An educational report on Non Conventional Machining processes like EDM, LBM, USM & ECM

1. March 8, 2016
Non-Conventional Machining
Name: Marwan Shehata Mohamed Zeitoun
Sec: 7 No: 159

2. PAGE 1
EDM (Electrical Discharge Machining)
EDM is the thermal erosion process in which metal is removed by
a series of recurring electrical discharges between a cutting tool
acting as an electrode and a conductive workpiece, in the presence
of a dielectric fluid. This discharge occurs in a voltage gap between
the electrode and workpiece. Heat from the discharge vaporizes minute particles of workpiece material, which
are then washed from the gap by the continuously flushing dielectric fluid.
There are two main types of EDMs; the ram and the wire-cut. Each are used to produce very small and accurate
parts as well as large items like automotive stamping dies and aircraft body components. The largest single use of
EDM is in die making. Materials worked with EDM include hardened and heat-treated steels, carbide,
polycrystalline diamond, titanium, hot and cold rolled steels, copper, brass, and high temperature alloys.
However, any material to be machined with the EDM process must be conductive.
The Benefits of EDM
1- EDM is a non-contact process that generates no cutting forces, permitting the production of small and
fragile pieces
2- Burr-free edges are produced
3- intricate details and superior finishes are possible
4- EDM machines with built-in process knowledge allow the production of intricate parts with minimum
operator intervention
The limitations of EDM
1- low metal removal rates compared to chip machining
2- lead time is needed to produce specific, consumable electrode shapes
Ram EDM
In ram EDM, the electrode/tool is attached to the ram which is connected to one pole, usually the positive pole,
of a pulsed power supply. The workpiece is connected to the negative pole. The work is then positioned so that
there is a gap between it and the electrode. The gap is then flooded with the dielectric fluid. Once the power
supply is turned on, thousands of direct current, or DC, impulses per second cross the gap, beginning the erosion
process. The spark temperatures generated can range from 14,000° to 21,000° Fahrenheit. As the erosion
continues, the electrode advances into the work while maintaining a constant gap dimension.
The finished EDM'd workpiece can exhibit several distinct layers. The surface layer will have small globules of
removed workpiece metal and electrode particles adhering to it, which are easily removed. The second layer is
called the “white” or “recast” layer where EDM has altered the metallurgical structure of the workpiece. The third
layer is the heat-affected zone or “annealed” layer. This layer has been heated but not melted.
Wire EDM
The wire EDM process uses a consumable, electrically charged wire to effect very fine and intricate cuts. The
process is particularly useful in cutting fine details in pre-hardened stamping and blanking dies. A wire drive
system constantly presents fresh wire to the work so electrode wear is not a problem. Typical wire diameters
range from .002 to .013 inches. These wires will produce a kerf slightly larger than their own diameter. A .012 wire
will leave a .015 kerf, just .003 inches larger. Wire EDM’s can run for long periods without operator attention.

3. PAGE 2
The four basic wire EDM subsystems include:
• the DC power supply
• the dielectric system
• the wire feeding system
• the work positioning system
LBM (Laser Beam Machining)
Modern machining methods are established to
fabricate difficult-to-machine materials such as
high-strength thermal-resistant alloys; various
kinds of carbides, fiber-reinforced composite
materials, Stellites, and ceramics. Conventional
machining of such materials produces high cutting
forces that, in some particular cases, may not be
sustained by the workpiece. Laser beam machining
(LBM) offers a good solution that is indeed more
associated with material properties such as
thermal conductivity and specific heat as well as
melting and boiling temperatures.
the unreflected light is absorbed, thus heating the
surface of the specimen. On sufficient heat the
workpiece starts to melt and evaporates. The physics of laser machining is very complex due mainly to scattering
and reflection losses at the machined surface.

4. PAGE 3
Applications of LBM
LBM can make very accurate holes as small as 0.005 mm in refractory metals ceramics, and composite material
without warping the work pieces. This process is used widely for drilling and cutting of metallic and non-metallic
materials. Laser beam machining is being used extensively in the electronic and automotive industries.
Limitations of LBM
 High capital cost
 High maintenance cost
 Assist or cover gas required
 Tapers are normally encountered in the direct drilling of holes.
 A blind hole of precise depth is difficult to achieve with a laser.
 The thickness of the material that can be laser drilled is restricted to 50 mm.
 Adherent materials, which are found normally at the exit holes, need to be removed.
Parameters affecting the quality of machined holes using LBM
Advantages of LBM
 Tool wear and breakage are not encountered.
 Holes can be located accurately by using an optical laser system for alignment.
 Very small holes with a large aspect ratio can be produced.
 A wide variety of hard and difficult-to-machine materials can be tackled.

5. PAGE 4
 Machining is extremely rapid and the setup times are economical.
 Holes can be drilled at difficult entrance angles (10° to the surface).
 Because of its flexibility, the process can be automated easily such as the on-the-fly operation for thin
gauge material, which requires one shot to produce a hole.
 The operating cost is low.
USM (Ultrasonic Machining)
Ultrasonic machining (USM) is the removal of hard and brittle materials using an axially oscillating tool at
ultrasonic frequencies [18–20 kilohertz (kHz)].
During that oscillation, the abrasive slurry of B4C or SiC is continuously fed into the machining zone between a
soft tool (brass or steel) and the workpiece. The abrasive particles are, therefore, hammered into the workpiece
surface and cause chipping of fine particles from it.
The oscillating tool, at amplitudes ranging from 10 to 40 μm, imposes a static pressure on the abrasive grains and
feeds down as the material is removed to form the required tool shape. Balamuth first discovered USM in 1945
during ultrasonic grinding of abrasive powders. The industrial applications began in the 1950s when the new
machine tools appeared. USM is characterized by the absence of any deleterious effect on the metallic structure
of the workpiece material.
The machining system is composed mainly from the magnetostrictor, concentrator, tool, and slurry feeding
arrangement. The magnetostrictor is energized at the ultrasonic frequency and produces small-amplitude
vibrations. Such a small vibration is amplified using the constrictor (mechanical amplifier) that holds the tool.
The abrasive slurry is pumped between the oscillating tool and the brittle workpiece. Astatic pressure is applied
in the tool-workpiece interface that maintains the abrasive slurry.

6. PAGE 5
Factors affecting material removal rate
 Tool oscillation: The amplitude of the tool oscillation has the greatest effect of all the process variables.
The material removal rate increases with a rise in the amplitude of the tool vibration. The vibration
amplitude determines the velocity of the abrasive particles at the interface between the tool and
workpiece. Under such circumstances the kinetic energy rises, at larger amplitudes, which enhances the
mechanical chipping action and consequently increases the removal rate.
 Abrasive grains: Both the grain size and the vibration amplitude have a similar effect on the removal
rate. The removal rate rises at greater grain sizes until the size reaches the vibration amplitude, at which
stage, the material removal rate decreases. When the grain size is large compared to the vibration
amplitude, there is a difficulty of abrasive renewal in the machining gap. Because of its higher hardness,
B4C achieves higher removal rates than silicon carbide (SiC) when machining a soda glass workpiece. The
rate of material removal obtained with silicon carbide is about 15 percent lower when machining glass, 33
percent lower for tool steel, and about 35 percent lower for sintered carbide
 Workpiece impact-hardness: The machining rate is affected by the ratio of the tool hardness to the
workpiece hardness. In this regard, the higher the ratio, the lower will be the material removal rate. For
this reason, soft and tough materials are recommended for USM tools.
 Tool shape: The machining rate is affected by the tool shape and area. An increase in the tool area
decreases the machining rate due to the problem of adequately distributing the abrasive slurry over the
entire machining zone.
Electrochemical Machining (ECM)
Electrochemical machining (ECM) is a modern machining process that relies on the removal of workpiece atoms
by electrochemical dissolution (ECD) in accordance with the principles of Faraday (1833). Gusseff introduced the
first patent on ECM in 1929, and the first significant development occurred in the 1950s, when the process was
used for machining high-strength and heat-resistant alloys.
Principles of electrolysis
Electrolysis occurs when an electric current passes between two electrodes dipped into an electrolyte solution.
The system of the electrodes and the electrolyte is referred to as the electrolytic cell. The chemical reactions,
which occur at the electrodes, are called the anodic or cathodic reactions. ED of the anodic workpiece forms the
basis for ECM of metals. The amount of metal dissolved (removed by machining) or deposited is calculated from
Faraday’s laws of electrolysis, which state that
1- The amount of mass dissolved (removed by machining), m, is directly proportional to the amount of
electricity. m ∝ It
2- The amount of different substances dissolved, m, by the same quantity of electricity (It) is proportional to
the substances’ chemical equivalent weight ε. m∝ ε
Setup and Equipment
The figure next page shows the main components of the ECM machine: the feed control system, electrolyte
supply system, power supply unit, and workpiece holding device. As shown in the figure, the feed control system
is responsible for feeding the tool at a constant rate during equilibrium machining. The power supply drives the
machining current at a constant dc (continuous or pulsed) voltage.

7. PAGE 6
ECM Elements
ECM System Components

8. PAGE 7
Parameters
 Power supply. The dc power supply for ECM has the following features:
1. Voltage of 2 to 30 volts (V) (pulsed or continuous)
2. Current ranges from 50 to 10,000 amperes (A), which allow current densities of 5 to 500 A/cm2
3. Continuous adjustment of the gap voltage
4. Control of the machining current in case of emergency
5. Short circuit protection in a matter of 0.001 s
6. High power factor, high efficiency, small size and weight, and low cost
 Electrolytes. The main functions of the electrolytes in ECM are to
1. Create conditions for anodic dissolution of workpiece material
2. Conduct the machining current
3. Remove the debris of the electrochemical reactions from the gap
4. Carry away the heat generated by the machining process
5. Maintain a constant temperature in the machining region
The electrolyte solution should, therefore, be able to
1. Ensure a uniform and high-speed anodic dissolution
2. Avoid the formation of a passive film on the anodic surface (electrolytes containing anions of
Cl, SO4, NO3, ClO3, and OH are often recommended)
3. Not deposit on the cathode surface, so that the cathode shape remains unchanged (potassium
and sodium electrolytes are used)
4. Have a high electrical conductivity and low viscosity to reduce the power loss due to electrolyte
resistance and heat generation and to ensure good flow conditions in the extremely narrow interelectrode
gap
5. Be safe, nontoxic, and less erosive to the machine body
6. Maintain its stable ingredients and pH value, during the machining period
7. Have small variation in its conductivity and viscosity due to temperature rise
8. Be inexpensive and easily available
References
1- www.unl.edu
2- Advanced Machining Processes (Hassan El-Hofy)
3- Cambridge educational PDFs