oxy-hydrogen 3.Resistance Welding Butt Spot Seam Projection Percussion Classification of welding processes

6. 4.Thermit Welding 5.Solid State Welding Friction Ultrasonic Diffusion Explosive 6.Newer Welding Electron-beam Laser 7.Related Process Oxy-acetylene cutting Arc cutting Hard facing Brazing Soldering Continued …

7. Alternating Current (from Transformer) More efficiency Power consumption less Cost of equipment is less Higher voltage – hence not safe Not suitable for welding non ferrous metals Not preferred for welding thin sections Any terminal can be connected to the work or electrode Comparison of A.C. and D.C. arc welding

8. Direct Current (from Generator) Less efficiency Power consumption more Cost of equipment is more Low voltage – safer operation suitable for both ferrous non ferrous metals preferred for welding thin sections Positive terminal connected to the work Negative terminal connected to the electrode Continued …

9. Welding transformer consists of a step-down transformer with a tapped secondary having an adjustable reactor in series with it for obtaining drooping V/I characteristics. It has a magnetic core with primary winding which is thin and has large number of turns on one arm. A secondary winding with less number of turns and high cross-sectional area on the other arm. So we get less voltage and high current from the secondary winding output. Construction

10. The secondary is tapped to give different voltage/current settings. Continued…

11. A dc welding transformer also has same type of winding the only difference is that we connect a rectifier(which converts ac to dc) at the secondary to get dc output. We also connect a inductor or filter to smooth the dc current. This will be construction of dc welding transformer. The diagrams are shown below. Continued…

12. The welding transformer reduces the voltage from the source voltage to a lower voltage that is suitable for welding. Usually between 15 and 45 volts. The secondary current is quit high and it may be typically 200A to 600A, but it could be much higher. The secondary may have several taps for adjusting the secondary voltage to control the welding current. The taps are typically connected to a several high-current plug receptacles or to a high-current switch. One end of the secondary is connected to the welding electrode, whereas the other end is connected to the pieces to be welded .If any high current flows, heat is produced due to the contact resistance between the electrode and the pieces to be welded. Working

13. Continued … When a high current flows a large amount of I2R heat is produced due to contact resistance between welding pieces and electrode. The generated heat melts a trip of the electrode and the gap between the two pieces is filled.

14. The four basic types of welding transformers are The saturable high reactance type The external reactor type The integral reactor type The reactor type Types of welding transformer

15. In the diagram these partial fluxes have been marked as ɸ L1  and ɸ L2 . In other words, they are responsible for the reactance of the coils and the respective reactive voltage drops across them. As the current increases, the leakage fluxes also increase and so does the e.m.f . of self-induction. This is why an increase in the primary or secondary current results in increase in the reactive voltage drop across the respective windings. The High Reactance Type Welding Transformer

16. This type of welding transformer consists of a normal reactance, single phase, step down transformer and a separate reactor or choke. The inductive reactance’s and resistances of the windings in such a welding transformer are low, so that its secondary voltage varies but a little with the welding current. The required drooping or negative volt-ampere char­acteristic is ensured by the reactor placed in the secondary of the welding circuit The reactor consists of a steel core and a winding wound with a wire designed to carry the maximum allowable current. External Reactor Type Welding Transformer

17. the arc voltage decreases with increase in current, or with in­crease in voltage drop across the reactor. This gives a negative or drooping volt-ampere characteristic. Continued …

18. The welding transformer of the integral reactor type, has a primary winding I, a secondary winding II, and a reactor winding III. Apart from the main limbs, the core has additional limbs carrying the reactor winding. The current is adjusted by means of moving core C placed between the additional limbs. Integral Reactor Type Welding Transformer

19. In this welding transformer an isolated low voltage, low amperage dc circuit is employed to change the effective magnetic characteristics of the magnetic core. Thus, a large amount of ac is controlled by using a relatively small amount of dc, hence making it possible to adjust the output volt-ampere characteristic curve from minimum to maximum. For example, when there is no dc flowing in the reactor coil, it has its minimum impedance and thus maxi­mum output of the welding transformer. Saturable Reactor Type Welding Transformer

20. As the magnitude of dc is increased with the help of rheostat in the dc circuit, there are more continuous magnetic lines of force thus the impedance of the reactor is increased and the output current of the welding transformer is decreased. This method has the advantage of removing movable parts and flexing conductors and is often used for gas tungsten arc welding power supplies. To achieve the desired aim of low voltage and high current the reactor coils are connected in opposition to the dc control coil. Continued …

21. as shown in figure, Placing an air-gap in the reactor core is one method of reducing this distortion. Alternatively, a large choke can be inserted in the dc control circuit. Either method, or a combination of the two, will produce the desired result. Continued …

22. A generator (D.C.) or Transformer (A.C.) Two cables- one for work and one for electrode Electrode holder Electrode Protective shield Gloves Wire brush Chipping hammer Goggles Auxiliary equipment

23. Continued…

24. Low operation and maintenance cost Low wear No arc blow Less post welding cleaning Greater affidavit rates High welding speeds This setup can be move easily for different operation places. Size is relatively less than other welding process’s equipments. No chances of blasting during operation like gas welding. Controlling is easy during operation. Advantages of electric arc welding

25. Higher introductory setup cost. Higher upkeep cost due to requirement of additional electronic parts. Highly skilled labour is required. Its polarity cannot be changed. Internal residual is set up in part which is welded due to continue heating and cooling of that part during operation. It is not suitable for welding of cast iron and non-ferrous metals. Disadvantages

26. there are various types in electric arc welding so they are used for different types of application based on metal type and operation. Gas metal arc welding (GMAW) Gas tungsten arc welding (GTAW) Shielded metal arc welding (SMAW) Flux cored arc welding (FCAW) Energy beam arc welding (EBW) Atomic hydrogen welding (AHW) Plasma arc welding Application

27. Aerospace industry Aviation industry Welding of non ferrous metals Space vehicles Components made of magnesium and aluminum To weld thin joints Sealing of nuclear fuel canisters before burial. Gas tungsten arc welding (GTAW)

28. This type of welding can be used for welding of following metals Low alloy and high tensile steels Low carbon steels Stainless stell and high-resisting steels Cast iron Shielded metal arc welding (SMAW)

29. Electronic welding Instrument panels welding Fuel tanks Energy beam arc welding (EBW) This process is used in those application where rapid welding is needed is necessary Eg . Stainless steels and special alloys Atomic hydrogen welding (AHW)

30. Marine and aerospace industries Electronic industry Used for repair tools, die and mold Used for welding of turbine blade. Welding of titanium parts Plasma arc welding

31. Thank You