Department of Mechanical EngineeringIIT Kharagpur

NONTRADITIONAL MANUFACTURING PROCESSES: MF30604End Semester Exam Time: 3 hours Maximum Marks 100

USE SEPARATE ANSWER SCRIPTS FOR PART-A AND PART-B

Attempt all Questions of Part-A and Part-B

Part-A

1. Answer the following in brief (5x5=25)

I. Considering the energy balance derive an expression for the drilling speed in laser drillingprocess. What is the material removal mechanism in laser drilling? Among various lasersavailable for material processing which one will you prefer for drilling precision holes?

11. What is the main difference between the conventional forming and high energy rate forming(HERF)? Describe a HERF method for crimping a thin walled copper tube onto a corrugatedend-fitting.

111. Schematically show the construction of an abrasive water jet machine and briefly mention therole of its various components. How does the material removal rate vary with the abrasivemixing ratio?

1v. What is the role of magnetic field in magnetron sputtering process and what are itsadvantages? What are the factors that influence the quality of deposited film?

v. Why is gallium commonly used in focused ion beam machine and how are the gallium ionsproduced? What is the mechanism of material removal in this process and what are the factorsthat decide the material removal rate?

2(a) Derive an expression for the material removal rate of a ductile material in abrasive jetmachining. (8)

2(b) A 200 mm diameter glass substrate has a 10 um thick aluminum coating on its surface. Thestrength of aluminum coating is 300 MPa. Coating is to be removed by abrasive jet of gritdiameter 50 urn and grit density of 4000 kg/nr', What should be the velocity of the AJ so thatthe 10 urn thickness of coating gets removed in a single impact of abrasive grit? What shouldbe the AJ mass flow rate to clean up the entire coating in 10 seconds of machining time?

(2+4= 6)

3. A 200 urn diameter hole is to be drilled in a 3 mm thick tungsten sheet with an electron beamat 20 kW power. The e-beam can be operated in pulsed mode having pulse duration in 1OJ..lS-Ims range. For drilling a good quality hole what should be the e-beam pulse duration?How many pulses will be needed to drill a through hole if the material is removed throughvaporization and the electron beam power coupling efficiency during the drilling process is~30%.?The thermo-physical properties of tungsten are as the following:Density = 19300 kglm3, Specific heat =140J/kgOC, Melting Temperature =3410OC, Boilingtemperature = 5930°C, Latent heat of fusion = 185kJ/kg. Latent heat of vaporization = 4020kJ/kg, Thermal conductivity = 164 WlmK

(2+5= 7)

4. If the sputtering yield S in focused ion beam machining varies proportional to Sin2e, where e isthe angle of incidence, then at what angle of incidence the sputtering rate will be maximum?

(4)

Part - B (to be answered on separate answer script]

5 (a) The average surface roughness (Ra) achieved in ECM is in the range of 0.1 11m- 2.5 urn. Amore common finish in ECM is R, = 111m. Despite ECM being an atomic level dissolution,why can not a better finish be obtained?

S (b) An aircraft wing made of aluminium aJloy is to be machined by chemical milling for increase ofstrength to weight ratio. What type of mask would you use to carry out the task and why?

S (c) In a photochemical blanking operation a rectangular slit 300 micron width was attempted to bemade on a copper-beryllium sheet of 200 micron thickness by selectively exposing only the topsurface with a mask. It resulted in a tapered slit for which the dimension at the top was more thedimension in the bottom.Suggest some change in the approach while continuing with the same process so that avertical slit could be obtained. (Use suitable diagram for explanation)

S (d) Why is the life of electrochemical grinding wheel much higher as compared to that of aconventional grinding wheel?

See) Why does micro-ECM require a power supply capable of producing pulses of ultra-shortduration?

(3xS=15 marks)

6(a) Making use of the Faraday's laws of electrolysis derive an expression to find out thevolumetric material removal rate (cm3/min) in electrochemical machining (ECM) for analloy having n number of constituent elements where each element may have different weightpercentage, valency, atomic weight and density. Given density ofthe alloy in p g/cnr'.

6(b) An iron workpiece is machined in an ECM die-sinking machine using a copper tool andaqueous NaCI solution as electrolyte. The copper electrode has a uniform interaction area of 100ern". A constant working gap of 0.05 em is maintained. The ECM machine has a supplyvoltage of25V. Specific resistance of the electrolyte is 5.0 ohm-em. For iron, atomicweight=56, valency=2, density=7.8 g/crrr', Faraday's constant= 96500 Coulomb. A currentefficiency of 100% may be assumed.Calculate the (i) Material removal rate and (ii) Electrode feed rate.

6( c) What are the possible applications of electrochemical honing?

7 (a)

7 (b)7 (c)

8(a)

8 (b)

8 (c)

8 (d)

[6+(2+2)+2=12 marks]

Explain the conditions under which a electrical discharge can occur in an electrolyte inelectrochemical discharge machining.Explain Laser assisted chemical etching process.For what type of materials ultrasonic assisted electrochemical machining suitable and why?

(4+3+3=10 marks)

Prove that buckling strength to weight ratio of an Euler colwnn increases if its lineardimensions are scaled down.

In contrast to a bulk ultrasonic machining what are the critical process parameters that need tobe controlled so that we may work in the domain of micro-ultrasonic machining?What are the possible sources of stray capacitance in micro-EDM? How can these straycapacitances be minimized?Current efficiency for a pulsed micro-electrochemical dissolution process in an iron sheet is50% at a current density of200 Alcm2• Calculate the average dissolution depth per pulse.Given: density of iron = 7.8 g/crrr', valency = 2, atomic weight = 56, frequency of the pulse depower supply = 50 MHz.

[3+3+(3+1)+3=13 marks]

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