Introduction to Manufacturing

Classification of
Engineering
Materials
Material :- A material is a substance or mixture of substances that constitutes an object.
 It may be solid, liquid or gas.
Engineering Materials:- The materials which are used in the field of Engineering are called engineering materials

Classifications of Engineering Materials:-

There are different types of engineering materials, such as
1. Metals
2. Polymers/Organic polymers
3. Ceramics
4. Composites
5. Semiconductor
6. Biomaterials
7. Advanced materials
1. Metals: -
 Metals are good conductor of heat & electricity.
 They are capable of changing their shape permanently.
 They are opaque.
There are mainly two types of metals,
(i) Ferrous Metals:- Which contain iron as main constituent.
Ex- Cast iron, Mild steel
(ii) Non – ferrous Metals:- Which do not contain iron as main constituent.
Ex- Copper, Zinc, Aluminum etc.
2. Polymers/Organic polymers:-
These are organic compound containing Carbon, Hydrogen and other metallic components
Ex- Plastic, Rubber, Polyester etc.
There are different types of polymers like,
• Natural Polymers
• Semi-synthetic Polymers
• Synthetic Polymers
• Linear Polymers
• Branched-chain Polymers
• Cross-linked Polymers
• Elastomers
• Fibers
• Thermoplastics polymers
• Thermosetting polymers
Thermoplastic polymers and Thermosetting polymers:
3. Ceramics:-
• These are compounds containing metallic and nonmetallic elements.
• Good insulator of heat and electricity

Ex- cement, glass, sand, concrete etc.

4. Composites:-
These are combination of two or more materials.

Ex- GRP (Glass Reinforced Plastic) This is combination of glass, fiber & plastic.
5. Semiconductor:-
• These materials have properties between conductor & insulator.

• There are different types of semiconductor like,

(i) p-type (ii) n-type
Ex - Carbon, silicon, germanium etc.
6. Biomaterials:-
• These materials are used to prepare artificial human parts for replacement.
• These materials may be metals, polymers, ceramics, composites.
7. Advanced Materials:-
• These materials are used on advanced technology.
• These materials may be metals, polymers, ceramics, composites.
Ex- CD,DVD,VCR,LCD,LED etc.

Properties of Engineering Material:-

There are different properties of engineering materials such as,
• Physical properties
• Chemical properties
• Mechanical properties
• Electrical properties
• Optical properties
• Magnetic properties
• Technological properties
Different Mechanical Properties of Engineering Material:-
The different Mechanical Properties of Engineering Material are,
1. Elasticity:- It is the property of a material to regain its original shape after
deformation .
2. Plasticity:- It is the property of a material which retains the deformation produced
under load permanently.
3. Ductility:- It is the property of a material can be be drawn into wire .
4. Brittleness:- It is the property by which a material breaks without visible
deformation.
It is the property of a material opposite to ductility.
5. Malleability:- It is property of a material which permits materials to be rolled into
thin sheets.
6. Strength:- It is the ability of a material to resist the externally applied forces
without breaking.
7. Toughness:- It is the ability of a material to absorb energy up to fracture.
8. Hardness:- It is the property by which material offers resistance against indentation.
9. Creep :- When a part is subjected to a constant stress at high temperature for a long period of time, it will
undergo a slow and permanent deformation called creep.
10. Resilience:- It is the property of a material to absorb energy and to resist shock and
impact loads.
11. Fatigue:- When a material is subjected to repeated stresses, it fails at stresses
below the yield point stresses. Such type of failure of a material is known as
fatigue.
 MANUFACTURING PROCESSES
CASTING/FOUNDRY PROCESS
INTRODUCTION:
The casting process can be defined as a primary shaping process in which a molten metal is poured
into a mould cavity and allowed to solidify for pre-determined time so as to take the shape of the
mould, after complete solidification, it is taken out from the mould. The product of casting is also
known as casting and the place where casting work is done is known as ‘foundry shop’.

CLASSIFICATION OF CASTING PROCESS:

Casting process can be classified on the basis of expandable mould and multiple-use mould as
shown in Figure.
A model of mould used in sand casting is shown in Figure. Moulding material that is packed around
the pattern to provide the mould cavity is green sand. The various parts of mould can be defined as
follows:
(Cross section of a two-part sand mould)

Flask: It is a rigid box which opens at top and bottom that holds the complete mould. Flask may be
divided into three parts-the upper, middle, and lower.
Drag: It is the lower part of flask.
Cope: It is the upper part of flask.
Cheek: It is the middle part of flask.
Parting Line: It is the dividing line between the two moulding flasks that makes up the sand mould
Core: It is used for making hollow cavities in castings.
Pouring basin: It is a small funnel shaped cavity into which at the top of the mould into which
molten metal is poured.
Sprue/Downsprue: The passage through which the molten metal from the pouring basin reaches
to the mould cavity.
Mould Cavity: It is a cavity of casting shape in the mould connected to runner and riser.
It is used to pour the molten metal in which metal solidifies and gets the shape of cavity.
Gating System: It is a network of channels that deliver the molten metal to the mould cavity.
Runner: It is horizontal channels which connects the downsprue and gates.
Gate: It controls the amount of flow of molten metal at the entrance of cavity.
Riser: It is the reservoir of the molten metal provided in the casting so that the hot metal can flow
into the mould cavity when there is a reduction in volume of metal due to solidification.

Steps in Sand Casting:

Sand is the most suitable material for expandable mould. It has sufficient properties of moulding
materials such as refractoriness, permeability, flowability, adhesiveness, cohesiveness etc. Sand
casting is the most versatile and common form of casting. In this method, a mould of sand with
binding materials and water is prepared in which molten metal is poured and allowed to solidify. The
entire casting process can be represented as a chain as shown in Figure.
Die Casting:
There are two types of high pressure die casting.
1. Hot-chamber die casting.
2. Cold-chamber die casting.
Hot-chamber Die Casting:
A hot-chamber die casting machine is shown in Figure below .This machine is used with alloys of low
melting points because of the difficulties encountered such as increased corrosion of the machine
parts at high temperatures. Since many metals have an affinity for iron, only those casting alloys are
used that do not attack the immersed metal parts. Alloys of zinc, tin, and lead are particularly
recommended for these machines. In the hot-chamber die casting method, the melting pot is
included within the machine and the injection cylinder is immersed in the molten metal. The
injection cylinder is actuated by either air or hydraulic pressure, which forces the metal into the
die cavity. The metal is held under pressure until it solidifies.
Cold-chamber Die Casting:
Cold-chamber die casting is used for relatively high melting point non-ferrous alloys such as
aluminium, magnesium, and brass which require higher pressure and temperature for melting. These
metals are not melted in a self-contained pot as in hot-chamber die casting due to short life of pot.
Therefore, the metal is melted in an auxiliary furnace and is ladled to the plunger cavity next to
the dies. It is then forced into the dies under hydraulic pressure. The cold-chamber die casting
machines operating by this method are built very strong and rigid to withstand the heavy pressure
exerted on the metal as it is forced into the dies.

Advantages of Die Casting:

1) Production rate is very high.
2) Parts have good dimensional accuracy and surface finish.
3) Because of high pressure a thin wall up to 0.5 mm of casting can be produced.
4) No riser is used due to use of high pressure injection of molten metal.
Disadvantages of Die Casting:
1) Die casting has a porosity problem as gases tend to be entrapped.
2) The process is economical for large production run only.
Advantages of casting process:
 Complex shape can be easily produced.
 Practically any material can be casted.
 Ideal method is by producing small quantities
 Due to small cooling rate from all directions, the properties of casting are same in all
directions.
 Any size of casting can be produced up to 200 tons.
 Casting is the often cheap.
 Casting is best suited for composite components requiring different properties in various
directions.
Disdvantages of casting process:
 With normal sand casting process, the dimensional accuracies and surface finish is
less.
 Defects are unavoidable.
 Sand casting is labor intensive.
Casting Defects :
 It is an unwanted irregularities that appear in the casting during metal casting process.
 Some of the defects produced may be neglected or tolerated and some are not acceptable, it must be eliminated for better
functioning of the parts.
Types:-
1. Gas Porosity: Blowholes, open holes, pinholes
2. Shrinkage defects: shrinkage cavity
3. Mold material defects: Cut and washes, swell, drops, metal penetration, rat tail
4. Pouring metal defects: Cold shut, misrun, slag inclusion
5. Metallurgical defects: Hot tears, hot spot.
 WELDING PROCESS
Welding:- It is a joining process which joins two similar or dissimilar metallic components with the
application of heat , with or without application of pressure and filler material.

Weldability: It is the ability or property of a metal due to which it can be easily welded.
It depends on the following factors.
• Heat applied during the welding process.
• Welding process, i.e., types of welding used to make the joint.
• Thermal conductivity of the work materials.
• Constituents of the materials.
• Melting point of the parent metal.

Types of Welding Positions:-

According to welding position the welding can be classified as,
flat, horizontal, vertical, and overhead welding.
 CLASSIFICATION OF WELDING PROCESS:
Forehand welding and Backhand welding:-
 Differences between forehand welding and backhand welding:-

Backhand Welding or Forward Welding Backhand Welding or Backward Welding

It is also called forward welding or push welding It is also called backwards welding or pull
welding
Here the flame or electrode is pointed towards the direction of Here the flame or electrode is pointed away from
weld progression the direction
Filler metal is applied ahead of the torch. Filler metal is applied behind the torch.
Pre-heating of the base metals takes place automatically. No pre-heating occurs here.
No post-heating occurs here. Backhand welding technique facilitates post-
heating of the deposited weld bead.
It increases the filler deposition rate but cannot fetch deeper It assists in achieving deeper penetration, though
penetration. filler deposition rate is slow.
This technique offers good visibility to the welder. The weld zone has poor visibility.
It is preferred for joining thin plates (usually up to 3.0 mm without It is preferred for joining thicker plates.
edge preparation).

Different types of gases used in gas welding:-

The different types of gases used in gas welding are as follows:
i) Acetylene
ii) Hydrogen
iii) Methane
iv) City gas
v) Natural gas
Oxyacetylene Welding:
 The highest temperature obtained in oxyacetylene welding is 3,200°C.
 Acetylene can be used as a gas from a separate cylinder or through reaction of water on calcium carbide.
 Three different types of flames such as neutral, oxidizing, and carburizing are generated at the tip of welding
torch by regulating the amount of acetylene and oxygen with the help of pressure regulators and control valve.
The different types of flame used are,

1. Neutral Flame:
2. Oxidizing Flame:
3. Carburizing Flame or Reducing Flame

1. Neutral Flame:-
 It is generated at the tip of welding torch with equal volume of oxygen and acetylene.
 This is type of flame has maximum temperature of about 31000C .
 This is used to weld mild steel, stainless steel, cast iron, copper, and aluminum etc.
2. Oxidizing Flame:-
 It is generated when oxygen content is more than acetylene in the gas mixture.
 This is type of flame has maximum temperature of about 33000C .
• This is used to weld brass, zinc, bronze, gold, etc.
3. Carburizing Flame or Reducing Flame:-
 In this flame, acetylene is used in excess amount than the theoretically required.
 This is type of flame has maximum temperature of about 29000C.
 This flame is used to weld high carbon steel, aluminum, nonferrous metals like monel metal, nickel, etc.
Arc Welding:-
 It is a welding process, in which heat is generated by an electric arc struck between an electrode and the work
piece.
 Electric arc is luminous electrical discharge between two electrodes through ionized gas.
Principle of Arc Welding:-
Any arc welding method is based on an electric circuit consisting of the following parts:
 Power supply (AC or DC)
 Welding electrode
 Work piece
 Welding leads (electric cables) connecting the electrode and work piece to the power supply.
• In electric arc welding ,when electrode is brought in contact with the work and it is then quickly separated by a
short distance (approximately 1.5 to 3 mm) such that the current continues to flow through a path of ionized
particles, an electric arc is formed .
• The arc is sustained due to continuous presence of thermally ionized column of gas.
• The circuit is operates low voltage and high current, therefore arc is established due to thermionic emission from
electrode (Cathode) to work piece (Anode) .
• This arc produces a temperature of the order of 55000C or higher.
• In this way a pool of molten metal consisting of work piece metal and filler metal is formed at the welding zone.

Difference between AC and DC Arc Welding:

Metal forming processes
Metal forming: Large set of manufacturing processes in which the material is deformed plastically to take the shape of
the die geometry. The tools used for such deformation are called die, punch etc. depending on the type of process.

Plastic deformation: Stresses beyond yield strength of the workpiece material is required.
Categories: Bulk metal forming, Sheet metal forming

General classification of metal forming processes:

Forging
(Extrusion) (Extrusion) ( Wire drawing)

Bulk forming: It is a severe deformation process resulting in massive shape change. The
surface area-to-volume of the work is relatively small. Mostly done in hot working conditions.

Rolling:- In this process, the workpiece in the form of slab or plate is compressed between two rotating rolls in
the thickness direction, so that the thickness is reduced. The rotating rolls draw the slab into the gap and compresses
it. The final product is in the form of sheet.
 Forging:- The workpiece is compressed between two dies containing shaped contours. The die
shapes are imparted into the final part.
Extrusion:- In this, the workpiece is compressed or pushed into the die opening to take the shape of the die hole
as its cross section.
Wire or rod drawing:- Similar to extrusion, except that the workpiece is pulled through the die
opening to take the cross-section.

Classification of basic sheet metal forming processes:

(Bending) (Deep drawing) (Shearing)

Sheet forming:- Sheet metal forming involves forming and cutting operations performed on metal sheets, strips, and
coils. The surface area-to-volume ratio of the starting metal is relatively high.
Tools include punch, die that are used to deform the sheets.
Bending :- In this, the sheet material is strained by punch to give a bend shape (angle shape) usually in a straight axis.
Deep (or cup) drawing:- In this operation, forming of a flat metal sheet into a hollow or concave shape like a cup,
is performed by stretching the metal in some regions. A blank-holder is used to clamp the blank on the die, while the punch
pushes into the sheet metal.
Shearing:- This is nothing but cutting of sheets by shearing action.