Machine Design is the innovation of new and

effective machines and improving the existing ones.

A new or effective machine is one which is more

economical in the overall cost of production and

operation.

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Classifications of Machine Design

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1. Adaptive design:

In this the designer’s work is concerned with adaptation of existing designs. The

designer only makes minor alternation or modification in the existing designs of the

product.

2. Development design:

This type of design needs scientific training and design ability in order to modify the

existing designs into a new idea by adopting a new material or different method of

manufacture.

3. New design:

This type of design needs lot of research, technical ability and creative thinking. Only

those designers who have personal qualities of a sufficiently high order can take up

the work of a new design

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4. Rational design:

This type of design depends upon mathematical formulae of principle of mechanics.

5. Empirical design:

This type of design depends upon empirical formulae based on the practice and past

experience.

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6. Industrial design:

This type of design depends upon the production aspects to manufacture any machine

component in the industry.

7. Optimum design:

It is the best design for the given objective function under the specified constraints. It

may be achieved by minimizing the undesirable effects.

8. System design:

It is the design of any complex mechanical system like a motor car.

9. Element design:

It is the design of any element of the mechanical system like piston, crankshaft,

connecting rod, etc.

10. Computer aided design:

This type of design depends upon the use of computer systems to assist in the creation,

modification, analysis and optimization of a design.

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General Procedure in Machine

Design

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1. Need or Aim:

First of all, make a complete statement of the problem, indicating the need, aim or

purpose for which the machine is to be designed.

2. Synthesis (Mechanisms):

Select the possible mechanism or group of mechanisms which will give the desired

motion.

3. Analysis of forces:

Find the forces acting on each member of the machine and the energy transmitted

by each member.

4. Material selection:

Select the material best suited for each member of the machine.

5. Design of elements (Size and Stresses):

Find the size of each member of the machine by considering the force acting on the

member and the permissible stresses for the material used. It should be kept in mind

that each member should not deflect or deform than the permissible limit.

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6. Modification:

Modify the size of the member to agree with the past experience and judgment to

facilitate manufacture. The modification may also be necessary by consideration of

manufacturing to reduce overall cost.

7. Detailed drawing:

Draw the detailed drawing of each component and the assembly of the machine

with complete specification for the manufacturing processes suggested.

8. Production:

The component, as per the drawing, is manufactured in the workshop

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What is Stress Concentration

Definition, Causes, effects and

Prevention?

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Definition Stress concentration is the

accumulation of stress in a body due to sudden change in its geometry. When there is a sudden change in the geometry of the body due to cracks sharp corners, holes and decrease in the cross section area, then there is an increase in the localised stress near these cracks, sharp corners, holes, and decreased cross section area. The body tends to fail from these places where the stress concentration is more. So to prevent a body from getting failed, the stress concentration should be avoided or reduced.

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Cause: The stress concentration in a body happens because of sudden

change in the geometry of the body due to cracks, sharp

corners, holes, decrease in the cross section area. Due to these

irregularities, there is an increase in the intensity of stress in

the body.

Effect When a body has stress concentration in it, the chances of its

failure increases. The body tends to fail from the place where

it is has more concentration of stress. A body has less life that

has more irregularities within it. In order to increase the life

of the body, the intensity of stress should be reduced.

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Methods to Reduce Stress

Concentration

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1. There are no of ways to reduce stress concentration in a body and

some of these are avoiding sharp corners by providing a fillet radius

at the sharp corners. By providing the fillet radius at sharp corners,

the cross section area decreases gradually instead of suddenly. And

this distributes the stress in the body more uniformly. This is shown

in the figure given below.

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2. By providing small holes near big hole. If we have an object, that has an

internal hole within it. Then the intensity of stress near that hole is more. To

avoid this, some smaller holes are created near that hole. This distributes the

stress more uniformly than it was before. This is shown in the figure given

below.

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3. By decreasing the nominal diameter of a threaded object and make it equal

to the core diameter. Suppose we have a threaded object. And the intensity of

stress at threaded part is more. The chances of object may fail is more at the

threaded part. This can be avoided by decreasing the nominal diameter of the

shank and make it equal to the core diameter. This will distribute the stress

more uniformly in the object with threads.

4. By providing notches or undercut at the sharp corners.

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Mechanical Properties of

Engineering Materials

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Strength

It is the property of material which opposes the deformation or breakdown of material in

presence of external forces or load. Material which we finalize for our engineering product,

must have suitable mechanical strength to be capable to work under different mechanical

forces or loads.

Toughness

It is the ability of material to absorb the energy and gets plastically deformed without

fracturing. Its numerical value is determined by the amount of energy per unit volume. It

unit is Joule/ m3. Value of tough ness of a material can be determines by stress-strain

characteristics of material. For good toughness material should have good strength as well

as ductility.

Hardness

It is the ability of material to resist to permanent shape change due to external stress. There

are various measure of hardness – Scratch Hardness, Indentation Hardness and Rebound

hardness.

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Hardenability

It is the ability of a material to attain the hardness by heat treatment processing. It is

determined by the depth up to which the material becomes hard. The SI unit of

hardenability is meter (similar to length). Hardenability of material is inversely

proportional to the weld-ability of material.

Brittleness

Brittleness of a material indicates that how easily it gets fractured when it is subjected

to a force or load. When a brittle material is subjected to a stress is observes very less

energy and gets fractures without significant strain. Brittleness is converse to ductility

of material. Brittleness of material is temperature depended. Some metals which are

ductile at normal temperature become brittle at low temperature.

Malleability

Malleability is property of solid material which indicates that how easily a materials

gets deformed under compressive stress. Malleability is often categorized by the ability

of material to be formed in the form of a thin sheet by hammering or rolling. This

mechanical property is an aspect of plasticity of material. Malleability of material is

temperature dependent. With rise of temperature, the malleability of material increases.

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Ductility

Ductility is a property of a solid material which indicates that how easily a materials

gets deformed under tensile stress. Ductility is often categorized by the ability of

material to get stretched into a wire by pulling or drawing. This mechanical property

is also an aspect of plasticity of material and temperature dependent. With rise of

temperature, the ductility of material increases.

Creep and Slip

Creep is the property of material which indicates the tendency of material to move

slowly and deform permanently under the influence of external mechanical stress. It

results due to long time exposure to large external mechanical stress with in limit of

yielding. Creep is more severe in material that are subjected to heat for long time.

Slip in material is a plane with high density of atoms.

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Resilience

Resilience is the ability of material to absorb the energy when it is deformed

elastically by applying stress and release the energy when stress is removed.

Proof resilience is defined as the maximum energy that can be absorbed without

permanent deformation. The modulus of resilience is defined as the maximum

energy that can be absorbed per unit volume without permanent deformation. It

can be determined by integrating the stress-strain cure from zero to elastic limit.

Its unit is joule/m3.

Fatigue

Fatigue is the weakening of material caused by the repeated loading of material.

When a material is subjected to cyclic loading, and loading greater than certain

threshold value but much below the strength of material (ultimate tensile strength

limit or yield stress limit, microscopic cracks begin to form at grain boundaries

and interfaces. Eventually the crack reached to a critical size. This crack

propagates suddenly and the structure gets fractured. The shape of structure

effects the fatigue very much. Square holes and sharp corners lead to elevated

stresses where the fatigue crack initiates.

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Shaft- Defination, Types of

Shafts, Materials for Shafts and

Standard Sizes of Shafts

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Defination:-

A shaft is a rotating machine element, usually circular in cross section, which is used

to transmit power from one part to another, or from a machine which produces power to a

machine which absorbs power. The various members such as pulleys and gears are

mounted on it.

Types:-

Transmission shafts are used to transmit power between the source and the machine

absorbing power; e.g. counter shafts and line shafts.

Machine shafts are the integral part of the machine itself; e.g. crankshaft.

Materials:-

The material used for ordinary shafts is mild steel. When high strength is required,

an alloy steel such as nickel, nickel-chromium or chromium-vanadium steel is used.

Shafts are generally formed by hot rolling and finished to size by cold

drawing or turning and grinding.

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Machine shafts:-

Up to 25 mm steps of 0.5 mm

Transmission shafts:- 25 mm to 60 mm with 5 mm steps

60 mm to 110 mm with 10 mm steps

110 mm to 140 mm with 15 mm steps

140 mm to 500 mm with 20 mm steps

The standard lengths of the shafts are 5 m, 6 m and 7 m.

Stresses:- Shear stresses due to the transmission of torque (due to torsional load).

Bending stresses (tensile or compressive) due to the forces acting upon the machine

elements like gears and pulleys as well as the self weight of the shaft.

Stresses due to combined torsional and bending loads.

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Keys and Types of Keys

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.

There are three major types of key that are mostly used in mechanical Industry :

1.Sunk Key 2.Saddle Key 3. Tagent key

1. Sunk Key:

Sunk Key is that kind of key that was mount half a side in hear or pulley and half a side in shaft

keyway. There are six different types of Sunk key which are mostly used in Mechanical industry.

•Rectangular Sunk Key

•Square Sunk key

•Parallel Sunk Key

•Gib Head Sunk Key

•Feather Key

•Woodruf Key

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2. Saddle Key: Saddle Key is a key that fit in the keyway of the Hub.There are two different types of Saddle Key

•Flat Saddle Key

•Hollow Saddle Key

Tagent Key always mount as a pair in Shaft.Ever key will fight with only one direction.

Tagent key always use for heavy duty works.

3. Tagent Key:

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Cams

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A cam is a rotating or sliding piece in a mechanical linkage that drives a mating component

known as a follower. From a functional viewpoint, a cam-and-follower arrangement is very

similar to the linkages. The cam accepts an input motion (rotary motion or linear

motion) and imparts a resultant motion (linear motion or rotary motion) to a follower.

Cam Nomenclature

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Cam profile: Cam profile is outer surface of the disc cam.

Base circle: Base circle is the smallest circle, drawn tangential to the cam profile.

Trace point: Trace point is a point on the follower, trace point motion describes the

movement of the follower.

Pitch curve: Pitch curve is the path generated by the trace point as the follower is rotated

about a stationery cam.

Prime circle: Prime circle is the smallest circle that can be drawn so as to be tangential to

the pitch curve, with its centre at the cam centre.

Pressure angle: The pressure angle is the angle between the direction of the follower

movement and the normal to the pitch curve.

Pitch point: Pitch point corresponds to the point of maximum pressure angle.

Pitch circle: A circle drawn from the cam center and passes through the pitch point is

called Pitch circle.

Stroke: The greatest distance or angle through which the follower moves or rotates.

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Types of Cams:- Cams can be classified into the following three types based on their shapes.

Plate or disk cams: Plate or disk cams are the simplest and most common type of cam.

A plate cam is illustrated in figure 3 (a). This type of cam is formed on a disk or plate.

The radial distance from the center of the disk is varied throughout the circumference of

the cam. Allowing a follower to ride on this outer edge gives the follower a radial

motion.

Cylindrical or drum cam: A cylindrical or drum cam is illustrated in figure 3 (b). This

type of cam is formed on a cylinder. A groove is cut into the cylinder, with a varying

location along the axis of rotation. Attaching a follower that rides in the groove gives the

follower motion along the axis of rotation.

Linear cam: A linear cam is illustrated in figure 3 (c). This type of cam is formed on a

translated block. A groove is cut into the block with a distance that varies from the plane

of translation. Attaching a follower that rides in the groove gives the follower motion

perpendicular to the plane of translation.

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1. Based on Follower Motion

Based on the follower motion, followers can be classified into the following two

categories:

(i). Translating followers are constrained to motion in a straight line and are shown in

figure .

(ii). Swinging arm or pivoted followers are constrained to rotational motion and are

shown in figure .

2. Based on Follower Position

Based on the follower position, relative to the center of rotation of the cam, is typically

influenced by any spacing requirements of the machine. The position of translating

followers can be classified into the following two categories:

(i). An in-line follower exhibits straight-line motion, such that the line of translation

extends through the center of rotation of the cam and is shown in figure .

(ii). An offset follower exhibits straight-line motion, such that the line of the motion is

offset from the center of rotation of the cam and is shown in figure .

In the case of pivoted followers, there is no need to distinguish between in-line and

offset followers because they exhibit identical kinematics.

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3. Based on Follower Shape

Finally, the follower shape can be classified into the following four categories:

(i). A knife-edge follower consists of a follower that is formed to a point and drags on

the edge of the cam. The follower shown in figure 4(a) is a knife-edge follower. It is

the simplest form, but the sharp edge produces high contact stresses and wears

rapidly. Consequently, this type of follower is rarely used.

(ii). A roller follower consists of a follower that has a separate part, the roller that is

pinned to the follower stem. The follower shown in figure 4(b) is a roller follower. As

the cam rotates, the roller maintains contact with the cam and rolls on the cam surface.

This is the most commonly used follower, as the friction and contact stresses are lower

than those for the knife-edge follower. However, a roller follower can possibly

jam during steep cam displacements.

(iii). A flat-faced follower consists of a follower that is formed with a large, flat

surface available to contact the cam. The follower shown in figure 4(c) is a flat-

faced follower. This type of follower can be used with a steep cam motion and does

not jam. Consequently, this type of follower is used when quick motions are required.

However, any follower deflection or misalignment causes high surface stresses. In

addition, the frictional forces are greater than those of the roller follower because of

the intense sliding contact between the cam and follower. 32

(iv). A spherical-faced follower consists of a follower formed with a radius face that

contacts the cam. The follower shown in figure 4(d) is a spherical-face follower. As with

the flat-faced follower, the spherical- face can be used with a steep cam motion without

jamming. The radius face compensates for deflection or misalignment. Yet, like the flat-

faced follower, the frictional forces are greater than those of the roller follower.

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Terminology for Spur Gears

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Pitch surface : The surface of the imaginary rolling cylinder (cone, etc.) that the

toothed gear may be considered to replace.

Pitch circle: A right section of the pitch surface.

Addendum circle: A circle bounding the ends of the teeth, in a right section of the gear.

Root (or dedendum) circle: The circle bounding the spaces between the teeth, in a right

section of the gear.

Addendum: The radial distance between the pitch circle and the addendum circle.

Dedendum: The radial distance between the pitch circle and the root circle.

Clearance: The difference between the dedendum of one gear and the addendum of the

mating gear.

Face of a tooth: That part of the tooth surface lying outside the pitch surface.

Flank of a tooth: The part of the tooth surface lying inside the pitch surface.

Circular thickness (also called the tooth thickness) : The thickness of the tooth

measured on the pitch circle. It is the length of an arc and not the length of a straight

line.

Tooth space: The distance between adjacent teeth measured on the pitch circle.

Backlash: The difference between the circle thickness of one gear and the tooth space of

the mating gear.

Circular pitch p: The width of a tooth and a space, measured on the pitch circle.

Diametral pitch P: The number of teeth of a gear per inch of its pitch diameter. A

toothed gear must have an integral number of teeth. The circular pitch, therefore, equals

the pitch circumference divided by the number of teeth. The diametral pitch is, by

definition, the number of teeth divided by the pitch diameter. 36

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•Module m: Pitch diameter divided by number of teeth. The pitch diameter is usually

specified in inches or millimeters; in the former case the module is the inverse of

diametral pitch.

•Fillet : The small radius that connects the profile of a tooth to the root circle.

•Pinion: The smaller of any pair of mating gears. The larger of the pair is called simply

the gear.

•Velocity ratio: The ratio of the number of revolutions of the driving (or input) gear to

the number of revolutions of the driven (or output) gear, in a unit of time.

•Pitch point: The point of tangency of the pitch circles of a pair of mating gears.

•Common tangent: The line tangent to the pitch circle at the pitch point.

•Line of action: A line normal to a pair of mating tooth profiles at their point of contact.

•Path of contact: The path traced by the contact point of a pair of tooth profiles.

•Pressure angle : The angle between the common normal at the point of tooth contact

and the common tangent to the pitch circles. It is also the angle between the line of action

and the common tangent.

•Base circle :An imaginary circle used in involute gearing to generate the involutes that

form the tooth profiles.

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