Welding and it's types ( Electrical Engineering)

Topic includes 

- Welding

-Types of welding
- Arc welding
- Equipment
- Carbon arc welding
- Metallic arc welding
- Advantages of coated electrode

- Resistance welding

- Polarity

- Spot welding

- Projection welding

- Seam welding

- Butt welding

- TIG welding
- MIG welding

- Ac and DC welding
- Equipments of welding
- Comparison table
- Welding control

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Welding

• Welding is a process of joining similar metals by application of heat with or
without application of pressure and addition of filler material.

Types of welding

1.Plastic Welding

• In Plastic welding or pressure welding, the pieces of metal to be joined are
heated to plastic state and then forced together by external pressure.

2. Fusion Welding

• In fusion welding or non pressure welding , the material at the joint is heated
to molten state and allowed to solidify.

Welding Processes

1. Gas welding

 i. Oxyacetylene
 ii. Air-acetylene
iii. Oxy-hydrogen

2. Arc Welding

i. Carbon Arc
ii. Metal Arc
iii. Gas Metal Arc ( MIG)
iv. Gas Tungsten Arc ( TIG)
v. Atomic-hydrogen arc
vi. Plasma Arc
vii. Submerged Arc welding
viii. Flux-cored arc
ix. Electro-slag

3. Resistance welding

i. Butt welding
ii. Spot welding
iii. Seam welding
iv. Projection welding
v. Percussion welding

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4. Thermit welding

5. Solid State welding

i. Friction
ii. Ultrasonic
iii. Diffusion
iv. Explosive

6. Newer Welding Processes

i. Electron Beam
ii. Laser

7. Related processes

i. Oxyacetylene cutting
ii. Arc cutting
iii. Hard facing
iv. Brazing
v. Soldering

 Electric Arc Welding

The definition of arc welding is a welding process which is used for welding the metals with the help of electricity to generate sufficient heat for softening the metal, as well as when the softened metal is cooled then the metals will be welded. This kind of welding uses a power supply to make an arc among a metal stick & the base material to soften the metals at the end of the contact.

Working Principle of Electric Arc Welding

The working principle of arc winding is, in a welding process the heat can be generated with an electric arc strike among the workpiece as well as an electrode. This is glowing electrical discharge among two electrodes throughout ionized gas.

Equipment

The arc welding equipment mainly includes AC machine otherwise DC machine, Electrode, Holder for the electrode, Cables, Connectors for cable, Earthing clamps, Chipping hammer, Helmet, Wire brush, Hand gloves, Safety goggles, sleeves, Aprons, etc.

Carbon arc Welding

Carbon Arc Welding (CAW) is a welding process, in which heat is generated by an electric arc struck between an carbon electrode and the work piece.

Carbon Arc Welding

Low cost of equipment and welding operation;

High level of operator skill is not required;

The process is easily automated;

Low distortion of work piece.

Metallic arc welding

Shielded metal arc welding (SMAW), also known as manual metal arc welding, is a manual arc welding process that uses a consumable and protected electrode. As the electrode melts, a cover that protects the electrode melts and protects the weld area from oxygen and other atmospheric gases

The advantage of using coated welding electrodes

Coated electrodes are used with stick welding, or Shielded Metal Arc Welding (SMAW). The coating on welding electrodes is important for a few reasons. It provides more control over the arc, helps protect the molten metal from impurities, and allows for cleaner, stronger welds

Resistance welding

It is a group of welding processes in which welding heat is obtained from resistance of the work to the flow of Electric current and by the application of pressure.

No filler metal or flux is added.

Resistance welding is differ from arc arc welding

in that pressure is used but filler are not used.

Polarity

It so defined as the type of potential given to the workpiece or electrode. In direct current that is DC power source, positive and negative terminals
are fixed whereas in alternating current that is ac power is varying.

It is of two types

- Straight Polarity

In this, electrode is having negative terminal whereas workpiece is connected to the positive terminal of the DC power.

- Reverse Polarity

In reverse Polarity, electrode is connected to positive terminal whereas workpiece is connected to the negative terminal of DC power source.

Some important resistance welding are

Butt welding, seam welding, flash welding, spot welding, projection welding.

Spot welding

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Spot welding (or resistance spot welding) is a type of electric resistance welding used to weld various sheet metal products, through a process in which contacting metal surface points are joined by the heat obtained from resistance to electric current.

The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together. Work-pieces are held together under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020 to 0.118 in) thickness range. Forcing a large current through the spot will melt the metal and form the weld. The attractive feature of spot welding is that a lot of energy can be delivered to the spot in a very short time (approximately milliseconds).That permits the welding to occur without excessive heating of the remainder of the sheet.

Application

Spot welding is typically used when welding particular types of sheet metal, welded wire mesh or wire mesh. Thicker stock is more difficult to spot weld because the heat flows into the surrounding metal more easily. Spot welding can be easily identified on many sheet metal goods, such as metal buckets. Aluminium alloys can be spot welded, but their much higher thermal conductivity and electrical conductivity requires higher welding currents. This requires larger, more powerful, and more expensive welding transformers.

Projection welding

Projection welding is a resistance weld where the design or shape of the part is used to make discreet individual point contacts to concentrate the current during the welding process. In most applications multiple small projections are formed on one surface of the parts to be welded. These projections can be round dimples, elongated ridges, circular, or the extended corners of weld nuts. Two round wires placed together at 90 degrees form a point contact. This would also be a projection weld. When the mating parts are brought together these projections concentrate the current flow and generate the heat in these locations. When the projections get hot they collapse as the weld nugget forms. After cooling the result is several weld nuggets holding the part together. Of course in the case of cross wire welding there is one weld per crossing location but normally many are welded at the same time as in fencing.

Seam welding

Seam welding is the process of joining two similar or dissimilar materials at the seam by the use of electric current and pressure. The process is mostly used on metals since they conduct electricity easily and can sustain relatively high pressures.

Seam welding is possible thanks to contact resistance created between the two metals.

As current passes between the metals, heat gets generated at the small gap. Electrodes maintain and control the flow of electricity.

Butt welding

Butt welding is a commonly used technique in welding that can either be automated or done by hand on steel pieces. Butt welding can also be done with brazing for copper pieces. It is used to attach two pieces of metal together such as pipe, framework in factories, and also flanges. A flange is something that either is internal or external that provided to strengthen a piece of material. In factories butt welding has shown how economical it can be for companies to use when building things out of metal. This is because if they wanted to make something out of metal without welding it together they would have to bend everything and reinforce the structure which costs more than welding the two pieces together. Butt welding is accomplished by heating up two pieces of metal, or applying pressure, or doing both of those.Penetration while welding the metal is important to maintain and with thin pieces of metal this is possible however, with thick pieces edge preparation may have to be done to prepare the metal.Full penetration butt welds are made when they are in the within the parent(bigger, stronger) metal. In butt welding the strongest welds will have the fewest imperfections. To achieve this the heat input is controlled, which decreases the size of the weld.In commercial welding when this is done it also reduces cost but in order to maintain the strength of the weld double butt welds will be used. In butt welding there are two types used to achieve the specific welds and then there are also a variety of joints considered to be butt joints.

Butt welding is best performed with MIG or TIG welding applications due to their natural ability to connect two pieces of metal together.Using different types of welding electrodes for the welder will determine the properties of the weld such as its resistance against corrosion and strength.Electrodes conduct current through the metal being welded in order join the two pieces.The metal determines the type of welding that is required.

TIG welding 

Tungsten inert gas welding

In this process, the heat necessary to melt the metal is provided by a very intense electric arc which is struck between a virtually non consumable tungsten electrode and metal workpiece. The electrode does not melt and become a part of the weld . On joints where filler metal is required, a welding rod is fed into the weld zone and melted with base metal in the same manner as that used with oxyacetylene welding. The weld zone is shielded from the atmosphere by an inert gas which is ducted directly to the weld zone where it surrounds tungsten.

The major inert gases that are used are argon and helium.

MIG welding

 Metallic inert gas welding

The inert gas consumable electrode process or the MIG process is a refinement of the TIG process..

In this process the tungsten electrode has been replaced with a consumable electrode. The electrode is driven through the same type of collect that holds a tungsten electrode by a set of drive wheels. The consumable electrode in MIG process acts as the supply for the filler material.

Diff between ac and DC welding

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.

Equipments

TIG and MIG Welders

The most common welder used in basic projects by homeowners and hobbyists is the stick welder. Also known as the shielded-metal arc welder, most people prefer it due to how easy it is to buy and the lack of a special environment needed to use it. But the electrodes in a stick welder require frequent replacement compared with other forms of welding. These include the gas tungsten arc machines, TIG and gas metal arc welder, known as MIG welders. You will also need some sort of gas feed with this type of welder.

Charged Electrode

An electrode is the tip of the tool that passes the current from the welder to the material being welded, making it so hot it becomes liquid. In the cases of the stick and MIG welders, the type of metal and the heat to melt it drives the type of electrode tip needed. But in a TIG welder, the electrode tip is made of non-consumable tungsten, and does not require replacement.

Wire and Electrode Feeds

Some welds require a feed to strengthen the joint due to the geometry or weakness of the weld. Stick welding uses the electrode to feed; MIG welding often uses a wire feed. And TIG welding likewise uses a feed due to its non-consumable nature.

Other Tools

Most welders also use an angle grinder to help smooth out joints, wire brushes, to clean metal surfaces or abrade them before welding, a chipping slag hammer, C-clamps, ball peen hammer, electrode tip cleaners, flint strikers, needle nose and linesmen cutting pliers. Other tools to have on hand: cold chisels, flat-head and Phillips screwdrivers, round and flat files, levels and squares.

Safety Equipment

Due to the temperature and elements involved, welding is highly dangerous and can be lethal if handled incorrectly. Before you touch a welding setup, wear a welding helmet that protects your eyes, ear plugs, solid boots to protect your feet from sparks or slag, welding gloves to protect your hands and leathers to cover the rest of your body. Do not weld without these, as you will likely get hurt.

Comparison ac and DC arc Welding

Control

The DC welding current is controlled with a simple and robust control circuit. ... With this control level, gas metal arc welding and flux-cored arc welding can be applied. The current control and the DC voltage control can also be applied in different cycles depending on a external signal.

Welding position

The welding position (flat, vertical, horizontal or overhead) and proximity of the welder to the fume plume affect exposure. As the welder naturally bends over the workpiece, the flat position induces the highest level of fume in the breathing zone. The welder should adopt a working position which ensures that his head is away from the plume.

Location and type of workplace

Welding in a large workshop, or outdoors, prevents build-up of fume and gases. However, in a small workshop, fume will not be readily dispersed and the welder may be subjected to a higher than average exposure. Working in confined spaces, in particular, requires an efficient, monitored, ventilation system so exposure is controlled and there is no depletion of oxygen in the working atmosphere.

Exposure duration

The long-term occupational exposure limit (OEL) given in Job Knowledge for Welders No. 31 relates to the average concentration over an eight-hour period. Exposure will be intermittent, mainly during the arcing period. There should be relatively little exposure between arcing periods but this may be influenced by the presence of other welders, effectiveness of control measures and general ventilation. Furthermore, as work patterns (arcing time and down time) vary from day to day, average exposure may often only be assessed by frequent sampling.

- Respiratory protection equipment
- Safe practise and accident avoidance

- Safety first