Transcript PRODUCTION PROCESSES AND EQUIPMENT Kristo Karjust MET0180_Basic of Production Engineering

PRODUCTION PROCESSES
AND EQUIPMENT
Kristo Karjust
MET0180_Basic of Production Engineering
Cutting processes will divide:
• Mechanical cutting
processes;
• Electrical and
chemical cutting
processes;
• Thermal cutting
processes.
Mechanical cutting processes
Chip-removal operations
Turning
The turning process is characterized by
solid work material, two-dimensional
forming and a shear state of stress. The
workpiece (W) is supported [clamped in a
chuck (C) and supported by a center] and
rotated (the primary motion R). Through the
primary motion (R) and the translator feed
(Ta =axial feed for turning and Tr = radial
feed for facing) of the tool (V) the
workpiece is shaped.
Possible workable shapes and typical turning tools
Turning is used primarily in the production of various cylindrical components with
nearly unlimited number of external and internal axial cross-sectional shapes
(including tapers, threads etc.). Facing is used for both regular and irregular shapes.
Turning is the most extensively used industrial process, because it is quite cheap
and easy.
In the turning process is important workpiece quality, for instance if we want to
get surface quality IT6, then blank quality should be IT7. The material should not
be too hard (HB<300) and should possess a minimum of ductility to confine
deformation mainly to the shear zone. Generally turning provides close tolerances,
often less than ± 0.01 mm. Tighter tolerances may be obtained. The surface
roughness after turning is in the range 0.02 ≤ Ra ≤ 3.2 µm and quality at least IT6.
Cutting-Tool Geometry
Tool geometry—external turning [18].
Lathe cutting equipment
A wide variety of lathes are on the market: for instance, the engine lathe, the turret
lathe, single- and multispindle screw machines, automatic lathes and NC lathes. In
figure 1.1.1.3 is shown some lathes. Lathes are most frequently used machine in
industry, because they are available in a wide range of sizes.
Horizontal lathe and vertical lathe
If heavy and large workpieces are to be machined, the horizontal lathe is
impractical. Therefore, the vertical boring mill, which can be considered as a
vertical lathe, has been developed [2].
Drilling
The drilling process is characterized by solid work material, two-dimensional
forming and a shear state of stress. The workpiece (W) is clamped on a table (B)
and the tool (V) is given a rotation (the primary motion R) and translator feed (T).
In drilling lathes, the workpiece is rotated and the feed is applied to the tool.
Thrust forces and torque in drilling operation [18].
The drilling process is primarily used to produce interior circular, cylindrical
holes. Through various tools (twist drills, combination drills, spade drills, etc.)
different hole shape can be produced as cylindrical holes, drilled and
counterbored, drilled and countersunk, multiple diameter holes, etc. drilling is an
important industrial process.
Plants and equipment. Twist drills are manufactured in a wide variety of types
and sizes. Various surface treatments such as cyaniding and nitriding are applied
to high-speed-steel drills in order to increase the hardness of the outer layer of
material. Special polishing and black oxiding are beneficial to minimize friction
between the drill and the workpiece or the chips in the flutes.
Drilling
Spiraalpuur
Spiraalpuur puidule
Reguleeritav puur
Tapipuur
Tüüblipuur
Betoonipuur
Betooni haamerpuur
Freespuur
Freespuur
Juhtmepuur
Keermepuur
NC-tsentripuur
Oksapuur
Astmeline puur
Kooniline plekipuur
Kooniline plekipuur
Puur kahhelkivile
Tsentripuur
Topelttsentripuur
Tsentripuur
Milling
The milling process is characterized by solid work material, two-dimensional
forming (one dimensional forming may be used in a few cases) and a shear state
of stress. The workpiece (W) is clamped on the table (B), which is given a
translatory feed (T), that together with the primary motion (R) of the cutter (V)
provides the many geometrical possibilities.
The milling process, through the various types of cutters and the wide variety
of machines, is a versatile high-production process. Typical milling cutters
like arbor-mounted cutters (a) and shank mounted (b) cutters. Milling cutters
are usually made of hard alloys, sometimes also diamonds and metal
ceramics. Hard alloy cutters permit roughness in steel Rz = 1...2 m and cast
Rz = 4...7 m. Generally diamonds and metal ceramics cutters is used quit
little, because they are slight [5].
Kalasabafrees
Otsfrees
2-he teraline sõrmfrees
Sõrmfrees – 2-he teraline soonfrees
3-me teraline sõrmfrees
Mitmeteraline sõrmfrees
Ümardusfrees- sõrmfrees
Mitmeteraline sõrmfrees laastujagajaga
Otsraadiusega sõrmfrees
T-soonefrees
Kõvasulamplaadiga nurgafrees
Kõvasulamplaadiga otsfrees
Kõvasulamplaadiga sõrmfrees
There are: a - key-seating milling with disk cutters; b - slot milling with disk
cutter; c - difficult contour cutting with different cutters (1,2,3,4,5); d – angle
milling with angle cutter; e - T- slot milling with T-slot cutter; f- step milling
with end mill; g – slot milling with T-slot cutter; h – two sided angle milling with
angle cutter; i – incline surface milling with tool bit angle cutter. Generally the
milling process comes close to turning in extensive industrial use, since the
geometrical possibilities are enormous and the removal rate high [3].
Typical milling operations
Surface quality and accuracy. The hardness of the material should not be
too high ( HB < 250 – 300) and a minimum of ductility is advisable. The
obtained tolerances are ±0.05 mm, surface roughness is 3.2 ≤ Ra ≤ 6.3 µm
and the quality IT7. Manufacturing depends on material structure and
strength [5]
Cutting action in up-and-down milling [18].
Many different milling machines are on the market: for instance universal
column-and-knee-type milling machines (plain column-and-knee-type milling
machines supplied with a swivel on the saddle, enabling helices to be cut when
swiveling the work table), ram-type milling machines and planer-type milling
machines. Milling machines can also be used for drilling and boring. Milling
machines are among the most important machine tools, as they can produce
wide variety of machined surfaces [2].
Horizontal milling machine and plain column-and-knee-type milling machine
Reaming
Reaming is a sizing or scraping operation in which the tool cuts slightly
larger than its own diameter, usually direct proportion to the amount of
stock to be removed. For efficient operation, reamers must be cutting at all
times, which is possible only when they are being used in properly drilled
holes. Removal of too much stock by reaming often causes oversize and
rough holes.
Surface quality and accuracy. We can ream cylindrical and conical holes,
different materials like steel, cast iron, colored metals and alloys. Accuracy is
generally 5..6 IT and the surface roughness will normally be in the range 0,08 <
Ra < 0,63 µm
Product design factors related to reaming
Plants and equipment. A reamer is a
rotary cutting tool, generally of
cylindrical or conical shape, intended
for enlarging and finishing holes to
accurate dimensions. It is usually
equipped with two or more peripheral
grooves or flutes, either parallel to its
axis or in a right-or left-hand helix as
required. Those with helical flutes
provide smooth shear cutting and
produce a better finish. The flutes form
cutting teeth and provide grooves for
removing the chips.
Commercial types of reamers
Broaching
Broaching is a high-production metal removal process that sometimes is required to
make one-of-a-kind parts. Broaching is at its best in machining simple surfaces or
complex contours. Properly used modern broaching processes can greatly increase
productivity, hold tight tolerances, produce precision finishes and eliminate the need
for highly skilled machine operators. The length of a broaching tool is determined
by the practice by the amount of stock to be removed and limited by the machine
stroke, bending moments, stiffness, accuracy and other factors. The length of an
internal push broach should not exceed 25 times the diameter of the finishing teeth,
a pull broach usually is limited to 75 times the finishing diameter.
Standard broach part and nomenclature [18].
The broaching tool may be pulled or pushed across a workpiece surface or the
surface may move across the tool. Internal broaching requires a starting hole
or opening in the workpiece for insertion of the broaching tool. The final
shape may be a smoother, flatter surface, a larger hole or a complex splined,
flanged, toothed, notched, curved, spiral or irregularly shaped section.
Possible workable shapes
Examples of types of broaching tools
A simple classification scheme for broaching machines
Surface quality and accuracy. Generally any material that can be machined
can be broached. Good tolerances can be obtained ( ± 0.1 mm ± 0.02 mm)
and accuracy generally IT 7. The surface roughness will normally be in the
range 0,8 < Ra < 2,0 µm [5].
Planing
The planning process is characterized by solid work material, two-dimensional
forming (sometimes one-dimensional forming) and a shear state of stress. The
workpiece (W) is clamped on the table (B), which is given a translatory primary
motion (Tb) and the tool (V) is given a translator feed (Tv), providing the
geometrical possibilities[2].
The hardness of the material should generally not exceed HB = 300 and a
minimum of ductility is advisable. Planing depends on material structure and
strength. Surface quality depends on cutting velocity and depths. The obtained
tolerances are normally ± 0.05 to ± 0.10 mm and accuracy generally IT 3..4.
The surface roughness is in the range 0.63 ≤ Ra ≤ 2.5 µm [5].
There are used straight and clinced planing cutters in planing machines. a –
straight cutters; b – loop cutters; c – expansive loop cutters; d – edge cutters; e –
slash cutters.
There are many different types of planing machines like pit-type planer,
double housing planer, open-side planer, edge or plate planers.
The planing process is in general used to produce large horizontal, vertical,
inclined flat surfaces, also T – slot and angle-shape grooves. Some planing
examples are shown in figure, where: a – horizontal, vertical and incline surface
planing; b – groove planing; c – T –slot planing; d – angle planing; e – dificult
surface planing.
Grinding
The grinding process is characterized by solid work material, two-dimensional
forming (one-dimensional may occur) and a shear state of stress. The
workpiece (W) is supported between centers (P) or clamped on a table (B) and
given a rotary (R) and translatory (T) feed. The tool V (the grinding wheel) is
given a rotary primary motion (Rv) and depending on the particular process,
sometimes a feeding motion also.
Tolerances are around ± 0.001 mm and surface roughness is 0,04 µm < Ra <
0,32 µm. the surface accuracy should be at least IT 7 and in plain grinding IT
6. The grinding processes have a low material removal rate [5].
where a – straight profile plain wheel, which is used for cylindrical,
internal, center less and surface grinding; b, c – conical profile plain
wheels, which are used for thread, gear etc. grinding; d – opened hole
plain wheels, which are used for cylindrical and surface grinding; e –
sheet wheels (thickness 0.5 … 5 mm), which are used for cutting; f, g, h –
band and pan wheels, which are used for flat grinding.
The grain size of the abrasive is an important factor in selecting the
correct grinding wheel. Grain sizes are classified in accordance with an
international mesh size in mesh/inch, ranging from 8 (coarse) to 1200
(super-fine).
In the case of diamond and boron nitride grinding wheels, European
grinding wheel manufacturers indicate grain size by the diameter of the
abrasive grains in microns
The most frequently used grinding tool is the grinding
wheel used for cylindrical or plain grinding.
Grinding offers close dimensional control and fine
surface finishes and has become extremely important in
recent years, because of the increasing demands of high
accuracy and surface quality.
Formerly grinding was used only for finishing
operations, but rapid development is taking place with
regard to roughing (high-speed) grinding, which may
substitute for turning and milling [2].
The grinding processes are used primarily in finishing cylindrical or flat
surfaces which have been produced by various other processes.
Different grinding operations.
Today roughing grinding including profile grinding at high cutting
speeds, can sometimes substitute for turning, milling or planing.
Different grinding operations.
Typical grinding machines: (A) grinding wheel; (B) workpiece
Honing
Honing is a low-velocity abrading process using bonded-abrasive stick for
removing stock from metallic and nonmetallic surfaces. As one of the last
operations performed on the surface of a part, honing generates functional
characteristics specified for a surface and involves the correction of errors
resulting from previous operations. Functional characteristics generated by
honing include geometric accuracy, dimensional accuracy and surface
character (roughness, lay pattern and integrity)
In honing the tolerances are around ±
0.001 mm and surface roughness is
0,08 µm < Ra < 0,32 µm. The surface
accuracy should be at least IT 6 and in
flat honing IT 4. [5, lk2900]
Common types of fixtured honing tools
The most common application of honing is on the internal cylindrical
surfaces. However, honing is also used to generate functional
characteristics on external cylindrical surfaces, flat surfaces, truncate
spherical surfaces and toroidal surfaces (both internal and external).
Honing operations: (A) internal cylindrical surface honing; (B) external
cylindrical surface honing; (C) flat surface honing; (1) tool; (2) workpiece
Electrical and chemical finishing
processes
• Electrical, chemical and electrochemical
machining are relatively new methods of
removing metal directly by electrical, chemical
and/or thermal energy and without mechanical
forces.
• Such processes have been called nonconventional
or nontraditional, several them (especially
electrical-discharge machining, electrochemical
machining and electrochemical grinding) are now
being widely used and should be considered with
the standard manufacturing methods.
Electrical – discharge machining
(EDM)
Electrical-discharge machining
(EDM) is a method of removing
metal by a series of rapidly recurring
electrical discharges between an
electrode (the cutting tool) and the
workpiece in the presence of a liquid
(usually hydrocarbon dielectric).
Minute particles of metal or “chips”
(generally in the form of hollow
spheres) are removed by melting and
vaporization and are flushed from
the gap between tool and work.
Basic components of an electrical discharge machine
Types of power-supply circuits used for EDM
The EDM tool electrode is the means by which electric
current is transported to the work piece.
Shape of the electrode establishes a pattern whereby sparks
will occur between the tool and work piece and the desired
shape will be machined. Shapes machined are the opposite
of the electrode shapes.
A requirement for any material used for an EDM electrode
is that it be a conductor of electricity. Insulating materials
are not usable.
A wide variety of materials are used in the manufacture of
electrodes. Most used materials are graphite, copper, brass,
copper tungsten, silver tungsten, carbide and zinc alloys.
The several methods of introducing dielectric fluid to the arc gap fall into four
broad classifications: normal flow; reverse flow; jet flushing; immersion
flushing.
Several methods of introducing dielectric fluid
Generally the surface roughness is Ra 1,6...3,2 µm, but it could be also
0,05...0,1 µm. Generally EDM provides close tolerances, often 50 µm and IT
7.. As a result, the smoothness of surfaces produced by EDM is generally
limited more by economics than by the technological potential of the process.
Electrochemical machining
Electrochemical machining (ECM) is important method of removing metal
without the use of mechanical or thermal energy.
Electric energy is combined with a chemical to form a reaction of reverse
plating. Direct current at relatively high amperage and low voltage is
continuously passed between that anodic work piece and cathodic tool
(electrode) through a conductive electrolyte.
At the anode surface, electrons are removed by the current flow and the
metallic bonds of the molecular structure of this surface broken. These
surface atoms proceed to go into solution as metal ions. Simultaneously
positive hydrogen ions are attracted to the negatively charged surface and
emitted at the cathode surface to form hydrogen atoms, which combine to
form hydrogen molecules.
Dissolved material is removed from the gap between work and tool by the
flow of electrolyte, which also aids in carrying away the heat and hydrogen
formed.
Schematic of arrangement for electrochemical machining
Schematics of electrochemical machining (ECM) operations. (a) die sinking; (b)
shaping of blades; (c) drilling; (d) milling; (e) turning; (f) wire ECM; (g) drilling
of curvilinear holes; (h) deburring and radiusing.
A typical ECM machine consists of a table for mounting the work
piece and a platen mounted on a ram or quill for mounting the
cathode tool, inside an enclosure.
The work piece is mounted on the table and connected in a manner
ensuring good electrical contact to the positive side of the power
supply. The tool is mounted on the platen, with electrical connection
to the negative side of the power supply.
Electrolyte is pumped under pressure between the work and tool. As
the tool feeds into the work with current flowing, the electrolyte
carries away machining products.
Electrochemical machining equipment schematic. (1) tool electrode;
(2) finishing workpiece; (3) tank of electrolyte; (4) clamping system;
(5) electrolyte supply system; (6) power supply. [6 ]
Materials used for ECM tools must have good electrical and thermal
conductivity, be corrosion resistant and machinable, and be stiff enough to
withstand the electrolyte pressures without vibrating or distorting. Copper,
brass, bronze, copper-tungsten, stainless steel and titanium are most
frequently used. Graphite can also be used, but it must be coated to prevent
rapid erosion. The tools must be smoothly finished to assure uniform
electrolyte flow and produce good surface finishes on the work.
Cathode accuracy directly affects product accuracy in ECM, because the
product cannot be more accurate than the cathode tool whish produced it.
Part accuracy is also affected by irregularities in electrolyte flow or current
flow. Average surface finishes obtained range from 0,1 to 1,0 m and
accuracy IT 7 [5].
Applications. Major advantages of the ECM process include stress and burrfree machining, no burning or thermal damage to workpiece surface and
elimination of tool wear. Small thin disks are being consistently machined to
tolerances within 0,007 mm on such machines. Die sinking is a major
application with over cut throughout the surface being consistently
maintained within 0,05 mm. Aircraft and aerospace components are
frequently produced with this method because the high-strength, temperature
resistant materials used are difficult to machine in other ways.
Electrochemical discharge grinding
Electrochemical discharge grinding (ECDG), sometimes called ECDM
grinding, is a combination of electrochemical grinding (ECG) and electrical
discharge grinding (EDG), with some modifications.
Most of the stock is removed by ECG, with the oxides that from on the
positively charged workpiece surfaces being removed by the intermittent spark
discharges of EDG.
A bounded graphite wheel without any abrasive grains is used and the
conductive electrolyte is generally a water solution of inorganic salts.
Alternating current or a pulsing type d-c circuit at relatively high amperage
and low voltage, is used to obtain random spark discharges.
No arc or spark suppressor circuit is required, since the work is held in direct
contact with the wheel under low pressure. For profile grinding, the workpiece
is traversed along the periphery of a performed wheel.
Electrical discharge grinding.
Wheel rotation is necessary in ECDG to introduce clean
electrolyte through the gap and reduce the possibility of gapspark information. Rotation also increases electrolyte pressure
at the gap and helps to avoid electrolyte boiling.
Accuracy can be held to  0,01 mm under carefully controlled
conditions and about  0,02 mm in normal operations (IT 5-6). A
surface finish of 0,2 m can be obtained in grinding tungsten carbide
with the ECDG process.
Applications.
An advantage is the use of a low cost wheel. Application of this
process, howerver, has been limited [5].
Photochemical machining
• Photochemical machining or chemical blanking is
the process of producing metallic and non metallic
parts by chemical action.
• The process consists of placing a chemicalresistant image of the part on a sheet of metal and
exposing the sheet to chemical action which
dissolves all the metal except the desired part.
• The photographic-resist process of photochemical
machining is by far the most common one in use
today.
Metal can be chemically cleaned in numerous ways, including
degreasing, pumice scrubbing, electro cleaning or chemical cleaning.
The cleaned metal is coated with photographic material which, when
exposed to light of the proper wavelength, will polymerize and remain
on the panel as it goes through a developing stage.
This polymerized layer then acts as the barrier to the etching solution
applied to the metal. After coating with resist, it is necessary to bake
the panel prior to exposing it. This is used to drive off solvents in a
simple drying operation.
The metallic coated panel is placed between sets of negatives (either
film or glass) and is clamped by either vacuum or pressure. Certain
resist require an additional baking operation following development.
The next step is etching to remove the unwanted metal unprotected by
the photo resist.
Process steps involved in the photographic-resist process of photochemical machining
Applications. The use of photochemical machining is generally limited
to relatively thin materials, from 0,002 to 1,2 mm thick. The limit on
material thickness is generally a function of the tolerance desired on
finished parts. Photochemical machining has a number of applications
wherein it provides unique advantages, for instance:
• work on extremely thin materials where handling difficulties and die
accuracies preclude the use of normal mechanical methods;
• working on hardened or brittle materials where mechanical action
would cause breakage or stress-concentration points;
• production of parts which must be absolutely burr-free;
• production of extremely complex parts where die cost would be
prohibitive [5].
Thermal finishing processes
Ion beam machining
• Ion beam machining (IBM) is sometimes
considered a thermoelectric process, but it does
not rely primarily on heating the workpiece locally
to the evaporation temperature.
• Instead it depends on sputtering and therefore
differs fundamentally from electron- or laser-beam
machining.
• In this sputter etching process, bombarding ions
disclose surface atoms by the transfer of kinetic
energy from the incident ions.
• The use of IBM to provide selective removal of material has found
only limited commercial application, mostly in micromachining.
• Ion beam equipment can be designed having greater resolution than
equivalent energy electron beam equipment.
• Limitations include the relatively high cost of the capital equipment
and the extremely slow stock removal rate.
• IBM equipment using a d-c power source is simpler in less expensive,
but it can be used only for etching conductive materials. For dielectrics
more costly radio frequency equipment must be used.
• Little heat is generated in the process, but the workpiece can be cooled
to increase removal rate. One application is etching surfaces of
specimens prior to studying their microstructure.
• A promising application is etching circuit patterns on integratedcircuit substrates.
• Advantage over chemical etching is better resolution, since
undercutting is eliminated and there is no need to rely on powerful
enchants that can propagate along cracks and possible degrade the
photoresist mask.
• Also IBM can be used to etch multilayered structures regardless of the
materials.
Ion beam machining equipment
Ion-beam machining is a precise process. Because of the small beam diameter,
tolerances of  0,001nmm can be held (IT 2-3). Surface roughness is normally
in the range Ra 1 m [1].
Electron beam machining
• Electron beam machining (EBM) uses electrical energy to
generate thermal energy for removing material.
• A pulsating stream of high-speed electrons produced by a
generator is focused by electrostatic and electromagnetic
fields to concentrate energy on a very small area of work.
• High-power beams are used with electron velocities
exceeding one-half the speed of light. As the electrons
impinge on the work, their kinetic energy is transformed
into thermal energy and vaporizes the material locally.
Electron-beam machining
The electron beam is formed inside an electron gun which is basically a
triode and consists of cathode which is a hot tungsten filament emitting
high-negative-potential electrons, a grid cup negatively biased with respect
to the filament and an anode at ground potential through which the
accelerated electrons pass.
EBM is generally limited to drilling extremely small holes and cutting
narrow slots or contours in thin materials to close tolerances. There is
no tool wear or pressure on the work. Stock removal rate is generally
about 1,5 mm3/s. Using this process, it is possible to drill a crossshaped hole, for example, through a piece of stainless steel 1 mm
thick.
Extremely high energy density makes it possible to drill the hole while,
a few thousandths of an mm away from the wall of the hole, the work
piece remains at room temperature. We can make hole which diameter
is 1,5 mm and length 10 mm. Any known material, metal or nonmetal
that will exist in high vacuum can be cut.
Electron-beam machining is a precise process. Because of the small
beam diameter, tolerances of  0,001 to 0,005 mm can be held (IT 23). Surface roughness is normally in the range Ra 5-20 m [1].
Laser beam machining (LBM)
• Laser beam machining (LBM) is based on the conversion of electrical
energy to light energy and then into thermal energy.
• In a typical system, electrical energy stored in capacitors is discharged
through a gas-filled flash lamp to produce an intense flash of white
light. Radiation from the lamp is directed into the laser, where the light
is amplified and emitted as a coherent, highly collimated beam of
single wavelength.
• This narrow beam is focused by an optical lens to produce a small
intense spot of light on the work surface. Optical energy is converted
into heat energy upon impact and temperatures generated can be made
sufficient to melt and vaporize every known material.
• Low efficiency with respect to power consumption and slow stock
removal make this process costly.
Typical setup for laser beam machining
Laser-beam machining.
Many types of lasers exist which produce highly directive beams of
optical or infrared radiation.
They can be classified as solid-state, gas or liquid. Solid-state units have
laser rods made of any one of a number of a number of solid materials
including ruby, neodymium-doped glass and neodymium-doped
yttrium-aluminum-garnet (called YAG).
Gas units have glass tubes filled with CO2, helium-neon, cadmium gas
or argon (figure 3.10.3). Only a few of the many types of lasers are
practical for metalworking.
Ruby lasers produce the highest energy and peak power outputs, but
they cost more. They generally used where a large amount of material
must be removed with a single pulse. CO2 lasers are most efficient with
respect to converting electrical energy to laser light energy.
They are generally used in a repetitively pulsed mode for metalworking
and are sometimes assisted by air, inert gas or oxygen to facilitate
coupling energy from the beam to the work piece.
Solid-state laser
CO2-, N2-, He- laser
To meet the basic requirements for industrial
applications, the laser systems must meet the
following specifications:
•
•
•
•
•
•
sufficient power output;
controlled pulse length;
suitable focusing system;
adequate repetition rate;
reliability of operation;
suitable safety characteristics.
Machining of small holes in thin parts is a typical application.
The process is being used to pierce diamond wire-drawing dies and
to remove metal from work pieces without stopping their rotation
during dynamic balancing.
Other applications include hole drilling, resistor trimming and
scribing of silicon wafers. It should be emphasized that laser is
unlikely to replace any of the common drilling processes, but rather
will continue to supplement them and enhance productivity. One of
the present drawbacks in laser applications is cost.
Other limitations include low efficiency, slow repetition rate, limited
durability and reliability, and the necessity for careful control and
effective safety procedures.
Because of the laser’s ability to melt or vaporize any known metal and
operate in any desired atmospheric environment, it is sometimes
preferred over EBM.
Other advantage include the ability to machine areas not readily
accessible and extremely small holes, the fact that there is no direct
contact areas between the tool (laser) and the work piece, small heat
affected zones, and easy control of beam configuration and size of
exposed areas. [5]
To the sheet metal we can machine 60 … 240 holes/minute. Surface
roughness is Ra 0,4...0,10 μ m, which depends workable material and
machining process. Structural changes could be in depth 1...100 μm [1].
Ultrasonic machining
• Ultrasonic machining uses high frequency
vibrations in a cleaning system.
• In the process a cleaning solution is
subjected to the rapid oscillation of
longitudinal waves, identical to audible
waves but of higher frequency.
Before ultrasonic can be used effectively, it
is important to realize the following:
• Parts to be cleaned must be immersed in a
liquid;
• The entire volume of liquid must be
supplied with ultrasonic energy;
• The use of ultrasonic does not eliminate the
need for cleaning chemicals.
Workpieces to be cleaned are placed in the solution and the rapid
oscillation of the solution resulting from the high-frequency sound
waves creates minute vapor voids in the solution that implode against
the workpiece and effectively clean its surfaces.
Mechanically held contamination is released from the surfaces, soluble
materials are rapidly dissolved and oil and similar contaminants are
easily emulsified.
Industrial ultrasonic cleaning systems are composed of three basic
components: generator, transducer and tank containing the cleaning
solution. The generator transforms standard line current of 50 or 60 Hz
into desired higher frequency.
This high-frequency current is converted into sound waves
(mechanical energy) of a corresponding frequency via a transducer,
which radiates the waves into a cleaning solution in the tank.
Ultrasonic machining scheme
There are two major types of ultrasonic cleaning units: integrated
and modular. Integrated units have all components, including the
tank for the cleaning solution in a single enclosure. Modular systems
consist of a separate generator linked to either tanks equipped with
transducers or immersible transducers.
The number of transducer elements per tank is determined by the
tank volume and its designated power rating. It is important that the
selected tank and generator have matched ratings for power and
frequency, otherwise serious damage will result, usually the
generator.
Tank heating is the common option for tanks with transducers and is
specified by a majority of users to keep the cleaning solution at its
best temperature for cavitations and cleaning effectiveness.[9]
Plasma-Beam Machining
• Plasma-beam machining (PBM) removes material by using
a superheated stream of electrically ionized gas.
• The 20,000–50,000F (11,000–28,000C) plasma is created
inside a water-cooled nozzle by electrically ionizing a
suitable gas, such as nitrogen, hydrogen, or argon, or
mixtures of these gases.
• The process does not rely on the heat of combustion
between the gas and the workpiece material, it can be used
on almost any conductive metal.
• Generally, the arc is transferred to the workpiece, which is
made electrically positive.
• The plasma—a mixture of free electrons, positively
charged ions, and neutral atoms—is initiated in a confined,
gas-filled chamber by a high-frequency spark.
• The high-voltage dc power sustains the arc, which exits
from the nozzle at near-sonic velocity. The high-velocity
gases blow away the molten metal ‘‘chips.’’
• Dual-flow torches use a secondary gas or water shield to
assist in blowing the molten metal out of the kerf, giving a
cleaner cut.
• PBM is sometimes called plasma-arc cutting (PAC).
• PBM can cut plates up to 6.0 in. (152 mm) thick.
• Kerf width can be as small as 0.06 in. (1.52 mm) in cutting
thin plates.
Plasma-beam machining [18].
Plasma-beam machining
Water-Jet Machining
• is low-pressure hydrodynamic machining. The
pressure range for WJM is an order of magnitude
below that used in HDM.
• There are two versions of WJM: one for mining,
tunneling, and large-pipe cleaning that operates in
the region from 250 to 1000 psi (1.7 to 6.9 MPa);
and one for smaller parts and production shop
situations that uses pressures below 250 psi (1.7
MPa).
Water-jet machining.
• The first version, or high-pressure range, is
characterized by use of a pumped water supply
with hoses and nozzles that generally are handdirected.
• In the second version, more production-oriented
and controlled equipment is involved.
• In some instances, abrasives are added to the fluid
flow to promote rapid cutting.
• Single or multiple-nozzle approaches to the
workpiece depend on the size and number of parts
per load.
• The principle is that WJM is high-volume, not
high-pressure.
Water-jet machining
Rapid Prototyping and Rapid
Tooling
• In the past, when making a prototype, a full-scale
model of a product, the designed part would have
then machined or sculptured from wood, plastic,
metal, or other solid materials.
• Now there is rapid prototyping, also called
desktop manufacturing, a process by which a solid
physical model of a product is made directly from
a three-dimensional CAD drawing.
Rapid Prototyping using laser to photopolymerize the liquid photopolymer.
Rapid Prototyping using Sintering Process (powder).
• Rapid prototyping entails several different
consolidation techniques and steps: resin curing,
deposition, solidification, and finishing.
• The conceptual design is viewed in its entirety and
at different angles on the monitor through a threedimensional CAD system.
• The partis then sliced into horizontal planes from
0.004 to 0.008 in. (0.10 to 0.20 mm).
• Then a helium:cadmium (He:Cd) laser beam
passes over the liquid photopolymer resin.
• The ultraviolet (UV) photons harden the
photosensitive resin. The part is lowered only one
layer thickness.
• The recoater blade sweeps over the previously
hardened surface, applying a thin, even coat of
resin.
• Upon completion, a high-intensity broadband or
continuum ultraviolet radiation is used to cure the
mold.
• Large parts can be produced in sections, and then
the sections are welded together.
• Other techniques, such as selective laser sintering
(SLS) (Fig. 60), use a thin layer of heat-fusable
powder that has been evenly deposited by a roller.
A CO2 laser, controlled by a CAD program, heats
the powder to just below the melting point and
fuses it only along the programmed path.
1. Vällo, A. Eritöötlusviisid. TTÜ. Tallinn, 1994, 69 p.
2. Alting, L. Manufacturing engineering processes. New York. 1994, 492 p.
3. Ostapenko, N. Krapivnitski, N. Metallide tehnoloogia. Tallinn, 1975, 297 p.
4. Poluhhin, P.I. Grinberg, B.G. Metallide tehnoloogia. Tallinn, 1969, 424 p.
5. Daniel B.Dallas. Tool and manufacturing engineers handbook. SME, 1976, 2932 p.
6. Cotell, C. Sprague, J. ASM Handbook. Volume 5. Surface Engineering. ASM International.
1994, 1039 p.
7. Handbuch feubearbeitung. Prof. Werner Degner, Hans-Christian Böttger. VEB VERLAG
HECHNIK. Berlin, 1979, 474 p.
8. Delstar Metal Finishing Inc. Electropolishing. Houston, Texas, 1998, 25 p.
9. Veilleux, F.R. Tool and manufacturing engineers handbook. Volume 3. Materials, Finishing
and Coating. SME, 1985, 2530 p.
10. AFP/SME. Finishing processes Tech Trends 2001, 28 p.
11. MTA/SME. Machining Tech Trends 2002, 39 p.
12. SlipNaxos AB. Precision grinding product guide. Sweden. 2000, 4 p.
13. Uddeholm. Grinding of tool steel. Germany. 1998, 15 p.
14. Lepikson. H. Masinaehitaja käsiraamat I.Tallinn. 1968, 688 p.
15. Lepikson. H. Masinaehitaja käsiraamat II.Tallinn. 1971, 868 p.
16. Косиловой. А. Г. Справочник технолога-машиностроителя. Том 1, 1986, 655 c.
17. Косиловой. А. Г. Справочник технолога-машиностроителя. Том 2, 1986, 495 c.
18. Kutz, M. Mechanical Engineers' Handbook. Third Edition, 2006, 785 p