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1.13 CUTTING AND OTHER EDGE PREPARATION PROCESSES
1. Flame cutting2. Plasma cutting3. Laser cutting4. Water jet cutting5. Comparsion6. Metal powder gas cutting7. Oxygen lancing 8. Chemical flux injection cutting
9. Arc oxygen cutting10. Arc pressure air gouging11. Metallic air cutting12. Tungsten arc cutting13. Machining14. Grinding and cutting wheels15. Shearing16. Multi processes17. CNC
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Cutting methods
Thermal cutting
Oxygen cutting
Oxy‐fuel
Oxygen lancing
Metal powder
Chemical
Oxygen‐arc
Arc cutting
Metallic arc
Oxygen arc
Arc carbon air
Tungsten arc
Plasma arc
Laser beam cutting
Mechanical cutting
Water jet
Machining
Cutting wheels
Shearing
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Welding joint preparation
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1. Flame cutting
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‐ is a chemical reaction between pure oxygen and steel to form iron oxide
‐ For cutting are neaded :1) Preheat flame
To raise surface temperature to about 1000c and cleaning
2) Fine, pressure stream pure oxygen To oxidizing and blow down away to form a cavity
‐ It can be described as rapid, controlled rusting
Principle
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Suitable material for flame cutting:a) capacity of burning in a stream of oxygenb) Ignition temperaturec) The melting temperature of oxide layerd) Viscosity of burning slage) Heat conductivityMild and low alloy steels
unsuitable material for flame cutting:Aluminum , High‐alloy steel , Copper , Grey cast iron
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Hand , machin flame torches
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Flame cuttrr nozzle
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Characteristic of different fuel gases
CHARACTERISTIC UNIT ACETYLENE PROPAN NATURAL
Density(15C,1bar) Kg/m3 1.09 2.0 0.8
Ignition temp. in O2 C 300 490 645
Mixing ratio for O2/fuel gas 1.5 4.3 1.8
Flame temp. C 3170 2850 2770
Combustion velocity Cm/s 1350 370 330
Flame power Kcal/cm2s 10.20 2.45 2.03
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Rating criteria of cutting surfaces acc.to DIN EN ISO 9013:05.95
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A quality oxy‐fuel cut has :1) Square top corner (with minimum radius)2) Cut face flat top to bottom (no undercut)3) Cut face square with respect to top surface4) Clean smooth surface with near vertical drag lines5) Little to no slag on bottom edge (easily removed)
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Parameters for quality of flame cutting
Operating gas nozzle machine material•Pressure•Amount•Temprature•Type•Purity•Mixing ratio•Flowcharacteristic
•Construction•Age•Condition•Distance to sheet•Cutting angle
•Construction•Age•Condition•Cutting velocity
•Composition•Thickness•Condition•Errors•Temperatutre•Reaction FeO2
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2.Plasma cutting
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Plasma : collection of charged particles ... containing about equal numbers of positive ions and electrons and exhibiting some properties of a gas but differing from a gas in being a good conductor of electricity ...“ Ionized gas can freely exchange electrons between atoms
For arc cutting 1) PLASMA
carry cutting amperage during direct current arc struck between a tungsten cathode and metallic work piece
1) COPPER NOZZLE focus energy of ionized gas stream to small cross section
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Starting plasma arc1) Pilot arc between the
negative electrode andpositive Nozzle after to swirlthe gas
2) The pilot arc is blown outof the nozzle by the gasflow, and contacts thework piece.
3) The nozzle relay opensremoving the nozzle fromthe circuit and The main arcis created
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Gas Swirling1) increases cooling of copper Nozzle2) At high Amp. increase the age of Nozzle
because 30/70% ratio is changed
3) Increases cut quality(The other side having a 5 to 8 degree bevel)
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Shielded gas1) Is injected in the plasma stream after ionization
process2) Further arc constricting and
cooling Nozzle
Water injection 1) Further constricting the arc due to
Swirling in the same direction as the gas
2) More cooling of Nozzle due to Formation of steem layer between arc and Nozzle
Plasma gas types :1) Inert gas : Ar , Ar‐H2 , N2 ,with Tungsten electrode
2) Air or Oxygen with copper‐hafnium electrode Shielded gas types:
1) Steel : Air,Oxygen,Nitrogen2) Stainless steel : Nitrogen,Argon‐H2,Co23) Aluminum : Ar –H2 ,Nitrogen/Co2
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Gas purity
• Essential for good cut quality and long electrode life
• Minimum purity requirements : Nitrogen at 99.995% Oxygen at 99.5 %
• If Purity less than recommended minimum – Inability of the arc to penetrate thin materials at any current– Depending on the degree contamination,variation in cut
quality. – Extreme short electrode life. – When cutting with N2, appearance of a black film residue on
the face of the electrode and in the nozzle bore.
• If the gas is pure, the electrode and nozzle bore will take on a sand blasted appearance. www.mechshop.ir
Advantages of Plasma Arc Cutting1)cuts carbon steel up to 10 times faster than oxy‐fuel cutting, with equal quality more economically.
2)It leaves a narrower kerf3)Plasma cutting being primarily a melting process can cut any metal. Disadvantages of plasma arc cuttingHigh initial cost of the equipment
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3.LASER CUTTING
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What is laserLight Amplification by Stimulated Emission of Radiation
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A laser consist of :1) A laser enable medium(atoms,ions,molecules,crystals)2) An excited source3) An optic resonator
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LASRER Types1) Eximer (ArF,KrF,XeCl)2) Solid state(Ruby,Nd‐yag,Nd‐glass)3) Semi‐conductor (GaAr,GaAlAs)4) Gas (Co2)
Laser types differ from the1) Wave length2) Intensity of radiation
Absorbtion depend on :1) material2) Temperature3) Wavelength4) Intensity
Solid‐state or Co2‐laser is good for cutting steels For cutting and welding the co2‐laser is preferred
(4.5%Co2,13.5%N2,82%He)www.mechshop.ir
Laser cutting principle1. CO2 laser resonator2. rear mirror3. gas excitation generates single
wavelength light4. output mirror5. polarizing mirror6. telescope mirror7. beam bender8. machine gantry9. constant beam length carriage10. beam bender11. beam bender12. cutting carriage13. beam bender14. adaptive mirror15. window16. focusing mirror17. cutting head18. cutting nozzle
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Laser cutting methods
1) Fusion Cutting ( high pressure cutting)• Laser beam fused the material and Nitrogen(10‐20bar) drive
out slag and protect focusing optic• Is used for stainless steel and Al and their alloys
2) Oxidation Cutting (laser torch cutting):• Laser beam heat up the material to combustion temperature
and oxygen (0.4‐5bar) for oxidizing the matarial , protect the focusing optics from splashes and slag out of the kerf
• Is quickest and economical fo carbon steelswww.mechshop.ir
Parameters Affecting Laser Cutting1) Laser power (at least 1000W for cutting carbon steel thicker than 8mm)2) Pulse frequency (reduced for small contours and piercing) 3) Type and pressure of cutting gas 4) Diameter and type of nozzle 5) Distance between the cutting nozzle and the work‐piece 6) Focal length of the focusing optics 7) Focal position (in the sheet for aluminum and on/above for steel sheet)8) Cutting speed 9) Acceleration 10) Material 11) Work‐piece surface 12) Work‐piece shape 13) Material thickness 14) Work‐piece support
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Some limitations for laser cutting• Steel with a high alloying content is more difficult to cut than sheet with a
low content.• Aluminum alloys Due to the high reflectance and thermal conductivity,
can only be cut in thicknesses up to approx. 30% of the cutting thickness achieved in carbon steel
• Brass and copper can only be cut to a limited extent due to the very high reflectance and thermal conductivity. The maximum sheet thickness for brass is approx. 2 mm and for copper 1 mm
• Organic natural materials can be cut with good results, but a slight discoloration due to carbonization
• Organic synthetics can be parted with good results, but measures must be taken to capture and treat hazardous fumes which may be generated.
• edge length / diameter small than 2x sheet thickness sometimes give problems with laser cutting
• Thickness of section(6 mm in plain carbon steel)• Shiny material surfaces, such as for example pure aluminum, produce
strong reflection of the laser beam and therefore also poor cutting result
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• Advantages1) Due to rapid rate of operation, the (heat) distortion to the base
metal is minimum.2) The narrowness and accuracy of the cut together with relatively
shallow HAZ with negligible surface cracking are major advantages of this process.
3) Even most complicated profiles can be cut.4) Very hard material like silicon carbide, friable material like glass,
sticky material like confectionery etc., can be cut by laser.5) Laser is a faster process than sawing or nibbling and is very
efficient.
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Phases of technology “laser cutting”
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4. WATER JET CUTTING Highest precision cutting on any material Leaving a smooth and precision cut surface. Limitations is highly brittle materials(tempered glass and
some ceramics)
Very slow and expensive process compared to plasma Can be combined with plasma or oxy fuel abrasive does the actual cutting using a mechanical sawing type action. except soft materials, such as rubber, leather, cloth, paper, cardboard, insulation, foam, etc
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Basic
diamond / sapphire 0.127 to 0.5mm
(over 50,000 psi)
over 50,000 psi
Intensifier pump
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5. COMPARSION
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Kerf between different cutting methods
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Kerf between different cutting methods
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6.METAL POWDER GAS CUTTING
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Principple
1) Iron particles are rapidly oxidized 2) Increase of heat on the metal surface3) The refractory oxides that form on the metal
surface are melted and consequently flushed from the cutting area.
4) Cutting flame of the torch come in contact with the iron of the metal and thus cutting proceeds without interference
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Metals Cut by Powder Cutting1) Stainless steel.2) Cast iron.3) Nickel‐chrome, Nickel and chrome alloys (oxidation resistant steels).4) Aluminum5) Bronzes6) Steels containing more than 5% alloy.7) Copper
Advantages1) Powder cutting method can cut oxidation resistant steels at
approximately the same speed as oxy‐acetylene cutting of carbon steels of equivalent thickness.
2) This method (mechanized) can cut metals up to150 cm thick.
Disadvantages1) Powder cutting rises quite a bit of smoke that may interfere with
other operations in the area.2) Extra work is required to grind off powder contamination of the cut
surface
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7.Chemical Flux Injection Cutting principle1) a mixture of oxygen and flux flows from the oxygen
orifice of the torch tip2) The flux is designed to react with oxides of
chromium and nickel, to produce compounds with melting points near those of iron oxide.
3) the flux increases the fluidity of the refractory oxides so that they are blown from the kerf
AdvantageStainless steel can be cut without torch oscillation and at almost same speeds at which oxy acetylene cutting cuts carbon steel of the same thickness.
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8.OXYGEN LANCING
1) Preheating
2) Oxygen blowing
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Advantages1) Oxygen lance cutting can cut heavy thick steel
sections which cannot be done so by oxy fuel gas cutting.
2) It economically cuts large steel and cast iron sections.
Applications1) Oxygen lance cutting can cut steels having
thickness up to 240 cm.2) It is an excellent tool for piercing holes in steel
plates and castings.3) It is routinely used in tapping blast and open
hearth steel furnaces.
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9. ARC OXYGEN CUTTING
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Principle and applications
1) This method of cutting is quite similar to oxy‐acetylene cutting process, except that the heat is supplied by the electric arc(tubular electrode)
2) Arc is maintained throughout the cutting operation. 3) current values are approximately the same as for
welding, but a higher voltage (30‐45 volts) is usually employed.
4) Oxygen arc process is primarily used in under water cutting applications.
5) It is not well suited for cutting non‐ferrous metals.
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10.ARC PRESSURE AIR CUTTING
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Electrode types1) AC copper‐coated2) DC copper‐coated3) DC plain
DC copper‐coated is better because of 1) long electrode life2) Stable arc characteristics3) groove uniformity
Power source 1) Any three‐phase welding power source with 100% duty cycle 2) The arc voltage is 35 to56 V and OCV at least 60V
Polarity : DCEP is better
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Advantages1) process removes metal physically not chemically2) it can gouge or cut metals that the OFC process can’t3) Arc air torch is relatively inexpensive to operate.4) Speeds upto 60 cm per minute are readily attained.5) Little or no distortion occurs in the metal.
Disadvantages1) The process is quite noisy.2) Hot metal particles tend to be blown out over a
substantial area.3) Carbon may be absorbed by the metal being cut.
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11. METALIC ARC CUTTING Special coated mild steel electrodes are used for
cutting purposes. For a 4 mm electrode 250‐350 Amps current is
needed Standard arc welding AC or DC machines can be
employed This type of arc cutting was employed for
1) Cutting cast iron and steel for salvage purposes2) Cutting up scrap3) Cutting of rivets or bolts4) Piercing of holes.
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12.TUNGSTEN ARC CUTTING Metals Cut1) Stainless steel2) Aluminium3) Magnesium4) Copper5) Silicon bronze6) Nickel7) Copper nickel.
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MULTI PROCESS CUTTING Advantages
1) Productivity enhanced by automation2) Reduce processing time3) Improve accuracy4) Produce Better parts ,at lower cost by one machine
Type example:1) Water jet / Plasma (accuracy/speed)2) Water jet / Oxy fuel(accuracy/speed on thicker metal)3) Plasma / Drill (larger hole/precision small holes)
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CNC
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Nesting , Sheat align
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FLAME CLEANING
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• ProcedureIn gas jet laser cutting of metal, the surface of the workpiece heated by the laser is reacted upon by an oxygen jet which increases the cutting performance of the laser by ten times. The heat is provided by a CO2 laser beam which is directed via the center of the oxygen stream.
The apparatus comprises a small vessel placed between the focusing lens and the workpiece surface. Oxygen for metal cutting enters through the side of the vessel and exits through a small nozzle of 1 to 2 mm in diameter in the base of the vessel. The focused laser beam, therefore, impinges on the surface of the workpiece with a velocity of typically 100 m/s. The cutting oxygen fulfils the following functions: (i) It oxidizes the surface of the metal so that laser energy is readily absorbed.(ii) It produces additional heat from the exothermic oxidation reaction.(iii) The high speed gas stream sweeps the molten metal oxide from the cut. Non‐metals (since their thermal conductivity is lower compared with metals and therefore less heat is lost into the surrounding) can be cut rapidly by vaporization with the laser alone. However, gas jet if employed can be of an inert gas such as nitrogen or argon.
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With this type of automatic system, either constant current(CC) or constant voltage (CV) power supplies can be used.When on CC, the arc length is maintained through a voltage
signal system. A predetermined voltage setting is set onthe system controller, which then advances or retracts theelectrode through a stepping motor to maintain the arc
length.On a CV power supply, amperage sensing controls the feedor retract of the electrode to maintain the right arc current
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• The air carbon‐arcSince the air carbon‐arc process doesn’t need oxidation to maintain the cut, carbon steel, stainless steel and other ferrous alloys; gray, malleable and ductile iron; aluminum; nickel; copper alloys and other nonferrous metals.
• Use of combustible compressed gases can cause explosions resulting in personal injury or death..
• Normal pressures range between 80 psi and100 psi at the torch
• Electrode types AC copper‐coated ,DC copper‐coated, DC plain
• DC copper‐coated is most widely used because of its comparatively long electrode life, stable arc characteristics and groove uniformity
• Any three‐phase welding power source with enough capacity may be used for the air carbon‐arc gouging process. With 100% duty cycle
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