Metal processing technology_ Part I

Metal Processing Technology (MEng 5273)
Mulualem Hailu (MSc.)
School of Mechanical and Industrial Engineering
Mechanical Engineering Department
Dire Dawa University Institute of Technology
Dire Dawa, Ethiopia
December, 2021
1

Part I : Introduction to metal processing
1.1 Manufacturing Defined
1.2 Metal Fabrication Techniques
1.3 Metal Defined
1.4 Metal Processing
2

1.1 Manufacturing Defined
Manufacturing is defined two ways: Technological and Economical
1. Technologically, Manufacturing is application of physical and
chemical processes to alter the geometry, properties, and/or
appearance of a starting material to make parts or products.
 It is carried out as a sequence of operations to bring the
material closer to the desired final state.
Fig. 1. Definition of Manufacturing, Technologically
3

Cont…
2. Economically, Manufacturing is the transformation of materials into
items of greater value by means of one or more processing and/or
assembly operations.
 Iron ore into steel,
 Sand into glass,
 Petroleum is refined into plastic,
 Scrap into Billet into re-bar
Fig. 2. Definition of Manufacturing, Economically
4

1.2 Metal Fabrication Techniques
Four basic Metal Fabrication Techniques.
1. Metal casting: to give a shape by pouring in liquid metal into
a mold that holds the required shape, and letting harden the
metal without external pressure :expendable and permanent
mold
2. Metal Forming : To give shape in solid state by applying
pressure: Shearing, rolling, forging, extrusion,
3. Material Removal / Machining : in which material is removed
in order to give it the required shape: Conventional Processes
(turning, drilling, milling, grinding …) nontraditional
machining (chemical, thermal, etc)
4. Joining: where different parts are joined by various means:
welding, brazing, soldering, adhesive bonding, mechanical
joining, etc.
5

Manufacturing Process Selection Criteria
1) Material selection with environment and recycling aspects
2) Process selection (casting, forming, sheet metal, powder
metallurgy, machining, etc).
3) Shape and appearance of the final product
4) Dimensional tolerance and surface finish aspects
5) Economics of tooling
6) Design and Functional requirements
7) Production quantity requirements
8) Safety and environmental concerns
9) Cost of production
6

1.3 What is Metal ?
• Metals are opaque, lustrous elements that are good conductors of
heat and electricity. Most metals are malleable and ductile and are,
in general, denser than the other elemental substances.
What are some applications of metals?
Metals are used in:
 Transportation -- Cars, buses, trucks, trains, ships, and airplanes.
 Aerospace -- Unmanned and manned rockets and the space shuttle.
 Computers and other electronic devices that require conductors
(TV, radio, stereo, calculators, security devices, etc.)
 Communications including satellites that depend on a tough but
light metal shell.
7

Cont…
 Food processing and preservation -- Microwave and conventional
ovens and refrigerators and freezers.
 Construction -- Nails in conventional lumber construction and
structural steel in other buildings.
 Biomedical applications -- As artificial replacement for joints and
other prostheses.
 Electrical power production and distribution -- Boilers, turbines,
generators, transformers, power lines, nuclear reactors, oil wells,
and pipelines.
 Farming -- Tractors, combines, planters, etc.
 Household conveniences -- Ovens, dish and clothes washers,
vacuum cleaners, blenders, pumps, lawn mowers and trimmers,
plumbing, water heaters, heating/cooling, etc.
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1.4 Metal Processing
In industry, Molten metal is cooled to form the solid. The solid
metal is then mechanically shaped to form a particular product.
How these steps are carried out is very important because heat
and plastic deformation can strongly affect the mechanical
properties of a metal.
 Grain Size Effect
 Quenching and Hardening
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Grain Size Effect
It has long been known that the properties of some metals could be
changed by heat treating. Grains in metals tend to grow larger as the metal
is heated.
Dislocations cannot cross grain boundaries easily, so the size of grains
determines how easily the dislocations can move. As expected, metals
with small grains are stronger but they are less ductile.
Figure 3: Grains and Grain Boundaries for a Metal.
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Quenching and Hardening
There are many ways in which metals can be heat treated.
 Annealing is a softening process in which metals are heated and then allowed to
cool slowly.
 Annealing is a heat treatment that alters the physical and sometimes chemical
properties of a material to increase its ductility and reduce its hardness, making it
more workable.
 Most steels may be hardened by heating and quenching (cooling rapidly). This
process was used quite early in the history of processing steel.
 Quenching results in a metal that is very hard but also brittle.
 Tempering is a process of heat treating, which is used to increase the toughness
of iron-based alloys. Tempering is usually performed after hardening, to reduce
some of the excess hardness, and is done by heating the metal to some
temperature below the critical point for a certain period of time, then allowing it
to cool in still air.
11

Part II
Metal Forming Process (Flat Rolling process)
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2.1 Overview of Metal Forming
 Metal forming: a large set of manufacturing processes in which
the material is deformed plastically to take the shape of the die
geometry.
 Its a primary shaping processes in which a mass of metal or alloy
is subjected to mechanical forces.
 The tools used for such deformation are called die, punch etc.
depending on the type of process
 Deformation results from the use of a tool, usually called a die in
metal forming, which applies stresses that exceed the yield
strength of the metal.
 Metal forming processes can be classified into two basic
categories:
I. Bulk deformation processes
II. sheet metalworking processes.
13

Cont…
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Fig. 4. General Classification of Metal Forming Processes.

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1.2 Basic Types of Deformation Processes
Generally Bulk deformation and Sheet metal working processes
characterized by-
Bulk deformation :
 Significant deformation
 Massive shape change
 Surface area to volume of the work is small
 Mostly done in hot working conditions
Sheet metal working :
 Surface area to volume of the work is large
 Mostly done in cold working conditions

 Rolling is a metal forming (deformation) process in which the thickness of the
work is reduced by compressive forces exerted by two rolls rotating in
opposite direction.
 There are two types of metal rolling processes; the first one is the flat metal
rolling process. In flat metal rolling processes, metal parts are formed into flat
shapes such as strips, slabs, sheets, etc.
 The other type of metal rolling process is the shape metal rolling process.
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Rolling Process

FLAT ROLLING AND ITS ANALYSIS
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Problems
#1 . A 300-mm-wide strip 25-mm thick is fed through a rolling mill with two
powered rolls each of radius = 250 mm. The work thickness is to be reduced
to 22 mm in one pass at a roll speed of 50 rev/min. The work material has a
flow curve defined by K = 275 MPa and n = 0.15, and the coefficient of
friction between the rolls and the work is assumed to be 0.12. Determine if the
friction is sufficient to permit the rolling operation to be accomplished. If so,
calculate the roll force, torque, and horsepower.
#2 . A 42.0-mm-thick plate made of low carbon steel is to be reduced to 34.0
mm in one pass in a rolling operation. As the thickness is reduced, the plate
widens by 4%. The yield strength of the steel plate is 174 MPa and the tensile
strength is 290 MPa. The entrance speed of the plate is 15.0 m/min. The roll
radius is 325 mm and the rotational speed is 49.0 rev/min. Determine (a) the
minimum required coefficient of friction that would make this rolling
operation possible, (b) exit velocity of the plate, and (c) forward slip.
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Metal processing technology_ Part I

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Metal processing technology_ Part I