Manufacturing Engineering - WELDING

A group of welding processes where joining (Coalescence) is produced by heating with a gas flames with or without the application of pressure and with or without the use of filler material.

Oxyacetylene welding, commonly referred to as gas welding, is a process which relies on combustion of oxygen and acetylene. When mixed together in correct proportions within a hand-held torch or blowpipe, a relatively hot flame is produced with a temperature of about 3,200 deg.C. The chemical action of the oxyacetylene flame can be adjusted by changing the ratio of the volume of oxygen to acetylene.

Advantages

• Low cost versatile equipment and usually portable.

• Can weld most of the common materials.

• Operation temperature is lower and easily controllable.

• Well adapted for short production runs.

Disadvantages

• O2 & C2H2 gas are expensive.

• Safety issues regarding handling & supply

• Flame takes considerably large amount of time to heat up the metal.

• HAZ occurrence is more.

The inner and outer cone of the flame has different color of flame because of different level of combustion occurrence. The inner cone has red or orange coloration whereas the outer zone is usually blue.

There are 3 types of flames in gas welding - Oxidizing, Carburizing & Neutral

Neutral - The neutral flame has a one-to-one ratio of acetylene and oxygen. It obtains additional oxygen from the air and provides complete combustion. It is generally preferred for welding. The neutral flame has a clear, well-defined, or luminous cone indicating that combustion is complete.

Oxidizing - The oxidizing flame is the flame produced with an excessive amount of oxygen. When the amount of oxygen increases, the flame shortens, its color darkens, and it hisses and roars.

Carburizing - The carburizing flame has excess acetylene, the inner cone has a feathery edge extending beyond it.

Torch angle is the angle between axis of torch & axis of workpiece. Whereas flame density is the ratio of heat supplied to the exposed area.

Selection of Torch Angle (TA)

(1) For joining of high melting point plates –

High temperature = High flame density = Higher TA (Torch Angle) will be required.

(2) For high thickness material –

High flame density = Higher TA (Torch Angle) will be required.

(3) High conductivity plates –

Due to high conductivity, the heat dissipation to the base metal will be high hence lesser heat will be available for the welding.

Hence large amount of heat will be required = High flame density = More TA

(4) Based on location of welding –

At the beginning of the welding, Since the plates are at room temperature. Large amount of heat will have to be supplied so that the plates come to the melting point temperature. Therefore, we will use high flame density & high TA at the BEGINNING of welding.

At the end of the welding, since this portion is already heated up because of conduction of heat from the other portions, a pool of molten metal will be collected there & if we use higher torch angle, this pool of molten metal will move out leaving behind a cavity called as “Crater defect”. And hence we use lower TA at the END of welding.

In case of AAW, Whatever amount of oxygen is required for complete combustion of acetylene is obtained entirely from the atmosphere.

Because the total O2 has to be taken from the atmosphere, the flame has to travel longer distance for complete combustion. This leads to longer flame length & hence more loss of heat to the atmosphere. Hence average temperature range is 500 – 700 deg.C

Usage – Welding of low melting point metals like Pb,Sn,Zn,Cd etc.

Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals, when cool, result in a binding of the metals.

The primary functions of the power source are to produce sufficient heat to melt the joint and to generate a stable arc and metal transfer. As the welding processes require high current (50-300A) at relatively low voltage (10-50V),the high voltage mains supply (230 or 400V) must be reduced by a transformer.

There are three types of power supply in arc welding – DCSP,DCRP & AC

An electrode is a coated metal wire. It is made of materials similar to the metal being welded.There is a code designation for coated stick electrodes for metal arc welding, for selecting a correct electrode for a specific application as IS : 815-1974.

Various types of arc welding processes are discussed in this lecture - CAW,SMAW,GTAW,GMAW,SAW etc.

Resistance welding is the joining of metals by applying pressure and passing current for a length of time through the metal area which is to be joined. The key advantage of resistance welding is that no other materials are needed to create the bond, which makes this process extremely cost effective.

There are several different forms of resistance welding (e.g. spot and seam, projection, flash, and upset welding) which differ primarily by the types and shapes of weld electrodes that are used to apply the pressure and conduct the current. The electrodes, typically manufactured from copper-based alloys due to superior conductive properties, are cooled by water flowing through cavities inside the electrode and the other conductive tooling of the resistance welding machine.

The explosive welding technique has found major use for cladding low cost plate (usually carbon steel) with more expensive corrosion resistant materials. This clad plate is typically used in the chemical and petrochemical industries as tube sheet for heat exchangers.

Explosive welding differs from other traditional joining processes as it does not depend on melting of two metals to be joined, or on plastic deformation of the surfaces in contact as occurs with cold or hot pressure welding.

Friction welding (FRW) is a solid-state welding process that generates heat through mechanical friction between workpieces in relative motion to one another, with the addition of a lateral force called "upset" to plastically displace and fuse the materials.

Ultrasonic welding is an industrial process whereby high frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics and metals, and especially for joining dissimilar materials.

Diffusion bonding or diffusion welding is a solid-state welding technique used in metalworking, capable of joining similar and dissimilar metals. It operates on the principle of solid-state diffusion, wherein the atoms of two solid, metallic surfaces intersperse themselves over time.

Forge welding (FOW) is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then hammering them together. It may also consist of heating and forcing the metals together with presses or other means, creating enough pressure to cause plastic deformation at the weld surfaces.

Cold welding, also known as contact welding, is a solid-state welding process in which two metals are bonded together by applying pressure at room temperature without any need for heat or melting. It’s unique because the materials maintain their solid state throughout, and the bond is formed by intimate contact between the clean, atomically pure surfaces of the metals. This process is used extensively in the electronics, aerospace, and automotive industries, particularly for joining soft metals like aluminum, copper, and other ductile materials.

Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.

Brazing differs from welding in that it does not involve melting the work pieces and from soldering in using higher temperatures for a similar process, while also requiring much more closely fitted parts than when soldering. The filler metal flows into the gap between close-fitting parts by capillary action.

Soldering is a joining process used to join different types of metals together by melting solder. Solder is a metal alloy usually made of tin and lead which is melted using a hot iron.

Weldability is the ability of any material (usually metals and its alloys) to weld with similar materials. Many metals and thermoplastics can be welded together to fabricate a final material that is required further in the fabrication process or any other industrial process.

Various welding defects are discussed in this lecture.

So with this.We conclude our course.I hope you understood everything well and will apply the same.Remember! you have a lifetime access to the course and you can always ask for anything in the Q/A section.Do not forget to leave a review and download completion certificate.

The complete course material in PDF format is attached herewith.

All the very BEST !!