A Mechanical Engineer's Blog
Hot Working and Cold Working of metals
Basically
metal forming is the process of getting permanent changes in the shape of the
body under plastic deformation by the use of external forces on the metal
component.
Purpose
Of Metal Forming
In
order to get the desired shape of components from ingot and thereby cut down
the further machining cost, materials & time to make it economical.
It
can improve the mechanical properties of metal by refinement of grain structure
which is achieved by directional control of flow lines.
Reducing
any kind of blowhole, voids as well as cavities.
To
equally distribute the impurities in the metals if at all exist.
And
this process of deformation can be carried out under two conditions:
- Hot working
- Cold working
1)
Hot Working Of Metals
Hot
working can be explained simply as the plastic deformation of metals and alloys
under such conditions of temperature where recovery and re-crystallization
takes place simultaneously during the deformation.
And
hot working of the materials is carried out under 0.7 to 0.9 times the melting
point of the metals to obtain a refined grain structure.
Advantages
Of Hot Working
- By hot working the physical or mechanical properties of the metals like strength, ductility or toughness can be improved further.
- Also the metal density or the component density can be improved by removing the present voids or cavities.
- Here the deformation can be done by application of low pressure in order to get the possible desired shape.
- The present impurities can be divided uniformly all over the metal so that its effect can be reduced.
- The grain structure of metals can be refined.
- It can even cut down the machining cost to make the component economical.
- The atoms of the metals are arranged uni-directionally to achieve their maximum strength.
Disadvantages
Of Hot Working
Although
we have a lot of benefits due to hot working but still there are a few things
that can’t be overcome.
- Due to oxidation at high temperature better surface finish is rather not possible.
- As the metals after forming needs to be cooled hence accurate size and shape of component is not possible incase if close tolerances are needed.
- Since the process are carried out at high temperature so the tool life reduces.
- The handling costs are comparatively high.
Principal
Methods Of Hot Working
- Hot rolling
- Hot forging
- Hot drawing
- Hot extrusion
- Hot spinning
- Hot piercing
2)
Cold Working Of Metals
Cold
working can be explained simply as the plastic deformation of metals and alloys
under such conditions of temperature such that work hardening or strain
hardening is not relieved.
Basically
in cold working the temperature is below the re-crystallization temperature. However
cold working is usually carried out at room temperature.
Advantages
Of Cold Working
- Cold working usually improves the physical properties of metals like strength, hardness.
- Since here there is no oxidation issue so we can get better surface finish.
- Also better accuracy can be obtained as there is no change in operating temperature.
- As heating of metal is not needed so the cost and time both reduces automatically.
Disadvantages
Of Cold Working
- Though it increases the strength and hardness but decreases ductility on the other hand making it difficult to work on it.
- Need of external force is quite high compared to hot working to get desired shape.
- Cold working produces internal stresses & residual stresses which is not ggod for the components life.
- It automatically decreases the ability of component to resist corrosion.
- Distortion takes place in metals in its atomic structure.
- On metals undergoing cold working annealing is done on it for the second time which increases its cost.
Principal
Methods For Cold Working
- Cold rolling
- Cold drawing
- Cold extrusion
- Cold spinning
- Other methods include squeezing, bending & hobbing etc
Why Metal Joining is necessary in Engineering & its Classification
Whichever engineering production field you choose
almost all of them require joining of component at some stages or other.
And these necessary joints can be
particularly of two kinds.
- Temporary joint
- Permanent joint
When we talk about temporary joint it
encircles parts that are joined or fastened by nut, bolt, screw, clamps,
coupling etc.
Most probably you find such kind of
joints in household machineries or furniture etc.
And the other one is permanent joint
that includes fastening that can’t be removed once done.
It is required possibly in areas where
high safety is concerned like in boiler shells, turbines etc.
Permanent joint includes riveting,
soldering, brazing and the most important is welding which is very widely used
in industries, workshops, fabrication, building construction and also in
aircraft industries.
Now every metal joining process is
unique in its own way and all of them have their advantages, limitations and
area of application.
1) WELDING
However we all know and have heard much
about welding.
Welding is the most convenient form
of joining in any industry
When we have a product of very big size
to be manufactured then doing so by casting or machining is rather very
difficult.
Under such scenario its easy to
manufacture it in parts and then joining them by welding to produce it as a big
whole product component.
So welding is very important metal
joining process and it gives us a permanent kind of joint.
By welding method you can join two
pieces of metal either of same kind or different metals together.
The metal pieces can be joined by
heating the ends of the metals to be joined, and there can be application of
pressure or without pressure, by adding of filler metal or without filler metal
to join them. This whole process of joining is called as welding.
2) SOLDERING
When two or more pieces of sheet metal
needs to be joined by means of some fusible alloy or metal called as solder
which is applied in the molten state then this whole process is called as
soldering.
The solders are usually made out of
metals like lead and tin.
The soldering process used for metal
joining can be either
- Soft soldering
- Hard soldering
Soft soldering
Soft soldering is used where thin metal
sheets are to be joined. And the work piece joined shouldn’t undergo high temperature
or high pressure.
Under soft soldering the melting point
of the solder i.e. tin and lead is nearly around 150o C to 350o C.
In soldering process the soldering iron
is generally heated by use of electric power so that the heat of the iron can
melt the solder metal.
Hard soldering
The melting point of hard solder is
quite high as compared to that of soft solder.
Hard solder is usually done to obtain
good strength.
And here the solder contains tin and
silver instead of tin and lead. Thus the melting point rises to 600oC
to 900oC.
The solder is in form of paste which is
applied on the sheets by the help of brush and then a blow torch is used to
melt the solder parts.
3) BRAZING
Brazing also is a metal joining process
where you can join any two metals but the filler metal that you need to use is
non-ferrous filler metal or alloy.
The melting point of the filler metal
is above 450oC but lower compared to that of base metal.
The filler metal is introduced between
the metal surfaces by the help of capillary action.
Usually for brazing copper base alloy
and silver base alloys are used as filler metal. And along with this a suitable
flux named borax is also used.
The brazing filler metals are available
in the form of the tin wires, rod or plate which makes it easier to enter into
the joints of metals by capillary action.
However its important to know that when
we compare soldering and brazing then brazing provides us better mechanical
strength.
4) RIVETING
A rivet also tends to be a permanent
mechanical fastener that gives us permanent joint.
At the initial stages a rivet is in the
form of a smooth cylindrical shaft having a head on one end. And the end
opposite to head is called tail.
During its installation the rivet is
inserted into a punched or drilled hole of two metal and the free end i.e. the
tail is hammered hard so that the tail forms the shape of head .
Since both the sides now possess head
after riveting so the metal gets tightened together.
Introduction To Engineering Mechanics
Definition
The
branch of applied mathematics or Engineering science dealing with motion and
forces producing motion is called mechanics. It basically deals with various
laws of nature and by using them we can find solutions to our Engineering
problems.
It
can be further divided in two main branches:
- Statics: It deals with the study of bodies at rest.
- Dynamics: It deals with the study of bodies in motion.
Fundamental
Concepts
- Space: To fix the position of a point
- Time: To relate the sequence of events
- Mass: To distinguish behaviour of the two bodies under the action of an identical force.
- Force: It is an essential agency which changes or tend to change the state of rest or uniform motion of body.
Fundamental
Principles
- Newton's Three Laws of motion
- Newton's Law of Gravitation
- The parallelogram Law for Addition of forces
- The principle of transmissibility of forces.
Fundamental
units
In
mechanics there are three basic units to express any unit which is
internationally accepted.
- Length
- Mass
- Time
Derived
units
Those
units derived from the fundamental units are called derived units.
Eg.
Unit of velocity, area, volume, pressure etc
System
of Units
- C.G.S. - centimeter-gram-second system
- F.P.S. - foot-pound-second system
- M.K.S. - metre-kilogram-second system
- S.I. - International system of units
Quantities
It
may be either scalar or vector
- Scalar quantity: Those quantities which have magnitude only such as length, mass, time, distance, volume, density, temperature etc.
- Vector quantity: those quantities which have both magnitude and direction such as force, displacement, velocity, acceleration, momentum etc.
Methods
of problem solution
On
the basis of definitions of concurrent, co-planer, non concurrent, non co-planer
forces, there are mainly two methods for problem solutions:
Analytical
methods
Law
of parallelogram, Lami's theorem, Resolution and addition of forces, Conditions
of equilibrium, free body diagrams, Joint method in truss, section method in
truss etc.
Graphics
Statics
In
general this deals with drawing space diagram and vector diagram
e.g.
law of triangle, Funnicular Polygon etc.
Why Metal Shaping is necessary in Engineering & its Classification
Manufacturing process
Manufacturing processes have become such an intricate part of
our lives that we all are surrounded by it still we often don’t realize or
think about it.
There are so many things that we use nowadays right from the
time we get up in the morning till we sleep. And all those things from a simple
paper pin to mobile phones, pens nib to pants zip each and everything
that gives us an ease of work through our lives are all manufactured and
has come to us after going through certain manufacturing processes.

Manufacturing process
simply means a process of converting raw materials into final product.
Also it can be looked as a
collection of technologies that specifies the exact method to manufacture and
get the final product using the available materials and resources.
The basic idea of
manufacturing is to create or produce something that has an important meaning
or purpose to its existence, something that can serve us in better ways
providing us comfort on the go.
Any manufacturing process
that we use can be categorized under these following branches.
1) Metal Shaping
or Metal Forming
Metal forming can be
defined as the process of permanent deformation in the shape of a body under
the action of external forces. And this process can be done either under hot or
cold conditions to obtain desired accuracy.
Now
metal shaping includes numerous processes under it.
Casting: Casting being the oldest and the
easiest process forms the pioneer of manufacturing industry. It is a widely
used process and also very economical in comparision tto other processes.
This
process has been used since the primitive time as the evidence is found in many
ancient civilization.
It
is the process in which a liquid metal is poured into a mould that contains a
hollow cavity of desired shape and then it is allowed to cool and solidify to
get the desired shape of the product.
Later
the casting product is machined for desired accuracy and shape.
Rolling: It is a process in which the metal
stocks are deformed ito semi-finished or finished condition by passing these
between one or more pairs of rolls to reduce the thickness and get the desired
thickness of the component.
Forging: Forging is the process of metal
shaping using localized compressive forces to get the desired shape. Here the
operation can be carried out either hot or cold.
It
is usually carried out when the temperature is in plastic range and then a
pressure is applied on metal to get desired shape and size.
Drawing: It is a cold working process in
which the metal is pulled through a tapered hole in a die to reduce its
diameter.
Most
probably it is used for wires to change its diameter.
It
offers clean and accurate dimensions besides excellent quality of surface to
the component.
Extrusion: It is an important process of
manufacturing where a metal block is passed through die with application of
force. And all this is done when the material is under the plastic temperature
range.
Extrusion
is used for rod, tube, channel, I or Z section as well as circular and square
shaped hollow or solid parts.
Forming: Forming can be explained simply as
the operation where we change the shape of a component by following ways
- Curling operation
- Bulging operation
- Stretching operation
- Tube forming
Embossing: Embossing is done to get a required
impression on a sheet metal by application of pressure. Here the pressure is
applied in form of die and punch.
The
sheet metal is kept between a punch and die and the required design is
impressed on it by application of right amount of pressure.
Most
usually used to emboss letters on a surface
Bending: It is the method of transforming a
straight line component into some curved length component by application of
pressure.
Bending
is a very common process used in order to change sheet metals and plates into
channels, drums, tanks etc.
Spinning: A method where circular cross
sections are to be made is done by spinning. Here a blank is made to surface on
the rotating chuck and by application of pressure the blank is pressed over the
rotating block to get the desired shape.
Coining: the blank here is placed between
the die and punch to get the impression by application of pressure.
Usually
such impression or projection is done on coins or metal ornaments.
Thank
you readers to spare your valuable time to read my article.
In
the next article we’ll see about the ‘Metal Joining’ manufacturing
process and have an overview about it.
Steps for Designing a Machine Member
Specifically
there is no fixed machine design procedure for any new machine element of the
machine to be designed as there are a
number of options that have to be considered during the design.
The
designer who develops the habit of following a fixed line of steps for
designing the machine or machine elements cannot come out with the best
product. When the new product is to be developed the problems keep on arising
at design stage, and these can be solved only by having flexible approach and
considering various ways.
Important Steps for Designing a Machine
Here
are some guidelines as to how the machine design engineer can proceed with the
design:
1) Make the written
statement
Make
the written statement of what exactly is the problem for which the machine
design needs to be done.
This statement should be very clear and precise, as detailed as possible. Say if you want to develop a new product write down the details about the project so that the further criteria could be fulfilled.
This statement should be very clear and precise, as detailed as possible. Say if you want to develop a new product write down the details about the project so that the further criteria could be fulfilled.
2) Consider the
possible mechanisms
When
you design the machine consider all the possible mechanisms that could help you get the desired
motion or the group of motions in your proposed machine. From the various available options the suitable best can be selected as required.
3) Transmitted forces
Machine
is made up of various machine elements on which various forces are applied.
These elements become the transmitting link among the machine members. Calculate the forces acting on each of the element and the amount of energy transmitted by them.
These elements become the transmitting link among the machine members. Calculate the forces acting on each of the element and the amount of energy transmitted by them.
4) Material selection
Now for manufacturing your machine components there would be wide range and variety of materials available to choose.
Select the appropriate materials for each element of the machine so that they can sustain all the forces and at the same time they should have least possible cost.
Select the appropriate materials for each element of the machine so that they can sustain all the forces and at the same time they should have least possible cost.
5) Find allowable
stress
All
the machine elements are subjected to stress whether small or large during their operation period.
Considering the various forces acting on the machine elements, their material and other factors that affect the strength of the machine calculate the allowable or design stress for the machine elements so that a safety limit can be assigned called as safety factor.
Considering the various forces acting on the machine elements, their material and other factors that affect the strength of the machine calculate the allowable or design stress for the machine elements so that a safety limit can be assigned called as safety factor.
6) Dimensions of the
machine elements
Now this step involves finding out the appropriate dimensions for the machine elements considering the forces
acting on it, the material, and the allowable design stress. The size of the machine elements
should be such that they should not distort or break and should have the capacity to withstand any physical defect when loads are applied.
7) Consider the past
experience
This is the most important factor that plays a vital role in the design steps. If
you have a past experience of designing the machine element or possess any earlier records of the company, consider them and make the necessary changes in the
design as required. The designer can also consider his own personal judgment so as to
facilitate the production of the machine and machine elements.
8) Make drawings
Once you complete all the above designing steps for the machine and machine elements now you need to make the assembly drawings of the
whole machines and detailed drawings of all the elements of the machine. In the
drawings clearly specify and mention the dimensions of the assembly and the machine elements,
their total number required, the material required and method of their production. The
designer should also specify the accuracy, surface finish and other related
parameters for the machine elements.
Thus by following all these crucial steps of designing you can manufacture any machine member or machine element to design your machine.
Thus by following all these crucial steps of designing you can manufacture any machine member or machine element to design your machine.
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