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Chapter 28:
Nontraditional Manufacturing Processes
DeGarmo’s Materials and Processes in
Manufacturing
28.1 Introduction
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Non-traditional machining (NTM) processes have
several advantages
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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 are possible to mass
produce
NTM Processes
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Four basic groups of material removal using
NTM processes
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Chemical
Electrochemical
Thermal
Mechanical
Disadvantages of Machining Processes
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Machining processes that involve chip
formation have a number of limitations
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Large amounts of energy
Unwanted distortion
Residual stresses
Burrs
Delicate or complex geometries may be difficult or
impossible
Conventional End Milling vs. NTM
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Typical machining parameters
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Feed rate
Surface finish
Dimensional accuracy
Workpiece/feature size
NTM processes typically have lower feed
rates and require more power consumption
The feed rate in NTM is independent of the
material being processed
28.2 Chemical Machining Processes
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Typically involves metals, but ceramics and
glasses may be etched
Material is removed from a workpiece by
selectively exposing it to a chemical reagant
or etchant
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Gel milling- gel is applied to the workpiece
Maskant- selected areas are covered and the
remaining surfaces are exposed to the etchant
Masking
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Several different
methods
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Cut-and-peel
Scribe-and-peel
Screen printing
Etch rates are slow in
comparison to other
NTM processes
Figure 28-1 Steps required to produce a stepped contour
by chemical machining.
Defects in Etching
Figure 28-2 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.
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If baths are not agitated properly, defects result
Advantages and Disadvantages of
Chemical Machining
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Advantages
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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
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Disadvantages
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Requires the handling of
dangerous chemicals
Disposal of potentially
harmful byproducts
Metal removal rate is
slow
Photochemical Machining
Figure 28-4 Basic steps in photochemical machining (PCM).
Design Factors in Chemical Machining
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If artwork is used, dimensional variations can occur
through size changes in the artwork of phototool film
due to temperature and humidity changes
Etch factor (E)- describes the undercutting of the
maskant
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Areas that are exposed longer will have more metal
removed from them
E=U/d
d- depth
U- undercutting
Anisotropy (A)- directionality of the cut, A=d/U
Etch Rates
28.3 Electrochemical Machining Process
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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 28-6 Schematic diagram of
electrochemical machining process
(ECM).
Electrochemical Processing
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Pulsed-current ECM (PECM)
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Pulsed on and off for durations of approximately
1ms
Pulsed currents are also used in
electrochemical machining (EMM)
Electrochemical polishing is a modification of
the ECM process
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Much slower penetration rate
Other Electrochemical Processing
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Electrochemical hole machining
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Used to drill small holes with high aspect ratios
Electrostream drilling
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Shaped-tube elecrolytic machining (STEM)
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High velocity stream of charged acidic, electrolyte
Capable of drilling small holes in difficult to
machine materials
Electrochemical grinding (ECG)
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Low voltage, high-current variant of ECM
Figure 28-8 The shaped-tube electrolytic
machining (STEM) cell process is a specialized
ECM technique for drilling small holes using a
metal tube electrode or metal tube electrode with
dielectric coating.
Figure 28-9 Equipment setup and electrical circuit for electrochemical grinding.
Other Electrochemical Processes
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Electrochemical deburring
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Electrolysis is accelerated in areas with small
interelectrode gaps and prevented in areas with
insulation between electrodes
Design factors in electrochemical machining
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Current densities tend to concentrate at sharp
edges or features
Control of electrolyte flow can be difficult
Parts may have lower fatigue resistance
Advantages and Disadvantages of
Electrochemical Machining
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Advantages
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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
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Disadvantages
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Initial tooling can be
timely and costly
Environmentally harmful
by-products
28.4 Electrical Discharge Machining
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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
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Ram EDM/ sinker EDM
Wire EDM
Figure 28-10 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.
EDM Processes
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Slow compared to
conventional machining
Produce a matte
surface
Complex geometries
are possible
Often used in tool and
die making
Figure 28-11 Schematic diagram of equipment
for wire EDM using a moving wire electrode.
EDM Processes
Figure 28-12 (left) Examples of wire EDM
workpieces made on NC machine (Hatachi).
Figure 28-13 (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 28-14 The principles of
metal removal for EDM.
Considerations for EDM
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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
The dielectric fluid has four main functions
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Electrical insulation
Spark conductor
Flushing medium
Coolant
Advantages and Disadvantages of EDM
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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
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Disadvantages
Produces a hard recast
surface
Surface may contain
fine cracks caused by
thermal stress
Fumes can be toxic
Electron and Ion Machining
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Electron beam machining
(EBM) is a thermal process
that uses a beam of highenergy 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 28-15 Electron-beam machining uses a highenergy electron beam (109 W/in.2)
Laser-Beam Machining
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Laser-beam machining (LBM) uses an intensely
focused coherent stream of light to vaporize or
chemically ablate materials
Figure 28-16 Schematic
diagram of a laser-beam
machine, a thermal NTM
process that can
micromachine any material.
Plasma Arc Cutting (PAC)
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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
Figure 28-18 Plasma arc machining or cutting.
Thermal Deburring
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Used to remove burrs
and fins by exposing
the workpiece to hot
corrosive gases for a
short period of time
Thermal deburring can
remove burrs or fins
from almost any
material but is
especially effective with
materials of low thermal
conductivity
Figure 28-20 Thermochemical machining
process for the removal of burrs and fins.