Numerical and Experimental Evaluation of Chip Evacuation and Lubricant Flow using Optimized Drill Heads for Ejector Deep Hole Drilling

TL;DR

This work tackles the high energy cost of chip evacuation in ejector deep hole drilling by combining SPH-DEM simulations with experimental validation of two flow-optimized drill head designs. The study demonstrates that an extended chip mouth with angled coolant outlets significantly lowers the minimum MWF flow required for stable drilling (up to ~43% reduction) and improves chip transport, while a narrowed mouth reduces flow reliability due to edge chipping. The simulations and experiments align, supporting design guidelines that reduce energy use while maintaining bore quality. The authors also outline a path toward further optimization via modular ejector nozzle adapters and additive manufacturing to push hydraulic efficiency toward higher limits, enhancing the sustainability of EDHD in industrial settings.

Abstract

Ejector deep hole drilling offers great potential to utilize the typical advantages of deep hole drilling processes on conventional machining centers in a cost-effective and resource-efficient manner. However, maintaining reliable chip evacuation and stable process conditions often relies on high flow volumes of metalworking fluid, resulting in considerable energy consumption in industrial settings. Therefore, to analyze the highly sophisticated chip evacuation dynamics of the process, two flow-optimized drill heads and a reference drill head were evaluated with smoothed particle hydrodynamics simulation using experimentally obtained chip shapes. In addition, modified drill heads were additively manufactured and experimentally investigated to validate the numerical results and to determine the positive effect on the necessary fluid flow for a stable ejector drilling process. The modifications aim to improve chip evacuation by reducing vortex formation and optimizing flow conditions near the cutting zone. Therefore, the minimum volume flow required for a stable drilling process without chip clogging is reduced, leading to an energy-efficient sustainable ejector drilling process.

Figures (10)

• Figure 1: Ejector drill head Botek type 62 (D = 30mm)
• Figure 2: Resulting chip shapes from the cutting edges and final STL models for the simulations Gerken2024.
• Figure 3: Chip positioning at $\textrm{t = 0.01\,s}$ for drill head top view.
• Figure 4: Reference drill head and the modified designs with changes to the chip mouth highlighted according to Baumann2024.
• Figure 5: Positions of the inner and outer chips (numbered according to generation) during the transient phase of chip evacuation.