1. Nontraditional Machining and Thermal Cutting Processes
Nontraditional machining refers to a group a processes which removes excess material by various techniques involving mechanical, thermal, electrical or chemical energy
These processes do not use a sharp cutting tool in the conventional sense

2. Nontraditional processes have been developed in response to new and unusual machining requirements, including
The need to machine newly developed materials with special properties (high strength, high hardness, high toughness)
The need for unusual and/or complex geometries
The need to avoid surface damage

3. Classification of nontraditional manufacturing processes by principle form of energy
Mechanical - mechanical energy in some form different from the action of a conventional cutting tool; erosion of the workpiece material is typical
Electrical - electrochemical energy to remove material

4. Thermal - thermal energy generally applied to a small portion of the work surface, causing removal by fusion and/or vaporization; thermal energy is generated by conversion of electrical energy
Chemical - most materials are susceptible to chemical attack by certain acids or other etchants; chemicals selectively remove material from portions of the workpiece, while other portions of the surface are protected

5. Available nontraditional material removal processes
Mechanical
AFM - abrasive flow machining
AJM - abrasive jet machining
HDM - hydrodynamic machining
LSG - low stress grinding
RUM - rotary ultrasonic machining
TAM - thermally assisted machining
TFM - total form machining
USM - ultrasonic machining
WJM - water jet machining

6. Electrical
ECD - electrochemical deburring
ECDG - electrochemical discharge grinding
ECG - electrochemical grinding
ECH - electrochemical honing
ECM - electrochemical machining
ECP - electrochemical polishing
ECS - electrochemical sharpening
ECT - electrochemical turning
ES - electro-stream
STEM - shaped tube electrolytic machining

7. Thermal
EBM - electron beam machining
EDG - electrical discharge grinding
EDM - electrical discharge machining
EDS - electrical discharge sawing
EDWC - electrical discharge wire cutting
LBM - laser beam machining
LBT - laser beam torch
PBM - plasma beam machining

8. Chemical
CHM - chemical machining
ELP - electropolish
PCM - photochemical machining
TCM - thermochemical machining
TEM - thermal energy machining
While many processes are available, only the most commercially important processes are discussed here

9. Mechanical Energy Processes
Ultrasonic machining (USM)
Abrasives contained in a slurry are driven at high velocity against the work by a tool vibrating at low amplitude (.003in) and high frequency (20-100khz)
The tool oscillates in a direction perpendicular to the workpiece surface and is fed slowly into the workpiece so that the shape of the tool is formed in the part

10. The action of the abrasives impinging against the work surface performs the cutting
Tool materials - soft steel, stainless steel
Abrasive materials - boron nitride, boron carbide, aluminum oxide, silicon carbide and diamond
The vibration amplitude should be set approximately equal to the grit size, and the gap size should be maintained at about two times the grit size

12. The ratio of work material to tool material removed during the cutting process ranges from ~100:1 for cutting glass down to ~1:1 for cutting tool steel
Workpiece materials: hard and brittle such as ceramics, glass and carbides; successfully used on certain metals such as stainless steel and titanium
Shapes obtained by USM include nonround holes, holes along a curved axis and coining operation, in which an image pattern on the tool is imparted to a flat work surface

13. Water jet cutting (WJC)
Nozzle diameter: in
Pressure: up to 60,000psi
Jet velocity: up to 3000 ft.Sec
Nozzle made of sapphire, ruby or diamond
Cutting fluids: polymer solutions; preferred because of their tendency to produce a coherent stream

14. Important process parameters: standoff distance, nozzle operating diameter, water pressure and cutting feed rate
Typical feed rates: 12 in/min to well over 1200 in/min
The water jet cutting process is usually automated using CNC robots to manipulate the nozzle unit along the desired trajectory
Materials cut by water jet: plastic, textile, composites, tiles, carpet, leather and cardboard

15. Advantages: no crushing or burning of the work surface, minimum material loss because of the narrow cut slit, no environmental pollution, and easy automating the process
Limitation: not suitable to cut brittle material because of their tendency to crack during cutting

17. Abrasive water jet cutting (AWJC)
Introduction of abrasive particles into the stream adds to the number of parameters that must be controlled; among these are: abrasive type, grit size and flow rate
Type of abrasive materials: aluminum, oxide, silicon dioxide and garnet (a silicate mineral)
Grit size: ranges between 60 and 120
Flow rate: approximately 0.5 lb/min
Nozzle orifice diameter: in; somewhat larger that in water jet cutting to permit higher flow rates and more energy to be contained in the stream prior to the infection of abrasives

18. Abrasive jet machining (AJM)
A high velocity stream of gas containing small abrasive particles
Pressure: psi
Nozzle orifice diameter: in
Velocities: ft/min
Gases: dry air, nitrogen, carbon dioxide and helium
The process is usually carried out manually by an operator
AJM is normally used as a finishing process
Applications: deburring, trimming and deflashing, cleaning and polishing
Applied on hard, brittle materials (glass, silicon, mica and ceramics) that are in the form of thin flat stock
Typical abrasives: aluminum oxide (for aluminum and brass), silicon carbide (for stainless steel and ceramics), and glass beads (for polishing)

19. Grit sizes are small, 15-40m in diameter and must be very uniform in size for a given application
No recycling of abrasives; abrasive grains are fractured, worn and contaminated

20. Electrochemical Machining Processes
Electrochemical machining (ECM)
It removes metal from an electrically conductive workpiece by anodic dissolution, in which the shape of the workpiece is obtained by a formed electrode tool in close proximity to, but separated from the work by a rapidly flowing electrolyte
Underlying principle: material is deplated from the anode and deposited onto the cathode in the presence of an electrolyte bath

23. The difference in ECM is that the electrolyte bath flows rapidly between the two poles to carry off the deplated material
The electrode tool, usually made of copper, brass or stainless steel, is designed to posses approximately the inverse of the desired final shape of the part
Gap distance: usually from in
A water solution of sodium chloride is commonly used as the electrolyte

24. Electrolyte serves for:
Carrying off the material that has been removed from the workpiece
Removing hear and hydrogen bubbles created in the chemical reactions of the process
Removed material in the form of microscopic particles must be separated from the electrolyte through centrifuge, sedimentation or other means
Large amount of electrical power is required to perform ECM

25. The material is very hard or difficult to machine or
Voltage is kept relatively low to minimize arcing across the gap
Use when:
The material is very hard or difficult to machine or
Where the workpiece geometry is difficult or impossible to accomplish by conventional machining methods
Typical ECM applications
Die sinking
Multiple hole drilling
Holes that are not round
Deburring

26. Little surface damage to the work part
Advantages:
Little surface damage to the work part
No burrs as in conventional machining
Low tool wear
Relatively high metal removal rates for hard and difficult to machine metals
Disadvantages
Significant cost of electrical power to drive the operation
Problems of disposing of the electrolyte sludge

27. Electrochemical deburring (ECD)
An adaptation of ECM designed to remove burrs or round sharp corners
The same ECM principles of operation apply to ECD
Much less material is removed in ECD, thus cycle times are much shorter

28. Electrochemical grinding (ECG)
Special form of ECM
A rotating grinding wheel with a conductive bond material is used to augment the anodic dissolution of the metal workpart surface
Bond material: metallic (diamond abrasives) or resin bond impregnated with metal particles (aluminum oxide)
Most of the machining is accomplished by electrochemical action, therefore the grinding wheel lasts much longer

29. Applications:
Sharpening of cemented carbide tools
Grinding of surgical needles, other thin wall tubes and fragile parts

32. Thermal Energy Processes
Electric discharge machining (EDM)
One of the most widely used nontraditional processes
Shape of the finished work surface is produced by a formed electrode tool
EDM process must take place in the presence of a dielectric fluid

34. Discharge region heated to extremely high temperature so that a small portion of the work surface is melted and removed
Individual discharges occur hundreds or thousands of times per second to give a gradual erosion of the entire surface
Process variables:
Discharge current
Frequency of discharges

36. The high spark temperature causes the tool to melt, resulting in a small cavity opposite the cavity produced in the work
Wear ratio:
Work material removed/tool material removed
Ranges from depending on the combination of work and electrode materials
Electrode materials: graphite, copper, brass, copper tungsten, silver tungsten, etc.
Metal removal rate:
MRR = KI/Tm1.23

37. Dielectric fluids used: hydrocarbon oils, kerosene and distilled or deionized water
Applications:
tool fabrication and parts production
delicate parts
hole drilling with hole axis at an acute angle to the surface
production machining of hard and exotic metals

38. Electric Discharge Wire Cutting (EDWC or wire EDM)
special form of EDM using a wire as the electrode
cutting action achieved by thermal energy from electric discharges between the electrode wire and the workpiece

39. Workpiece fed continuously and slowly past the wire to achieve cutting path
NC used to control workpart motions
Wire EDM must be carried out in the presence of a dielectric
Wire diameters: in.
Wire materials: brass, copper, tungsten and molybdenum
Dielectric fluids: deionized water or oil

40. Overcut ranges from 0. 0008 - 0. 002in
Overcut ranges from in. And remains fairly constant and predictable once cutting conditions are established

41. Electron Beam Machining (EBM)
A high velocity stream of electrons is focused on the workpiece surface to remove material by melting and vaporization
Electron beam gun accelerates a stream of electrons to ~3/4 c and focused through an electromagnetic lens
Kinetic energy of beam converted to thermal energy of extremely high density, melting or vaporizing material in a very localized area
EBM must be carried out in a vacuum

42. Can be used on any known material
Applications:
drilling of extremely small diameter holes - down to in
drilling holes with high depth/diameter ratios, greater than 100:1
Limitations:
need of a vacuum
high energy required
expensive equipment

43. Laser Beam Machining (LBM)
Uses light energy from a laser to remove materials by vaporization and ablation
Types of lasers:
CO2
solid-state
Energy is concentrated optically and in terms of time
Light beam pulsed so that the released energy results in an impulse against the work surface, producing evaporation and melting

44. Used for:
drilling - down to in
slitting
slotting
scribing
marking
Not considered a mass production process; generally used on thin stock
Range of work materials virtually unlimited

46. Plasma Arc Cutting (PAC)
Plasma - a superheated, electrically ionized gas
PAC uses a plasma stream operating at temperatures in the range from 18,000o - 25,000o F to cut metal
The high-velocity plasma stream is directed at the workpiece, melting it and blowing the molten metal through the kerf

47. Plasma arc generated between an electrode inside the torch
Plasma flows through a water-cooled nozzle, which constricts and directs the stream
Hot enough to cut through metal 6 in thick
Gases used:
nitrogen, argon-hydrogen or a mixture (primary gases)
secondary gases or water directed to surround the plasma jet to confine the arc and clean the kerf

48. Most applications consist of cutting flat metal sheets and plates
Can be used to cut nearly any electrically conductive metal
Feed rates:
as high as 430 in/min for 1/4 in. aluminum
200 in/min for 1/4 in. steel
20 in/min for 4 in. aluminum

49. Advantage: high productivity
Disadvantages: rough cut surface, metallurgical damage

50. Air Carbon Arc Cutting
arc generated between a carbon electrode and the metallic work
High-velocity air jet used to blow away the melted portion of the metal
Used to form a kerf for severing the piece or to gouge a cavity in the pat
Used on a variety of metals, including cast iron, carbon steel, low alloy and stainless steels
Sputtering of molten metal is a hazard

51. Other Arc Cutting Processes
Gas metal arc cutting
Shielded metal arc cutting
Gas tungsten arc cutting
Carbon arc cutting

52. Chemical Machining Mechanics and Chemistry of Chemical Machining
Differences in applications and the ways in which the steps are implemented account for the different forms of CHM; the steps are
Cleaning - to ensure that material will be removed uniformly from the surfaces to be etched

53. Masking - maskant, chemically resistant to the etchant, applied to portions of the work surface not to be etched
Etching - the material removal step; part immersed in an etchant that chemically attacks unmasked portions; part removed and washed when desired amount of material has been removed
Demasking - maskant removed from the part
Masking and etching involve significant variations in methods, materials and process parameters

54. Maskant materials: neoprene, polyvinyl chloride, polyethylene and other polymers
Masking methods
Cut and peel - performed by hand, used for large workparts, low production quantities and where accuracy is not a critical factor
Photographic resist - normally applied where small parts are produced in high quantities and close tolerances are required
Screen resist - used in applications that are between the other two masking methods in terms of accuracy, part size and production quantity

55. Etchant selection - depends on work material, desired depth and rate of etch, and surface finish requirements

56. Chemical Milling First CHM process to be commercialized
Used largely in the aircraft industry
Applicable to large parts where substantial amounts of metal are removed
Cut and peel maskant method employed
As depth increases, surface finish becomes worse
Metallurgical damage very small

58. Chemical Blanking
Uses chemical erosion to cut very thin sheet-metal parts, down to in. and/or for intricate cutting patterns
Produces burr free parts
Photoresist or screen resist method applied
Maximum stock thickness ~0.030 in.
Hardened or brittle materials can be processed

60. Chemical Engraving
A chemical machining process used for making flat panels that have lettering and/or artwork on one side
Can be used to make raised or recessed lettering by reversing the portions of the panel to be etched
Masking done by either photoresist or screen resist methods
Filling operation to apply paint or other coating follows etching

61. Photochemical Machining (PCM)
Chemical machining in which the photoresist masking method is used
Employed in metalworking when close tolerances and/or intricate patterns are required
Used extensively in electronics industry (makes VLSI possible)
Photoresist materials in current use are sensitive to UV light, but not other wavelengths

62. No need to carry out process in a darkroom
Anisotropy: depth of cut d divided by undercut u; reciprocal of the etch factor
A=1/Fe = d/u
A: degree of anisotropy
Fe: etch factor

64. Application Considerations
Workpart Geometry Features
Very small holes - (below in. in diameter) use LBM
Holes with large depth/diameter ratios (d/D > 20) use ECM and EDM
Nonround holes - use EDM and ECM
Narrow slots that are not straight - use EBM, LBM, wire EDM, WJC and AWJC

65. Micromachining - use PCM, LBM and EBM
Shallow pockets and surface details in flat parts - use CHM and its variations
Creation of special contoured shapes for mold and die applications - (die sinking) use EDM and ECM

66. Work Materials

67. Performance of Nontraditional Processes
Nontraditional processes are generally used when conventional methods are not practical or economical