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

2. 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
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3. 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
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4. Introduction
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5. 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
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6. Chemical Machining Chemical Milling
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7. 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
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8. 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
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9. 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
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10. 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
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11. 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
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12. Electrochemical Machining
Process Capabilities
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13. 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
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14. 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
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15. 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
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16. 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
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17. 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
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18. 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
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19. 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
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20. Electrical-discharge Machining
Principle of Operation
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21. 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
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22. 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
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23. 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
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24. 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
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25. 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
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26. 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
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27. 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
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28. Laser-beam Machining
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29. 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
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30. 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
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31. 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
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32. 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
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33. 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
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34. 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
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35. 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
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36. Water-jet Machining
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37. 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
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38. 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
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39. 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
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40. Economics of Advanced Machining Processes
CASE STUDY 27.2
Manufacture of Small Satellites
Propulsion system for a small satellite
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41. Economics of Advanced Machining Processes
CASE STUDY 27.2
Manufacture of Small Satellites
Photochemically etched and blanked components for micro- and nanosatellites
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42. Economics of Advanced Machining Processes
CASE STUDY 27.2
Manufacture of Small Satellites
Processing sequence for photochemical etching of microsatellite components
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