Exploring the Difficulties of Metal Laser Cutting Thick Plate


1、The laser cutting machine has no problem in cutting steel plates less than 10mm thick, but if you want to cut thicker steel plates, you often need to help high-power lasers with output power more than 5kW, and the cutting quality is also significantly reduced. Because the high power laser equipment is expensive and its output laser mode is not conducive to laser cutting, the traditional metal laser cutting method does not have advantages when cutting thick steel plates.




2、The Metal Laser Cutting Machine Has The Following Technical Difficulties:


  • It Is Difficult To Maintain The Quasi Steady Combustion Process


In the actual cutting process of metal laser cutting machine, the plate thickness that can be cut through is limited, which is closely related to the unstable combustion of iron at the cutting front. For the combustion process to continue, the temperature at the top of the slit must reach the ignition point. In fact, the energy released by iron oxide combustion reaction alone cannot ensure the continuous combustion process.


On the one hand, because the slit is continuously cooled by the oxygen flow ejected by the nozzle, the temperature of the cutting front is reduced; On the other hand, the ferrous oxide layer formed by combustion covers the surface of the workpiece, hindering the diffusion of oxygen. When the oxygen concentration decreases to a certain extent, the combustion process will be extinguished.


When the traditional convergent beam is used for laser cutting, the area where the laser beam acts on the surface is very small. Because of the high laser power density, the workpiece surface temperature reaches the ignition point not only in the area of laser radiation, but also in a wider area due to heat conduction.


The diameter of the oxygen flow acting on the surface of the workpiece is larger than that of the laser beam, which indicates that not only in the laser radiation area, strong combustion reaction will occur, but also in the periphery of the light spot irradiated by the laser beam.


When cutting thick plates, the cutting speed is quite slow, and the speed of iron oxide burning on the workpiece surface is faster than the speed of the cutting head. After the combustion lasts for a period of time, the combustion process is extinguished due to the decrease of oxygen concentration. Only when the cutting head moves to this position, the combustion reaction starts again. The combustion process at the cutting front is carried out periodically, which will lead to the temperature fluctuation at the cutting front and the poor quality of the incision.


  • It Is Difficult To Maintain Constant Oxygen Purity And Pressure In The Plate Thickness Direction


When cutting thick steel plate with metal laser cutting machine, the decrease of oxygen purity is also an important factor affecting the quality of incision.


The purity of oxygen flow has a strong influence on the cutting process. When the purity of oxygen flow decreases by 0.9%, the combustion rate of iron oxide will decrease by 10%; When the purity decreases by 5%, the combustion rate will decrease by 37%. The decrease of combustion rate will greatly reduce the energy input into the cutting seam during the combustion process and reduce the cutting speed.


At the same time, the content of iron in the liquid layer of the cutting surface will increase, which will increase the viscosity of the slag, causing difficulty in discharging the slag. In this way, there will be serious slag hanging at the lower part of the notch, making the notch quality unacceptable.


In order to keep the cutting stable, it is required that the purity and pressure of the cutting oxygen flow in the plate thickness direction should be basically constant. In the traditional laser cutting process, the common conical nozzle is often used, which can meet the requirements in sheet metal cutting However, when cutting thick plates, with the increase of air supply pressure, shock waves are easy to form in the flow field of the nozzle. Shock waves are harmful to the cutting process, reducing the purity of oxygen flow and affecting the quality of the incision.


3、There Are Generally Three Ways To Solve This Problem:


  •  Add preheating flame around the cutting oxygen flow
  • Add auxiliary oxygen flow around the cutting oxygen flow
  • Reasonably design the inner wall of the nozzle to improve the characteristics of the airflow field


About HGTECH: HGTECH is the pioneer and leader of laser industrial application in China, and the authoritative provider of global laser processing solutions. We have comprehensively arranged laser intelligent machine, measurement and automation production lines, and smart factory construction to provide overall solutions for intelligent manufacturing.