electrochemical machining principles and process parameters

This ppt has electrochemical machining prinicples, process parameters, advantage, limitaitons

1. Electro Chemical Machining 1

2. Electro chemical machining 2

3. ECM physical setup 3

4. Elements of ECM Cathode(Tool)- Electrically conductive Anode(Work Piece)-Electrically conductive Source of DC Power Supply(A high current-low voltage ) Electrolyte a conductive liquid 4

5. Mechanism Of ECM 5 2H 2 O + 2e - H 2 +2 OH - Fe-2e2Fe 2+ Fe 2+ + 2(OH) -  Fe (OH) 2 Fe+2H 2 OFe(OH) 2 + H 2 4 Fe(OH) 2 +2H 2 O + O 2 4Fe(OH) 3

6. 2H 2 O + 2e - H 2 +2 OH - Fe-2e2Fe 2+ Fe 2+ + 2(OH) -  Fe (OH) 2 Fe+2H 2 OFe(OH) 2 + H 2 4 Fe(OH) 2 +2H 2 O + O 2 4Fe(OH) 3 6

7. Electro chemical Machining: it is reverse of electrochemical plating 7

8. ECM The difference in ECM is that the electrolyte bath flows rapidly between the two poles to carry off the depleted material The electrode tool, usually made of copper, brass or stainless steel , is designed to posses approximately the inverse of the desired final shape of the part Gap distance: usually from 0.003 - 0.030 in (0.0147-0.147mm) A water solution of sodium chloride is commonly used as the electrolyte 8

9. electrolytes Electrolyte serves : In completing the electric circuit between the tool and the workpiece . Allowing desirable machining reactions to occur Carrying off the material that has been removed from the work piece Removing hydrogen bubbles created in the chemical reactions of the process Carrying away the heat generated during the chemical reactions Removed material in the form of microscopic particles must be separated from the electrolyte through centrifuge, sedimentation or other means for reuse 9

10. Electrolytes Composed of inorganic salts that produce insoluble by-products – Sludging electrolytes( NaCl , KCl , NaNo 3 , Nacl 2 ) Those composed of acids and alkalis that result in by-products that do go into the solution-Non sludging electrolytes Selection of Electrolyte is based on Workpiece material Tool material The application 10

11. Sodium chloride Most commonly used due to its Low cost Good conductor Stable over broad pH range Corrosive, produces large amount of sludge Cannot be used on WC or Mo 11

12. Sodium nitrate Is popular Used for machining Al or Cu Causes passivity in work piece (Oxide layer built up reduces electrolytic speed) Surface finishes are not as good as Nacl 12

13. Non sludging electrolytes H 2 SO 4 or NaOH : Do not produce large amount of sludge For Mo: ------- N on sludging electrolytes produces the best results Electrical conductivity of an electrolyte changes as a function of temperature Nacl increases its conductivity by 100% when temperature increased from 24 o to 71 C Voltage is kept relatively low to minimize arcing across the gap 13

14. Material Removal Rate (ECM) a) If the workpiece is not an alloy (pure metal): Use Faraday’s First Law : MRR=IM/ nF ρ Where: I = Current in Amperes M = Atomic mass of the metal (g/mol) n = Number of electrons involved per metal ion (valency) F = Faraday's constant (≈ 96,500 C/mol) ρ = Density of the material (g/cm³) Units of MRR : typically in cm³/s or mm³/min

15. b) If the workpiece is an alloy : In alloys, multiple elements with different atomic weights and valencies are present, so average values are used. Where: w i ​ = Weight fraction of the ithi ^{ th } ith element in the alloy M i ​ = Atomic weight of ithi ^{ th } ith element n i ​ = Valency of i th element ρ = Density of the alloy This weighted formula gives a composite MRR based on all constituent metals. Material Removal Rate (ECM)

16. In an Electrochemical Machining process, a pure copper workpiece is machined with a current of 1000 A . The atomic weight of copper is 63.5 g/mol , its valency is 2 , and its density is 8.96 g/cm³ . Calculate the material removal rate (MRR) in cm³/s. Use Faraday’s constant: 96,500 C/mol .

17. A pure iron component is machined using ECM with a current of 800 A . Given: Atomic weight of iron = 55.85 g/mol Valency = 2 , Density = 7.87 g/cm³ Faraday’s constant = 96,500 C/mol Find the MRR in cm³/s.

18. An aluminum workpiece is being electrochemically machined using a current of 500 A . Atomic weight of Al = 26.98 g/mol Valency = 3 Density = 2.70 g/cm³ Calculate the material removal rate using Faraday’s law.

19. A brass alloy (70% Cu and 30% Zn by weight) is machined using ECM at 1000 A current. Atomic weights: Cu = 63.5 , Zn = 65.4 Valency: Cu = 2 , Zn = 2 Density of brass = 8.4 g/cm³ Calculate the MRR in cm³/s.

20. Q5. Stainless steel composed of Fe (70%), Cr (18%), and Ni (12%) is machined using ECM with a current of 1200 A . Atomic weights: Fe = 55.85 , Cr = 52 , Ni = 58.7 Valency: Fe = 2 , Cr = 3 , Ni = 2 Density = 7.8 g/cm³ Calculate the material removal rate in cm³/s.

21. A bronze alloy (88% copper, 12% tin) is machined in ECM using a current of 900 A . Atomic weights: Cu = 63.5 , Sn = 118.7 Valency: Cu = 2 , Sn = 4 Density of bronze = 8.8 g/cm³ Calculate the MRR in cm³/s.

22. Advantages of ECM Ability to machine complex 3D curved surfaces like gas and steam turbine blades Capable of machining metals and alloys irrespective of their strength and hardness Machine surface is stress free and high surface finish(0.5 micron) eg ., hardened and tempered die blocks In case of hard materials, MRR is as high as compared to conventional machining method There is a little or no wear of the tool in the process, it is advantageous because a large number of components can be machined without the tool have to be replaced. Burr free machining No thermal damage to the workpiece 28

23. Disadvantages/Limitations of ECm Non conductive materials cannot be machined In ability to machine sharp interior edges and corners (less than o.2mm radius) due to high current densities at these points Blind holes cannot be machined in solid block in one stage , simple and straight forward shapes can be rapidly produced by conventional machining rather than ECM The length of the components produced by the shaped electrodes is restricted to about half a meter . However improved tooling can overcome the limitation Corrosion and rust of the ECM machine can be a hazard Space and floor area requirements are also higher compared to conventional machining methods. Additional maintenance of machine tool requirements such as power supply, voltage, electrolyte handling and tool feed servo system 29

24. Applications of ECM The different fields of application of the ECM process are Forming Die sinking, particularly deep narrow slots and holes Cavity sinking Profiling and any odd shape contouring Drilling(Multiple hole drilling) Milling, Broaching. Slitting, Grinding Internal Forming, honing, Turning (facing and turning of complex 3D surfaces) Machining Internal Helical Splines Finishing Cavities after EDM etc 30

25. Electro Chemical Machining Methods 31

26. Typical parts made by Electrochemical Machining 32

27. The tool may be connected to a cnc machine to produce more complex shapes with a single tool 33

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29. Electrochemical Deburring 35

30. Electrochemical deburring 36

31. Electrochemical honing: Tool construcution eg ., carburizedpinion gear made of 8620 steel and hardened to HRc60-62 was honed by ECH 37

32. The electrochemical grinding process 50-300 amps Current density- up to 620 amp/cm 2 2A/cm 2 in grinding WC 3A/cm 2 in grinding Steels 5 to 15 V DC 15 to 32 C 0.13 to 1.4MPa Gap is 0.25mm 1200 to 1800 surfaces /min Depth of cut : Max 19mm Cu, brass,Ni - tool mat. 38

33. advantages Advantages: Little surface damage to the work part No burrs as in conventional machining Low tool wear Relatively high metal removal rates for hard and difficult to machine metals Disadvantages Significant cost of electrical power to drive the operation Problems of disposing of the electrolyte sludge 39

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35. Process Parameters of ECM The metal removal in ECM process is primarily controlled by current density ECM Machines are available that deliver currents from 50-40,000amp Current density of 8-233amp/cm 2 at the workpiece Tool penetration rate is directly proportional to the current density ECM metal removal rate is 1.6 cm 3 per minute for every 100 amp. of current Size of the gap between tool and workpiece 0.025mm-0.76mm Most often used gap is 0.25mm 41

36. Process Parameters of ECM The flow velocity of electrolyte  important parameter affecting the surface finish and removal rate Electrolyte flow  15-60 m / sec If electrolyte velocity is low, the heat and by-products of the reaction(hydrogen gas bubbles and sludge) build in the gap causing non-uniform material removal A high velocity will cause cavitation, and produces uneven material removal Electrolyte flow is 0.95 litre/min in case of NaCl 42

37. Process Parameters of ECM Electrolyte pressure and temperature plays an important role in controlling the process Electrolyte pressure is dependent on the flow rate and varies between 69KPa and 2.7MPa ( depending on the application) Temperature of electrolyte  24- 65 o C ( affects electrical conductivity and process repeatability) Feed rate  0.5 – 0.9 mm/min ( overcut depends on feed rate; low feed ratea large overcut and high feed rate  reduces the amount of overcut) Current density increases feed rate increasesOvercut is reduced  surface finish improves 43

38. Process capabilities MRR in ECM process for various pure metals are as shown below Mrudula Prashanth, Amrita School of Engineering, Bengaluru 44 Material Density(g/cc) Removal rate g/1000amp. hr Cc/min Aluminium 2.7 299 1.9 Beryllium 1.8 150 1.3 Cobalt 8.9 978 1.9 Copper 8.9 2129 3.9 Iron 7.8 937 2.1 Lead 11.3 3479 5.0 Molybdenum 10.1 1069 1.8 Nickel 8.9 978 1.9 Titanium 4.5 534 1.9 Tungsten 19.3 1997 1.8

39. Process capabilities Under ideal conditions ECM is capable of producing tolerances of approximately ±0.012mm, in daily production it is closer to ±0.05mm Typical overcut at the side of the tools is ~0.12mm Depending upon the tool design being used, taper can be held to 0.025mm/mm Surface finish is dependent upon the Workpiece material Type of tool used The electrolyte flow and The current density 45

40. Process capabilities Surface finish at the tip of the tool will be 0.1-1.5 μ The side of the tools may produce surface finishes as rough as 5 μ because of low current density Using hollow tubing as the ECM tool, holes as small as 0.76mm in diameter can be drilled L/D ratios up to 20:1 can be accomplished 46

41. Economics and products 47

42. Applications Aerospace Industry for mass production of turbine blades Turbine blade made of nickel alloy , 360 HB Thin slots on 4340 steel roller Bearing cage Airfoils on compressor disc Jet engine parts and Nozzles Facing and turning complex 3D surface Die sinking, particularly deep narrow slots and holes Profiling and any odd shape contouring Multiple hole drilling Trepanning Broaching Deburring Grinding Honing etc., 48