Non Traditional Machining10ME665 NON-TRADITIONAL MACHINING Subject Code: 10ME665 IA Marks: 25 Hours/Week: 04 Exam Hours: 03 Total Hours: 52 Exam Marks: 100 PART – A UNIT - 1 Introduction:History, Classification, comparison between conventional and Nonconventional machining process selection. 05 Hours UNIT - 2 Ultrasonic Machining (USM):Introduction, equipment, tool materials & tool size, abrasive slurry, cutting tool system design:- Effect of parameter: Effect of amplitude and frequency and vibration, Effect of abrasive grain diameter, effect of applied static load, effect of slurry, tool & work material, USM process characteristics: Material removal rate, tool wear, Accuracy, surface finish, applications, advantages & Disadvantages of USM. 08 Hours UNIT - 3 Abrasive Jet Machining (AJM):Introduction, Equipment, Variables in AJM: Carrier Gas, Type of abrasive, size of abrasive grain, velocity of the abrasive jet, mean number. abrasive particles per unit volume of the carrier gas, work material, standoff distance (SOD), nozzle design, shape of cut. Process characteristics-Material removal rate, Nozzle wear, Accuracy & surface finish. Applications, advantages & Disadvantages of AJM. Water Jet Machining: Principal, Equipment, Operation, Application, Advantages and limitations of water Jet machinery 07 Hours UNIT - 4 Electrochemical Machining (ECM):Introduction, study of ECM machine, elements of ECM process : Cathode tool, Anode work piece, source of DC power, Electrolyte, chemistry of the process, ECM Process characteristics – Material removal rate, Accuracy, surface finish, ECM Tooling: ECM tooling technique & example, Tool & insulation materials, Tool size Electrolyte flow arrangement, Handling of slug, Economics of ECM, Applications such as Electrochemical turning, Electrochemical Grinding, Electrochemical Honing, deburring, Advantages, Limitations. 06 Hours PART – B UNIT - 5 Chemical Machining (CHM): Introduction, elements of process, chemical blanking process : Preparation of work piece, preparation of masters, masking with photo resists, etching for blanking, accuracy of chemical blanking, applications of chemical blanking, chemical milling (contour machining): process steps –masking, Etching, process characteristics of CHM: material removal rate, accuracy, surface finish, Hydrogen embrittlement, advantages & application of CHM. 06 Hours DEPARTMENT OF MECHANICAL ENGG, SJBIT Page 1 Non Traditional Machining 10ME665 UNIT - 6 Electrical Discharge Machining (EDM): Introduction, mechanism of metal removal, dielectric fluid, spark generator, EDM tools (electrodes) Electrode feed control, Electrode manufacture, Electrode wear, EDM tool design, choice of machining operation, electrode material selection, under sizing and length of electrode, machining time. Flushing; pressure flushing, suction flushing, side flushing, pulsed flushing synchronized with electrode movement, EDM process characteristics: metal removal rate, accuracy, surface finish, Heat Affected Zone. Machine tool selection, Application, EDM accessories / applications, electrical discharge grinding, Traveling wire EDM. 08 Hours UNIT - 7 Plasma Arc Machining (PAM): Introduction, equipment, non-thermal generation of plasma, selection of gas, Mechanism of metal removal, PAM parameters, process characteristics. Safety precautions, Applications, Advantages and limitations. 05 Hours UNIT - 8 Laser Beam Machining (LBM): Introduction, equipment of LBM mechanism of metal removal, LBM parameters, Process characteristics, Applications, Advantages & limitations. Electron Beam Machining (Ebm): Principles, equipment, operations, applications, advantages and limitation of EBM. 07 Hours TEXT BOOKS: 1. Modern machining process, Pandey and Shan, Tata McGraw Hill 2000 2. New Technology, Bhattacharya 2000 REFERENCE BOOKS: 1. Production Technology, HMT Tata McGraw Hill. 2001 2. Modern Machining Process, Aditya. 2002 3. Non-Conventional Machining, P.K.Mishra, The Institution of Engineers (India) Test book series, Narosa Publishing House – 2005. 4. Metals Handbook: Machining Volume 16, Joseph R. Davis (Editor), American Society of Metals (ASM) DEPARTMENT OF MECHANICAL ENGG, SJBIT Page 2 Non Traditional Machining 10ME665 CONTENT 1. Introduction 04-07 2. Ultrasonic Machining (USM) 08-14 3. Abrasive Jet Machining (AJM) 15-21 4. Electrochemical Machining (ECM) 22-26 5. Chemical Machining (CHM) 27-32 6. Electrical Discharge Machining (EDM) 33-36 7. Plasma Arc Machining (PAM) 37-40 8. Laser Beam Machining (LBM) 41-45 DEPARTMENT OF MECHANICAL ENGG, SJBIT Page 3 Non Traditional Machining 10ME665 UNIT-1 1.1 Introduction Manufacturing processes can be broadly divided into two groups and they are primary manufacturing processes and secondary manufacturing processes. The former ones provide basic shape and size to the material as per designer’s requirement. Casting, forming, powder metallurgy are such processes to name a few. Secondary manufacturing processes provide the final shape and size with tighter control on dimension, surface characteristics etc. Material removal processes are mainly the secondary manufacturing processes. Material removal processes once again can be divided into mainly two groups and they are “Conventional Machining Processes” and “Non-Traditional Manufacturing Processes”. Examples of conventional machining processes are turning, boring, milling, shaping, broaching, slotting, grinding etc. Similarly, Abrasive Jet Machining (AJM), Ultrasonic Machining (USM), Water Jet and Abrasive Water Jet Machining (WJM and AWJM), Electro discharge Machining (EDM) are some of the Non Traditional Machining (NTM) Processes. 1.2 History of Non Traditional processes Although, the non conventional machining processes have created a revolution in the field of machining technology by the development of idea of various processes were initiated as early as in nineteen- twenties in USSR. 1920 The initiation was first made by Gussev towards the end of 1920 in USSR. He suggested a method of machining by combination of Chemical and mechanical means. His work is basis for all Electro Chemical processes known today. 1941 Burgess, American Scientist had demonstrated the possibility of ECM process by drawing a sharp contrast between the mechanical and electrolyte methods in metal removal 1942 The idea of Ultrasonic machining was invented by Balamuth at the He invented at the time of investigation of dispersion of solids in Liquids with the help of a vibrating magne-tostrictive nickel tube However, the origination of the process was made by Rosenberg DEPARTMENT OF MECHANICAL ENGG, SJBIT Page 4 the idea of Ultrasonic machining began to to develop widely in USSR and basis of this development was laid on extensive investigation that took place in the mechanism of ultrasonic machining and in the design of Magneto-strictive transducers. 1. 1950 The basis of laser machining was established by the process which Which were developed by Basov. 1. converters and wave guides. SJBIT Page 5 .3 Classification of NTM processes Classification of NTM processes is carried out depending on the nature of energy used for material removal. Electro-Thermal Processes a) Electro-discharge machining (EDM) b) Laser Jet Machining (LJM) DEPARTMENT OF MECHANICAL ENGG. 1960 The concept of whirling jet machining was innovated. 1950 Electro chemical Grinding has practically been developed in about 1950. Electrochemical Processes a) Electrochemical Machining (ECM) b) Electro Chemical Grinding (ECG) c) Electro Jet Drilling (EJD) 3. Mechanical Processes a) Abrasive Jet Machining (AJM) b) Ultrasonic Machining (USM) c) Water Jet Machining (WJM) d) Abrasive Water Jet Machining (AWJM) 2. They first developed the idea of spark erosion machining. In the early nineteen-sixties. Prokhorov and Fabrikanth in USSR in 1950.Non Traditional Machining 10ME665 1943 DM was developed by B R Lazarenko and N I Lazarenko in USSR. Surface finish and tolerances arelimited by High surface finish(up to 0.se miconductingmaterials Relative motion between the tooland work is Many NTM are capable of producingcomplex 3D typically rotary orreciprocating. In some nontraditional process tool wear exists. SJBIT Page 6 .ceramics.composites. 1 The cutting tool and work piece arealways in physical contact withrelative motion with each other. micro sized. In spite of CNC systems.blind holes or Machining of small cavities. Thus the shape shapes and cavities ofwork is limited to circular or flatshapes.Non Traditional Machining 10ME665 c) Electron Beam Machining (EBM) 4. DEPARTMENT OF MECHANICAL ENGG.1 micron)and machining inaccuracies tolerances (25 Microns)can beachieved High metal removal rate. Machining of small cavities . 2 Material removal rate is limited bymechanical properties of workmaterial.large aspect ratio. shall entry angleholes are easy using NTM Use relative simple and inexpensivemachinery and Nontraditional processes requiresexpensive tools readily availablecutting tools and equipment as wellas skilled labour.production of 3D surfaces is still adifficult task. which increase theproduction cost significantly Capital cost and maintenance cost islow Capital cost and maintenance cost ishigh Traditional processes are wellestablished and Mechanics of Material removal of Someof NTM physics of processis well understood process are still under research Conventional process mostly usesmechanical Most NTM uses energy in direct formFor example energy : laser.which results in friction and toolwear. Chemical Processes a. Electron beam inits direct forms are used in LBM andEBM respectively. slits . slits andProduction of through holes aredifficult non-circular. 3 4 5 6 7 8 9 10 Non Conventional Process There is no physical contact betweenthe tool and work piece.nimonics. Low material removal rate.SST.4 Comparison between conventional and Non-conventional machining process selection. Sl Conventional Process No. Photochemical Milling (PCM) 1. Chemical Milling (CHM) b. NTM can machine difficult to cut andhard to cut materials liketitanium. SJBIT Page 7 .Non Traditional Machining 10ME665 1.5 Applications Some of the applications of NTM are given below: DEPARTMENT OF MECHANICAL ENGG. 2. High Power sine wave generator 2. Tool Holder 4. SJBIT Page 8 . in which abrasives contained in aslurry are driven against the work by a tool oscillating at low amplitude (25-100 microns) and high frequency (15-30kHz). Tool DEPARTMENT OF MECHANICAL ENGG.2 Equipment: Ultrasonic Machining consists of : 1.Non Traditional Machining 10ME665 UNIT-2 2. Magneto-strictive Transducer 3.1 Introduction Ultrasonic Machining is a non-traditional process. Magneto-stricitve transducer. SJBIT Page 9 . Magneto-strictive transducer: These also change its length when subjected to strong magnetic field. These transducers are made of nickel. crystal attains its original size and shape. Such transducers are available up to 900 Watts. When the current is removed. Piezo electric crystals have high conversion efficiency of 95%. Piezo electric transducer: These transducer generate a small electric current when they are compressed. Transducer The high frequency electrical signal is transmitted to traducer which converts it into high frequency low amplitude vibration. nickel alloy sheets. Essentially transducer converts electrical energy to mechanical vibration. Piezo electric transducer 2. There are two types of transducer used 1.Non Traditional Machining 10ME665 High power sine wave generator This unit converts low frequency (60 Hz) electrical power to high frequency (20kHz) electrical power. Their conversion efficiency is DEPARTMENT OF MECHANICAL ENGG. Also when the electric current is passed though crystal it expands. Non Traditional Machining 10ME665 about 20-30%. stainless steel. Amplitude of vibration d. SiC. SJBIT Page 10 . 7. Volume concentration of abrasive in water slurry 11. Amplitude of vibration ( 15 to 50 microns) 2. titanium. B4C. high resistance to fatigue cracking. Commonly used tool holders are Monel. Work material DEPARTMENT OF MECHANICAL ENGG. Tool a.3 Process parameters 1. Material of tool b. Feed pressure 5. Shape c. It virtually transmits the energy and in some cases. The tool holder holds and connects the tool to the transducer. Material of tool should have good acoustic properties. Such transducers are available up to 2000 Watts. The value of ratio of TWR and MRR depends on kind of abrasive. Strength developed in tool 12. Abrasive size 6. The maximum change in length can be achieved is about 25 microns. Contact area of the tool 10. amplifies the amplitude of vibration. Boron silicarbide. Frequency of vibration ( 19 to 25 kHz). 2. demand higher operating cost. 3. Tool Tools are made of relatively ductile materials like Brass. Abrasive material Al203. Tool holder OR Horn. Flow strength of the tool material 9. Frequency of vibration e. Stainless steel or Mild steel so that Tool wear rate (TWR) can be minimized. Due measures should be taken to avoid ultrasonic welding between transducer and tool holder. Flow strength of the work material 8. Feed force (F) related to tool dimensions 4. Tool holders are more expensive. work material and tool materials. Diamond. Used for machining hard. Surface finish -0. Surface fatigue strength 13. ceramics. Slurry a. Abrasive – hardness.75 micron 7.25 micron to 0. Hole depth of 152mm deep is achieved by special flushing techniques. Large number of holes of small diameter. Non directional surface texture is possible compared to conventional grinding 8. Material b.32mm has been reported ( Benedict. Tolerance range 7 micron to 25 microns 3. square.Non Traditional Machining 10ME665 a. ceramics.5 Applications 1. 6. glass. Radial over cut may be as low as 1. DEPARTMENT OF MECHANICAL ENGG. Aspect ratio 40:1 has been achieved 5. flow rate c. Used for machining round. Impact strength c. Used to machine fragile components in which otherwise the scrap rate is high 3. tungsten glass that cannot be machined by conventional methods 2. 4.4 Process capability 1. grinding and milling operations on all materials which can be treated suitably with abrasives. Machining of cavities in electrically non-conductive ceramics 2. Pressure d. size. USM can perform machining operations like drilling. Density 2. Used in machining of dies for wire drawing. punching and blanking operations 8. shape and quantity of abrasive flow b. viscosity. irregular shaped holes and surface impressions. brittle metallic alloys. SJBIT Page 11 . 2. carbides etc. Liquid – Chemical property. 7. semiconductors. Can Machine work piece harder than 40 HRC to 60 HRC like carbides.025 to 25mm/min 6. Linear material removal rate -0.5 to 4 times the mean abrasive grain size. 930 holes with 0. 1973) using hypodermic needles 5. Holes up to 76 micron have been drilledhole depth upto 51mm have been achieved easily. Used for multistep processing for fabricating silicon nitride (Si3N4) turbine blades 4. Tool wear rate is high due to abrasive particles.ECG. 5. USM can be used only when the hardness of work is more than 45 HRC. It can be used machine hard. 2. Throwing of abrasive grains ii. Cutting holes with curved or spiral centre lines and cutting threads in glass and mineral or metallo-ceramics 2.Non Traditional Machining 10ME665 9. Glass. No heat is generated in work. USM is used for grinding Quartz. 3. USM can be used to cut industrial diamonds 13. 4. USM enables a dentist to drill a hole of any shape on teeth without any pain 11. tungsten carbide. MS or tool steel will wear from the action of abrasive grit with a ratio that ranges from 1:1 to 200:1 4.ECM.6 Advantages 1. Hammering of abrasive grains iii. 2. Chemical erosion due to micro –agitation Material removal due to throwing and hammering is significant and MR due to cavitations and chemical erosion can be ignored.8 Material removal models in USM Theoretical analysis and experimental results have revealed that USM is a form of abrasion and material removal in the form of small grains by four mechanisms i. 10.7 Disadvantages 1. It is burr less and distortion less processes. DEPARTMENT OF MECHANICAL ENGG. precision mineral stones can be machined using USM 12. brittle. as slurry movement is restricted. SJBIT Page 12 . iv. and ceramics 14. Non-metal (because of the poor electrical conductivity) that cannot be machined by EDM and ECM can very well be machined by USM. Low Metal removal rate 2. Cavitations in the fluid medium arising out of ultrasonic vibration of tool. It can be adopted in conjunction with other new technologies like EDM. Tools made from brass. It is difficult to drill deep holes. Ferrites and steel parts . therefore no significant changes in physical structure of work material 3. fragile and non-conductive material 2. USM has been used for piercing of dies and for parting off and blankingoperations. then particle is hammered over the work surface. If the size of the particle is small and gap between the tool and work is large. Abrasive particles move under high frequency vibrating tool.Non Traditional Machining 10ME665 Abrasive particles are assumed to be spherical in shape having diameter dg. If the size of the particle is large and gap between tool and work is small. There are two possibilities whenthe tool hit the particle. SJBIT Page 13 . then particle will be thrown by tool to hit the work piece. From the geometry DEPARTMENT OF MECHANICAL ENGG. Non Traditional Machining DEPARTMENT OF MECHANICAL ENGG. SJBIT 10ME665 Page 14 . The high velocity abrasive particles remove the material by micro-cutting action as well as brittle fracture of the work material. a focused stream of abrasive particles. DEPARTMENT OF MECHANICAL ENGG. carried by high pressure air or gas is made to impinge on the work surface through a nozzle and the work material is made to impinge on the work surface through a nozzle and work material is removed by erosion by high velocity abrasive particles. abrasive particles are made to impinge on the work material at a high velocity. SJBIT Page 15 . 3.2 Abrasive Jet Machining Equipment In Abrasive Jet Machining (AJM).1 Definition In abrasive jet machining.Non Traditional Machining 10ME665 UNIT-3 3. Non Traditional Machining 10ME665 A schematic layout of AJM is shown above. air filter cum drier should be used to avoid water or oil contamination of abrasive powder. Gas should be nontoxic. SJBIT Page 16 . Abrasive jet Machining consists of 1. Gas propulsion system 2. Abrasive feeder 3. The velocity of the abrasive stream ejected through the nozzle is generally of the order of 330 m/sec. It should not excessively spread when discharged from nozzle into atmosphere. The propellant consumption is of order of 0. easily available. Gas may be supplied either from a compressor or a cylinder. The gas stream is then passed to thenozzle through a connecting hose. In case of a compressor.008 m3/min at a nozzle pressure of 5bar DEPARTMENT OF MECHANICAL ENGG. AJM Nozzle 5.3 Gas Propulsion System Supplies clean and dry air. cheap. Abrasives 3. Air. Machining Chamber 4. Nitrogen and carbon dioxide to propel the abrasive particles. friction etc is minimum possible. the divergence ofjet stream increases resulting in more stray cutting and high inaccuracy. Machining chamber It is well closed so that concentration of abrasive particles around the working chamber does not reach to the harmful limits. Wear rate of the nozzle However.4 Process parameters For successful utilization of AJM process. The sieve is made to vibrate at 50-60 Hz and mixing ratio is controlled by the amplitude of vibration of sieve. Process criteria are generally influenced by the process parameters as enumerated below: Abrasives a) material – Al2CO3 SiC Glass beads Crushed glass Sodium bi carbonate DEPARTMENT OF MECHANICAL ENGG. With increase in wear of a nozzle. 1. Special consideration should be given to dust collection system if the toxic material (like beryllium) are being machined. The nozzle is made of either circular or rectangular cross section and head can be head can be straight. It is so designed that loss of pressure due to the bends. The nozzle imparts high velocity to mixture which is directed at work piece surface. AJM nozzle AJM nozzle is usually made of tungsten carbide or sapphire ( usually life – 300 hours for sapphire . Material removal rate 2. Required quantity of abrasive particles is supplied by abrasive feeder. The particles are propelled by carrier gas to a mixing chamber. Geometry and surface finish of work piece 3. The filleted propellant is fed into the mixing chamber where in abrasive particles are fed through a sieve. or at a right angle. Abrasive Feeder. SJBIT Page 17 .Non Traditional Machining 10ME665 and abrasiveflow rate varies from 2 to 4 gm/min for fine machining and 10 to 20 gm/min forcutting operation. Air abrasive mixture moves further to nozzle. 3. 20 to 30 hours for WC) which has resistance to wear. Machining chamber is equipped with vacuum dust collector. it is necessary to analyze the following process criteria. semiconductor processing can also be done effectively. silicon etc. cutting titanium foils 4.2 to 10 bar e) Flow rate . Cleaning of metallic smears on ceramics. DEPARTMENT OF MECHANICAL ENGG.Non Traditional Machining 10ME665 b) shape – irregular/regular c) Size – 10 to 50 microns d) Mass flow – 2-20 gm/min Carrier Gas a) Composition – Air. resistive coating etc. 20 to 30 hours for WC 3.5 to 15mm. CO2. engraving registration numbers on toughened glass used for car windows 5. de burring of plastics.2 to 0. SJBIT Page 18 .3 kg/m3 c) Velocity . This is used for abrading and frosting glass more economically as compared to etching or grinding 2. Register treaming can be done very easily and micro module fabrication for electrical contact. d) Impingement angle – 60 to 90 deg Nozzle a) Material – WC/Sapphire b) Diameter – 0. Deflating small castings.500 to 700 m/s d) Pressure . AJM is useful in manufacture of electronic devices . making of nylon and Teflon parts permanent marking on rubber stencils.5 Applications 1.5 to 30 microns Abrasive Jet a) Velocity . Used for cutting thin fragile components like germanium.100 to 300 m/s b) Mixing ratio – Volume flow rate of abrasives/Volume flow rate of gas c) Standoff distance – SOD.0. oxides on metals. 3. 6. drilling of glass wafers. N2 b) Density – 1.8 mm c) Life – 300 hours for sapphire. silicon. A dust collection system is a basic requirement to prevent atmospheric pollution and health hazards. DEPARTMENT OF MECHANICAL ENGG. mica. 8. mica. quartz. deburring etching and polishing of hard and brittle materials. so it can machine delicate and heat sensitive material 4. Short standoff distances when used for cutting. 7. Nozzle life is limited (300 hours) 7. cutting. Limited capacity due to low MRR. Capital cost is low and it is easy to operate and maintain AJM. It has the capability of cutting holes of intricate shape in hard materials.5 microns) 3.7 Disadvantages of AJM 1. 3. Thin sections of hard brittle materials like germanium. SJBIT Page 19 . 8. Process is free from chatter and vibration as there is no contact between the tool and work piece 5. Used for drilling. ceramics germanium . Stray cutting is difficult to avoid 5. especially while machining soft material like elastomers or soft plastics. Most suitable for machining brittle and heat sensitive materials like glass. 9. It provides cool cutting action. Depth of damage is low ( around2.6 Advantages of AJM 1. damages the nozzle. The accuracy of cutting is hampered by tapering of hole due to unavoidable flaring of abrasive jet. Abrasives may get embedded in the work surface. glass and ceramics can be machined. 4. sapphire. 6. 3. 6. silicon and gallium. High surface finish can be obtained depending upon the grain sizes 2. 3. MRR for glass is 40 gm/minute 2.Non Traditional Machining 10ME665 7. Abrasive powders cannot be reused as the sharp edges are worn and smaller particles can clog the nozzle. It is also good method for deburring small hole like in hypodermic needles and for small milled slots in hard metallic components. MRR decreases with further increase of abrasive flow rate. If the density ofabrasive particles is gradually increased exit velocity will go on decreasing for the same pressure condition. But after reaching optimum value. 2. Effect of abrasive flow rate and grain size on MRR It is clear from the figure that at aparticular pressure MRR increase with increase of abrasive flow rate and is influenced by size of abrasive particles. The exit velocity of gas can be increased to critical velocity when the internal gas pressure is nearly twice the pressure at exit of nozzle for the abrasive particle density is zero. It is due to fact that Kinetic energy of gas is utilized for transporting the abrasive particle DEPARTMENT OF MECHANICAL ENGG. wear rate of the nozzle Process criteria are generally influenced by the process parameters The characteristics of above process parameters on process criteria are as follows 1. Geometry and surface finish of work piece 3.8 Machining characteristics Following are the AJM process criteria 1. SJBIT Page 20 . Material removal rate 2. This is owing to the fact that Mass flow rate of gas decreases with increase of abrasive flow rate and hence mixing ratio increases causing a decrease in material removal rate because of decreasing energy available for erosion. Effect of exit gas velocity and abrasive particle density The velocity of carrier gas conveying the abrasiveparticles changes considerably with the change of abrasive particle density as indicated in figure.Non Traditional Machining 10ME665 3. SJBIT Page 21 . the material removal ratewill increase with the increase in gas pressureKinetic energy of the abrasive particles is responsible for the removal of material by erosion process. As a matter of fact. DEPARTMENT OF MECHANICAL ENGG. It is convenient to explain to this fact by term MIXING RATIO. 4. This is only possible by increasing the internal gas pressure as shown in the figure. Effect of mixing ratio on MRR Increased mass flow rate of abrasive will result in a decreased velocity of fluid and will therebydecreasesthe available energy for erosion and ultimately the MRR.Non Traditional Machining 10ME665 3. Effect of Nozzle pressure on MRR The abrasive flow rate can be increased by increasing the flow rate of the carrier gas. As the internal gas pressure increases abrasive mass flow rate increase and thus MRR increases. The abrasive must impinge on the work surface with minimum velocity for machining glass by SIC particle is found to be around 150m/s. Thus 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. 4. SJBIT Page 22 . ECM is opposite of electrochemical or galvanic coating or deposition process. Fig.1 Introduction Electrochemical Machining (ECM) is a non-traditional machining (NTM) process belonging to electrochemical category. 1 schematically shows the basic principle of ECM.Non Traditional Machining 10ME665 UNIT – 4 4.2 Equipment The electrochemical machining system has the following modules: • Power supply • Electrolyte filtration and delivery system • Tool feed system • Working tank DEPARTMENT OF MECHANICAL ENGG. Thus DEPARTMENT OF MECHANICAL ENGG. The first law states that the amount of electrochemical dissolution or deposition is proportional to amount of charge passed through the electrochemical cell. material removal takes place due to atomic dissolution of work material.Non Traditional Machining 10ME665 4.3 Modelling of material removal rate Material removal rate (MRR) is an important characteristic to evaluate efficiency of a nontraditional machining process. which may be expressed as: m∝Q. Where m = mass of material dissolved or deposited Q = amount of charge passed The second law states that the amount of material deposited or dissolved further depends on Electrochemical Equivalence (ECE) of the material that is again the ratio atomic weigh and valency. In ECM. Electrochemical dissolution is governed by Faraday’s laws. SJBIT Page 23 . SJBIT 10ME665 Page 24 .Non Traditional Machining DEPARTMENT OF MECHANICAL ENGG. cuttingof curvilinear slots. grinding. Machinability of the work material is independent of its physical andmechanical properties. High capital cost of equipment 2. Hydrogen libration at the tool surface may cause hydrogen embrittlementof the surface. treplaning.Non Traditional Machining 10ME665 4. 4. production ofintegrally bladed nozzle for use in diesel locomotives. broaching. The process is capable of machining metals andalloys irrespective of their strength and hardness. ECM can machine highly complicated and curved surfaces in a singlepass.plunge cutting etc. machining of intricate patterns. ECM principle has be employed for performing a number of machiningoperations namely. almost automatic operation. and reduced inventory expenses. production of longcurved profiles. die sinking. deburring. 4. 5. Machined surfaces are stress and burr free having good surface finish 5. 2. 4. Design and tooling system is complex 3. fine holedrilling. 4. Theoretically tool life is high 3. 1. There is no thermal damage and burr free surface can be produced. It yields low scrap. Spark damage may become sometimes problematic 5. Fatigue properties of the machined surface may reduce as compared toconventional techniques (by 20%) DEPARTMENT OF MECHANICAL ENGG.6 Disadvantages 1. piercing.4 Applications 1. ECM can be used to make disc for turbine rotor blades made up ofHSTR alloys 2. machining of thin large diameterdiaphragms. low overall machiningtime. ECM can also be used to generate internal profile of internal cams. production ofsatellite rings and connecting rods. SJBIT Page 25 . ECM can be used for copying of internal and external surfaces. 4. turning. machining of gears and chain sprockets. A single tool can be used to machine a large number of pieces withoutany loss in its shape and size. ECM can be used for slotting very thin walled collets 3. 6.5 Advantages ECM offers impressive and long lasting advantages. Space and floor area requirement are also higher than for conventionalmachining methods. Non-conductive material cannot be machined.025mm (2D) and 0.075 to 0. Some additional problems related to machine toolrequirements such as power supply. Brass. Side over cut 0.300 kpa 3. SJBIT Page 26 . Flow rate – 16 LPM to 20 LPM Velocity – 1500 m/min to 3000 m/min Inlet pressure – 2200 kPa. Feed rate 0.Non Traditional Machining 10ME665 6. Working Gap 0. Outlet Pressure. Tolerance 0. electrolyte handling and tool feed servo 4. Blind holes cannot be machined in solid block in one stage 8.5 microns DEPARTMENT OF MECHANICAL ENGG. Electrolyte Type – Nacl. Corrosion and rust of ECM machine can be hazard 9. Roughness 1. Temperature – 26 to 50 deg.40000A Current Density – 500 A/Cm2 2. Power supply Type – DC Voltage – 30V Current .125 to 1mm 5.7 Process Parameters 1. Proprietary mixtures.500 to 13 mm/min 6. Electrode material Copper . 7. NaNo3.050mm(3D) 8.75mm 4. Bronze 7. Non Traditional Machining 10ME665 UNIT – 5 5. SJBIT Page 27 . which forms cathode in the ECM setup. MRR in this process can easily be calculated according to Faraday’s law. Only electrically conducting materials can be processed by ECM. The working principle and process details are shown in the Figure.1 Introduction Chemical machining is one of the non-conventional machining processes where material is removed by bringing it in contact of a strong chemical enchant. chemical blanking. The workpiece is made anode of the setup and material is removed by anodic dissolution. stainless steel. 5. Tool is made cathode and kept in close proximity to the workpiece and current is passed through the circuit. Proper allowances are given in the tool size to get the dimensional accuracy of the machined surface. Tool A specially designed and shaped tool is used for ECM. The tool is usually made of copper. brass. Both electrodes are immersed into the electrolyte solution. Process details of ECM are shown in Figure and described as below: Workpiece Workpiece is made anode. and it is a mirror image of the desired machined cavity. Material of workpiece is removed by anodic dissolution.2 Working Principle of ECM Electrochemical machining removes material of electrically conductor workpiece. DEPARTMENT OF MECHANICAL ENGG. etc. photochemical machining. There are different chemical machining methods base on this like chemical milling. electrolyte is pumped between workpiece and the tool. The cavity machined is the mirror image of the tool. This works on the basis of Faraday’s law of electrolysis. Connecting wires are required to connect electrodes to the power supply. possess the following properties: 1. Maskants should. It is recycled by a pump after filtration. Synthetic or rubber basematerials are frequently used.3 Tooling for CHM Tooling for CHM is relatively inexpensive and simple to modify. It is necessary to maintain a constant gap between the workpiece and tool so tool feed rate is kept accordingly while machining.1 shows the different maskantsand etchants for several materials together with the etch rate and etchfactor. Table 3. The tank is made of transparent plastic which should be non-reactive to the electrolyte.Non Traditional Machining 10ME665 Power Supply DC power source should be used to supply the current. Normally water soluble NaCl and NaNO3 are used as electrolyte. Electrolyte Water is used as base of electrolyte in ECM. In addition to the above whole process is carried out in a tank filled with electrolyte. Tool Feed Mechanism Servo motor is used to feed the tool to the machining zone. etchants. scribing templates. Power supply supplies low voltage (3 to 4 volts) and high current to the circuit. 5. Electrolyte facilitates are carrier of dissolved workpiece material. however. SJBIT Page 28 . Maskants: Maskants are generally used to protect parts of theworkpiece where CD action is not needed. Tool is connected with the negative terminal and workpiece with the positive terminal of the power source. and accessories. Four different types of tools are required: maskants. Be tough enough to withstand handling DEPARTMENT OF MECHANICAL ENGG. Non Traditional Machining 10ME665 2. and previously induced stresses. therefore. Control of selective and intergranular attack 4. Their main technical goals are to achieve the following: 1. the metal is dissolved by the CD action. for fine surface quality of uniform appearance. Good surface finish 2. Fine grain size and homogenous metallurgical structure are. Maintenance of air quality and avoidance of possible environmentalProblems 5. Adhere well to the workpiece surface 3. Uniformity of metal removal 3. SJBIT Page 29 . Be inert to the chemical reagent used 5. orientation. Best price and reliability for the materials to be used in the constructionof the process tank 7. This machining phase takes place both at the individual grain surfaces as well as at the grain boundaries. Scribe easily 4. Surfaces machined by CHM do not have a regular lay pattern. Based on the grain size. every material has a basic surface DEPARTMENT OF MECHANICAL ENGG. Be able to withstand the heat generated by etching 6. Be removed easily and inexpensively after etching Etchants:Etchants (see below Table) are acid or alkaline solutionsmaintained within a controlled range of chemical composition andtemperature. heat treatment.4 Accuracy and surface finish In CHM. Control of hydrogen absorption in the case of titanium alloys 5. necessary. Maintenance of personal safety 6. shot peening or grit blasting can restore it. The machining rate affects the surface roughness and hence the tolerance produced. and recast structure are easily removed by CHM. The orientation of the areas being etched withrespect to the rolling direction or the direction of the grain in the workpiece is also important for good CHM surfaces.Non Traditional Machining 10ME665 finish that results from CHM for a certain period of time. having thelargest grain size. For low machining depths. Figure 3.05 μm become possible (Machining Data Handbook. while at higher depths a slight change in the roughness is evident. nickel. It increases as the metal ion concentration rises in the etchant. under special conditions. 5. Aluminum and magnesium alloys can be controlled more closely than steel. or titanium alloys. SJBIT Page 30 .025 mm/mm with tolerances of ±10 percent of the cut width can be achieved depending on the workpiece material and depth of cut.025 to 0. <200 μm. 1997). slow etching will produce a surface finish similar to the original one.7 shows typical surface roughnesses for different materials.7 shows the dependence of the surface roughness and etch rate on the workpiece material.8 μm.and. can be obtained. As shown in Figs. waviness. dents. decarburized layer. depending on the initial roughness. The depth of cut tolerance increases when machining larger depths at high machining rates. An etching rate of 0. In this regard surface conditions such as a titanium oxide layer (alpha case). any prior surface irregularities. However. show the roughest surface together with the lowest DEPARTMENT OF MECHANICAL ENGG. however. resulting in an improvement in the properties of the finished parts. surface roughnesses of 0. roughnesses of 0. The surface roughness is also influenced by the initial workpiece roughness. Typically. castings. the roughness sharply increases with the depth of cut. The removal of such layers results in a change in the average mechanical properties of the finished parts. CHM can affect the mechanical properties of the machined parts when the surface layers have different mechanical properties from those of the base metal.1 to 0. Figure 3. or scratches will be slightly altered and reproduced in the machined surface. While surface imperfections will not be eliminated by CHM. Some loss of fatigue properties has been reported after CHM of aluminum.5 Material removal rate The material removal or etch rate depends upon the chemical and metallurgicaluniformity of the workpiece and the uniformity of the solutiontemperature. Generally. 4. Drilling of small and deeper holes with very good quality of internal surface finish. Electrochemical Grinding: This can also be named as electrochemical debrruing. heat resistant materials without any problem. The quality of finish largely depends on the quality of finish of the tool. 3. This is used for anodic dissolution of burrs or roughness a surface to make it smooth. DEPARTMENT OF MECHANICAL ENGG. This is applied in internal finishing of surgical needles and also for their sharpening.25 to 0.6 CHM average roughness of some alloys after removing 0. brittle.4 mm 5.7 surface roughnesses and etch rate of some alloys after removing 0. 2. Machining of hard. Any conducting material can be machined by this process.Non Traditional Machining 10ME665 Figure 3.6 Applications of ECM Process There are large numbers of applications of ECMs some other related machining and finishing processes as described below: 1.25 to 0.4 mm Figure 3. SJBIT Page 31 . Designing and making tool is difficult but its life is long so recommended only for mass production. 2. 4. 4. 5. DEPARTMENT OF MECHANICAL ENGG. 2. It is used for making inclined and blind holes and finishing of conventionally machined surfaces.7 Advantages of ECM Process Following are the advantages of ECM process: 1. 5. Accurate feed rate of tool is required to be maintained. Total material and workpiece material should be chemically stable with the electrolyte solution 3. Machining of cavities and holes of complicated and irregular shapes. Complex shapes can also be easily machined. Very close tolerances can be obtained.8 Disadvantages and Limitations of ECM There are some disadvantages and limitations of ECM process as listed below: 1. 6. There is no application of force.Non Traditional Machining 10ME665 5. There is almost negligible tool wear so cost of tool making is only one time investment for mass production. no direct contact between tool and work and no application of heat so there is no scope of mechanical and thermal residual stresses in the workpiece. SJBIT Page 32 . 5. 3. Machining of hard and brittle material is possible with good quality of surface finish and dimensional accuracy. All electricity non-conducting materials cannot be machined. Lazarenko invented the relaxation circuit (RC).The evolution of wire EDM in the 1970s was due to the powerful generators. planetary and orbital motion techniques. Since 1940.1 Introduction The history of electro discharge machining (EDM) dates back to the daysof World Wars I and II when B. SJBIT Page 33 . Using a simple servo controller they maintainedthe gap width between the tool and the workpiece. The process is burr-free. the machining speed has gone up by 20 times.which has decreased machining costs by at least 30 percent and improvedthe surface finish by a factor of 15. and the adaptive control systems.new wire tool electrodes. This removes (erodes) very tiny pieces of metal from the workpiece at a controlled rate.computer numerical control (CNC). DEPARTMENT OF MECHANICAL ENGG. reduced arcing. die sinking by EDM has beenrefined using pulse generators. andbetter flushing. 6. Recently. 2. 3. During the 1960s the extensive research led the progress of EDMwhen numerous problems related to mathematical modeling were tackled. The use of EDM is not affected by the hardness of the work material. and N. The metal-removal process is performed by applying a pulsating (ON/OFF) electrical charge of highfrequency current through the electrode to the workpiece.2 Principles of EDM Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used to remove metal by means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the workpiece to produce the finished part to the desired shape.Non Traditional Machining 10ME665 UNIT – 6 6. R. Cavities with thin walls and fine features can be produced. andmade EDM more profitable. improved machine intelligence. I. Difficult geometry is possible. EDM has the following advantages: 1. 4. is shaped to the form of the cavity it is to reproduce. DEPARTMENT OF MECHANICAL ENGG. The electrode and the workpiece are both submerged in a dielectric fluid. 6. A continuous-travelling vertical-wire electrode. A pre shaped or formed electrode (tool). II. which takes the shape opposite to that of the cutting tool or electrode. With the EDM process both the workpiece material and the electrode material must be conductors of electricity. SJBIT Page 34 . which is generally light lubricating oil. A servomechanism maintains a space of about the thickness of a human hair between the electrode and the work. The formed electrode is fed vertically down and the reverse shape of the electrode is eroded (burned) into the solid workpiece. is controlled by the computer to follow a programmed path to erode or cut a narrow slot through the workpiece to produce the required shape. the diameter of a small needle or less. preventing them from contacting each other.Non Traditional Machining 10ME665 6.3 EDM Process EDM spark erosion is the same as having an electrical short that burns a small hole in a piece of metal it contacts. The EDM process can be used in two different ways: I. usually made from graphite or copper.4 Conventional EDM In the EDM process an electric spark is used to cut the workpiece. 6. The dielectric oil. Flushing these particles out of the gap between the workpiece to prevent them from forming bridges that cause short circuits. SJBIT Page 35 .Non Traditional Machining 10ME665 In EDM ram or sinker machining. 6. There are a number of flushing methods used to remove the metal particles efficiently while assisting in the machining process. resulting in slower metal removal. 6. The EDM process produces a cavity slightly larger than the electrode because of the overcut. This removes suspended particles of workpiece material and electrode from the work cavity. The electrode in wire-cut EDM is about as thick as a small diameter needle whose path is controlled by the machine computer to produce the shape required. Too little pressure will not remove the chips quickly enough and may result in short-circuiting the erosion process DEPARTMENT OF MECHANICAL ENGG. It does not require a special shaped electrode.8 Flushing Ram Type EDM Flushing is the most important function in any electrical discharge machining operation. Too much fluid pressure will remove the chips before they can assist in the cutting action. that provides a means of flushing.5 Wire-Cut EDM The wire-cut EDM is a discharge machine that uses CNC movement to produce the desired contour or shape. or even carbide.7 Flushing One of the most important factors in a successful EDM operation is the removal of the metal particles (chips) from the working gap. Flushing applied incorrectly can result in erratic cutting and poor machining conditions. which is an electrical insulator that helps to control the arc discharge. 6.6 Dielectric Fluids – Conventional EDM During the EDM process the workpiece and the electrode are submerged in the dielectric oil. instead it uses a continuoustraveling vertical wire under tension as the electrode. Flushing is the process of introducing clean filtered dielectric fluid into the spark gap. is pumped through the arc gap. a relatively soft graphite or metallic electrode can be used to cut hardened steel. The EDM process is burr-free. orbital. X. Any material that is electrically conductive can be cut using the EDM process. ii. helical. v.10 The Servo Mechanism Both wire and vertical EDM machines are equipped with a servo control mechanism that automatically maintains a constant gap of about the thickness of a human hair between the electrode and the workpiece. spin and indexing machining cycles. Complex dies sections and molds can be produced accurately. iv. This versatility gives Electrical Discharge Machines many advantages over conventional machine tools. Thin fragile sections such as webs or fins can be easily machined without deforming the part. Y.11 Advantages of EDM Conventional EDM machines can be programmed for vertical machining. faster. DEPARTMENT OF MECHANICAL ENGG. rotational. and Z axes movements allow for the programming of complex profiles using simple electrodes. iii. i. 6. If red sparks occur during the cutting operation. otherwise arcing could damage the workpiece and break the wire. vi. the water supply is inadequate. conical. It is important for both machine types that there is no physical contact between the electrode and the workpiece.9 Wire EDM Dielectric Fluids The dielectric fluid must be circulated under constant pressure to flush (wash) away the metal particles and assist in the machining or erosion process. vectorial. increase the flow of water until blue sparks appear. Hardened workpieces can be machined eliminating the deformation caused by heat treatment. and at lower costs. 6. To overcome this problem. SJBIT Page 36 .Non Traditional Machining 10ME665 6. directional. The servomechanism advances the electrode into the workpiece as the operation progresses and senses the work-wire spacing and controls it to maintain the proper arc gap which is essential to a successful machining operation. The gas in this stage is termedplasma. SJBIT Page 37 .1 Introduction When the temperature of a gas is raised to about 2000°C.Non Traditional Machining 10ME665 UNIT – 7 7. these atoms become ionized. Recently machining of both metallic and nonconductivematerials has become much more attractive. During that time the process limitationsregarding the low cutting speed. and the unreliableequipment were clear. Plasma state is the superheated and electrically ionized gases at approximately 5000oC.30.and other nonferrous metals. poor machining quality. the gas moleculesbecome dissociated into separate atoms. Working principle and process details are shown in below Figure.2 Working Principle of PAM In this process gases are heated and charged to plasma state. Machining by plasma was adopted in the early 1950s as an alternativemethod for oxy-gas flame cutting of stainless steel. At higher temperatures. These gases are directed on the workpiece in the form of high velocity stream. aluminum.000°C. 7. DEPARTMENT OF MECHANICAL ENGG. An importantfeature of plasma beam machining (PBM) is that it is the only fabricatingmethod that works faster in stainless steel than it does in mild steel. The resulting cuttingrates and hence the machinability depend on the workpiece beingmachined as well as the type of the cutting and shielding gases that determinethe maximum DEPARTMENT OF MECHANICAL ENGG. plasma state gases works as a cutting tool. The electrode is given negative polarity and nozzle of the gun is given positive polarity. Cooling Mechanism As we know that hot gases continuously comes out of nozzle so there are chances of its overheating. There is a collision between molecules of gas and electrons of the established arc. A water jacket is used to surround the nozzle to avoid its overheating. All those material which can be processed by LBM can also be processed by PAM process. As a result of this collision gas molecules get ionized and heat is evolved. The plasma torch blows the molten andevaporated metal away as a fine spray or vapor. A tungsten electrode is inserted to the gun and made cathode and nozzle of the gun is made anode.3 Material removal rate During PBM absorbing the heat energy from the plasma jet directed to theworkpiece activates metal removal. A strong arc is established between the two terminals anode and cathode. Workpiece Workpiece of different materials can be processed by PAM process. The established arc is controlled by the supply rate of gases. hydrogen or mixture of these gases. Focused spray of ho0t. These materials are aluminium. argon. magnesium. Plasma Gun Gases are used to create plasma like. Power Supply and Terminals Power supply (DC) is used to develop two terminals in the plasma gun. The plasma gun consists of a tungsten electrode fitted in the chamber. SJBIT Page 38 . 7. Tooling There is no direct visible tool used in PAM. Supply of gases is maintained into the gun.Non Traditional Machining 10ME665 Process Details of PAM Details of PAM are described below. nitrogen. stainless steels and carbon and alloy steels. Heavy potential difference is applied across the electrodes to develop plasma state of gases. This hot and ionized gas called plasma is directed to the workpiece with high velocity. Non Traditional Machining 10ME665 temperature transfer rates. and aluminum.As the power is increased. During plasmamachining of 12-mm-thick steel plate using 220 kW the machining speedis 2500 mm/min. the efficient removal of melted metal isfound to need a corresponding rise in the gas flow rate. DEPARTMENT OF MECHANICAL ENGG. stainless steel. is shown in below Figuresshows the power consumption factor needed in plasma beam rough turningof some alloys. SJBIT Page 39 . The maximum machiningspeed. A low factor indicates either low energy required orhigh removal rates. as an index of machinability for dual gas plasma of carbonsteel. The machining speed is found to decrease withincreasing the thickness of the metal or the cut width in case of beveling. which is 5 times greater than that for oxy-gas cutting. Large tolerances of ±1.Non Traditional Machining 10ME665 7. This is also recommended for smaller machining of difficult to machining materials.7 Disadvantages of PAM Process i. 7. 7. Small cavities can be machined with good dimensional accuracy. Very hard and brittle metals can be machined. It gives faster production rate.6 mm can be achieved.6 mm. ii. Some of the workpiece materials are very much prone to metallurgical changes on excessive heating so this fact imposes limitations to this process. ii. 7. Additionally due to the rapid cooling. therefore. The high machiningspeed does not allow the heat to penetrate more than a few microns from the edges of the cut which produces little or no distortion in the cut workpiece. The cut edge of the material tends to be harder than the base material.4 Accuracy and surface quality The edges of the workpieces cut by PBM are often beveled. It is uneconomical for bigger cavities to be machined. Finish cuts are.12 mm has been reported. The left-handedge is beveled to about 15° due to the clockwise swirling of the machininggas. cracks may arise beyond the heat-affected zone to 1. iii.25 to 1. Owing to the high rate of heat transfer the depth of fused metalextends to about 0. Afurther heat-affected zone (HAZ) of thickness 0. DEPARTMENT OF MECHANICAL ENGG. iii. Its initial cost is very high.5 Applications of PAM The chief application of this process is profile cutting as controlling movement of spray focus point is easy in case of PAM process. McGeough (1988) reported that the right side of the plasma arc relative to the cutting direction produces a square edge to within ±3°. The process requires over safety precautions which further enhance the initial cost of the setup. required when narrow tolerances are required.6 Advantages of PAM Process Advantages of PAM are given below: i. SJBIT Page 40 . iv. A clean. smooth surface is produced by PBM.18 mm below the cut surface. The beam is pulsed so that the released energy results in an impulse against the work surface that does melting and evaporation. It can provide up to 50 kW power in pulsed mode and 1 kW in continuous-wave mode.Non Traditional Machining 10ME665 UNIT – 8 8. Lasers can be used to cut. Nd:YAG: Neodymium-doped Yttrium-Aluminum-Garnet (Y3Al5O12) laser is a solidstate laser which can deliver light through a fibre-optic cable. LBM is particularly suitable for making accurately placed holes. weld and mark.1 Introduction Laser-beam machining is a thermal material-removal process that utilizes a high-energy. drill. 8. The working principle and the process details (setup) are indicated in Figure 5. coherent light beam to melt and vaporize particles on the surface of metallic and non-metallic workpieces. A schematic of laser beam machining is shown in below Figure. It can provide up to 25 kW in continuous-wave mode.2 Working Principle of LBM LBM uses the light energy of a laser beam to remove material by vaporization and ablation. In this process the energy of coherent light beam is focused optically for predecided longer period of time. Different types of lasers are available for manufacturing operations which are as follows: CO2 (pulsed or continuous wave): It is a gas laser that emits light in the infrared region. Here the way of metal removing is same as that of EDM process DEPARTMENT OF MECHANICAL ENGG.6. SJBIT Page 41 . Laser Tube and Lamp Assembly This is the main part of LBM setup. an amplification source. This enables the light to travel to and fro between two reflecting mirrors. It is used for very thin stocks. A good workpiece material high light energy absorption power.Non Traditional Machining 10ME665 but method of generation of heat is different. rubber wood. This highly amplified stream of light is focused on the workpiece with the help of converging lense. which absorb the radiation of incoming light energy. The converging lense is also the part of this assembly. low melting point and low latent heat. one at each end of the tube. a power supply unit and a cooling system. scribing operations. slitting. Other applications are listed below: DEPARTMENT OF MECHANICAL ENGG. Tool Feed Mechanism There is no tool used in the LBM process. that excites the atoms of the inside media. Cooling Mechanism A cooling mechanism circulates coolant in the laser tube assembly to avoid its overheatingin long continuous operation. a pair of reflectors. This whole setup is fitted inside a enclosure. As the requirement of being focused shifts during the operation. poor thermal conductivity. poor reflectivity. This movement of the converging lense is the tool feed mechanism in LBM process. In this setup the flash lamp goes to laser tube. Workpiece The range of workpiece material that can be machined by LBM includes high hardness and strength materials like ceramics. Focusing laser beam at a pre-decided point in the workpiece serve the purpose of tool.3 Applications of LBM LBM is used to perform different machining operations like drilling. It is used for drilling holes of small diameter of the order of 0. its focus point can also be shifted gradually and accordingly by moving the converging lense in a controlled manner. The application of heat is very finely focused in case of LBM as compared to EDM.025 mm. 8. The partial reflecting mirror does not reflect the total light back and apart of it goes out in the form of a coherent stream of monochromatic light. glass to softer materials like plastics. etc. which carries good quality reflecting surfaces inside. a flash tube or lamp. low specific heat. SJBIT Page 42 . slotting. It consists of a laser tube. No tool wear 9. No cutting lubricants required 8. High accuracy parts can be machined. 4. 2. Machining of mechanical components of watches. 6. Sticky materials are also can be cut by this process. SJBIT Page 43 . It is a cost effective and flexible process.5 Limitations of laser cutting 1 Uneconomic on high volumes compared to stamping 2 Limitations on thickness due to taper 3 High capital cost 4 High maintenance cost 5 Assist or cover gas required DEPARTMENT OF MECHANICAL ENGG.Non Traditional Machining i.4 Advantage of laser cutting 1. Narrow heat effected zone 8. No limit to cutting path as the laser point can move any path. The process is stress less allowing very fragile materials to be laser cut without any support. ii. 7. 5. 8. Very hard and abrasive material can be cut. 10ME665 Making complex profiles in thin and hard materials like integrated circuits and printed circuit boards (PCBS). iii. 3. Smaller machining of very hard material parts. The tungsten filament cathode is heated to about 2500 to 3000°C in order to emit electrons. and heat treatment are a set of modernapplications used in semiconductor manufacturing as well as micromachiningareas.Electron beam machining (EBM) has been used in industry since the1960s. A measure of this effect is the emission current. 8. electrons. Corresponding current densities lie between 5 and 15 A/cm2.Non Traditional Machining 10ME665 Electron Beam Machining 8. initially in nuclear and aerospace welding applications. focused by the field. travel through a hole in the anode. equipment and operation ofElectron Beam Machining The main components of EBM installation. The electron beam isthen refocused by a magnetic or electronic lens system so that the beam is directed under control toward the workpiece.7 Principles. Drillingsmall holes. typically 0. over a well-defined area.25 mm in diameter. cutting. After acceleration.43 arehoused in a vacuum chamber. shown in Fig.6 Introduction The earliest work of material removal utilizing an electron beam wasattributed to Steigerwald who designed a prototype machine in 1947. and the high voltage that is usually about 150 kV. The electrons the velocity (228 × 103 km/s) imparted by the acceleration voltage until they strike the workpiece. the magnitude of which varies between 20 and 100 mA. DEPARTMENT OF MECHANICAL ENGG. engraving. Emission current depends on the cathode material. 5. SJBIT Page 44 . evacuated to about 10–4 torr. Such a high voltage accelerates a stream of electrons in the direction of the workpiece. temperature. Long production time due to the time needed to generate a vacuum iii. iv. The process produces the best surface finish compared to otherprocesses. High capital equipment cost ii. vi. No limitation is imposed by workpiece hardness. The presence of a thin recast layer iv.8 Advantages Electron Beam Machining i. thus causing material removal by evaporation.55 MW/mm2 involved in EBM. Drilling is possible at high rates (up to 4000 holes per second). Need for auxiliary backing material DEPARTMENT OF MECHANICAL ENGG. virtually all engineering materials can be machined by this machining technique. ductility. 8. Accurate manipulation of the workpiece coupled with the precise control of the beam is reported by McGeough (1988) to yield a machining process that can be fully automated. iii. 8. No difficulty is encountered with acute angles.9 Disadvantages Electron Beam Machining i. vii. The process is capable of achieving high accuracy and repeatabilityof 0. to well above its boiling point. No mechanical distortion occurs to the workpiece since there is no contact. causing a corresponding rapid increase in the temperature of the workpiece. Drilling parameters can easily be changed during machining. and surfacereflectivity.Non Traditional Machining 10ME665 The kinetic energy of the electrons is then rapidly transmitted intoheat. The cost is relatively small compared to other processes used to producevery small holes. SJBIT Page 45 . ii.1 mm for position of holes and 5 percent for the hole diameter. viii. With power densities of 1. v.
Report "Mech Vi Non Traditional Machining [10me665] Notes"