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

1. By hot working the physical or mechanical properties of the metals like strength, ductility or toughness can be improved further.
2. Also the metal density or the component density can be improved by removing the present voids or cavities.
3. Here the deformation can be done by application of low pressure in order to get the possible desired shape.
4. The present impurities can be divided uniformly all over the metal so that its effect can be reduced.
5. The grain structure of metals can be refined.
6. It can even cut down the machining cost to make the component economical.
7. 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.

1. Due to oxidation at high temperature better surface finish is rather not possible.
2. 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.
3. Since the process are carried out at high temperature so the tool life reduces.
4. The handling costs are comparatively high.

Principal Methods Of Hot Working

1. Hot rolling
2. Hot forging
3. Hot drawing
4. Hot extrusion
5. Hot spinning
6. 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

1. Cold working usually improves the physical properties of metals like strength, hardness.
2. Since here there is no oxidation issue so we can get better surface finish.
3. Also better accuracy can be obtained as there is no change in operating temperature.
4. As heating of metal is not needed so the cost and time both reduces automatically.

Disadvantages Of Cold Working

1. Though it increases the strength and hardness but decreases ductility on the other hand making it difficult to work on it.
2. Need of external force is quite high compared to hot working to get desired shape.
3. Cold working produces internal stresses & residual stresses which is not ggod for the components life.
4. It automatically decreases the ability of component to resist corrosion.
5. Distortion takes place in metals in its atomic structure.
6. On metals undergoing cold working annealing is done on it for the second time which increases its cost.

Principal Methods For Cold Working

1. Cold rolling
2. Cold drawing
3. Cold extrusion
4. Cold spinning
5. 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.

1. Temporary joint
2. 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

1. Soft soldering
2. 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 150^o C to 350^o 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 600^oC to 900^oC.

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 450^oC 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:

1. Statics: It deals with the study of bodies at rest.
2. Dynamics: It deals with the study of bodies in motion.

Fundamental Concepts

1. Space: To fix the position of a point
2. Time: To relate the sequence of events
3. Mass: To distinguish behaviour of the two bodies under the action of an identical force. 
4. Force: It is an essential agency which changes or tend to change the state of rest or uniform motion of body.

Fundamental Principles

1. Newton's Three Laws of motion
2. Newton's Law of Gravitation
3. The parallelogram Law for Addition of forces
4. The principle of transmissibility of forces.

Fundamental units

In mechanics there are three basic units to express any unit which is internationally accepted.

1. Length
2. Mass
3. 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

1. C.G.S. - centimeter-gram-second system
2. F.P.S. - foot-pound-second system
3. M.K.S. - metre-kilogram-second system
4. S.I. - International system of units
   

Quantities

It may be either scalar or vector

1. Scalar quantity: Those quantities which have magnitude only such as length, mass, time, distance, volume, density, temperature etc.
2. 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.

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.

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.

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.

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.