PSI - Issue 53

Francisco Matos et al. / Procedia Structural Integrity 53 (2024) 270–277 Francisco Matos et al. / Structural Integrity Procedia 00 (2023) 000–000

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4. Fluid supply CFD simulation

4.1. Numerical procedure

Conventional milling cutters coolant channels are usually conventionally manufactured which can result in sharp edges, which adversely a ff ect the flow characteristics of the cutting fluid. During the design phase, abrupt changes in channels direction were avoided, given that elbow geometries are susceptible to negatively impact lubrication flow control and its uniform distribution. Moreover, flow velocity increases with the decrease of the curvature radius of the pipe elbow, resulting in a more homogeneous lubricant flow Lakner et al. (2019); Lin et al. (2021). Several researchers were able to generate approximated solutions of coolant flow in the internals of cutting tools with the aid of computational fluid dynamics methods Lakner et al. (2019); Fallenstein and Aurich (2014); Biermann and Oezkaya (2017). CFD simulation was used to investigate the lubricant flow in the cooling channels and fluid interaction with the cutting insert zone, in order to validate if the lubricate was being e ffi ciently directed to the cutting zone. The CFD simulation software ANSYS FLUENT was used. Cutting fluid properties were simplified with the properties of water. The simulation of turbulent flow involves the application of turbulence models that rely on the Reynolds-Averaged Navier-Stokes equations (RANS). Hence, the RANS modelling significantly reduces the computational workload and resource demands, making it a widely adopted method for practical engineering purposes. The chosen turbulence modelwas κ − ω SST (shear stress transport), a widely used turbulence model which combines the favorable near-wall characteristics of the κ − ω model with the robust properties of the κ − ϵ model at free flow regions, such as inlets and areas far from walls Menter et al. (2003). The coupled method, that solves the momentum and pressure-based continuity equations together, was used as the solution algorithm. Average surface roughness was considered in the simulation of the coolant channel geometries.

Table 4: CFD simulation fluid properties

Property

Air

Water

Density, kg / m 3

1.225 998.2

Specific heat, J / kgK

1

4216

Thermal conductivity, W / mK

0.024 0.677 1.79e-5 0.001

Viscosity, kg / ( ms )

4.2. Coolant jet numerical characterization and experimental validation

To validate and find critical zones in the channel geometry, the cutting fluid velocity distribution within the coolant channels was simulated. The simulation revealed a higher tendency for the cutting fluid to flow through the lower channel. In an ideal design, the fluid would be evenly distributed between the two channels. However, it is evident that due to the design, the fluid encounters less resistance when exiting through the lower channel, following a more straightforward path and avoiding the directional changes observed in the top channel. This phenomenon is possibly created by fluid recirculation in the top channel. Despite this, the creation of separate lubricant entries for the top and lower cooling channel was not feasible due to the relatively small tool size and lack of space for independent channels. It can clearly be seen, that the designed channel geometries and the outlet location of the coolant channels leads to a focused coolant flow, directed to the active cutting zone. Simulation results correlated well with the experimental testing of the tool, confirming that the fluid was suc cessfully directed at the cutting zones, ensuring a good lubrication of the tool-chip interface. In addition, the fluid exiting by the lower channel exhibits a more concentrated flow, whereas the upper channel demonstrates higher fluid dispersion.