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Ex/PG/ME/T/128K/165/2012

MASTEROF MECHANICAL ENGINEERING EXAMINATION , 2012

( 2nd Semester )

ADVANCED MANUFACTURING SCIENCE

Time : Three hours Full Marks : 100

Answer any fivequestions.

1. a) Discuss about Trescas maximum shear stress criterion and

Von Mises maximum distortion energy criterion. Hence

derive the relationship between tensile and shear yield

stresses in each case.

b) A cold rolled steel cup with an inside diameter 60mm and

thickness 3mm is to be drawn from a blank of radius 40

mm. The shear yield stress and maximum allowable stress

of the material can be taken as 210N/mm2 and 600 N/mm2

respectively.

i) Determine the drawing force, assuming that the

coefficient of friction = 0.1 and the factor for

calculating the blank holder force = 0.05.

ii) Determine the minimum possible radius of the cup

which can be drawn from the given blank without

causing a fracture. 10+10

2. a) Derive an expression for forging force per unit length of a

strip. State the assumptions made for this purpose. Give

necessary sketches.

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b) Two gating designs for a mould of 50cm 5 25cm 5 15cmare shown below. The cross-sectional area of the gate is

5cm2. Determine the filling time for both the designs.

c) Why the section of a sprue reduces downwards ? Explain.

5+10+5=20

8. a) What is centre-line feeding resistance ?

b) Write a short note on inspection of castings.

c) Describe the method of centrifugal casting.

d) What is directional solidification ? Explain it with the help

of a diagram. 4+6+6+4=20

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b) A strip of lead with initial dimensions 24 5 24 5 150 mm isforged to final size of 6 5 96 5 150 mm. Two flat dies areused. The coefficient of friction between the job and the

dies is 0.8. Determine the maximum forging force if theaverage yield stress of lead in tension is 7 N/mm2 . 12+8

3. a) Two thick slabs are to be joined and the welding process

selected for this is electro slag welding process. Justify the

selection and discuss the process with suitable sketches.

b) Two different pairs of sheets of the same material have to be

spot welded. In one pair, there are 25 bridges per cm2 and

the average radius of each bridge is 0.1 mm. The other pair

of sheets contains 50 bridges per cm2

with the same averageradius of each bridge. Determine the ratio of the voltages to

be applied in these two cases in order to generate the same

rate of heating per unit area. 10+10

4. a) Explain the different chemical heat sources as used in

welding. Write the necessary equations in each case.

b) Explain and show the potential across the arc space in arc

welding process.

c) Discuss the different forces acting on a droplet during are

welding process. 4+4+12

5. a) Why are most die-castings not made out of high strength

material ?

b) With a neat sketch describe a cold chamber die casting

process.

c) Why is aluminium preferred to be done by cold-chamber

die-casting process than hot-chamber die casting process ?

d) Large parts cannot be manufactured by the centrifuging

process. Explain. 3+8+4+5=20

6. a) Calculate the size of a cylindrical riser (height and diameter

equal) necessary to feed a steel slab casting of dimensions

25 5 25 5 6 cm with a side riser, casting poured horizontallyinto the mould.

b) Why it is necessary to use unpressurized gating system for

nonferrous metals ?

c) Differentiate between the following casting defects with

reference to the causes and method of prevention.

i) Cold shut and Misrun

ii) Blow hole and pinhole porosity. 10+4+6=20

7. a) While casting an L-section, a shrinkage cavity is formed, as

shown in fig-a. Explain physically why the formation of a

shrinkage cavity should be avoided in situations of the type

in Fig. b and c.

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