The document discusses different types of power supplies required for electrical welding. It describes constant voltage and constant current power supplies, and how they differ in how they maintain output voltage or current. Transformer, generator/alternator, and inverter-based power supplies are described. The document also summarizes different types of electric welding including resistance welding (butt, flash, spot, projection), electric arc welding using metallic electrodes or carbon arc, and their applications.

1. GUJARAT TECHNOLOGICAL UNIVERSITY
GOVERNMENT ENGINEERING COLLEGE,
VALSAD.
A TOPIC IS:
POWER SUPPLY REQUIRED FOR ELECTRICAL WELDING
UNDER SUBJECT OF UEET(2160907)
BE – SEMESTER:- 6 (ELECTRICAL BRANCH)
SR NO. NAME ENROLLMENT NO.
1. RAJPUT DHARMIN A. 170190109045
2. RATHAWA SAVAN H. 170190109046
FACULTY GUIDE :-
:-
1. PROF. D.C.PARMAR
2. PROF.J.D.PATEL
SUBMITTED BY:
HEAD OF DEPARTMENT:- PROF. K.L.MOKARIYA

2. Introduction :-
 Selection of a welding process is determined primarily by the characteristics of the joint, the materials involved, their shape and thickness, and joint design.
Additionally, production requirements, such as rate and quality, must also be considered.
 A welding power supply is a device that provides an electric current to perform welding.Welding usually requires high current (over 80 amperes) and it can need
above 12,000 amperes in spot welding. Low current can also be used; welding two razor blades together at 5 amps with gas tungsten arc welding is a good
example. A welding power supply can be as simple as a car battery and as sophisticated as a high-frequency inverter using IGBT technology, with computer
control to assist in the welding process.
 Welding machines are usually classified as constant current (CC) or constant voltage (CV); a constant current machine varies its output voltage to maintain a
steady current while a constant voltage machine will fluctuate its output current to maintain a set voltage. Shielded metal arc welding and gas tungsten arc welding
will use a constant current source and gas metal arc welding and flux-cored arc welding typically use constant voltage sources but constant current is also possible
with a voltage sensing wire feeder.
Constant Voltage Power Supply :
 The other basic type of arc welding power supply produces a constant voltage. Thus at any voltage setting current may vary from zero to an extremely high short circuit current.
Such a machine is designed specifically for gas shielded metal arc welding and is not generally suitable for stick electrode welding.
 Actually, no welding machine can produce a truly constant voltage. In practice, voltage drops at least 1 volt for each 100 amp output. Nevertheless, short circuit currents may be as
high as several thousand amperes.
 Normally, constant voltage machines have lower open circuit voltages than the constant current machines, about 50 volts maximum as compared to 80 volts. As a means of
obtaining the desired arc voltage, the operator sets open circuit voltage, rather than current, at the machine. Settings may range from 10 to 48 volts.
 Welding current can reach several thousand amperes at short circuit. Current adjusts itself to burn off filler metal at a rate sufficient to maintain the arc length required by the present
voltage and is thus determined by the rate of electrode feed.

3. A.C. welding:-
 In AC, the flow of electrons keeps switching directions, going back and forth. It can change its polarity 120 times per second. Every time the polarity goes from
DC negative to DC positive, the output for a split second has zero amperage. This no output moment results in that the arc tends to wander or extinguish. To
overcome this problem, look for electrodes specifically designed for AC welding. They have special coating that keeps the arc ignited. However, the arc will still
have more fluctuation and flutter than on DC polarity.
 Alternating current helps to transmit electricity over large distances. So you can typically find this current used in high voltage devices, such as household outlets
and appliances.
 AC is usually a secondary choice in welding. However, there are a few instances where AC would be preferred. First of all, you can use it if it’s the only power
supply available. For example, low cost, entry-level machines sometimes offer only AC power.
 Secondly, switching to AC can help to fix arc blow problems, which means that the arc starts wandering or blows out of the joint. The cause of arc blow can be
magnetism of the metal you’re welding or the arc’s current. The alternating current between positive and negative polarity enables a steadier arc when welding
magnetic parts. Arc blow problems can also have external causes, such as windy conditions.
Constant Current Power Supply :
 The conventional stick electrode welder is sometimes called a ’constant current machine’. It is also called a ’dropper’ because its voltage drops as welding current
increases, thus its volt- ampere output curve ’droops’.
 With the machine turned on but with no arc, and hence no current flowing, it has a relatively high open circuit voltage of 70-80 volts. Generally speaking welding is
done at the steeper portions of the curve and this is ideal for manual stick electrode welding.
 But, since rate of burn off of filler metal is determined by the amount of current, burn off stays substantially constant if current doesn’t vary.
 There are many variations of this type of machine based upon power input (single or three phase), output (ac, dc, or ac/dc), and the type of output control
(mechanical or electrical).

4.  DC polarity is used in most welding applications. It produces a smoother welding output compared to AC. It creates a more stable arc, easier welding and less
spatter. You can also either use DC negative for faster deposition rates when welding thin sheet metal or use DC positive for more penetration into the steel.
 DC currents have the electrons flowing in a steady single direction. It has constant polarity, which can be either positive or negative.
 DC is often used in low voltage devices, such as cell phone batteries and remote controls.
Applications Of AC Welding:
 TIG welding aluminum since AC supports welding at a higher temperature. Aluminum also has a tenacious oxide film on the surface and when AC switches to
electrode positive, it helps to remove the oxide and clean the surface.
 In shipbuilding when you need deeper penetration of plate metals.
 When welding materials that have a magnetized field.
 Drawbacks Of AC Welding:
 The quality of the weld is usually not as smooth as with DC welding.
 It also creates more spatter.
 The arc is more difficult to handle and it’s not as reliable as when DC welding.
D.C. Welding:-

5. Applicationsa Of DC Welding:
 It’s used in most stick welding applications.
 Overhead and vertical welding.
 Stainless steel TIG welding.
 When welding thinner metals.
 Single carbon brazing.
 Drawbacks Of DC Welding.
 Can’t fix arc blow.
 DC currents usually require an internal transformer for switching the current, which makes DC welders more expensive.
 It’s doesn’t work well for welding aluminum as it can’t produce the necessary high-intensity heat.
Transformer :
 A transformer-style welding power supply converts the moderate voltage and moderate current electricity from the utility mains (typically 230 or 115 VAC) into a high current and
low voltage supply, typically between 17 and 45 (open-circuit) volts and 55 to 590 amperes. A rectifier converts the AC into DC on more expensive machines.
 This design typically allows the welder to select the output current by variously moving a primary winding closer or farther from a secondary winding, moving a magnetic shunt in
and out of the core of the transformer, using a series saturating reactor with a variable saturating technique in series with the secondary current output, or by simply permitting the
welder to select the output voltage from a set of taps on the transformer's secondary winding. These transformer style machines are typically the least expensive.
 The trade off for the reduced expense is that pure transformer designs are often bulky and massive because they operate at the utility mains frequency of 50 or 60 Hz. Such low
frequency transformers must have a high magnetizing inductance to avoid wasteful shunt currents. The transformer may also have significant leakage inductance for short circuit
protection in the event of a welding rod becoming stuck to the work piece. The leakage inductance may be variable so the operator can set the output current.

6. Generator and alternator :
 Welding power supplies may also use generators or alternators to convert mechanical energy into electrical energy. Modern designs are usually driven by an internal combustion
engine but older machines may use an electric motor to drive an alternator or generator. In this configuration the utility power is converted first into mechanical energy then back
into electrical energy to achieve the step-down effect similar to a transformer. Because the output of the generator can be direct current, or even a higher frequency AC, these older
machines can produce DC from AC without any need for rectifiers of any type, or can also be used for implementing formerly-used variations on so-called heliarc (most often
now called TIG) welders, where the need for a higher frequency add-on module box is avoided by the alternator simply producing higher frequency ac current directly.
Inverter:
 Since the advent of high-power semiconductors such as the insulated gate bipolar transistor (IGBT), it is now possible to build a switched-mode power supply
capable of coping with the high loads of arc welding. These designs are known as inverter welding units. They generally first rectify the utility AC power to DC;
then they switch (invert) the DC power into a step down transformer to produce the desired welding voltage or current. The switching frequency is typically 10 kHz
or higher. Although the high switching frequency requires sophisticated components and circuits, it drastically reduces the bulk of the step down transformer, as the
mass of magnetic components (transformers and inductors) that is required for achieving a given power level goes down rapidly as the operating (switching)
frequency is increased. The inverter circuitry can also provide features such as power control and overload protection. The high frequency inverter-based welding
machines are typically more efficient and provide better control of variable functional parameters than non-inverter welding machines.
 The IGBTs in an inverted based machine are controlled by a micro controller, so the electrical characteristics of the welding power can be changed by software in
real time, even on a cycle by cycle basis, rather than making changes slowly over hundreds if not thousands of cycles. Typically, the controller software will
implement features such as pulsing the welding current, providing variable ratios and current densities through a welding cycle, enabling swept or stepped variable
frequencies, and providing timing as needed for implementing automatic spot-welding; all of these features would be prohibitively expensive to design into a
transformer-based machine, but require only program memory space in a software-controlled inverter machine. Similarly, it is possible to add new features to a
software-controlled inverter machine if needed, through a software update, rather than through having to buy a more modern welder.
 Additional types of welders also exist, besides the types using transformers, motor/generator, and inverted. For example, laser welders also exist, and they require an
entirely different type of welding power supply design that does not fall into any of the types of welding power supplies discussed previously. Likewise, spot welders
require a different type of welding power supply, typically containing elaborate timing circuits and large capacitor banks that are not commonly found with any other
types of welding power supplies.
Other Types of Supply :

7. Types of Electric Welding :
Electric Welding
1. Resistance welding
 Butt Welding
 Flash Welding
 Spot Welding
 Projection Welding
2. Electric Arc Welding
 Metallic Arc Welding
 Carbon Arc Welding
 Atomic Hydrogen Welding
 Shielded Arc Welding
In this method current is passed through the inherent resistance of the joint to be welded means heat generated as per the equation I^2Rt kilojoule.
1. Resistance Welding :

8.  This type of welding is employed generally for over lapping joints. Two metal sheets are over lapped and two sharp copper electrodes are kept at the place where
welding is required. Proper pressure is applied to the electrode before passing current.
 When current passes, the spot at which sheets are fixed by electrodes gets hes melting point and gets welded. Electrodes are made hollow and water is circulated in
all types of resistance welding.
I. Butt Welding:
 In this type of welding, the two metal to be joined are kept close together and fitted in the copper electrode holder
 Current is passed through the joint. Due to resistance of joint heat is produced and reaches to the melting point, at the same time pressure is applied, joint gets upset
and welded pressure is kept till joint gets cool-down.
Application :
(1) To weld non ferrous metal strips, rod, pipes etc.
(2) To weld aluminum or copper winding wires of big transformer
II. Flash butt welding:
 In this type of welding two metals pieces to be joined are not kept in close contact, but are kept in loose contact.
 When current is passed due to loose contact air in between gets ionized and forms a spark (Flash). Both metal ends are heated to melting point by this spark, then
pressure is applied to close them and welding takes place. Due to flash unevenness of joint is removed and strong weld results.
Application :
(1) Mostly used for steel and ferrous alloys.
(2) Used in automobile industries to weld main body axle, frame etc.
III. Spot welding :

9. IV. Projection Welding :
 This type of welding is also used for over lapping metal sheets, where series of welds is required.
 Roller or wheel electrodes are used.
 Electrodes are rotated in opposite direction, pushes object forward. Intermittent current is passed. which allows series of welds.
 Around 200 to 500 spot welds are there in one meter length.
Application :
(1) In the manufacturing of sheet metal frame, boxes, automobile body work, toys refrigerator, kitchen utensils, etc.
(2) In the manufacture of body of cars, bus and sheet metal works.
(3) In construction of ship where air and water proof joints are required.
V. Seam welding:
 It is the modified form of spot welding. In this type welding electrodes are made flat and hollow. Before welding to metal sheets, projections are created on one piece
by means of press. During welding current passes only through projections and welding is carried out at the projections only.
Applications:
(1) To join thin metal sheets like container of oil .
(2) To get strong joint for two of different thickness sheets
(3) More suitable for punching, forming, stamping surfaces.
(4) It is more efficient than spot welding due to less maintenance of electrode, speedy process, accurate

10. 2. Electric Arc Welding :
 In this method of producing localized heat electricity is conducted in the form of an arc which is established between the two metallic surface.
 This type of welding is more popular in the industries.
 Arc welding name given as the are is used as source of heat.
 In this process of welding arc is struck between the joint of two metal pieces and an electrode.
 The electrode first is brought together in contact with two metal pieces to be joined and than pulled away by 2 to 4 mm. As a result arc is struck between them. Air between
electrode and metal joint gets inosied and becomes conductive and an are is struck.
 To sustain the arc voltage required is about 20 volt while current in the range of 2000 to 3000 ampere and the arc temperature is in the order of 3000°C to 5000°C.
 The heat produced is sufficient for fusion of metal joint. On cooling metal solidifies to form welded joint.
Applications :
(1) In dairy industries for making containers.
(2) Leak proof tanks like transformer tank, gas line tank.
(4) Oil industries for manufacturing of tin container.

11. I. Metal arc welding :
 Metal arc welding has large utility.
 It is mainly used for mechanical maintenance work.
 Same metal rod is used for welding the two metal pieces. The metal rod is made +ve and work piece to be welded is made -ve. Metal rod it self melts and as a filler
metal for filling joint cavity.
 Both types of supply a.c. or d.c. can be used for metal arc welding. For a.c. supply voltage is kept 70 to 100 volts while for d.c. it is 50 to 60 volts.
 In this type of welding, only disadvantages is arc blow.
 It makes joint to cool down resulting in more consumption of energy. Flux is used to over come this welding difficultly, which produces layer of slag on the welding
and maintains welding temperature.

12. Electrodes used for metal Are Welding :
Electrode is a filler material in the form of a wire or rod which either base or coated uniformly with the flux.
The following materials are commonly used for coating :
(i) Titanium Oxide
(ii) Ferro-Maganese
(iii) Silica-Flour
(iv) Asbestos Clay
(v) Calcium Carbonate etc.
 In this type of welding electrode is of carbon and the polarity of supply is changed as that in metal arc welding. Work piece is made +ve and electrode made -ve. If the
electrode made +ve then carbon particles makes the joint brittle. Separate filler metal is required to fill up joint cavity. This type of welding is carried out by two ways
(i) Using flux and (ii) Without using flux. Flux is used in form of pest or powder either of silicon or of phosphorus. Normally flux is used for non-ferrous metal welding
and flux is not required for ferrous metal welding
II. Carbon arc welding :
Application:
(1) It is suitable for galvanized sheets using Cu-Si-Mn alloy filler metal.
(2) Useful for welding thin-high nickel alloys.
(3) Employed for welding stainless steel of thinner gauges.
(4) With this process, model metal can be easily welded by using a suitable coated filler rod.

13. Electrodes :
(i) In this process, electrodes are made of either carbon or graphite usually 30 mm long and 2.5 mm to 12 mm in diameter.
(ii) Graphite electrodes are harder, more brittle and last longer than carol electrodes.
 In this type of welding arc is not struck between electrode and work piece but is struck between two tungsten electrodes in the vicinity of hydrogen gas around electrode
and arc.
 Due to high temperature of arc hydrogen gas is converted in form of atomic hydrogen. This atomic hydrogen passes through welding chamber, it again comes to
molecular form emitting large amount of heat. Total amount of heat reaches temperature of about 4000°C.
 This heat is utilized for fusion welding. Welding is done in the atmosphere of hydrogen makes the joint free from oxygen and nitrogen. Filler of same metal is used.
 It is used for welding of stainless steel, carbon steel and aluminium.
Applications:
(1) This process of welding being very expensive is used mainly for high grade work in stainless steel and non-ferrous metals.
I. Atomic hydrogen welding :
 This type of welding is same as atomic hydrogen are welding, but here instead of hydrogen, an inert gas like argon or helium gas is used. Welding is done in the atmosphere
of any inert gas like argon or helium which creates shield of inert gas around weld piece. Welding becomes free from oxidation, strong and without use of flux.
 This type of welding is used for welding of aluminium alloys, magnesium and its alloys.
III. Inert gas welding :

14. IV. Shielded Arc Welding :
 In this process, molten metal protected from action of atmosphere by an envelope of chemically reducing or inert gas. Due to some chemical reactions metal becomes
weak, brittle and corrosion resistance. Thus, several methods of shielding have been developed.
 Simplest is the use of a flux coating on electrode which in addition to producing a slag which floats on top of molten metal and protects it form atmosphere and produce
an envelope of inert gas around are and weld.
 Weld made with this process are more superior to those deposited by an ordinary arc.
D.C. WELDING EQUIPMENTS :
 In D.C. Welding d.c. supply is used and it is obtained from motor-generator set.
 Normally squirrel cage induction motor coupled to d.e differential compound generator is used.
 The characteristics of this generator is that voltage decreases rapidly as current increases. To control current, shunt is used in parallel to series field winding. This method
produces steady arc gives better welding conditions.
 Only disadvantage of this method is that capital and running cost are high.
A.C. WELDING EQUIPMENTS:
 In a.c. welding, step down transformer giving low voltage about 70 to 100 volt is used.
 Control of current is achieved by using regulating reactor working below saturation point, It has low power factor and low efficiency.

15. 1. Gas Metal Arc Welding (GMAW/MIG)
Welding has been used in metallurgy for millennial with forge welding performed by blacksmiths as the only real viable technique. This all changed in the 19th century when
newer methods like arc-welding and oxyfuel welding were developed.
Some of the most common welding processes commonly employed day include.
MIG - Gas Metal Arc Welding (GMAW)
TIG - Gas Tungsten Arc Welding (GTAW)
Stick - Shielded Metal Arc Welding (SMAW)
Flux-Cored Arc Welding (FCAW)
Energy Beam Welding (EBW)
Atomic Hydrogen Welding (AHW)
Gas Tungsten-Arc Welding
Plasma Arc Welding
 This style of welding is also referred to as Metal Inert Gas (MIG). It uses a shielding gas along the wire electrode, which heats up the two metals to be joined. This
method requires a constant voltage and direct-current power source, and is the most common industrial welding process. It has four primary methods of metal transfer:
globular, short-circuiting, spray and pulsed-spray.
2. Flux Cored Arc Welding (FCAW)
 This was developed as an alternative to shield welding. The semi-automatic arc weld is often used in construction projects, thanks to its high welding speed and portability

16. 4. Gas Tungsten Arc Gas Welding (GTAW/TIG)
 Welding together thick sections of stainless steel or non-ferrous metals is the most common use for this method. It is also an arc-welding process that uses a tungsten
electrode to produce the weld. This process is much more time consuming than the other three and much more complex.
Metal Inert Gas (MIG)
3. Shielded Metal Arc Welding (SMAW)
 With this particular type of welding, the welder follows a manual process of stick welding. The stick uses an electric current to form an arc between the stick and the
metals to be joined. This is often used in the construction of steel structures and in industrial fabrication to weld iron and steel.

17. THANK YOU