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ME 350 – Lecture 21 – Chapter 26. NONTRADITIONAL MACHINING PROCESSES Mechanical Energy Processes (USM, WJC, AJM) - high velocity stream of abrasives or fluid (or both) Electrochemical Processes (ECM) - reverse of electroplating Thermal Processes (EDM, Wire EDM, EBM, LBM, PAC)

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me 350 lecture 21 chapter 26
ME 350 – Lecture 21 – Chapter 26

NONTRADITIONAL MACHINING PROCESSES

  • Mechanical Energy Processes (USM, WJC, AJM)

- high velocity stream of abrasives or fluid(or both)

  • Electrochemical Processes (ECM)

- reverse of electroplating

  • Thermal Processes (EDM, Wire EDM, EBM, LBM, PAC)

- vaporizing of a small area of work surface

  • Chemical Processes (CHM, Chemical Blanking, PCM)

- chemical etching of areas unprotected by “maskant”

Nontraditional machining is characterized by material removal that:

nontraditional processes used when
Nontraditional Processes Used When:
  • Material is either very hard, brittle or both; or material is very ductile:
  • Part geometry is complex or geometric requirements impossible with conventional methods:
  • Need to avoid surface damage or contamination that often accompanies conventional machining:
1 mechanical energy processes
1. Mechanical Energy Processes
  • Ultrasonic machining (USM)
  • Water jet cutting (WJC)
  • Abrasive jet machining (AJM)
1a ultrasonic machining usm
1a) Ultrasonic Machining (USM)

Abrasives in a slurry are driven at high velocity against work by a vibrating tool (low amplitude & high frequency)

  • Tool oscillation is perpendicular to work surface
  • Abrasives accomplish material removal
  • Tool is fed slowly into work
  • Shape of tool is formed into part
usm applications
USM Applications
  • Used only on hard and brittle work materials:
  • Shapes include non-round holes, holes along a curved axis
  • “Coining operations” - pattern on tool is imparted to a flat work surface
  • Produces virtually stress free shapes
  • Holes as small as 0.076 mm have been made
slide6
1b) Water Jet Cutting (WJC)
  • Uses high pressure, high velocity stream of water directed at work surface for cutting
wjc applications
WJC Applications
  • Usually automated using CNC or industrial robots
  • Best used to cut narrow slits in flat stock such as:
  • Not suitable for:
  • When used on metals, you need to add to the water stream:
  • Smallest kerf width about 0.4 mm for metals, and 0.1mm for plastics and non-metals.
  • More info: http://www.waterjets.org/index.html
wjc advantages
WJC Advantages
  • No crushing or burning of work surface
  • Minimum material loss
  • No environmental pollution
  • Ease of automation
slide9
1c) Abrasive Jet Machining (AJM)

High velocity gas stream containing abrasive particles (aka: sand blasting or bead blasting)

  • Normally used as a finishing process rather than cutting process (e.g. gas sandpaper)
  • Applications: deburring, cleaning, and polishing.
2 electrochemical machining processes
2. Electrochemical Machining Processes
  • Electrical energy used in combination with chemical reactions to remove material
  • Reverse of:
  • Work material must be a:
  • Feature dimensions down to about 10 μm

Courtesy of AEG-Elotherm-Germany

slide11
Electrochemical Machining (ECM)

Material removal by anodic dissolution, using electrode (tool) in close proximity to work but separated by a rapidly flowing electrolyte

ecm operation
ECM Operation

Material is deplated from anode workpiece ( pole) and transported to a cathode tool ( pole) in an electrolyte bath

  • Electrolyte flows rapidly between two poles to carry off deplated material, so it does not:
  • Electrode materials: Cu, brass, or stainless steel
  • Tool shape is the:
    • Tool size must allow for the gap
ecm applications
ECM Applications
  • Die sinking - irregular shapes and contours for forging dies, plastic molds, and other tools
  • Multiple hole drilling - many holes can be drilled simultaneously with ECM
  • No burrs created – no residual stress

Schuster et al, Science 2000

Trimmer et al, APL 2003

material removal rate of ecm
Material Removal Rate of ECM
  • Based on Faraday's First Law: rate of metal dissolved is proportional to the current

MRR = Aƒr = ηCI

whereI = current;A = frontal area of the electrode (mm2), ƒr = feed rate (mm/s), and η = efficiency coefficient

  • = specific removal rate with work material;
  • M = atomic weight of metal (kg/mol)
  • r= density of metal (kg/m3),
  • F = Faraday constant (Coulomb)
  • n = valency of the ion;
equations for ecm cont
Equations for ECM (Cont’)
  • Resistance of Electrode:

Gap, g

Area, A

r is the resistivity of the electrolyte fluid (Ohm∙m)

example ecm through a plate
Example: ECM through a plate
  • Aluminum plate, thickness t = 12 mm;
  • Rectangular hole to be cut:

L = 30mm, W = 10mm

  • Applied current: I = 1200 amps.
  • Efficiency of 95%,

Determine how long it will take to cut the hole?

10mm

30mm

Ideal CAl = 3.44×10-2 mm3/amp∙s

- other ‘C’ values in Table 26.1

3 thermal energy processes overview
3. Thermal Energy Processes - Overview
  • Very high temperatures, but only:
    • Material is removed by:
  • Problems and concerns:
    • Redeposition of vaporized metal
    • Surface damage and metallurgical damage to the new work surface
    • In some cases, resulting finish is so poor that subsequent processing is required
3 thermal energy processes
3. Thermal Energy Processes
  • Electric discharge machining (EDM)
  • Electric discharge wire cutting (Wire EDM)
  • Electron beam machining (EBM)
  • Laser beam machining (LBM)
  • Plasma arc cutting or machining (PAC)
slide20
3a) Electric Discharge Machining (EDM)
  • One of the most widely used nontraditional processes
  • Shape of finished work is inverse of tool shape
  • Sparks occur across a small gap between tool and work
  • Holes as small as 0.3mm can be made with feature sizes (radius etc.) down to ~2μm
work materials in edm
Work Materials in EDM
  • Work materials must be:
  • Hardness and strength of work material are:
  • Material removal rate depends primarily on:
  • Applications:
    • Molds and dies for injection molding and forging
    • Machining of hard or exotic metals
    • Sheetmetal stamping dies.
slide22
3b) Wire EDM
  • EDM uses small diameter wire as electrode to cut a narrow kerf in work – similar to a:
material removal rate of edm
Material Removal Rate of EDM
  • Weller Equation (Empirical); Maximum rate: RMR =

whereK = 664 (°C1.23∙mm3/amp∙s);I= discharge current; Tm = melt temp of work material

  • Actual material removal rate:

MRR = vf∙h∙wkerf

wherevf= feed rate;h= workpiece thickness;wkerf = kerf width

While cutting, wire is continuously advanced between supply spool and take‑up spool to:

wire edm applications
Wire EDM Applications
  • Ideal for stamp and die components
    • Since kerf is so narrow, it is often possible to fabricate punch and die in a single cut
  • Other tools and parts with intricate outline shapes, such as lathe form tools, extrusion dies, and flat templates
slide25
3c) Electron Beam Machining (EBM)
  • Part loaded inside a vacuum chamber
  • Beam is focused through electromagnetic lens, reducing diameter to as small as 0.025 mm
  • Material is vaporized in a very localized area
ebm applications
EBM Applications
  • Ideal for micromachining
    • Drilling small diameter holes ‑ down to 0.05 mm (0.002 in)
    • Cutting slots only about 0.025 mm (0.001 in.) wide
  • Drilling holes with very high depth‑to‑diameter ratios
    • Ratios greater than 100:1
  • Disadvantage: slow and expensive
slide27
3d) Laser Beam Machining (LBM)
  • Generally used for: drilling, slitting, slotting, scribing, and marking operations
  • Holes can be made down to 0.025 mm
  • Generally used on thin stock material
slide28
3e) Plasma Arc Cutting (PAC)
  • Uses plasma stream at very high temperatures to cut metal 10,000C to 14,000C
  • Plasma arc generated between electrode in torch and workpiece
  • The plasma flows through water‑cooled nozzle that constricts and directs plasma stream to desired location
applications of pac
Applications of PAC
  • Most applications of PAC involve cutting of metal sheets and plates
  • Hole piercing and cutting along a defined path
  • Can be operated by hand‑held torch or automated by CNC
  • Can cut any:
  • Hole sizes generally larger than 2 mm
4 chemical machining chm
4. Chemical Machining (CHM)

CHM Process:

  • Cleaning ‑ to insure uniform etching
  • Masking ‑ a maskant (resist, chemically resistant to etchant) is applied to portions of work surface not to be etched
  • Patterning of maskant
  • Etching ‑ part is immersed in etchant which chemically attacks those portions of work surface that are not masked
  • Demasking ‑ maskant is removed
maskant photographic resist method
Maskant - Photographic Resist Method
  • Masking materials contain photosensitive chemicals
  • Maskant is applied to work surface (dip coated, spin coated, or roller coated) and exposed to light through a negative image of areas to be etched
    • These areas are then removed using photographic developing techniques
    • Remaining areas are vulnerable to etching
  • Applications:
    • Small parts on thin stock produced in high quantities
    • Integrated circuits and printed circuit cards
material removal rate in chm
Material Removal Rate in CHM
  • Generally indicated as penetration rates, i.e. mm/min.
  • Penetration rate unaffected by exposed surface area
  • Etching occurs downward and under the maskant
  • In general, , Etch Factor: Fe=

(see Table 26.2 pg 637)

chemical blanking
Chemical Blanking
  • Uses CHM to cut very thin sheetmetal parts ‑ down to 0.025 mm thick and/or for intricate cutting patterns
  • Conventional punch and die does not work because stamping forces damage the thin sheetmetal, or tooling cost is prohibitive

Parts made by chemical blanking (photo courtesy of Buckbee-Mears St. Paul).

chm possible part geometry features
CHM Possible Part Geometry Features
  • Very small holes
  • Holes that are not round
  • Narrow slots in slabs and plates
  • Micromachining
  • Shallow pockets and surface details in flat parts
  • Special contoured shapes for mold and die applications
quotes
Quotes:
  • We are what we repeatedly do. Excellence, then, is not an act, but a habit. - Aristotle
  • If you want others to be happy, practice compassion. If you want to be happy, practice compassion. - Dalai Lama
  • When the heart grieves over what it has lost, the spirit rejoices over what it has left. - Sufi Epigram
  • A great pleasure in life is doing what people say you cannot do. - Walter Bagehot
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