Drilling of Inconel 718 with Geometry-modified Twist Drills

Abstract

The drilling process of Inconel 718, a nickel-based superalloy, is very challenging due to the material properties, the operating conditions and the high quality requirements. Carbides within the material matrix cause an excessive amount of abrasive tool wear. Moreover, a large amount of the heat caused by the machining process, especially in drilling, has to be dissipated by the tool and the coolant, due to the low thermal conductivity of Inconel 718. This high thermal load also restricts the cutting speed. The combination of all attributes limits productivity and economic efficiency when drilling Inconel 718 with cemented carbide twist drills.This paper presents a method to adapt twist drills considering the mentioned demands by using geometry-modified tools. The aim is to increase the resistance against abrasive wear and to reduce the thermal loads; so that, tool life and bore quality can be improved. The analysis of the new tool geometry was realized by advanced Computational-Fluid-Dynamics (CFD) simulations. The simulations provide detailed information about the coolant flow and consequently the improved cooling of tool regions which are, on the suggested geometry, exposed to very high thermal loads. Experiments showed that the tool life can be increased by up to 50% in contradiction to a standard twist drill. The improvement on the bore quality was shown by determining the roundness deviation and the average surface roughness. In addition, micro hardness tests and metallurgy preparations were conducted to investigate the surface integrity of the bore surface layer. Although the presented geometry only represents a prototype status, the results are impressive. The tool life and the bore quality have been improved, and the simulations showed clearly that there is a significantly better coolant flow, when using the new geometry.

A comparison of laser beam machining of micro-channels under dry and wet mediums

“…Hence, such materials are considered as difficult-to-cut materials. Although the conventional machining methods are employed to deal with these difficult-to-machine materials especially Inconel 718 [25][26][27][28][29]30], in general, the conventional machining processes are found to be uneconomical [31]. Nickel-based superalloys are grouped into this class of difficult-to-machine materials.…”

Experimental studies and CFD simulation of the internal cooling conditions when drilling Inconel 718

“…The simulation of cutting fluids was also applied for drilling processes with twist drills. Beside general investigations on the coolant flow of emulsion and MQL for twist-drills, the influence of small areas within the flank face on the coolant flow has been analyzed [5,37]. Other publications focus on the position of the coolant channel at the flank face, which has a great influence on the heat which can be absorbed by the MWF [4].…”

“…The diameter of the tool's coolant channels and the pressure of the coolant mainly influence the resultant mass flow of the MWF. Other influencing factors are the position of the coolant outlet at the flank face and the resulting space between the flank face and bore bottom [4,5]. In fact, many investigations focus on the coolant, which are listed in Chapter 1.3, but for cooling during drilling no detailed information about the coolant flow is available [4,6].…”

A Numerical Investigation of Through-Tool Coolant Wetting Behaviour in Twist-Drilling

“…As a result, it is difficult to improve the usage of coolant with little knowledge of the underlying delivery mechanisms. In light of these limitations studies are typically limited to post-experiment tool inspection [5,6] or through cutting force telemetry data analysis. These experimental challenges have lead to numerous research papers adopting Computational Fluid Dynamics (CFD) to numerically study coolant performance.…”

“…Beer et al [6] used a CFD model, validated by tool wear inspections, to investigate the effects of grooves in the flank face on tool life and hole quality in the drilling of inconel 718. The addition of grooves in the flank face was found to increase tool life by up to 50%.…”