MECHANICAL ENGINEERING 2011
Paper-1





SECTION-A

1.
An elevator starts from rest and raises vertically 40 m to attain its maximum velocity in T seconds, with acceleration record shown in the figure. Determine the time T and the maximum velocit reached by the elevator.
src='./qimages/1090-1a.jpg'>
For a conventional type 2-stroke cycIe four cylinder inline reciprocating engine sketch the primary and secondary crank diagrams for firing order of I-II-IV-III and find out balancing condition of the engine for primary and secondary effects. 10
(c)Sketch the displacement velocity and acceleration curves for rise motion alone if the cam-follower is executing uniform and equal acceleration and retardation. State the main disadvantage of this type follower motion. Cd) How ductility of structural steel is evaluated from static tension test? What is the effect of gauge length on the value of ductility,?

A cast iron sample when tested in compression fails along approximately 45° plane from its axis while when tested in torsion also fails along a 45° (approx.) helical plane from its axis. Explain the reason for such failure and mention about dominating stresses causing failure.

Classify stainless steels based on the metallugical
considerations.
Write main characteristic of each class of stainless steels.

2. A model rocket of mass 0.1 kg is launched vertically from rest at time with a constant thrust of 10 N for one second and no thurst for t>1 second. Neglecting the air resistance and decrease in the mass of rocket determine
maximum height reached by the rocket,
time required to reach maximum height. 15

An automobile of mass 1225 kg starts from rest and travels a distance of 400 m. The co-efficient of static friction between tyre and road is 0.70, and air resistance is equivalent to D 0.575 v2, is velocity in m/s. The automobile has front wheel drive and front wheel supports 62% of the total weight of vehicle. Detennine the maximum speed reached by the automobile after travelling 400 m distance. 15


Stress concentration factor is not considered harmful for ductile materials in static loading but for brittle materials it has demanding effect in both static and dynamic loading.
Justify the above statement giving illustrations.
A hollow shaft of outside diam inside diameter 50 mm inside diameter 20mm is subjected to a torque of T N.m.
If the tensile yield stress of the shaft material is
250 N/mm2, what is the maximum permissible value of T to avoid failure according to avoid failure according to Tresca's failure theory? take a factor of safety of 2.0 for a given ation. 15

3.
A cantilever beam of length is subjected to two concentrated loads of 2P and P at its mid­length and free end respectively. If deflection at its free end is limited to L/5OO, what should be value of P Take flexural rigidity of the beam as E1. 15

The shaft of as mall turbine with a single disc is found to have a static deflection of 0.355 mm. Find the critical speed of the shaft-disc system and calculate percentage change in the diameter of the shaft that will be required to raise the critical speed to 2100 rpm. If the initial displacement of the centre of the mass of the disc from the axis of shaft is 0.5 mm, compare the deflection of the shaft at 1500 rpm in the two cases.

A beam ABCD is loaded as shown in Fig. given below. The beam is of rectangular section 50 mm x 100 mm

Sketch the S.F. and B.M. diagram for the beam.
Determine the maximum bending stress at section B of the beam.
src='./qimages/1090-3c.jpg'>

4.
A 1 m x 1m mild steel sheet of 1 mm thickness is stretched in its own plane by stresses (sigma)x 20 MPa and (sigma)y 30 MPa as shown in figure below. Point O is centre of the plate. OC and OD are two mutually perpendicular lines inclined at 45(degrees) each to x and y directions respectively before application of stress. Determine the change in angle (in degrees) between OC and OD after application of stresses. Take modulus of rigidity of plate material G 80 GPa.
src='./qimages/1090-4a.jpg'>

A simple gear train consists of three spur gears 2 and where gear l is the driver, gear 2 idler gear and gear 3 driven gear. The axes of all the 3 gears are in the horizontal plane.The bearing centers of gears 2 and 3 are designated as B and C respectively. Gear 1 has 10 mm module, pressure angle 20° and 35 teeth. Gears 2 and 3 are having 45 teeth and 60 teeth respectively. The driver is rotating at 1000 rpm clockwise and delivers 30 kW of power Find:
distance between A and C

speed ratio of the gear train.
Draw the free body diagram of the driven gear and show all the forces acting on it.


Differentiate between point defects and line defects in a crystalline solid.

With a neat diagram show two types of line defects. How are they formed 15

What are ceramic materials How do they differ
from other materials
How are the ceramic toughened? Give one example. 15


Section B

5.
For punching a 10 mm circular hole, and cutting a rectangular blank of 50 x 200 mm from a sheet of 1 mm thickness (mild steel, shear stress 240 N/mm2 calculate, in each case:

Siz punch
Size of die
Force required. 10

Sketch the international prototype metre. Explain briefly, with reasons, its:

material
cross section
(iii)support points
plane of marking
environment. 10

Sketch a mould for two hollow components to be cast. On the diagram, indicate runner, gate, riser, core, cope, sprue, pouring basin, sprue well drag, parting line.

An interference assembly, of nominal diameter 20 mm, is of a unilateral holes and a shafts. The
manufacturing tolerances for the holes are twice that for the shaft. Permitted interference values are 0.03 to 0.09 mm. Determine the sizes, with limits, for the two mating parts. 10
State the mechanism of cutting by abrasive jet. What are the advantages and disadvantages of AJM? Mension two applications. 10


(i)Identify four major costs associated with poor quality.
Name the tools for improving quality.
The operations and their reliabilities for a beauty-product are given below

Operation Reliability
Mix 0'99
Fill 0·98
Cap 0·99
Label 0·97

What is the reliability of the system?

The feedback from customers shows the following:

Defect frequency
Lumps of un-mixed product 7
Over or underfilled jars 18
Jar lids did not seal 6
Labels rumpled or missing 29
Draw the Pareto chart to identify vital defects. 10

6.
Draw a self explanatory sketch of Sigma mechanical comparator. Explain how shock load is avoided,
oscillations of the pointer are damped. 10

Explain, at least two, characteristics each of NC, CNC and DNC. 10

Compare smith forging, drop forging, press forging and upset forging. Mention three points for each. 10

Determine the optimum speed for achieving maximum production rate in a machining operation. The data is as follows

Machining time/job 6 min.
Tool life 90 min.
Taylor's equation constants C 100, n 0·5
Job handling time 4 min/job
Tool changing time 9 min. 10

Three processes viz. automatic, semi-automatic and manual can be used to produce an item. The initial annual fixed cost and variable cost/unit

src='./qimages/1090-6e.jpg'>
Draw the total annual cost curves for the processes
Find the range of production volume for each process when it is most economical.
which process will you recommend if the forecasted production is 8000 units/annum? 20

7.
An activity has four elements. The activity is work-measured and the times are recorded on continuous basis over five cycles. The observations are given in table:


Work Element Observations Rating

Cycle->l 2 3 4 5 Factor
1 0.50 3.30 5.70 8.20 10.85 1.1
2 0.75 3.45 5.95 8.55 11.10 1.2 3 1.45 4·05 6·50 9·25 11.75 1.2
4 2·75 5.25 7.60 10.35 13.05 0.9
The time r is recorded at the end of work element.
Calculate.:
Normal time of the activity
Standard time for the activity, if the allowance is 20%.

What is the appropriate sample size for estimating the time for element 2 within ±l0% of the true mean 95% confidence; the standard deviation for the time for element 2 is 0.0742. 30

Draw a 'explanatory sketch of oxy-acetylene gas cutting torch. Briefly explain how cutting is effected. 20

In an NC drilling operation, the tool tip is at a loca ion 100). The datum is left hand lower corner on top surface of the workpiece, which is rectangular (300 mm x 300 mm x 15 mm thick). A thru' hole of 10 mm diameter is to be drilled in the centre of the workpiece. Using only rapid positioning and linear interpolation functions, write the program blocks, in absolute mode.
Assume permitted cutting speed 32 m/min and feed rate 150 mm/min. 10

8.
Six operators are to be assigned to six machines. Their efficiency on the machines is given in the matrix below
src='./qimages/1090-8a.jpg'>

Assign the operator to the machines to maximize to overall efficiency.
State the steps clearly.
Is there any alternative optimal solution? Justify your answer. 30

What is the principle of electro-chemical machining (ECM
What are the advantages and disadvantages of ECM over conventional drilling
Comment on the surface finish and the accuracy of the ECM. 20

A seasonal fashion item is to be ordered. The acquisition cost is Rs 300 and the selling price is Rs 450. If the salvage value after the season is Rs 150, what should be the order quantity? The probability of demand occurring is known as under

Demand items 100 110 120 130 140 150
Probability 0·1 0·2 0·2 0·3 0·1 0·1 10