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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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GrindingGrinding – 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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Grain size – size of the abrasive particlesTypical grain size: 8-250 (mesh size: lines/in)Grit size 8: coarse grain – for harder materialGrit size 250: fine grain – for soft material, and for

lapping and superfinishing

Grinding Wheel

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Grinding WheelBonding materials – requires strength,

toughness, hardness, and temperature resistance.Vitrified bond: baked clay and ceramics, most

commonSilicate: low heat generation, tool grindingRubber: flexible, cutoff operation Resin: thermosets, rough grinding and cuttoffShellac: Varnish, strong but not rigid, good finishMetallic: Usually bronze, diamond of cubic boron

nitride wheels

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Grinding WheelWheel structure and Wheel grade

Wheel structure – relative spacing of the abrasive grains in the wheel

Vg+ Vb+ Vp = 1.0Vg - proportion of abrasive grain in the wheelVb - proportion of bond material in the wheelVp - 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).

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Grinding Wheel SpecificationWheel 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 SpecificationWheel 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

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Grinding AnalysisMaterial removal rate, MRR

= vwwdvw = work speed

w = cutting widthd = depth of cut

Specific energy = Fcv / vwwdFc = 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

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Surface Grindinghttp://www.witherstool.com/surfacegrinding.html

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Cylindrical Grinding

http://www.youtube.com/watch?v=bhjuM85fx8c

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Centerless Grinding

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

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Honing

Honing speed typically 0.3 – 3 m/sGrit size typically 30 – 600

http://www.youtube.com/watch?v=3O0XnA_fwyU

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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 300 - 600 http://www.youtube.com/watch?v=GZY3UU8a2U8

http://www.youtube.com/watch?v=Ao9s4VCFaOc

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Superfinishing

Similar to honingShorter stroke ~ 4.5 mm up to 1500 strokes / minuteLower pressure between tool and workpieceLower work speed ~ 0.25 m/sSmaller 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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BuffingBuffing

– 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

MECH152-L24-1 (1.0) - 23Non-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

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Ultrasonic MachiningUltrasonic machining

Abrasive slurry driven over the workpiece by an ultrasonic vibration tool at about 20kHz

Amplitude vibration of 0.076mmTool materials – soft steel and stainless steelAbrasive materials – boron nitride, boron carbide,

aluminum oxide, silicon carbide, diamondGrit size – 100 to 2000Gap size – about 2 times grit size

Adobe Acrobat Document

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Ultrasonic MachiningThe grit size determines the surface finishThe concentration of abrasive in the water-based slurry

is between 20% to 60%.

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Water Jet CuttingUses a fine, high-pressure water jet to cut the workpieceDiameter of nozzle – 0.1~0.4 mmWater jet pressure – 400 MPaNozzle material – sapphire, ruby or diamond

Filtration system to separate swarfProcess 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=XNGrVxQFrdI

http://www.youtube.com/watch?v=tJYSn9yDSzg

http://www.youtube.com/watch?v=_iqJouVi4NU

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Abrasive Jet MachiningAbrasive water jet cutting

Abrasive particles, aluminum oxide, silicon oxide, added to the jet stream to facilitate cutting

Grit size: 60 -120Nozzle diameter: 0.25 – 0.63 mm

Abrasive jet machiningHigh velocity gas jet with abrasive materialsDry gas (air, nitrogen, carbon dioxide, and helium)

at 0.2 to 1.4 MPaNozzle diameter – 0.075 to 1 mmJet velocity – 2.5 to 5 m/s

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Electrochemical Machining Processes• Electrochemical machining• Electrochemical deburring and grinding

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Removes metal from an electrically conductive workpiece by anodic dissolutionWorkpiece (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 steelFeed rate of tool = metal removal rate

Electrochemical Machining (ECM)

http://www.youtube.com/watch?v=Z_U_ZZty5Ns&feature=related

http://www.youtube.com/watch?v=oxJf5B2LnFY

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Electrochemical Machining (ECM)

yresistiviteElectrolytgapElectrodeVoltagettanconsspecificMaterialMRR

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Typical electrode gap distance = 0.075 to 0.75 mmElectrolyte – 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

Electrochemical Machining (ECM)

MECH152-L24-1 (1.0) - 33Electrochemical Deburring and Grinding

Electrochemical deburring (ECD)Adapting ECM for deburring and rounding sharp corners on metal parts

http://www.youtube.com/watch?v=wDOXQkHvl4g&feature=PlayList&p=3AFB507B668AF162&index=32

MECH152-L24-1 (1.0) - 34Electrochemical 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%

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

MECH152-L24-1 (1.0) - 36Electric 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.

MECH152-L24-1 (1.0) - 37Electric 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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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.

Electric Discharge Machining (EDM)

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Electric Discharge Machining (EDM)

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Electric Discharge Wire CuttingSpecial 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 mmWire material – brass, copper, tungsten, and molybdenum.

http://www.youtube.com/watch?v=Sr0kC3eRIC8&feature=PlayList&p=3AFB507B668AF162&index=36

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Electric Discharge Wire Cutting

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Electron Beam MachiningHigh velocity stream of electrons focused on the workpiece surface to weld, cut or heat-treat itConducted in vacuumBeam diameter down to 0.025 mm

Hole depth-to-diameter – 100:1

Thicknees: 0.25 to 6.3 mmNo tool wear

http://www.youtube.com/watch?v=fDYuSleApiQ

http://www.youtube.com/watch?v=qBOoyfuO5rM&feature=related

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Laser Beam MachiningLaser to remove material by vaporization and ablationTypes 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

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Arc Cutting ProcessesElectric 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 kerfTemperature – 10,000 to 14,000CNozzle is water cooledCNC operation possible

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Arc Cutting ProcessesPlasma 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 ProcessesFlame cutting using energy from exothermic reaction of the metal with oxygen

Fuels include acetylene, propylene, and propane.

http://www.youtube.com/watch?v=ksM5KNjQxkU

http://www.youtube.com/watch?v=1XDHC0_K7sI

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Chemical Machining• Chemical Milling• Chemical Blanking• Chemical Engraving• Photochemical Machining

Tolerance as close as 0.0025 mm

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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.

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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.

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Chemical blanking

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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

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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 ConsiderationsVery 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