Advanced Machining Processes Presentation slide for courses, classes, lectures et al.

Chapter Outline Introduction Chemical Machining Electrochemical Machining Electrochemical Grinding Electrical-discharge Machining Laser-beam Machining Electron-beam Machining Water-jet Machining Abrasive-jet Machining Hybrid Machining Systems Economics of Advanced Machining Processes Copyright © 2010 Pearson Education South Asia Pte Ltd

Introduction Machining processes involved material removal by mechanical means: chip formation, abrasion, or microchipping Situations where mechanical methods are not satisfactory, economical or possible: Very high strength and hardness Material is too brittle Workpiece is too flexible Shape of the part is complex Surface finish and dimensional tolerance requirements Temperature rise during processing Copyright © 2010 Pearson Education South Asia Pte Ltd

Introduction Copyright © 2010 Pearson Education South Asia Pte Ltd

Chemical Machining Chemical machining (CM) is the process where chemicals attacking and etching metals, stones, and some ceramics, and remove small amounts of material from the surface Carried out by chemical dissolution using reagents or etchants Chemical Milling Shallow cavities are produced on plates, sheets, forgings and extrusions Overall reduction of weight Copyright © 2010 Pearson Education South Asia Pte Ltd

Chemical Machining Chemical Milling Copyright © 2010 Pearson Education South Asia Pte Ltd

Chemical Machining Chemical Milling Used in aerospace industry to remove shallow layers of material from large aircraft components, missile skin panels and extruded parts for airframes Copyright © 2010 Pearson Education South Asia Pte Ltd

Chemical Machining Chemical Blanking Similar to the blanking of sheet metals Used to produce features which penetrate through the thickness of the material Applications are the burr-free etching of printed-circuit boards and decorative panels Photochemical Blanking Material is removed by photographic techniques Also called photochemical machining Used for etching Copyright © 2010 Pearson Education South Asia Pte Ltd

Chemical Machining Design Considerations for Chemical Machining Design guidelines for chemical machining are: Sharp corners, deep and narrow cavities, severe tapers, folded seams, or porous workpiece materials should be avoided 10% tolerance thickness should maintained Bulk of the workpiece should be shaped by other processes prior to chemical machining Controlling work environment and artwork Protocol should be compatible with the equipment Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Machining The reverse of electroplating An electrolyte acts as current carrier and the high rate of electrolyte movement in the tool washes metal ions away from the workpiece (anode) before they have a chance to plate onto the tool (cathode) The material-removal rate (MRR) in electrochemical machining is I = current in amperes C = material constant Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Machining Process Capabilities Used to machine complex cavities and shapes in high- strength materials Aerospace industry for the mass production of turbine blades, jet-engine parts and nozzles Modification of ECM, shaped-tube electrolytic machining (STEM), is used for drilling small-diameter deep holes ECM process leaves a burr-free, bright surface and can be used as a deburring process Available as numerically controlled machining centers with high production rates, high flexibility, and close dimensional tolerances Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Machining Process Capabilities Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Machining CASE STUDY 27.1 Electrochemical Machining of a Biomedical Implant 2 total knee-replacement systems, showing metal implants (top pieces) with an ultrahigh-molecular- weight polyethylene insert (bottom pieces) Cross section of the ECM process as applied to the metal implant Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Machining: Pulsed Electrochemical Machining The process uses very high current densities but the current is pulsed rather than direct current This is to eliminate the need for high electrolyte flow rates PECM improves fatigue life and eliminate the recast layer left on die and mold surfaces by electrical- discharge machining Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Grinding The process combines electrochemical machining with conventional grinding Similar to a conventional grinder but the wheel is a rotating cathode embedded with abrasive particles Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Grinding The abrasives have 2 functions: Serve as insulators between the wheel and the workpiece Mechanically remove electrolytic products from the working area ECG process is suitable for applications similar to those for milling, grinding and sawing but not cavity- sinking operations Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrochemical Grinding Design Considerations for Electrochemical Grinding ECG requires that: Designs should avoid sharp inside radii Electrochemically ground surface should be narrower than the width of the grinding wheel Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining Process is based on the erosion of metals by spark discharges When two current-conducting wires are allowed to touch each other, an arc is produced At the point of contact between the two wires, a small portion of the metal eroded away and leave a small crater Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining Principle of Operation EDM system consists of a electrode and the workpiece, connected to a DC power supply and placed in a dielectric fluid When the potential difference is high, the dielectric breaks down and a transient spark discharges through the fluid, removing a small amount of metal Can be used on any material that is an electrical conductor The material-removal rate can be estimated from I = current in amperes Tw = melting point Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining Principle of Operation Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining Dielectric Fluids The functions of the dielectric fluid are to: Act as an insulator until the potential is sufficiently high Provide a cooling medium Act as a flushing medium and carry away the debris in the gap Electrodes Electrodes are made of graphite, brass, copper or copper–tungsten alloys Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining Electrodes Can be shaped by forming, casting, powder metallurgy, or CNC machining techniques Wear ratio is defined as the ratio of the volume of workpiece material removed to the volume of tool wear Tool wear is related to the melting points of the materials involved Lower the melting point of the electrode, the higher is the wear rate Tool wear can be minimized by reversing the polarity and using copper tools Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining Process Capabilities Stepped cavities can be produced by controlling the relative movements of the workpiece in relation to the electrode High rates of material removal produce rough surface finish with poor surface integrity and low fatigue properties Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining Design Considerations for EDM General design guidelines: Parts should be designed so that the required electrodes can be shaped properly and economically Deep slots and narrow openings should be avoided The surface finish specified should not be too fine. Bulk of material removal should be done by conventional processes Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining: Wire EDM Similar to contour cutting with a band saw A slowly moving wire travels along a prescribed path will cut the workpiece Wire is made of brass, copper, tungsten, molybdenum, zinc- or brass-coated or multicoated Copyright © 2010 Pearson Education South Asia Pte Ltd

Electrical-discharge Machining: Electrical-discharge Grinding The grinding wheel is made of graphite or brass and contains no abrasives Material is removed from the workpiece surface by spark discharges between the rotating wheel and the workpiece EDG process can be combined with electrochemical grinding called electrochemical-discharge grinding (ECDG) Material-removal rate in EDG is I = current K = workpiece material factor Copyright © 2010 Pearson Education South Asia Pte Ltd

Laser-beam Machining The source of energy is a laser which focuses optical energy on the surface of the workpiece The highly focused, high-density energy source melts and evaporates portions of the workpiece in a controlled manner Copyright © 2010 Pearson Education South Asia Pte Ltd

Laser-beam Machining Copyright © 2010 Pearson Education South Asia Pte Ltd

Laser-beam Machining The cutting depth is expressed as Laser beams may be used in combination with a gas stream to increase energy absorption (laser-beam torch) for cutting sheet metals t = depth C = constant for the process P = power input v = cutting speed d = laser-spot diameter Copyright © 2010 Pearson Education South Asia Pte Ltd

Laser-beam Machining Process Capabilities It is used for drilling, trepanning, and cutting metals, nonmetallic materials, ceramics, and composite materials Laser-beam machining is being used increasingly in the electronics and automotive industries Also used for welding, small-scale and localized heat treating of metals and ceramics, and marking of parts Copyright © 2010 Pearson Education South Asia Pte Ltd

Laser-beam Machining Design Considerations for LBM General design guidelines: Sharp corners should be avoided Deep cuts will produce tapered walls Reflectivity of the workpiece surface Adverse effects on the properties of the machined materials Copyright © 2010 Pearson Education South Asia Pte Ltd

Laser-beam Machining EXAMPLE 27.1 Combining Laser Cutting and Punching of Sheet Metal Advantages and drawbacks of punching: Requires large lot sizes in order to economically justify purchasing tooling Relatively simple parts, Small range of part thicknesses Fixed and limited punch geometries Rapid production Integration with subsequent processing after punching Copyright © 2010 Pearson Education South Asia Pte Ltd

Electron-beam Machining The energy source is high-velocity electrons, which strike the workpiece surface and generate heat Used for very accurate cutting of a wide variety of metals Surface finish is better and kerf width is narrower than in other thermal cutting processes Should be used only by highly trained personnel Copyright © 2010 Pearson Education South Asia Pte Ltd

Electron-beam Machining Design Considerations for EBM Guidelines for EBM: Individual parts or batches should closely match the size of the vacuum chamber for a high production rate per cycle Manufacture in small batches Plasma-arc Cutting Used to rapidly cut ferrous and nonferrous sheets and plates Highly automated Copyright © 2010 Pearson Education South Asia Pte Ltd

Water-jet Machining Force is utilized in cutting and deburring operations Advantages of this process: Cuts can be started at any location No heat is produced No deflection of the workpiece Little wetting of the workpiece takes place The burr produced is minimal Environmentally safe manufacturing process Copyright © 2010 Pearson Education South Asia Pte Ltd

Water-jet Machining Copyright © 2010 Pearson Education South Asia Pte Ltd

Abrasive-jet Machining A high-velocity jet of dry air, nitrogen, or carbon dioxide containing abrasive particles is aimed at the workpiece surface under controlled conditions Copyright © 2010 Pearson Education South Asia Pte Ltd

Hybrid Machining Systems Able to handle a variety of materials, including metals, ceramics, polymers, and composites Examples of integration of systems: Abrasive machining and electrochemical machining Abrasive machining and electrical discharge machining Abrasive machining and electrochemical finishing Water-jet cutting and wire EDM Machining and blasting Combinations of various forming, machining, and joining processes Copyright © 2010 Pearson Education South Asia Pte Ltd

Economics of Advanced Machining Processes Depends on the: Costs of tooling and equipment Cperating costs Material-removal rate required Level of operator skill required The cost of tooling and equipment and operator skill required varies considerably Copyright © 2010 Pearson Education South Asia Pte Ltd

Economics of Advanced Machining Processes CASE STUDY 27.2 Manufacture of Small Satellites Propulsion system for a small satellite Copyright © 2010 Pearson Education South Asia Pte Ltd

Economics of Advanced Machining Processes CASE STUDY 27.2 Manufacture of Small Satellites Photochemically etched and blanked components for micro- and nanosatellites Copyright © 2010 Pearson Education South Asia Pte Ltd

Economics of Advanced Machining Processes CASE STUDY 27.2 Manufacture of Small Satellites Processing sequence for photochemical etching of microsatellite components Copyright © 2010 Pearson Education South Asia Pte Ltd