Unit-3 What is meant by conventional machining process?
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UNIT-3
In conventional machining process, metal is removed by using some sort of tool which is harder than the work piece and is subjected to wear. In this process, tool and work piece being in direct contact with each other.
The UCM processes do not employ a conventional 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.
In these methods, heat energy is concentrated on a small area of the work piece to melt and vaporize the tiny bits of work material. The required shape is obtained by the continued repetition of this process.
In these methods, material is removed by ion displacement of the work piece material in contact with a chemical solution.
9. What is mechanical energy methods of UCM? In mechanical energy methods, the material is removed by mechanical erosion of the work piece material. 10. 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. 11. Write the Faraday’s first law of electrolysis? The amount of any material dissolved or deposited is proportional to the quantity of electrolyte passed. 12.Write the Faraday’s second law of electrolysis? The amount of different substances dissolved or deposited by the same quantity of electricity are proportional to their chemical equivalent weight. 13. 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.
Copper and copper alloys, titanium, aluminum, brass, bronze, carbon, Monel and reinforced plastic. 15. 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.
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.
15 -20 % Nacl in water, sodium nitrate, potassium nitrate, sodium sulphate, sodium chromate and potassium chloride. 18.What are the results which is in improper selection of electrolyte in ECM? (i) Low machining rate. (ii) Over cut and stray cutting. 19. 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.
(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.
22. What are the limitations of ECM?
23. 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. 24.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. 25.What are functions of dielectric fluid used in EDM? 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. 26. 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. 27.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.
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.
1.Copper, brass, alloys of Zinc &tin. 2.Hardend plain carbon steel 3.copper tungsten, silver tungsten, tungsten 4.Copper graphite and graphite.
A crater is produced in the electrode, which is likewise dependent on the electrode material and the energy of the discharge. 31.Define wear ratio? Wear ratio=Work piece material removed/Loss of electrode material. 32. List the advantages of WEDM.? 1. It gives high surface finish 2. Complicated shapes can be efficiently machined. 3. Tool manufacturing and storage is avoided. 4. It is economical for small batch production.
1. Capital cost is high. 2. Cutting rate is slow. 3. It is not suitable for large work piece. 34. List the applications of WEDM.? It is best suited for the pro9duction of gears, tools, dies, rotors, turbine blades and cams for small to medium size production. 35. What are the materials cannot be machined in EDM process? Non-conducting materials. 36. What is the shape of electrode in traveling wire EDM process? A very thin wire made of brass or molybdenum having circular cross section is used as electrode in traveling wire EDM process. 37.What is Laser? It is acronym of light amplification by stimulated emission of radiation. 38.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. 39.What are the characteristics of Laser beam? 1.Material removal 2.Material shaping 3.Welding 4.Thermo kinetic change.
The gases commonly used are: He, Ne, Argon, Co2 etc.
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. 42.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. 43.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. 44.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. 45) 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. 46.What is the characteristic of the electron beam?
47) Write the application of electron beam? - Thin film machining. - Surface treatment. - Engraving metals and non-metals. - Cutting of materials.
1.Electron Gun. 2.Beam focusing and deflecting units. 3.Work Table. 4.Vacuum chamber
It converges the beam into a narrow spot into the work piece. 50) What are the two types of EBM? (i) Thermal type. (ii) Non-thermal Type. 51) 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. 52) Explain Non-thermal type EBM? In this type, the EBM produces a chemical reaction. 53) 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. 54) Write the disadvantages of EBM? (i) High cost of equipment. (ii) Skilled operator is required for operation. (iii) Limited to 10mm material thickness. 55) 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. 56. Why vacuum is needed in EBM? 1) To reduce corrosion 2) To get correct focusing 57. What is the drawback of electron beam machining? 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. Yüklə 28,12 Kb. Dostları ilə paylaş:
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