NONTRADITIONAL MACHINING PROCESSES

NONTRADITIONAL MACHINING PROCESSESPROCESSES

1. Mechanical energy processesgy p2. Electrochemical machining processes3. Thermal energy processes3. Thermal energy processes4. Chemical machining5. Application considerations5. Application considerations

©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes

Nontraditional Processes Defined

A group of processes that remove excess material by g p p yvarious techniques involving mechanical, thermal, electrical, or chemical energy (or combinations of

)these energies) They do not use a sharp cutting tool in the

ti lconventional senseDeveloped since World War II in response to new and unusual machining requirements that could notand unusual machining requirements that could not be satisfied by conventional machining methods


Importance of Nontraditional Processes R1Processes

Need to machine newly developed metals and

R1

y pnon-metals with special properties that make them difficult or impossible to machine by conventional methodsNeed for unusual and/or complex part geometries th t t dil b li h d b ti lthat cannot readily be accomplished by conventional machining Need to avoid surface damage that oftenNeed to avoid surface damage that often accompanies conventional machining


Classification of Nontraditional Processes R2Processes

Mechanical - mechanical erosion of work material by

R2

ya high velocity stream of abrasives or fluid (or both) Electrical - electrochemical energy to remove material (reverse of electroplating)material (reverse of electroplating) Thermal – thermal energy applied to small portion of work surface, causing that portion to be fused and/orwork surface, causing that portion to be fused and/or vaporizedChemical – chemical etchants selectively remove material from portions of workpart, while other portions are protected by a mask


Mechanical Energy Processes

Ultrasonic machininggWater jet cuttingAbrasive water jet cuttingAbrasive water jet cuttingAbrasive jet machining Abrasive flow machiningAbrasive flow machining


Ultrasonic Machining (USM) R3

Abrasives contained in a slurry are driven at high y gvelocity against work by a tool vibrating at low amplitude and high frequencyTool oscillation is perpendicular to work surfaceAbrasives accomplish material removalTool is fed slowly into workShape of tool is formed into part


Ultrasonic Machining


USM Applications

Hard, brittle work materials such as ceramics, glass, , , g ,and carbidesAlso successful on certain metals, such as stainless steel and titaniumShapes include non-round holes, holes along a curved axis“Coining operations” - pattern on tool is imparted to a fl t k fflat work surface


Water Jet Cutting (WJC) R4

Uses high pressure, g p ,high velocity stream of water directed at

f fwork surface for cutting


WJC Applications

Usually automated by CNC or industrial robots to y ymanipulate nozzle along desired trajectoryUsed to cut narrow slits in flat stock such as plastic, textiles, composites, floor tile, carpet, leather, and cardboardNot suitable for brittle materials (e.g., glass)


WJC Advantages

No crushing or burning of work surfaceg gMinimum material lossNo environmental pollutionNo environmental pollutionEase of automation


Abrasive Water Jet Cutting (AWJC)(AWJC)

When WJC is used on metals, abrasive particles , pmust be added to jet stream usually Additional process parameters: abrasive type, grit size, and flow rate

Abrasives: aluminum oxide, silicon dioxide, and garnet (a silicate mineral)Grit sizes range between 60 and 120 Grits added to water stream at about 0.25 kg/min (0.5 lb/min) after stream exits nozzle


Abrasive Jet Machining (AJM)

High velocity stream of gas containing small abrasive g y g gparticles


AJM Application Notes

Usually performed manually by operator who aims y p y y pnozzleNormally used as a finishing process rather than cutting processApplications: deburring, trimming and deflashing, cleaning, and polishingWork materials: thin flat stock of hard, brittle

t i l ( l ili i i )materials (e.g., glass, silicon, mica, ceramics)


Abrasive Flow Machining

Abrasive particles mixed in viscoelastic polymer are p p yforced to flow through and around part surfaces and edgesPolymer has consistency of puttyApplications: deburring and polishing difficult-to-reachareas of parts

Particularly well-suited for internal passageways th t t b ibl b ti lthat may not be accessible by conventional methods

R5 AWJC / AJM / AFM의차이점©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes

R5; AWJC / AJM / AFM의차이점

Electrochemical Machining ProcessesProcesses

A group of processes in which electrical energy is used g p p gyin combination with chemical reactions to remove materialReverse of electroplatingWork material must be a conductorProcesses:

Electrochemical machining (ECM)R6

Electrochemical deburring (ECD)Electrochemical grinding (ECG)g g ( )


Electrochemical Machining (ECM)

Material removal by yanodic dissolution, using electrode (the

)tool) in close proximity to work but separated by aseparated by a rapidly flowing electrolytey


ECM Operation

Material is deplated from anode workpiece (positive p p (ppole) and transported to a cathode tool (negative pole) in an electrolyte bathElectrolyte flows rapidly between two poles to carry off deplated material, so it does not plate onto tool Electrode materials: Cu, brass, or stainless steelTool has inverse shape of part

Tool size and shape must allow for the gap


Physics of ECM

Based on Faraday's First Law: amount of chemical ychange (amount of metal dissolved) is proportional to the quantity of electricity passed (current x time)

V= C l twhere V = volume of metal removed; C = specific removal rate which work material; l = current; and t time


ECM Applications

Die sinking - irregular shapes and contours for g g pforging dies, plastic molds, and other toolsMultiple hole drilling - many holes can be drilled simultaneously with ECM Holes that are not round

Rotating drill is not used in ECMDeburring


Electrochemical Deburring (ECD)

Adaptation of ECM to remove burrs or sharp corners p pon holes in metal parts produced by conventional through-hole drilling


Electrochemical Grinding (ECG)

Special form of ECM in which grinding wheel with p g gconductive bond material augments anodic dissolution of metal part surface


Applications and Advantages of ECGAdvantages of ECG

Applications:Applications:Sharpening of cemented carbide toolsGrinding of surgical needles and other thin wallGrinding of surgical needles and other thin-wall tubes, and fragile parts

Advantages:Advantages:Deplating responsible for 95% of metal removalBecause machining is mostly by electrochemicalBecause machining is mostly by electrochemical action, grinding wheel lasts much longer

R7; Disadvantages> cost of E sludge©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes

R7; Disadvantages> cost of E, sludge

Thermal Energy Processes -OverviewOverview

Very high local temperatures y g pMaterial is removed by fusion or vaporization

Physical and metallurgical damage to the new workPhysical and metallurgical damage to the new work surfaceIn some cases, resulting finish is so poor that , g psubsequent processing is required


Thermal Energy Processes

Electric discharge machining g gElectric discharge wire cuttingElectron beam machiningElectron beam machiningLaser beam machining


Electric Discharge Processes

Metal removal by a series of discrete electrical ydischarges (sparks) causing localized temperatures high enough to melt or vaporize the metalCan be used only on electrically conducting work materials Two main processes:1. Electric discharge machining 2. Wire electric discharge machining


Electric Discharge Machining (EDM)

(a) Setup of process and (b) close-up view of gap,

( )

( ) p p ( ) p g p,showing discharge and metal removal

R9; overcut (kerf in WEDM)©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes

; ( )

EDM Operation

One of the most widely used nontraditional processesy pShape of finished work surface produced by a shape of electrode toolSparks occur across a small gap between tool and workRequires dielectric fluid, which creates a path for each discharge as fluid becomes ionized in the gap

R8; If current up, RR higher and surface worse©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes

Work Materials in EDM

Work materials must be electrically conductingy gHardness and strength of work material are not factors in EDMMaterial removal rate depends on melting point of work material


EDM Applications

Tooling for many mechanical processes: molds for g y pplastic injection molding, extrusion dies, wire drawing dies, forging and heading dies, and sheetmetal stamping dies Production parts: delicate parts not rigid enough to

ith t d ti l tti f h l d illiwithstand conventional cutting forces, hole drilling where hole axis is at an acute angle to surface, and machining of hard and exotic metalsmachining of hard and exotic metals


Wire EDM

Special form of EDM that uses a small diameter wireSpecial form of EDM that uses a small diameter wire as electrode to cut a narrow kerf in work


Operation of Wire EDM

Work is fed slowly past wire along desired pathy p g pSimilar to a bandsaw operation

CNC used for motion controlCNC used for motion controlWhile cutting, wire is continuously advanced between supply spool and take-up spool to maintain a pp y p p pconstant diameterDielectric required, using nozzles directed at tool-work interface or submerging workpart


Wire EDM

Definition of kerf and overcut in electric discharge wireDefinition of kerf and overcut in electric discharge wire cutting


Wire EDM Applications

Ideal for stamping die componentsp g pSince kerf is so narrow, it is often possible to fabricate punch and die in a single cutp g

Other tools and parts with intricate outline shapes, such as lathe form tools, extrusion dies, and flat templates


Wire EDM Application

Irregular outline cut from aIrregular outline cut from a solid slab by wire EDM (photo courtesy of LeBlond(photo courtesy of LeBlond Makino Machine Tool Co.).


Electron Beam Machining (EBM)

Uses high velocity g ystream of electrons focused on workpiece

fsurface to remove material by melting and vaporizationand vaporization


EBM Operation

EB gun accelerates a continuous stream of electrons gto about 75% of light speed Beam is focused through electromagnetic lens, reducing diameter to as small as 0.025 mm (0.001 in)On impinging work surface, kinetic energy of electrons is converted to thermal energy of extremely high density which melts or vaporizes material in a very localized areavery localized area


EBM Applications

Works on any material yIdeal for micromachining

Drilling small diameter holes - down to 0.05 mmDrilling small diameter holes down to 0.05 mm (0.002 in)Cutting slots only about 0.025 mm (0.001 in.) Cu g s o s o y abou 0 0 5 (0 00 )wide

Drilling holes with very high depth-to-diameter ratios g y g pRatios greater than 100:1


Laser Beam Machining (LBM)

Uses the light energy g gyfrom a laser to remove material by vaporization and ablation


Laser Beam Machining

Laser = Light amplification by stimulated emission of g p yradiation" Laser converts electrical energy into a highly coherent light beam with the following properties:coherent light beam with the following properties:

Monochromatic (single wave length) Highly collimated (light rays are almost perfectlyHighly collimated (light rays are almost perfectly parallel)

These properties allow laser light to be focused,These properties allow laser light to be focused, using optical lenses, onto a very small spot with resulting high power densities


Laser Beam Machining

• Laser beam cutting goperation performed on sheet metal (photo

f C C )courtesy of PRC Corp.)


LBM Applications

Drilling, slitting, slotting, scribing, and marking g, g, g, g, goperationsDrilling small diameter holes - down to 0.025 mm (0.001 in)Generally used on thin stockWork materials: metals with high hardness and strength, soft metals, ceramics, glass and glass

l ti bb l th d depoxy, plastics, rubber, cloth, and wood


Chemical Machining (CHM)

Material removal through contact with a strong chemical g getchantProcesses include:

Chemical millingChemical blankinggChemical engravingPhotochemical machiningPhotochemical machining

All utilize the same mechanism of material removal


Steps in Chemical Machining R10

1. Cleaning - to insure uniform etching g g2. Masking - a maskant (resist, chemically resistant to

etchant) is applied to portions of work surface not to be etched

3. Etching - part is exposed to etchant that chemically attacks those portions of work surface not masked

4. Demasking - maskant is removed


Maskant in Chemical Machining

Materials: neoprene, polyvinylchloride, polyethylene, p , p y y , p y y ,and other polymersMasking accomplished by any of three methods:

Cut and peelPhotographic resist R11g pScreen resist


Cut and Peel Maskant Method

Maskant is applied over entire part by dipping, pp p y pp g,painting, or sprayingAfter maskant hardens, it is cut by hand using a scribing knife and peeled away in areas of work surface to be etched Used for large workparts, low production quantities, and where accuracy is not a critical factor


Photographic Resist Method

Masking materials contain photosensitive chemicalsg pMaskant is applied to work surface and exposed to light through a negative image of areas to be etched

These areas are then removed using photographic developing techniquesRemaining areas are vulnerable to etchingRemaining areas are vulnerable to etching

Applications:Small parts produced in high quantitiesSmall parts produced in high quantitiesIntegrated circuits and printed circuit cards

R12 PR©2012 John Wiley & Sons, Inc. M P Groover, Introduction to Manufacturing Processes

R12; PR

Screen Resist Method

Maskant applied by “silk screening” methods pp y gMaskant is painted through a silk or stainless steel mesh containing stencil onto surface areas that are not to be etched Applications:

Between other two masking methodsFabrication of printed circuit boards


Etchant

Factors in selection of etchant:Work materialDepth and rate of material removalDepth and rate of material removalSurface finish requirements

Etchant must also be matched with the type ofEtchant must also be matched with the type of maskant to insure that maskant material is not chemically attackedy


Material Removal Rate in CHM

Generally indicated as penetration rates, mm/min y p ,(in/min), since rate of chemical attack is directed into surface Penetration rate is unaffected by surface area Typical penetration between 0.020 and 0.050 mm/min (0.0008 and 0.002 in./min)


Undercut in CHM

Etching occurs downward and sideways under the g ymaskant


Chemical Milling

Processing sequence: (1) clean raw part, (2) apply maskant, g q ( ) p ( ) pp y(3) scribe, cut, and peel maskant from areas to be etched, (4) etch, and (5) remove maskant and clean finished part


Applications of Chemical Milling

Remove material from aircraft wing and fuselage g gpanels for weight reduction Applicable to large parts where substantial amounts of metal are removedCut and peel maskant method is used


Chemical Blanking

Chemical erosion to cut very thin sheetmetal yparts - down to 0.025 mm (0.001 in) thick and/or for intricate cutting patterns Conventional punch and die does not work because stamping forces damage the thin sheetmetal, or t li t i hibiti b thtooling cost is prohibitive, or bothMaskant methods are either photoresist or screen resistresist


Chemical Blanking

Collection of parts pmade by chemical blanking ( f(photo courtesy of Buckbee-Mears St Paul)St. Paul)


Chemical Blanking

C ll ti f tCollection of parts produced by photochemical p o oc e cablanking (image courtesy of the George E KaneGeorge E Kane Manufacturing Technology Lab, gyLehigh University)


Photochemical Machining (PCM)

Uses photoresist masking method p gApplies to chemical blanking and chemical engraving when photographic resist method is used Used extensively in the electronics industry to produce intricate circuit designs on semiconductor wafersAlso used in printed circuit board fabrication


Summary: Possible PartSummary: Possible Part Geometries in Nontraditional ProcessesProcesses

Very small holesyHoles with large depth-to-diameter ratios Holes that are not roundHoles that are not roundNarrow slots in slabs and platesMicromachiningMicromachiningShallow pockets and surface details in flat parts Special contoured shapes for mold and dieSpecial contoured shapes for mold and die applications


Summary: Work Materials for Nontraditional ProcessesNontraditional Processes

As a group the nontraditional processes can be g p papplied to metals and non-metals

However, certain processes are not suited to pcertain work materials

Several processes can be used on metals but not nonmetals:

ECMEDM and wire EDMPAM


19.6 The frontal working area of the electrode in an ECM operation is 2000 2 Th li d t 1800 d th lt 12 lt2000 mm2. The applied current = 1800 amps and the voltage = 12 volts. The material being cut is nickel (valence = 2). (a) If the process is 90% efficient, determine the rate of metal removal in mm3/min. (b) If the resistivity of the electrolyte = 140 ohm-mm, determine the working gap.resistivity of the electrolyte 140 ohm mm, determine the working gap.

(a) From Table 19.1, C = 3.42 x 10-2 mm3/A-sFrom Eq. (19.6) RMR = frA = (CI/A)A = CI = (3.42 x 10-2 mm3/A-s)(1800 A)

= 6156 x 10-2 mm3/s = 61.56 mm3/s = 3693.6 mm3/minAt 90% efficiency RMR = 0.9(3693.6 mm3/min) = 3324.2 mm3/min

(b) Given resistivity r = 140 ohm-mm, I = EA/gr in Eq. (19.2). Rearranging, g = EA/Irg = (12 V)(2000 mm2)/(1800 A)(140 ohm-mm) = 0 095 mmg (12 V)(2000 mm )/(1800 A)(140 ohm mm) 0.095 mm


19. 16 Chemical milling is used in an aircraft plant to create pockets in wing sections made of an aluminum alloy. The starting thickness of one workpart of interest is 20 mm. A series of rectangular-shaped pockets 12

d t b t h d ith di i 200 b 400 Thmm deep are to be etched with dimensions 200 mm by 400 mm. The corners of each rectangle are radiused to 15 mm. The part is an aluminum alloy and the etchant is NaOH. Use Table 19.2 to determine the penetration rate and etch factor for this combination. Determine (a) metalpenetration rate and etch factor for this combination. Determine (a) metal removal rate in mm3/min, (b) time required to etch to the specified depth, and (c) required dimensions of the opening in the cut and peel maskant to achieve the desired pocket size on the part.

From Table 19.2, the penetration rate = 0.025 mm/min and the etch factor = 1.75. (a) Neglecting the fact that the initial area would be less than the given dimensions of 200 mmb 400 d th t th t i l l t (R ) ld th f i d i th tby 400 mm, and that the material removal rate (RMR) would therefore increase during the cut as the area increased, area A = 200 x 400 – (30 x 30 - π(15)2) = 80,000 – 193 = 79,807 mm2

RMR = (0.025 mm/min)(79,807 mm2) = 1995.2 mm3/min

(b) Time to machine (etch) Tm = 12/0.025 = 480 min = 8.0 hr.

(c) Given Fe = 1.75, undercut u = d/Fe = 12/1.75 = 6.86 mmM k t i l th L 2 400 2(6 86) 386 28Maskant opening length = L – 2u = 400 – 2(6.86) = 386.28 mmMaskant opening width = W – 2u = 200 – 2(6.86) = 186.28 mmRadius on corners = R – u = 15 – 6.86 = 8.14 mm


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NONTRADITIONAL MACHINING PROCESSES

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