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8/8/2019 Cutting Methods
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The Main Types of Cutting:1-Gas Cutting
2-Mechanical Cutting3-Numerical Cutting
4-Plasma Cutting5-Laser Cutting
1-Gas CuttingOxy-fuel welding (commonly called oxyacetylene welding, oxy
welding, or gas welding in the U.S.) and oxy-fuel cutting are processes
that use fuel gases and oxygen to weld and cut metals, respectively.
French engineers Edmond Fouch and Charles Picard became the first
to develop an oxygen-acetylene welding set-up in 1903.Pure oxygen, instead of air (20% oxygen/80% nitrogen), is used to
increase the flammable temperature to allow localized melting of the
workpiece material (e.g. steel) in a room environment. A common
propane/air flame burns at about 2,000 C (3,630 F), a
propane/oxygen flame burns at about 2,500 C (4,530 F), and an
acetylene/oxygen flame burns at about 3,500 C (6,330 F.(
Welding torch :
A welding torch head is used to weld metals. It can be identified by
having only one or two pipes running to the nozzle and no oxygen-
blast trigger and two valve knobs at the bottom of the handle letting
the operator adjust the oxygen flow and fuel flow.
Rose-bud torch:
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A rose-bud torch is used to heat metals for bending, straightening, etc.
where a large area needs to be heated. It is called as such because the
flame at the end looks like a rose-bud. A welding torch can also be used
to heat small area such as rusted nuts and bolts.
Injector torch:
A typical oxy-fuel torch, called an equal-pressure torch, merely mixes
the two gases. In an injector torch, high pressure oxygen comes out of asmall nozzle inside the torch head so that it drags the fuel gas along wit
it, via venturi effect.
Fuel:
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Oxy-fuel processes may use a variety of fuel gases, the most common
being acetylene. Other gases that may be used are propylene, liquified
petroleum gas (LPG), propane, natural gas, hydrogen, and MAPP gas.
Many brands use different kinds of gases intheir mixes.
Cutting:
For cutting, the set-up is a little different. A cutting torch has a 60- or
90-degree angled head with orifices placed around a central jet. Theouter jets are for preheat flames of oxygen and acetylene. The central
jet carries only oxygen for cutting. The use of a number of preheating
flames, rather than a single flame makes it possible to change thedirection of the cut as desired without changing the position of the
nozzle or the angle which the torch makes with the direction of the cut,
as well as giving a better preheat balance. Manufacturers have
developed custom tips for Mapp, propane, and polypropylene gases to
optimize the flames from these alternate fuel gases.
The flame is not intended to melt the metal, but to bring it to its
ignition temperature.
The torch's trigger blows extra oxygen at higher pressures down the
torch's third tube out of the central jet into the workpiece, causing themetal to burn and blowing the resulting molten oxide through to the
other side. The ideal kerf is a narrow gap with a sharp edge on either
side of the workpiece; overheating the workpiece and thus melting
through it causes a rounded edge.
2-Mechanical Cutting
I.e. using machine to shear metals
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Here are some pictures of those machines:
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3-Numerical Cutting
Using computer to control the cutting process
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4-Plasma CuttingPlasma cutting is a process that is used to cut steel and other metals ofdifferent thicknesses (or sometimes other materials) using a plasma torch.
In this process, an inert gas (in some units, compressed air) is blown at
high speed out of a nozzle; at the same time an electrical arc is formed
through that gas from the nozzle to the surface being cut, turning some of
that gas to plasma. The plasma is sufficiently hot to melt the metal being
cut and moves sufficiently fast to blow molten metal away from the cut.
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Starting Method:Plasma cutters use a number of methods to start the arc. In some units,
the arc is created by putting the torch in contact with the work piece.
Some cutters use a high voltage, high frequency circuit to start the arc.This method has a number of disadvantages, including risk of
electrocution, difficulty of repair, spark gap maintenance, and the large
amount of radio frequency emissions. Plasma cutters working near
sensitive electronics, such as CNC hardware or computers, start the
pilot arc by other means. The nozzle and electrode are in contact. The
nozzle is the cathode, and the electrode is the anode. When the plasma
gas begins to flow, the nozzle is blown forward. A third, less common
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method is capacitive discharge into the primary circuit via a silicon
controlled rectifier.
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Laser Cutting:Laser cutting is a technology that uses a laser to cut materials, and is typical
used for industrial manufacturing applications, but is also starting to appear
schools. Laser cutting works by directing the output of a high-power laser, bcomputer, at the material to be cut. The material then melts, burns, vaporize
away, or is blown away by a jet of gas, leaving an edge with a high-quality
surface finish. Industrial laser cutters are used to cut flat-sheet material as w
as structural and piping materials.
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The laser generator and external optics (including the focus lens)
require cooling. Depending on system size and configuration, waste
heat may be transferred by a coolant or directly to air. Water is a
commonly used coolant, usually circulated through a chiller or heattransfer system.
Advantages and disadvantages:
Advantages of laser cutting over mechanical cutting include easier
workholding and reduced contamination of workpiece (since there is
no cutting edge which can become contaminated by the material or
contaminate the material). Precision may be better, since the laserbeam does not wear during the process. There is also a reduced chance
of warping the material that is being cut, as laser systems have a small
heat-affected zone. Some materials are also very difficult or
impossible to cut by more traditional means.
Laser cutting for metals has the advantages over plasma cutting of
being more precise and using less energy when cutting sheet metal,however, most industrial lasers cannot cut through the greater metalthickness that plasma can. Newer lasers machines operating at higher
power (6000 watts, as contrasted with early laser cutting machines'
1500 watt ratings) are approaching plasma machines in their ability to
cut through thick materials, but the capital cost of such machines is
much higher than that of plasma cutting machines capable of cutting
thick materials like steel plate.The main disadvantage of laser cutting is the high power consumption.
Industrial laser efficiency may range from 5% to 15%. The power
consumption and efficiency of any particular laser will vary depending
on output power and operating parameters. This will depend on type of
laser and how well the laser is matched to the work at hand. Theamount of laser cutting power required, known as heat input, for a
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particular job depends on the material type, thickness, process
(reactive/inert) used, and desired cutting rate.