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CHEMICAL AND ELECTROCHEMICAL ENERGY BASED PROCESSES
- 1. RAMCO INSTITUTE OFTECHNOLOGY Mr.M.LAKSHMANAN Assistant Professor (Senior Grade) Department of Mechanical Engineering
- 2. UNIT IV CHEMICAL AND ELECTROCHEMICALENERGY BASED PROCESSES
- 3. CHEMICAL MACHINING (CHM) Principle: Themetal is removed from the workpiece through controlled etching of the workpiece material in contact with a chemical solution.
- 4. Procedure 1. The workpieceto be machined is first cleaned in Trichlorethylene vapour or in a solution of mild alkaline at 85 to 90 ˚C, followed by washing in a clean water. This removes dust and oil from the workpiece. 2. After cleaning, workpiece is dried and coated with the maskant material. 3. The workpiece is then immersed in a chemical reagent. So chemical reaction takes place and the metal is removed from the workpiece.
- 5. 4. The timeof immersion of the workpiece depends upon the amount of material removed by chemical action. 5. Caustic soda is used as etching reagent for aluminium, Solution of Hydrochloric and Nitric Acids for steel and iron chloride for Stainless steels. 6. Uniform depth of metal removal based on Temperature control and stirring of chemical reagent. 7. After Machining, workpiece should be washed thoroughly to prevent reaction with any chemical etching reagent residues.
- 7. ETCHANTS The chemical Reagent(Etchant) is used to remove the metal from the workpiece. The metal is removed by the chemical conversion of the metal into metallic salt.
- 8. Maskant / Resistant Ifselective machining is desired the areas of the workpiece which are not to be machined are covered with a resistant material called a Resistant / Maskant.
- 9. Methods of Masking •Scribed and Peeled Maskants • Photoresists Maskants
- 10. Scribed and PeeledMaskants • Maskant (Paint) is applied to the entire surface of the workpiece by dip, spray or brush. • After the maskant hardens, its removed unwanted surfaces by scribing with knife and peeling away the desired surfaces. Templates can be used to assist in scribing. • This method is not suitable for critical dimensional tolerances.
- 11. Photoresists Maskants • Itsan excellent method of masking, its used for complex work in thin surfaces with closed dimensional tolerances. 1. Cleaned metal is dried and photoresist material is applied to the workpiece by dipping, spraying, Brushing or roller coating. 2. Coating is then dried and hardened by heating in an oven upto 125˚ C.
- 12. 3. Master photographicnegative is placed over the dried photoresist coated surface of the workpiece and exposed to ultraviolet light, which hardens the exposed areas. 4. After exposure, the workpiece is then developed by immersing it into a tank which contains an organic solvent bath solution. The unexposed portions are dissolved out during the developing process, While the exposed portions remains on the workpiece.
- 13. 5. Finally thetreated workpiece is dipped into the etching solution. After 5 to 15 minutes the unwanted metal is removed from the workpiece and the finished part is washed thoroughly to eliminate all chemical residues.
- 14. • Photo ChemicalMachining - Photo Chemical Etching - Kemac • https://www.youtube.com/watch?v=xTFqHst Q42s • Photo Chemical Machining Process - Northwest Etch • https://www.youtube.com/watch?v=NDp3OPI 6dgo • PCMI - A look into Photo Chemical Machining • https://www.youtube.com/watch?v=zJmPgA_ aj-k
- 15. • Chemical EtchingProcess Video https://www.youtube.com/watch?v=2HR7qtbXM_4 Chemical Machining https://www.youtube.com/watch?v=yG_ZeAEiZ_g • Photo Chemical Machining Process - Northwest Etch https://www.youtube.com/watch?v=NDp3OPI6dgo &list=PLAXPptxu31u4De78l2eXlat22ibtIbjlA
- 16. ELECTRO-CHEMICAL MACHINING (ECM) This processis based on the principle of Faraday’s laws of electrolysis which may be stated as follows: • The first law states that the amount of any material dissolved or deposited, is proportional to the quantity of electricity passed. • The second law proposes that the amount of charge produced in the material is proportional to its electrochemical equivalent of the material.
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- 19. 1. Workpiece 2. Tank 3.Tool (Cathode) 4. Servomotor for controlled tool feed 5. D.C. power supply 6. Electrolyte 7. Pump 8. Motor for pump 9. Filter 10.Reservior
- 21. • Tool Materialsare stainless steel, Titanium, Brass and Copper. • Electrolytes are Sodium Nitrate, Sodium Chloride in water, Sodium Hydroxide, Sodium Sulphate, Sodium Flouride, Pottasium Nitrate and Pottasium Chloride. • Tool and work piece are controlled by servo motor. The gap between work piece is 0.05 to 0.5mm. • Electrolyte velocity 30 to 60m/s.
- 22. • D.C. Voltageabout 5 to 30 Volts is applied between the tool and workpiece. • Current Density 20 to 300A/cm2. • The electrochemical reaction takes place due to this flow of ions and it causes the removal of metal from the workpiece in the form of sludge.
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- 25. Reaction at cathode(Tool) Reaction at Anode (Workpiece)
- 26. W = EIt F W– Mass of ions dissolved in Kg E – Equivalent weight of a substance dissolved or deposited I – Current flowing through the electrolyte cell in Ampheres t – Time in sec F – Faraday’s constant = 26.8 Amp.hr (96,500Columbs)
- 27. MRR = W Apt A– Machined area in m2 P – Density of the workpiece in Kg/m3 MRR = EI/ FAp
- 28. • The feedrate of electrode f = V/Psh X E /F P V = machined voltage in volts Ps = Specific resistance of electrolyte in ohm.m h = Tool work gap in m
- 29. Factors affecting CurrentFlow • Gas evolution (H2) at the cathode surface may reduce the current flow. • Polarized ionic layers may build up at electrode, causing large voltage drops near the surfaces. • When electrolyte is heated more, it results in boiling. It automatically reduces the electrolytic action.
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- 32. Tool Design • Determinethe tool shape, so that the desired shape of the job is obtained under existing machining conditions. • Design the tool by considering the electrolyte flow, insulation strength.
- 33. ELECTROLYTE • It carriesthe current between tool and workpiece. • It cools the cutting zone which becomes hot due to the flow of high current. • It removes products of machining from the cutting zone. • Sodium and potassium salts are commonly used electrolyte.
- 35. Characteristics of Electrolyte •Good conductor of electricity • Non corrosive property • Non – Toxicity and chemical stability. • Low viscosity and high specific heat.
- 36. Factors affecting SurfaceFinishing • Machining Voltage • Tool Feed Rate • Temperature of electrolyte • Concentration of electrolyte Surface finish 0.2 to 0.8 micron with a tolerance of 0.005mm.
- 37. Advantages of ECMProcess • MRR by this process is high compared to conventional machining. • Wear and tear of tool is negligible. • Machining is done at low voltage. • Intricate and complex shapes can be machined easily through this process. • The machined work surface is free of stresses. • No cutting forces are involved in this process.
- 38. • High surfacefinish (0.2 to 0.8microns) • Very thin sections, such as sheet metal can be easily machined without any damage. • Its an accurate process and close tolerances of the order 0.005mm can be easily obtained. • No burrs are produced and this process can be easily automated.
- 39. Disadvantages • Non conductingmaterials can not be machined. • Consumption of power is nearly 100 times more than in turning or milling the steel. • Machining process is comparatively slow. • Initial investment is high. • More space is required. • To vary the tool feed rate and supply of electrolyte, constant monitoring is needed. • Difficulty in designing a proper tooling system.
- 40. • Sharp internalcorners cannot be obtained. • Post machining cleaning is needed to reduce the corrosion of the workpieces.
- 41. Applications of ECM •Machining complicated profiles such as jet engine blades, turbine blades, turbine wheels etc., • Drilling small deep holes (Nozzles) • Machining of cavities and holes of irregular shapes. • Machining of forging dies. • Machining of hard materials and heat resistant materials.
- 42. Characteristics of ECM •Material Removal Technique: Based on Faraday’s laws of Electrolysis and reverse electroplating. • Work material: Conducting materials • Tool Material: Copper, Brass or steel • Voltage: 5 – 30V • Current : 50 – 40,000A • MRR : 27mm3/s
- 43. • Electrolyte: 20%Nacl solution in water, Mixture of brine and H2SO4 • Surface finish : 0.2 to 0.8Micrometre • Tolerance : 0.005mm
- 46. • ElectroChemical Machining(ECM) • https://www.youtube.com/watch?v=pI1QGpmKq ow • Electro-Chemical Machining(Explain) • https://www.youtube.com/watch?v=WufD41ww 96E • How Electrochemical Machining Works • https://www.youtube.com/watch?v=Ej- GWNPYFVM • Electro chemical machining EMAG ECM/PECM - EMAG Videos • https://www.youtube.com/watch?v=VzmVrJAIhe w
- 47. • Electrochemical machineECF-A1 • https://www.youtube.com/watch?v=iwbhZab- iNg • https://www.youtube.com/watch?v=4ybj- mS3jRM
- 48. S.No. EDM ECM 1Workpiece is submerged in dielectric fluid Workpiece need not be submerged in electrolyte. 2 Tool wear takes place There is no tool wear 3 Control system is required to maintain constant gap between tool and workpiece. Control system is not required. 4 Machining can not be done at low voltages Machining can be done at low voltages 5 MRR is slow MRR is high 6 Energy consumed is less Huge amount of energy is consumed.
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- 52. ELECTRO CHEMICAL GRINDING (ECG)OR ELECTROLYTIC GRINDING This work is machined by the combined action of electrochemical effect and conventional grinding operation. But major portion of the metal (90%) is removed by electrochemical effect.
- 53. • Sodium nitrate,sodium chloride and potassium nitrate with a concentration of 0.150 to 0.300 kg/litre of water are usually used as electrolyte with temperature of 15˚C to 30˚C. • A constant gap of 0.025mm is maintained between the grinding wheel and workpiece. • Grinding wheel is made of fine diamond particles. • Grinding wheel runs at a speed of 900 to 1800m/min. • The workpiece is connected to positive terminal (Anode) of battery and grinding wheel is connected negative terminal (cathode). (Voltage -3 to 30V)
- 55. Process Parameters • CurrentDensity • Electrolyte • Feed Rate • Grinding Wheel speed
- 56. Advantages of ECG •Tool wear is negligible. • Work is free of surface cracks and distortion because heat is not generated in the process. • Good surface finish is obtained. (0.2 to 0.4micrometre) • Burr free stress free components are produced.
- 57. Disadvantages • MRR islower than conventional machining. • Non conducting materials can not be machined. • Power consumption is high. • Initial cost is High. • Maintenance cost is high. • Preventive measures are needed against corrosion by electrolyte.
- 58. Applications • Very precisiongrinding of hard metals Tungsten Carbide tool tips, High speed steel tools. • Cutting thin section of hard materials without any damage or distortion.
- 60. • VG1000 CNCElectrochemical Vertical Grinde • https://www.youtube.com/watch?v=9fR1cZ2d 0mQ • UG824 Ultragrind CNC Electrochemical Surface Grinder • https://www.youtube.com/watch?v=fHSUWz NI96I
- 61. ELECTROCHEMICAL HONONG (ECH) •Electrochemical honing is similar to electrochemical grinding. The work is machined by the combined action of electrochemical effect and conventional grinding operation. • Uses rotating and reciprocating, non conducting bonded honing stones instead of a conducting grinding wheel. • Most of the metal is removed by electrochemical effect.
- 62. • Workpiece isconnected to positive terminal (Anode) and Tool is connected to negative terminal (Cathode). • Gap between tool and workpiece is usually maintained between 0.075 to 0.125mm at the start of the cycle. It increases by the amount of stock removal per cycle upto 0.50mm. • Electrolyte is passed between tool and workpiece through several rows of small holes in the tool body.
- 63. • Electrolyte issupplied about 122 lit/min under the pressure of upto 1.05 N/mm2 depending upon the workpiece size. • Bonded abrasive honing stones are inserted in slots in the tool and these stones are fed out with equal pressure in all direction, So that cutting faces are in constant contact with the cylinder surface. • Its suitable for internal cylindrical grinding with a size tolerance of 0.012mm on the diameter.
- 65. ADVANTAGES • MRR isfaster with reduced tool wear, its about 10 times faster than conventional honing and 4times faster than internal grinding. • Burr free stress free components are produced. • Less pressure is required between honing stones and workpiece. • Noise and distortion are reduced when honing thin walled tubes.
- 66. • Cylinder BoreHoning - Engine Building Video - Hone Piston Wall • https://www.youtube.com/watch?v=HQfh6AZ xL08 • Electrochemical Honing of helical Gears • https://www.youtube.com/watch?v=qaECkm w4vqY