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

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Optical flow measurement in two-phase flows is particularly challenging because refraction of light due to the usually unknown, fluctuating refractive index field can lead to unknown measurement deviations. This applies in particular to the cooling lubricant (CL) supply during grinding. Since flow field measurements are indispensable for a fundamental understanding of the cooling mechanism and thus for a design of the grinding process, the aim of the project is to validate particle image velocimetry (PIV) for the first time for the investigation of coolant flow fields and to use it to clarify the correlation between the coolant flow behavior and the cooling performance. For near-process PIV measurements during grinding, an in-depth measurement uncertainty analysis is carried out based on a fiber-optical, experimental approach in order to quantify the influence of refractive index variations. The effect of the refractive index field variations on the determination of the particle position as well as the deflection of the light sheet is measured with spatial and time resolution. The resulting measurement error of the flow velocity fields is reduced by means of temporal averaging and model-based correction. In addition, it is to be examined whether an average refractive index field can be modeled on the basis of the mean coolant jet geometry, which can be used by means of geometric optics to estimate systematic deviations of the particle position. Flow measurements near the grinding wheel are required to identify CL flow characteristics relevant for cooling. For this purpose, a boundary layer-optimized PIV evaluation is used and the disturbing influence of direct reflections of the light sheet on the grinding wheel surface is characterized, including the resulting indirect flow illumination. For selected operating points the resulting flow fields of the CL supply is measured by PIV without tool-workpiece contact and separately the corresponding cooling performance is measured by means of a grinding-analogy test rig. The aim is to investigate the connection between the cooling performance and the investigated CL flow that is independent from the workpiece, whereas ramp grinding tests are used to check whether the results can be directly transferred to the machining process of metallic components. For the enhanced study of complex CL flow phenomena, the measurement uncertainty of stereoscopic and time-resolved PIV measurements is analyzed, and a sensory grinding wheel and a 3-component dynamometer are implemented to investigate the effect of the CL flow on to the thermomechanical load collective during grinding.