Adaptive cryogenic high performance cooling for turning tools

• Applicant: Professor Dr.-Ing. Martin Dix
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540971848

The increasing power densities in all product areas lead to an increased demand for high-performance materials (nickel-based and titanium alloys, such as Inconel 718 or Ti 6Al 4V). The associated high characteristic values for hot strength and hot hardness produce high temperatures in the primary shear zone (over 1000°C) during machining in combination with high mechanical loads on the cutting edge. This significantly reduces tool life and tool travel. A reduction of the process temperatures is achieved by cooling lubrication as a non-value-adding additional system of the machine tool. At the high process temperatures, the cooling capacity of conventional cooling lubricant full-jet cooling is often insufficient to cool the cutting edge of the tool sufficiently. Cryogenic cooling has the potential to increase the temperature gradient and quickly dissipate the process heat, but boiling at a warm contact surface (Leidenfrost effect) can cause an undesirable insulating effect and thus a low efficiency of the cooling capacity. Increasing the lubricant supply, especially by high-pressure cooling with liquid phase of the cryogen, increases the cooling effect, also breaks up the insulation layer by the boiling liquid and therefore improves the penetration of the cooling lubricant into the process zone. Indirect cooling of the tool cutting edge can thereby be improved by converting film boiling into bubble boiling by increasing the speed or mass flow and hence increasing the heat transfer to the tool cutting edge. The aim of the planned research project is the development of a predominantly primary indirect cryogenic tool cooling with liquid nitrogen (LN2) for turning operations (external cylindrical and grooving), in which the temperature of the tool cutting edge is minimised without lowering the necessary high temperatures in the primary shear zone for minimum process forces with high-performance materials. For this, the cryogenic cooling effect must be localised and maximised in the area of the cutting edge. The design and definition of the internal geometry of the tool holder, which will be additively manufactured, as well as the necessary parameters of the LN2 mass flow are simulation-based. However, the simulation-based design of cryogenic cooling is very uncertain due to the lack of heat transfer parameters for specific geometries and the serial stringing together of partial models. Therefore, in the proposed project, the necessary calculation parameters of the LN2 supply, the internal transfer in the tool holder, the internal radiation area and the gas discharge into the process zone will be identified in stages. For this purpose, special test facilities will be implemented that allow reliable measurement of the temperature on the outer surfaces of cooled components. The basics for a control and regulation concept under the specific conditions of cryogenic cooling will also be created.

• DFG Programme: Research Grants