http://orcid.org/0000-0002-4309-2238
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ABSTRACT
The use of cooling lubricants in metal machining increases both the tool life and the quality of workpieces and improves the overall sustainability of production systems. In addition to fulfilling these main functions, the focus of machining processes is also related to the reduction of environmental pollution. This can for example be achieved by an optimized arrangement of the cutting tool cooling channels. Therefore, the active cutting edges of the tool should be effectively supplied with a sufficient amount of cooling lubricant. An analysis of the tribological stress is rather difficult because the complex contact zone is inaccessible. Hence, optical investigations are often limited to only observing the chip formation or analyzing the process without considering the influence of the chips.
This article presents an innovative method, which enables a deeper three-dimensional insight into the chip formation zone during drilling with internal cooling channels, considering the cooling lubricant distribution and chip formation. The chip formation simulation based on the finite element method and the computational fluid dynamics flow simulation are combined. In this way, the differences between the different geometric models that do not allow any joint generation of numerical information due to missing interfaces are overcome.
Acknowledgments
The authors would like to thank Guehring oHG, Albstadt, Germany for supporting this research. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Nomenclature
| A | = | yield stress, N/mm2 |
| B | = | strain hardening exponent |
| C | = | dimensionless strain rate |
| D | = | ductile damage |
| da | = | diameter (bore hole wall), mm |
| dc | = | diameter (cylinder), mm |
| di | = | diameter (cooling channel), mm |
| dt | = | diameter (tool), mm |
| f | = | feed, mm |
| fi | = | density of volume force, kg/m3 |
| la | = | length (bore hole wall), mm |
| lc | = | length (cylinder), mm |
| m | = | exponent for the softening |
| n | = | hardening coefficient |
| n | = | material-dependent parameter |
| p | = | static pressure, N/m2 |
| S∅ | = | specific right side |
| Sij | = | shear rate tensor |
| T | = | temperature, °C |
| Tm | = | melting temperature, °C |
| Tr | = | initial temperature, °C |
| t | = | time, s |
| u | = | shear stress, N/m2 |
| v | = | velocity, m/s |
| x, y, z | = | space coordinates, m |
Greek symbols
| ϵ | = | turbulent dissipation, m²/s³ |
| = | equivalent plastic strain rate, 1/s | |
| = | reference equivalent plastic strain rate, 1/s | |
| ϵf | = | value results from η |
| ϵf(η) | = | value from failure curve |
| ϵn | = | plastic effective strain, m2/s3 |
| = | rate of plastic effective strain | |
| η | = | fracture strain depending on the stress multi-axiality |
| κ | = | turbulent kinetic energy, m2/s3 |
| μ | = | dynamic viscosity, kg/m s |
| ρ | = | density, kg/m3 |
| σ | = | equivalent stress, N/mm2 |
| δ | = | Kronecker symbol (1 for i = j; 0 for i ≠ j) |
| τij | = | tresses tensor, m²/s² |
| ω | = | specific rate of dissipation, 1/s |
Mathematical symbols
| ∂(.)/∂(.) | = | partial differential (gradients) |
Indications
| i, j, k | = | direction in space |
| ∅ | = | transport size |
Abbreviations
| 3D | = | three dimensional |
| CAD | = | computer-aided design |
| CFD | = | computational fluid dynamics |
| FEM | = | finite element method |
| MWF | = | metalworking fluid |
| MQL | = | minimum quantity lubrication |
| CMM | = | coordinate measuring machine |
| R | = | rotation |
| SST | = | shear stress transport |
| STEP | = | Standard for the Exchange of Product model data |
| STL | = | Standard Triangulation Language |
| NURBS | = | non-uniform rational Bézier-splines |
| IGES | = | Initial Graphics Exchange Specification |