Welding

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Welding processDayalbagh Education Institute

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The process of permanently joining two or more metal parts, by melting both materials. The molten materials quickly cool, and the two metals are permanently bonded.

Advantage:Higher mechanical propertiesFixing stress cracksReinforcing weak jointsCutting or shaping new parts

Welding

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GAS WELDING Oxygen-Acetylene Welding

Oxygen tank (green)

Acetylene tank (red, or black with a red top)

Oxygen pressure valves have a right-hand internal thread

Acetylene pressure valve has an external left-hand thread.

An oxygen-acetylene flame is very hot, approaching 3500°F.

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GAS WELDINGFusion weld is to place the two pieces against

each other and melt their surfaces together.Reducing flame is used to melt low-melting-point

metals and alloys because it does not oxidize or corrode the metals.

Neutral flame is the hottest one possible and is the proper adjustment for welding.

Oxidizing flame that can cause corrosion in the metal. It is only used for cutting flames or burning pieces of metal from a piece of stock. (Fig 14-9)

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ELECTRICAL WELDINGResistance Welding – The two parts are

pressed together and an alternating current (A/C) is passed through the contact zone.

Spot welding – used extensively on sheet metals (holds handles on pots, car body together)

Ribbon welding rollers. - parts to be welded are drawn between electrodes rollers while electricity is applied.

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Arc WeldingA sustained arc generates the heat for

melting the work piece and filler material.

Consumable electrodes

Non-consumable electrodes

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Consumable electrodes Flux Core Arc Welding (FCAW) developed in the

early 1950s as an adaptation to SMAW to overcome limitation imposed by the use of a stick electrodes. Uses a spool of filler wire fed through the hand-piece. A core of flux is inside the wire

Two versions Self-shielded flux-cored arc welding – includes not

only fluxes but also ingredients that generate shielding gases for protecting the arc.

Gas-shielded flux-cored arc welding – developed primarily for welding steels, obtains a shielding from externally supplied gases, similar to GMAW

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Consumable electrodes Submerged Arc Welding (SAW) – uses a continuous,

consumable bare wire electrode, and arc shielding is provided by a cover of granular flux. Low-carbon, low alloy, and stainless steels can be readily welded by SAW.

Electrogas Welding (EGW) – uses a continuous consumable electrode (either flux-cored wire or bare wire with externally supplied shielding gases) and molding shoes to contain the molten metal.

Shielded Metal Arc Welding (SMAW) (stick) – arc is struck between the rod (shielded metal covered by flux) and the work pieces to be joined, the impurities rise to the top of the weld in the form of slag (18-19a, handout pg. 40)

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A sustained arc, shielded by molten slag, is maintained in consumable-electrode welding by the (a) shielded metal-arc, (b) submerged arc, and (c) electro gas methods.

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“The process of giving a desired shape to a metal piece by heating and hammering is known as forging”.

Forging

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It increase the strength and toughness of the metals by producing directional grains.

It refines the structure of the metal and thus renders it more dense.

The internal defects like segregation, cracks and porosity are eliminated.

Advantages of Forging:

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Brittle material like cast iron cannot be forged.

Complex shapes can easily be produced by casting and not by forging.

Cost of forging dies is high.

Disadvantage of forging:

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A forged component has the ability to withstand higher load during service.

A forged components can be produced to close tolerance.

It reduces the machining time, material and labor considerably.

Advantages of Forging:

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Upsetting:upsetting is the process in which

the cross sectional diameter of a hot metal work piece is increased with a corresponding reduction in its length.

During this process the hot metal piece is held in a tong and placed on the anvil in vertical position and then is stroke with a hammer.

Forging Operations:

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Upsetting:

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Upsetting:

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It is also known as drawing down.

Exactly the reverse of upsetting

Contrary to upsetting this process is used to reduce the thickness/width/diameters or increasing the length of red hot work piece.

Drawing out:

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Cutting operation is required for removing extra metal from the job.

For cutting operation three major things required, hammer, cutting tool set and the stock.

Cutting:

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The process of giving the desired angle or curves to a hot metal work piece is known as bending.

The process is done on the edge of anvil.Circular shaped, eye bolts, hooks or any other

types of bent shape can be prepared with this operation.

Bending:

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Punching is the operation in which a rough hole is made into the hot work piece by forcing a punch through it.

A red hot job is placed on the anvil and by using a sledge hammer, the punch is forced to the pierce the metal up to half of its thickness.

Punching:

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Then by inverting the work piece same process is repeated at the same point to get a rough hole.

Punching:

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Is an operation of finishing and enlarging the hole by hammering a tapered drift into the hole until the required bore size is reached.

Is similar to punching and followed by it.

Drifting:

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Swaging is the operation of reducing and finishing a work piece to different desired shapes usually circular, hexagonal and square.

Swaging operation is performed with the help of swages and swag blocks.

Swages are used for small jobs.Swag blocks are used for large jobs.

Swaging:

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It is the operation of reducing the thickness of a work piece.

In this process the bottom fuller is held in the hole of the anvil.

Hot work piece is placed in the grooves of the lower fuller and then the top fuller is placed over it.

The hammering operation is carried out until the piece gets squared thickness.

Fullering:

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This operation is performed to level the job surface.

The red hot metal work piece is placed on the anvil and is stroked hardly using hammer set to flatten the metal work piece.

Flattening:

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The process of joining two metals by heating and hammering is known as forge welding.

The metal pieces to be joined are cleaned and heated in a furnace up to the welding temperature.

With the help of tongs these are kept overlapping each other at the one of their ends on the anvil and are subjected to hammering.

Forge welding:

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Forging Temperature:

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Forge/Furnace/Hearth : Heating furnaceAnvil :Supporting ToolHammers & set Hammers : Striking ToolTongs: Holding ToolChisels: Cutting Or Shaping ToolFullers: Grooving ToolSwages & Swage Block: Shaping Tools

Forging Tools:

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Forging Tools

Anvil Hammers

Tong chisel Swage Block

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Pitting: occurs on the surface of forging due to scales.

Cold shuts or laps : Short cracks that occurs on the corners of the surface that are at right angles to each other

Die shift : Caused due to misalignment between to halves of forging dies.

Defects in forging:

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Dents :Caused due to careless working.

Oxidation & Decarburization : Occur due to overheating of stock.

Fins and rags : Small projection or loose metal driven into the forging surface

Defects In Forging

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Some other common defect are(a) Incomplete filing of dies(b) Burnt and overheated metals(c) Flakes: Internal breaks and rupture(d) Incorrect size of forging(e) Tears(f) Blowholes(g) Internal cracks

Defects in forging:

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Thank you

Credit to : Amit Gupta