Maharashtra State Board of Technical Education 2008-3rd Year Diploma Mechanical Engineering for Design of Machine Element - Question Paper

Sample ques. Paper

Course Name : Diploma in Mechanical Engineering
Course Code : ME

9150

Semester : 6th
Subject Title : Design of Machine Elements
Marks : 80 Time: three Hrs.

Instructions:

1. All ques. are compulsory.
2. Illustrate your answers with neat sketches wherever necessary.
3. Figures to the right indicate full marks.
4. presume suitable data if necessary.
5. Preferably, write the answers in sequential order.
Q.1 Attempt any 4 of the following: 16 Marks
a) elaborate the steps involved in general design procedure?
b) Draw stress – strain diagram for ductile and brittle materials. Name the different
points on the diagrams.
c) provide 2 examples where screwed joints are preferred over welded joints.
d) discuss with neat sketch, elaborate the modes of failure in the Knuckle Pin?
e) describe factor of safety. provide 4 factors on which it depends.
f) provide the importance of shape and size in aesthetic design.

Q.2 Attempt any 3 of the following: 12 Marks
a) State significance of Wahl’s Correction Factor.

b) A plate 80 mm wide and 10 mm thick is to be welded to a different plate by means of
parallel filled welds. The plates are subjected to a load of 40 KN. obtain the length of
the weld so that the maximum stress does not exceed 50 MPa. Consider the joint
under static loading.

c) What is stress concentration? How will it be reduced, discuss with 2 examples.
Illustrate your ans with neat sketches.

d) State the theories of failures and discuss the Guest’s Theory (Maximum shear
stress theory)


Q.3 Attempt any 2 of the following: 12 Marks
a) elaborate the advantages of square thread profile? Draw a thread profile used in

Power Screw.

b) Draw a neat sketch of screw Jack. provide the design procedure of screw.

c) The lead screw of a lathe has square threads of 24 mm. outside diameter and five mm

pitch. In order to drive the tool carriage, the screw exerts an axial pressure of 2.5
KN. obtain the efficiency of the screw and power needed to drive the screw, if it is
to rotate at 30 rpm. Neglect bearing friction. presume the coefficient of frictio of
screw thread as 0.12.

Q.4 Attempt any 2 of the following: 16 Marks
a) Determine the diameter for a hollow shaft having inside diameter 0.6 times outside
diameter. The maximum allowable shear stress for the shaft is 60MPa. The shaft is
driven by a 900 mm diameter overhang pulley placed vertically beneath it. The
weight of the pulley is 600 N. The tension on the tight and slack side of the belt is
2900 N and 1000 N respectively. The overhand is 250 mm. presume angle of lap of
the belt on the pulley to be 1800.
b) Draw a neat sketch of socket and spigot cotter joint and state its strength equations.
c) The spindle of a drilling machine is subjected to a maximum axial load of 10KN
during operation. Determine the diameter of the solid cast iron column if the
permissible tensile stress is 40 MPa. The distance ranging from the axis of the spindle
and the axis of the column is 400 mm.

Q.5 Attempt any 2 of the following: 12 Marks
a) What is the procedure for selection of bearings from the manufacturer’s catalogue?

b) Fine the diameter of the screwed boilar stays. every stay supports an area equal to
200 mm * 180 mm. The steam pressure is one N/mm2 . The permissible tensile stress
for the stay material is 35 MPa.

c) Design and draw a protective kind of cast iron flange coupling for a steel shaft
transmitting 20 KW at 259 rpm and having an allowable shear stress of 40 MPa.
The working stress in the bolts should not exceed 90 N/mm2. presume that the identical
material is used for shaft and key and that the crushing stress is twice the value of its
shear stress. The maximum torque is 25% greater than the full load torque. The
shear stress for cast iron is 14 N/mm2.


Q.6 Attempt any 3 of the following: 12 Marks
a) Write Lewis formula for the strength of gear tooth. provide the meaning of every
term.
b) For a square key equally strong in shearing and crushing, show that the permissible
crushing stress is 2 times the shear stress.
c) Design a helical compresiion spring for a maximum load of 1000N for a deflection
of 25 mm using the vale of spring index as five and Wahl’s correction factor as 1.3.
The maximum permissible shear stress for the spring wire is 400 MPa and modulus
of rigidity is 84 KN/mm2.
d) discuss with neat sketch constructional details of leaf spring. State any 2
applications.



Earning:   Approval pending.