1. Tertiary Manufacturing Processes

2. Tertiary Manufacturing Processes
Grinding and Abrasive Processes
Grinding
Honing, Lapping, Super-finishing, Polishing and Buffing
Non-traditional Machining and Thermal Cutting Processes
Mechanical Energy Processes
Electrochemical Machining Processes
Thermal Energy Processes
Chemical Machining

3. Grinding
Grinding – material removal by an abrasive bonded grinding wheel rotating a high speed.
Grinding Wheel – basic parameters:
Abrasive material
Grain size
Bonding material
Wheel grade
Wheel structure

4. Grinding Wheel Abrasive materials
Aluminum oxide: grinding ferrous and high-strength alloys (Knoop hardness ~ 2100)
Silicon carbide: grinding aluminum, brass, and stainless steel, cast irons and certain ceramics (Knoop hardness ~ 2500)
Cubic boron nitride: grinding hardened steels and aerospace alloys (Knoop hardness ~ 5000)
Diamond: grinding ceramics, cemented carbides, and glass (Knoop hardness ~ 7000)

5. Grinding Wheel Grain size – size of the abrasive particles
Typical grain size: (mesh size: lines/in)
Grit size 8: coarse grain – for harder material
Grit size 250: fine grain – for soft material, and for lapping and superfinishing

6. Grinding Wheel
Bonding materials – requires strength, toughness, hardness, and temperature resistance.
Vitrified bond: baked clay and ceramics, most common
Silicate: low heat generation, tool grinding
Rubber: flexible, cutoff operation
Resin: thermosets, rough grinding and cuttoff
Shellac: Varnish, strong but not rigid, good finish
Metallic: Usually bronze, diamond of cubic boron nitride wheels

7. Grinding Wheel Wheel structure and Wheel grade
Wheel structure – relative spacing of the abrasive grains in the wheel
Vg+ Vb+ Vp = 1.0
Vg - proportion of abrasive grain in the wheel
Vb - proportion of bond material in the wheel
Vp - proportion of pores in the wheel
Wheel grade – bond strength between abrasive grits, largely depending on Vb. Grade is measured on a scale between soft (A) and hard (Z).

8. Grinding Wheel Specification
Wheel specification: 30A46H6VXX
30 – Prefix (manufacturer’s symbol for abrasive, optional)
A – Abrasive type (A – aluminum oxide, C – silicon carbide, etc.)
46 – Grain size (coarse = 8,10,12,14,16,20,24; medium = 30,36,46,54,60; fine = 70,80,…,180; very fine = 220,240,….,600)
H – Grade (A = soft, M = medium, Z = hard)
6 – Structure (1 = very dense, 15 = very open)
V – bond type (B-resinoid, E-shellac, R-rubber, S-silicate, V-vitrified)
XX – Manufacturer’s record (optional)

9. Grinding Wheel Specification
Wheel specification: XXD150PYYMZZ1/8
XX – Prefix (manufacturer’s symbol for abrasive, optional)
D – Abrasive type (D – diamond, B – cubic boron nitride)
150 – Grain size (coarse = 8,10,12,14,16,20,24; medium = 30,36,46,54,60; fine = 70,80,…,180; very fine = 220,240,….,600)
P – Grade (A = soft, M = medium, Z = hard)
YY – Concentration (manufacturer’s designation)
M – Bond type (B-resin, M-metal, V-vitrified)
ZZ – Bond modification (manufacturer’s notation)
1/8 – Depth of abrasive (in inches or mm)

10. Grinding Wheel Configurations

11. Grinding Analysis Material removal rate, MRR = vwwd
vw = work speed
w = cutting width
d = depth of cut
Specific energy = Fcv / vwwd
Fc = cutting force
v = wheel speed
Improving surface finish: Increasing wheel speed and/or wheel surface grit density

12. Grinding Process
Specific energy is much greater than conventional machining
Most of the energy in grinding results in high work surface temperature
Workpiece temperature can be lowered by grinding fluid.

13. Surface Grinding

14. Cylindrical Grinding

15. Centerless Grinding http://www.youtube.com/watch?v=k557Zoeu38s&NR=1

16. Related Abrasive Processes
Honing – round hole
Lapping – flat or slightly spherical surface
Superfinishing – flat surface, external cylinder
Polishing – Miscellaneous shapes
Buffing - Miscellaneous shapes

17. Surface Roughness Values

18. Honing Honing speed typically 0.3 – 3 m/s Grit size typically 30 – 600

19. Lapping For production of surface of extreme accuracy and smoothness
Fluid suspended abrasive particles between workpiece and lapping tool having the shape of the workpiece
Grit size

20. Superfinishing Similar to honing
Shorter stroke ~ 4.5 mm up to 1500 strokes / minute
Lower pressure between tool and workpiece
Lower work speed ~ 0.25 m/s
Smaller grit size ~ up to 1000

21. Polishing
Polishing
Removing scratches and burrs by means of abrasive grains attached to a polishing wheel rotating at high speed of around 38 m/s.
Abrasive grains are glued to the outside periphery of flexible wheel.
Grit size ranges from 20 to 120.

22. Buffing
Buffing
Similar to polishing but used to form high luster surface
Wheels are softer
Very fine grit size mixed in buffing compound
Speed – 40 to 85 m/s
Perform manually

23. Non-traditional Machining and Thermal Cutting Processes
Mechanical Energy Processes
Electrochemical Machining Processes
Thermal Energy Processes
Chemical Machining

24. Mechanical Energy Processes
Ultrasonic Machining
Water Jet Cutting
Abrasive Jet Machining

25. Ultrasonic Machining Ultrasonic machining
Abrasive slurry driven over the workpiece by an ultrasonic vibration tool at about 20kHz
Amplitude vibration of 0.076mm
Tool materials – soft steel and stainless steel
Abrasive materials – boron nitride, boron carbide, aluminum oxide, silicon carbide, diamond
Grit size – 100 to 2000
Gap size – about 2 times grit size

26. Ultrasonic Machining The grit size determines the surface finish
The concentration of abrasive in the water-based slurry is between 20% to 60%.

27. Water Jet Cutting
Uses a fine, high-pressure water jet to cut the workpiece
Diameter of nozzle – 0.1~0.4 mm
Water jet pressure – 400 MPa
Nozzle material – sapphire, ruby or diamond
Filtration system to separate swarf
Process parameters – standoff distance (3.2 mm), nozzle diameter, jet pressure, and feed rate (5 mm/s – 500 mm/s)
Not suitable for brittle materials

28. Abrasive Jet Machining
Abrasive water jet cutting
Abrasive particles, aluminum oxide, silicon oxide, added to the jet stream to facilitate cutting
Grit size:
Nozzle diameter: 0.25 – 0.63 mm
Abrasive jet machining
High velocity gas jet with abrasive materials
Dry gas (air, nitrogen, carbon dioxide, and helium) at 0.2 to 1.4 MPa
Nozzle diameter – to 1 mm
Jet velocity – 2.5 to 5 m/s

29. Electrochemical Machining Processes
Electrochemical deburring and grinding

30. Electrochemical Machining (ECM)
Removes metal from an electrically conductive workpiece by anodic dissolution
Workpiece (anode) is formed by electrode tool (cathode) at close proximity, setting up an electrolytic action or a deplating operation
The electrolyte flows rapidly to remove the deplated material
Tool material – copper, brass or stainless steel
Feed rate of tool = metal removal rate

31. Electrochemical Machining (ECM)

32. Electrochemical Machining (ECM)
Typical electrode gap distance = to 0.75 mm
Electrolyte – water plus salt (NaCl or NaSO3)
Removed work material is in the form of micro particles which require separation and handling
Voltage in ECM is kept relatively low to avoid arcing across the gap.
Applies to hard metal or complex work geometry components for good finish
Low tool wear

33. Electrochemical Deburring and Grinding
Electrochemical deburring (ECD)
Adapting ECM for deburring and rounding sharp corners on metal parts

34. Electrochemical Deburring and Grinding
Electrochemical grinding (ECG)
A rotating grinding wheel with conductive bonding material to augment anodic dissolution of metal workpiece surface
Deplating 95%
Grinding 5%

35. Thermal Energy Processes
Electric Discharge Machining
Electron Beam Machining
Laser Beam Machining
Arc Cutting Processes
Oxyfuel Cutting Processes

36. Electric Discharge Machining (EDM)
Metal removal is effected by pulsating electric arcing from a formed electrode tool acting as a cathode. The workpiece anode is separated from the tool by a small gap filled with dielectric fluid. The dielectric fluid ionized along the path of discharge.

37. Electric Discharge Machining (EDM)
Material melted by the discharge and removed by the flowing dielectric.
Metal removal is increased by higher frequency and higher current.
Best surface finish obtained by higher frequency and low current.
Overcut in EDM is produced when electrical discharges occur at the sides of the tool and at the end.

38. Electric Discharge Machining (EDM)
Tool wear occurs with high spark temperature.
The work material removal versus tool wear ratio is between 1 to 100
Electrode material - graphite, copper, brass, copper tungsten, etc.
Hardness and strength of the work material do not affect the process, while the melting point is a governing factor.
Dielectric fluids include hydrocarbon oils, kerosene, and distilled or deionized water.
Used for tool fabrication and parts production.

39. Electric Discharge Machining (EDM)

40. Electric Discharge Wire Cutting
Special form of EDM using a small-diameter wire as the electrode to cut a narrow kerf in the work.
Workpiece is fed continuously and slowly past the wire to achieve the cutting path
Wire diameter – to 0.3 mm
Wire material – brass, copper, tungsten, and molybdenum.

41. Electric Discharge Wire Cutting

42. Electron Beam Machining
High velocity stream of electrons focused on the workpiece surface to weld, cut or heat-treat it
Conducted in vacuum
Beam diameter down to mm
Hole depth-to-diameter – 100:1
Thicknees: 0.25 to 6.3 mm
No tool wear

43. Laser Beam Machining
Laser to remove material by vaporization and ablation
Types of lasers – carbon dioxide gas lasers and YAG lasers
Drilling, slitting, slotting, scribing, and marking
Hole size down to mm
Unlimited workpiece material

44. Arc Cutting Processes
Electric arcing between an electrode and the workpiece to generate intense heat for welding or cutting metal
Plasma arc cutting –
Plasma is a superheated, electrically ionized gas (nitrogen, argon-hydrogen, or mixture)
Secondary gas to confine the arc and clean the kerf
Temperature – 10,000 to 14,000C
Nozzle is water cooled
CNC operation possible

45. Arc Cutting Processes Plasma arc cutting –
Maximum workpiece thickness – 150 mm
Maximum feed rate – m/s
Rough cutting surface and metallurgical damage

46. Oxyfuel Cutting Processes
Flame cutting using energy from exothermic reaction of the metal with oxygen
Fuels include acetylene, propylene, and propane.

47. Chemical Machining Chemical Milling Chemical Blanking
Chemical Engraving
Photochemical Machining
Tolerance as close as mm

48. Chemical Milling
Sequence of processing steps in chemical milling (1) clean raw part, (2) apply maskant, (3) scribe, cut, and peel the maskant from areas to be etched, (4) etch, and (5) remove maskant and clean to yield finished part.

49. Chemical Blanking
Sequence of processing steps in chemical blanking (1) clean raw part, (2) apply resist (maskant) by painting through screen, (3) etch (shown partially etched), (4) etch (completed), and (5) remove resist and clean to yield finished part.

50. Chemical blanking

51. Chemical Engraving
Process similar to the other chemical processes except:
Filling to apply paint or other coating into the recessed area
Panel immersed in a solution to dissolves the resist but not the coating material
Resist is removed highlighting the coating pattern

52. Photochemical Machining (PCM)
Sequence of processing steps in photochemical machining (1) clean raw part, (2) apply resist (maskant) by dipping, spraying, or painting, (3) place negative to resist, (4) expose to ultraviolet light, (5) develop to remove resist from areas to be etched, (6) etch (shown partially etched), (7) etch (completed), (8) remove resist and clean to yield finished part.

53. Application Considerations
Very small holes below mm diameter. (Laser beam machining, LBM)
Holes with large depth-to-diameter ratio, d/D>20. (ECM or EDM)
Holes that are not round (ECM or EDM)
Narrow slots in slabs or plates (ECM, LBM, EDM, water jet, abrasive jet)
Micromachining (PCM, LBM, EBM)
Shallow pockets and surface details in flat parts (Chemical machining)
Special contoured shapes for mold and die applications (EDM or ECM)

54. Application Considerations
Special shapes for which the non traditional processes are appropriate (a) very small diameter holes, (b) holes with large depth-to-diameter ratios, (c) nonround holes, (d) narrow, non-straight slots, (e) pockets, and (f) die sinking

55. Materials Consideration

56. Machining Characteristics

57. Design for Manufacturing
Part Drawing
Select stock
Process Plan
Check tolerances and datum
Select process
Set up
Fixture
Process conditions
Measurement
Packaging
Maintenance