J. Leschke

Optimization of the laser cutting of steel sheets under water

25.-27. August
Type: Konferenzbeitrag
The dismantling of nuclear components is often carried out in the remaining cooling water of the reactor due to the strategy of immediate dismantling. As the avoidance of secondary wastes is a huge topic in the nuclear decommissioning industry, there is an urgent need for tools that offer capabilities to reduce the generation of chips and debris, which are distributed into the surrounding water. In contrast to conventional cutting processes, the laser cutting process provides a variety of possible kerf qualities by modifying the applied process parameters. This allows to bind removed kerf material in form of dross on the backside of the sample, while maintaining a considerably small kerf width. The deployed laser is a Yb:YAG disc laser used at a maximum laser power of 4 kW. The process was carried out at approx. 0.7 m water depth. By using a design of experiments approach the effects of the factors laser power, cutting gas pressure, cutting speed and nozzle dia meter have been determined for 3 mm thick 1.4301. The responses were the weight loss per meter, the amount of dross per meter and area of the cut as an indicator for the ejected volume. Using air as cutting gas the results facilitate a significantly lower weight loss and particle distribution of up to 95 \% compared to sawing or water jet cutting, while utilizing a low cutting gas pressure of 0.25 bar, which corresponds to a cutting gas flow of 25 l/min due to the applied setup. The knowledge about the factor effects have then been transferred to specimen of 6 and 15 mm thickness. The samples with 6 mm thickness allowed for similar parameter usage, resulting in a reduced weight loss of about 6 g/m which represents a weight loss that is about 90 \% lower compared to sawing techniques. For the cutting of 15 mm thick 1.4301 the influence of the gas pressure shows contrary behavior since the lowest weight loss was obtained by using a gas pressure of 6 bar which results in a weight loss of about 37 g/m, representing approx. 80 \% lower weight loss in comparison. For validation, the process is transferred into a water tank with 4 m water depth, verifying the waterproofness of the system and the functionality under increased water pressure. In conclusion, the laser process significantly lowers the mass reduction of the dismantled components and allows for cost savings due to a decreased need for filtering and storage, since no additional material is introduced to the process.