mprocesses notes 9

8/13/2019 MProcesses Notes 9

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Advanced Machining

Processes

Manufacturing

Processes


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Outline

Chemical Milling

Photochemical Blanking

Electrochemical Machining

Pulsed Electrochemical Machining

Electrochemical Grinding

Electrical-Discharge Machining

Electrical-Discharge Grinding

Electrical-Discharge Wire Cutting

Laser-Beam Machining

Electron Beam Machining

Plasma Arc Cutting

Water Jet Machining

Abrasive Water Jet Machining

Abrasive Jet Machining


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Examples of Parts


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Chemical Milling

Produces shallow cavities on a

workpiece, usually to reduce

weight

The area affected by the

chemical reagent is controlledby masking or by partial

immersion


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Chemical Milling


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Chemical Milling

Procedure:

1. Relieve residual stresses to

prevent warping2. Clean the material surface

3. Apply masking material

4. Remove the masking on regions

that require etching

5. Apply the reagents

6. Wash the part

7. Remove remaining masking8. Additional finishing or chemical

milling procedures may be used


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Uses chemicals and

photographic processes to

remove material, usually froma thin sheet

Can produce complex shapes onmetals as thin as .0025 mm

without forming burrs


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Examples of Parts


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Procedure:

1. Prepare the design at amagnification of up to 100x; make

a photographic negative andreduce it to the size of the part

2. Coat the blank withphotosensitive material

3. Place the negative over the partand expose it to ultraviolet light toharden the exposedphotosensitive coating

4. Dissolve the unexposed coating

5. Apply the chemical reagent6. Remove the masking and wash

the part


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Chemical Machining

Design Considerations:

- Avoid sharp corners, deep narrowcavities, steep tapers, foldedseams and porous workpieces

- Undercuts may develop

- Most of the workpiece should beshaped by other processes tospeed production

- Variations may occur dependingonhumidity and temperature

- Computerized designs must beconverted to a format compatiblewith the photochemical artworkequipment


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Electrochemical

MachiningUses an electrolyte and electrical

current to ionize and remove

metal atoms

Can machine complex cavities inhigh-strength materials

Leaves a burr-free surface

Not affected by the strength,hardness or toughness of thematerial


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Electrochemical

Machining


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Electrochemical

Machining


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Electrochemical

MachiningDesign Considerations:

- The electrolyte erodes away

sharp profiles

- It is difficult to control

electrolyte flow; irregular

cavities may not be formedaccurately

- Allow for small taper in holes

made this way


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Pulsed Electrochemical

MachiningA form of electrochemical

machining; the current is

pulsed to eliminate the needfor high electrolyte flow

Improves fatigue life of the part


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Electrochemical

GrindingUses a rotating cathode

embedded with abrasive

particles for applicationscomparable to milling, grinding

and sawing

Most of the metal removal is

done by the electrolyte,

resulting in very low tool wear

Adaptable for honing


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Electrochemical

Grinding


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Electrochemical

GrindingDesign Considerations:

(in addition to those for

electrochemical machining)

- Avoid sharp inside radii

- Flat surfaces to be ground

should be narrower than thewidth of the grinding wheel


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Electrical-Discharge

MachiningUses a shaped electrode and

electric sparks to remove

metal; discharges sparks atabout 50-500 kHz

A dielectric (nonconductive) fluid

removes debris and acts as aninsulator until the potentialdifference is high enough

Can be used on any material thatconducts electricity


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Machining


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Machining


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MachiningDesign Considerations:

- Design parts so that the

electrodes can be madeeconomically

- Avoid deep slots and narrow

openings- Do not require very fine

surface finish

- Most of the material removalshould be done by other

processes to speed production


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GrindingThe grinding wheel lacks

abrasives and removes

material by electricaldischarges

Can be combined withelectrochemical grinding

Can be used for sawing, in whichthe saw has no teeth


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Wire CuttingThe wire moves through the

workpiece like a band saw,

removing material by electricaldischarge

Dielectric fluid is applied to thework area

The wire is generally used onlyonce; it is inexpensive


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Wire Cutting


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Wire Cutting

Example of a wire EDM machine

Courtesy of Edison Industrial Service Center


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Wire Cutting

Example of a wire EDM machine



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Wire Cutting

Example of a wire used for an EDM machine

This wire has been used; the wave pattern was

formed during take-up



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Wire Cutting

Example of cores removed from a part using wire

EDM to create the cavity in a high-pressure nozzleHoles were drilled in the interiors so that the wire

could be strung through



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Uses a concentrated beam of

light to vaporize part of the

workpiece

Usually produces a rough

surface with a heat-affectedzone

Can cut holes as small as .005mm with depth/diameter ratios

of 50:1


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Example of a part cut by laser-beam machining

Splatter marks appear where the laser first cuts into

the material


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Design Considerations:

- Non-reflective workpiece

surfaces are preferable

- Sharp corners are difficult to

produce; deep cuts produce

tapers- Consider the effects of high

temperature on the workpiece

material


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Electron Beam

MachiningVaporizes material using

electrons accelerated to 50-

80% the speed of light

Produces finer surface finish and

narrower cut width than otherthermal cutting processes

Requires a vacuum; generateshazardous X rays


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Electron Beam

Machining


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Electron Beam

Machining

An electron beam in a very low-pressure

atmosphere of helium


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Plasma Arc Cutting

Uses plasma (ionized gas) to

rapidly vaporize material

Material removal rates are much

higher than those for laser

beam machining and electronbeam machining; produces

good surface finish and thin cut

width


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Plasma Arc Cutting


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Plasma Arc Cutting

Close-up view of a plasma arc


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Plasma Arc Cutting


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Electron Beam Machining

and Plasma Arc CuttingDesign Considerations:

(in addition to those for laser-

beam machining)

- Parts should match the size of

the vacuum chamber

- Consider manufacturing thepart as a number of smaller

components


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Water Jet Machining

A pressurized jet of water cuts a

groove in the material

Effective for many nonmetallic

materials

Cuts can be started at any

location; does not produce

heat; produces very littleburring


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Water Jet Machining


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Water Jet Machining


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Abrasive Water Jet

MachiningThe water jet contains abrasive

particles; this increases the

material removal rate

Can cut metallic, nonmetallic,

and advanced compositematerials

Suitable for heat-sensitivematerials


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A high-speed jet of dry air,

nitrogen or carbon dioxide

carries abrasive particles

Good for cutting hard or brittle

materials

Can be used for deburring,

cleaning, or removing oxides orsurface films


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Summary

Advanced machining processes

offer alternatives where

conventional procedures wouldbe insufficient or uneconomical


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The End

mprocesses notes 9

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