Modern Manufacturing Processes RUBIAT MUSTAK Modern Machining Unconventional

Modern Manufacturing Processes RUBIAT MUSTAK

Modern Machining / Unconventional Machining Process • As the world advancing forth technically in the field of space research, missile and nuclear industry; very complicated and precise component having some special requirements are demanded by these industries. • Some metals like hastalloy, nitralloy, nimonics etc , are such that they can’t be machined by conventional methods but requied some special technicques. Hastalloy C-276 Element Ni Mo Cr Fe W Uses Content 55 % 15 - 17 % 14. 5 - 16. 5 % 4 -7% 3 - 4. 5 % 1. 2. 3. 4. 5. Pollution control Chemical processing Waste treatment Marine engineering Pulp and paper production

Modern Machining / Unconventional Machining Process(cont. . ) • The method are not limited by hardness, toughness, and brittleness of material • It can produce any intricate shape on any work piece. • It has suitable control over the various physical parameters of the processes. • It is only complementing the conventional machining methods.

Classified into various groups • Types of energy required to shape the material • Mechanical • Thermal • Electro thermal • Chemical and electro chemical • Basic mechanism involve in the process • Erosion • Ionic dissolution • Vaporization

Classification(cont. . ): • Source of energy required for material removal • Hydrostatic pressure • High current density • High voltage • Ionized material • Medium for transfer of these energy • High velocity particles • Electrolyte • Electron • Hot gases

Classification(cont. . ) § In thermal and electro thermal method- heat energy is concentrated on a small area of the work piece, to melt and vaporize the tiny bits of work material. (EDM, LBM, PAM, EBM, IBM) § In chemical and electro chemical method- the work piece material in contact with a chemical solution is etched in a controlled manner. (ECM, ECG, ECH and ECD) § In mechanical method- the material is removed by mechanical erosion of the work piece material. ( USM, AJM, and WJM)

Our concern: 1. Electro Discharge Machining (EDM) 2. Electro Chemical Machining (ECM) 3. Laser Beam Machining (LBM) 4. Ultrasonic Machining (USM) 5. Plasma Arc Machining (PAM)

Electrochemical Machining (E. C. M. ): • Electrochemical machining (ECM) is an electrolytic material removal process involving a negatively charged shaped electrode (cathode), a conductive fluid (electrolyte), and a conductive workpiece (anode). • ECM is an electrolytic process and its basis is the phenomenon of electrolysis, whose laws were established by Faraday in 1833.

Electrochemical Machining (E. C. M. )(cont. . ) In the ECM process, the dc power source charges the workpiece positively and charges the tool negatively. As the machine slowly brings the tool and workpiece close together, perhaps to within 0. 010 of an inch, the power and electrolyte flow are turned on. Electrons flow across the narrow gap from negative to positive, dissolving the workpiece into the shape as the tool advances into it. The recirculating electrolytic fluid carries away the dissolved material as a metal hydroxide.

Electrochemical Machining (E. C. M. )(cont. . ) • In ECM one employs a cathode electrode shaped to provide the complementary structure in an anode work piece. • A highly conductive electrolyte stream separates the cutting tool from the work piece, and metal removal is accomplished by passing a dc current of up to 100 A/cm 2 through the salt solution cell. As the cathode tool approaches the anode work piece it erodes its complementary shape in it. • Thus complex shapes may be made from a material such as soft copper and used to produce negative duplicates of it. The process is also called electrochemical sinking.

Electrochemical Machining (E. C. M. )(cont. . ) Material Removal Rate (MRR): According to Faraday’s first law of electrolysis, mass of ion liberated by the substance, M= ZIt Where, I = current flowing through the electrolytic cell t= time in sec Z= constant known as the electro- chemical equivalent of the substance.

Principle: • Based on the principle of Faraday’s law of electrolysis. Characteristic: • Small gap between tool and work-piece (≈ 0. 5 mm). • Wok-piece stationary, feed by tool. • Electrolyte: Aqueous solution of common salt, dilute acid. • Pressure of electrolyte ≈ 14 kg/cm 2 • Velocity of electrolyte = 30 to 60 m/sec. • Temperature of electrolyte = 25 to 60°C. • Voltage of electrolyte = 5 to 15 V

ECM: Advantages • Components are not subject to eithermal or mechanical stress. • There is no tool wear in ECM. • Non-rigid and open work pieces can be machined easily as there is no contact between the tool and work piece. • Complex geometrical shapes can be machined repeatedly and accurately. • ECM is a time saving process when compared with conventional machining • During drilling, deep holes can be made or several holes at once. • Fragile parts which cannot take more loads and also brittle material which tend to develop cracks during machining can be machined easily in ECM • Surface finishes of 25 µ in. can be achieved in ECM

ECM: Disadvantages o Keeping the solution conductivity constant. o More expensive than conventional machining. o Need more area for installation. o Electrolytes may destroy the equipment. o Not environmentally friendly (sludge and other waste) o High energy consumption. o Chemical attack by electrolytes. o The danger of a burn in the case of a short circuit between the positive and negative leads. o The danger of a fire damp explosion. o Material has to be electrically conductive

ECM Applications • The most common application of ECM is high accuracy duplication. Because there is no tool wear, it can be used repeatedly with a high degree of accuracy. • It is also used to make cavities and holes in various products. • It is commonly used on thin walled, easily deformable and brittle material because they would probably develop cracks with conventional machining. Products • The two most common products of ECM are turbine/compressor blades and rifle barrels. Each of those parts require machining of extremely hard metals with certain mechanical specifications • Some of these mechanical characteristics achieved by ECM are: *Stress free grooves. *Any groove geometry. *Any conductive metal can be machined. *Repeatable accuracy of 0. 0005”. *High surface finish. *Fast cycle time.

Function of Electrolyte in ECM: • Completes the electric circuit between tool and work piece. • Allows desirable machining to occur. • Carries away products of reaction from the zone of machining. • Carries away heat generated during chemical reactions. Properties of Electrolyte For ECM: • High electrical conductivity. • Chemical stability. • High specific heat and low viscosity.

Electrical Discharge Machining (EDM): • Its a manufacturing process whereby a desired shape is obtained using electrical discharges (sparks). • Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. • One of the electrodes – ‘tool-electrode’ or ‘tool’ or ‘electrode’. • Other electrode - workpiece-electrode or ‘workpiece’. • As distance between the two electrodes is reduced, the current intensity becomes greater than the strength of the dielectric (at least in some points) causing it to break.

Electrical Discharge Machining (EDM)(cont. . ): • It is a process of metal removal based on the principle of material removal by an interrupted electric spark discharge between the electrode tool and the work piece. • In EDM, a potential difference is applied between the tool and workpiece. • Essential - Both tool and work material are to be conductors. • The tool and work material are immersed in a dielectric medium. • Generally kerosene or deionised water is used as the dielectric medium. • A gap is maintained between the tool and the workpiece

Electrical Discharge Machining (EDM)(cont. . ):

Electrical Discharge Machining (EDM)(cont. . ): • Depending upon the applied potential difference (50 to 450 V) and the gap between the tool and workpiece, an electric field would be established. • Generally the tool is connected to the negative terminal (cathode) of the generator and the workpiece is connected to positive terminal (anode). • As the electric field is established between the tool and the job, the free electrons on the tool are subjected to electrostatic forces. • If the bonding energy of the electrons is less, electrons would be emitted from the tool. • As they gain velocity and energy, and start moving towards the job, there would be collisions between the electrons and dielectric molecules. • Such collision may result in ionization of the dielectric molecule.

Electrical Discharge Machining (EDM)(cont. . ): • all of a sudden, a large number of electrons will flow from tool to job and ions from job to tool. • Such movement of electrons and ions can be visually seen as a spark. • Thus the electrical energy is dissipated as thermal energy of the spark. • The kinetic energy of the electrons and ions on impact with the surface of the job and tool respectively would be converted into thermal energy or heat flux. • Such intense localized heat flux leads to extreme instantaneous confined rise in temperature which would be in excess of 10, 000 o. C. • Such localized extreme rise in temperature leads to material removal.

• Material removal occurs due to instant vaporization of the material as well as due to melting. • The molten metal is not removed completely but only partially. Applications: § Drilling of micro-holes, thread cutting, helical profile milling, rotary forming, and curved hole drilling. § Delicate work piece like copper parts can be produced by EDM. § Can be applied to all electrically conducting metals and alloys irrespective of their melting points, hardness, toughness, or brittleness. § Other applications: deep, small-dia holes using tungsten wire as tool, narrow slots, cooling holes in super alloy turbine blades, and various intricate shapes. § EDM can be economically employed for extremely hardened work piece. § Since there is no mechanical stress present (no physical contact), fragile and slender work places can be machined without distortion. § Hard and corrosion resistant surfaces, essentially needed for die making, can be developed.

Principle: When a potential difference is applied between two conductors immersed in a dielectric fluid. The fluid will be ionized and a spark will occurs. If the potential difference is maintained, the spark will develop into an arc. Characteristic of EDM: A suitable gap between tool and work-piece called spark maintained (0. 01 to 0. 5 mm) gap must be More erosion on anode (+ve), so the work-piece is kept +ve. Dielectric fluid (Paraffin, kerosene, transformer oil etc. ) D. C. voltage: 40 -300 V, Current: 0. 5 to 400 Amp, local temperature 10000°C A true replica of the tool surface will be produced on the work-piece. Dielectric fluid is circulated to maintain a certain temperature.

EDM Advantages: Some of the advantages of EDM include machining of: § Complex shapes that would otherwise be difficult to produce with conventional cutting tools. § Extremely hard material to very close tolerances. § Very small work pieces where conventional cutting tools may damage the part from excess cutting tool pressure. § There is no direct contact between tool and work piece. Therefore delicate sections and weak materials can be machined without any distortion. § A good surface finish can be obtained.

Disadvantages: Some of the disadvantages of EDM include: § The slow rate of material removal. § For economic production, the surface finish specified should not be too fine. § The additional time and cost used for creating electrodes for ram/sinker EDM. § Reproducing sharp corners on the workpiece is difficult due to electrode wear. § Specific power consumption is very high. § "Overcut" is formed. § Excessive tool wear occurs during machining. § Electrically non-conductive materials can be machined only with specific setup of the process

Function of Dielectric Fluid: Serves as a conducting medium and convey the spark. Cools the work-piece and tool. Carries away the eroded metal. Properties of Dielectric Fluid: Should not evolve toxic vapours or gases. Must be inflammable. Chemically inert on tool and work-piece Tool material: Brass, copper or alloy of copper, cast iron used as cutting tool material.

Ultrasonic Machining (USM): • 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 workpiece, is oscillated by the Booster and Sonotrode at a frequency of about 20 k. Hz 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 workpiece, to impact normally and successively on the work surface, thereby machining the work surface. • 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

Ultrasonic Machining (USM) (cont. . )

Ultrasonic Machining (USM) (cont. . ) • 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 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 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

Advantages ultrasonic machining: • Machining of any material regardless of conductivity. • Precision machining of brittle hard materials. • Does not produce electric, thermal or chemical defects at the surface. • Can drill circular or non-circular holes in very hard materials. • Less stress because of its non-thermal nature. Disadvantages ultrasonic machining: • Low material removal rate. • Tool wears fast. • Machining area and depth are quite restricted.

Abrasives: Selection on the type of work-piece material, hardness of work- piece, metal removal rate, desired surface finish etc. Types: Al 2 O 3, Sic, Boron Carbide etc. Water slurry with 30 to 60% by volume of abrasive. Applications: 1) For machining intricate shaped products. 2) Small holes. 3) Machining of hard and non-conductive material.

Plasma Arc Machining(PAM): • When a flowing gas is heated to sufficiently high temperature of the order of 16500 o. C to become partially ionized, it is known as “Plasma”. • Heat for machining produced by high temperature plasma and also due to direct electro bombardment. • Metal removal rate can be increased by increasing gas flow rate. There are two type of plasma arc system 1. 2. Transferred arc type Non transferred are type

Laser Beam Machining (LBM): Laser is an electro magnetic radiation. For production of laser beam, generally ruby rod used in which aluminum is the main ingredient Laser beam techniques involves Pumping of energy. Production of stimulated effect

Advantages: • No direct contact between tool and work-piece • Laser beam can be sent from longer distance • Micro shaped hole can be laser drill. Limitation: • High initial cost • Overall low efficiency • Not able to drill too deep hole

Applications: 1) Small holes, suitable for fine and minute holes. 2) Welding like temperature protect) material. 3) Cutting complex profiles on hard materials. 4) Partial cutting etc. non-conducting and refractory (high