Development Development of harder and difficult to machine materials such as hastalloy, nitra alloy, waspalloy, nimonics, carbides, stainless steel, heat resisting steels and many other HSTR alloys Used in aerospace industry, nuclear engineering and other industries owing to their high strength to weight ratio, hardness and heat resisting quality.
CHIPS FORMATION INCONVENTIONAL MACHININGPROCESS CHIP TOO L WORKPIE CE Thus the major characteristics of conventional machining are: • Generally macroscopic chip formation by shear deformation • Material removal takes place due to application of cutting forces – energy domain can be classified as mechanical • Cutting tool is harder than work piece at room temperature as well as under machining conditions TOOL WORKPIECE CHIP
Schematic representation of various metal cutting operations .
The broad classification is given as follows: Thus classification of NTM processes is carried out depending on the nature of energy used for material removal. Mechanical Processes ⎯ Abrasive Jet Machining (AJM) ⎯ Ultrasonic Machining (USM) ⎯ Abrasive Water Jet Machining (AWJM) Electrochemical Processes ⎯ Electrochemical Machining (ECM) ⎯ Electro Chemical Grinding (ECG) ⎯ Electro Jet Drilling (EJD)
• Electro-Thermal Processes ⎯ Electro-discharge machining (EDM) ⎯ Laser Beam Machining (LBM) ⎯ Electron Beam Machining (EBM) • Chemical Processes ⎯ Chemical Milling (CHM) ⎯ Photochemical Milling (PCM) etc.
Electrolyte An electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible. Function of electrolyte- Carrying current between tool and work peice Remove products of machining and other insoluble products from cutting region Dissipate heat produced in the operation.
Characteristics of Electrolyte Good electrical conductivity Non toxicity and chemical stability Non corrosive property Low viscosity and high specific heat Electrolyte used- Sodium chloride
Dielectric Fluid A dielectric is an electrical insulator that can be ionized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Characteristic- Low viscosity High fluidity Controlled level of toxicity Cheap and easily available
Function of Dielectric Fluid Insulation Until required breakdown voltage attained. Should act as conductor after required breakdown voltage attained. Should demonize rapidly after the discharge has been occurred. Clean spark gap by carrying away the molten metal. Should cool the tool work piece and spark region.Dielectric Used:- light hydro carbon oil, kerosene, paraffin, transformer oil, try ethylene glycol.
Difference between EDM & ECM1. Uses dielectric fluid as a 1. Using electrolyte as a conducting medium between conducting medium between tool and work piece. tool and work piece.2. Wear of tool takes place during 2. No wear of tool during process the process. so tool life is high.3. Heat is generated during the 3. No heat is generated during the process. process.4. Low metal removal rate. 4. Metal removal rate is high.5. It works on the principle of 5. It works on principle of spark erosion. Faraday’s law of electrolysis.6. Metal is removed by melting 6. Metal is removed by and vaporization. electrochemical reaction.7. Tools used are oversize for 7. Tool used are of required size of machining inside surfaces and the work piece. undersize for machining outside surfaces.
Dielectric Electrolyte1. It is used as conducting 1. It used as conducting medium in EDM medium in ECM process. process.2. It act as conductor and 2. It always provide insulator both. passage for supply of3. Tool wear takes place electricity. in the dielectric fluid. 3. The electrolyte selected4. It may or may not be is such that there is no corrosive in nature. wear of tool. 4. It should be non corrosive in nature.
EBM LBM excited atoms 1. When1. When high velocity releases photons in the electrons strikes the work form of chain, a LASER piece its kinetic energy beam is generated which converted into heat energy. strikes on w/p & melts it.2. Electron gun is used as a 2. LASER material is used as tool. tool.3. Accuracy is good. 3. Accuracy is comparatively4. Metal removal rate is low. more.5. The complete process 4. Metal removal rate is high. should kept in vacuum. 5. Vacuum is required6. Usually only metals. between flash lamp and ruby rod. 6. Any material but not only suitable for plastic.
Questions1. Which of the following process uses mechanical energy as principle energy sourcea. ECGb. LBMc. Conventional millingd. USMe. WJMf. WEDM
2. Chemical milling is used inwhich of the following applicationa. Drilling holes with high depth.b. Making intricate patterns on thin sheet metalc. Removing material to make shallow pockets in metal.d. Removing metals from aircrafts wing panels.e. Cutting of plastic sheets.
3. Which of the following process would be bestsuited for cutting a hole of 0.003 inch dia?a. AJMb. CHMc. EDMd. LBMe. WEDM
4. Ultra sonic machining can be used forboth metallic and non metallic materials? True False
5. Which of the following process could beused to cut a large piece of 1/2inch thick?a. AJMb. CHMc. EDMd. LBMe. WEDM