Near process flow measurements of the cooling lubricant supply in grinding processes

• Applicants: Professor Dr.-Ing. Andreas Fischer; Dr.-Ing. Daniel Meyer
• Subject Area: Measurement Systems
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 415003387

Grinding processes are usually used at the end of a process chain. There is a risk of thermal damage to the workpiece due to locally generated heat. To avoid this, cooling lubricants (coolants) are used to ensure efficient heat dissipation in the contact zone between the workpiece and the tool and to reduce friction. Although empirically determined knowledge of optimum grinding parameters for cooling performance exists, the mechanisms underlying cooling are unexplored because the cooling lubricant flow behavior after impact of the free jet on the moving grinding wheel surface is difficult to describe and a suitable approach is lacking for measurements close to the grinding wheel with severely limited accessibility. Therefore, the overall research objective of the project is to achieve a fundamental understanding of the cooling effect of the coolant flow during grinding in order to create the basis for a targeted maximization of the cooling efficiency as well as a minimization of the coolant demand. For this purpose, both the cooling lubricant flow in the contact zone and the flow-dependent heat transfer coefficient during tool-workpiece interaction are to be investigated. Both the flow measurement and the determination of the heat transfer coefficient will take place in analogy tests without machining. For the flow measurement in the grinding machine a transparent workpiece is implemented, which allows an optical accessibility into the contact zone. Through this access, the flow is measured using methods based on particle image velocimetry and shadow image velocimetry. The occurring cross-influences will be investigated and quantified within the scope of the work. The determination of the heat transfer coefficient is enabled by extending an existing test rig with additional temperature sensors. It is clarified, which deviations of the heat balance occur and how their influence on the coefficient determination can be minimized. A joint experimental design will be carried out with the two test rigs in order to understand the interrelationships between the fluid dynamics and the heat transfer coefficient. The model developed to describe the heat transfer coefficient is then integrated into a grinding process model to predict the cooling performance. The coefficient model is validated by a comparison with machining tests and it is clarified to what extent the grinding process model still has to be adapted to manufacturing and material-physical parameters. As a result, with a deeper understanding of the cooling mechanisms and taking into account the fluid-dynamic influences, a process model is created that describes the influence of different flow conditions upstream and especially in the contact zone on the cooling performance and the workpiece temperature.

• DFG Programme: Research Grants