Thursday, 12 January 2017

Ultrasonic welding:


Ultrasonic welding is a cold-joining process(I.e.,solid- state welding).In this case ,a bond is produced by ultrasonic vibratory energy in the weld region.The equipment necessary for ultrasonic welding is shown in fig.It includes a transducer,a velocity transformer with a sonotrode tip and a suitable anvil.The prob induces lateral vibrations on workpieces such that surface films are broken and bond results due to slip between clean surfaces under pressure.The operation should be stopped as soon as weld is complete. This is to avoid bonding of prob with upper workpiece.


ADVANTAGES:

1) Absence of generated heat.

2) Dissimilar metals can be joined.

3) No oxidation and distortion

4) The welding time is only about one second or less.

DISADVANTAGE:

1) The maximum thickness is limited to 0.3 to 2.5mm


APPLICATIONS:

The ultrasonic welding is employed for spot welding and seam welding of thin strips or foils.It can also be used for welding aluminium up to 2.5mm thick.The process is mostly used for welding dissimilar metals such as aluminium to stainless steel and aluminum to copper l.It has been used for refractory metals such as titanium and zirconium. 

SUBMERGED ARC WELDING:


Submerged arc welding is used for the production of long continuous weldings.In this case,a bare electrode (1.5-10mm) in the form of continuous wire is used; and the arc is struck between electrode wire and work piece under the flux,consisting of lime,silica,magnesium oxide,calcium fluoride and other elements.The flux is fed as a powder in front of the electrode.the flux near the arc melts and forms a protective coating of slag, which is easily detached from finished weld.The rate of cooling of the weld metal is slow,and it is also protected from atmosphere while cooling.The principle of submerged arc welding is shown in fig.In this case,an automatic feeding device ensures that the gap between the electrode and the base metal is constant.Electric current usually range between 300A and 2000A.The power supply is from a standard single or three phase power lines with a primary rating up to 440V.




ADVANTAGES:

The process offers the following advantages:

1)High rate of deposition

2)No visible arc with little fumes and spatter

3)Smooth weld surface for long lengths

4)High quality welds of excellent penetration,and

5)Weld area is free from surface ripples.

LIMITATIONS:

The process has the following limitations:

1) process is not flexible,and reqires costly equipment.

2) Slag must be removed after each pass

3) Process is not suitable for thin plates and for overhead welding,and limited to the flat or horizontal position welds.

APPLICATIONS:

Developed in the 1940s,submerged arc welding (SAW) Process is best suited for the continuous welding of components having 12 to 50mm thickness. This process is used to weld a variety of carbon and alloy steel,and stainless steel sheets.Typical applications are the welding of pressure vessels,boiler plates and pipes.

Wednesday, 11 January 2017

METHODS OF APPLICATIONS OF CUTTING FLUIDS :



The method of application of a cutting fluid is very important and depends on the particular operation. These methods vary from hand applications such as use of brush or oil-can to high pressure applications.For high production. The following methods are used.

   1)Flood method,

   2) Jet method,and

   3) Mist method.

1) Flood method :

In this method,a reciprocating pump is used to force the coolant over the work and tool.The outlet of the pump is connected to a nozzle through flexible pipe.The nozzle can be adjusted to direct the stream of the fluid at the cutting zone.This is the most common method of application of cutting fluid.


2) jet method :

In jet method,a small jet of fluid at high speed is directed at the point of metal separation from the underneath the tool.In high-speed jet system gear or vane type pump is used to maintain high pressure.


3) Mist method :

In mist method,the fluid is passed through a specially designed nozzle to form very fine droplets(mist).This mist is directed at the cutting zone at high speed.It has better cooling effect than flood or jet methods.

METHODS OF LUBRICATION:

Various methods are used to apply the lubricant to the machine tools.Lubricating oil is generally applied to sliding parts with the help of oil-can.Lubricants are also applied by the following systems.

       1)Gravity feed system.

       2) Pressure feed system.

In the gravity feed system lubricant is applied to the sliding parts through oilcups which are located at the higher levels of sliding parts l.In this oil flows to the parts due to gravity.

Pressure feed system is generally used in automobiles where lubricants are applied under pressure by using oil pump which is situated below the engine.

Monday, 9 January 2017

Law of conservation of energy:

Total energy in a system is constant.Energy cannot be created cannot be destroyed but one form of energy is converted into another form


ADVANTAGES AND LIMITATIONS OF BROACHING:

Broaching is an interesting machining process which is used in mass production. It has certain advantages and limitations as compared to the other machining processes.these are given below.

ADVANTAGES :

1) Fast and simple process.

2)High degree of accuracy and finish is possible.

3)Any shape of profile can be easily machined.

4) Machining process is completed with one stroke of broach.

5) Life of broach tool is high.

6)Cutting temperature and tool wear is low.

7) Doesn't require a highly skilled operator.

8)Cutting force acts in the clamping direction I.e.,it doesn't tends to lift the workpiece from fixture.

9)cutting fluids can be applied more easily and effectively.

10)Most economical for mass production of components.



LIMITATIONS:

1) Not economical for small quantity productions.

2)Cost of broach is high.

3) Tool grinding (broach sharpening) is difficult and expensive.

4) Not suitable to machine a surface having obstruction.

5) The work must be strong enough to with stand cutting forces.

6) Very light and delicate jobs cannot broached easily.

7)Large amount of metal cannot be removed by broaching.

APPLICATIONS OF BROACHING :

The operation of broaching was originally developed for machining small,internal surfaces such as key way in a small diameter which is relatively difficulty for slotter.Broaching is widely used in present day industry for machining a large variety of jobs which were formerly milled or shaped.

Internal broaching is used for machining and sizing of round holes,square,hexagonal,and many other shapes of holes.Internal keyways,splines and gears are easily produced by broaching.External or surface broaching is increasingly used in mass production as an alternatively to milling.It can machine plane or complex shapes easily and economically.

CLASSIFICATION OF BROACHING :



According to method of operation broaching is classified as follows

1) Pull broaching
    -The broach is pulled through stationary        work.

2) Push broaching
    - The broaching is pushed through                      stationary work

3) Surface broaching
    - The broach moves across the work or              vice versa.

4) Continuous broaching
    - The work is moved continuously against        stationary broaches.

PRINCIPLE OF BROACHING MACHINE:

In broaching, the broach is pushed or pulled over a external flat surface of a stationary workpiece. In internal broaching the broach is pushed or pulled through the hole in the stationary workpiece.In certain machines,the braich is held stationary and the workpiece translates over the broach.For broaching no separate feed is required as the feeding action is in built in the teeth form.Each successive tooth is a little higher than the one preciding it.Therefore each tooth removes a layer of workpiece material.The first fee teeth on broach are low to permit the small end of the tool to be passed through work.The intermediate teeth remove the most of the metal; and the last few teeth finish the surface to size machining operation completes in one pass of the broach.The cutting action of broach teeth is shown in fig.


PROPERTIES OF CUTTING FLUIDS:

To get the optimum benefits, the cutting fluid should possess the following qualities.

1) They should possess good lubricating properties to minimise the friction.

2)They should possess high heat absorption capacity so as to carry away the heat generated.

3)They should present no fire or accidental hazards.

4) They should not cause skin irritation.

5)They should not emit obnoxious odours and vapours harmful to the operator, workpiece or surrounding area.

6) They should be of low viscosity to permit free flow and easy separation from chips collected.

7)They should prevent rusting of the
Machine slidings and working surfaces.

8) They should be suitable for a variety of cutting operations, and should be easily available at low price so as to minimise production cost.

9) They should be chemically stable.

10) they should not deteriorate in storage.

11) They should have high flash point.

CUTTING SPEED,FEED AND DEPTH OF CUT IN PLANER MACHINE

CUTTING SPEED:

The cutting speed in planing is the speed of the work in the direction of cutting motion when the metal is being cut. it is expressed in m/min.

FEED:

The feed in planer is the distance the tool head moves at the beginning of each cutting stroke.it is expressed in mm per full stroke (double stroke).

DEPTH OF CUT:

Depth of cut is the thickness of metal removed in one cut or pass.it is measured in the direction perpendicular to the machined surface.it is expressed in mm.

Tailstock

The tailstock is located on right side of the bed i.e.right hand side of the operator. The main purpose of a tailstock on an engine lathe is to support free end of a work during operation.it is also used to hold tools for making holes (twist drills,reamers) adjusted along the bed of the lathe accommodate different lengths of stock.it is provided with set over screw at its base for taper turning alignment.it has cast iron body with bore to accommodate tailstock spindle,and the top portion contains the spindle,tailstock hand wheel, and a spindle clamp for locking the spindle in position. The end of the spindle has a taper bore for holding dead centre,taper shank drills and other tools.the spindle can centre,taper shank drills and other tools.The spindle can be moved in and out of the tailstock by the rotation of hand wheel in anticlockwise and clock wise direction respectively.A tailstock is shown in fig.

What is absorbent

A material which, due to an affinity for certain substances, extracts one or more such substances from a liquid or gaseous medium with which it contacts and which changes physically or chemically, or both, during the process. Calcium chloride is an example of a solid absorbent, while solutions of lithium chloride, lithium bromide, and ethylene glycols are liquid absorbents.

Emergency break.

In cars,emergency brake is a latching brake usually used to keep the vehicle stationary. It is sometimes also used to prevent a vehicle from rolling when the operator needs both feet to operate the clutch and throttle pedals.


Rack-and-pinion

A rack-and-pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack", rotational motion applied to the pinion causes the rack to move, thereby translating the rotational motion of the pinion into the linear motion of the rack.


What is Air bag?

A safety device fitted inside a road vehicle, consisting of a cushion designed to inflate rapidly and protect passengers from impact in the event of a collision.


Sunday, 8 January 2017

What is crank shaft.

A crankshaft is a mechanical part able to perform a conversion between reciprocating motion and rotational motion. In a reciprocating engine, it translates reciprocating motion of the piston into rotational motion, whereas in a reciprocating compressor, it converts the rotational motion into reciprocating motion. In order to do the conversion between two motions, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rods from each cylinder attach.

What is bolt and nut.

A pair of objects with matching screw threads. When either the bolt or the nut is turned, it moves with great force. Often used as fixing devices. The nut is the circular piece that looks like a ring with threads on the inside hole. The bolt is the shaft with threads.

Fuel supply system in diesel engine


Fuel supply system is a seperate system used to deliver diesel at correct time in correct quantity, to a diesel engine (or C.I engine), for smooth and efficient operation.
The operation of a diesel engine is different from that of a petrol engine. In a petrol engine, air-fuel mixture is supplied by a carburetor to the engine, at the beginning of the suction stroke. But in a diesel engine, fuel (without air) is supplied at the end of the compression stroke, by means of a fuel supply system.
Fuel supply system is the food pipe of a vehicle.

Diagram of fuel supply system in diesel engine:

Fuel Supply System in Diesel Engine

Components:

Fuel supply system in diesel engine is made of the following components:
  1. Diesel tank or reservoir
  2. Low pressure pump
  3. Filter
  4. Fuel injection pump
  5. Fuel injectors

1. Diesel tank or reservoir:

Whenever you supply fuel to a diesel engine vehicle, it is stored in the diesel tank. Diesel tank temporarily stores diesel that is to be supplied to the engine.

2. Low pressure pump:

It pumps the diesel at a low pressure to the fuel injection pump through a filter.

3. Filter:

Before diesel is supplied to an engine, it must be filtered to remove any unwanted impurities. Filter is used for this purpose.

4. Fuel injection pump:

This is the most important component of the fuel injection system.
Fuel injection pump pressurizes the fuel to the required level and injects it correctly at the end of the compression stroke, during each cycle of operation of the engine.

5. Fuel injectors:

Injectors are devices used to inject the fuel to the cylinder. In diesel engine, when fuel is injected, it is automatically atomized.

Working:

Diesel is pumped from the diesel tank by a low pressure pump. It is passed through a filter. The filter removes any unwanted impurities in the diesel.
Filtered diesel is supplied to the inlet port of the fuel injection pump. The fuel injection pump automatically pressurizes the diesel to the required level and supplies it to the fuel injector. The fuel injector forces the fuel into the cylinder at the end of the compression stroke, during each cycle of operation of the engine.
Fuel injection pump is operated by means of a cam shaft. CAV fuel injection is the most common fuel injection pump used in diesel engines.
Any leak-off diesel from the fuel injection pump is supplied back into the filter as shown in the diagram above.

Characteristics of a good fuel supply system:

  1. A good fuel supply system should be able to deliver the fuel correctly at the end of the compression stroke.
  2. It must be able to properly atomize the fuel.
  3. It must operate smoothly and sharply during each cycle of operation of the engine.
  4. It must be able to supply the fuel above atmospheric pressure.

Two stroke engine

2-Stroke Engine ani.gif
two-stroke, or two-cycleengine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a "four-stroke engine", which requires four strokes of the piston to complete a power cycle. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust (or scavenging) functions occurring at the same time.
Two-stroke engines often have a high power-to-weight ratio, power being available in a narrow range of rotational speeds called the "power band". Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and so can be more compact and significantly lighter.

Four stroke petrol engine

Four-stroke cycle used in gasoline/petrol engines. 1 = Intake, 2 = Compression, 3 = Power, 4 = Exhaust. The right blue side is the intake port and the left brown side is the exhaust port. The cylinder wall is a thin sleeve surrounding the piston head which creates a space for the combustion of fuel and the genesis of mechanical energy.
four-stroke engine (also known as four cycle) is an internal combustion (IC) engine in which the piston completes four separate strokes while turning a crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
  1. Intake: also known as induction or suction This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: also known as power or ignition This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: also known as outlet. During the exhaust stroke, the piston once again returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve

Four stroke diesel engine or CI engine with working principle

In this article I going to describe you about how does a four stroke diesel engine work.


Diesel engine which is also known as compression ignition engine is widely used in automobile industries. Many big vehicles such as truck, bus, car etc. used diesel engine as the power unit because of its higher torque and greater mileage than petrol engine. Diesel engine is very popular in Indian market as well as in other countries because of lower price of diesel than petrol in many countries. So the requirement of diesel engine is much more than petrol engine.
The ignition temperature of diesel is lower than petrol so the working of diesel engine is slightly different than petrol engine.

Working of Four Stroke Diesel Engine

The power generation process in four stroke diesel engine is also divided into four parts. Each part is known as piston stroke. In IC engine, stroke is referred to the maximum distance travel by the piston in a single direction. The piston is free to move only in upward and downward direction. In four stroke engine the piston move two time up and down and the crankshaft move two complete revolution to complete four piston cycle. These are suction stroke, compression stroke, expansion stroke and exhaust stroke.

Suction stroke:

In the suction stroke or intake stroke of diesel engine the piston start moves from top end of the cylinder to bottom end of the cylinder and simultaneously inlet valve opens. At this time air at atmospheric pressure drawn inside the cylinder through the inlet valve by a pump. The inlet valve remains open until the piston reaches the lower end of cylinder. After it inlet valve close and seal the upper end of the cylinder.
How does four stroke diesel engine (compression ignition engine) works?

Compression stroke:

After the piston passes bottom end of the cylinder, it starts moving up. Both valves are closed and the cylinder is sealed at that time. The piston moves upward. This movement of piston compresses the air into a small space between the top of the piston and cylinder head. The air is compressed into 1/22 or less of its original volume. Due to this compression a high pressure and temperature generate inside the cylinder. Both the inlet and exhaust valves do not open during any part of this stroke. At the end of compression stroke the piston is at top end of the cylinder.
How does four stroke diesel engine (compression ignition engine) works?

Power stroke:

At the end of the compression stroke when the piston is at top end of the cylinder a metered quantity of diesel is injected into the cylinder by the injector. The heat of compressed air ignites the diesel fuel and generates high pressure which pushes down the piston. The connection rod carries this force to the crankshaft which turns to move the vehicle. At the end of power stroke the piston reach the bottom end of cylinder.
How does four stroke diesel engine (compression ignition engine) works?

Exhaust stroke:

When the piston reaches the bottom end of cylinder after the power stroke, the exhaust valve opens. At this time the burn gases inside the cylinder so the cylinder pressure is slightly high from atmospheric pressure. This pressure difference allows burn gases to escape through the exhaust port and the piston move through the top end of the cylinder. At the end of exhaust all burn gases escape and exhaust valve closed. Now again intake valve open and this process running until your vehicle starts.

How does four stroke diesel engine (compression ignition engine) works?

Brinell hardness test

Hardness is a characteristic of a material, not a fundamental physical property. It is defined as the resistance to indentation, and it is determined by measuring the permanent depth of the indentation. More simply put, when using a fixed force (load) and a given indenter, the smaller the indentation, the harder the material. Indentation hardness value is obtained by measuring the depth or the area of the indentation using one of over 12 different test methods. Click here to learn more about hardness testing basics.

The Brinell hardness test method as used to determine Brinell hardness, is defined in ASTM E10. Most commonly it is used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested using another test method, e.g., castings and forgings. Brinell testing often use a very high test load (3000 kgf) and a 10mm wide indenter so that the resulting indentation averages out most surface and sub-surface inconsistencies.

The Brinell method applies a predetermined test load (F) to a carbide ball of fixed diameter (D) which is held for a predetermined time period and then removed. The resulting impression is measured across at least two diameters – usually at right angles to each other and these result averaged (d). A chart is then used to convert the averaged diameter measurement to a Brinell hardness number. Test forces range from 500 to 3000 kgf.

A Brinell hardness result measures the permanent width of indentation produced by a carbide indenter applied to a test specimen at a given load, for a given length of time. Typically, an indentation is made with a Brinell hardness testing machine and then measured for indentation diameter in a second step with a specially designed Brinell microscope or optical system. The resulting measurement is converted to a Brinell value using the Brinell formula or a conversion chart based on the formula. Most typically, a Brinell test will use 3000 kgf load with a 10mm ball. If the sample material is aluminum, the test is most frequently performed with a 500 kgf load and 10mm ball. Brinell test loads can range from 3000 kgf down to 1 kgf. Ball indenter diameters can range from 10mm to 1mm. Generally, the lower loads and ball diameters are used for convenience in “combination” testers, like Rockwell units, that have a small load capacity. The test standard specifies a time of 10 to 15 seconds, although shorter times can be used if it is known that the shorter time does not affect the result. There are other conditions that must be met for testing on a round specimen, spacing of indentations, minimum thickness of test specimens, etc.

 Test Method Illustration

D  = Ball diameter
d   = impression diameter
F   = load
HB = Brinell result 
Brinell Application 

Typically the greatest source of error in Brinell testing is the measurement of the indentation. Due to disparities in operators making the measurements, the results will vary even under perfect conditions. Less than perfect conditions can cause the variation to increase greatly. Frequently the test surface is prepared with a grinder to remove surface conditions. The jagged edge makes interpretation of the indentation difficult. Furthermore, when operators know the specifications limits for rejects, they may often be influenced to see the measurements in a way that increases the percentage of “good” tests and less re-testing.

Two types of technological remedies for countering Brinell measurement error problems have been developed over the years. Automatic optical Brinell scopes use computers and image analysis to read the indentations in a consistent manner. This standardization helps eliminate operator subjectivity so operators are less-prone to automatically view in-tolerance results when the sample’s result may be out-of-tolerance.

Brinell units, according to ASTM E103, measure the samples using Brinell hardness parameters together with a Rockwell hardness method. This method provides the most repeatable results (and greater speed) since the vagaries of optical interpretations are removed through the use of an automatic mechanical depth measurement. Using this method, however, results may not be strictly consistent with Brinell results due to the different test methods – an offset to the results may be required for some materials. It is easy to establish the correct values in those cases where this may be a problem. 

Rockwell test

The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload.
    Tinius Olsen has many types of hardness testers available that can rapidly and accurately determine the hardness value of a wide variety of materials including metals, plastics, large parts, small precision parts. Whether you need are bench mounted testers, large scale floor mounted testers or dedicated testers that are integrated into your production lines, we can help you with your application. 

What is drilling machine and its types

Drilling machines or drill presses are one of the most common machines found in the machine shop. A drill press is a machine thatturns and advances a rotary tool into a workpiece. The drill press is used primarily for drilling holes, but when used with the proper tooling, it can be used for a number of machining operations. The most common machining operations performed on a drill press are drilling, reaming, tapping, counterboring, countersinking, and spotfacing.
There are many different types or configurations of drilling machines, but most drilling machines will fall into four broad categories: upright sensitive, upright, radial, and special purpose.
UPRIGHT SENSITIVE DRILL PRESS

Figure 1 Upright sensitive drill press
The upright sensitive drill press (Figure 1) is a light-duty type of drilling machine that normally incorporates a belt drive spindle head. This machine is generally used for moderate-to-light duty work. The upright sensitive drill press gets its name due to the fact that the machine can only be hand fed. Hand feeding the tool into the workpiece allows the operator to "feel" the cutting action of the tool. The sensitive drill press is manufactured in a floor style or a bench style.
UPRIGHT DRILL PRESSThe upright drill press (Figure 2) is a heavy duty type of drilling machine normally incorporating a geared drive spindle head. This type of drilling machine is used on large hole-producing operations that typically involve larger or heavier parts. The upright drill press allows the operator to hand feed or power feed the tool into the workpiece. The power feed mechanism automatically advances the tool into the workpiece. Some types of upright drill presses are also manufactured with automatic table-raising mechanisms.

Figure 2
 Upright drill press
RADIAL ARM DRILL PRESSThe radial arm drill press (Figure 3) is the hole producing work horse of the machine shop. The press is commonly refered to as a radial drill press. The radial arm drill press allows the operator to position the spindle directly over the workpiece rather than move the workpiece to the tool. The design of the radial drill press gives it a great deal of versatility, especially on parts too large to position easily. Radial drills offer power feed on the spindle, as well as an automatic mechanism to raise or lower the radial arm. The wheel head, which is located on the radial arm, can also be traversed along the arm, giving the machine added ease of use as well as versatility. Radial arm drill presses can be equipped with a trunion table or tilting tableThis gives the operator the ability to drill intersecting or angular holes in one setup.

Figure 3  Radial arm drill press

SPECIAL PURPOSE DRILL MACHINES
There are a number of types of special purpose drilling machines. The purposes of these types of drilling machines vary. Special purpose drilling machines include machines capable of drilling 20 holes at once or drilling holes as small as 0.01 of an inch.
Gang Drilling Machines

Figure 4 Gang drill press
The gang style drilling machine (Figure 4) or gang drill press has several work heads positioned over a single table. This type of drill press is used when successive operations are to be done. For instance, the first head may be used to spot drill. The second head may be used to tap drill. The third head may be used, along with a tapping head, to tap the hole. The fourth head may be used to chamfer.
Multiple Spindle Drilling Machine

The multiple spindle drilling machine is commonly refered to as a multispindle drill press. This special purpose drill press has many spindles connected to one main work head (Figure 5).All of the spindles are fed into the  workpiece at the same time. This type of drilling machine is especially useful when you have a large number of parts with many holes located close together.

Figure 5 Multispindle drill press

Casting process


INTRODUCTION:
Manufacture of a machine part by heating a metal or alloy above its melting point and pouring the liquidmetal/alloy in a cavity approximately of same shape and size as the machine part is called casting process. After the liquid metal cools and solidifies, it acquires the shape and size of the cavity and resembles the finished product required. The department of the workshop, where castings are made is called foundry.
The manufacture of a casting requires:
(a) Preparation of a pattern,
(b) Preparation of a mould with the help of the pattern,
(c) Melting of metal or alloy in a furnace,
(d) Pouring of molten metal into mould cavity,
(e) Breaking the mould to retrieve the casting,
(f) Cleaning the casting and cutting off risers, runners etc., (this operation is called ‘fettling’),
and
(g) Inspection of casting.
Castings are made in a large number of metals and alloys, both ferrrous and non-ferrous. Grey cast iron components are very common; steel castings are stronger and are used for components subject to higher stresses. Bronze and brass castings are used on ships and in marine environment, where ferrous items will be subjected to heavy corrosion. Aluminium and aluminium-magnesium castings are used in automobiles. Stainless steel castings are used for making cutlery items.
Casting is an economical way of producing components of required shape either in small lots or in larger lots. However, castings are less strong as compared to wrought components produced by processes such as forging etc. However castings offer the possibility of having slightly improved properties in certain part of the casting by techniques such as use of chill etc. In casting process, very little metal is wasted.
Casting Process

Foundry