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Unit 3
- 1. UNIT -III CHEMICAL ANDELECTRO-CHEMICAL ENERGY BASED PROCESSES
- 2. INTRODUCTION • The metalis removed from the work piece through controlled etching or chemical attack of the work piece material in contact with a chemical solution
- 3. CHEMICAL MACHINING In thismethod , the metal is removed by ion displacement of the work piece material in contact with a chemical solution
- 4. Examples 1. Electro-chemical machining(ECM) 2. Electro-chemical Grinding (ECG) 3. Electro-chemical Honing (ECH) 4. Electro-chemical Deburring (ECD)
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- 6. Processes in ECM Maskantcoating Cleaning Drying Dipping in chemical solution Stirring & Heating – For uptain Uniform Depth washing
- 7. Maskant Coating Selective Machining Theselective portions (un-machining areas) covered by resistant material. called maskants
- 8. CLEANING • Trichloroethylene vapour Or •Solution of mild alkaline at 85 – 90 degree celcius The above solutions are used to remove oil and dust from the work piece
- 9. Drying After cleaning thework piece is dried in air
- 10. Dipping in Chemicalsolution • Caustic soda - for Aluminium • Hydrochloric acid and nitric acid – for steel • Iron chloride – for stainless steel The metal is removed by the chemical conversion of metal into metallic salt Dipping time will varies from amount of material to removed from work piece
- 11. Stirring & Heating Forobtain uniform depth of metal removal , temperature control and stirring of chemical reagent is important
- 12. washing • To preventfurther reaction after require shape obtained, the metal is cleaned properly
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- 15. • Scribed andPeeled Maskants • Photo resists Maskants METHODS OF MASKANTS
- 16. Scribed and PeeledMaskants For ordinary work piece a paint like material sprayed or dipped or brushed over the metal
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- 18. Photo resists Maskants • Forclose tolerance and dimensional accuracy needed places • Paint spray type work is done for preparing master copy • The master drawing is photographed and it reduced to the size of the finished part
- 19. Photo resists Maskants • Thenthe material is placed over the work piece. • And it exposed to UV light to harden • Then its dipped in organic solution for maskanting. • Finally it dipped in chemical solution for machining
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- 22. Principle Faraday,s Law ofElectrolysis FIRST LAW Amount of metal deposited directly proportional to quantity of electricity SECOND LAW Amount of Change in metal is directly proportional to its electrochemical equivalent of the material
- 23. Basic electroplating concept •So work piece Negative terminal (Cathode) • Things to be coated is connected to positive Terminal (Anode)
- 24. ECM – REVERSEOF ELECTROPLATING Our objective is - Metal should be removed from the work piece So work piece positive terminal (Anode) Tool is connected to Negative Terminal (Cathode) When current is passed , the work piece loses metal and the dissolved metal is carried out by circulating an electrolyte between them
- 25. . TOOL - Titanium ,stainless steel, brass and copper ELECTROLYTE -Sodium Nitrate SERVO MOTOR - To Control Tool Feed Rate Tool and Work piece Gap 0.05 – 0.5mm
- 26. Electrochemical Machining (ECM) •Reverse of electroplating • Work material must be a conductor • Material removal by anodic dissolution • Electrical energy + chemical energy Voltage 5-30 volts Tool Velocity 30 – 60 m/s Current 20 -300A/cm2
- 27. During process ------- •Due to applied voltage, the current flows through the electrolyte with positively charged ions and negatively charged ions. • The positive ions move towards the tool (Cathode) while negative ions move towards work piece (Anode) So , Electro-chemical Reaction takes place due to this flow.
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- 29. PRINCIPLE Machining operation bythe combined action of Electro-chemical effect and conventional grinding operation 90 % - Metal removed by chemical Action 10 % -Metal removed by Grinding Action
- 30. Electro-chemical Grinding (ECG) WorkPiece +Ve Terminal Grinding Wheel - Ve Terminal D.C.Voltage 3 – 30 V
- 31. Gap 0.025mm ELECTROLYTE Sodium Nitrate SodiumChloride Potassium Nitrate + Water Grinding Wheel – Fine Diamond Particle Grinding Wheel speed – 900 -1800 m/min
- 32. PROCESS PARAMETERS 1. CurrentDensity 100 – 200 A / cm2 The MRR increases with the Increase of Current Density – which results high Surface Finish
- 33. PROCESS PARAMETERS 2. Electrolyte SodiumNitrate Sodium Chloride Potassium Nitrate The MRR increases with the correct composition of electrolyte with water – which results high Surface Finish Maintained at a Temperature of 15 – 30 Degree Celcius
- 34. PROCESS PARAMETERS 3. FeedRate Slow feed Poor Surface Finish High feed Excess Tool Wear – Poor Surface Finish Optimum feed Good Surface Finish
- 35. ADVANTAGES OF ECG 1.Life of the grinding wheel is high (because 90% material removed by chemical process) 2. No heat is produced in the process so the work surfaces are free from cracks. 3. Less cutting force only required 4. Good surface finish is obtained. 5. Work material not subjected to any structural changes 6. Burr free and stress free components are made. 7. No Frequent dressing of grinding wheel required.
- 36. DIS -ADVANTAGES OFECG 1. High initial cost 2. Power consumption is high 3. MRR is lower than conventional method 4. Non – conducting material cannot be machined. 5. Need safety things for acid usage in process. 6. Maintenance cost is high
- 37. Applications of ECG Itsbest suited for 1. precision grinding on hard materials 2. Cutting of hard material with thin sections without any damage
- 38. ELECTRO-CHEMICAL HONING for Internalgrinding Combined action of electro- Chemical attack and Honing stone effect
- 39. MRR is 10times faster than conventional internal Grinding Less tool Wear Less Pressure is required between Honing tool and work piece Burr Free and Stress free Components are produced Tolerance 0.012mm
- 40. Work Piece +Ve Terminal (Anode) Tool -Ve Terminal (Cathode) Gap = 0.075 to 0.125 mm Electrolyte Supply = 112 lit /min Voltage = 25 V
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