L1-Introduction to Manufacturing Processes (2)

8/11/2019 L1-Introduction to Manufacturing Processes (2)

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Ferdous Sarwar, PhDAssistant Professor

Department of IPE, BUET


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Manufacturing

Technologically, Manufacturing is the application of physical and

chemical processes to alter the geometry, properties and/or

appearance of a given starting material to make parts or products.

Economically, Manufacturing is the transformation of the material

into items of greater value (Value addition) by means of one or

more processing and/or assembly operations.

Materials in manufacturing:

Metals

Ceramics

Polymers

Composites

Manufacture Two Latin words:

Manus (Hand) & Factus (Make)


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Some 50 different types of welding processes have been catalogued by the

American Welding Society (AWS)

Welding processes can be divided into two major categories:

1. Fusion welding:

Joining processes that melt the base metals

In many fusion welding operations, a filler metal is added to themolten pool to facilitate the process and provide bulk and added

strength to the welded joint

A fusion welding operation in which no filler metal is added is

called an autogenous weld

2. Solid state welding:

Joining processes in which coalescence results from application

of pressure alone or a combination of heat and pressure

If heat is used, temperature is below melting point of metals

being welded

No filler metal is added in solid state welding

Types of Welding


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Commonly Welded Base Metals

Metals can be classified as

1. Ferrous 2. Non- Ferrous

Wrought Iron

Cast Iron

Carbon Steel (Low, Medium

and High Carbon Steels)

Cast SteelsAlloy Steels

Stainless Steels

Aluminium and its alloys

Copper and its alloys

Magnesium and its alloys

Nickel and its alloysZinc and its alloys, etc


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dvantages of Welding

A good weld is as strongas the base metal

General welding equipment is not very costly

Portablewelding equipments are available

Welding permits considerable freedom in design

A large number of metals/alloys both similar and dissimilar can be

joined by welding.

Welding can join work pieces through spots, as continuous

pressure tight seams, end-to-end and in a number of other

configurations

Welding can be mechanized


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Welding as Compared to Casting

Welding is economicaland fasteras compared to casting.

Fabricated mild steel structures are lighterand have more tensile

strength as compared to cast iron.

Cost of pattern making and storing is eliminated in welding.

Welding can join dissimilar metals and thus different part of the

structure can be fabricated with different metals.

Welding fabrication involve inventory much less ascompared to

casting.

As compared to casting and riveting fewer persons are involved in a

welding process.Structural shapes can be easily produced by welding than casting.


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Welding as Compared to Casting

Casting better than welding

Reducing cost:

Shortening machining time

Speeding assembly by reducing the number of individual partsWhen mass production of a part is needed

Adding value

Company names and logo may be cast into the part -- even your

phone number!


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Welding as Compared to Riveting


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Welding as Compared to Riveting

Much faster and economical than riveting

Being noiseless as compared to riveting

Welded pressure vessels are more (fluid and) pressure tight as

compared to riveted ones

Ratio between weight of weld metal and the entire weight of structure is

much lesser than the ratio between the weight of rivets and the entire

weight of the structure

Welding can carried out as any point but riveting need enough

clearance

Layout for punching or drilling of holes is not required in welding100% efficient joint difficult by riveting


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Types of welds

Double fillet tee joint

Inside single fillet

Outside single fillet

Double fillet lap joint

Square groove weld

Single bevel groove weld

Single V-groove weld

Single U-groove weld

single J-groove weld

Double V-groove weld for thicker sections

Plug weldSlot weld

Fig: Fillet welds

Fig: Groove welds


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Butt Joints

A butt joint is formed when the pieces to be

welded are laid side by side and it is one of the

most widely used types of joint. The edges ofthe butt joint may be prepared for welding as

shown in figure.

Lap Joints

A Lap joint is formed when one piece to be

welded is laid down and another piece is

overlapped to form an edge.

A plug weld is made by welding holes evenly

spaced across the length of one or both sides

of the joint. A slot weld is similar except slots

are made instead of holes.

Types of weld joint

A weld joint is the junction of the edges or

surfaces of parts that have been joined by

welding.

Fig: Butt joint-edge preparation types of weld

Fig: Lap joint-edge preparation types of weld


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T Joints

A T joint is formed when one piece of metal to be welded is

placed vertically on another piece lying horizontally.

The edges of the T joint may be

prepared for welding as shown in

figure.

Types of weld joint

The vertical member is usually placed at 90 deg to the

horizontal member. One of the most widely used types of

weld applied to a T joint is the fillet weld. When a single

pass or multiple passes are made against the joint, the weld

resembles a Triangle when viewed from the side.

Fig: T joint-edge preparation types of weld


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Corner joint

A corner joint is formed by placing one piece

to be welded on the other so that a corner is

formed. The corner may be Flush; Half

Open; or Fully Open.

An edge preparation may be applied to one,or both of the pieces of the joint for

penetration and strength

Edge joint

An Edge joint is formed when the two edges

of the pieces to be welded come together.

This joint may be formed as a result of

another structural shape and is not as widely

used as some of the other joints.

Types of weld joint

Fig: Edge joint-edge preparation types of weld

Fig: Corner joint-edge preparation types of weld


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Welding Flux

During welding, if the metal is heated/melted in air, oxygen from the

air combines with the metal to form oxides which result in poor quality,

low strength welds or, in some cases, may even make welding impossible.

A flux is a material used to prevent, dissolve or facilitate removal of

oxides and other undesirable substances.

A flux prevents the oxidation of molten metal.

The flux (material) is fusible and non metallic.

During welding, flux chemically reacts with the oxides and a slag is

formed that floats to and covers the top of the molten puddle of metal

and thus helps keep out atmospheric oxygen and other gases.

Fluxes are available powders, pastes or liquids

L1-Introduction to Manufacturing Processes (2)

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