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Tertiary Manufacturing Processes
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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
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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 http://www.youtube.com/watch?v=RnTNqSccW-M&feature=PlayList&p=3AFB507B668AF162&index=41
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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)
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Grinding Wheel
Grain size – size of the abrasive particles Typical grain size: 8-250 (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
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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
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Grinding Wheel
Wheel structure and Wheel grade Wheel structure – relative spacing of the abrasive grains in the wheel V g + V b + V p = 1.0
V g - proportion of abrasive grain in the wheel V b - proportion of bond material in the wheel V p - proportion of pores in the wheel Wheel grade – bond strength between abrasive grits, largely depending on V b . Grade is measured on a scale between soft (A) and hard (Z).
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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)
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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)
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Grinding Wheel Configurations
Grinding Analysis
Material removal rate, MRR =
v w wd v w =
work speed
w
= cutting width
d
= depth of cut Specific energy =
F c
v /
v w wd F c =
cutting force
v
= wheel speed Improving surface finish: Increasing wheel speed and/or wheel surface grit density
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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.
http://www.efunda.com/processes/machining/grind.cfm
Surface Grinding
http://www.witherstool.com/surfacegrinding.html
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Cylindrical Grinding
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http://www.youtube.com/watch?v=bhjuM85fx8c
Centerless Grinding
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http://www.youtube.com/watch?v=k557Zoeu38s&NR=1 http://www.youtube.com/watch?v=K_E7lZMkuw4&feature=related
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Related Abrasive Processes
• Honing – round hole • Lapping – flat or slightly spherical surface • Superfinishing – flat surface, external cylinder • Polishing – Miscellaneous shapes • Buffing - Miscellaneous shapes
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Surface Roughness Values
Honing
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Honing speed typically 0.3 – 3 m/s Grit size typically 30 – 600 http://www.youtube.com/watch?v=3O0XnA_fwyU
Lapping
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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 300 - 600 http://www.youtube.com/watch?v=GZY3UU8a2U8 http://www.youtube.com/watch?v=Ao9s4VCFaOc
Superfinishing
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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 http://www.youtube.com/watch?v=RiNmLHBR7dk
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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.
http://www.youtube.com/watch?v=wcYFOH09_w4 http://www.youtube.com/watch?v=Xkm4KRJQV2s&feature=related
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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 http://www.youtube.com/watch?v=lIsc1nDzLak
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Non-traditional Machining and Thermal Cutting Processes
• Mechanical Energy Processes • Electrochemical Machining Processes • Thermal Energy Processes • Chemical Machining
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Mechanical Energy Processes
• Ultrasonic Machining • Water Jet Cutting • Abrasive Jet Machining
Ultrasonic Machining
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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
Ultrasonic Machining
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The grit size determines the surface finish The concentration of abrasive in the water-based slurry is between 20% to 60%.
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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 http://www.youtube.com/watch?v=tJYSn9yDSzg http://www.youtube.com/watch?v=XNGrVxQFrdI http://www.youtube.com/watch?v=_iqJouVi4NU
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Abrasive Jet Machining
Abrasive water jet cutting Abrasive particles, aluminum oxide, silicon oxide, added to the jet stream to facilitate cutting Grit size: 60 -120 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 – 0.075 to 1 mm Jet velocity – 2.5 to 5 m/s
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Electrochemical Machining Processes
• Electrochemical machining • Electrochemical deburring and grinding
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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 http://www.youtube.com/watch?v=oxJf5B2LnFY http://www.youtube.com/watch?v=Z_U_ZZty5Ns&feature=related
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Electrochemical Machining (ECM)
MRR
Material specific cons tan t
Voltage Electrode gap
Electrolyt e resistivit y
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Electrochemical Machining (ECM)
Typical electrode gap distance = 0.075 to 0.75 mm Electrolyte – water plus salt (NaCl or NaSO 3 ) 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
Electrochemical Deburring and Grinding
Electrochemical deburring (ECD)
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Adapting ECM for deburring and rounding sharp corners on metal parts http://www.youtube.com/watch?v=wDOXQkHvl4g&feature=PlayList&p=3AFB507B668AF162&index=32
Electrochemical Deburring and Grinding
Electrochemical grinding (ECG) A rotating grinding wheel with conductive bonding material to augment anodic dissolution of metal workpiece surface
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Deplating 95% Grinding 5%
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Thermal Energy Processes
• Electric Discharge Machining • Electron Beam Machining • Laser Beam Machining • Arc Cutting Processes • Oxyfuel Cutting Processes
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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.
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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.
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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.
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Electric Discharge Machining (EDM)
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Electric Discharge Wire Cutting
http://www.youtube.com/watch?v=Sr0kC3eRIC8&feature=PlayList&p=3AFB507B668AF162&index=36 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 – 0.076 to 0.3 mm Wire material – brass, copper, tungsten, and molybdenum.
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Electric Discharge Wire Cutting
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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 0.025 mm Hole depth-to-diameter – 100:1 Thicknees: 0.25 to 6.3 mm No tool wear http://www.youtube.com/watch?v=fDYuSleApiQ http://www.youtube.com/watch?v=qBOoyfuO5rM&feature=related
Laser Beam Machining
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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 0.025 mm Unlimited workpiece material
Arc Cutting Processes
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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
Arc Cutting Processes
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Plasma arc cutting – Maximum workpiece thickness – 150 mm Maximum feed rate – 0.182 m/s Rough cutting surface and metallurgical damage http://www.youtube.com/watch?v=n2XmlFNc7L4&feature=related http://www.youtube.com/watch?v=mJJydOxHwZU&feature=related http://www.youtube.com/watch?v=cE_TKqD2oB4&feature=related
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Oxyfuel Cutting Processes
Flame cutting using energy from exothermic reaction of the metal with oxygen Fuels include acetylene, propylene, and propane.
http://www.youtube.com/watch?v=1XDHC0_K7sI http://www.youtube.com/watch?v=ksM5KNjQxkU
Chemical Machining
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• Chemical Milling • Chemical Blanking • Chemical Engraving • Photochemical Machining Tolerance as close as 0.0025 mm
Chemical Milling
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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.
Chemical Blanking
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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.
Chemical blanking
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Chemical Engraving
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• 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
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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.
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Application Considerations
Very small holes below 0.125 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)
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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
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Materials Consideration
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Machining Characteristics
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Design for Manufacturing
• Part Drawing • Select stock • Process Plan – Check tolerances and datum – Select process • Set up • Fixture • Process conditions – Measurement • Packaging • Maintenance