Waterjet cutting is a proven industrial manufacturing process for processing various materials. In this process, the cutting medium is compressed to a pressure of several thousand bar before being expanded through a nozzle to atmospheric conditions to create a jet. [1] Instead of water, other liquids can also be used as the cutting medium. By using liquid carbon dioxide (CO2) instead of water, residue-free and dry processing of water-sensitive materials can be made possible, as the carbon dioxide evaporates completely after hitting the workpiece. [2]

In the specific case of CO2 jet cutting, the medium cannot be in the liquid state under atmospheric conditions in thermodynamic equilibrium due to its triple point pressure of 5.18 bar. Nevertheless, liquid CO2 jets can be observed under certain conditions. Extensive pre-cooling of the carbon dioxide enables the generation of liquid jets, which separate into a gas and a solid phase after a few centimeters of jet length. To do this, it is necessary to cool the carbon dioxide to near the solidification limit before it expands through the nozzle. The resulting coherent liquid jet can be used to process and separate soft materials such as polymers, metal foils or natural materials. [3]

In recent years, intensive research has been carried out into CO2 jet cutting. This has shown that the cutting properties, such as jet stability or jet length, are significantly influenced by factors such as the pre-expansion temperature and pressure as well as the density of the atmosphere into which the jet is expanded. By adjusting these parameters, it has so far been possible to produce liquid CO2 jets that are suitable for cutting soft materials. Conventional water jet technology with additional modifications was used to generate the jets. Due to the complex cooling process, a stationary nozzle was previously used. It was therefore not possible to move the cutting head and thus the jet, which limited the flexibility and range of application of CO2 jet cutting. As part of the research work, a completely redesigned jet cutting system was developed for the use of carbon dioxide. The system is characterized by a compact and modular design. An efficient cooling concept enables the use of a cutting head that can be moved in two directions and thus the cutting of complex 2D geometries.

Fig. 1: Generation of a liquid CO2 jet at different pre-expansion temperatures and pressures. [3]

Fig. 2: Leather processed with liquid CO2 jets.