unit_05_MP_III

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Manufacturing processes III : NONTRADITIONAL (OR) UNCONVENTIONAL MACHINING:

Manufacturing processes III : NONTRADITIONAL (OR) UNCONVENTIONAL MACHINING RAKESH V ADAKANE DEPARTMENT OF MECHANICAL ENGINEERING YCCE NAGPUR 1 Rakesh V Adakane , YCCE Nagpur

Slide 2:

The requirements that lead to the development of nontraditional machining. Very high hardness and strength of the material. (above 400 HB.) The work piece is too flexible or slender to support the cutting or grinding forces. The shape of the part is complex, such as internal and external profiles, or small diameter holes. Surface finish or tolerance better than those obtainable conventional process. Temperature rise or residual stress in the work piece are undesirable. 2 Rakesh V Adakane, YCCE Nagpur

Unconventional Machining Methods:

Unconventional Machining Methods Chemical machining Electro chemical machining Electrical discharge machining Wire EDM Ultrasonic Machining Laser beam machining Electron-beam machining plasma-arc machining Water-jet machining Abrasive-jet machining 3 Rakesh V Adakane, YCCE Nagpur

Examples of parts made by advanced Machining Processes:

Examples of parts made by advanced Machining Processes Fig : Examples of parts made by advanced machining processes. These parts are made by advanced machining processes and would be difficult or uneconomical to manufacture by conventional processes. (a) Cutting sheet metal with a laser beam.(b) Microscopic gear with a diameter on the order of 100 µm, made by a special etching process. 4 Rakesh V Adakane, YCCE Nagpur

Slide 5:

Chemical machining 5 Rakesh V Adakane, YCCE Nagpur

Chemical machining:

Chemical machining Chemical attacks metals and etch them by removing small amounts of material from the surface using reagents or etchants Fig : (a) Missile skin-panel section contoured by chemical milling to improve the stiffness-to weight ratio of the part. (b) Weight reduction of space launch vehicles by chemical milling aluminum-alloy plates. These panels are chemically milled after the plates have first been formed into shape by processes such as roll forming or stretch forming. The design of the chemically machined rib patterns can be modified readily at minimal cost. 6 Rakesh V Adakane, YCCE Nagpur

Slide 7:

Chemical milling: Shallow cavities produced on plates, sheets, forgings, and extrusions Procedure for chemical milling Steps : 1 – Residual stresses should relieved in order to prevent warping 2 – Surfaces to be thoroughly degreased and cleaned 3 - Masking material ( tapes, paints , elastomers & plastics ) is applied 4 – masking is peeled off by scribe and peel technique 5 – The exposed surfaces are etched with etchants 6 – After machining the parts to be thoroughly washed to prevent further reactions with residue etchant 7 – rest of the masking material is removed and the part is cleaned and inspected 8 – additional finishing operations are performed on chemically milled parts 9 – this sequence is repeated to produce stepped cavities and various contours 7 Rakesh V Adakane, YCCE Nagpur

Slide 8:

Process capabilities: Chemical milling used in the aerospace industry Tank capacities for reagents are as large as 3.7m x15m Process also used for micro electronic devices Surface damage may result due to preferential etching and intergranular attack Chemical blanking: Chemical blanking is similar to chemical milling Material is removed by chemical dissolution rather than by shearing Burr free etching of printed-circuit boards, decorative panels, thin sheet metal stampings as well as production of small and complex shapes 8 Rakesh V Adakane, YCCE Nagpur

Chemical Machining:

Chemical Machining Fig : Schematic illustration of the chemical machining process. Note that no forces or machine tools are involved in this process . 9 Rakesh V Adakane, YCCE Nagpur

Slide 10:

Photochemical blanking : Modification of chemical milling Material removed from flat thin sheet by photographic techniques 10 Rakesh V Adakane, YCCE Nagpur

Steps for photochemical blanking:

Design is prepared at a magnification of 100x Photographic negative is reduced to the size of finished part Sheet blank is coated with photosensitive material (Emulsion) Negative placed over coated blank and exposed to ultra violet light which hardens the exposed area Blank is developed which dissolves the exposed areas Blank is then immersed into a bath of reagent or sprayed with the reagent which etches away the exposed areas The masking material is removed and the part is washed thoroughly to remove all chemical residues Steps for photochemical blanking 11 Rakesh V Adakane, YCCE Nagpur

Application:

Application Chemically milled parts find wide applications in Aerospace, aviation, Automotive, electronic and instrument making industry Chemically blanked parts are used in- tape recorders, computers ,camera, television sets, electric motors ,timers, medical instruments. Chemical contour machining is used to make special surface in aircraft wing and fuselage section, used to produce pockets on surface of bulkheads, skin panels. Contour machining is used to produce decorative surfaces on Elevators, ashtrays, panels, metal tags. 12 Rakesh V Adakane, YCCE Nagpur

Slide 13:

Electro Chemical Machining 13 Rakesh V Adakane, YCCE Nagpur

Electro Chemical Machining:

Electro Chemical Machining Fig : Schematic illustration of the electrochemical-machining process. This process is the reverse of electroplating. 14 Rakesh V Adakane, YCCE Nagpur

Electrochemical machining:

This process is reversal of the electro plating Electrolyte acts as current carrier High rate of electrolyte movement in tool work piece gap washes metal ions away from the work piece ( ANODE) This is washed just before they have a chance to plate on the tool ( cathode) Shaped tool made of brass , copper , bronze , or stainless steel Electrolyte is pumped at a high rate through the passages in the tool Machines having current capacities as high as 40,000 A and as low as 5A are available Electrochemical machining 15 Rakesh V Adakane, YCCE Nagpur

Slide 16:

FIGURE : Typical parts made by electrochemical machining. (a) Turbine blade made of a nickel alloy, 360 HB. Source : Metal Handbook , 9 th ed., Vol. 3, Materials Park, OH: ASM International, 1980, p. 849. (b) Thin slots on a 4340-steel roller-bearing cage. (c) Integral airfoils on a compressor disk. Parts made by Electrochemical Machining 16 Rakesh V Adakane, YCCE Nagpur

Process capabilities :

Process capabilities Used to machine complex cavities in high strength material Applications in aerospace industry,jet engines parts and nozzles ECM process gives a burr free surface No thermal damage Lack of tool forces prevents distortion of the part No tool wear Capable of producing complex shapes and hard materials 17 Rakesh V Adakane, YCCE Nagpur

Slide 18:

Advantages of ECM Process leaves a burr free surface. Does not cause any thermal damage to the parts. Lack of tool force prevents distortion of parts. Capable of machining complex parts and hard materials ECM systems are now available as Numerically Controlled machining centers with capability for high production, high flexibility and high tolerances. 18 Rakesh V Adakane, YCCE Nagpur

Biomedical Implant:

Biomedical Implant Fig : (a) Two total knee replacement systems showing metal implants (top pieces) with an ultrahigh molecular weight polyethylene insert (bottom pieces) (b) Cross-section of the ECM process as applied to the metal implant. 19 Rakesh V Adakane, YCCE Nagpur

Application:

Application It has wide application in rocket, aircraft and gas turbine industry It is standard process for machining for gas turbine blade Die sinking, embossed surfaces, blind holes, irregular holes, complex external shapes. 20 Rakesh V Adakane, YCCE Nagpur

Slide 21:

Electrochemical Grinding Combines electrochemical machining with conventional grinding Fig : Schematic illustration of the electrochemical – grinding process. (b) Thin slot produced on a round nickel – alloy tube by this process. 21 Rakesh V Adakane, YCCE Nagpur

Slide 22:

Electrochemical Grinding (ECG) 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. 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. 22 Rakesh V Adakane, YCCE Nagpur

Slide 23:

Electrical-Discharge Machining 23 Rakesh V Adakane, YCCE Nagpur

Electrical-Discharge Machining:

Electrical-Discharge Machining FIGURE 9.32 Schematic illustration of the electrical-discharge-machining process. 24 Rakesh V Adakane, YCCE Nagpur

Slide 25:

Electrical discharge machining (EDM) Based on erosion of metals by spark discharges. EDM system consist of a tool (electrode) and work piece, connected to a dc power supply and placed in a dielectric fluid. when potential difference between tool and work piece is high, a transient spark discharges through the fluid, removing a small amount of metal from the work piece surface. This process is repeated with capacitor discharge rates of 50-500 kHz. 25 Rakesh V Adakane, YCCE Nagpur

Slide 26:

dielectric fluid – mineral oils, kerosene, distilled and deionized water etc. role of the dielectric fluid 1. acts as a insulator until the potential is sufficiently high. 2. acts as a flushing medium and carries away the debris. 3. also acts as a cooling medium. Electrodes – usually made of graphite. EDM can be used for die cavities, small diameter deep holes, turbine blades and various intricate shapes. 26 Rakesh V Adakane, YCCE Nagpur

Electrical-Discharge Machining:

Electrical-Discharge Machining Fig : (a) Schematic illustration of the electrical-discharge machining process. This is one of the most widely used machining processes, particularly for die-sinking operations. (b) Examples of cavities produced by the electrical-discharge machining process, using shaped electrodes. Two round parts (rear) are the set of dies for extruding the aluminum the aluminum piece shown in front. (c) A spiral cavity produced by ECM using a slowly rotating electrode, similar to a screw thread. (a) (b) (c) 27 Rakesh V Adakane, YCCE Nagpur

Examples of EDM:

Examples of EDM Fig : Stepped cavities produced with a square electrode by the EDM process. The work piece moves in the two principal horizontal directions (x-y), and its motion is synchronized with the downward movement of the electrode to produce these cavities. Also shown is a round electrode capable of producing round or elliptical cavities. Fig : Schematic illustration of producing an inner cavity by EDM, using a specially designed electrode with a hinged tip, which is slowly opened and rotated to produce the large cavity. 28 Rakesh V Adakane, YCCE Nagpur

Application:

Application Die sinking of dies of moulding, die casting, plastic moulding, wire drawing, forging, extrusion and press tool. Use of punch as a tool to machine its own mating die is commonly employed in EDM. Blanking of parts from sheets. Small holes about 0.13 mm in dia. And as deep as 20 times dia can be drilled. Orifices or slots in diesel fuel injector nozzels 29 Rakesh V Adakane, YCCE Nagpur

WIRE EDM:

WIRE EDM FIGURE : Schematic illustration of the wire EDM process. As much as 50 hours of machining can be performed with one reel of wire, which is then discarded. 30 Rakesh V Adakane, YCCE Nagpur

Slide 31:

Wire EDM This process is similar to contour cutting with a band saw. a slow moving wire travels along a prescribed path, cutting the work piece with discharge sparks. wire should have sufficient tensile strength and fracture toughness. wire is made of brass, copper or tungsten. (about 0.25mm in diameter). 31 Rakesh V Adakane, YCCE Nagpur

Slide 32:

ULTRA SONIC MACHINING (USM) 32 Rakesh V Adakane, YCCE Nagpur

Slide 33:

Ultrasonic-Machining Process FIGURE 9.19 (a) Schematic illustration of the ultrasonic-machining process by which material is process by which material is removed through micro chipping and erosion. (b) and (c) typical examples of holes produced by ultrasonic machining. Note the dimensions of cut and the types of work piece materials. 33 Rakesh V Adakane, YCCE Nagpur

Slide 34:

Ultrasonic Machining of Ceramics 34 Rakesh V Adakane, YCCE Nagpur

Slide 35:

Ultrasonic waves: Magnetostrictive transducers Magnetostrictive transducers use the magnetostrictive effect to convert magnetic energy into ultrasonic energy. This is accomplished by applying a strong alternating magnetic field to certain metals, alloys and ferrites. Piezoelectric transducers employ the piezoelectric effect using natural or synthetic single crystals (such as quartz) or ceramics (such as barium titanate) which have strong piezoelectric behavior. Ceramics have the advantage over crystals in that they are easier to shape by casting, pressing and extruding. 35 Rakesh V Adakane, YCCE Nagpur

Slide 36:

Principle of Ultrasonic Machining In the process of Ultrasonic Machining, material is removed by micro-chipping or erosion with abrasive particles. In USM process, the tool, made of softer material than that of the work piece, is oscillated by the Booster and Sonotrode at a frequency of about 20 kHz with an amplitude of about 25.4 um (0.001 in). The tool forces the abrasive grits, in the gap between the tool and the work piece, to impact normally and successively on the work surface, thereby machining the work surface. 36 Rakesh V Adakane, YCCE Nagpur

Slide 37:

Principle of Ultrasonic Machining 1- standard mechanism used in most of the universal Ultrasonic machines 37 Rakesh V Adakane, YCCE Nagpur

Slide 38:

Principle of Ultrasonic Machining During one strike, the tool moves down from its most upper remote position with a starting speed at zero, then it speeds up to finally reach the maximum speed at the mean position. Then the tool slows down its speed and eventually reaches zero again at the lowest position. When the grit size is close to the mean position, the tool hits the grit with its full speed. The smaller the grit size, the lesser the momentum it receives from the tool. Therefore, there is an effective speed zone for the tool and, correspondingly there is an effective size range for the grits. 38 Rakesh V Adakane, YCCE Nagpur

Slide 39:

In the machining process, the tool, at some point, impacts on the largest grits, which are forced into the tool and work piece. As the tool continues to move downwards, the force acting on these grits increases rapidly, therefore some of the grits may be fractured. As the tool moves further down, more grits with smaller sizes come in contact with the tool, the force acting on each grit becomes less. Eventually, the tool comes to the end of its strike, the number of grits under impact force from both the tool and the work piece becomes maximum. Grits with size larger than the minimum gap will penetrate into the tool and work surface to different extents according to their diameters and the hardness of both surfaces. Principle of Ultrasonic Machining 39 Rakesh V Adakane, YCCE Nagpur

Slide 40:

Piezoelectric Transducer Piezoelectric transducers utilize crystals like quartz whose dimensions alter when being subjected to electrostatic fields. The charge is directionally proportional to the applied voltage. To obtain high amplitude vibrations the length of the crystal must be matched to the frequency of the generator which produces resonant conditions. Magnetostictive transducer Magnetostictive transducers work on the principle that if a piece of Ferro-magnetic material (like nickel) is magnetized, then a change in dimension occurs. The transducer has solenoid type winding of wire over a stack of nickel laminations (which has rapid dimensional change when placed in magnetic fields) and is fed with an A.C supply with frequencies up to 25,000 c/s. 40 Rakesh V Adakane, YCCE Nagpur

Slide 41:

Abrasive Slurry The abrasive slurry contains fine abrasive grains. The grains are usually boron carbide, aluminum oxide, or silicon carbide ranging in grain size from 100 for roughing to 1000 for finishing. It is used to microchip or erode the work piece surface and it is also used to carry debris away from the cutting area. Tool holder The shape of the tool holder is cylindrical or conical, or a modified cone which helps in magnifying the tool tip vibrations. In order to reduce the fatigue failures, it should be free from nicks, scratches and tool marks and polished smooth. 41 Rakesh V Adakane, YCCE Nagpur

Slide 42:

Tool Tool material should be tough and ductile. Low carbon steels and stainless steels give good performance. Tools are usually 25 mm long ; its size is equal to the hole size minus twice the size of abrasives. Mass of tool should be minimum possible so that it does not absorb the ultrasonic energy. 42 Rakesh V Adakane, YCCE Nagpur

Slide 43:

Materials that can be machined on USM Hard materials like stainless steel, glass, ceramics, carbide, quatz and semi-conductors are machined by this process. It has been efficiently applied to machine glass, ceramics, precision minerals stones, tungsten. Brittle materials Applications It is mainly used for (1) drilling (2) grinding, (3) Profiling (4) coining (5) piercing of dies (6) welding operations on all materials which can be treated suitably by abrasives. 43 Rakesh V Adakane, YCCE Nagpur

Slide 44:

Advantages of USM Machining any materials regardless of their conductivity USM apply to machining semi-conductor such as silicon, germanium etc. USM is suitable to precise machining brittle material. USM does not produce electric, thermal, chemical abnormal surface. Can drill circular or non-circular holes in very hard materials Less stress because of its non-thermal characteristics Disadvantages of USM USM has low material removal rate. Tool wears fast in USM. Machining area and depth is restraint in USM. 44 Rakesh V Adakane, YCCE Nagpur

Slide 45:

Laser Beam Machining 45 Rakesh V Adakane, YCCE Nagpur

Laser Beam Machining:

Laser Beam Machining Fig : Schematic illustration of the laser-beam machining process. ) Examples of holes produced in nonmetallic parts by LBM. 46 Rakesh V Adakane, YCCE Nagpur

LASER BEAM MACHINING:

LASER BEAM MACHINING 47 Rakesh V Adakane, YCCE Nagpur

Slide 48:

Laser beam machining (LBM) In LBM laser is focused and the work piece which melts and evaporates portions of the work piece. Low reflectivity and thermal conductivity of the work piece surface, and low specific heat and latent heat of melting and evaporation – increases process efficiency. application - holes with depth-to-diameter ratios of 50 to 1 can be drilled. e.g. bleeder holes for fuel-pump covers, lubrication holes in transmission hubs. 48 Rakesh V Adakane, YCCE Nagpur

Laser Beam Machining:

Laser Beam Machining Laser Concept Add energy to make electrons “jump” to higher energy orbit Electron “relaxes” and moves to equilibrium at ground-state energy level Emits a photon in this process (key laser component) Two mirrors reflect the photons back and forth and “excite” more electrons One mirror is partially reflective to allow some light to pass through: creates narrow laser beam Photon Emission Model Nucleus Electron Ground State Excited State Orbits Photon Electron is energized to the excited state Electron relaxes to ground state and photon is produced 49 Rakesh V Adakane, YCCE Nagpur

Slide 50:

More precise Useful with a variety of materials: metals, composites, plastics, and ceramics Smooth, clean cuts Faster process Decreased heat-affected zone Laser Beam Machining 50 Rakesh V Adakane, YCCE Nagpur

Slide 51:

ADVANTAGES Non contact process with no surface distortion. Minimum heat affected zone. Inaccessible areas can be processed. Multiple holes and welds are possible in one exposure. Precise operation. Does not need vacuum. APPLICATION Micromachining, holes as small as 0.005 mm. Holes in rubber baby bottle nipples Holes in nylon buttons Holes in spray nozzles, surgical and hypodermic needles, flow holes in gas and oil orifices. 51 Rakesh V Adakane, YCCE Nagpur

Slide 52:

ELECTRON BEAM MACHINING 52 Rakesh V Adakane, YCCE Nagpur

Electron-Beam Machining:

Electron-Beam Machining Fig : Schematic illustration of the electron-beam machining process. Unlike LBM, this process requires a vacuum, so workpiece size is limited to the size is limited to the size of the vacuum chamber. 53 Rakesh V Adakane, YCCE Nagpur

Slide 54:

Cutting and hole making on thin materials; very small holes and slots (0.1-0.3mm depending on thickness); heat affected zone; require vacuum, expensive equipment; 1-2 mm 3 /min. Electron beam machining ( line diagram) 54 Rakesh V Adakane, YCCE Nagpur

Slide 55:

Electron Beam Machining EBM is a metal removal process by a high velocity focused stream of electrons. As the electrons strike the work piece with high velocity , their kinetic energy is transformed into thermal energy which melts and vaporizes the material. The production of free electrons ( negatively charged particles) are obtained by electron gun. Due to pattern of electrostatic field produced by grid cup, electrons are focused and made to flow in the form of a converging beam through anode. The electrons are accelerated while passing through the anode by applying high voltage at anode A magnetic deflection coil is used to make electron beam circular and to focus electron beam at a point ( localized heating) The process is carried out in a vacuum chamber to prevent electrons from colliding with molecules of the atmospheric air and to prevent tungsten filament from getting oxidizing with air 55 Rakesh V Adakane, YCCE Nagpur

Slide 56:

Disadvantages of EBM Very small holes can be machined in every type of material with high accuracy There is no mechanical contact between tool and work piece, hence no tool wear. Advantages of EBM 1. Cost of equipment is high 2. Rate of material removal is low 3 . It can used for small cuts only 4 . Vacuum requirements limits the size of work piece Application of EBM Drilling of holes in pressure differential devices used in nuclear reactors, air craft engine Machining of wire drawing dies having small cross sectional area. 56 Rakesh V Adakane, YCCE Nagpur

Slide 57:

ABRASIVE JET MACHINING (AJM) 57 Rakesh V Adakane, YCCE Nagpur

Abrasive Jet Machining:

Abrasive Jet Machining Fig : Schematic illustration of Abrasive Jet Machining 58 Rakesh V Adakane, YCCE Nagpur

Slide 59:

Abrasive Jet Machining (AJM) In AJM a high velocity jet of dry air, nitrogen or CO2 containing abrasive particles is aimed at the work piece. Jet velocity is about 300 m/s The impact of the particles produce sufficient force to cut small hole or slots, deburring, trimming and removing oxides and other surface films. 59 Rakesh V Adakane, YCCE Nagpur

Slide 60:

Abrasive particle Aluminium oxide, silicon carbide, dolomite, glass powder Best cutting achieved at grain size 15-20 µm Gas Dry air, nitrogen or CO2 Gas flow at 150-300 m/s Nozzle Made of tungsten carbide(WC) or sapphire Area of orifice 0.05-.2 mm 2 WC last for 12-36 Hrs Sapphire lasts for300 Hrs 60 Rakesh V Adakane, YCCE Nagpur

Slide 61:

Advantages: Used for Hard and brittle metals, alloys and non metallic materials like germanium, silicon, glass, ceramics and mica. Amount of heat generated is not appreciable. Suitable for thin section Limitations: Not suitable for ductile material. Metal removal is slow. Abrasive powder once used can not be reused. Applications: Machining semi conductor like silicon, germanium. Making holes and slots in , glass, ceramics, quartz and mica. Cleaning ,deburring, scribing, polishing. Rakesh V Adakane, YCCE Nagpur 61

Slide 62:

WATER JET MACHINING (WJM) 62 Rakesh V Adakane, YCCE Nagpur

Water Jet Machining / Water jet cutting:

Water Jet Machining / Water jet cutting 63 Rakesh V Adakane, YCCE Nagpur

Slide 64:

Water jet machining (WJT) Water jet acts like a saw and cuts a narrow groove in the material. Pressure level of the jet is about 400MPa. Advantages - no heat produced - cut can be started anywhere without the need for predrilled holes - burr produced is minimum - environmentally safe and friendly manufacturing. Application – used for cutting composites, plastics, fabrics, rubber, wood products etc. Also used in food processing industry. 64 Rakesh V Adakane, YCCE Nagpur

Water Jet and Abrasive Water Jet Cutting:

Water Jet and Abrasive Water Jet Cutting Nozzle blast during cutting 65 Rakesh V Adakane, YCCE Nagpur

Water Jets & Abrasive Water Jets:

Water Jets & Abrasive Water Jets Water jets are used for soft material Abrasive water jets for hard material An abrasive element is added to the water beam to assist cutting Abrasive Water Jet Nozzle Diagram 66 Rakesh V Adakane, YCCE Nagpur

Water Jets & Abrasive Water Jets:

Water Jets & Abrasive Water Jets Water Jet Machinable Materials Soft rubber, foam, tin foil, carpet, soft gasket material Abrasive Water Jet Machinable Materials Titanium, aluminum, hard rubber, hardened tool steel 67 Rakesh V Adakane, YCCE Nagpur

Abrasive Waterjet and Waterjet Part Examples:

Abrasive Waterjet and Waterjet Part Examples Ceramic part cut with an abrasive water jet 68 Rakesh V Adakane, YCCE Nagpur

Slide 69:

Advantages of Water Jets Cuts all sorts of material with a single tool Minimum heat generation, material properties unaffected (unlike most other machining equipment) Makes it own start holes (unlike Electro Discharge Machinery) Smooth finish Cheaper than most machining options Programmable systems make accurate shapes with very good tolerances (+/- 0.02 inches ) Disadvantages of Water Jets Tolerances deteriorate with material hardness and thickness Abrasive water jet nozzles are subject to heavy wear hence increasing the maintenance cost 69 Rakesh V Adakane, YCCE Nagpur

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