1. What Is Meant by Conventional Machining Processes?

UNCONVENTIONAL MACHINING PROCESS

UNIT – 1 INTRODUCTION

1. What is meant by conventional machining processes? In conventional machining processes, metal is removed by using some sort of the tool which is harder than the work piece and is subjected to wear. In this process, tool and work piece in direct contact with each other.

2. What is meant by unconventional machining processes? The unconventional machining processes do not employ a conventional or traditional tool for metal removal, instead , they directly utilize some form of energy for metal machining. In this process, there is no direct physical contact between the tool and the work piece.

3. What is thermal energy methods of unconventional machining? In these methods, heat energy is concentrated on a small area of the workpiece to melt and vaporize the tiny bits of work material. The required shape is obtained by the continued repetition of this process. Ex : LBM, PAM,EBM, IBM

4. List the unconventional machining process which uses mechanical energy(AU,CMB,NOV 2010). a. Ultrasonic machining. b. Abrasive jet machining. c. Water jet machining.

5. List the unconventional machining process which uses electro-chemical energy. a. Electro chemical machining b. Electro chemical grinding. c. Electro chemical honing. d. Electro chemical deburring.

6. What is electro chemical energy methods of unconventional machining ?

1 In these methods, material is removed by ion displacement of the workpiece material in contact with a chemical solution.

7. What is chemical energy methods of unconventional machining ? The chemical energy methods involve controlled etching of the workpiece material in contact with a chemical solution.

8. What is mechanical energy methods of unconventional machining ? In mechanical energy methods, the material is removed by mechanical erosion of the work piece material.

9. What are the characteristics of unconventional machining processes? i) The unconventional machining processes do not employ a conventional or traditional tool for metal removal, instead, they directly utilize some form of energy for metal machinery. ii) The tool material need not be harder than the work piece material. iii) The machined surface do not have any residual stresses.

10. Name the unconventional machining processes for machining following materials. (AU,CMB,NOV 2010). a) Non metal like ceramics ,plastics and glass b) Refractories c) Titanium d) Super alloys and e) Steels. Ans: a) Non metal like ceramics, plastics and glass – USM, AJM, EBM, LBM b) Refractories- USM, AJM, EDM, EBM c) Titanium - EDM d) Super alloys – AJM, ECM, EDM , PAM e) Steels- ECM, CHM,EDM, PAM

11. Name the unconventional machining processes which produce surface finish. 1. Abrasive jet machining. 2. Electro chemical grinding. 3. Electro chemical deburring. 4. Ultrasonic machining.

2 12. What is ultrasonic machining? USM is a mechanical material removal process in which the material is removed by repetitive impact of abrasive particles carried in liquid medium on to the work surface, by a shaped tool, Vibrating at ultrasonic frequency.

13. What are the advantages of USM ? (AU,CMB,NOV 2010). Advantages 1. High accuracy and good surface finish 2. No heat generation during machining 3. Capability of drilling circular and non-circular holes in very hard materials. 4. No thermal effects on mechanical work piece. 5. Non-conductive materials can be machined.

14. What are the Disadvantages of USM? 1. Tool wear 2. Frequent turning is required 3. Low material removal rate. 4. Not economical for soft materials. 5. Not suitable for heavy stock removal.

15. What are the applications of USM? i. Almost all the material can be machined except some soft materials. ii. Diamond, Tungsten, Tungsten carbide, and synthetic ruby can be successfully machined. iii. USM can be used for drilling, grinding, profiling, coining, threading and even for welding. iv. For preparing wire drawing dies and tool room items. v. Used in jewellery for shaping jewels vi. Drilling of screw threads and curved holes in brittle materials.

16. What are the components of USM? 1. Ultrasonic transducer 2. Concentrator 3. Tool 4. Abrasive slurry 5. Abrasive feed mechanism 6. Tool feed mechanism

17. What is ultrasonic transducer?

3 The device used for converting any type of energy into ultrasonic wavers or vibration is called ultrasonic transducer. 18. Write short noted on piezoelectric crystals? Piezoelectric crystals are used foe inducing ultrasonic vibrations since they posses the capability of changing their dimensions to the given electrical energy or in other sense they have the capability converting electrical energy into mechanical vibrations.

19. What is magnetostrictive effect? It is the one in which the material changes its dimension is in response to a magnetic field.

20. What are the magnetostrivtive materials employed in USM? Nickel, Iron – cobalt called as permendum , iron – aluminum called as alter.

21. What is the purpose of concentrator used in USM? The main purpose of the concentrator is to increase the amplitude of the vibration obtained from the transducer.

22. What is abrasive Slurry? The abrasive slurry is nothing but a mixture of abrasive grains and the carrier fluid, generally water.

23. What are the different types of concentrators? (1) Conical Type (2) Exponential type (3) Stepped type.

24. What are the characteristics of carrier fluid? (1) Good wetting characteristic (2) High thermal conductivity (3) Non-toxic and non-corrosive. (4) Should have low viscosity.

25. What are the elements of Carrier Fluid? (1) Act as a coolant. (2) Act as an acoustic bond between the work piece and the tool. (3) Helps efficient transfer of energy. (4) Act as medium to carry the abrasive machined materials and worm abrasives

4 26. What are the types of feed mechanisms used in USM? (1) Spring type (2) Counter – weight type (3) Motor type (4) Pneumatic and hydraulic type

27. What is the effect of abrasive grain size on machining rate in USM? (AU, CHN,APR 2008) Material removal rate and surface finish are greatly influenced by grit or grain size of the abrasive. For roughing work operations, grit size of 200 – 400 are used and for finishing operation, grit size of 800 – 1000 are used.

28. State tool wear ratio. Wear ratio is defined as the ratio of volume of material removed from the work to volume of material eroded from tool. Volume of material removed from work Wear ratio = ------Volume of material eroded from tool

29. What is feed mechanism? Feed system is used to apply the static load between the tool and workpiece during ultrasonic machining operation. 30. What is piezoelectric effect? When mechanical force is applied to one pair of opposite faces of certain crystals like quartz, tourmaline, etc, equal and opposite electrical charges appear across its other faces.

31. State the working principle of USM process. In ultrasonic machining process, a slurry of small abrasive particles are forced against the workpiece by means of a vibrating tool and it causes the removal of metal from the workpiece in the form of extremely small chips.

32. What are the types of work materials for USM? Hard and brittle metals like tungsten carbide, boron carbide, tool steel, germanium etc., are used as work material in USM process. Non-metal like glass and ceramics are also used as work material.

33. What are the abrasives used in USM process?

5 The most commonly used abrasives are boron carbide, silicon carbide, aluminium oxide and diamond. Boron is the most expansive material and is best suited to cutting of tungsten carbide, tool steels, etc. Aluminium oxide is the softest abrasive and it is used for machining glass and ceramics.

34. What are the types of tool materials for USM? Generally, tough and ductile tool material is used in USM process. Low carbon steels and stainless steels are commonly used as tool materials.

35. What are the recent development in USM process? (AU,CHN,APR 2008), In ultrasonic machining process, abrasive slurry is used to remove the metal from the work piece but recently a new development has taken place that is instead of using slurry, the tool is impregnated with diamond dust. The tool is oscillated and rotated with ultrasonic frequencies. In some cases it is impossible to rotate the tool, in such situations the work piece can be rotated.

36. What are the industrial needs for unconventional machining processes? (Anna univ,Chennai,May/June’09) (AU,CMB,NOV 2010). (AU,CHN,APR 2008), Materials which are used in conventional edged tool machining is highly uneconomical and the degree of accuracy and surface finish attainable are poor. The unconventional machining processes have been developed to overcome these difficulties.

37. Name the important factors that should be considered during the selection of an unconventional machining process for given job.(AU CHN AP/MAY 2011) 1. Physical parameters 2. Shapes to be machined 3. Process capability or Machining characteristics 4. Economic consideration

38. Classify the modern machining process on the basis of the type of energy employed. (AU CHN AP/MAY 2011) 1. Thermal energy method 2. Electrical energy method 3. Electro chemical energy method 4. chemical energy method

6 5. Mechanical energy method

UNIT II – MECHANICAL PROCESS

1. Define AJM? It is the material removal process where the material is removed or machined by the impact erosion of the high velocity stream of air or gas and abrasive mixtrue, which is focused on to the work piece.

2. How does AJM differ from conventional sand blasting process? AJM differ from the conventional sand blasting process in the way that the abrasive is much finer and effective control over the process parameters and cutting. Used mainly to cut hard and brittle materials, which are thin and sensitive to heat.

3. What are the advantages of AJM process? 1. Low capital cost 2. Less vibration. 3. Good for difficult to reach area. 4. No heat is genera6ted in work piece. 5. Ability to cut intricate holes of any hardness and brittleness in the material. 6. Ability to cut fragile, brittle hard and heat sensitive material without damage.

4. What are the applications of AJM? (1) For abrading and frosting glass, it is more economical than acid etching and grinding. (2) For doing hard suffuses, safe removal of smears and ceramics oxides on metals. (3) Resistive coating etc from ports to delicate to withstand normal scrapping (4) Delicate cleaning such as removal of smudges from antique documents. (5) Machining semiconductors such as germanium etc.

5. Write the Disadvantages of AJM process? (1) Low metal removal rate. (2) Due to stay cutting accuracy is affected.

7 (3) Parivles is imbedding in work piece. (4) Abrasive powder cannot be reused.

6. Give the formula for find the material remove rate for brittle metal? MRR = 1.04 ( MV3/2 / 1/4H3/4 )

7. Give a summary of the abrasive of their application for different operation? ABRASSIVE APPLICATION (1) Aluminium Cleaning, Cutting and Deburrig (2) Silicon Carbide. Faster cleaning, Cutting. (3) Glass Heads Matt polishing, cleaning (4) Crushed glass Peening and cleaning.

8. Write the formula for find the MRR for ductile materials? MRR = 0.5 ( MV2 / H)

9. What are the Process parameters affecting the MRR in AJM? 1. Gas Pressure. 2. Velocity of Particles. 3. Abrasive mass flow rate. 4. Mixing ratio. 5. Nozzle Tip Distance.

10. What are the disadvantages of using abrasives again and again? 1. Cutting ability of the abrasives decreases after the large 2. Contamination of wears materials clogging the nozzle and the cutting unit orifices.

11. What are the different types of nozzles heads used in AJM? 1. Right angle head. 2. Straight head.

12. Why oxygen should not be used in AJM? Oxygen should not be used because of fire hazard problem.

13. What are the different types abrasives used in AJM? (AU,CMB,NOV 2010).

8 Aluminium oxides, silicon carbides, Crushed glass, Sodium bicarbonate, Dolomite.

14. Reuse of abrasives is not recommended in AJM. why? Reuse of abrasives is not recommented since the cutting ability of abrasive decrease after the usage and also the contamination of wear materials clogging the nozzle and the cutting unit orifice.

15. Name the carrier gases used in AJM process. Nitrogen, carbon dioxide, helium or compressed air are used as carrier gases in AJM process.

16. What are the desirable properties of carrier gas in AJM? (AU,CMB,NOV 2010). a. It should be cheap. b. It should not be non-toxic. c. It should be easily available. d. It should dry quickly.

17. What are the factors that affect the material removal rate in AJM process? The following factors will affect the material removal rate in AJM process. a. Mass flow rate b. Abrasive grain size. c. Gas pressure. d. Velocity of abrasive particles. e. Mixing ratio and f. Nozzle tip clearance.

18. Differentiate AJM and sand blasting process. AJM is basically meant for metal removal with the use of small abrasive particles, whereas the sand blasting process is a surface cleaning process which does not involve any metal cutting.

19. What is water jet machining ? In WJM, high pressure and high velocity stream of water is used to cut the relatively softer and non – metallic materials like paper board, wood, plastic, rubber, fibre glass, leather etc.

9 20. List the unique benefits offered by WJM process. (AU,CMB,NOV 2010). a. In WJM process, water is used as energy transfer medium. It is cheap, non –toxic and easy to dispose. b. Low operating cost. c. The work area remains clean and dust free. d. Low maintenance cost. 21. What are the properties of water jet machining about effect cutting action? High pressure, high velocity jet of water.

22. What are the types of units and its purpose used in water jet cutting system? (AU,CHN,APR 2008), a. Pump -- to generate high pressure b. Machining unit-- to actually cut the material with the jet nozzle. c. Filtration unit -- to clear the water after use.

23. Why we are using the diamond nozzle? a. High hardness metal b. Working life is more compared to other jewel nozzle such as ruby or sapphire.

24. Why do you select proper cutting fluid in WJM? Cutting fluids mainly depends on the operation requirement, quality of finish, cutting speed and overall cost.

25. Does there is any environmental effects while using the water jet machining. There is no environmental pollution such as dust suspended in the air because the water jet drains any dust simultaneously when cutting.

26. What are the advantages of WJM over conventional cutting methods? a. Because of point cutting WJM is able to cut materials almost any pattern. b. Material loss due to machining is minimum. c. WJC will not burn surfaces or produces a heat an affected zone.

10 d. No environmental pollution.

27. What are the applications of WJM? (Anna univ,Chennai,May/June’09) * Aero space * Automobile * Paper pulp industries

28. What are the commonly used additives in WJM? 1. Crly cerine 2. Polyethylene oxide 3. Long chain polymers

29. What is optical tracing system? It employs an optical scanner that traces a line drawing and produces electronic signals that control the X-rays.

30. What are the process parameters involved in USM methods? a. Metal removal rate. b. Tool material. c. Tool wear rate. d. Abrasive materials and abrasive slurry. e. Surface finish. f. Work material.

31. What are the characteristics of WJM? Some of the characteristics of WJM are a. Work material. e. Power b. Tool f. Feed rate c. Additives g. Nozzle material d. Pressure of water h. Stand off distance

32. What is mixing ratio in AJM process? Mixing ratio is defined as the ratio of mass flow rate of abrasive to the mass flow rate of gas. Mass flow rate of abrasive Mixing ratio = ------Mass flow rate of gas

11 33. What are the characteristics of AJM process? Some of the characteristics of AJM are a. Work material e. Pressure b. Abrasive f. Life of nozzle c. Size of abrasive g. Tolerance d. Velocity h. Nozzles material

34. What are the process parameters needed to utilize the WJM process successfully? i) Material removal rate ii) Geometry and surface finish of work material. iii) Wear rate of the nozzle.

35. What are the factors needed for Nozzle wear rate in WJM? a. Hardness of the nozzle material b. Pressure of the jet. c. Velocity of the jet d. Nozzle design.

36. Write down the energy transfer media, energy source and mechanism of metal removal for the following process. (Anna univ,Chennai,May/June’09) i) Water jet machining In WJM process, abrasive particles are added at high pressure and high stream of water is used to cut the relatively softer and non-metallic materials.

37. What are the variables that affect the cutting phenomena in abrasive jet machining? (Anna univ,Chennai,May/June’09) Mass flow rate, abrasive grain size, gas pressure, velocity of abrasive particles, mixing ratio, nozzle tip clearance.

38. What are the major elements of ultrasonic machining equipment? (Anna univ,Chennai,May/June’09)

12 Ultrasonic transducer, concentrators, tool, abrasive slurry, abrasive feed mechanism, tool feed mechanism

39. Why abrasive Jet machining process is not recommended to machine ductile materials? (AU CHN AP/MAY 2011) Abrasive Jet machining process is not suitable to machine ductile materials because there is always danger of abrasive particles getting embedded in the workpiece.

40. Explain why there exits an optimum stand off distance(SOD) for maximum stock removal rate in the case of Water Jet Macnining (WJM) process. (AU CHN AP/MAY 2011) Stand off Distance (SOD) is the distance between the nozzle tip and workpiece. If the stand Off distance is greater, the depth of penetration is reduced. If the stand off distance is smaller, workpiece is damaged by spatter. 41.List the process parameters of water jet machining process. 1.Water jet machinig process 2.Geometry and surface finish of work material 3. Wear rate of the material

UNIT III – ELECTRO-CHEMICAL PROCESS

1. Define ECM? It is the controlled removal of metals by the anodic dissolution in an electrolytic medium, where the work piece (anode) and the tool (cathode) are connected to the electrolytic circuit, which is kept, immersed in the electrolytic medium.

2. Write the Faraday’s first law of electrolysis? The amount of any material dissolved or deposited is proportional to the quantity of electrolyte passed.

3. Write the Faraday’s second law of electrolysis?

13 The amount of different substances dissolved or deposited by the same quantity of electricity are proportional to their chemical equivalent weight.

4. Write Ohm’s law? Current, I = V/R V = Voltage, R = resistance.

5. What are the factors that influence oxidation in ECM? (i) Nature of work piece. (ii) Type of electrolyte. (iii) Current density. (iv) Temperature of the electrolyte.

6. What are the materials used to make the tool electrode? (AU,CMB,NOV 2010). Copper and copper alloys, titanium, aluminum, brass, bronze, carbon, Monel and reinforced plastic.

7. What are the main functions of electrolysis in the ECM? i) For completing the electric circuit between the tool and the work piece and to allow the reaction to proceed efficiently. ii) To remove the products of machining from the cutting region. iii) To carry away the heat generated during the chemical reaction. iv) To avoid ion concentration at the work piece- tool gap.

8. What are the properties are expected from the electrolysis used in the ECM? i) High thermal conductivity. ii) Low viscosity and high specific heat. iii) Should chemically stable even at high temperature. iv) Should be non-toxic and non-corrosive.

9. What are the electrolysis commonly used in ECM? 15 -20 % Nacl in water, sodium nitrate, potassium nitrate, sodium sulphate, sodium chromate and potassium chloride.

10. What are the results which is in improper selection of electrolyte in ECM? (i) Low machining rate. (ii) Over cut and stray cutting.

14 11. What are the methods generally used to filter the electrolyte? (i) Running the system until it is contaminated completely and replace it. (ii) Centrifugal separation. (iii) Sedimentation. (iv) Use of clarifiers.

12. What are the characteristics of a good ECM tool? (i) It should be a good conductor of electricity and heat. (ii) Easily machinable. (iii) Resistant to chemical reaction. (iv) It offers resistance to the high electrolyte pressure.

13. What are the problems that occur while improperly selecting the electrolyte flow? Cavitations, stagnation and vortex formation.

14. What are the parameters that affect the MRR? (i) Feed rate. (ii) Voltage. (iii) Concentration of the electrolyte. (iv) Temperature of the electrolyte. (v) Current density (vi) Velocity of the electrolyte.

15. How the current density affect the MRR? Current density is controlled not only by the amount of current but also by the size of the gap between the tool and the work piece. A small gap results in high current density, which in turn produce more material removal.

16. What are the advantages of ECM? (i) ECM is simple, fast and versatile method. (ii) Surface finish can be extremely good. (iii) Fairly good tolerance can be obtained.

17. What are the limitations of ECM? (i) Large power consumption and the related problems. (ii) Sharp internal corners cannot be answered. (iii) Maintenances of higher tolerances require complicated contours.

15 18. What are the applications of ECM? ECM is used for sinking, profiling and contouring, multi hole drilling, trepanning, broaching, honing, steel mill applications, surfacing, sawing, contour machining of hand to hand machine materials.

19. Define ECG. (AU,CMB,NOV 2010). ECG is the material removal process in which the material is removed by the combination of Electro- Chemical decomposition as in ECM process and abrasive due to grinding.

20. Which material is used to make the grinding wheel? Metal bonded diamond (or) Aluminum oxide.

21. What are the important functions of abrasive particles used in ECG? It acts as insulator to maintain a small gap between the wheel and work piece. They are electrolysis products from the working area. To cut chips if the wheel should contact the work piece particularly in the event of power failure.

22. What are the advantages of ECG? i) No thermal damage to work piece. ii) Wheel wear is negligible. iii) No distortion of the work piece.

23. What are the disadvantages of ECG? High capital costs, because of the special wheel tool. Power consumption is quite high. Electrolyte is corrosive.

24. What are the limitations of ECG? 1. The work material must be conductive. 2. Nit suitable for machining soft material. 3. Require dressing tools for preparing the wheels.

16 25. What is the application of ECG? 1. Precision grinding of hand metals economically. 2. Grinding Carbide cutting tools inserts. 3. To grind end mill cutters more precisely.

26. What is ECH? Electrochemical honing is similar to ECG i.e the work is machined by the combined action of electrochemical effect and conventional grinding operation. ECH, however, uses rotating and reciprocating, non – conducting bonded honing stones instead of a conducting grinding wheel. 27. What are the advantages of ECH? i) Metal removal rate is faster with reduced tool wear, it is about 10 times faster than conventional honing and about 4 times faster than internal grinding. ii) Burr free and stress free components are produced. iii) It is used for machining burred edges. iv) Noise and distortion are reduced when honing thin walled tubes.

28. What are the requirements of tool manufacture in ECM process? a. It should be conductor of electricity. b. It should be chemically inert to the electrolyte. c. It should be easily machinable.

29. What are the factors to be considered while designing the tool? a. Determine the tool shape, so that the desired shape of the job is obtained under existing machining operations. b. Design the tool by considering the electrolyte flow, insulation strength and fixing arrangements.

30. What are essential characteristics of an electrolyte used in ECM process? a. It should be good conductor of electricity. b. I should have non –corrosive property. c. It should have low viscosity and high specific heat. d. It should be non –toxicity and chemical stability.

17 31. Name the electrolyte for iron base alloys and Ni base alloys. (AU,CMB,NOV 2010). Iron base alloys - 20 % of NaCl solution in water. Ni base alloys - Mixture of brine and sulphuric acie.

32. Name the electrolyte for Ti base alloys and Co-Cr base alloys.

Ti base alloys -10 % HF + 10 % HCl + 10 % HNO3 Co-Cr base alloys -NaCl

33. What are the materials used for tools in ECM? Most commonly used materials are Copper, brass, titanium, copper-tungsten and stainless steel when the electrolyte is made of sodium or potassium.

34. Name the electrolyte for WC based alloys. For WC based alloys strong alkaline solution is used as electrolyte.

35. What are the characteristics of ECM? (AU,CHN,APR 2008) Some of the characteristics of ECM are a. Work material. e. current b. Tool material f. voltage c. Metal removal rate g. electrolyte d. Surface finish h.Specific power consumption

36. What are the various process parameters which the effectiveness of electrochemical grinding process depend upon? (Anna univ,Chennai,May/June’09) Current density, electrolyte, feed rate and grinding wheel speed are the various process parameters which the effectiveness of electrochemical grinding process

37. What is the function of servo mechanism in EDM process? (AU CHN AP/MAY 2011) Its used to maintain very small gap known as ‘ sprak gap’ ranges of 0.005 to 0.05 mm between the workpiece and the tool.

18 38. What are the feasible dielectric flushing techniques applicable in EDM process? (AU CHN AP/MAY 2011) 1. Pressure flushing 2. suction flushing 3.side flushing

39.What are the desirable properties of the dielectric fluids.(AU APR/MAY 2010) 1. Stable dielectric strength to serve as insulation between toll and electrode 2. Low viscosity and good wetting capacity 3. chemically neutralized 4. High flash point 5. Cannot emit any toxic vapours

UNIT IV - THERMAL METAL REMOVAL PROCESSES - I

1. Define electrical discharge machining? EDM is the controlled erosion of electrically conductive materials by the initiation of rapid and repetitive spark discharge between the electrode tool to the cathode and work to anode separated by a small gap kept in the path of dielectric medium. This process also called spark erosion.

2. What are functions of dielectric fluid used in EDM? (AU,CMB,NOV 2010). 1. It acts as an insulating medium 2. It cools the spark region and helps in keeping the tool and work piece cool. 3. It maintains a constant resistance across the gap. 4. It carries away the eroded metal particles.

3. List the basic requirement of dielectric fluid used in EDM. 1. Stable Dielectric strength. 2. It should have optimum viscosity. 3. It should have high flash point. 4. It should be chemically stable at high temperature and neutral. 5. It should not emit toxic vapours.

19 4. What the dielectric fluids commonly used in EDM? 1. Petrolium based hydrocarbon fluids. 2. Parafin, white sprite, transformer oil. 3. Kerosine, mineral oil. 4. Ethylene glycol and water miscible compounds.

5. What are the prime requirements of tool material in EDM? 1. It should be electrically conductive. 2. It should have good mach inability. 3. It should have low erosion rate. 4. It should have low electrical resistance.

6. Name some of the tool material used in EDM? 1. Copper, brass, alloys of Zinc &tin. 2. Hardend plain carbon steel 3. Copper tungsten, silver tungsten, tungsten 4. Copper graphite and graphite.

7. What is the process parameter efficiency the MRR? 1. Energy discharge 2. Capacitance. 3. Size of work piece. 4. M/c tool design

8. Write the formula for finding the energy discharge in EDM? W=(1/2) X EIT W-discharge energy I-Current, T-time, E-voltage

9. What is the effect of capacitance in EDM? Increasing the capacitance causes the discharge to increase and increase both the peak current and discharge time.

10. How do you increase the inductance of the circuit? A piece of iron or steel be allowed to lodge between the leads it would increase the inductance of the circuit and reduce the M/C rate.

11. Define W/T ratio? It is the ratio of volume of work removed to the volume of tool removed.

20 12. What is cycle time? It is the sum of discharge time and waiting time.

13. Define over cut. (AU,CMB,NOV 2010). It is the discharge by which the machined hole in the work piece exceeds the electrode size and is determined by both the initiating voltage and the discharge energy.

14. Define Rehardening? While metal heated to a temperature above the critical and then rapidly cooled by the flowing dielectric fluid the metal is rehardened.

15. What is recast metal? (AU,CHN,APR 2008), Metal heated to a temperature above the melting point and which is not displaced by the action of the spark discharge, resoldifies as recast metal.

16. Explain electrode wear? A crater is produced in the electrode, which is likewise dependent on the electrode material and the energy of the discharge.

17. What are types of power supply circuits used in EDM? (AU,CMB,NOV 2010). 1. R-Ccircuit. 2. Rotary impulse generator. 3. Controlled pulse (vacuum tube). 4. Oscillator controlled pulse. 5. Transister pulsed circuit.

18. What are the design factors to be considered while selecting the machine tool? 1. Number of parts to be produced. 2. Accuracy. 3. Size of work piece. 4. Size of electrode. 5. Depth of cavity.

19. Why the servo controlled system is needed in EDM? (AU,CHN,APR 2008), EDM requires that a constant arc gap be maintained between the electrode and the work piece to obtain maximum machining efficiency. Therefore EDM tool in corporate some form of servo control.

21 20. Define tool wear ratio? Tool Wear ratio=Work piece material removed/Loss of electrode material.

21. What are the factors affecting metal removal rate? a. Metal removal rate increases with forced circulation of dielectric fluid. b. It increases upto optimum value of work-tool gap, after that it drops suddenly. c. Metal removal rate is maximum when the pressure is below atmosphere.

22. Indicate the range of pulse duration and current in EDM. The current density in the discharge of channel is of the order of 10000 A / Cm2. Spark discharge frequencies range from 200 – 500 kHz pulses per second at voltage level of 30-250V.

23. What are the drawbacks of using relaxation circuit? a. Though the discharge current in a relaxation circuit reaches a high value, it is of very short duration. b. The use of high frequencies is limited, since the time for changing the capacitor is high.

24. List the advantages of wire cut EDM process. i) It gives high surface finish. ii) Complicated shapes can be efficiently machined. iii) Tool manufacturing and storage is avoided. iv) It is economical for small batch production.

25. List the disadvantages of wire cut EDM process. (AU,CMB,NOV 2010). a. Capital cost is high b. Cutting rate is slow. c. It is not suitable for large workpiece. 26. Mention the application of wire cut EDM process. It is best suited for the production of gears, tools,dies,rotors, turbine blades, and cams for small to medium size batch production. 27. Difference between EDM and wire cut EDM process. S.No Wire cut EDM EDM 1 Very thin wire made of brass or molybdenum is Expensive alloy of silver and

22 used as the electrode. tungsten are used as electrode. 2 It is easy to machine complex two dimensional It is difficult to cut complex profiles. two dimensional problems. 3 The whole workpiece is not submerged in The whole workpiece is dielectric medium instead, working zone is submerged in dielectric supplied with a co-axial jet of dielectric medium. medium

28. What are the recent development in EDM process? a. EDM change from using relaxation circuits to faster and more efficient impulse circuits. b. Instead of using copper as electrode, harder tungsten-copper is preferred.

29 What are the characteristics of EDM? Some of the characteristics of EDM are e. Work material. e. Spark frequency f. Tool material f. Spark gap g. Metal removal rate g. Current h. Temperature h. Dielectric fluid

30. What are the units required for wirecut EDM process? a. Work piece movement control unit. b. Work piece mounting table. c. Dielectric fluid supplying unit. d. Power supplying unit.

31. What is EDG process? Electrical discharge grinding is a spark erosion process used for precision machining of electrically conductive workpieces. It is very similar in principle to EDM.

32. What is servodrive system? EDG servodrive system is a special feed back device, it must sense and always maintain a constant gap between the wheel and workpiece while feeding the workpiece into the wheel.

33. List the advantages of EDG.

23 a. Non contact grinding. b. Low cost wheels. c. Simple dressing procedure. d. Grinds any conductive material e. No distortion is produced during grinding.

34. List the limitations of EDG. a. Recast layer is produced. b. Oil fires are possible. c. Wheels are fragile.

35. Mention the applications of EDG. a. Any shape that is groun by conventional grinding can be done by EDG. b. Grinding carbide tools, dies, form tools and thin workpieces. c. Difficult to grind shapes such as grooves and slots can be ground by EDG.

36. What are the ways of gap-flushing used in EDM? (Anna univ,Chennai,May/June’09) The function of the servo mechanism is to maintain a very small gap, known as ‘spark gap’ ranges of 0.005 to 0.05 mm between the workpiece and the tool.

37. What are the categories into which the variety of power supply circuits in EDM process can be classified? (Anna univ,Chennai,May/June’09) a. Resistance –Capacitance circuit. b. R-C-L circuit. c. Rotary pulse generator circuit. d. Controlled pulse generator circuit.

38. why the life of electro chemical grinding(ECG) wheel is much higher than conventional grinding wheel.(AU CHN APR/MAY 2011) The work is machined by the combined action of electro chemical effect and conventional grinding operation. The major portion of the metal is removed by electro chemical effect so the life if electro chemical grinding wheel is much higher than the conventional grinding wheel.

24 39.Difference between chemical machining and electro chemical machining.(AU CHN NOV 2011) Chemical machining:The material is removed from the workpiece through a controlled etching or chemical attack of the workpiece material. Electro chemical machining:Material is removed by ion displacement of the workpiece material in contact with the chemical solution.

40.Give the applications of electro chemical honing process(AU CHN MAY 2010) Salaging out of tolerance parts and reconditioning worm surfaces.

UNIT V - THERMAL METAL REMOVAL PROCESSES -II

1. Define EBM? It is the thermo-electrical material removal process on which the material is removed by the high velocity electron beam emitted from the tungsten filament made to impinge on the work surface, where kinetic energy of the beam is transferred to the work piece material, producing intense heat, which makes the material to melt or vaporize it locally.

2. What is the characteristic of the electron beam? (i) High concentrated energy. (ii) Deep penetration into the metals. (iii) Low distortion. (iv) Any material either conductive or non-conductive can be processed.

3. Write the application of electron beam? 1. Thin film machining. 2. Surface treatment. 3. Engraving metals and non-metals. 4. Cutting of materials.

4. What are the main elements of the EBM equipment? 1. Electron Gun. 2. Beam focusing and deflecting units. 3. Work Table. 4. Vacuum chamber

25 5. What is the function of magnetic lens used in EBM? It converges the beam into a narrow spot into the work piece.

6. What are the two types of EBM? (i) Thermal type. (ii) Non-thermal Type.

7. Explain the thermal type EBM? In this type the electron beam is used to heat the material up to the point where it is selectively vaporized.

8. Explain Non-thermal type EBM? In this type, the EBM produces a chemical reaction.

9. Write the advantage of EBM? (i) High accuracy. (ii) Any type of material can be processed. (iii) No mechanical or thermal distortion. (iv) No physical or metallurgical damage results.

10. Write the disadvantages of EBM? (i) High cost of equipment. (ii) Skilled operator is required for operation. (iii) Limited to 10mm material thickness.

11. Write any four application of EBM? (i) Micro machining application on materials. (ii) Drilling of apertures for electron microscope. (iii) Drilling of holes in ruby and diamond crystal.

12. Write the Richardson-Dushman Equation? J=At2 e- (EW/KT) J = Current Density A =constant (120 Amphere/cm2deg2) K =Boltzman Constant (1.3x10-23 J/K)

26 T = Absolute temperature (Kelvin) W =work function (Volts)

13. Write general formula for focal length of a magnetic lens? f/(S + D) = 25V/(NT)2 V =Electron accelerating voltage NT =Ampere turns in the lens winding S =pole piece separation D =Bore diameter F =focal length

14. Why vacuum is needed in EBM? (AU,CMB,NOV 2010). 1. To reduce corrosion 2. To get correct focusing

15. What is the drawback of electron beam machining? (AU,CHN,APR 2008), One major diameter of electron beam welding has been the requirement of high degree of vacuum essential or satisfactory operation of this process because of degassing.

16. What is Laser? It is acronym of light amplification by stimulated emission of radiation.

17. What is Maser? Laser can be melt diamond when focused by lens system. The energy density being of two order 100,000 KW/cm2. This energy is due to atoms that have light energy level. When such an atom impinge with electromagnetic waves having resonant frequency.

18. What are the characteristics of Laser beam? 1. Material removal 2. Material shaping 3. Welding 4. Thermo kinetic change.

19. What are the gases commonly used in LASER?

The gases commonly used are: He, Ne, Argon, Co2 etc.

20. What are the advantages of Laser drilling?

27 No physical contact between work root pair hence there is no possibility if breakage or wear of root. Precision location is ensured by focusing of the beam Large aspect ratio can be achieved.

21. What are the characteristics of Laser used in Laser machining? 1. Can be focused to maximum intensity or to lower intensity as needed. 2. Can be moved rapidly on the work. 3. Remote cutting over long standoff distances.

22. What are the fundamentals of photons used in Laser? In the Laser the photons are in ground state at 0oC they are brought to the excited state by means of absorption of energy by temperature change, collision etc.

23. What are the emission lines? The atoms when this they are bringing down goes to the excited state by stimulated emission and emit photons within 10 nano secs. They have the same wavelength as the excited photons.

24. What is the Maser principle? The energy density of laser with 100,000Kw/cm2. The atoms at this state will impinge with electrons waves having resonate frequency. This is known as maser.

25. What is population inversion? If the atoms in the excited state are greater than that of the ground state then it is known as population inversion.

26. How does Laser melting works? It melts and vaporizes the unwanted material by means of narrow pulsed laser operating at 2 to 100pilses/sec Because of this high accuracy is not possible to micro sized holes.

27. What is solid state Laser? Solid state Laser is the Lasers, which consist of a hot nat, which may be crystalline solid/ glass, doped with an active material whose atoms provide the lasing action.

28 28. Define plasma Plasma is defined as the gas, which has been heated to a sufficiently high temperature to become ionized.

29. What are the advantages of plasma arc welding? a. Exothermic oxidation takes place. b. DC power supply

30. What are the metals that can't be machined by plasma arc machining? a. Stainless steel b. Monel c. Super alloys

31. What is the basic heating phenomenon that takes place in plasma arc welding? The basic heating phenomenon that takes place at the work piece is a combination of anode heating due to direct electron bombardment recombination of molecules on the work piece.

32. How does the basic plasma is generated? The basic plasma is generated by subjecting a stream of gas to the electron bombardment of the electric arc.

33. How the initial ionization is accomplished in plasma arc machining. A high voltage arc established between electrode and nozzle accomplishes initial ionization.

34. Why does gas formed in plasma do in P.A.M? This gas stabilizes the arc and prevents it from diverging.

35. How another source of heating achieved in P.A.M It is desirable to achieve a third source of heating by injecting oxygen into work area to take advantage of exothermic oxidation.

36. Write the principle of P.A.M (AU,CMB,NOV 2010). Once the material has been raised to molten point the high velocity gas stream blows the material away.

29 37. Write the circuitry details in PAM. + ve terminal connected to work piece and -- ve terminal connected to electrode.

38. Which type of power supply is used in P.A.M DC power supply is used.

39. Which part is constricted by plasma? Nozzle duct is constricted by plasma.

40. State the principles of chemical machining processes. In chemical machining process, material is removed from the workpiece through a controlled etching or chemical attack of the workpiece material.

41. What is the principle of etchants in chemical machining? Etchants are used to remove the metal from the workpiece. The metal is removed by the chemical conversion of the metal into metallic salt.

42. Name the etchants used in chemical machining process. (AU,CMB,NOV 2010). Caustic soda , Hydrochloric acid, Nitric acid, Iron chloride

43. What is the use of maskant in chemical machining? In chemical machining process, the areas of the workpiece which are not to be machined are covered with a resistant, called a resist or maskant.

44. Name some of the maskants used in CHM. Butyl rubber, Neoprene rubber, Polymers and Polythene

45. What is the principle of plasma arc machining? Anna univ,Chennai,May/June’09) In PAM, material is removed by directing at high velocity jet of high temperature ionized gas on the workpiece. This high temperature plasma jet melts the material of the workpiece.

30 46. In electron beam machining, why is a high vacuum created in the apparatus? (Anna univ,Chennai,May/June’09) In EBM process, to avoid the collision of accelerated electrons with air molecules, vacuum is required. So, the entire EBM set up is enclosed in a vacuum chamber, which carries vacuum of the order 10 -5 to 10 -6 mm of mercury.

47. What is the function of water muffler in PAM? (AU,CHN,APR 2008), It is used to cool the electrode and nozzle.

48. Can you machine electrically non-conducting materials using EBM process. All materials can be machined by using EBM process. (AU,CHN,APR 2008),

49. What do you meant by Etch factor? (AU,CHN,APR 2008), The chemical machining proceeds on all exposed surfaces to the etching medium, under cuts are always associated with this processing operation. This undesired cutting known as etch factor restricst not only the size of mask but also on depth of cutting and accuracy is lost when machining to higher depth.

50. Can you machine electrically non-conductive materials by PAM? Justify your answer. (AU CHN AP/MAY 2011) Yes. Indirct Arc plasma torches can be used for machining electrically non- conductive materials.

51. why vacuum is needed in Electron Beam Machining(EBM) processes? (AU CHN AP/MAY ’11) In order to avoid collision of accelerated electrons with air molecules, vacuum is required.

52. What are the advantages of laser beam machining(AU CHN NOV 2010) 1. Machining of material including non metal is possible 2. Micro sized holes can be machined 3. Soft materials like rubber and plastic can be machined 4. There is no direct contact between tool and workpiece 5. No tool wear takes place.