cutting methods

8/8/2019 Cutting Methods

1/17


2/17

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:


3/17

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:


4/17

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


5/17

Here are some pictures of those machines:


6/17


7/17

3-Numerical Cutting

Using computer to control the cutting process


8/17


9/17


10/17

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.


11/17

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


12/17

method is capacitive discharge into the primary circuit via a silicon

controlled rectifier.


13/17

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.


14/17


15/17


16/17

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


17/17

particular job depends on the material type, thickness, process

(reactive/inert) used, and desired cutting rate.

cutting methods

Documents