Dr.RAVINDER KUMAR B.E.( Hons.), M.E., Ph.D. 1 Dr.Ravinder Kumar

Transcription

1 ElectroChemical Machining & Grinding Dr.RAVINDER KUMAR B.E.( Hons.), M.E., Ph.D. 1 Dr.Ravinder Kumar

2 Overview Electro-Chemical Machining Advantages and Disadvantages (ECM) Electro-Chemical Grinding (ECG) Advantages and Disadvantages 2 Dr.Ravinder Kumar

3 Introduction ECM is opposite of electrochemical or galvanic coating or deposition process. ECM can be thought of a controlled anodic dissolution at atomic level of the work piece that is electrically conductive by a shaped tool due to flow of high current at relatively low potential difference through an electrolyte which is quite often water based neutral salt solution. 3 Dr.Ravinder Kumar

4 Electrochemical Machining Faraday s law s of electrolysis: Principle Involved: 1 st Law: The amount of a substance deposited on an electrode is directly proportional to the amount of charge passed through the electrolyte. W α Q 2 nd Law: The amounts of different substances deposited by the same quantity of electricity are proportional to their equivalent weights. 4 Dr.Ravinder Kumar Wα E

5 Electrochemical Machining (ECM) Involves electrolysis Work piece made anode, tool (inverse of desired shape) is the cathode. Current passed between the two electrodes. Surface metal ionizes, removed by solution Dr.Ravinder Kumar 5

6 Equipment The electrochemical machining system has the following modules: Power supply Electrolyte filtration and delivery system Tool feed system Working tank 6 Dr.Ravinder Kumar

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8 Effect of tool shape W T W T O O O O R O R O K L K L Initial stage of ECM Steady state of ECM 8 Dr.Ravinder Kumar Schematic principle of Electro Chemical Machining(ECM)

9 Mechanism Material is depleted from anode work piece and transported to a cathode tool in an electrolyte bath Electrolyte flows rapidly between the two poles to carry off depleted material, so it does not plate onto tool Electrode materials: Cu, brass, or stainless steel Tool has inverse shape of part Tool size and shape must allow for the gap No surface damage, no burr, low tool wear, high removal rate for hard-to machine materials 9 Dr.Ravinder Kumar

10 The electrode is fed at a constant velocity, and the electrolyte is fed through the tool. The tool is designed to eliminate deposition of the ionized metal on the electrode with use of electrolyte. 10 Dr.Ravinder Kumar

11 Process Physics ECM technique removes material by atomic level dissolution of the same by electrochemical action. Thus the material removal rate or machining is not dependent on the mechanical or physical properties of the work material. It only depends on the atomic weight and valence of the work material and the condition that it should be electrically conductive. Thus ECM can machine any electrically conductive work material irrespective of their hardness, strength or even thermal properties. 11 Dr.Ravinder Kumar

12 When Fe is made the anode and Cu is turned into a cathode dipped in brine solution (electrolyte). At Anode:- Fe Fe e At cathode:- 2H + + e - H 2 Finally, Fe OH - Fe(OH) 2 M.R.R Involved:- 12 Dr.Ravinder Kumar

13 Actual rates may vary from theory as other factors come into effect. The ECM process will erode material in a radial direction, so care must be made in tooling design. 13 Dr.Ravinder Kumar

14 Factors affecting Surface finish Selective dissolution Sporadic breakdown of the anodic film Flow separation and formation of eddies Evolution of hydrogen 14 Dr.Ravinder Kumar

15 Points to be noted Supply V = 8 to 20V, I = >1000A. Electrode gap is typically 0.1 to 0.2 mm. MRR is about 1600mm3/min. per 1000A, OR 3KWhr for mm3 (not very efficient, 30 times more than standard machining techniques). MRR is independent of material hardness. Good for low machinability, or complicated shapes Very little tool wear, Forces are large with this method because of fluid pumping forces. 15 Dr.Ravinder Kumar

16 Summary of ECM characteristics Mechanics of material removal - electrolysis medium - conducting electrolyte Tool material - Cu, brass, steel Material/tool wear - infinite Gap 50 to 300 µm. Maximum MRR 15*103 mm3/min Specific power consumption 7W/mm3/min Critical parameters - voltage, current, feed rate, electrolyte, electrolyte conductivity Materials application - all conducting metals and alloys Shape application - blind complex cavities, curved surfaces, through cutting, large through cavities. Limitations - high specific energy consumption (about 150 times that required for conventional processes), not applicable with electrically non-conducting materials and jobs with very small dimensions, expensive machines. Surface finishes down to 25 µm 16 Dr.Ravinder Kumar

17 Summary of ECM characteristics Power Supply Type direct current Voltage 2 to 35 V Current 50 to 40,000 A Current density 0.1 A/mm 2 to 5 A/mm 2 Electrolyte Material NaCl and NaNO 3 Temperature 20 o C 50 o C Flow rate 20 lpm per 100 A current Pressure 0.5 to 20 bar Dilution 100 g/l to 500 g/l Working gap 0.1 mm to 2 mm Overcut 0.2 mm to 3 mm Feed rate 0.5 mm/min to 15 mm/min Electrode material Copper, brass, bronze Surface roughness, R a 0.2 to 1.5 µm 17 Dr.Ravinder Kumar

18 Advantages Current and metal removal rate can be controlled Can create elaborate shapes and contours Tool lasts indefinitely once created No burrs created No residual stress introduced. The components are not subject to either thermal or mechanical stress. There is no tool wear during Electrochemical machining. Non-rigid and open work pieces can be machined easily as there is no contact between the tool and work piece. Complex geometrical shapes can be machined repeatedly and accurately Electrochemical machining is a time saving process when compared with conventional machining During drilling, deep holes can be made or several holes at once. ECM deburring can debur difficult to access areas of parts. Fragile parts which cannot take more loads and also brittle material which tend to develop cracks during machining can be machined easily through Electrochemical machining Surface finishes of 25 µ in. can be achieved during Electrochemical machining 18 Dr.Ravinder Kumar

19 Disadvantages Expensive equipment and tools Electrolytic solution is hazardous to environment as well as equipment high specific energy consumption (about 150 times that required for conventional processes), not applicable with electrically non-conducting materials and jobs with very small dimensions, expensive machines. surface finishes down to 25 µm 19 Dr.Ravinder Kumar

20 Electrochemical Grinding 20 Dr.Ravinder Kumar

21 Electrochemical Grinding Combines electrochemical machining with conventional grinding. The equipment used is similar to conventional grinder except that the wheel is a rotating cathode with abrasive particles. The wheel is metal bonded with diamond or Al oxide abrasives are used. Abrasives serve as insulator between wheel and work piece. A flow of electrolyte (sodium nitrate) is provided for electrochemical machining. Suitable in grinding very hard materials where wheel wear can be very high in traditional grinding. Electrochemical grinding combines electrical and chemical energy for metal removal with an EDM finish. It is a non-abrasive process and, therefore, produces precise cuts that are free of heat, stress, burrs and mechanical distortions. It is a variation on electrochemical machining that uses a conductive, rotating abrasive wheel. The chemical solution is forced between the wheel and the work piece. The shape of the wheel determines the final shape. 21 Dr.Ravinder Kumar

22 Electrochemical Grinding 22 Dr.Ravinder Kumar

23 Electrochemical Grinding Process Electrochemical Grinding Equipment (ECG) is an ideal machining process that provides a better, faster, and more cost effective metal cutting and grinding solution for today's toughest materials. Electrochemical Grinding offers the ability to machine difficult materials independent of their hardness or strength. Electrochemical Grinding is an entirely different machining process in which electrical energy combines with chemical energy for metal removal. Electrochemical Grinding Equipment does not rely solely on an abrasive process, the results are precise cuts free of heat, stress, burrs and mechanical distortions. 23 Dr.Ravinder Kumar

24 Process Characteristics Utilizes electrically conductive grinding wheels Removes material by electrochemical decomposition and abrasive action Depletes work piece materials and deposits them in electrolyte Wheels wear extremely slowly Work pieces are electrically conductive 24 Dr.Ravinder Kumar

25 THANK YOU. 25 Dr.Ravinder Kumar