Classification and application of the laser cutting

  17 Sep , 2020         Chris         8571

During the process of laser gasification and cutting, the surface temperature of the material rises to the boiling point at such a rate that it avoids the melting caused by heat transfer, so that some of the material vaporizes into steam and disappea

Vaporized cutting

   During the process of laser gasification and cutting, the surface temperature of the material rises to the boiling point at such a rate that it avoids the melting caused by heat transfer, so that some of the material vaporizes into steam and disappears, and some of the material is blown away from the bottom of the slit as an ejective by the auxiliary gas stream.This requires very high laser power.

  The thickness of the material must not greatly exceed the diameter of the laser beam in order to prevent the vapor condensing on the slit wall.
process is therefore suitable only for applications where the exclusion of molten material must be avoided.This process is actually only used in a very small field of iron - based alloys.

  The process cannot be used for materials, such as wood and certain ceramics, that do not have a melting state and are therefore less likely to allow the material to condense again.In addition, these materials are often used to achieve thicker incisions.In laser gasification cutting, the optimal beam focusing depends on the material thickness and beam quality.

   Laser power and gasification heat have only a certain influence on the optimal focus location.The maximum cutting speed is inversely proportional to the gasification temperature of the material when the thickness of the plate is certain.The required laser power density is greater than 108W/cm2 and depends on the material, cutting depth and beam focus.The maximum cutting speed is limited by the gas jet velocity when the plate thickness is certain, assuming enough laser power.


Melt and cut

   In laser fusion cutting, the workpiece is partially melted and the molten material is sprayed out by airflow.Because the material is transferred only in its liquid state, the process is called laser fusion cutting.

   The laser beam coupled with a high purity inert cutting gas causes the melted material to leave the slit, and the gas itself is not involved in the cutting.

   Laser fusion cutting can achieve higher cutting speed than gasification cutting.It usually takes more energy to gasify than to melt he material.In laser fusion cutting, the laser beam is only partially absorbed.
The maximum cutting speed increases with the increase of laser power and decreases almost inversely with the increase of plate thickness and material melting temperature.In the case of a certain laser power, the limiting factors are the pressure at the slit and the thermal conductivity of the material.Laser fusion cutting for iron and titanium materials can be obtained without oxidation incision.
The laser power density, which produces melting but less than gasification, is between 104W/cm2 and 105w /cm2 for steel materials.


Oxidation melting cutting

   Melting cutting generally USES an inert gas, if it is replaced by oxygen or other active gas, the material is ignited under the irradiation of a laser beam, and the oxygen has a fierce chemical reaction to produce another heat source, so that the material is further heated, known as oxidation melting cutting.

   Because of this effect, for structural steel of the same thickness, the cutting rate obtained by this method is higher than that obtained by melting cutting.On the other hand, this method may have a lower notch quality than melting cutting.In fact, it generates wider slits, more pronounced roughness, increased heat affected areas, and poorer edge quality.Laser flame cutting is not good for machining precision models and sharp corners (there is a danger of burning off sharp corners).A pulsed laser can be used to limit the thermal impact, and the power of the laser determines the cutting speed.In the case of a certain laser power, the limiting factors are the supply of oxygen and the thermal conductivity of the material.

Control fracture and cutting.

   For brittle materials which are easy to be damaged by heat, high-speed and controllable cutting can be done by laser beam heating, which is called controlled fracture cutting.The main content of this cutting process is: the laser beam heats a small area of brittle material, causing a large thermal gradient and serious mechanical deformation in the area, leading to the formation of cracks in the material.As long as the heating gradient is balanced, the laser beam can guide the crack in any desired direction.

CO2 gas laser

   Since laser technology was introduced to cut metal sheets, CO2 lasers have dominated the market.A CO2 laser requires a lot of energy to excite nitrogen molecules to collide with CO2 molecules (the laser gas), causing them to emit photons that eventually form a laser beam that cuts through metal.Molecular activity in the resonator emits heat as well as light, requiring a cooling system to cool the laser gas.

   This means more energy is used during cooling, further reducing energy efficiency.

Fiber laser

   Machine using fiber laser occupies a small area, and the laser light source and cooling system are also smaller.There is no laser gas pipeline and no need to adjust the lens.A 2kw or 3kw fiber-optic laser light source only needs 50% of the energy consumption of a 4kw or 6kw CO2 laser light source to achieve the same performance, and it is faster, consumes less energy and has less impact on the environment.

   The fiber laser USES solid-state diodes to pump molecules in the double-clad ytterbium-doped fiber. The excited light passes through the fiber core several times, and then the laser is transmitted through the fiber to the focusing head for cutting.Since all the molecular collisions take place inside the fiber, no laser gas is needed, so the energy required is greatly reduced -- about a third of that of a CO2 laser.As less heat is produced, the cooler can be reduced in size.In short, the overall energy consumption of the fiber laser is 70% lower than that of the CO2 laser under the same performance.

   The vector describes the path of the laser, which is smoother.Such a laser system cut out the edge of the cover film contour neat and round, smooth without burr, no overflow.The use of mold and other machining methods such as window opening window will be near the burr and overflow after punching, this burr and overflow after bonding bonding pad is very difficult to remove, will directly affect the quality of the subsequent coating.

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