Me 350 lecture 21 chapter 26
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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

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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


Me 350 lecture 21 chapter 26

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


Me 350 lecture 21 chapter 26

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


Me 350 lecture 21 chapter 26

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


Solution

Solution:


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)


Me 350 lecture 21 chapter 26

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.


Me 350 lecture 21 chapter 26

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


Me 350 lecture 21 chapter 26

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


Me 350 lecture 21 chapter 26

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


Me 350 lecture 21 chapter 26

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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