The difficulty of laser cutting processing thick plate is discussed

01. It is difficult to maintain a quasi-stable combustion process.

In the actual cutting process of the metal laser cutting machine, the thickness of the plate that can be cut is limited, which is closely related to the unstable burning of the iron at the cutting edge. To continue the combustion process, the temperature at the top of the slit must reach the ignition point. The energy released by the combustion reaction of iron oxide cannot guarantee the continuity of the combustion process.

On the one hand, because the oxygen from the nozzle continues to cool the slit, reducing the temperature of the cutting edge;

On the other hand, a layer of ferrous oxide formed by combustion covers the surface of the workpiece and prevents oxygen diffusion. When the oxygen concentration is reduced to a certain degree, the combustion process is extinguished.

When laser cutting is carried out using the traditional concentrated beam, the surface area of the laser beam is very small. Due to the high laser power density, the surface temperature of the workpiece not only reaches the ignition point in the laser radiation region, but also conducts heat in a wide area. The diameter of oxygen flow on the workpiece surface is larger than the diameter of the laser beam. This shows that there is a strong combustion reaction not only in the laser radiation region, but also around the laser spot.

When cutting thick plates, the cutting speed is quite slow, and the burning speed of iron oxide on the surface of the workpiece is faster than that of the cutting head. After the combustion continues for a period of time, the combustion process is extinguished due to the reduction of oxygen concentration. Only when the cutting head is moved to this position will the combustion reaction begin again. The burning process of the cutting edge is periodic, resulting in temperature fluctuations of the cutting edge and poor cutting quality.

02. In the direction of plate thickness, oxygen purity and pressure are difficult to maintain a constant.

When cutting thick plates with metal laser cutting machine, the reduction of oxygen purity is also an important factor affecting the cutting quality.

The purity of the oxygen flow has a great, great influence on the cutting process. Oxygen flow purity decreased by 0.9%, combustion rate decreased by 10%; When the purity is reduced by 5%, the combustion rate is reduced by 37%. The reduction of the 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 increase of iron content increases the viscosity of the slag, making it difficult to discharge the slag. In this way, there will be serious slag hanging phenomenon in the lower part of the incision, making the quality of the incision difficult to accept.

In order to maintain cutting stability, the purity and pressure of oxygen flow in the direction of sheet thickness should be kept constant. In the traditional laser cutting process, the commonly used conical nozzle can meet the requirements of plate cutting. However, when cutting thick plates, with the increase of gas supply pressure, the nozzle flow field is easy to form a shock wave, which causes great harm to the cutting process, reduces the purity of oxygen flow, and affects the cutting quality.

There are three ways to solve this problem.

(1) Heat the flame around the cutting oxygen flow.

(2) Add auxiliary oxygen flow around the cutting oxygen flow.

Reasonable design of nozzle inner wall to improve the flow field characteristics.