KNOWLEDGE INSTITUTE OF TECHNOLOGY DEPARTMENT OF MECHANICAL ENGINEERING
UNCONVENTIONAL MACHINING PROCESS
UNIT I - INTRODUCTION
Unconventional Machining Process – Need – Classification &
Brief overview.
MECH-KIOT Machining Processes
Machining Processes
Conventional Abrasive Nontraditional
Turning Drilling Milling Other Grinding Lapping Mechanical Energy Polishing Other Electrochemical Thermal Energy Chemical Machining
MECH-KIOT To reduce machining costs • Avoid excess machining allowances during primary processing • Achieve rough shape as “near net” as possible eg. Die casting a piston instead of sand casting reduces machining • Optimize initial shaping and final machining regarding the aspects like machine tools, cutting tools and cutting parameters
MECH-KIOT Single – Point Tools
Surface of revolution Plane (Job Surfaces rotating)
Tool Feed parallel to axis Feed not parallel Job reciprocates reciprocates of rotation to axis of rotation shaping slotting (Cylindrical planing surfaces)
External Internal turning, boring screw internal cutting screw cutting
At any angle Simultaneous (Conical two axes motion surfaces) contouring, copy turning External taper Internal turning, Taper facing boring
MECH-KIOT Multi – Point Tools
Cylindrical Surface Plane Surfaces
Two edge Multi edge Sizeable Chips Small Chips (Grinding) Surface Cutting cutting (Milling) Plane milling Broaching grinding Lapping drilling Gear shaping
Sizeable Chips (Milling, Gear Small Chips cutting) Spiral milling (Grinding) Gear hobbing Cylindrical grinding Centre less grinding
MECH-KIOT PEMP EMM2512
MECH-KIOT MECH-KIOT PEMP EMM2512
MECH-KIOT PEMP EMM2512
MECH-KIOT BASIC RULES OF METAL CUTTING • Strong cutting tools with good support • Strong m/c to avoid bending / twisting • Strong dovetail slide ways to give good support • Non excessive depth of cut • Secured work piece holding • Cutting force application to avoid work piece deformation
MECH-KIOT WORK PIECE HOLDING CONSIDERATIONS • Chip removal • Access for cutting tool • Design the components to facilitate holding during machining • Avoid / reduce frequency of work removal and re-setting • Use correct Fixtures and Jigs (if need be)
MECH-KIOT INTRODUCTION Mechanical Engineering
Design Manufacturing Thermal
Primary Manufacturing
Secondary Manufacturing
MECH-KIOT INTRODUCTION
• What is Manufacturing?
MECH-KIOT INTRODUCTION
Material removal processes can be further divided into mainly two groups 1. Conventional Machining Processes 2. Un Conventional Manufacturing Processes Examples of conventional machining processes are turning, boring, milling, shaping, broaching, slotting, grinding etc. Examples of non conventional ( or also called non traditional or unconventional) are 1. Abrasive Jet Machining (AJM), 2. Ultrasonic Machining (USM), 3. Water Jet and Abrasive Water Jet Machining (WJM and AWJM), 4. Electro-discharge Machining (EDM) , 5. Electro Chemical Machining (ECM).
MECH-KIOT CONVENTIONAL MACHINING PROCESS
MECH-KIOT Basic Process
MECH-KIOT Turning
Fig-2 Basic scheme of Turning • To produce rotational, axis-symmetric parts. • Feed motion • Feed relative to work piece.
MECH-KIOT Turning Operations • Facing • Parting • Grooving • Drilling • Screw cutting Workpiece Materials • Aluminum • Brass • Plastics • Cast Iron • Mild Steel
MECH-KIOT Drilling
• Drilling Operations • Reaming • Tapping • Counterboring • Countersinking Fig-3 Basic scheme of Drilling • Centering • Spot facing
MECH-KIOT Workpiece Materials • Aluminum alloys • Magnesium alloys • Copper alloys • Stainless steels • Cast iron • Plastics
MECH-KIOT Milling
Fig-4 Basic scheme of Milling
MECH-KIOT Milling Operations
• Slab Milling • Face Milling • End Milling
Fig-5 Slab Milling Fig-6 Face Milling
MECH-KIOT Workpiece Materials • Aluminum • Brass • Magnesium • Nickel • Steel • Thermostat plastics • Titanium • Zinc
MECH-KIOT Boring
Fig-7 Boring operation
MECH-KIOT Boring Operations • Single-Edge Boring • Multi-Edge Boring • Step Boring • Reaming
Workpiece Materials • Aluminum • Brass • Plastics • Cast Iron • Mild Steel MECH-KIOT Broaching
Fig-8 Broaching Tool Broaching Operations
• Surface Broaching • Pull down Broaching • Push Broaching
• Pot Broaching MECH-KIOT Workpiece Materials
• Aluminum • Brass • Bronze • Plastic • Malleable Iron
MECH-KIOT Ref: Tool and Manufacturing Engineers Handbook– Tom Drozda, Charles Wick, John T. Benedict, Raymond F. Veilleux Shaping
Fig-9 Basic scheme of Shaping
MECH-KIOT Planing
Fig-11 Basic scheme of Planing
MECH-KIOT INTRODUCTION
Types of Manufacturing Processes: • Manufacturing processes can be broadly divided into two groups 1. Primary manufacturing processes 2. Secondary manufacturing processes. • The Primary manufacturing process provides basic shape and size to the material as per designer’s requirement. For example: Casting, forming, powder metallurgy processes provide the basic shape and size. • The Secondary manufacturing processes provide the final shape and size with tighter control on dimension, surface characteristics etc. Most of Material removal processes are mainly the secondary manufacturing processes.
MECH-KIOT COMPARISON
Conventional Non Conventional Generally macroscopic chip Material removal may occur with chip formation or even no chip formation by shear deformation. formation may take place. For example in AJM, chips are of microscopic size and in case of Electrochemical machining material removal occurs due to electrochemical dissolution at Chip atomic level Formation Tool There may be a physical tool There may not be a physical tool present. For example in laser jet present. for example a cutting tool machining, machining is carried out by laser beam. However in in a Lathe Machine, Electrochemical Machining there is a physical tool that is very much required for machining.
MECH-KIOT Conventional Non Conventional Cutting tool is harder than work piece at room There may not be a physical tool temperature as well as under machining conditions present. For example in laser jet machining, machining is carried out by laser beam. However in Characteristic of Electrochemical Machining there is Tool a physical tool that is very much required for machining.
Material removal takes place due to application of Mostly NTM processes do not cutting forces – energy domain can be classified as necessarily use mechanical energy mechanical to provide material removal. They Material Removal use different energy domains to Process provide machining. For example, in USM, AJM, WJM mechanical energy is used to machine material, whereas in ECM electrochemical dissolution constitutes material removal.
MECH-KIOT Conventional Non Conventional
Conventional machining involves the direct contact of tool and work Whereas unconventional machining does not Tool Contact –piece require the direct contact of tool and work piece.
Surface Finish Lower accuracy and surface finish. Higher accuracy and surface finish.
MECH-KIOT Conventional Non Conventional Suitable for every type of material Not Suitable for every type of Material Economy economically. material economically
Tool life is less due to high surface Tool life is more Tool Life contact and wear.
Material Wastage Higher waste of material due to Lower waste of material due to low high wear. or no wear.
Noise Level Noisy operation mostly cause sound Quieter operation mostly no sound pollutions pollutions are produced.
Cost Lower capital cost Higher Capital Cost
MECH-KIOT Conventional Non Conventional Equipment Setup Easy set-up of equipment. Complex set-up equipment.
Operator level Skilled or un-skilled operator may Skilled operator required. required
Process Generally they are manual to Generally they are fully automated operate. process.
Efficiency They cannot be used to produce Can be used to produce prototype prototype parts very efficiently and parts very efficiently And economically. economically.
Spare Parts Easily Available Not so easily available
MECH-KIOT Conventional Vs Unconventional 1) Conventional machining process involved tool wearing as there is a physical contact between the tool and the work piece. In non-conventional process, this is not the case. 2) Non-conventional tools are more accurate and precise than the conventional tool. 3) No noise pollution is created as a result of non-conventional methods as these tools are much quieter. 4) Tool life is long for non-conventional processing. 5) Non-conventional tools are very expensive than the conventional tools. 6) Non-conventional tools have complex setup and hence requires a skilful operation by expert workers, whereas conventional tools do not require any special expert for its operation and are quite simple in set-up.
Conventional Vs Unconventional
7) Spare parts of conventional machines are easily available but not for non-conventional machines. 8) Extremely hard material can be cut easily with the help of non conventional machining but for conventional machining raw material should be less hard than cutting tool. 9) In conventional machining: Material removal takes place due to application of cutting forces – energy domain can be classified as mechanical. In Non Conventional Machining :Mostly NTM processes do not necessarily use mechanical energy to provide material removal. They use different energy domains to provide machining. For example, in USM, AJM, WJM mechanical energy is used to machine material, whereas in ECM electrochemical dissolution constitutes material removal. Conventional Vs Unconventional
10) Non Conventional machines can handle very complex jobs as compare to Conventional machining. 11) In Conventional machining because of scrap and chip formation more wastage of material .In case of non conventional machining no chip formation hence less scrap.
UNIT II - MECHANICAL ENERGY BASED PROCESSES
Abrasive Jet Machining – Water Jet Machining – Abrasive Water Jet Machining - Ultrasonic Machining.(AJM, WJM, AWJM and USM). Working Principles – Equipment Used – Process Parameters – MRR
MECH-KIOT PEMP EMM2512
MECH-KIOT PEMP EMM2512
MECH-KIOT PEMP EMM2512 Introduction
• Advanced Machining Processes or NTM can be used when mechanical methods are not satisfactory, economical or possible due to: – High strength or hardness – Too brittle or too flexible – Complex shapes – Special finish and dimensional tolerance requirements – Temperature rise and residual stresses
MECH-KIOT Introduction
• These advanced methods began to be introduced in the 1940's. • Removes material by chemical dissolution, etching, melting, evaporation, and hydrodynamic action. • These requirements led to chemical, electrical, laser, and high-energy beams as energy sources for removing material from metallic or non-metallic workpieces.
MECH-KIOT NTM Classification • Mechanical processes – Ultrasonic machining – Ultrasonically assisted machining – Rotary ultrasonically assisted machining – Abrasive jet machining – Water jet cutting – Abrasive water jet cutting • Electrical processes – Electrochemical machining – Electrochemical grinding – Electrochemical deburring – Electrochemical honing – Shaped tube electrolytic machining
MECH-KIOT NTM Classification
• Thermal processes – Electron beam machining – Laser beam machining – Electric discharge machining – Electric discharge wire cutting – Plasma arc machining – Plasma-assisted machining – Thermal deburring • Chemical processes – Chemical material removal – Chemical milling – Chemical blanking – Chemical engraving
MECH-KIOT P
M.S Ramaiah School of Advanced Studies - Bangalore 22
MECH-KIOT Mechanical Processing Ultra Sonic Machining • Hard materials(USM) like stainless steel, glass, ceramics, carbide, quartz and semi-conductors are machined by this process. • It has been efficiently applied to machine glass, ceramics, precision minerals stones, tungsten. • Brittle materials
MECH-KIOT Principle of Ultrasonic Machining • Material removal due to combination of four mechanisms – Hammering of abrasive particles in the work surface by the tool – Impact of free abrasive particles on the work surface – Cavitation erosion – Chemical action associated with the fluid employed
MECH-KIOT Principle of Ultrasonic Machining • In USM process, the tool, made of softer material than that of the workpiece, is oscillated by the Booster and Sonotrode at a frequency of about 20 kHz with an amplitude of about 25.4 m (0.001 in). • The tool forces the abrasive grits, in the gap between the tool and the workpiece, to impact normally and successively on the work surface, thereby machining the work surface.
MECH-KIOT Principle of Ultrasonic Machining
This is the standard mechanism used in most of the universal Ultrasonic machines
MECH-KIOT PEMP Principle of Ultrasonic EMM2512 • During oneMachining 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. • In the machining process, the tool, at some point, impacts on the largest grits, which are forced into the tool and workpiece.
MECH-KIOT • 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 workpiece 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.
MECH-KIOT Various work samples machined by USM
A plastic sample that has inner A plastic sample that has complex grooves that are machined using details on the surface USM A coin with the grooving done by USM
MECH-KIOT Mechanism
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.
MECH-KIOT Mechanis m
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.
MECH-KIOT Mechanis m 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.
MECH-KIOT Application s It is mainly used for • Drilling • Grinding, • Profiling • Coining • Piercing of dies
MECH-KIOT 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
MECH-KIOT Disadvantages of USM • USM has low material removal rate. • Tool wears fast in USM. • Machining area and depth is restraint in USM.
MECH-KIOT USM Characteristics Principle Oscillating tool in water-Abrasive slurry Abrasive B4C, Al2O3, SiC 100 to 800 grit size Frequency 15-30KHz Amplitude 0.03 to 0.10mm Tool material Soft tool steel Stock removal WC=1.5in (38mm) Glass=100in(254cm) Critical parameters Frequency, amplitude, tool holder shape, grit size, hole depth, slurry
Material application Metals and alloys (particularly hard metals) Non-metallic
Part applications Round and irregular holes Limitations Low metal removal rate Tool wear Hole depth
MECH-KIOT Water Jet Machining & Abrasive Water Jet Machining - Definition
• In these processes (WJM and AJWM), the mechanical energy of water and
abrasive phases are used to achieve material removal or machining.
MECH-KIOT Water Jet Machining & Abrasive Water Jet Machining
• WJM and AWJM can be achieved using different approaches and methodologies as enumerated below: • WJM - Pure • WJM - with stabilizer • AWJM – entrained – three phase – abrasive, water and air • AWJM – suspended – two phase – abrasive and water.
o Direct pumping o Indirect pumping o Bypass pumping
MECH-KIOT Water Jet Machining & Abrasive Water Jet Machining - Process
• Water is pumped at a sufficiently high pressure, 200-400 MPa (2000-4000 bar) using intensifier technology.
• Water at such pressure is issued through a suitable orifice (generally of 0.2-
0.4 mm dia).
• Potential energy of water is converted into kinetic energy, yielding a high velocity jet (1000 m/s).
MECH-KIOT Water Jet Machining
• In pure WJM, commercially pure water (tap water) is used for machining purpose. However as the high velocity water jet is discharged from the orifice, the jet tends to entrain atmospheric air and flares out decreasing its cutting ability.
• Hence, quite often stabilisers (long chain polymers) that hinder the fragmentation of water jet are added to the water.
MECH-KIOT Abrasive Water Jet Machining
• In AWJM, abrasive particles like sand (SiO2), glass beads are added to the water jet to enhance its cutting ability by many folds.
• AWJ are mainly of two types – entrained and suspended type as mentioned earlier.
• In entrained type AWJM, the abrasive particles are allowed to entrain in water jet to form abrasive water jet with significant velocity of 800 m/s.
MECH-KIOT Abrasive Water Jet Machining – Setup Entrained Type • LP Booster
• Hydraulic Drive
• Additive Mixer
• Direction Control
• Intensifier
• LP Intensifier
• HP Intensifier
• Accumulator
MECH-KIOT Abrasive Water Jet Machining(entrained) – Cutting Head • Diameter of the orifice 0.2 - 0.4mm.
• The velocity of the water jet is estimated, assuming no losses as vwj = (2pw / ρw)1/2 using Bernoulli’s equation where, pw is the water pressure and ρw is the density of water.
• The orifices are typically made of sapphire.
• Life of Sapphire 100-150 hours.
MECH-KIOT Abrasive Water Jet Machining(entrained) – Mixing
• Mixing means gradual entrainment of abrasive particles within the water jet and finally the abrasive water jet comes out of the focussing tube or the nozzle. MECH-KIOT Abrasive Water Jet Machining(entrained) – Mixing • Focussing tube is made up of Tungsten Carbide.
• Usual Dimensions of focussing tube
. Inner diameter : 0.8-1.6
. Length : 50-80mm.
• Tungsten Carbide is used due to its abrasive resistant property.
MECH-KIOT Abrasive Water Jet Machining – Suspended Type In suspension AWJM the abrasive water jet is formed quite differently.
There are three different types of suspension AWJ formed by direct, indirect and Bypass pumping method.
In suspension AWJM, preformed mixture of water and abrasive particles is pumped to a sufficiently high pressure and stored in pressure vessel.
MECH-KIOT Abrasive Water Jet Machining – Suspended Type Indirect Pumping Bypass Pumping
MECH-KIOT Abrasive Water Jet Machining – Catcher
“Catcher” is used to absorb the residual energy of the AWJ and dissipate the same.
Other Types: Pocket Type & Line Type
MECH-KIOT Water Jet &Abrasive Water Jet Machining – Applications
Paint removal Cleaning Cutting soft materials Cutting frozen meat Textile, Leather industry Mass Immunization Surgery Peening Cutting Pocket Milling Drilling Turning Nuclear Plant Dismantling
MECH-KIOT Water Jet &Abrasive Water Jet Machining – Materials
Steels Non-ferrous alloys Ti alloys, Ni- alloys Polymers Honeycombs Metal Matrix Composite Ceramic Matrix Composite Concrete Stone – Granite Wood Reinforced plastics Metal Polymer Laminates Glass Fibre Metal Laminates
MECH-KIOT PEMP EMM2512 Water Jet Machining • Also known as hydrodynamic machining • The water jet acts as a saw and cuts a narrow groove in the material • Pressures range from 60ksi to 200ksi (1500- 4000 MN/m2 ) • Jet velocity > 900m/s
MECH-KIOT PEMP EMM2512 Water Jet Machining
c (a) Schematic illustration of water-jet machining. (b) A computer-controlled, water-jet cutting machine cutting a granite plate. (c) Example of various nonmetallic parts produced by the water- jet cutting process.
MECH-KIOT PEMP EMM2512 Water Jet Machining • Process capabilities – Can be used on any material up to 1” thick – Cuts can be started at any location without predrilled holes – No heat produced – No flex to the material being cut • Suitable for flexible materials – Little wetting of the workpiece – Little to no burr produced – Environmentally safe
MECH-KIOT PEMP EMM2512 Pros and Cons • Pros: – No work hardening of pieces – Faster than EDM or Laser – Initial cost is less • Cons: – Accuracy is poor (0.003 inch) – Nozzle life is short (40 hours)
MECH-KIOT PEMP EMM2512 Abrasive Jet Machining
• Uses high velocity dry air, nitrogen, or carbon dioxide containing abrasive particles • Supply pressure is on the order of 125psi • The abrasive jet velocity can be as high as 100 ft/sec • Abrasive size is approximately 400- 2000 micro-inches
MECH-KIOT PEMP EMM2512 Abrasive Jet Machining
Schematic illustration of Abrasive Jet Machining
MECH-KIOT PEMP EMM2512 Abrasive Water Jet Machining • Very similar to water jet machining – Water contains abrasive material • Silicon carbide • Aluminum oxide – Higher cutting speed than that of conventional water jet machining • Up to 25 ft/min (7.5 m/min) for reinforce plastics – Minimum hole diameter thus far is approximately 0.12 inches (3 mm) – Maximum hole depth is approximately 1 inch (25mm)
MECH-KIOT Surface Roughness and Tolerance PEMP table EMM2512
M.S Ramaiah School of AdvancedMECH Studies-KIOT - Bangalore 49 UNIT III - ELECTRICAL ENERGY BASED PROCESSES
Electric Discharge Machining (EDM)- working Principle- equipment's -Process Parameters-Surface Finish and MRR- electrode / Tool – Power and control Circuits-Tool Wear – Dielectric – Flushing – Wire cut EDM – Applications.
MECH-KIOT PEMP EMM2512 Electrochemical Machining
• An electrolyte acts as a current carrier which washes metal ions away from the workpiece (anode) before they have a chance to plate on the tool (cathode). • The shaped tool is either solid or tubular. • Generally made of brass, copper, bronze or stainless steel. • The electrolyte is a highly conductive inorganic fluid. • The cavity produced is the female mating image of the tool shape
MECH-KIOT PEMP EMM2512 V CIt gr R A EA I gr C(EAt) V gr V f CE At r gr CI V: Volume of Metal Removed; C: Specific Removal Rate f R: Resistance; g: Gap between Electrode and Work r r: Resistivity of Electrode; E: Applied Voltage A
I: Current; t: Time; fr: Feed Rate
MECH-KIOT PEMP EMM2512 Electrochemical Machining • Process capabilities – Generally used to machine complex cavities and shapes in high strength materials. • Design considerations – Not suited for producing sharp square corners or flat bottoms. – No irregular cavities.
MECH-KIOT PEMP EMM2512
Typical parts made by electrochemical machining. (a) Turbine blade made of a nickel alloy, 360 HB; note the shape of the electrode on the right. (b) Thin slots on a 4340-steel roller-bearing cage. (c) Integral airfoils on a compressor disk.
MECH-KIOT PEMP EMM2512 • Pulsed electrochemical machining (PECM) – Refinement of ECM. – The current is pulsed instead of a direct current. – Lower electrolyte flow rate. – Improves fatigue life. – Tolerance obtained 20 to 100 micro-meters. (a) (b)
(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.
MECH-KIOT 57 PEMP EMM2512 • Electrochemical grinding (ECG) – Combines ECM with conventional grinding. – Similar to a conventional grinder, except that the wheel is a rotating cathode with abrasive particles. • The abrasive particles serve as insulators and they remove electrolytic products from the working area. – Less then 5% of the metal is removed by the abrasive action of the wheel.
Schematic illustration of the electrochemical – grinding process. (b) Thin slot produced on a round nickel – alloy tube by this process.
MECH-KIOT PEMP EMM2512 • Electrochemical honing – Combines the fine abrasive action of honing with electrochemical action. – Costs more than conventional honing. – 5 times faster than conventional honing. – The tool lasts up to 10 times longer. • Design considerations for ECG – Avoid sharp inside radii.
MECH-KIOT PEMP EMM2512 Electric Discharge Machining (EDM) • Principle of operation – Based on the erosion of metal by spark discharge • Components of operation – Shaped tool • Electrode – Workpiece • Connected to a DC power supply – Dielectric • Nonconductive fluid
MECH-KIOT PEMP EMM2512 (a) (b) (c)
(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.
MECH-KIOT Electric Discharge Machining • When the potential difference is sufficiently high, the dielectric breaks down and a transient spark discharges through the fluid, removing a very small amount of material from the workpiece • Capacitor discharge – 200-500 kHz • This process can be used on any electrically conductive material
MECH-KIOT Electric Discharge Machining Example A certain alloy whose melting point = 1100 C is to be machined in an EDM operation. If discharged current = 25 amps, what is the expected metal removal rate?
1.23 Use Equation (MRR=KI/T ), them anticipated metal removal rate is MRR = 664 (25)/(11001.23) = 3.01 mm3/s
KI MRR T 1.23
MECH-KIOT Electric Discharge Machining • Movement in the X&Y axis is controlled by CNC systems • Overcut (in the Z axis) is the gap between the electrode and the workpiece – Controlled by servomechanisms – Critical to maintain a constant gap
MECH-KIOT Electric Discharge Machining
• Dielectric fluids – Act as a dielectric – Provide a cooling medium – Provide a flushing medium • Common fluids – Mineral oils – Distilled/Deionized water – Kerosene – Other clear low viscosity fluids are available which are easier to clean but more expensive
MECH-KIOT Electric Discharge Machining • Electrodes – Graphite – Brass – Copper-tungsten alloys – Formed by casting, powder metallurgy, or CNC machining – On right, human hair with a 0.0012 inch hole drilled through
MECH-KIOT Electric Discharge Machining
• Electrode wear – Important factor in maintaining the gap between the electrode and the workpiece – Wear ratio is defined as the amount of material removed to the volume of electrode wear • 3:1 to 100:1 is typical – No-wear EDM is defined as the EDM process with reversed polarity using copper electrodes
MECH-KIOT Electric Discharge Machining
• Process capabilities – Used in the forming of dies for forging, extrusion, die casting, and injection molding – Typically intricate shapes
MECH-KIOT Electric Discharge Machining • Material removal rates affect finish quality – High removal rates produce very rough surface finish with poor surface integrity – Finishing cuts are often made at low removal rates so surface finish can be improved • Design considerations – Design so that electrodes can be simple/economical to produce – Deep slots and narrow openings should be avoided – Conventional techniques should be used to remove the bulk of material
MECH-KIOT PEMP
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.
MECH-KIOT Wire EDM • Similar to contour cutting with a bandsaw • Typically used to cut thicker material – Up to 12” thick – Also used to make punches, tools and dies from hard materials
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.
MECH-KIOT Wire EDM • Wire – Usually made of brass, copper, or tungsten – Range in diameter from 0.012 – 0.008 inches – Typically used at 60% of tensile strength – Used once since it is relatively inexpensive – Travels at a constant velocity ranging from 6-360 in/min – Cutting speed is measured in cross sectional area per unit time (varies with material) • 18,000 mm^2/hour • 28 in^2/hour
MECH-KIOT Wire EDM • Multiaxis EDM – Computer controls for controlling the cutting path of the wire and its angle with respect to the workpiece plane – Multiheads for cutting multiple parts – Features to prevent and correct wire breakage – Programming to optimize the operation
MECH-KIOT Electric Discharge Grinding • Similar to the standard grinder • Grinding wheel is made of graphite or brass and contains no abrasives • Material is removed by spark discharge between the workpiece and rotating wheel • Typically used to sharpen carbide tools and dies • Can also be used on fragile parts such as surgical needles, thin-wall tubes, and honeycomb structures • Process can be combined with electrochemical discharge grinding • Material removal rate is similar to that of EDM – MRR = KI where K is the workpiece material factor in mm^3/A- min
MECH-KIOT Laser Beam Machining • The source of the energy is the laser – Light Amplification by Stimulated Emission of Radiation • The focus of optical energy on the surface of the workpiece melts and evaporates portions of the workpiece in a controlled manner – Works on both metallic and non-metallic materials • Important considerations include the reflectivity and thermal conductivity of the material • The lower these quantities the more efficient the process
MECH-KIOT (a) Schematic illustration of the laser-beam machining process. (b) and (c) Examples of holes produced in nonmetallic parts by LBM. MECH-KIOT Laser Beam Machining • Lasers may be used in conjunction with a gas such as oxygen, nitrogen, or argon to aid in energy absorption – Commonly referred to as laser beam torches – The gas helps blow away molten and vaporized material • Process capabilities also include welding, localized heat treating, and marking • Very flexible process – Fiber optic beam delivery – Simple fixtures – Low setup times
MECH-KIOT Laser Beam Machining • Design considerations – Sharp corners should be avoided – Deep cuts will produce tapered walls – Reflectivity is an important consideration • Dull and unpolished surfaces are preferable – Any adverse effects on the properties of the machined materials caused by the high local temperatures and heat affected zones should be investigated
MECH-KIOT Electron Beam Machining • Energy source is high velocity electrons which strike the workpiece • Voltages range from 50- 200kV • Electron speeds range from 50- 80% the speed of light • Requires vacuum
MECH-KIOT Electron Beam Machining
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.
MECH-KIOT Plasma Arc cutting – Ionized gas is used to rapidly cut ferrous and nonferrous sheets and plates – Temperatures range from 9400-17,000 F (> 100000 C) – The process is fast, the kerf width is small, and the surface finish is good – Parts as thick as 6” can be cut – Much faster than the EDM and LBM process – Design considerations • Parts must fit in vacuum chamber • Parts that only require EBM machining on a small portion should be manufactured as a number of smaller components
MECH-KIOT Laser cutting Light Amplification by Stimulated Emission of Radiation • High energy density (small focus area) • Uses: Cutting, welding, precision holes
• Common lasers: CO2, Nd:YAG • Continuous power or Pulsed (more precise)
Nd:YAG laser cut: larger dia and heat-affected zone
Femtosecond laser cut: smaller diameter, lower thermal damage Microscope image of laser cut hole
MECH-KIOT Cost of Machining/Surface Finish Required
Increase in the cost of machining and finishing a part as a function of the surface finish required.
MECH-KIOT Ultrasonic Machining - Definition • Ultrasonic Machining is a non-traditional process, in which abrasives contained in a slurry are driven against the work by a tool of desired shape oscillating at low amplitude (25-100 microns) and high frequency (15-30 kHz)
MECH-KIOT Ultrasonic Machining - Process • It is employed to machine hard and brittle materials (both electrically conductive and non conductive material) having hardness usually greater than 40 HRC.
MECH-KIOT Ultrasonic Machining - Process • In Ultrasonic machining material removal is due to crack initiation, propagation and brittle fracture of material.
MECH-KIOT Ultrasonic Machining - Process
MECH-KIOT Ultrasonic Machining - Process High power sine wave generator • This unit converts low frequency (60 Hz) electrical power to high frequency (20kHz) electrical power. Transducer • The high frequency electrical signal is transmitted to traducer which converts it into high frequency low amplitude vibration. • Essentially transducer converts electrical energy to mechanical vibration. There are two types of transducer used 1.Piezo electric transducer 2.Magneto-stricitve transducer.
MECH-KIOT Piezo electric transducer
• These transducer generate a small electric current when they are compressed. Also when the electric current is passed though crystal it expands. When the current is removed , crystal attains its original size and shape.
• Such transducers are available up to 900 Watts.
• Piezo electric crystals have high conversion efficiency of 95%.
MECH-KIOT Magneto-stricitve transducer.
• These also changes its length when subjected to strong magnetic field. These transducer are made of nickel , nickel alloy sheets.
• Their conversion efficiency is about 20-30%.
• Such transducers are available up to 2000 Watts.
• The maximum change in length can be achieved is about 25 microns.
MECH-KIOT Ultrasonic Machining - Process Tool holder. OR Horn. • The tool holder holds and connects the tool to the transducer.
• It virtually transmits the energy and in some cases, amplifies the amplitude of vibration.
• Material of tool should have good acoustic properties, high resistance to fatigue cracking.
• Commonly used tool holders are Monel, titanium, stainless steel.
• Tool holders are more expensive, demand higher operating cost.
MECH-KIOT Ultrasonic Machining - Process Tool • Tools are made of relatively ductile materials like Brass, Stainless steel or Mild steel.
• Tool wear rate (TWR) can be minimized.
• The value of ratio of TWR and MRR depends on kind of abrasive, work material and tool materials.
MECH-KIOT Ultrasonic Machining - Process parameters
• Amplitude of vibration ( 15 to 50 microns) • Frequency of vibration ( 19 to 25 kHz). • Feed force (F) related to tool dimensions • Feed pressure • Abrasive size • Abrasive material
Al203, SiC, B4C, Boron silicarbide, Diamond. • Flow strength of the work material • Flow strength of the tool material • Contact area of the tool • Volume concentration of abrasive in water slurry
MECH-KIOT Ultrasonic Machining - Process parameters
• Tool Material of tool Shape Amplitude of vibration Frequency of vibration Strength developed in tool • Work material Material Impact strength Surface fatigue strength • Slurry Abrasive – hardness, size, shape and quantity of abrasive flow Liquid – Chemical property, viscosity, flow rate Pressure Density MECH-KIOT Abrasive Jet Machining - Definition
• In abrasive jet machining, a focused stream of abrasive particles, carried by
high pressure air or gas is made to impinge on the work surface through a
nozzle and the work material is removed by erosion by high velocity
abrasive particles.
MECH-KIOT Abrasive Jet Machining - Process
MECH-KIOT Abrasive Jet Machining - Process
The high velocity stream of abrasives is generated by converting pressure energy of carrier gas or air to its Kinetic energy and hence high velocity jet.
Nozzles directs abrasive jet in a controlled manner onto work material.
The high velocity abrasive particles remove the material by micro-cutting action as well as brittle fracture of the work material.
MECH-KIOT ULTRASONIC MACHINING • Introduction. • Equipment. • Tool Materials and Tool Size and 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 and work material. • USM process characteristics: Material removal rate, tool wear, Accuracy, surface finish, applications, • Advantages & Disadvantages of USM. MECH-KIOT
INTRODUCTION
• What is the Difference between Frequency, Wavelength and Amplitude? • Frequency tells us how many waves pass through a point at a second. • Wavelength tells us the length of those waves. • Amplitude tells us how big the wave is. • In USM, abrasives contained in a slurry are driven against the work by a tool oscillating at low amplitude (25-100 microns) and high frequency (15-30 kHz).
MECH-KIOT PRINCIPLE
• The machining zone (between the tool and the work piece) is flooded with hard abrasive particles generally in the form of water based slurry. • As the tool vibrates over the work piece, abrasive particles acts as indenter and indent both work and tool material . • Abrasive particles , as they indent , the work material would remove the material from both tool and work piece. • In Ultrasonic machining material removal is due to crack initiation, propagation and brittle fracture of material.
MECH-KIOT EQUIPMENT
MECH-KIOT EQUIPMENT
• Ultrasonic Machining consists of : 1. High Power sine wave generator. 2. Magneto-strictive Transducer. 3. Tool Holder. 4. Tool.
MECH-KIOT
MECH-KIOT High Power Sine Wave Generator
• This unit converts low frequency (50 Hz) electrical power to high frequency (20kHz) electrical power.
MECH-KIOT TRANSDUCER
• The high frequency electrical signal is transmitted to traducer which converts it into high frequency low amplitude vibration. • Essentially transducer converts electrical energy to mechanical vibration. There are two types of transducer used 1. Piezo electric transducer 2. Magneto-stricitve transducer.
MECH-KIOT MAGNETOSTRICTIVE TRANSDUCER
• These transducer are made of nickel , nickel alloy sheets. • Their conversion efficiency is about 20-30%. • Such transducers are available up to 2000 Watts. • The maximum change in length can be achieved is about 25 microns.
MECH-KIOT TOOL HOLDER OR HORN
• The tool holder holds and connects the tool to the transducer. It virtually transmits the energy and in some cases, amplifies the amplitude of vibration. • Material of tool should have good acoustic properties, high resistance to fatigue cracking. • Due measures should be taken to avoid ultrasonic welding between transducer and tool holder. • Commonly used tool holders are Monel, titanium, stainless steel. • Tool holders are more expensive, demand higher operating cost.
MECH-KIOT TOOL
• Tools are made of relatively ductile materials like Brass, Stainless steel or Mild steel so that Tool wear rate (TWR) can be minimized. • The value of ratio of TWR and MRR depends on kind of abrasive, work material and tool materials.
MECH-KIOT Mechanism of Material Removal
MECH-KIOT Material Removal Models in USM
The following are the Material Removal Models used in USM 1. Throwing of abrasive grains. 2. Hammering of abrasive grains. 3. Cavitations in the fluid medium arising out of ultrasonic vibration of tool. 4. Chemical erosion due to micro –agitations.
MECH-KIOT MECH-KIOT MECH-KIOT Effect of Slurry, Tool and Work Material
• MRR increases with slurry concentration. • Slurry saturation occurs at 30 to 40% abrasive/water mixture. • Material Removal rate drops with increasing viscosity. • The pressure with which the slurry is fed into the cutting zone affects MRR . • In some cases MRR can be increased even ten times by supplying the slurry at increased pressure. • The shape of the tool affects the MRR. Narrower rectangular tool gives more MRR compared to square cross section.
MECH-KIOT • Conical tool gives twice MRR compared to cylindrical tool. • The brittle behavior of material is important in determining the MRR. • Brittle material can be cut at higher rates than ductile materials.
MECH-KIOT APPLICATIONS
• Machining of cavities in electrically non-conductive ceramics • Used to machine fragile components in which otherwise the scrap rate is high • Used for multistep processing for fabricating silicon nitride (Si3N4) turbine blades • Large number of holes of small diameter could be machined. 930 holes with 0.32mm has been reported ( Benedict, 1973) using hypodermic needles • Used for machining hard, brittle metallic alloys, semiconductors, glass, ceramics, carbides etc.
MECH-KIOT • Used for machining round, square, irregular shaped holes and surface impressions. • Used in machining of dies for wire drawing, punching and blanking operations • USM can perform machining operations like drilling, grinding and milling operations on all materials which can be treated suitably with abrasives. • USM has been used for piercing of dies and for parting off and blanking operations. • USM enables a dentist to drill a hole of any shape on teeth without any
pain MECH-KIOT
• Ferrites and steel parts , precision mineral stones can be machined using USM • USM can be used to cut industrial diamonds • USM is used for grinding Quartz, Glass, ceramics • Cutting holes with curved or spiral centre lines and cutting threads in glass and mineral or metallo-ceramics.
MECH-KIOT ADVANTAGES
• It can be used machine hard, brittle, fragile and non conductive material • No heat is generated in work, therefore no significant changes in physical structure of work material • Non-metal (because of the poor electrical conductivity) that cannot be machined by EDM and ECM can very well be machined by USM. • It is burr less and distortion less processes. • It can be adopted in conjunction with other new technologies like EDM,ECG,ECM.
MECH-KIOT DISADVANTAGES
• Low Metal removal rate. • It is difficult to drill deep holes, as slurry movement is restricted. • Tool wear rate is high due to abrasive particles. Tools made from brass, 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. • USM can be used only when the hardness of work is more than 45 HRC.
MECH-KIOT UNIT IV - CHEMICAL AND ELECTRO- CHEMICAL ENERGY BASED PROCESSES
Chemical Machining and Electro-Chemical machining (CHM and ECM)-Etchants – Maskant - Techniques of Applying Maskants - Process Parameters – Surface Finish and MRR-Applications. Principles of ECM- Equipments- Surface Roughness and MRR Electrical Circuit- Process Parameters- ECG and ECH - Applications..
MECH-KIOT Chemical Process
Chemical machining –Uses chemical dissolution to dissolve material from the workpiece. –Can be used on stones, most metals and some ceramics. –Oldest of the advanced machining processes.
MECH-KIOT (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.
MECH-KIOT Chemical milling • Chemical milling - shallow cavities are produced on plates, sheets, forgings, and extrusions, generally for the overall reduction of weight. – Can be used with depths of metal removal as large as 12 mm. – Masking is used to protect areas that are not meant to be attacked by the chemical.
MECH-KIOT Chemical milling
(a)Schematic illustration of the chemical machining process. Note that no forces or machine tools are involved in this process. (b)Stages in producing a profiled cavity by machining; not the undercut.
MECH-KIOT Chemical Blanking • Similar to the blanking of sheet metals with the exception that the material is removed by chemical dissolution rather than by shearing. – Printed circuit boards. – Decorative panels. – Thin sheet-metal stampings. – Complex or small shapes.
MECH-KIOT • Photochemical blanking/machining – Modification of chemical milling. – Can be used on metals as thin as .0025 mm. • Applications – Fine screens. – Printed circuit boards. – Electric-motor laminations. – Flat springs. – Masks for color televisions
(i) Clean (ii) Apply resist (iii) UV exposure (iv) Development (v) Etching (v) Stripping
MECH-KIOT Chemical Machining Design Considerations • No sharp corners, deep or narrow cavities, severe tapers, folded seam, or porous workpiece materials. • Undercuts may develop. • The bulk of the workpiece should be shaped by other processes prior to chemical machining.
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