Combined 3D simulation method with focused analysis in the cutting fluid supply of twist drills and modified flank face geometry

Although drilling is the most commonly used machining operation, the developing of effective tools presents numerous difficulties compared to other cutting tools. Particularly when drilling nickel-based alloys like Inconel 718 the thermo-mechanical loads increase dramatically. This is on one hand since of their outstanding material properties of Inconel 718 and on the other hand the drilling operation is inside the workpiece. There is still to date exists a substantial need for further research regarding in drilling Inconel 718.

For calculate fundamental physical variables usually 2D analysis are use but it is an urgent need to move from 2D to 3D modeling, to consider the complex geometries of the cutting engagement. Especially for drilling it is necessary considered the mapping of the complex interactions such as the cutting fluid effects, to understand the adequately addressed core issues. Compared to the regular use Finite Element Method (FEM) only a few studies cover the influences of cutting fluids. On one hand the Computational Fluid Dynamic (CFD) offers a relatively new field of research when machining geometrically defined cutting edges and on the other hand such numerical as well as combined numerical simulations still represent very high challenges.

On this account, Doctor Ekrem Oezkaya, Milan Bücker and Professor Dirk Biermann from the TU Dortmund University in Germany presented a combined simulation method to develop an optimized flank face design with considered the cutting fluid supply for twist drills used for machining Inconel 718. Their three-dimensional approach involved the combination of both FEM and CFD simulations. In particular, the researchers used CFD simulation to investigate the influence of the cutting fluid flow rate and cooling channel position on tool wear, for drilling applications with internally cooled solid carbide twist drills. Their work is currently published in the International Journal of Mechanical Sciences.

To begin with, the research team conducted simulative investigations as well as especially the fluid modelling of the internal flow area and its meshing strategy and the comparison of the numerical solutions of the reference and modified tool. Based on the results obtained, the prototype tools were manufactured with a flank face retraction and experimental tests conducted.

The authors reported that by using a thermal Finite Element (FE) model, the spatial and temporal distribution of high-throughput drilling could be performed with an inverse heat transfer method in order to determine the heat at the tool-chip contact area and the convection heat transfer coefficient of the cutting fluid. The team further reported that CFD allowed for a qualitative prediction of both the flow distribution and flow velocity. Consequently, the use of simulation models significantly reduced the required time and the necessary field tests in the process of tool development.

In summary, the study employed a combination of FEM and CFD analysis to assess and determine the mechanical stresses inside the cutting material and the flow velocities at the cutting edge of both regular and modified twist drills during the machining of Inconel 718. Remarkably, the results of the simulations were backed up by force and temperature measurements from real experiments and showed a good agreement with the conducted tool life tests. In a statement to Advances in Engineering, Doctor Ekrem Oezkaya said that innovative 3D CFD simulation methods have a great potential to reduce the experimental investigations and the knowledge gained will be used to  make more targeted activities for optimization in machining technology for enhance productivity and workpiece quality.