NCER

1. Chapter 19Chapter 19
Electronic ElectrochemicalElectronic Electrochemical
ChemicalChemical
and Thermal Machiningand Thermal Machining
ProcessesProcesses
(Review)(Review)
EIN 3390 Manufacturing ProcessesEIN 3390 Manufacturing Processes
Spring, 2012Spring, 2012

2. 19.1 Introduction19.1 Introduction
Non-traditional machining (NTM) processes
have several advantages
◦ Complex geometries are possible
◦ Extreme surface finish
◦ Tight tolerances
◦ Delicate components
◦ Little or no burring or residual stresses
◦ Brittle materials with high hardness can be
machined
◦ Microelectronic or integrated circuits (IC) are
possible to mass produce

3. NTM ProcessesNTM Processes
Four basic groups of material removal using NTM
processes
◦ Chemical:
 Chemical reaction between a liquid reagent and
workpiece results in etching
◦ Electrochemical
 An electrolytic reaction at workpiece surface for
removal of material
◦ Thermal
 High temperature in very localized regions
evaporate materials, for example, EDM
◦ Mechanical
 High-velocity abrasives or liquids remove
materials

4. Limitations of ConventionalLimitations of Conventional
Machining ProcessesMachining Processes
Machining processes that involve chip
formation have a number of limitations
◦ Large amounts of energy
◦ Unwanted distortion
◦ Residual stresses
◦ Burrs
◦ Delicate or complex geometries may be
difficult or impossible

5. Conventional End Milling vs. NTMConventional End Milling vs. NTM
Typical machining parameters
◦ Feed rate (5 – 200 in./min.)
◦ Surface finish (60 – 150 µin) AA – Arithmetic
Average
◦ Dimensional accuracy (0.001 – 0.002 in.)
◦ Workpiece/feature size (25 x 24 in.); 1 in. deep
NTM processes typically have lower feed
rates and require more power
consumption
The feed rate in NTM is independent of
the material being processed

6. Table 19-1 Summary of NTM ProcessesTable 19-1 Summary of NTM Processes

8. 19.2 Chemical Machining19.2 Chemical Machining
ProcessesProcesses
Typically involves metals, but ceramics
and glasses may be etched
Material is removed from a workpiece by
selectively exposing it to a chemical
reagent or etchant
◦ Gel milling- gel is applied to the workpiece in
gel form.
◦ Maskant- selected areas are covered and the
remaining surfaces are exposed to the etchant.
This is the most common method of CHM.

9. MaskingMasking
Several different
methods
◦ Cut-and-peel
◦ Scribe-and-peel
◦ Screen printing
Etch rates are slow
in comparison to
other NTM processes
Figure 19-1 Steps required to produce a stepped contour
by chemical machining.

10. Defects in EtchingDefects in Etching
If baths are not agitated properly, defects
result
Figure 19-2 Typical chemical milling defects: (a) overhang: deep cuts with improper
agitation; (b) islands: isolated high spots from dirt, residual maskant, or work material
inhomogeneity; (c) dishing: thinning in center due to improper agitation or stacking of parts
in tank.

11. Advantages and DisadvantagesAdvantages and Disadvantages
of Chemical Machiningof Chemical Machining
Advantages
◦ Process is relatively
simple
◦ Does not require
highly skilled labor
◦ Induces no stress or
cold working in the
metal
◦ Can be applied to
almost any metal
◦ Large areas
◦ Virtually unlimited
shape
◦ Thin sections
Disadvantages
◦ Requires the handling
of dangerous
chemicals
◦ Disposal of
potentially harmful
byproducts
◦ Metal removal rate
is slow

12. 19.3 Electrochemical Machining19.3 Electrochemical Machining
ProcessProcess
 Electrochemical
machining (ECM)
removes material
by anodic
dissolution with
a rapidly flowing
electrolyte
 The tool is the
cathode and the
workpiece is the
anode
Figure 19-17 Schematic diagram of
electrochemical machining process
(ECM).

13. 19.3 Electrochemical Machining19.3 Electrochemical Machining
ProcessProcess
 Electrochemical
machining (ECM)
removes material
by anodic
dissolution with
a rapidly flowing
electrolyte
 The tool is the
cathode and the
workpiece is the
electrolyte
Figure 19-17 Schematic diagram of
electrochemical machining process
(ECM).

15. Advantages and DisadvantagesAdvantages and Disadvantages
of Electrochemical Machiningof Electrochemical Machining
Advantages
◦ ECM is well suited for
the machining of
complex two-
dimensional shapes
◦ Delicate parts may be
made
◦ Difficult-to machine
geometries
◦ Poorly machinable
materials may be
processed
◦ Little or no tool wear
Disadvantages
◦ Initial tooling can
be timely and
costly
◦ Environmentally
harmful by-products

16. Electrical Discharge MachiningElectrical Discharge Machining
Electrical discharge machining (EDM)
removes metal by discharging electric
current from a pulsating DC power
supply across a thin interelectrode gap
The gap is filled by a dielectric fluid, which
becomes locally ionized
Two different types of EDM exist based on
the shape of the tool electrode
◦ Ram EDM/ sinker EDM
◦ Wire EDM

17. Figure 19-21 EDM or spark erosion machining of metal, using high-frequency spark discharges in
a dielectric, between the shaped tool (cathode) and the work (anode). The table can make X-Y
movements.

18. Figure 19-21 EDM or spark erosion machining of metal, using high-frequency spark discharges in
a dielectric, between the shaped tool (cathode) and the work (anode). The table can make X-Y
movements.

19. EDM ProcessesEDM Processes
Slow compared to
conventional
machining
Produce a matte
surface
Complex
geometries are
possible
Often used in tool
and die making
Figure 19-22 Schematic diagram of equipment
for wire EDM using a moving wire electrode.

20. EDM ProcessesEDM Processes
Figure 19-24 (above) SEM micrograph of EDM
surface (right) on top of a ground surface in steel.
The spherical nature of debris on the surface is in
evidence around the craters (300 x).
Figure 19-23 (left) Examples of wire EDM
workpieces made on NC machine (Hatachi).

21. Effect of Current on-time andEffect of Current on-time and
Discharge Current on Crater SizeDischarge Current on Crater Size
MRR = (C I)/(Tm
1.23
),
Where MRR – material removal rate in in.3
/min.; C –
constant of proportionality equal to 5.08 in US customary
units; I – discharge current in amps; Tm – melting
temperature of workpiece material, 0
F.
Example:
A certain alloy whose melting point = 2,000 0
F is to be
machined in EDM. If a discharge current = 25A, what is the
expected metal removal rate?
MRR = (C I)/(Tm
1.23
) = (5.08 x 25)/(2,0001.23
)
= 0.011 in.3
/min.

22. The principles of metal
removal for EDM.

23. Effect of Current on-time andEffect of Current on-time and
Discharge Current on Crater SizeDischarge Current on Crater Size
From Fig : we have the conclusions:
◦ Generally higher duty cycles with higher
currents and lower frequencies are used to
maximize MRR.
◦ Higher frequencies and lower discharge
currents are used to improve surface finish
while reducing MRR.
◦ Higher frequencies generally cause increased
tool wear.

24. Considerations for EDMConsiderations for EDM
Graphite is the most widely used tool
electrode
The choice of electrode material depends
on its machinability and coast as well
as the desired MRR, surface finish,
and tool wear
Four main functions of dielectric fluid:
1) Electrical insulation
2) Spark conductor
3) Flushing medium
4) Coolant

25. Advantages and DisadvantagesAdvantages and Disadvantages
of EDMof EDM
Advantages
Applicable to all
materials that are
fairly good
electrical
conductors
Hardness,
toughness, or
brittleness of the
material imposes
no limitations
Fragile and
delicate parts
Disadvantages
Produces a hard
recast surface
Surface may
contain fine cracks
caused by
thermal stress
Fumes can be toxic

26. Electron and Ion MachiningElectron and Ion Machining
 Electron beam
machining (EBM) is a
thermal process that
uses a beam of high-
energy electrons focused
on the workpiece to melt
and vaporize a metal
 Ion beam machining
(IBM) is a nano-scale
machining technology
used in the
microelectronics industry
to cleave defective
wafers for
characterization and
failure analysis
Figure 19-26 Electron-beam machining uses a high-
energy electron beam (109
W/in.2
)

27. Laser-Beam MachiningLaser-Beam Machining
Laser-beam machining (LBM) uses
an intensely focused coherent
stream of light to vaporize or
chemically ablate materials

28. Schematic diagram of a laser-beam machine, a thermal NTM process that
can micromachine any material.

29. Plasma Arc Cutting (PAC)Plasma Arc Cutting (PAC)
Uses a superheated stream of
electrically ionized gas to melt and
remove material
The process can be used on almost any
conductive material
PAC can be used on exotic materials at
high rates

30. Plasma arc machining or cutting.