MACHlNES FOR NON-CONVENTIONAL TECHNOLOGIES
6.1 Classification and comparisons
Machines and equipments which do not apply machining technology based on cutting process
can be classified as non-conventional machines. The marking as “non-conventional” express
the special principle of technology such as electro-chemical, mechanical - so called “cool”
processes or electro-thermal processes.
Figure 6.1 illustrates the position occupied by erosion machines in the total complex of metal-
separation machines. According to the erosion principle involved, differentiation is made
between erosion through chemical and electrochemical action, erosion by discharge of an
electric spark, and erosion through high energy beams as in laser and electron-beam
Fig. 6.1 Classification of erosion and ultrasonic machining techniques
Ultrasonic machining is actually a chip-producing lapping technique, but owing to the similarity
of machines and applications, it is dealt within this chapter. Figure 6.2 makes comparisons of
the various techniques in relation to their physical performance limitations, their areas of
application, as well as their effects on tools and work materials. The use of erosion-type
machine tools is currently limited to the tool-making industry and the production of components
which, owing to their complicated geometric form or the properties of their material (hardness),
cannot be economically machined with a chip-forming process.
Technique Erosion method Applications Features
Electro-chemical Die sinking Tool: Formed or profiled electrode, no wear
Electro-chemical Current density = < 500 A/cm Grinding Work: Must be electrically conductive
machining (ECM) Voltages 5V – 30V Cutting Material composition and hardness non-critical
(Engraving, drilling) Possible combination with mechanical machining
Thermal Die sinking Tool: Formed, profiled or wire electrode, high wear rates
Electro discharge Max. energy density = Engraving Work: Must be electrically conductive
machining (EDM) = < 5 x 10 kW/cm Drilling Material composition and hardness non-critical
Electron beam Thermic Drilling Tool: Electron beam, min. diameter 10 µm
machining Energy density approximately Engraving Work: Electrically conductive or insulating
5 6 2
10 – 10 kW/cm Parting
Thermic Drilling Tool: Coherent light beam, optically focused
Laser machining Energy density approximately Parting Work: Electrically conductive or insulating
(light beam) 10 kW/cm
intermittent or continuous
Chemical machining Chemical Form etching Tool: Etching agent e.g. HCl
(etching) Erosion velocity 10-80 µm/min Printed circuits Work: Metallic or non-metallic
Mechanical Drilling Tool: Formed or profiled bar, medium wear rates works in
Ultrasonic Frequency approximately 20kHz Engraving conjunction with boron carbide B4C in suspension
machining Power available at tool Work: Electrically conductive or insulating
approximately 300 W Brittle materials preferred
Cutting Tool: Fluids
Water Jet Cleaning
machining __________________ Striping Work: Almost all materials
Fig. 6.2 Erosion and ultrasonic machining techniques
6.2 Electrochemical machines (ECM)
The principle underlying electrochemical machining (ECM) rests on an exchange of charge and
material between a positively charged anodic workpiece and a negatively charged cathodic tool
in an electrolyte. In such conditions, the anode dissolves whilst the cathode (tool) is not
affected. The volume of metal removal may be calculated according to Faraday's Law:
v= C I t
where C is a constant dependent on work material, I is the current flowing between the tool and
the work, and t is the time of erosion. The current is dependent on the gap between tool and
work, the are a of erosion and the conductivity of the electrolyte, as well as the supply voltage.
The working gap maintained between the electrode and work allows machining to' take place
without physical contact. The electrolyte (e.g. NaCl or NaNO3 in water solution) is pumped into
the working gap and also serves as a coolant which is necessary due to the high energy
density. The material which has been eroded from the work forms a sludge, and must be
separated from the electrolyte by filters or centrifuges.
6.2.1 Electrochemical die-sinking machines
Figure 6.3 presents, in schematic form, the main components of an electrochemical die-
sinking machine. A feeding device advances the tool towards the work in accordance with the
rate of metal removal. When producing internal forms, a design problem arises in relation to
the shape and size of the too1. The gap is not constant, but is a function of the state of the
surface to be eroded and the rate of tool advance. If, for example, a cylindrical bore is to be
sunk, a simple cylindrical tool (as shown in Fig. 6.4) is not suitable. This would result in a
constantly increasing gap size and the current density would decrease in proportion (Fig. 6.4,
left). With a tool suitably insulated on its sides (Fig. 6.4, right), the offending excessive erosion
of cylindrical sides will be suppressed.
The functions which must be performed by the individual elements of the machine are
summarized in Fig. 6.5. Owing to the small gap sizes which are used in electrochemical
machining, high electrolyte pressures (>20 bar) are necessary so that there is an adequate
flow for effective cooling and removal of the eroded material. In an erosion area of 10000 mm2,
forces in excess of 20 kN may be experienced, with which the tool-feeding system and the
machine structure must be able to cope. As the electrolyte consists of a corrosive salt solution,
.all machine components likely to come into contact with it must be corrosion-proof. An
important auxiliary installation is a short-circuit cut-out, which immediately stops the supply of
further electrical energy in the event of inadequate clearance of the eroded material and
insufficient gap between tool and work.
Fig. 6.3 Main components of an electrochemical machining plant
Fig. 6.4 Cavity development during electrochemical machining with different tool electrodes
Machine Stepless feed advance free from stick slip; Effect of feed rate on quality of finished product
sensitive controls; constant feed; accurate
positioning and repeatability
Rigid construction High electrolyte pressures
Corrosion-resistant materials Use of salt solutions
Power supply Stepless voltage selection Effect of voltage on quality of finished product
Constant voltage controls
Monitoring of working gap, very fast short Need for avoidance of short circuits
circuit cut out
Electrolyte supply Monitoring and regulation of electrolyte Influence of the electrolyte parameters on finished
and circuit parameters products
Filtering and cleaning Erosion products in electrolyte
Corrosion protection Use of salt solutions
Fig. 6.5 Requirements of an electrochemical machining plant
Electrochemical die-sinking machines are constructed in an open 'C' structure for small- to
medium-sized work, and for machines having larger work areas the dosed 'O' construction
form is used.
The preferred direction of tool feed is vertical. Figure 6.6 shows a machine built on a
building-block system, in which various combinations of machine bed, frame element s and
work .heads may be achieved. The tool advance is mostly electrohydraulic; however, electric
drives such as disc armature motors connected to a recirculating ball leadscrew and nut are
Figure 6.7 illustrates a two-station die-sinking machine in a twin 'C' structure frame with a
common work area. The two stations operate independently, so that they may be alternately
loaded. The tool advance is activated by an electrohydraulic stepping motor.
Fig. 6.6 Unit construction of electrochemical machining plants
Fig. 6.7 Electrochemical plant made in unit construction
6.2.2 Electrochemical de-burring machines
In contrast to electrochemical die-sinking, when ECM is used for de-burring there is no
advance of the tool. All other machine elements are identical. The work is mostly carried out in
a fixture as is shown by the example in Fig. 6.8 of a machine for de-burring gear wheels. The
fixture contains the tool electrode and holds the work. The working current is transmitted
through spring contacts. The cathodic areas consist of those points from which the material is
to be removed (in the example, the front and back of the tooth flank). The electrolyte is fed to
the same points. The extent to which the sharp edges and burrs are removed is dependent
upon the magnitude of the electric field.
Fig. 6.8 Diagrammatic construction of an electrochemical de-burring plant
6.3 Electrodischarge machines (EDM) (spark erosion)
When applying the EDM process, the material is eroded as a result of an electrical discharge
between tool and work. Due to the resultant short-lived, but very high, temperature rises, metal
particles at the point of discharge are molten, partially vapourized and removed from the melt
by mechanical and electromagnetic forces. The working medium is a dielectric, which washes
the eroded material away and simultaneously acts as a coolant.
As in the case of ECM, EDM is a copying process where there is no contact between tool
and work. Contrary to ECM, however, there is some erosion of the tool in EDM, which must be
allowed for in the tool design to ensure accuracy of machining.
A further difference arises from the fact that in EDM there is no fixed tool feed, but the gap
size must be maintained in accordance with the rate of metal removal and the conditions
existing within the gap.
6.3.1 Electrodischarge die-sinking machines
The construction principles of an EDM die-sinking machine are shown in Fig. 6.9. Spark
erosion takes place in a container filled with the dielectric, in which the work is clamped. The
controlled feed of the electrode is through an electrohydraulic or electromechanical servo
system. The electrical energy for erosion is provided by the erosion generator. The filtering unit
separates the eroded material from the dielectric. In the upper left of Fig. 6.9, a single
discharge is illustrated in enlarged form. The applied voltage ionizes the gap at the beginning
of the discharge. At the point of highest field strength, a channel is formed through which the
discharge current flows. At each end of the channel, the material melts and the channel and its
surrounding gas bubble expand. When the voltage is fully discharged, the channel collapses
and the molten material vaporizes, simulating a miniature explosion. The resultant crater is a
hallmark of the irregular and scarred surface finish of spark-eroded work.
Fig. 6.9 Electrodischarge erosion plant
According to the expected result, a number of setting factors must be attended to when
setting-up the machine for a new component (Fig. 6.10).
Fig. 6.10 Criteria for setting electrodischarge machines
In order to provide for repetitive and suitably timed discharges, the electrical energy must be
provided in a pulsating manner. Two types of generator have been developed. The first is a
relaxation-circuit generator, which operates on the principle illustrated in Fig. 6.11. The
discharge energy required for one discharge is stored in a variable condenser. When the
condenser reaches the breakdown voltage Vd required to cross the width of the gap, the
discharge takes place. The voltage end-current diagram shown in Fig. 6.11 illustrates the
electrical cycle characteristics. As the breakdown voltage is almost entirely dependent upon
the conditions existing in the gap, the discharges occur at irregular time intervals. The static-
pulse generator, the switching principle of which is illustrated in Fig. 6.12, is more frequently
used. It offers the advantage that the spark discharge through the gap is more regular and of
constant duration. The switching is achieved with the use of power transistors. The actual
working circuit with supply voltage Va may have a second high-resistance circuit switched in
parallel with a higher voltage Vz. The right-hand section of Fig. 6.12 indicates the possible
voltage and current situation in the gap. Idle pulses and dead shorts remove no material, but
during such a condition, the secondary voltage and current circuit illustrated in the diagram has
the typical form of a discharge through which material is eroded.
Fig. 6.11 Switching circuit of a relaxation circuit generator, and voltage-time and current-time diagrams
Fig. 6.12 Switching circuit of a pulse generator circuit generator, and voltage-time and current-time circuits
The spark-voltage control circuit, aided by the servo feed system, sets the gap to a value which
will provide the maximum possible number of discharges. Figure 6.13 shows a diagram of this
control circuit. The working process is monitored by observing the voltage conditions in the
Fig. 6.13 Automatic control diagram of the spark-voltage control circuit in a spark erosion machine
When an idle pulse occurs, the tool must travel nearer to the work (i.e. feed) and it must retract
after a short circuit. To achieve these conditions, the mean working voltage (obtained through a
smoothing element from the discharge voltage) is compared with a pre-set value. The result of
this comparison, i.e. the deviation from the pre-set value, is the activating signal for the servo
mechanism (feed mechanism of the electrode).
To produce the feed motion, most machines are fitted with an electrohydraulic piston and
cylinder system with a servo unit, as shown schematically in Fig. 6.14. In accordance with the
signal received, the servomotor is activated and the tool electrode advances to, or retracts
from, the work. As a result of the development of low-inertia DC motors, an increasing number
of electromechanical feed systems are also used.
An important part of a spark-erosion die-sinking machine is the dielectric supply unit, shown
schematically in Fig. 6.15. Paper filter units or, in larger units, alluvial filters (sand filters) are
used to keep the dielectric clean.
Fig. 6.14 Diagrammatic construction of an electrohydraulic feed unit of a spark erosion machine
Fig. 6.15 Basic lay-out of filtering and supply circuit for dielectric of a spark erosion machine
When compared with ECM, the forces in the gap during EDM are much smaller.
Consequently, there is not the same degree of stiffness required in the machine frame. A 'C'
form construction (following the shape of the letter C, see Fig. 6.6) is normally preferred. In
very large machines, in which correspondingly large and heavy electrodes are used (e.g. for
tools required for the production of motor car body components), c1osed 'O'-form constructions
are used (following the shape of the letter O, see Fig. 6.6). Figure 6.16 shows a machine of
medium size. The clamping plate for the tool and the connections for the dielectric may be
seen in the open work space. Below the container, the co-ordinate table may be manually
positioned. The electrohydraulic feeding system carrying the spindle with the electrode
c1amping unit is situated in the work head.
A number of installations have a numerically controlled positioning system added to the basic
machine. Other extra equipment may be flexible tool-clamping systems and control units for
the optimisation of the working process.
Fig. 6.16 Spark erosion die-sinking machine
6.3.2 Electrodischarge cutting machines
An important application of the spark-erosion process is the cutting of metal by wire electrodes.
The process is used for the production of apertures in cutting tools and the manufacture of tool
electrodes for EDM. Figure 6.17 illustrates the principle. The cutting tool is a thin copper or
brass wire, which enters the work during cutting without physical contact. This suffers wear as
a result of the action of spark erosion, and for this reason fresh wire is constantly supplied. The
apparatus required for wire feeding can be seen in Fig. 6.18. The degree of wire tension, the
rate of wire consumption and the reach of the wire support arms are adjusted in accordance
with the work to be done and the size of the workpiece. The working medium for
electrodischarge cutting is usually de-ionized water, which is fed to the work area with the use
of flushing jets.
Fig. 6.17 Numerically controlled EDM cutting Fig. 6.18 Wire-feed control for an EDM cutting machine
x and y right-angled co-ordinates
Figure 6.19 shows a complete picture of an electrodischarge installation. According to the
required contour of the workpiece, the table with the work clamped to it and the slide with the
wire feed unit must be suitably positioned. The relative advance of the cutting tool to the work
does not have a constant velocity, but must be varied in accordance with the conditions
existing in the gap throughout the process, depending on the progress of the cut, as was the
case in electrodischarge machining. The generator is situated on the left in Fig. 6.19, next to
the machine; on the right, the numerically controlled guide unit with its punched paper tape
reader may be seen.
Fig. 6.19 Numerically controlled EDM wire-electrode cutting machine
6.4 Electron-beam cutting installations
In electron-beam cutting, the work material is vaporized as a result of a beam of accelerated
electrons impinging on a point of contact. Within a few milliseconds, a channel is cut into the
work material. The vapour pressure forces the molten metal in the immediate vicinity out of the
channel. The depth, diameter and form of the cut can be controlled through the characteristics
of the beam.
The schematic arrangement of an electron-beam cutting machine is illustrated in Fig. 6.20.
Apart from the actual work chamber, a high-voltage source (up to 150 kV) is required, as are
devices for the positioning of the electron beam and the work in relation to it. The process
takes place in a vacuum in order to avoid the energy-absorbing collision of the electrons with
air molecules. The beam may be deflected sideways and focused through the use of a system
of magnetic lenses and deflection coils. The power density may be up to 106 kW cm-2 with a
minimum beam diameter of 2 µm.
Fig. 6.20 Block diagram of an electron-beam cutting machine
Figure 6.21 shows a computer-controlled perforation machine. The work chamber of the
machine has a volume of 0.6 m3, which can be evacuated in 2 min. The simultaneous on-line
guiding of the workpiece, beam deflection and beam focusing allow the perforation process to
be carried out with great speed and fully automatically.
6.5 Laser cutting machines
Laser cutting uses the erosion effect of high-energy light beams. As in the case of electron-
beam cutting, the work material is vaporized at the point of impact. A schematic illustration of
the laser-beam cutting process is illustrated in Fig. 6.22. According to the laser material used,
differentiation is made between solid and gas lasers. With solid lasers (e.g. ruby, neodymium-
yttrium-aluminium-garnet), the excitement of a light emission is achieved with the use of a flash
light (pump light), and when using a gas laser (e.g. CO2, helium-neon) through the provision of
a high voltage. A lens system focuses the monochromatic high-energy light. The power density
achievable at the point of contact with the work may be up to 107 kW cm-2.
Fig. 6.21 Computer-controlled electron-beam perforation machine
Fig. 6.22 Diagrammatic presentation of
Figure 6.23 shows a laser cutting machine which is used for the cutting and finishing of
resistors for electronic switch circuits. The work is positioned on an air-bearing table and cross
slide under the fixed laser gun. The drive is obtained from electric stepping motors. On the left
of Fig. 6.23, the electrical control cabinet and the numerically controlled positioning unit may
be seen standing next to the machine.
Fig. 6.23 Numerically controlled laser machining plant
6.6 Chemical etching machines
In contrast to the electrochemical processes, the chemical etching process does not use a
forming tool nor an external electric power. The work material is mainly removed as a result of
differences of potential at the grain boundaries according to the particular material being
worked. Figure 6.24 illustrates the principle involved. A variety of acids are used as activators.
Filters or centrifuges separate the removed material from the etching medium.
The work is carried out either in a bath of the etching medium (dip etching) or by spraying the
etching medium on to the work (spray etching). In order to obtain a particular work geometry,
the parts of the surface which are not to be machined are protected by masking. Frequently, a
photographic film technique is employed, whereby the workpiece is covered with a light-
sensitive film by rolling it on or dipping. A photographic image of the desired work geometry is
then projected on to the work surface, so that the illuminated areas of the work become
sensitive to the acid attack and the remaining areas are suitably masked.
Fig. 6.24 Chemical machining or etching
Fig. 6.25 Spray-etching plant
Figure 6.25 shows an installation for spray etching. A transportation unit brings the work into
the etching chamber and into the post-process units. As the operation takes place in
completely enclosed chambers with suitable extraction systems, the operator is fully protected.
Those parts of the installation which come into contact with the erosion medium are made from
special corrosion-resistant materials. As the waste products from the process itself and the
subsequent cleaning operations may be contaminated with poisonous substances, special
attention must be paid to the waste disposal installation.
Fig. 6.26 Principles of ultrasonic machining
6.7 Ultrasonic assisted machining units
Ultrasonic machining installations are mainly used for machining electrically non-conductive,
brittle materials (such as glass, ceramic oxides, precious stones, carbides, germanium,
silicons, graphite and hard metals). The principle is outlined in Fig. 6.26. A high-frequency
generator activates the magnetostrictive oscillator, which transmits the high-frequency
oscillations to the tool soldered to the tapered bronze transformer. The tool itself is only
indirectly active in the actual metal removal process. The work material is removed through
abrasive grains suspended in a slurry, which acts in a manner similar to that of the lapping
process (Chapter 8)-like a number of simultaneously acting chisel points. The slurry
suspension is externally applied to the work area and sucked up through the transformer. In
Fig. 6.27 is a spindle designed for ultrasonic assisted machining grinding machine.
In many installations, no separate feeding mechanism is provided. By a vertical arrangement
of the tool-work system, the tool advances into the work as a result of its own weight.
Fig. 6.27 Spindle designed for ultrasonic assisted machining grinding machine
6.8 Water Jet Machining Machines
An essential component of all water jet cutting and abrasive water jet cutting machine is the
high pressure pump. The heart of every pump unit is so-called intensifier. The oil pressure
generated in the hydraulic drive is increased to an operating pressure of up to 400 MPa in
accordance with the surface ratio of the low pressure piston on the oil side. Figure 6.28
illustrates the design of a high pressure system. Connection between pump pressure, flow rate
and nozzle diameter shows the Fig. 6.29. The figures indicated here correspond to average
consumption and were ascertained on the basis of experimental data. More detailed
information can be find in web-site.
Water jet machining technology (WJM) and WJM systems have been outstanding know-how in
high-tech fields. The wide-spectral applications make of this technology not only for cutting but
also for cleaning processes. WJM technology and systems offer to cut or to clean a lot of
materials such as austenit Cr-Ni steels, so called spring´s steel, or Al, Co, Mo, Ni, VaTiMg
alloys and Cu-based materials for example. WJM is universal engineering field applied for
cutting plastics, laminates, glass, ceramics, layered material, concrete, stones or super-hard
materials such as sapphire, ruby, etc. as well as soft materials.
WJM has some splendid features such as “ cold” cutting operation, minimum cutting forces, no
chatter vibration, precise cut with minimum waste and environmental impact.
There are a number of applications and using another medium of cutting jet like a water ( for
example – a cryogenic jet or discontinual jet, abrasive jet, etc.) bringing a new advanced
technology. These applications can be utilised in armament ( S 23 missiles), engineering
science (microsystems), nuclear equipment, in medical fields, in recycling processes ( waste
treatment), landmines for humanitarian demining, in hydrodemolition and cleaning – concrete
refurbishment ant the other fields of human activities.
Fig. 6.28 Design of a high pressure pump system Fig. 6.29 Connection between pump pressure,
flow rate and nozzle diameter.
The figures indicated here correspond
to average consumption and were
ascertained on the basis of empirical
6.9 Parallel kinematic machines
Rapid production of the quality contoured parts requires machine tools that combine speed,
accuracy, stiffness and multiaxis versatility. In addition, the manufacturers look for kinematics
that ensure quality production concerning easy of installation and moveability. In order to
enable a machine structure to be reconfigured a parallel kinematic machine have been
developed to meet changing market demands.
Fig. 6.30 illustrates a new concept of machine tool based on the parallel kinematic structure –
called Hexapod. Potentional benefit of hexapod machine includes increased stiffness, higher
accuracy, higher speed and acceleration due to reduced moving mass reducing idle time
machining and installation (fixed) costs.
Fig. 6.30 Hexapods
Fig.6.31 shows hexaglide that has a parallel kinematics as a Hexapod. Using of linear
technology this kinematic structure offer some advantages comparing to hexapod one. Expect
the joints it can be built using off the shelve parts. The workspace can easily be scaled in the
direction of the rails without increasing the other dimensions. This allows using especially high
speed machining of long parts.
Compared to hexapod the structure of hexaglide offers the following advantages:
- the workspace can be scaled in one direction without increasing the size of the
machine in the other directions,
- Except for the joints it can be built out of standard parts especially there are no
- Thermal drift in the legs can be easier compensated,
- Using of linear motors gives even higher dynamics of the structure,
- Guidelines are parallel and all in a plane due to required precision of the machine
- Last but not least a simplification of the structure brings lower fixed cost of the
Fig. 6.31 Hexaglides
Fig. 6.32 represents a new generation of a parallel kinematic structure. These machines are
under strong research and development activities on modelling, constraints and deformation
analysis for accuracy assessment of closed chains, redundability, structural and parametrical
synthesis, calibration or error analysis etc.
Fig. 6.31 Examples of tricepts
1. Can you classify the term “cutting tool with defined geometry“?
2. Can you draw up a motion combination for creating machines surfaces? How could you
produce a cube onto a lathe?
3. Can you marked the main parts of a machine structure with the main rotary motion?
4. Can you draw up a sketch of a multi-spindle machine? Make a positioning of the main
5. Could you make a sketch of a multioperational head?
6. Can you draw up a sketch of a deep-hole drilling machine? What ´s the BTA method of
7. Can you make a sketch of a machining centre (MC) for rotational workpiece machining?
8. What ´s mean the term “microfactory”? Show examples!
9. Can you find up a few applications of MET / MEMS in production engineering?