Eric Verna

Visualization and modeling of combustion effects at laser cutting of mild steel with oxygen

The iron-oxygen combustion front dynamics has a great influence on the surface quality of mild steel samples cut with laser. At the present work different modes of the combustion front propagation, such as: stationary attached to the laser beam, cyclic non-self-sustained, self-sustained, are explored both theoretically and experimentally. Theoretical model is based on the numerical solution of heat balance on the cut front. It allows to obtain 3D evolution of the cutting kerf. Numerical results are in a good agreement with the accompanying experiments. The experimental setup with one wall of the kerf being replaced with the glass is developed to register the process. High speed recordings with the frame rates up to 10 000 f/s are done for 4mm and 12mm thick mild steel plates cut with 2 KW fiber laser. Such phenomena as cyclical burn propagation and transition from cyclical reaction to side burn (self-sustained) mode are captured.The iron-oxygen combustion front dynamics has a great influence on the surface quality of mild steel samples cut with laser. At the present work different modes of the combustion front propagation, such as: stationary attached to the laser beam, cyclic non-self-sustained, self-sustained, are explored both theoretically and experimentally. Theoretical model is based on the numerical solution of heat balance on the cut front. It allows to obtain 3D evolution of the cutting kerf. Numerical results are in a good agreement with the accompanying experiments. The experimental setup with one wall of the kerf being replaced with the glass is developed to register the process. High speed recordings with the frame rates up to 10 000 f/s are done for 4mm and 12mm thick mild steel plates cut with 2 KW fiber laser. Such phenomena as cyclical burn propagation and transition from cyclical reaction to side burn (self-sustained) mode are captured.

Study of shielding nozzles for CO2 laser welding

The principle behind CO2 laser welding is to focus the laser beam onto the parts that need welding. The small size of the focal spot allows the energy to be concentrated so that very high power densities can be reached. These high power densities cause a high level of vaporization, which “hollows out” the welding pool, creating a deep and narrow capillary “keyhole” in the sheet metal, which is filled with a mixture of metallic vapours and plasma. When the capillary is created, the metallic vapour plasma that escapes from it, may, under certain conditions, cause the ionisation of the ambient environment and so lead to the appearance of a gaseous plasma. This plasma may absorb all or part of the incoming laser beam, and so leads to a significant decrease in penetration depths. This is why helium is usually used as shielding gas as its high ionisation potential removes any risk of this plasma appearance.The principle behind CO2 laser welding is to focus the laser beam onto the parts that need welding. The small size of the focal spot allows the energy to be concentrated so that very high power densities can be reached. These high power densities cause a high level of vaporization, which “hollows out” the welding pool, creating a deep and narrow capillary “keyhole” in the sheet metal, which is filled with a mixture of metallic vapours and plasma. When the capillary is created, the metallic vapour plasma that escapes from it, may, under certain conditions, cause the ionisation of the ambient environment and so lead to the appearance of a gaseous plasma. This plasma may absorb all or part of the incoming laser beam, and so leads to a significant decrease in penetration depths. This is why helium is usually used as shielding gas as its high ionisation potential removes any risk of this plasma appearance.